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BDS1 BAMS human systems > arteries, veins and peripheral vascular resistance > Flashcards

arteries, veins and peripheral vascular resistance Flashcards

1
Q

what are the components of the circulatory system?

A
  • arteries
  • arterioles
  • capillaries
  • venules
  • veins
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2
Q

what is the pressure in the arterial system?

A

high

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3
Q

what is the pressure in the venous system?

A

low

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4
Q

how do you calculate mean arterial pressure?

A

diastolic blood pressure + 1/3 pulse pressure
OR
cardiac output x total peripheral resistance

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5
Q

what is the pulse pressure?

A

the force the heart generates with each contraction to overcome arterial resistance

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6
Q

what is afterload?

A

the force against which the heart must contract to eject blood into the arteries

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7
Q

what are parameters that influence pulse pressure?

A
  • Stroke Volume
  • Ejection velocity of stroke volume
  • Arterial compliance
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8
Q

what is stroke volume?

A

the volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction

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9
Q

what is arterial complience?

A

the ability of the arterial wall to distend and increase volume with increasing transmural pressure

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10
Q

if arteries are less compliant what will happen to pulse pressure?

A

it will increase

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11
Q

where do arteries take blood?

A

away from the heart to tissues

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12
Q

what do arteries contain?

A

elastic tissue

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13
Q

what are the major branches of the aorta?

A

subclavian, common carotid and iliac

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14
Q

what is the cross section of capillaries like?

A

large

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15
Q

what is the rate of blood flow in capillaries like?

A

low

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16
Q

how many cells thick are capillary walls?

A

1 cell thick

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17
Q

what is the function of veins?

A

transport blood away from tissues back to the heart

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18
Q

compare the vessel wall of veins and arteries

A

veins have a thinner, less organised vessel wall than arteries

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19
Q

what do venous valves do?

A

prevent backflow of blood

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20
Q

what can happen if venous walls or valves lose their elasticity?

A
  • turbulent blood flow
  • varicose veins
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21
Q

what are the three layers of the vessel wall?

A
  • tunica intima
  • tunica media
  • tunica adventitia (externa)
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22
Q

what does the tunica intima consist of?

A
  • endothelial cells attached to basement membrane
  • underlying layer of ECM
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23
Q

what separates the tunica intima and tunica media in arteries?

A

internal elastic lamina

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24
Q

what does the tunica media consist of?

A
  • layers of elastin fibres and smooth muscle cells
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25
Q

what does the high elastin content in the tunica media allow?

A

expansion of vessel wall during systole and recoil during diastole

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26
Q

what separates the tunica media and tunica adventitia?

A

external elastic lamina

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27
Q

what does the tunica adventitia consist of?

A
  • thick connective tissue
  • network of nerve fibres and lymphatics
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28
Q

what are vasa vasorum?

A

In larger arteries, vasa vasorum (small arterioles) perfuse the outer media (are vessels of the vessels)

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29
Q

what is vascular compliance?

A

ability of a blood vessel wall to passively expand and recoil in response to changes in pressure

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30
Q

how would you calculate vascular complience?

A

change in volume/change in pressure

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31
Q

what is arteriosclerosis?

A

age related arterial stiffness due to calcification of elastin, collagen and the extracellular matrix

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32
Q

where are endothelial cells found?

A

form the inner lining of entire blood vessel system and the heart

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33
Q

what are the functions of endothelial cells?

A
  • Important role in local blood pressure control
  • Arranged along axis of blood vessel wall to minimise shear stress
  • Providing a friction – free surface for blood flow
  • Regulate permeability of blood vessels – form a selective barrier between blood and tissues
  • Endothelial cells are highly specialised cells that play a key role in cardiovascular function.
  • Regulation of platelet function and fibrinolysis
  • Promote angiogenesis and vessel remodelling
34
Q

what is vasoconstriction?

A

contraction of vascular smooth muscle to narrow vessel lumen and reduce radius

35
Q

what is vasodilation?

A

relaxation of vascular smooth muscle to widen vessel lumen and increase radius

36
Q

what is involved in local control of blood pressure?

A

small arteries and arteriolies, hormones

37
Q

how does adrenaline involved in local control of blood pressure?

A

it is released from adrenal medulla, circulates in blood and binds mostly to β2 - adrenoreceptors leading to vasodilatation via increase in cAMP and reduced Ca sensitivity for SMC contraction

At high concentrations, adrenaline binds to α1 – adrenoreceptors on arteriolar smooth muscle causing contraction and therefore vasoconstriction

38
Q

how is atrial natriuretic peptide involved in local control of blood pressure?

A

it is a potent vasodilator and influences BP due to regulation of Na+ balance and blood volume.

39
Q

how is angiotensin II involved in local control of blood pressure?

A

constricts arterioles and is important as part of the Renin – Angiotensin – Aldosterone System (RAAS)

40
Q

what is the RAAS?

A

Renin – Angiotensin – Aldosterone System (RAAS)

a key regulatory pathway in hormonal control of blood pressure and intravascular volume

41
Q

how does the Renin Angiotensin Aldosterone System work?

A
  • Reduced blood flow to kidney is sensed by receptors in juxta causing release of Renin from glomerular cells.
  • Renin acts on circulating Angiotensinogen (produced by liver) to convert it to Angiotensin I
  • Angiotensin I is converted by angiotensin converting enzyme (ACE) – released from endothelial cells – in the lungs and kidney to Angiotensin II
  • Angiotensin II is a potent vasoconstrictor
  • Stimulates Na and water reabsorption and stimulates release of aldosterone from adrenal cortex
    - Aldosterone acts on distal convoluted tubule (DCT) and collecting duct (CD) of kidney to increase sodium and water retention therefore increasing intravascular volume.
  • Angiotensin II stimulates antidiuretic hormone (ADH) release from posterior pituitary gland
    - ADH release causes increased water via aquaporin – 2 channels in DCT and CD of kidney and vasoconstriction of blood vessels via V1 receptors on vascular SMCs.
42
Q

what is the juxta?

A

glomerular apparatus in kidney

43
Q

how are endothelial cells involved in local control of blood pressure?

A

Endothelial cells produce vasoactive substances that regulate vascular tone- in smooth muscle

44
Q

what are some examples of vasodilators?

A
  • nitric oxide
  • prostaglandin
45
Q

how does nitric oxide act as a vasodilator?

A
  • Produced by Nitric Oxide Synthase (NOS) from L – arginine in vascular endothelial cell
  • NO diffuses into SMC and induces relaxation via cGMP activation of guanylate cyclase.
  • NO release occurs in response to factors such as binding of endothelium dependent vasodilators (e.g. acetylcholine, ATP and bradykinin) to receptors on surface membrane of endothelial cells and shear stress.
46
Q

how does prostaglandin act as a vasodilator?

A
  • Eicosanoid produced in endothelial cells
  • Activates adenylate cyclase to increase cAMP production, activating protein kinase A (PKA)
    Leads to vasodilation
47
Q

what are examples of vasoconstrictors?

A
  • enfothelin-1
  • thromboxane A2
48
Q

how does endothelin-1 act as a vasoconstrictor?

A
  • Belongs to endothelin family of peptide agents
  • Secreted by endothelial cells in response to stimuli such as pulsatile stretch, sheer stress, neurohormones and cytokines
  • Acts on ETA receptor on vascular smooth muscle cells to initiate vasoconstriction
49
Q

how does thromboxane act as a vasoconstrictor?

A
  • Eicosanoid
  • Activated by tissue injury and inflammation
50
Q

when does arterial pressure fall?

A

Pressure falls as blood circulates from left ventricle to right ventricle (systemic circulation and right ventricle to left ventricle (pulmonary circulation)

51
Q

what is the average pressure pushing blood around the circulatory system?

A

MAP

52
Q

what is distension/complience?

A

Blood is ejected into arteries by ventricles and the elastic artery wall is stretched out by raised pressure

53
Q

what is shear stress?

A
  • the force that blood flow exerts on the endothelial layer of the vessel wall
  • occurs due to blood travelling at different velocities within a blood vessel
54
Q

what can lead to physiologic adaptation or disease of the blood vessel wall?

A

alterations in the homeostatic conditions, such as under physiologic (exercise, pregnancy, growth) or pathologic (hypertension, flow reduction, flow overload)

55
Q

what is the prime site for exchange of fluid, electrolytes and gases?

A

the capillary system

56
Q

what are intercellular clefts?

A

the spaces/junctions separating endothelial cells in the capillary wall

57
Q

what are the three structural classifications of capillaries?

A
  • continuous
  • fenestrated
  • discontinuous
58
Q

what is continuous structure of capillaries?

A
  • continuous basement membrane with tight intercellular clefts.
  • continuous capillaries have the lowest permeability
59
Q

what is an example of where continuous capillaries are found?

A

muscle, skin, pulmonary system and CNS

60
Q

what is fenestrated structure of capillaries?

A
  • Perforations or fenestrations in endothelium
  • Enables relatively high permeability
61
Q

what is an example of where fenestrated capillaries are found?

A

exocrine glands, renal glomerull

62
Q

what is discontinuous capillary structure?

A

extremely high permeability due to large intercellular clefts and gaps in the basement membrane

63
Q

what is an example of where discontinuous capillaries are found?

A

the liver

64
Q

what are metarterioles?

A
  • terminal arterioles that do not contain a continuous layer of smooth muscle, instead smooth muscle fibers encircle the vessel at intermittent points along its length
  • connect arterioles and venules and branch off to capillaries
65
Q

why is blood through capillaries not continuous and flow intermittently?

A

due to vasodilation

66
Q

what is the branch site of capillaries from metarterioles surrounded by?

A

a ring of smooth muscle
- muscle the precapillary sphincters that contract and relax in response to local metabolic factors.
- contraction closes the entry to the capillary.

67
Q

what is hydrostatic pressure in capillary systems?

A

tends to force fluid and dissolved substances through capillary intercellular spaces to the interstitial spaces

68
Q

what is osmotic pressure?

A

caused by plasma proteins (Colloid Osmotic Pressure) tends to force fluid movement from interstitial space to the blood via capillary intercellular spaces

69
Q

what will there be if net filtration pressure is positive in capillary systems?

A

a net fluid filtration across capillaries

70
Q

what will there be if net filtration pressure is negative in capillary systems?

A

a net fluid absorption from interstitial spaces into capillaries

71
Q

if blood pressure drops, what happens to hydrostatic pressure?

A

also drops

72
Q

what happens to colloid pressure of a drop of blood pressure?

A

remain the same as proteins are too big to leave the capillary

73
Q

where does fluid move in and out of capillaries?

A

fluid will move out capillaries at the arterial end and move into capillaries at the venous end

74
Q

what happens to any disequilibrium of fluid in capillaries?

A

Any disequilibrium that occurs accounts for fluid that is returned to the circulation via the Lymphatic System, otherwise the build up of fluid in tissues would lead to oedema.

75
Q

what id the lymphatic system?

A

a network of small lymph nodes and lymphatic vessels through which Lymph (a fluid derived from interstitial fluid) flows
- aids fluid movement and moves absorbed fat into the circulation

76
Q

what three things does the lymphatic system play a crucial role in controlling?

A

Concentration of proteins in interstitial fluids
Volume of interstitial fluids
Interstitial fluid pressure

77
Q

what happens if colloid osmotic pressure is increased?

A

Increasing colloid osmotic pressure in interstitial fluid shifts the balance of forces at the membrane of blood capillaries in favour of fluid filtration

78
Q

what happens if interstitial fluid pressure is increased?

A

Increasing interstitial fluid pressure increases the rate of lymph flow – carries excess interstitial fluid volume and protein that accumulates in interstitial away.

79
Q

Is pulmonary hydrostatic or systemic hydrostatic pressure lower?

A

pulmonary

80
Q

are pulmonary colloid or systemic colloid pressure lower?

A

Colloid pressures are equivalent between pulmonary and systemic circulations

81
Q

what does net fluid transfer at both ends do?

A

prevent pulmonary oedema (excess fluid in lungs that collects in the alveoli)

82
Q

what can pulmonary eodema induced by?

A
  • Heart failure
    Left side heart failure – capillary hydrostatic pressure is increased, particularly in extremities
    Right sided heart failure
  • High altitude exposure
  • Lung damage due to severe infection
  • Adult respiratory distress syndrome
  • Following major injury

BDS1 BAMS human systems (47 decks)

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