arteries, veins and peripheral vascular resistance Flashcards
1
Q
what are the components of the circulatory system?
A
- arteries
- arterioles
- capillaries
- venules
- veins
2
Q
what is the pressure in the arterial system?
A
high
3
Q
what is the pressure in the venous system?
A
low
4
Q
how do you calculate mean arterial pressure?
A
diastolic blood pressure + 1/3 pulse pressure
OR
cardiac output x total peripheral resistance
5
Q
what is the pulse pressure?
A
the force the heart generates with each contraction to overcome arterial resistance
6
Q
what is afterload?
A
the force against which the heart must contract to eject blood into the arteries
7
Q
what are parameters that influence pulse pressure?
A
- Stroke Volume
- Ejection velocity of stroke volume
- Arterial compliance
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
9
Q
what is arterial complience?
A
the ability of the arterial wall to distend and increase volume with increasing transmural pressure
10
Q
if arteries are less compliant what will happen to pulse pressure?
A
it will increase
11
Q
where do arteries take blood?
A
away from the heart to tissues
12
Q
what do arteries contain?
A
elastic tissue
13
Q
what are the major branches of the aorta?
A
subclavian, common carotid and iliac
14
Q
what is the cross section of capillaries like?
A
large
15
Q
what is the rate of blood flow in capillaries like?
A
low
16
Q
how many cells thick are capillary walls?
A
1 cell thick
17
Q
what is the function of veins?
A
transport blood away from tissues back to the heart
18
Q
compare the vessel wall of veins and arteries
A
veins have a thinner, less organised vessel wall than arteries
19
Q
what do venous valves do?
A
prevent backflow of blood
20
Q
what can happen if venous walls or valves lose their elasticity?
A
- turbulent blood flow
- varicose veins
21
Q
what are the three layers of the vessel wall?
A
- tunica intima
- tunica media
- tunica adventitia (externa)
22
Q
what does the tunica intima consist of?
A
- endothelial cells attached to basement membrane
- underlying layer of ECM
23
Q
what separates the tunica intima and tunica media in arteries?
A
internal elastic lamina
24
Q
what does the tunica media consist of?
A
- layers of elastin fibres and smooth muscle cells
25
what does the high elastin content in the tunica media allow?
expansion of vessel wall during systole and recoil during diastole
26
what separates the tunica media and tunica adventitia?
external elastic lamina
27
what does the tunica adventitia consist of?
- thick connective tissue
- network of nerve fibres and lymphatics
28
what are vasa vasorum?
In larger arteries, vasa vasorum (small arterioles) perfuse the outer media (are vessels of the vessels)
29
what is vascular compliance?
ability of a blood vessel wall to passively expand and recoil in response to changes in pressure
30
how would you calculate vascular complience?
change in volume/change in pressure
31
what is arteriosclerosis?
age related arterial stiffness due to calcification of elastin, collagen and the extracellular matrix
32
where are endothelial cells found?
form the inner lining of entire blood vessel system and the heart
33
what are the functions of endothelial cells?
- 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
what is vasoconstriction?
contraction of vascular smooth muscle to narrow vessel lumen and reduce radius
35
what is vasodilation?
relaxation of vascular smooth muscle to widen vessel lumen and increase radius
36
what is involved in local control of blood pressure?
small arteries and arteriolies, hormones
37
how does adrenaline involved in local control of blood pressure?
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
how is atrial natriuretic peptide involved in local control of blood pressure?
it is a potent vasodilator and influences BP due to regulation of Na+ balance and blood volume.
39
how is angiotensin II involved in local control of blood pressure?
constricts arterioles and is important as part of the Renin – Angiotensin – Aldosterone System (RAAS)
40
what is the RAAS?
Renin – Angiotensin – Aldosterone System (RAAS)
a key regulatory pathway in hormonal control of blood pressure and intravascular volume
41
how does the Renin Angiotensin Aldosterone System work?
- 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
what is the juxta?
glomerular apparatus in kidney
43
how are endothelial cells involved in local control of blood pressure?
Endothelial cells produce vasoactive substances that regulate vascular tone- in smooth muscle
44
what are some examples of vasodilators?
- nitric oxide
- prostaglandin
45
how does nitric oxide act as a vasodilator?
- 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
how does prostaglandin act as a vasodilator?
- Eicosanoid produced in endothelial cells
- Activates adenylate cyclase to increase cAMP production, activating protein kinase A (PKA)
Leads to vasodilation
47
what are examples of vasoconstrictors?
- enfothelin-1
- thromboxane A2
48
how does endothelin-1 act as a vasoconstrictor?
- 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
how does thromboxane act as a vasoconstrictor?
- Eicosanoid
- Activated by tissue injury and inflammation
50
when does arterial pressure fall?
Pressure falls as blood circulates from left ventricle to right ventricle (systemic circulation and right ventricle to left ventricle (pulmonary circulation)
51
what is the average pressure pushing blood around the circulatory system?
MAP
52
what is distension/complience?
Blood is ejected into arteries by ventricles and the elastic artery wall is stretched out by raised pressure
53
what is shear stress?
- 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
what can lead to physiologic adaptation or disease of the blood vessel wall?
alterations in the homeostatic conditions, such as under physiologic (exercise, pregnancy, growth) or pathologic (hypertension, flow reduction, flow overload)
55
what is the prime site for exchange of fluid, electrolytes and gases?
the capillary system
56
what are intercellular clefts?
the spaces/junctions separating endothelial cells in the capillary wall
57
what are the three structural classifications of capillaries?
- continuous
- fenestrated
- discontinuous
58
what is continuous structure of capillaries?
- continuous basement membrane with tight intercellular clefts.
- continuous capillaries have the lowest permeability
59
what is an example of where continuous capillaries are found?
muscle, skin, pulmonary system and CNS
60
what is fenestrated structure of capillaries?
- Perforations or fenestrations in endothelium
- Enables relatively high permeability
61
what is an example of where fenestrated capillaries are found?
exocrine glands, renal glomerull
62
what is discontinuous capillary structure?
extremely high permeability due to large intercellular clefts and gaps in the basement membrane
63
what is an example of where discontinuous capillaries are found?
the liver
64
what are metarterioles?
- 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
why is blood through capillaries not continuous and flow intermittently?
due to vasodilation
66
what is the branch site of capillaries from metarterioles surrounded by?
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
what is hydrostatic pressure in capillary systems?
tends to force fluid and dissolved substances through capillary intercellular spaces to the interstitial spaces
68
what is osmotic pressure?
caused by plasma proteins (Colloid Osmotic Pressure) tends to force fluid movement from interstitial space to the blood via capillary intercellular spaces
69
what will there be if net filtration pressure is positive in capillary systems?
a net fluid filtration across capillaries
70
what will there be if net filtration pressure is negative in capillary systems?
a net fluid absorption from interstitial spaces into capillaries
71
if blood pressure drops, what happens to hydrostatic pressure?
also drops
72
what happens to colloid pressure of a drop of blood pressure?
remain the same as proteins are too big to leave the capillary
73
where does fluid move in and out of capillaries?
fluid will move out capillaries at the arterial end and move into capillaries at the venous end
74
what happens to any disequilibrium of fluid in capillaries?
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
what id the lymphatic system?
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
what three things does the lymphatic system play a crucial role in controlling?
Concentration of proteins in interstitial fluids
Volume of interstitial fluids
Interstitial fluid pressure
77
what happens if colloid osmotic pressure is increased?
Increasing colloid osmotic pressure in interstitial fluid shifts the balance of forces at the membrane of blood capillaries in favour of fluid filtration
78
what happens if interstitial fluid pressure is increased?
Increasing interstitial fluid pressure increases the rate of lymph flow – carries excess interstitial fluid volume and protein that accumulates in interstitial away.
79
Is pulmonary hydrostatic or systemic hydrostatic pressure lower?
pulmonary
80
are pulmonary colloid or systemic colloid pressure lower?
Colloid pressures are equivalent between pulmonary and systemic circulations
81
what does net fluid transfer at both ends do?
prevent pulmonary oedema (excess fluid in lungs that collects in the alveoli)
82
what can pulmonary eodema induced by?
- 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
