Cardiovascular physiology forts. Flashcards
Non-adrenergic transmission: role of ATP and neuropeptide Y:
The vasoconstrictor response of the pulmonary artery and most veins to sympathetic stimulation is completely abolished by drugs that block ……..-adrenorecptors (e.g phentolamine, phenoxybenzamine), but the vasoconstrictor response of many systemic ……. and ……… to sympathetic nerve activity is only partially prevented by alpha-blockers.
The vasoconstrictor response of the pulmonary artery and most veins to sympathetic stimulation is completely abolished by drugs that block alpha-adrenorecptors (e.g phentolamine, phenoxybenzamine), but the vasoconstrictor response of many systemic arteries and arterioles to sympathetic nerve activity is only partially prevented by alpha-blockers.
This led to the discovery of additional neurotransmitters (co-transmitters) in the sympathetic variocosities, namely the purine ATP and the peptide neuropeptide Y. Their relative abundance and the importance vary from tissue to tissue.
Additional neurotransmitters (co-transmitters) in the sympathetic variocosities, namely the purine ATP and the peptide neuropeptide Y. Their relative abundance and the importance vary from tissue to tissue.
ATP is synthesized in the ………. and is released along with the NA in some large arteries and small mesenteric arteries. It sitmuleas post junctional purinergic recpetore (P2 receptors) and evokes a fast, brief ……..
ATP is synthesized in the nerve terminal and is released along with the NA in some large arteries and small mesenteric arteries. It sitmuleas post junctional purinergic recpetore (P2 receptors) and evokes a fast, brief depolarization.
Neuropeptied Y has been identified in the vasomotor nerves of skeletal muscle, kidney, salivary gland, spleens and nasal mucosa. It is released chiefly in response to…….., which occurs naturally only under …… conditions, and it produces a much slower, more prolonged depolarization than ATP.
Neuropeptied Y has been identified in the vasomotor nerves of skeletal muscle, kidney, salivary gland, spleens and nasal mucosa. It is released chiefly in response to high frequency stimulation, which occurs naturally only under stress conditions, and it produces a much slower, more prolonged depolarization than ATP.
Neuropeptide Y also acts as a neuromodulator, exerting a prejuncitonal inhibitory effect on …… release.
Neuropeptide Y also acts as a neuromodulator, exerting a prejuncitonal inhibitory effect on NA release.
Table 11.2:
Sympathetic vasoconstrictor fibre:
- NA
- ATP
- neuropeptide Y (NPY)
Parasympathetic dilator fibre:
-Acethylcholine (ACh)
.Vasoactive intestinal polypeptide (VIP)
Sensory-dilator axons (C fibre)
- Substance P (SP)
- Calcitonin-gene related peptide (CGRP)
- ATP
Tonic sympathetic activity and the effects of altered impulse frequency:
Symp vasoconstricotr nerves discharge contibually at about 1 impulse per second or else in resting subjects; the max frequency is only 8-10 s in vivo. The tonic activity of the system at rest, though low, contributes substantially to vessel tone and if it is interrupted by nerve sectioning or pharmacological blockade vasodilatation ensues.
Symp vasoconstricotr nerves discharge contibually at about 1 impulse per second or else in resting subjects; the max frequency is only 8-10 s in vivo. The tonic activity of the system at rest, though low, contributes substantially to vessel tone and if it is interrupted by nerve sectioning or pharmacological blockade vasodilatation ensues.
Vasodilatation induced by a fall in sympathetic noradrenergic nerve activity is physiologically very important, being part of the …………………….. reflex which prevents excessive ………. in blood pressure.
It is also important in producing cutaneous vasodilatation during the regulation of body temperature.
Vasodilatation induced by a fall in sympathetic noradrenergic nerve activity is physiologically very important, being part of the baroreceptor reflex which prevents excessive rises in blood pressure.
It is also important in producing cutaneous vasodilatation during the regulation of body temperature.
Fig 11.11: Effects of increased sympathetic vasomotor activity.
Effects of increased sympathetic vasomotor activity.
Effects of increased sympathetic vasomotor activity.
- Local blood flow is reduced: This can be sustained for hours in some tissues (e.g skin) but in the intestine the ……….. quickly “escape” from the vasoconstriction; the ….. however do not.
- Local blood flow is reduced: This can be sustained for hours in some tissues (e.g skin) but in the intestine the arterioles quickly “escape” from the vasoconstriction; the veins however do not.
Effects of increased sympathetic vasomotor activity.
- The volume of blood in an organ is reduced by active …………., which can displace several ml of blood from different organsystems. In skeletal muscle, the venous system lacks an effective enervation, but nevertheless up to 7,5 ml/kg in people can be displaced passively because venous pressure falls secondarily to …….. ……….
- The volume of blood in an organ is reduced by active venoconstriction, which can displace several ml of blood from different organsystems. In skeletal muscle, the venous system lacks an effective enervation, but nevertheless up to 7,5 ml/kg in people can be displaced passively because venous pressure falls secondarily to arteriolar contraction.
Effects of increased sympathetic vasomotor activity.
- Capillary pressure is reduced by the arteriolar constriction causing a transient ……………… of interstitial fluid into the plasma compartment.
- Capillary pressure is reduced by the arteriolar constriction causing a transient absorption of interstitial fluid into the plasma compartment.
Effects of increased sympathetic vasomotor activity.
- If the increase in sympathetic outflow is widespread (which is not inevitably the case), the total peripheral resistance and cardiac output ……….., altering the arterial blood pressure. The regulation of …………is perhaps the single most important function of the sympathetic vasomotor system.
- If the increase in sympathetic outflow is widespread (which is not inevitably the case), the total peripheral resistance and cardiac output rise, altering the arterial blood pressure. The regulation of blood pressure is perhaps the single most important function of the sympathetic vasomotor system.
The mentioned 4 effects (……………) together from part of a life-preserving response to hemorrhage and shock.
The mentioned 4 effects (reduced peripheral flow, reduced peripheral blood volume, fluid translocation and blood pressure maintenance) together from part of a life-preserving response to hemorrhage and shock.
It should be appreciated, however, that while the changes in sympathetic activity are sometimes widespread, as during a hemorrhage, altered discharge can also be confined to a single tissue (e.g skin during temperature changes) and confined even to a particular kind of vessel (e.g. arteriovenous anastomoses in skin9: the sympathetic activity is far from an “all-or none” affair.
Sympathetic activity fluctuates in phase with respiration. In conjunction with sinus arrhythmia, this produces small oscillations in blood pressure in phase with respiration, called ………….. waves, but these have no known functional significance.
Traube-Hering
Vasodilator nerves:
In a limited number of tissues, the arterioles are innervated by vasodilator fibres as well as by ubiquitous sympathetic vasoconstrictor fibres.
Vasodilator fibres occur within the sympathetic, parasympathetic and sensory systems and, unlike the vasoconstrictor fibres they are not ………………
In a limited number of tissues, the arterioles are innervated by vasodilator fibres as well as by ubiquitous sympathetic vasoconstrictor fibres.
Vasodilator fibres occur within the sympathetic, parasympathetic and sensory systems and, unlike the vasoconstrictor fibres they are not tonically active.
In dogs and cats, the arterioles of skeletal muscle are innervated not only by sympathetic vasoconstrictor nerves but also by sympathetic ……… nerves whose neurotransmitter is ……….
Selective excitation of the sympathetic cholinergic nerves causes vascular ……… and increased muscle blood flow. The effect is mediated by …….. receptors, being blocket by atropine, but whether the acetylcholine is acting directly on the VSM or is acting indirectly by stumbling the endothelial cell to produce EDRF is less clear.
In dogs and cats, the arterioles of skeletal muscle are innervated not only by sympathetic vasoconstrictor nerves but also by sympathetic vasodilator nerves whose neurotransmitter is acetylcholine.
Selective excitation of the sympathetic cholinergic nerves causes vascular relaxation and increased muscle blood flow.
The effect is mediated by muscarinic receptors, being blocket by atropine, but whether the acetylcholine is acting directly on the VSM or is acting indirectly by stumbling the endothelial cell to produce EDRF is less clear.
(Evidently, not all VSM responds identically to acetylcholine, for aortic and pulmonary artery VSM contracts in response to acetylcholine after endothelial destruction.)
The sympathetic cholinergic system differs from the vasoconstrictor system in more ways than one. Which ones?
1) The cholinergic system is controlled by the forebrain, and is activated solely as part of the “altering response” of fear and danger
2) The central fibres do not synapse in the brainstem vasomotor regions
3) The distribution is confined to the skeletal muscle vasculatur of some species
4) The respons in only transient
5) The fibres take no part in the baroreflex control of blood pressure.
Table 11.3
Table 11.3
Main neurotransmitter of the sympathetic constrictor nerve: ……..
Main neurotransmitter of the sympathetic dilator nerve: ………
Main neurotransmitter of the sympathetic constrictor nerve: NA
Main neurotransmitter of the sympathetic dilator nerve: Acetylcholine (and VIP)
Distribution of the sympathetic constrictor nerve: ……….
Distribution of the sympathetic dilator nerve:…….
Distribution of the sympathetic constrictor nerve: Most organs and tissue
Distribution of the sympathetic dilator nerve: Restricted to skeletal muscle and sweat glands
Sympathetic constrictor nerve: Tonically active? ……..
Sympathetic dilator nerve: Tonically active? ……
Sympathetic constrictor nerve: Tonically active? Yes
Sympathetic dilator nerve: Tonically active? No
Sympathetic constrictor nerve: Central control? ……..
Sympathetic dilator nerve:
Central control? ………..
Sympathetic constrictor nerve: Central control? Brainstem
Sympathetic dilator nerve:
Central control? Forebrain
Sympathetic constrictor nerve: Role in blood pressure homeostasis? ………
Sympathetic dilator nerve:
Role in blood pressure homeostasis? …….
Sympathetic constrictor nerve: Role in blood pressure homeostasis? Very important
Sympathetic dilator nerve:
Role in blood pressure homeostasis? None
Sympathetic constrictor nerve: Duration of effect? ——
Sympathetic dilator nerve:
Duration of effect? …….
Sympathetic constrictor nerve: Duration of effect? Mostly well sustained.
Sympathetic dilator nerve:
Duration of effect? Transient.
The alerting or defense response, which is the natural stimulus for sympathetic ………… activity in carnivores, is induced by fear-flight-fight situations. It is tempting to assume that the ………. blood flow improves muscle nutritions in readiness for action (very limited effect).
The alerting or defense response, which is the natural stimulus for sympathetic vasodilator activity in carnivores, is induced by fear-flight-fight situations. It is tempting to assume that the increased blood flow improves muscle nutritions in readiness for action (very limited effect).
Metabolic hyperaemia, by contrast, cause capillary recruitment which facilitates the transfer of all solutes.
It cannot be emphasized too strongly that ………………….., not sympathetic vasodilator nerves, cause the hyperemia associated with normal, non-emotional exercise.
Metabolic hyperaemia, by contrast, cause capillary recruitment which facilitates the transfer of all solutes.
It cannot be emphasized too strongly that local metabolic factors, not sympathetic vasodilator nerves, cause the hyperemia associated with normal, non-emotional exercise.
Perhaps a greater advantage of the rapid cholinergic vasodilation is that it prevents …………………….. when the heart rate suddenly increases, as it does in the alerting response.
Perhaps a greater advantage of the rapid cholinergic vasodilation is that it prevents an excessive rise in blood pressure and afterload when the heart rate suddenly increases, as it does in the alerting response.
Sympathetic NANC vasodilatation:
A few tissues, such as the cat paw pad, are innervated by sympathetic vasodilator nerves whose neurotransmitter is neither acetylcholine nor adrenaline. Which one is it?
The non-cholinergic non-adrneergic (NANC) transmitter seems to be a neuropeptide called vasoactive intestinal polypeptide (VIP).
Parasympathetic vasodilator nerves: Parasympathetic perganglionic fibres are much …….. than their sympathetic counterparts and leave the central nervous system in 2 outflows: The cranial nerve outflow (e.g. vagus) and the sacral spinal outflow.
Parasympathetic perganglionic fibres are much longer than their sympathetic counterparts and leave the central nervous system in 2 outflows: The cranial nerve outflow (e.g. vagus) and the sacral spinal outflow.
The distribution of parasymp vasodilator fibres distribution is ……………. than that of sympathetic vasoconstrictor fibres. The ……… preganglionic fibres synapse with postganglionic neurons …… the end-organ, and these send ……….. postganglionic fibres to the arterioles. The fibres are not tonically active, firing only when organ function demands a …… in blood flow.
The distribution of parasymp vasodilator fibres distribution is less universal than that of sympathetic vasoconstrictor fibres. The long preganglionic fibres synapse with postganglionic neurons within the end-organ, and these send short postganglionic fibres to the arterioles. The fibres are not tonically active, firing only when organ function demands a rise in blood flow.
The postganglionic fibres release the classical neurotransmitter ………., which hyperpolarizes some VSM cells to cause vascular ………… Fig 11.13, resulting in an increased blood flow.
The postganglionic fibres release the classical neurotransmitter acethylcholine, which hyperpolarizes some VSM cells to cause vascular relaxation. Fig 11.13, resulting in an increased blood flow.
It has become clear in recent years that most parasympathetic postganglionic fibres can release not only acetylcholine but also ……………………(NANC) transmitters with a vasodilator action.
(accordingly, nerve-induced dilatation of some arteries, is only partially prevented by atropine)
The predominant NANC vasodilator transmitter is a neuropeptide, …………… which aslo occurs in sympathetic cholinergic fibres.
It has become clear in recent years that most parasympathetic postganglionic fibres can release not only acetylcholine but also non-cholinergic, non-adrenergic (NANC) transmitters with a vasodilator action.
(accordingly, nerve-induced dilatation of some arteries, is only partially prevented by atropine)
The predominant NANC vasodilator transmitter is a neuropeptide, vasoactive intestinal polypeptide (VIP), which aslo occurs in sympathetic cholinergic fibres.
Hormonal control of the circulation:
Several endocrine secretions have acute effects on the heart and circulation, but these need to be viewed in perspective; in normal healthy animals …………. are of less importance for short-term cardiovascular regulation than is ……………..control.
Several endocrine secretions have acute effects on the heart and circulation, but these need to be viewed in perspective; in normal healthy animals hormones are of less importance for short-term cardiovascular regulation than is neural control.
If however neural control is impair, as in transplanted hearts or if a pathological event such as hemorrhage arises, then ……….. secretions become very important.
If however neural control is impair, as in transplanted hearts or if a pathological event such as hemorrhage arises, then endocrine secretions become very important.
Hormones such as ………are also of major importance in the long-term regulation of plasma volume.
Hormones such as aldosterone are also of major importance in the long-term regulation of plasma volume.
Adrenaline: The medulla (core) of the adrenal gland secretes adrenaline (epinephrine) and noradrenaline (norephinephrine)., which are known collectively as the c……………..
The medulla (core) of the adrenal gland secretes adrenaline (epinephrine) and noradrenaline (norephinephrine)., which are known collectively as the catecholamines.
Adrenaline is a …………. form of noradrenaline.
Adrenaline is a methylated form of noradrenaline.
The medulla develops, embryologically, from ……… ……… neurons, and it retained an innervation by preganglionic sympathetic fibres which run in the splanchnic nerve and control the gland.
The medulla develops, embryologically, from postganglionic sympathetic neurons, and it retained an innervation by preganglionic sympathetic fibres which run in the splanchnic nerve and control the gland.
Although both adrenaline and noradrenaline are secreted, adrenaline forms over ……… of the secretion in man (in diving mammals, by contrast, the secretion is mainly noradrenaline: this induces muscle vasoconstriction during dives and thereby conserves oxygen)
Although both adrenaline and noradrenaline are secreted, adrenaline forms over 3/4 of the secretion in man
The catecholamines are secreted in response to …..(4)?
exercise, fear-flight -fight situations, hypotension and hypoglycemia.
Adrenaline affects both the heart and vasculature but these effects are quite small at physiological concentrations compared with the effects of the autonomic nerves and local factors (The metabolic effects of adrenaline are at least as important as its cardiovascular effects; namely the stimulation of liver glycogenolysis, and fat lipolysis, which releases glucose into the blood streatm).
Adrenaline affects both the heart and vasculature but these effects are quite small at physiological concentrations compared with the effects of the autonomic nerves and local factors (The metabolic effects of adrenaline are at least as important as its cardiovascular effects; namely the stimulation of liver glycogenolysis, and fat lipolysis, which releases glucose into the blood streatm).
Adrenaline and noradrenaline show some similarities and some differences in their effect on the circulation: See Fig 11.5. Describe the similarities:
Both hormones stimulate the cardiac beta-adrenoceptors, so their direct action is to increase heart rate and contractility.
Both hormones at physiological concentrations cause the arterioles and veins to contract in many tissues and at high concentrations both cause vasoconstriction in all tissues. This is due to activation of the VSM alpha adrenoceptors. (many students have an ingrained belief that adrenaline necessarily causes vasodilatation but this is simply not true).
As an exception to the rule that catecholamines cause vasoconstriction, adrenaline at physiological concentrations causes vasodilatation in three tissues; namely? Why?
Skeletal muscle,
Myocardium,
Liver
This is due to the abundance of beta-adrenoceptors in these tissues, coupled with the high affinity of adrenaline for beta-receptors.
After beta-blockade by propranolol, adrenaline causes vasoconstriction even in skeletal muscle. Why?
Because it activates alpha-receptors too.
Noradrenaline normally causes vasoconstriction. Why?
Because it has a higher affinity for alpha-receptors than beta receptors.
Noradrenaline and noradrenaline thus have opposite effect on …………., the single most abundant tissue in the body (approximately 40% body weight), and as a result their overall effects on the systemic circulation differ considerably in an intact animal.
Noradrenaline and noradrenaline thus have opposite effect on skeletal muscle, the single most abundant tissue in the body (approximately 40% body weight), and as a result their overall effects on the systemic circulation differ considerably in an intact animal.
Effects on skeletal muscle: IV Noradrenaline causes a generalized ……………, which raises the peripheral resistance and blood pressure markedly. (see Fig 11.15). This elicits a ………….. reflex which reduces the sympathetic drive to the heart and increases the ………. drive. These reflexes………. the heart and ………………….. its output, offsetting the direct stimulatory effect of noradrenaline on the myocardium.
IV Noradrenaline causes a generalized vasoconstriction, which raises the peripheral resistance and blood pressure markedly. (see Fig 11.15). This elicits a baroreceptor reflex which reduces the sympathetic drive to the heart and increases the parasympathetic drive.
These reflexes slow the heart and reduce its output, offsetting the direct stimulatory effect of noradrenaline on the myocardium.
Effects on skeletal muscle: IV adrenaline by contrast …………. the total peripheral resistance slightly, because muscle …….. outweighs …………… in other tissues. Mean blood pressure therefore changes little, and the direct stimulation of the heart by circulating adrenaline proceeds without signifiant opposition by the baroreflex.
IV adrenaline by contrast reduces the total peripheral resistance slightly, because muscle vasodilatation outweighs vasoconstriction in other tissues. Mean blood pressure therefore changes little, and the direct stimulation of the heart by circulating adrenaline proceeds without signifiant opposition by the baroreflex.
Effects on skeletal muscle: Since adrenaline is the predominant catecholamine secreted by the human medulla, the overall effect of adrenal stimulation is to increase ……………….
Since adrenaline is the predominant catecholamine secreted by the human medulla, the overall effect of adrenal stimulation is to increase cardiac output.
A rare tumor of the adrenal medulla, the phaeochromocytoma, secretes a mixture of catecholamines, causing hypertension. The latter can be treated with alpha-antagonisists like phentolamine.
A rare tumor of the adrenal medulla, the phaeochromocytoma, secretes a mixture of catecholamines, causing hypertension. The latter can be treated with alpha-antagonisists like phentolamine.
The remaining important hormones all have roles in the regulation of renal fluid excretion as well as vascular tone.
The remaining important hormones all have roles in the regulation of renal fluid excretion as well as vascular tone.
Vasopressin is a peptide produced by the magnocellular neurons in the supraoptic and paraventricular nuclei of the …………………. From the cell bodies, the vasopressin is transported along the axons, through the pituitary stalk and into the ……… lobe of the pituitary gland. There, the vasopressin is released into the blood stream.
Vasopressin is a peptide produced by the magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus. From the cell bodies, the vasopressin is transported along the axons, through the pituitary stalk and into the posterior lobe of the pituitary gland. There, the vasopressin is released into the blood stream.
The secretion of vasopressin is regulated by? (2)
Partly by hypothalamic cells sensitive to tissue fluid osmolarity (osmoreceptors) and partly by cardiovascular pressure receptors.
The main action of vasopressin at normal plasma levels?
To promote water retention by the kidney.
The cardiovascular effects of vasopressin are seen at higher concentrations, such as occur during …………….. in response to reduced pressure receptor traffic.
The cardiovascular effects of vasopressin are seen at higher concentrations, such as occur during haemorrhagic hypotension in response to reduced pressure receptor traffic.
High concentrations of vasopressin cause a strong …………. in most tissues which helps to support arterial pressure and contributes to the pallor of the hypovolaemic patient.
High concentrations of vasopressin cause a strong vasoconstriction in most tissues which helps to support arterial pressure and contributes to the pallor of the hypovolaemic patient.
The cerebral and coronary vessels, by contrast, respond to vasopressin with an EDRF-mediated …………..; vasopressin thus produces a ………. of the cardiac output in favor of the brain and heart, as is appropriate in hypovolaemia.
The cerebral and coronary vessels, by contrast, respond to vasopressin with an EDRF-mediated dilatation; vasopressin thus produces a redistribution of the cardiac output in favor of the brain and heart, as is appropriate in hypovolaemia.
In dogs with diabetes insipid us and in Brattleboro rats, both of which lack vasopressin, blood pressure is abnormally depressed during dehydration or hemorrhage.
In dogs with diabetes insipid us and in Brattleboro rats, both of which lack vasopressin, blood pressure is abnormally depressed during dehydration or hemorrhage.
RAAS:: Angiotensin II is a circulating ………. with a powerful vasoconstrictor action.
Angiotensin II is a circulating octapeptide with a powerful vasoconstrictor action.
Ang II production is initiated by an enzyme: renin, which is secreted into the bloodstream by the juxtaglomerular cells of the kidney in response to ……..and ……………. Renin enzymatically cleaves an …………… in plasma (angiotensionogen) to produce a peptide, Ang I. Ang I is then modified by an enzyme on the surface of ………..cells (converting enzyme) to form any II. This process taking place mainly in the ……….
Ang II production is initiated by an enzyme: renin, which is secreted into the bloodstream by the juxtaglomerular cells of the kidney in response to hypotension and renal sympathetic nerve activity. Renin enzymatically cleaves a n alpha-globulin in plasma (angiotensionogen) to produce a peptide, ang I. Ang I is then modified by an enzyme on the surface of endothelial cells (converting enzyme) to form any II. This process taking place mainly in the lungs.
At normal plasma concentrations, the main role of angiotensin II is to?
At normal plasma concentrations, the main role of angiotensin II is to stimulate the secretions of aldosterone, an adrenal cortical hormone that causes the kidney to retina salt and water.
At higher concentrations, however, Ang II elicits vasoconstriction and does so in a rather interesting fashion. How? (2)
Not only does it directly stimulate the VSM cell, but it also enhances noradrenaline release by the sympathetic fibres barrier at the area postrema to simulate sympathetic activity (central action).
Renin and angiotensin levels are particularly high after a ……….. and help to support the blood pressure in this situation.
Renin and angiotensin levels are particularly high after a hemorrhage and help to support the blood pressure in this situation.
ANP: this peptide is secreted by specialized myocytes in the …..in respond to high cardiac filling pressures.
this peptide is secreted by specialized myocytes in the atria in respond to high cardiac filling pressures.
ANP. In contrast to vaspressin and the RAAS, ANP enhances the renal excretion of ………….. and has a modest relaxing effect on resistance vessels. It also ………….. plasma volume to a greater extent that can be accounted of by diuresis alone, which may be due to a …….. in capillary pressure and an ……… in the hydraulic conductance of the capillary wall.
ANP. In contrast to vaspressin and the RAAS, ANP enhances the renal excretion of salt and water and has a modest relaxing effect on resistance vessels. It also reduces plasma volume to a greater extent that can be accounted of by diuresis alone, which may be due to a rise in capillary pressure and an increase in the hydraulic conductance of the capillary wall.
Special features of venous control: The control of the peripheral capacitance vessels is very important: Why?
Because these vessels govern the distribution of blood volume between the periphery and thorax, they therefore regulate cardiac filling pressure and thereby influence stroke volume.
Differentiation of the venous system: With regard to control and function, the venos system may be divide into 4 parts (Fig 11.16). Which parts?
The passive thoracic vessels and 3 peripheral systems (splanchnic veins, skeletal muscle veins and cutaneous veins).
Splanchnic veins: The veins of the gastrointestinal tract, liver and spleens contain about ……% of the total blood volume at rest. They are well innervated by sympathetic ……. nerves and possess ……..
The veins of the gastrointestinal tract, liver and spleens contain about 20% of the total blood volume at rest. They are well innervated by sympathetic constrictor nerves and possess alpha-adrenoreceptors.
Splanchnic veins are well innervated b sympathetic constriction nerves and possess alpha-adrenoreceptors. They contract actively during ……. and ……….. due to increased sympathetic activity and circulating catecholamines. See Fig 11.17). This helps to maintain ……… at times of circulatory stress.
Splanchnic veins are well innervated b sympathetic constriction nerves and possess alpha-adrenoreceptors. They contract actively during exercise and hypotension due to increased sympathetic activity and circulating catecholamines. See Fig 11.17). This helps to maintain CVP at times of circulatory stress.
Skeletal muscle veins: The intramuscular veins are very poorly ……… . Their volume is influenced chiefly by ………. and by the ………….. Although direct sympathetic control of these veins is almost nonexistent, their constriction ………… the downstream pressure, allowing the venous system to recoil elastically and displace blood centrally.
The intramuscular veins are very poorly enervated. Their volume is influenced chiefly by body posture (i.e gravity) and by the muscle pump. Although direct sympathetic control of these veins is almost nonexistent, their constriction reduces the downstream pressure, allowing the venous system to recoil elastically and displace blood centrally. (Fig 11.11)
Cutaneous veins:
These are richly innervated by sympathetic noradrenergic fibres. Their done is greatly influenced by?
Temperature. High core temperature elicit a reduction in cutaneous sympathetic nerve actiity producing venodilatation. Conversely, raised sympathetic activity causes the skin veins to contract strongly, as happens in hypotensive patients as part of the baroreflex.
High core temperature elicit a reduction in cutaneous sympathetic nerve actiity producing venodilatation.
A sympathetic mediated constriction of the skin veins is also elicited by ……(2)?
A sympathetic mediated constriction of the skin veins is also elicited by emotional stress and by deep inspiration.
Comparison between venous control and arteriolar contral:
Veins response in the same way as arterioles to many stimuli; int the skin for ex; bot are constricted during hypotension; but there are also differences between venous and arteriolar behavior. Which ones?
Most veins and venues have little basal tone i the absence of sympathetic activity, unlike arterioles, and they show little myogenic response to stretch (except for the portal vein). The responsens to certain hormones, autocoids and drugs also differ. Ang II for ex has little direct effect on veins but a powerful effect of sympathetic nerves on human veins (neuromodulatory action), and this action contributes to the intense venoconstrciton seen in patients with cardiac failure, who commonly hava high angiotension levels.
Ang II for ex has little direct effect on veins but a powerful effect of sympathetic nerves on human veins (neuromodulatory action), and this action contributes to the intense venoconstrciton seen in patients with cardiac failure, who commonly hava high angiotension levels.
Histamine effect on veins resp arterioles?
Histamine causes veins to constrict but arterioles to dilate.
Glyceryl trinitate effect on veins resp arterioles?
Glyceryl trinitrate has a greater dilator effect on veins than on arterioles, and its efficacy in relieving angina is now recognized as being due partly to the reduction of cardiac filling pressure (and therefore cardiac work) following ventilation.
Summary: Although very complex in detail, the control of blood vessels can be conceptualized fairly simply as a hierarchy of 3 control systems; each able to override the lower one. The lowest level of control is the …………., which tends to maintain a constant blood flow and capillary pressur in the face of arterial pressure fluctuations (auto regulation).
The lowest level of control is the Bayliss myogenic response, which tends to maintain a constant blood flow and capillary pressur in the face of arterial pressure fluctuations (auto regulation).
Although very complex in detail, the control of blood vessels can be conceptualized fairly simply as a hierarchy of 3 control systems; each able to override the lower one. The second level of control is that exerted by ……………….., which reset blood flow and auto regulation to a level appropriate to the tissue’s metabolic activity. This process is predominant in the heart and brain, and in exercising skeletal muscle.
The second level of control is that exerted by local metabolites, which reset blood flow and auto regulation to a level appropriate to the tissue’s metabolic activity. This process is predominant in the heart and brain, and in exercising skeletal muscle.
Although very complex in detail, the control of blood vessels can be conceptualized fairly simply as a hierarchy of 3 control systems; each able to override the lower one.
The third levels of control is the neuroendocrine system, which manipulates the vasculature of tissues like the skin and the splanchninc region for the benefit of the organism as a whole, or rather, for the benefit of the brain, which has ultimate control over the vasculature.
The third levels of control is the neuroendocrine system, which manipulates the vasculature of tissues like the skin and the splanchninc region for the benefit of the organism as a whole, or rather, for the benefit of the brain, which has ultimate control over the vasculature
Specialization in individual circulations:
The coronary circulation must deliver oxygen at a high rate to keep pace with cardiac demand. Autoregulation is well developed in the coronary circulation and is reset by metabolic vasodilatation to operate at a higher flow.
Specialization in individual circulations:
The coronary circulation must deliver oxygen at a high rate to keep pace with cardiac demand. Autoregulation is well developed in the coronary circulation and is reset by metabolic vasodilatation to operate at a higher flow.
As the pulmonary vessels are thin-walled, their compliance is …..
high.
Coronary circulation: Flow during basal cardiac output in man: ….. ml min -1 -100 g -1
70-80 ml
Coronary circulation: Flow during maximal cardiac output in man: ….. ml min -1 -100 g -1
300-400
The right and left coronary arteries arise from?
From the aorta immediately above the cusps of the aortic valve, the left coronary artery supplying mainly the left ventricle and septum and the right artery mainly the right ventricle; though this distribution is somewhat variable in man.
Most of the venous blood drains via the coronary …… directly into the ……. (95%) and the rest drains into the cardiac chambers via the anterior coronary and theBesian veins.
Most of the venous blood drains via the coronary sinus directly into the RA (95%) and the rest drains into the cardiac chambers via the anterior coronary and theBesian veins.
The coronary circulation is the shortest in the body, the mean transit time of the coronary blood being only 6-8 s at rest.
The coronary circulation is the shortest in the body, the mean transit time of the coronary blood being only 6-8 s at rest.
Special tasks of the coronary circulation: The coronary circulation must deliver oxygen at a high rate to keep pace with cardiac demand. Even in a resting subject, the myocardial oxygen consumption is very high, namely approximately ….. ml of oxygen per min per 100 g; this is ……. times greater than in resting skeletal muscle.
Special tasks of the coronary circulation: The coronary circulation must deliver oxygen at a high rate to keep pace with cardiac demand. Even in a resting subject, the myocardial oxygen consumption is very high, namely approximately 8 ml of oxygen per min per 100 g; this is 20 times greater than in resting skeletal muscle.
In exercise, where cardiac work rate can increase over fivefold, the coronary circulation must increase its delivery of oxygen correspondingly
In exercise, where cardiac work rate can increase over fivefold, the coronary circulation must increase its delivery of oxygen correspondingly
Myocardial capillary density is very high; there being ………….. capillaries per mm2 cross-section, or roughly one capillary per myocyte. See Fig 12.1. This facilitates the efficient delivery of oxygen and nutrients to the cell, partly be creating a very large endothelial area for exchange and partly by reducing the maximum diffusion distance to only 9 um (the myocyte being approximately 18 um wide)
Myocardial capillary density is very high; there being 3000-5000 capillaries per mm2 cross-section, or roughly one capillary per myocyte. See Fig 12.1. This facilitates the efficient delivery of oxygen and nutrients to the cell, partly be creating a very large endothelial area for exchange and partly by reducing the maximum diffusion distance to only 9 um (the myocyte being approximately 18 um wide)
In a resting subject, the blood flow per unit weight of myocardium is roughly ten times the average value for the whole body. Even so, the myocardium extracts ……. % of the oxygen from the coronary blood, in contrast to the whole body average of ….. % at rest. See Fig 12.2.
In a resting subject, the blood flow per unit weight of myocardium is roughly ten times the average value for the whole body. Even so, the myocardium extracts 65-75% of the oxygen from the coronary blood, in contrast to the whole body average of 25% at rest. See Fig 12.2.
The high extraction reduces the oxygen content from 195 ml/litre in arterial blood to only 50-70 ml/litre in coronary sinus blood.
The corresponding oxygen pressure (PO2) in coronary venous blood is only ….. mmHg, and in the myocardial fibre itself the PO2 is only about …. mmHg, falling further during exercise.
The corresponding oxygen pressure (PO2) in coronary venous blood is only 20 mmHg, and in the myocardial fibre itself the PO2 is only about 6 mmHg, falling further during exercise.
In heavy exercise, coronary oxygen extraction can rise to 90% leaving just …… ml oxygen in each litre of venous blood at a PO2 of only 10 mmHg.
In heavy exercise, coronary oxygen extraction can rise to 90% leaving just 20 ml oxygen in each litre of venous blood at a PO2 of only 10 mmHg.
The extraction of fatty acid from coronary blood is also …….(………….%), but glucose extraction is usually ….. (……%), reflecting the substrate preference of myocardium.
The extraction of fatty acid from coronary blood is also high (40-70%), but glucose extraction is usually low (2-3%), reflecting the substrate preference of myocardium.
Metabolic hyperaemia, the dominant control process:
The extra oxygen required at high work rates is supplied chiefly by an increase in …………..rather than extraction; the latter can increase only modestly.
The extra oxygen required at high work rates is supplied chiefly by an increase in blood flow rather than extraction; the latter can increase only modestly.
Coronary blood flow increases in almost linear proportion to myocardial oxygen consumption at light to moderate work rates, whilst at high work rates the flow increase lags a little and oxygen ……… rises.
Coronary blood flow increases in almost linear proportion to myocardial oxygen consumption at light to moderate work rates, whilst at high work rates the flow increase lags a little and oxygen extraction rises.
Fig 12.3
Myocardial metabolism evidently generates vasodilator messags in a q…….. manner (metabolic hyperemia). The nature of the vasodilator substances, however, remains a well-sought but carefully guarded secret of nature.
Myocardial metabolism evidently generates vasodilator messags in a quantitate manner (metabolic hyperemia). The nature of the vasodilator substances, however, remains a well-sought but carefully guarded secret of nature.
The major contenders for the role are interstitial…… and …….. released by myocytes following ATP degradation. Both candidates dilate coronary arterioles, and the adenosine versus hypoxia controversy remains unresolved.
The major contenders for the role are interstitial hypoxia and adenosine released by myocytes following ATP degradation. Both candidates dilate coronary arterioles, and the adenosine versus hypoxia controversy remains unresolved.
Autoregulation is well developed in the coronary circulation and is reset by metabolic …………………to operate at a higher flow.
Autoregulation is well developed in the coronary circulation and is reset by metabolic vasodilatation to operate at a higher flow.
Autoregulation protects myocardium against underperfusion during periods of low blood pressure, though only down to about …… mmHg.
Autoregulation protects myocardium against underperfusion during periods of low blood pressure, though only down to about 50 mmHg.
The coronary vasomotor nerves: Myocardial arteries and arterioles are well innervated by sympathetic …………… fibres, whose tonic discharge contributes to the arteriolar tone.
Myocardial arteries and arterioles are well innervated by sympathetic vasoconstrictor fibres, whose tonic discharge contributes to the arteriolar tone.
Myocardial arteries and arterioles are well innervated by sympathetic vasoconstrictor fibres, whose tonic discharge contributes to the arteriolar tone.
This effect is overcome, in a graded fashion, during metabolic vasodilatation. If all the sympathetic fibres to the heart are excited, including those to the pacemaker and myocytes, the ensuing increase in heart rate and contractility raises the cardiac work and the concomitant metabolic vasodilatation outweighs the increased vasoconstrictor nerve activity: blood flow ………
This effect is overcome, in a graded fashion, during metabolic vasodilatation. If all the sympathetic fibres to the heart are excited, including those to the pacemaker and myocytes, the ensuing increase in heart rate and contractility raises the cardiac work and the concomitant metabolic vasodilatation outweighs the increased vasoconstrictor nerve activity: blood flow increases.
This metabolic “over-riding” of vasoconstriction ensures that any generalize activation of the sympathetic system does not adversely affect the blood flow to this vital organ.
Adrenaline, secreted at times of stress, reinforces the coronary hyperemia by preferentially activating ……….on the coronary VSM, causing ………….. There is some evidence that parasympathetic cholinergic fibres too can ………… coronary arteries but this is not though to be important in exercise.
Adrenaline, secreted at times of stress, reinforces the coronary hyperemia by preferentially activating beta-adrenoreceptors on the coronary VSM, causing dilatation. There is some evidence that parasympathetic cholinergic fibres too can dilate coronary arteries but this is not though to be important in exercise.
The branches of the coronary arteries within the myocardium are compressed during each systole. This effects is at its worst in the LV during ………………… when pressure with the ventricular wall reaches approximately 240 mmHg and coronary vessels transiently ………. them so that coronary blood flow ceases briefly and even reverses in early systole. See Fig 12.4.
The branches of the coronary arteries within the myocardium are compressed during each systole. This effects is at its worst in the LV during isovolumetric contraction when pressure with the ventricular wall reaches approximately 240 mmHg and coronary vessels transiently closes them so that coronary blood flow ceases briefly and even reverses in early systole. See Fig 12.4.
A modest coronary flow is restored during the ejection phase as stress in the ventricle wall eases and the arterial pressure rises, but flow is only restored fully during …… Roughly 80% of coronary flow occurs in ……………. at basal heart rates.
A modest coronary flow is restored during the ejection phase as stress in the ventricle wall eases and the arterial pressure rises, but flow is only restored fully during diastole. Roughly 80% of coronary flow occurs in diastole at basal heart rates.
Although cross-connection exist between the branches of the coronary arteries they are few in number and small in diameter in man, and can transmit only a low flow.
Although cross-connection exist between the branches of the coronary arteries they are few in number and small in diameter in man, and can transmit only a low flow.
Human coronary arteries have been called “functional” end arteries: because if an atheromatous artery is suddenly blocked by thrombosis, the residual blood flow to the tissue downstream is less than 10% of normal, which is insufficient to support normal contraction and metabolism (ischemia).
Human coronary arteries have been called “functional” end arteries: because if an atheromatous artery is suddenly blocked by thrombosis, the residual blood flow to the tissue downstream is less than 10% of normal, which is insufficient to support normal contraction and metabolism (ischemia).
The ischaemic myocardium becomes acidotic, causing severe cardiac pain and malfunction. The residual flow may be so low that myocutes begin to die after a few hours (necrosis see Fig 1.2). This sequence of events is called myocardial infarction or a heart attack, and is the single commonest cause of death in the West.
The ischaemic myocardium becomes acidotic, causing severe cardiac pain and malfunction. The residual flow may be so low that myocutes begin to die after a few hours (necrosis see Fig 1.2). This sequence of events is called myocardial infarction or a heart attack, and is the single commonest cause of death in the West.
Myocardial infarcts are more frequent and largest in the subendocardium (inner tissue. Why?
Because the wall stress during systole is greatest here and selectively curtails endocardial blood flow at low perfusion pressures.
Angina pectoris can be relieved by nitrodilator drugs, like ……………….. which causes peripheral ………. and …………. This lowers the filling pressure and arterial pressure, which in turn reduced cardiac work and oxygen demand.
Angina pectoris can be relieved by nitrodilator drugs, like glyceryl trinitrate which causes peripheral ventilation and vasodilation. This lowers the filling pressure and arterial pressure, which in turn reduced cardiac work and oxygen demand; this lowers the filling pressure and arterial pressure, which in turn reduced cardiac work and oxygen demand.
Beta-adrenergic blockers like propranolol reduce ……..demand by reducing……and…….
Beta-adrenergic blockers like propranolol reduce oxygen demand by reducing heart rate and contractility.
Assessment of human coronary circulation: located by arteiography (coronary angiography). Blood flow can be measure more quantitatively by the coronary sinus thermodilution method.
PET (positron emission tomography) is another method for imaging myocardial perfusion.
Assessment of human coronary circulation: located by arteiography (coronary angiography). PET (positron emission tomography) is another method for imaging myocardial perfusion.Assessment of human coronary circulation: located by arteiography (coronary angiography). Blood flow can be measure more quantitatively by the coronary sinus thermodilution method.
PET (positron emission tomography) is another method for imaging myocardial perfusion.
Circulations of skeletal muscle and cardiac muscle: In common :predominance of …………control
But there are aslo some marked differences, such as the greater role of ……….. reflexes in the regulation of resting skeletal muscle flow.
In common :predominance of metabolic control
But there are aslo some marked differences, such as the greater role of nervous reflexes in the regulation of resting skeletal muscle flow.
During exercise, the circulation must deliver ……….. and …………….to the muscle fibres at an increased rate and remove waste products and heat at a increased rate.
During exercise, the circulation must deliver oxygen and glucose to the muscle fibres at an increased rate and remove waste products and heat at a increased rate.
The regulation of arterial pressure is a less obvious but very important duty of skeletal muscle vascular. Skeletal muscle constitutes about …. % of the adult body mass, and the resistance of this large vascular bed has a substantial effect on blood pressure.
The regulation of arterial pressure is a less obvious but very important duty of skeletal muscle vascular. Skeletal muscle constitutes about 40% of the adult body mass, and the resistance of this large vascular bed has a substantial effect on blood pressure.
Skeletal muscle arterioles are richly innervated by sympathetic vasoconstrictor fibres whose tonic discharge enhances arteriolar tone in resting muscle; a high arteriolar tone is of course a prerequisite if …………. (loss of tone) is to be possible.
Skeletal muscle arterioles are richly innervated by sympathetic vasoconstrictor fibres whose tonic discharge enhances arteriolar tone in resting muscle; a high arteriolar tone is of course a prerequisite if dilatation (loss of tone) is to be possible.
The vasoconstrictor nerve activity is controlled reflexly by blood pressure receptors in the ……. and ……, and when vasoconstrictor activity is increased by these reflexes (as in orthostasis and hypovolemia) the resistance of the muscle circulation ……..
Aided by similar changes in the …….. and ……… circulations this plays an important part in the regulation of arterial pressure, which depends on peripheral resistance and cardiac output.
The vasoconstrictor nerve activity is controlled reflexly by blood pressure receptors in the thorax and neck, and when vasoconstrictor activity is increased by these reflexes (as in orthostasis and hypovolemia) the resistance of the muscle circulation increases.
Aided by similar changes in the splanchnic and renal circulations this plays an important part in the regulation of arterial pressure, which depends on peripheral resistance and cardiac output.
After a severe haemorrhage, the vasoconstrictor discharge to skeletal muscle reaches its maximum rate, namely 6-10 per s, and flow is ……… …………….
After a severe haemorrhage, the vasoconstrictor discharge to skeletal muscle reaches its maximum rate, namely 6-10 per s, and flow is reduced to around 1/5 the normal level —an exceedingly low perfusion indeed.
Skeletal muscle: During strenuous exercise the mean flow through phasic muscle can increase more then ……-fold; indeed, it is estimated that if all the muscle groups were maximally vasodilator at the same time the output capacity of the heart would be greatly exceeded. During strenuous exercis, the muscle blood flow in fact accounts for up to …….% och the cardiac output (cf. ……% at rest)
During strenuous exercise the mean flow through phasic muscle can increase more then 20-fold; indeed, it is estimated that if all the muscle groups were maximally vasodilator at the same time the output capacity of the heart would be greatly exceeded. During strenuous exercis, the muscle blood flow in fact accounts for up to 80-90% och the cardiac output (cf. 18% at rest)
Skeletal muscle: The muscle hyperemia during exercise is due almost entirely to a fall in vascular resistance occasioned by …………….., rather than to the relatively modest changes in arterial pressure.
The muscle hyperemia during exercise is due almost entirely to a fall in vascular resistance occasioned by metabolic vasodilatation, rather than to the relatively modest changes in arterial pressure.
Skeletal muscle: As in myocardium, the flow rises almost linearly with local …… rate, and the nature of the vasodilator agents is again controversial.
Skeletal muscle: As in myocardium, the flow rises almost linearly with local metabolic rate, and the nature of the vasodilator agents is again controversial.
Skeletal muscle: During the first few minutes of exercise, potassium ions released locally by the contracting muscle raise the interstitial potassium concentration around the vessels, causing ………… The local venous concentration of potassium is up to 0.1 mM higher than the arterial value, and this causes a gradual rise in mixed plasma potassium.
Skeletal muscle: During the first few minutes of exercise, potassium ions released locally by the contracting muscle raise the interstitial potassium concentration around the vessels, causing dilatation. The local venous concentration of potassium is up to 0.1 mM higher than the arterial value, and this causes a gradual rise in mixed plasma potassium.
A rise in interstitial osmolarity is important in the early stages of exercise too; the venous effluent osmolarity can increase by 20-30 mOsm. The vasodilator effect of both these factors (………) is potentiated by local …….
A rise in interstitial osmolarity is important in the early stages of exercise too; the venous effluent osmolarity can increase by 20-30 mOsm. The vasodilator effect of both these factors (potassium ion release locally and increased interstitial osmolarity) is potentiated by local hypoxia. ‘The osmolarity level soon decreases, and there are conflicting reports on the potassium levels over long periods,so it is far from clear what maintains the vasodilatation during prolonged exercise.
Only about …… of the capillaries in resting skeletal muscle is well perfused at any one instant. (see Fig 11.1). metabolic vasodilatation increases the well perfused fraction by dilating the terminal arterioles. The capillary ………shortens the extravascular diffusion distances and thus speeds up the exchange process.
Only about a third of the capillaries in resting skeletal muscle is well perfused at any one instant. (see Fig 11.1). metabolic vasodilatation increases the well perfused fraction by dilating the terminal arterioles. The capillary recruitment shortens the extravascular diffusion distances and thus speeds up the exchange process.
Resting skeletal muscle extracts only ……. % of the oxygen from blood, whereas in severe exercise the extraction can reach …..%.
Resting skeletal muscle extracts only 25-30% of the oxygen from blood, whereas in severe exercise the extraction can reach 80-90%.
Intracellular oxygen tension, which in only few mmHg even at rest, falls so low in severe exercise than anaerobic …….. begins to predominate and …….. production increases. The quantity of …….. formed is an index of the deficit in oxygen supply and this “oxygen dept” can reach several litres.
Intracellular oxygen tension, which in only few mmHg even at rest, falls so low in severe exercise than anaerobic glycolysis begins to predominate and lactic acid production increases. The quantity of lactate formed is an index of the deficit in oxygen supply and this “oxygen dept” can reach several litres.
The local lactic acidosis stimulates nociceptive … fibres, causing pain and the termination of violent exercise. The lactate also stimulates muscle “work …….” involved in the reflex control of the circulation.
The local lactic acidosis stimulates nociceptive C fibres, causing pain and the termination of violent exercise. The lactate also stimulates muscle “work receptors” involved in the reflex control of the circulation.
At the end of exercise, a period of post exercise hyperemia re-supplies the muscle with oxygen (which takes only seconds) and more gradually washes out the accumulated lactate and other vasodilator substances. Only a little of the lactate is oxidized locally; most diffuses into the bloodstream and is either taken up by the liver for resynthesis into …….. or by the ……as a primary substrate.
At the end of exercise, a period of post exercise hyperemia re-supplies the muscle with oxygen (which takes only seconds) and more gradually washes out the accumulated lactate and other vasodilator substances. Only a little of the lactate is oxidized locally; most diffuses into the bloodstream and is either taken up by the liver for resynthesis into glycogen or by the heart as a primary substrate.
Although exercise hyperaemis is due chiefly to a fall in vascular resistance, the massaging effect of rhythmic muslce contrition on the deep veins assists limb perfusion.
2 other special adaptions of the skeletal muscle circulation are the sympathetic …………. found in predators like cats and dogs, and the vasodilator response of skeletal muscle arterioles to ……….
Although exercise hyperaemis is due chiefly to a fall in vascular resistance, the massaging effect of rhythmic muslce contrition on the deep veins assists limb perfusion.
2 other special adaptions of the skeletal muscle circulation are the sympathetic vasodilator nerves found in predators like cats and dogs, and the vasodilator response of skeletal muscle arterioles to adrenaline.
When skeletal muscle contracts with 30-70% of its maximum voluntary force, it compresses the intramuscular vessels sufficiently to impair the blood flow. In sustained strong contraction, however, the impairment of flow is maintained, and since the store of oxygen in the muscle’s myoglobin only suffices for 5-10 s of ischemia, the fibres quickly before …… and …………accumulates, leading to pain and fatigue. The rapid loss of strength during a strong sustained contraction will be familiar to anyone who has struggled along with a heavy suitcase.
When skeletal muscle contracts with 30-70% of its maximum voluntary force, it compresses the intramuscular vessels sufficiently to impair the blood flow. In sustained strong contraction, however, the impairment of flow is maintained, and since the store of oxygen in the muscle’s myoglobin only suffices for 5-10 s of ischemia, the fibres quickly before hypoxic and lactate accumulates, leading to pain and fatigue. The rapid loss of strength during a strong sustained contraction will be familiar to anyone who has struggled along with a heavy suitcase.
The problem of fluid translocation across capillaries in exercising muscle, leading to a …..% fall in plasma volume, was described din section 9.9.
The problem of fluid translocation across capillaries in exercising muscle, leading to a 10-15% fall in plasma volume, was described din section 9.9.
The temperature of the human “core” (the brain, thoracic and abdominal organs) is normally kept within a degree or so of 37 grader in people by balancing the internal heat production and the heat loss from the surface. The surface in question depends on the species; the skin in man, the tongue in dogs and the ears in rabbits.
The temperature of the human “core” (the brain, thoracic and abdominal organs) is normally kept within a degree or so of 37 grader in people by balancing the internal heat production and the heat loss from the surface. The surface in question depends on the species; the skin in man, the tongue in dogs and the ears in rabbits.
Heat is lost by 4 processes: …………………… (See fig 12.5)
Heat is lost by 4 processes: radiation, conduction, convection and evaporation. (See fig 12.5)
The cutaneous circulation participates in many cardiovascular reflexes: Hypotension, caused by hypovolemia or acute cardiac failure (shock) reflexly elicits a ………. of the cutaneous veins and arterioles producing the pale, cold skin characteristic of shock. The rise in cutanesous vascular resistance helps to support arterial pressure while the ……. displaces blood centrally and helps to support central venous pressure.
The cutaneous circulation participates in many cardiovascular reflexes: Hypotension, caused by hypovolemia or acute cardiac failure (shock) reflexly elicits a constriction of the cutaneous veins and arterioles producing the pale, cold skin characteristic of shock. The rise in cutanesous vascular resistance helps to support arterial pressure while the venoconstriction displaces blood centrally and helps to support central venous pressure.
The life-preserving vale of venoconstriction became clear on the battlefields of France during World War I; when it was noticed that wounded men who were rescued quickly and warmed in blankets (producing cutaneous dilatation) survived severe hemorrhages less successfully than the men who could not be reached for some time, and therefore inadvertently retained their natural cutaneous vasoconstriction.
The life-preserving vale of venoconstriction became clear on the battlefields of France during World War I; when it was noticed that wounded men who were rescued quickly and warmed in blankets (producing cutaneous dilatation) survived severe hemorrhages less successfully than the men who could not be reached for some time, and therefore inadvertently retained their natural cutaneous vasoconstriction.
Exercise initially evokes a sympathetically mediated ……… in skin, but this later gives way to ……. if core temperature rises.
Exercise initially evokes a sympathetically mediated vasoconstriction in skin, but this later gives way to dilatation if core temperature rises.
Cutaneous vascular response to trauma: The ensuing hyperemia and increased capillary permeability enhance the delivery of the defensive element (white cells and immunoglobulins) to the injured tissue.
Exercise initially evokes a sympathetically mediated vasoconstriction in skin, but this later gives way to dilatation if core temperature rises.
Dilatation of cutaneous veins in a hot environment can lower the ………… and thereby predispose the subject to postural fainting, the classic example being the guardsman who faints while standing at attention in hot weather. Cutaneous ………… also increases the local capillary filtration pressure leading to interstitial swelling; this is why a ring often feels tighter on the finger during hot weather.
Dilatation of cutaneous veins in a hot environment can lower the central venous pressure and thereby predispose the subject to postural fainting, the classic example being the guardsman who faints while standing at attention in hot weather. Cutaneous vasodilatation also increases the local capillary filtration pressure leading to interstitial swelling; this is why a ring often feels tighter on the finger during hot weather.
Cerebral circulation: The brain receives …..% of the resting cardiac output and most of this goes to the grey matter.
The brain receives 14% of the resting cardiac output and most of this goes to the grey matter.
Cerebral circulation: special tasks:
1. Need for a totally secure oxygen supply. Grey matter has a very high rate of oxidative metabolism, and its oxygen consumption accounts for nearly ……% of human oxygen consumption at rest. Grey matter is exquisitely sensitive to hypoxia, and in man consciousness is lost after just a few ……… of cerebral ischaemia, with irreversible cell damage following within minutes. The primary task of the cerebral circulation, and indeed of the entire cardiovascular system, is therefore to secure an uninterrupted delivery of oxygen to the brain.
Cerebral circulation:
1. Need for a totally secure oxygen supply. Grey matter has a very high rate of oxidative metabolism, and its oxygen consumption accounts for nearly 20% of human oxygen consumption at rest. Grey matter is exquisitely sensitive to hypoxia, and in man consciousness is lost after just a few seconds of cerebral ischaemia, with irreversible cell damage following within minutes. The primary task of the cerebral circulation, and indeed of the entire cardiovascular system, is therefore to secure an uninterrupted delivery of oxygen to the brain.
Cerebral circulation: special tasks:
2. Adjustment of local supply to local demand. Many mental functions are localized in well-defined regions; for example visual interpretation is located in the occipital visual cortex. External monitoring of the uptake of radio labeled glucose and oxygen in the human brain has proved that local neuronal activity increases the local metabolic rate. The cerebral circulation must therefore be capable of………….to meed the varying metabolic rate of each region.
Cerebral circulation: special tasks:
2. Adjustment of local supply to local demand. Many mental functions are localized in well-defined regions; for example visual interpretation is located in the occipital visual cortex. External monitoring of the uptake of radio labeled glucose and oxygen in the human brain has proved that local neuronal activity increases the local metabolic rate. The cerebral circulation must therefore be capable of regional adjustment to meed the varying metabolic rate of each region.
Cerebral blood flow, like that to other tissues, depends on vascular conductance and arterial pressure. Unlike any other organ, however, the brain is able to safeguard its own blood supply by controlling the ……….. and the vascular resistance of other organs via its autonomic outflow. Perfusion of peripheral organs (except the ………..) is scarified to preserve cerebral perfusion, when necessary.
Cerebral blood flow, like that to other tissues, depends on vascular conductance and arterial pressure. Unlike any other organ, however, the brain is able to safeguard its own blood supply by controlling the cardiac output and the vascular resistance of other organs via its autonomic outflow. Perfusion of peripheral organs (except the heart) is scarified to preserve cerebral perfusion, when necessary.
Cerebral autoregulation: Autoregulation is very well developed in the brain; a fall in blood pressure causes the resistance vessels to dilate and thereby maintain flow (see Fig 12.7). Below approximately ….mmHg, however, autoregulation fails and cerebral blood flow declines steeply leading to mental confusion and syncope.
Cerebral autoregulation: Autoregulation is very well developed in the brain; a fall in blood pressure causes the resistance vessels to dilate and thereby maintain flow (see Fig 12.7). Below approximately 50 mmHg, however, autoregulation fails and cerebral blood flow declines steeply leading to mental confusion and syncope.
Cerebral auto regulation: The upper limit of autoregulation is probably ……. mmHg. Cerebral auto regulation seems to involve both …….. and …….. mechanisms.
Cerebral auto regulation: The upper limit of autoregulation is probably 175 mmHg. Cerebral auto regulation seems to involve both myogenic and metabolic mechanisms.
Cerebral vessels have a well-developed response to arterial carbon dioxide: Hypercapnia causes ……….. and hypocapnia ……… (see Fig 12.7). These effects are mediated by changes in the ……. concentration, and therefore ……… ion concentration, in the interstitial fluid around the cerebral vessels.
Cerebral vessels have a well-developed response to arterial carbon dioxide: Hypercapnia causes vasodilatation and hypocapnia vasoconstriction (see Fig 12.7). These effects are mediated by changes in the carbonic acid concentration, and therefore hydrogen ion concentration, in the interstitial fluid around the cerebral vessels.
Cerebral vessels have a well-developed response to arterial carbon dioxide: Other intravascular acids like lactic acid are ineffective because unlike carbon dioxide they cannot ………………..
Cerebral vessels have a well-developed response to arterial carbon dioxide: Other intravascular acids like lactic acid are ineffective because unlike carbon dioxide they cannot penetrate the blood-brain barrier.
If arterial PCO2 is reduced to 15 mmHg by hyperventilation (normal value 40 mmHg), cerebral blood flow shelved and …….. can be observed directly in the retina. the retina being embryologiallcy an extension of the brain. Owing to this effect, hysterical hyperventilation can lead to disturbed vision, dizziness, and even fainting.
If arterial PCO2 is reduced to 15 mmHg by hyperventilation (normal value 40 mmHg), cerebral blood flow shelved and vasoconstriction can be observed directly in the retina. the retina being embryologiallcy an extension of the brain. Owing to this effect, hysterical hyperventilation can lead to disturbed vision, dizziness, and even fainting.
The traditional remedy is said to be a paper bag over the subject’s head to cause rebreathing of expired carbon dioxide.
Cerebral vessels dilate in response to local hypoxia, but if the arterial blood is hypoxic it stimulates ventilation too, and the ensuing ………… causes …………………
Cerebral vessels dilate in response to local hypoxia, but if the arterial blood is hypoxic it stimulates ventilation too, and the ensuing hypocapnia causes vasoconstriction.
The cause of cortical metabolic hyperemia is in part an increase in interstitial K+ koncentration, which can rise from its normal level of 3 mM to as much as 10 mM owing to outward current from the active neurons.Other causative factors include?
A rise in interstitial H+ concentration and adenosine concentration, secondary to increased neuronal metabolism.
The intracerebral arterioles are innervated rather poorly whereas the cerebral arteries outside the substance of the brain are well innervated by sympathetic vasoconstrictor nerves. Paricipation of brain vessels in the baroreceptor refelc is, however, negligible, which is clearly a good thing teleologically.
The intracerebral arterioles are innervated rather poorly whereas the cerebral arteries outside the substance of the brain are well innervated by sympathetic vasoconstrictor nerves. Paricipation of brain vessels in the baroreceptor refelc is, however, negligible, which is clearly a good thing teleologically.
The cerebral vessels have few alpha-adrenoreceptors, and the vasoconstriction is probably mediated chiefly by ………….. which is abundant in cerebral sympathetic fibres.
The cerebral vessels have few alpha-adrenoreceptors, and the vasoconstriction is probably mediated chiefly by neuropeptide Y, which is abundant in cerebral sympathetic fibres.
The role of the vasoconstrictor innervation may be to protect the blood-brain barrier against disruption should ………. rise suddenly.
The role of the vasoconstrictor innervation may be to protect the blood-brain barrier against disruption should arterial pressure rise suddenly.
Perivascular nerve fibres also contain 5-hydroxytryptamine, possibly co-stored with ……….; 5-HT hasa powerful ……….effect on cerebral arteries and, along with a high ………. level, is though to contribute to the vasospasm that follows a subarachnoid hemorrhage.
Perivascular nerve fibres also contain 5-hydroxytryptamine, possibly co-stored with noradrenaline; 5-HT hasa powerful vasoconstrictor effect on cerebral arteries and, along with a high K+ level, is though to contribute to the vasospasm that follows a subarachnoid hemorrhage.
Cerebral arteries are innovated by dilator fibres, probably of parasympathetic origin. They contain ……….. and …… but their role is obscure.
Cerebral arteries are innovated by dilator fibres, probably of parasympathetic origin. They contain acetylcholine and VIP but their role is obscure.
Lipid-soluble molecules like ……, …… and xenon diffuse freely between the plasma and brain interstitium but ionic solutes like the dye Evans blue fail to penetrate from plasma into most regions of the brain, demonstrating the existence of a barrier to ……. solutes.
Lipid-soluble molecules like oxygen, carbon dioxide and xenon diffuse freely between the plasma and brain interstitium but ionic solutes like the dye Evans blue fail to penetrate from plasma into most regions of the brain, demonstrating the existence of a barrier to lipid-insoluble solutes.
Because of the blood-brain barrier, the neuronal environment is the most tightly-controlled cellular environment on the body, and the neurons are protected from the fluctuating levels of …. and ….. in the bloodstream.
Because of the blood-brain barrier, the neuronal environment is the most tightly-controlled cellular environment on the body, and the neurons are protected from the fluctuating levels of ions and catecholamines in the bloodstream.
The blood-brain barrier can be disrupted experimentally by hyperosmotic infusions, and is disrupted clinically by acute hypertension or cerebral ischaemia.
There are a few regions where the barriers is normally absent; these being regions where plasma solutes have access to receptors (e.g to the osmoreceptores in the circumventricular regions.)
The blood-brain barrier can be disrupted experimentally by hyperosmotic infusions, and is disrupted clinically by acute hypertension or cerebral ischaemia.
There are a few regions where the barriers is normally absent; these being regions where plasma solutes have access to receptors (e.g to the osmoreceptores in the circumventricular regions.)
People: Gravity influence cerebral blood flow indirectly in that central venous pressure and stroke volume are reduced in the upright posture. The ensuing postural ……………. can reduce cerebral flow to the point of dizziness or fainting (postural syncope) in the absence of brisk autonomic reflexes.
Gravity influence cerebral blood flow indirectly in that central venous pressure and stroke volume are reduced in the upright posture. The ensuing postural hypotension can reduce cerebral flow to the point of dizziness or fainting (postural syncope) in the absence of brisk autonomic reflexes.
Except in the neonate, the brain is enclosed in a rigid bony box. Any space occupying lesion ( a cerebral tumour or hemorrhage) raises the intracranial pressure and forces the …… down into the ………… As the ………..becomes compressed, altered activity in the neurons controlling the sympathetic system causes a rise in sympathetic vasomotor drive, and thus a …….. in arterial blood pressure (…… reflex).
Any space occupying lesion ( a cerebral tumour or hemorrhage) raises the intracranial pressure and forces the brainstem down into the foramen magnum. As the brainstem becomes compressed, altered activity in the neurons controlling the sympathetic system causes a rise in sympathetic vasomotor drive, and thus a rise in arterial blood pressure (Cushing’s reflex).
Cushing’s reflex: The elevated blood pressure also evokes a ……… via the baroreceptor reflex, and the combination of ………….and acute hypertension is recognized by neurologists as the hallmark of a large, space-occupying lesion
Cushing’s reflex: The elevated blood pressure also evokes a bradycardia via the baroreceptor reflex, and the combination of bradycardia and acute hypertension is recognized by neurologists as the hallmark of a large, space-occupying lesion
Pulmonary circulation:
The lung circulation differs very substantially from the various systemic circulations. The entire output of the right ventricle flows through the …….., so their perfusion vastly exceeds their nutritional needs and ………factors exert no influence on flow.
The lung circulation differs very substantially from the various systemic circulations. The entire output of the right ventricle flows through the alveoli, so their perfusion vastly exceeds their nutritional needs and metabolic factors exert no influence on flow.
Pulmonary circulation:
The metabolic needs of the bronchi are met by an independent systemic, ………..
The metabolic needs of the bronchi are met by an independent systemic, bronchial circulation.
Pulmonary circulation:
There is only a low basal tone in the pulmonary circulation and no ……… Sympathetic vasomotor nerves exist but have no ………..
There is only a low basal tone in the pulmonary circulation and no auto regulation. Sympathetic vasomotor nerves exist but have no well-defined physiological role.
Pulmonary vascular resistance is about an eighth that of the systemic circulation so the arterial pressure is low: Typically ….. mmHg in systole and ….. mmHg in diastole.
Pulmonary vascular resistance is about an eighth that of the systemic circulation so the arterial pressure is low: Typically 20-25 mmHg in systole and 6-12 mmHg in diastole.
Pulmonary arteries and arterioles are shorter and have thinner, less muscular walls than systemic vessels and whereas arterioles dominate vascular resistance in most systemic organs, resistance in the lungs is shared between the arterial vessels (….%), microvasculature :arterioles to venules, (…..%) and veins (….%).
Pulmonary arteries and arterioles are shorter and have thinner, less muscular walls than systemic vessels and whereas arterioles dominate vascular resistance in most systemic organs, resistance in the lungs is shared between the arterial vessels (30%), microvasculature: arterioles to venues (50%) and veins (20%).
