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HYMS Y1 > Block 2 W4 > Flashcards

Block 2 W4 Flashcards

1
Q

What is the normal blood pressure?

A

120/80

Due to our environment and increases with age.

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2
Q

Why is high blood pressure needed?

A

Overcome effects of gravity to pump blood to brain.
High metabolic rate
High rate of toxin production

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3
Q

What are the functions of the heart?

A
  1. Pump function

2. Endocrine function - atrial natriuretic hormone

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4
Q

Describes the pressure difference between right and left side of heart.

A

Right side has lower pressure than left:
pulmonary arterial pressure = 0-5 — 4-12
systemic arterial pressure = 20-25 — 90-130

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5
Q

What is the blood pressure equation?

A

BP = CO x TPR

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6
Q

What is the blood flow equation?

A

Q = △T/R
Or
CO = mean arterial pressure - right atrial pressure/TPR

Q - flow (CO) ml/min
△T - pressure gradient mmHg
R - resistance mmHg/ml/min

Pressure gradient drives blood flow, thus blood flows from high to low pressure.
Blood flow is inversely proportional to resistance of vessels.

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7
Q

In which system is the pressure drop greatest?

A

Greater drop in pressure in systemic (arterioles) than pulmonary system as systemic resistance is greater than pulmonary.
Pressure is highest in aorta and large arteries and lowest in vena cava.

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8
Q

How do metabolising tissues during exercise receive more blood?

A

Tissues determine how much blood is needed. Task of circulation is to maintain continuous pressure for tissues.
Peripheral resistance within muscles decreases - change in pressure remains the same -> increases flow.
Viscera blood flow decreases during exercise.

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9
Q

Describe the resistance equation.

A

R = 8nl/πr^4

R - resistance
n - viscosity of blood
l - length of blood vessel
r^4 - radius of blood vessel to 4th power.

Resistance is directly proportional to viscosity of blood. Directly proportional to length of vessel. Inversely proportional to 4th power of vessel radius - flow is very sensitive to radius.

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10
Q

What is the role of pre-capillary sphincters?

A

Pre-capillary sphincters - arterioles with rings of smooth muscles around them -> control peripheral resistance as it enables vasodilation and vasoconstriction.
Tissues at work releases metabolic products e.g. K+, H+, adenosine, hypoxia, CO2, sheer stress -> causes relaxation of pre-capillary sphincters - vasodilation.

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11
Q

Describe the velocity of blood flow equation.

A

V = Q/A

V - velocity cm/sec
Q - flow ml/min
A - cross-sectional area cm^2

Velocity is directly proportional to blood flow and inversely proportional to the cross-sectional area at any level of CV system.
e.g. blood velocity is higher in aorta (small cross-sectional area) than capillaries (large cross-sectional area).
Low velocity of blood in capillaries optimises condition for nutrient exchange.

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12
Q

Define laminar and turbulent flow.

A

Laminar flow is streamlined with fastest velocity in centre of vessel and slowest velocity at wall of vessel.
Turbulent flow has random direction due to blockage of vessel.

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13
Q

Define bruits.

A

Audible vibrations of turbulent flow of blood in a vessel.

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14
Q

Describe the capacitance equation.

A

Describes the distensibility of blood vessels. Capacitance is inversely related to elastance (stiffness).
Describes how volume changes in response to change in pressure.

C = V/P

C - capacitance/compliance ml/mmHg
V - volume ml
P - pressure mmHg

Greater in veins than arteries so more blood contained in veins.
Capacitance of arteries decreases with age - arteries become stiffer and less distensible.

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15
Q

How is mean arterial pressure calculated?

A

Average arterial pressure with respect to time.

Diastolic pressure + 1/3(pulse pressure).

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16
Q

How does tissue demand control cardiac output?

A

By matching venous return to cardiac output.
As venous return increases, cardiac output increases too.
Blood is pumped by heart (cardiac output) at the rate entering the heart (venous return) regardless of after load (BP).
As BP increases, blood to tissues remain stable.

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17
Q

What is the short term BP control?

A

Fast, neurological baroreceptor mechanism via ANS.
Sympathetic fibres innervate all vessels except capillaries - release NA -> binds a-receptors = vasoconstriction -> increases peripheral resistance -> increased BP.

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18
Q

What are the effects of SNS stimulation?

A
  • constriction everywhere except muscles -> vasodilation as muscles need blood flow
  • venous constriction -> increased venous return -> increases CO
  • increased inotropy, chronotropy and lusitropy.
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19
Q

Describe the arterial baroreceptors.

A

Stimulated by stretch and transmit to vasomotor centre in medulla.
Situated in walls of carotid sinus near the bifurcation of common carotid arteries and aortic arch.
Systole -> firing rate increases. Diastole -> firing rate decreases.
Firing rate increases more dramatically over physiological range.

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20
Q

Describe the barorceptor reflex.

A

Pressure falls -> decreases stretch on carotid sinus walls -> decreases firing rate to carotid sinus nerve -> medulla -> increases sympathetic tone to heart and vessels and decreases parasympathetic tone to heart -> increases BP.

Pressure rises -> increases stretch on carotid sinus walls -> increases firing rate to carotid sinus nerve -> medulla -> decreased sympathetic tone and increases parasympathetic tone -> decreases BP.

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21
Q

What are the responses of the vasomotor centre?

A
  • increased chronotropy due to decreases parasympathetic tone and increased sympathetic tone to SA node
  • increased inotropy and stroke volume
  • increased vasoconstriction of arterioles due to increased sympathetic tone -> TPR and pressure increases
  • increases vasoconstriction of veins -> decreases unstressed volume and increases venous return to heart.
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22
Q

Describe the blood pressure changes that occur when moving from supine to standing position.

A

Stand -> venous pooling in lower extremities due to high compliance of veins -> venous return decreases -> SV and CO decreases -> arterial pressure decreases due to reduction in CO -> sensed by carotid sinus baroreceptors -> baroreceptor reflex -> BP increases.

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23
Q

Describe the blood pressure changes that occur during exercise.

A

The central command originates in motor cortex or from reflexes initiated in muscle proprioceptors when exercise is anticipated and causes changes:
- sympathetic tone increased
- parasympathetic tone decreased
- CO increased
- venous return increased due to venoconstriction
- arteriolar resistance in skin, splanchnic regions, kidneys and inactive muscles is increases -> blood flow to these organs decreases
Increased metabolic activity of skeletal muscle releases vasodilator metabolites (lactate, K+ and adenosine) -> causes arteriolar vasodilation in active skeletal muscles and reduces TPR -> increased blood flow to skeletal muscle.

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24
Q

What are the other neural mechanisms of regulating BP.

A
  • Atrial stretch -> causes renal arteriole dilation and decreases ADH
  • Chemoreceptors -> low BP -> reduced partial pressure of O2 -> activate vasomotor centre -> rise in BP.
  • CNS ischaemia -> increased PCO2 -> chemoreceptors in vasomotor centre respond by increases sympathetic tone of heart and vessels -> rises BP.
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25
Q

What is the long term control for BP?

A

Slow, hormonal renin-angiotensin-aldosterone system.

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26
Q

Define pressure diuresis.

A

As BP increases, urine output increases.
In kidney diseases - to remove same amount of salt water, need higher BP -> renal diseases causes hypertension.
High salt diet - need higher BP to get rid of it.

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27
Q

Describe the renin-angiotensin-aldosterone system.

A

Decrease in renal perfusion pressure -> juxta-glomerula apparatus secretes renin (enzyme) -> catalyses conversion of angiotensinogen (liver made) into angiotensin I in circulation.
Angiotensin converting enzyme (ACE) catalyses conversion of angiotensin I to angiotensin II -> effector molecule.

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28
Q

What are the effects of angiotensin II?

A
  1. stimulates aldosterone secretion by adrenal cortex -> increases Na+ reabsorption by renal distal tube which increases ECF volume, blood volume and pressure.
  2. increases Na+/H+ exchanger in proximal convoluted tube - directly increases Na+ reabsorption.
  3. increases thirst
  4. vasoconstriction of arterioles -> increases TPR and BP.
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29
Q

Define coarctation.

A

Descending aorta is occluded -> kidney hypo-perfused -> RAAS activated -> upper body hypertension and lower body hypotension.

30
Q

What are other hormones that regulate BP?

A
  • Natriuretic peptides -> released by heart in response to high BP and travel to kidneys. Respond to stretch -> salt water loss -> vasodilation.
  • Arginine vasopressin (ADH) - released by pituitary gland -> vasoconstriction and water retention.
31
Q

What are the treatments of BP?

A
  • diuretics
  • beta-blockers
  • alpha-blockers
  • calcium antagonists
  • ACE inhibitors
  • angiotensin receptor blocker (ARB)
32
Q

Describe the actions of diuretics.

A

Decreases blood volume and increases Na+ excretion -> reduces BP.
e.g. thiazide
Risk of stoke lowered.

33
Q

Describe the actions of beta-blockers.

A

-olol
Negatively inotropic - decreases cardiac contractility -> decreases CO.
Reduces renin release
Central sympathetic inhibition
These outweigh the vasoconstriction -> common side effect -> peripheral coldness.

34
Q

Describe the actions of alpha-blockers.

A

Vasodilation - causes reflex tachycardia and postural hypotension.
e.g. doxazosin.

35
Q

Describe the actions of calcium antagonists.

A

-ipine
Vasodilation - causes reflex tachycardia, salt water retention -> ankle swelling.
Inhibits influx of Ca2+ in smooth muscle cells -> relax -> reduces BP.
e.g. dihydropyridine
Common side effect - gout.

36
Q

Describe the actions of ACE inhibitors.

A

-pril

Blocks ACE so blocks synthesis of angiotensin II - work via AT1 and AT2 receptors.

37
Q

Describe the actions of angiotensin receptor blocker (ARB)

A

-sartan

Blocks AT1 and AT2 receptors - causes vasoconstriction and aldosterone release.

38
Q

Describe the actions of spironolactone.

A

Aldosterone inhibitor - causes Na+ and H2O retention.

39
Q

What are the 3 layers of the blood vessels?

A

Tunica interna -> tunica media -> tunica externa

40
Q

What are the layers of the tunica interna?

A

Tunica interna - inner lining of blood vessel, in direct contact with blood. Composed of:

  • endothelium -> continuous with endocardial lining of heart (simple squamous epithelium).
  • basement membrane/subendothelial layer -> provides physical support base of endothelium.
  • internal elastic lamina -> thin sheet of elastic fibres with holes for diffusion.
41
Q

What are the layers of the tunica media?

A

Tunica media - made of smooth muscle and elastic fibres. Primary role of smooth muscle - regulate diameter of lumen for vasodilation, vasoconstriction and vascular spasm.
- external elastic membrane -> separates tunica media from externa.

42
Q

What are the layers of the tunica externa?

A

Tunica externa - outer covering, which consists of elastic and collagen fibres.
Contains numerous autonomic nerves (Nervi vasorum) and vasa vasorum -> vessels to vessels, supplies blood to vessels.

43
Q

Describe the difference between arteries and veins.

A 
Arteries:
- small lumen
- no valves
- smooth muscle cells
Veins:
- larger lumen
- valves
- less smooth muscle cells
44
Q

Describe the structure and function of large elastic arteries.

A

Tunica media - substantial elastic fibres
Allows expansion and recoiling during cardiac cycle as blood at high pressure. Helps maintain constant flow of blood during diastole.

45
Q

Describe the structure and function of medium muscular arteries.

A

Tunica media - mostly smooth muscle fibres

Allows vessels to regulate their diameter and control flow of blood to different parts of body.

46
Q

Describe the structure and function of arterioles.

A

Tunica media - 3 layers of smooth muscle fibres and internal elastic lamina absent.
Site of highest resistance - directly contributes to blood pressure. Have alpha and beta-adrenergic receptors.
Metarterioles - intermediate rings of smooth muscle - pre-capillary sphincters -> control flow to capillaries.

47
Q

Describe the structure and function of capillaries.

A

One layer of endothelium + basement membrane -> smallest diameter but largest cross-sectional diameter.
Especially adapted for nutrient/gaseous exchange.

48
Q

What are the 3 types of capillaries?

A
  1. Continuous - most common, exchange occurs through flattened out cytoplasm of endothelial cells (skeletal muscles).
  2. Fenestrated - endothelium contains pores for exchange, high exchange function (small intestines, kidney).
  3. Sinusoids - intercellular gaps + irregular fenestrations + incomplete basement membrane -> allows molecule exchange (liver).
49
Q

Describe the structure and function of venules.

A

Tunica media - thin smooth muscle layer.

Drain capillaries.

50
Q

Describe the structure and function of small and medium veins.

A

Thin smooth muscle tunica media and interna.

Thickest layer - tunica externa.

51
Q

Describe the structure and function of large veins.

A

Thicker tunica interna.
Tunica media - circular smooth muscle
Tunica externa - longitudinal smooth muscle, thickest layer.
Hold low pressure blood but contain highest proportion of blood. Have alpha-adrenergic receptors.

52
Q

Describe the function of the capillary bed.

A

Anastomotic network of smaller blood vessels where the exchange of substances between blood and tissue fluid occurs.

53
Q

Describe the development events of the heart on day 18.

A

Heart begins to develop as the angiogenic cells from the mesoderm.
Forms pair of elongated tubes - cardiogenic cords (filled with cardiac jelly).
Becomes hollow -> endocardial tubes.

54
Q

Describe the development events of the heart on day 21.

A

Due to lateral folding of embryo, paired tubes join and fuse into single tube -> primitive heart.
Splanchnic mesoderm surrounding tube develops into myocardium and epicardium.

55
Q

What are the 5 regions of the primitive heart and what will they go on to form?

A
  1. Truncus arteriosus - aorta and pulmonary trunk
  2. Bulbus cordis - conus arteriosus and aortic vestibule.
  3. Primitive ventricle - trabeculated parts of both ventricles.
  4. Primitive atrium - trabeculated parts of both atrium.
  5. Sinus venosus- sinus venorum, coronary sinus and oblique vein.
56
Q

Describe the development events of the heart on day 28.

A

Primitive heart tube begins to loop and fold, bringing the arterial and venous ends and moving the ventricle caudally and atrium cranially.

57
Q

What is the term used when heart loops to left?

A

Dextrocardia - abnormal as heart normally loops to right.

58
Q

Describe the partition of the primitive ventricles.

A

Interventricular septum begins to develop and grows upwards towards endocardial cushion. It should fuse to form the proper 2 ventricles.
The atrioventricular canals on either side of endocardial cushion will eventually close off by the formation of valves.

59
Q

Describe the partition of the primitive atrium.

A
  • Septum primum grows towards the endocardial cushion from the roof of the primitive atrium.
  • Septum secundum forms to the right of the septum premium and fuses with the septum primum to form the atrial septum, separating right and left atria.
  • Foramen primum forms between the free edges of the septum primum and the AV septum, allowing a passage between right and left atria. The foramen is closed by growth of septum primum.
  • Foramen secundum forms in centre of septum primum.
  • Foramen ovale is an oval opening in the septum secundum that provides a communication between atria.
60
Q

What is the role of foramen ovale?

A

Acts like a valve to allow blood to travel from right atria to left atria but prevents backflow of blood to right atria.

61
Q

Describe the partition of the truncus arteriosus.

A

The truncal ridges and bulbar ridges derived from neural crest mesenchyme grow in a spiral fashion and fuse to form the aorticopulmonary (AP) septum.
The AP septum divides the truncus arteriosus into aorta and pulmonary trunk.

62
Q

Define tetralogy of Fallot and list the consequences of it.

A

When there is an unequal division of the truncus arteriosus and the AP septum fails to align properly with the AV septum.

  • pulmonary stenosis
  • ventricular septal defect
  • overriding aorta
  • right ventricular hypertrophy.
63
Q

Define transposition of the great vessels and list the consequences of it.

A

When the AP septum fails to develop in a spiral fashion, causing the aorta to arise from right ventricle and the pulmonary trunk to arise from left ventricle.

  • ventricular septal defect
  • atrial septal defect
  • patent ductus arteriosus.
64
Q

What is the primary difference between fatal circulation and neonatal circulation?

A

Fetal circulation derives oxygenated blood from the placenta, not the lungs as the lungs do not receives air. Whereas neonatal circulation derives oxygenated blood from the lungs.

65
Q

What is the role of foramen ovale and what does it go on to form?

A

Right atrium receives oxygenated blood from the umbilical vein via the IVC and deoxygenated blood from SVC. The blood within the heart mixes and the right atrium shunts the blood to the left atria through the foramen ovale and out through the aorta and pulmonary trunk.
Foramen ovale closes -> fossa ovalis.

66
Q

What is the role of ductus arteriosus and what does it go on to form?

A

The pulmonary trunk is full of partially oxygenated blood and some get sent to lungs but majority passes to the aorta via the ductus arteriosus.
Communication vessel between pulmonary trunk and aorta.
Closes off -> ligamentum ateriosum.

67
Q

What is the role of ductus venosus and what does it go on to form?

A

The umbilical vein carries oxygenated blood from placenta towards the heart via the ductus venosus near the liver.
It is a blood vessel - closes off in neonatal circulation -> ligamentum venosum and the round ligament of liver.
The umbilical arteries form medial umbilical ligament.

68
Q

What are the 3 paired veins that drain into the tubular heart?

A
  1. Common cardinal veins -> SVC
  2. Vitelline veins
  3. Umbilical veins -> IVC
69
Q

What is the relationship between aortic arches and the pharyngeal arches?

A

Aortic arches are paired with one pharyngeal arch each.

Aortic arches branch from dorsal aorta and all fuse together at aortic sac above the truncus arteriosus.

70
Q

What happens to the aortic sac?

A

Aortic sac forms right and left horns.
Right - becomes brachiocephalic artery
Left - ascending aorta.

71
Q

Describe the aortic arch derivatives.

A

Aortic arch 1 - disappears
AA2 - disappears
AA3 - forms common carotid arteries and the first part of internal carotid arteries.
AA4 - forms aortic arch on the left and the brachiocephalic artery and proximal subclavian artery on right.
AA5 - disappears
AA6 - forms proximal pulmonary arteries and ductus arteriosus.

72
Q

What does the dorsal aorta form?

A

Descending aorta.

If right dorsal aorta doesn’t break off from the left -> persistent right dorsal aorta.

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