Special Circulation Flashcards

Question

Contrast blood flow in skeletal muscle in rest and contraction

Answer 1

At rest- vasoconstriction - rich sympathetic innervation mediated basal vasoconstriction - normal TPR & MAP - Low concentrations of vasoactive metabolites at rest do notovverrude sympathetic control During exercise- vasodilation - functional sympatholysis: local control (active/reactive hyperemia due to vasoactive metabolites like lactate, K+, adenosine) overrides sympathetic vasoconstriction - massive increase in blood flow to muscle (capillary recruitment) - TPR & MAP changes depending on static vs dynamic exercise

Answer 2

Phasic, dynamic exercise - e.g. running - active hyperemia due to metabolites - blood flow is not interrupted - capillary recruitment—> reduced local resistance - sympathetic control maintains global TPR & MAP Static exercise - e.g. weightlifting - sustained contractions block blood flow—> increased local resistance & TPR - increased TPR abd cardiac output can lead to increased MAP - vasodilation after contraction due to ischemia and build-up metabolites - reactive or ischemia hyperemia

Answer 3

Pain and cramping in legs during exercise Caused by peripheral vascular disease due to atheromatous plaques in arteries supplying legs

Answer 4

At rest, the cerebral circulation receives about 15% of CO, a large proportion because the human brain has high O2 consumption abd metabolic needs. Local control dominates, sympathetic innervation is sparse

Answer 5

Critical circulation, maintained at any cost - disruption of blood flow for seconds- unconsciousness - for minutes- irreversible brain damage, death - Circle of Willis: interconnecting arterial vessels safety mechanism fir cerebral perfusion, especially if an artery occluded Brain requires glucose as energy source - ketones can also be metabolized during starvation - some cells, e.g. retinal photoreceptors, can only use glucose as they do not have mitochondria Mechanical effects: increased intracranial pressure—> decreased blood flow Vasoactive metabolites: CO2, H+ (pH), adenosine

Answer 6

Blood flow remains at constant at pressures 60-180 mmHg Due to autoregulation (bayliss myogenic response) Less than 60 mmHg—> decreased perfusion —> confusion, unconsciousness Chronic high blood pressure shifts autoregulation curve to right, maintaining blood flow at higher pressures

Answer 7

-Large drop in PO2(hypoxemia) required fir significant increases in blood flow (below 50 from normal 95 mm.Hg)

Answer 8

- blood flow sensitive to small changes in PCO2 - PCO2 alters pH via formation of carbonic acid, sensed by chemoreceptors - Increased PCO2 (hypercapnia)—> vasodilation - Decreased PCO2 (hypocapnia)—> vasoconstriction

Answer 9

- central perfusion (whole brain): - (bayliss) myogenic autoregulation - regional changes - metabolic hyperemia is dominant control mechanism - regional increased in neuronal activity —> increased oxygen demand - metabolic hyperemia links blood flow to metabolic demand - astrocytes are important in ‘neurovascular coupling’ - research use: BOLD fMRI infers neuronal activity by measuring local blood oxygen levels Sympathetic control: - minimal effect on cerebral blood flow - sparse sympathetic innervation in cerebral arterioles and arteries

Answer 10

CPP (Cranial perfusion pressure)= MAP - ICP Not MAP - CVP (central venous pressure) as in other tissues Not elevated ICP, e.g.m due to TBI( concussion), is very dangerous

Answer 11

ICP increased by: -intracranial bleeding - cerebral edema - tumor

Answer 12

- collapse veins | - decreases effective CPP reduces blood flow

Answer 13

All of CO enters the pulmonary circulation. Local control of blood flow is most important, sympathetic control least important. Mechanical effects due to lung inflation also play a role Differences to other circulations - low pressure (8- 20 mmHg at rest) - low resistance to flow - receives 100% cardiac output (CO), from right ventricle Hypoxia causes local vasoconstriction in the lungs - purpose of lungs is to oxygenate blood - blood flow is optimized to alveolar regions rich in oxygen by reducing flow to poorly oxygenated alveoli - vasoconstriction around oxygen-poor alveoli via O2 sensing K+ channels (Euler-Liljestrand mechanism) Vasoactive metabolites also cause vasoconstriction in hypoxic alveoli

Answer 14

Skin has a relatively constant, low metabolic rate, receiving about 4% of CO at rest (1-60% with extreme cold/heat). Oxygen needs are easily met by low blood flow, increased blood flow is most important for temperature regulation

Answer 15

``` Sympathetic control (most important): -Arteriovenous (AV) anastomoses are bypass vessels between cutaneous arteries, and veins, Innervated by adrenergic sympathetic fibers ``` - vasodilation of AV shunts allows blood to enter venous plexuses without having to pass through the skin surface capillaries, thus reducing heat loss - key for temperature control - flow through AV shunts can range from 0 to 1 L/min, severely reducing TPR and MAP Local control (weak): - temperature - weak reactive hyperemia - weak autoregulation

Answer 16

Normothermic conditions -low skin blood flow (about 5% of cardiac output) During cold stress - increased sympathetic vasoconstrictor activity (cutaneous vessels ) - reduced skin blood flow improves thermal insulation During heat stress - increased sympathet8c cholinergic vasodilator activity - increased skin blood flow, can reach 60% of CO! - allows more heat dissipation as high skin blood flow delivers heat to the skin surface - cutaneous pooling out of blood due to heat exposure without sufficient acclimatization can reduce MAP dangerously - can induce syncope (fainting) and ischemic damage in O2^- sensitive organs like intestines

Answer 17

- under nonthermic conditions, skin blood flow is relatively low (approx. 5% of cardiac output ) and skin vessels receive relatively minor neural inputs from active vasoconstrictor and vasodilator nerves - During cold stress, reductions of skin and internal temperatures lead to reflex increases in sympathetic nonadrenergic vasoconstrictor nerve activity. Increased vasoconstrictor system tone reduces skin blood flow, th7s increasing thermal insulation and conserving body heat. - During heat stress, increasing skin and internal temperatures lead to reflex increases in sympathetic cholinergic sudomotor activity. Increased activity of the vasodilator system leads to potentially dramatic increases in skin blood flow that can reach 60% of cardiac output. High skin blood flow delivers heat to the skin surface where it is removed to the environment primarily through evaporation of sweat

Answer 18

- thermoregulation reflexes are mediated by the afferent inputs 9f internal and skin temperature - These afferent inputs are integrated in the preoptic anterior hypothalamus and spinal cord areas of the central nervous system - Efferent control of blood vessels and sweat glands in glabrous skin is mediated by nomadrenergic vasoconstrictor nerves and cholinergic sudomotor nerves, respectively - In nonglaborous skin regions, efferent control of blood vessels is effected through a system of dual sympathetic innervation, nor adrenergic active vasoconstrictor nerves and cholinergic active vasodilator nerves - Sweat glands also receive cholinergic sympathetic innervation; however, whether cholinergic sudomotor nerves are one and the same is not known

Special Circulation Flashcards

(42 cards)