Circulation

Outline the circulation structure

Systemic arteriole circulation (high pressure/low volume). Pulmonary venous circulation (high volume/low pressure), capacitance system. Capillary beds (gas exchange), arterioles. Aorta (conductance artery)

1 of 62

The veins hold how much blood volume?

~60% (capacitance vessels)

2 of 62

What are resistance vessels?

Arterioles and capillaries, responsible for blood pressure regulation and regulation of flow through organs (BP = mean arteriole pressure = CO x total peripheral resistance). Total peripheral resistance controlled by diameter of blood vessels

3 of 62

Describe features of the resistance vessels

Elastic artery (thick vascular wall, layer of smooth muscle, elastin fibres). Muscular artery (thick muscle layer, constrict/dilate to regular flow/pressure). Arterioles (thin wall, endothelial layer, outer layer/smooth muscle cells/supporting cells)

4 of 62

Describe features of capillaries

Single endothelium cells. Exchange small molecules in gases. No regulation of flow

5 of 62

Describe features of capacitance vessels

Venules (similar to arterioles). Smaller and larger veins (similar to arteries but have thinner walls and a larger diameter lumen to wall thickness ratio)

6 of 62

What is the relationship between flow velocity, pressure and resistance in the vascular tree? (1)

Flow velocity is the highest in the arteries. Decreases as vessels get smaller. Capillaries (very low flow velocity). Venous (lower flow velocity due to larger lumen). Veins have ~60% of blood volume. Blood volume on circulation side ~12% (small)

7 of 62

What is the relationship between flow velocity, pressure and resistance in the vascular tree? (2)

Pressure high on the arteriole side compared to capillaries and veins

8 of 62

What is the relationship between flow velocity, pressure and resistance in the vascular tree for vascular resistance? (2)

Most of the vascular resistance is in the arterioles (where flow regulation occurs). Changes in resistance affects flow and BP

9 of 62

Which blood vessels have the largest cross-sectional area and largest SA?

Capillaries - larger number, large SA (gas exchange)

10 of 62

What is Darcy's Law?

Flow is proportional to the change in pressure across a length of a vessels, inversely related to resistance (increase resistance/decrease flow). Pressure is proportional to flow x resistance

11 of 62

What is the BP equation?

Mean arteriole blood pressure = CO x TPR (change TPR/change BP, adjusts CO to regulate arteriole BP) or mean arteriole BP = diastolic BP + ([systolic BP - diastolic BP]/3)

12 of 62

Is mean arteriole pressure halfway between DBP and SBP?

No - it is a third of the difference (shown in BP equation)

13 of 62

Which factor has the biggest effect on MABP?

Total peripheral resistance. Most resistance in arterioles

14 of 62

What is laminar flow?

Fluid flowing through tube. Layers of flow. Flow velocity will be fastest in the centre. Flow on outside with vessel will be slower due to friction

15 of 62

What is turbulent flow?

Caused by narrowing of tube or flow velocity exceeds parameters at which laminar flow can occur. Link between diameter and flow dynamics

16 of 62

What is the garden hose effect?

Relationship between radius and flow velocity. Narrowing of tube decreases flow but velocity of fluid in tube increases (total flow is less but flow velocity across restriction increases) e.g. r/2 leads to 4v (results in turbulent flow)

17 of 62

What is Reynold's Number?

Re = plv/n (Re <2000 - laminar flow, Re >2000 - turbulent flow)

18 of 62

Describe the laminar and turbulent flow in blood vessels

Aorta (high flow velocity, high Re, laminar flow), arteries (high flow velocity, turbulent flow) - vessels can stretch/reduces pressure. Turbulent flow is prevented by distensibility (ability to stretch)

19 of 62

Describe the laminar and turbulent flow in stenosis (disease progression)

Narrowing of blood vessel leads to laminar flow turning into turbulent flow. Aorta divides (bifurications) into iliac arteries (bifurications in carotid arteries), build up of clots, flow due to reflection of waves off walls, turbulent flow,

20 of 62

State the areas in the vascular tree where clots build up

Atherosclerotic build up around bifurcations. Coronary arteries (heart attacks), carotid arteries (stroke). Peripheral vascular disease in the leg, ischaemic legs (diabetes/leg amuptations)

21 of 62

What is Laplace's Law? (1)

More tension is related to pressure which is inversely related to the radius/diameter of the artery. Increasing diameter decreases pressure. A small diameter vessel requires less tension to contain a given pressure

22 of 62

What is Laplace's Law? (2)

Arterioles (BP regulation due to higher wall thickness to lumen diameter ratio, able to contain pressure). Higher pressure, thicker wall (e.g. aorta, capillary), not much thickness required to contain pressure

23 of 62

Describe features of the pressure trace (graph)

Diastolic pressure equal to the minimum in aorta during diastole. Increases to peak of 120 mmHg (to systolic pressure, normal BP reading). Aortic valve closes (dicrotic notch, slight reflective wave of valve, slight increase in aortic pressure)

24 of 62

Describe features of rigidity

Aortic rigid (open aortic valve, pressure in increase, diameter decreases, causes resistance to flow, flow velocity increases, measure change in pressure during contraction becomes steep, can cause damage, pressure decrease in diastole)

25 of 62

Describe features of elasticity

LV contracts, aortic valve opens, filling, pressure in aorta increases/expands to contain pressure, decreases height of pressure change, starts at higher pressure/dampening effect/Windkessel effect). Expands/absorb pressure. Diastole, elastic recoil

26 of 62

What is the Windkessel function?

An elastic (compliant) aorta helps smooth out the variation in arterial BP and store energy

27 of 62

What is the significance of elastic recoil?

Maintain blood flow in forward direction during diastole (no contraction). Maintain flow to tissues and BP. Damps pressure, protects end organs, maintains flow

28 of 62

What is the relationships between the cross-sectional area of blood vessels and distending pressure

Normal - increase in cross-sectional area of artery leads to increase in distending pressure. Veins (small change in area/change in pressure due to being stretchy). 70 yr old (large change in pressure/little area change, decrease elastin/calcified)

29 of 62

Which type of patients have calcification?

Diabetics, hypertensive patients (could get end organ damage)

30 of 62

Describe the pressure changes within systemic and pulmonary circulation

Larger arteries (most change in pressure), as vessels get smaller (change in pressure gets smaller) until reaching capillaries where pulse flow changes to continuous flow due to dampening effect

31 of 62

Describe features of the iliac artery

Bifurcations, pressure changes are steeper than pressure changes in aorta due to summation of reflected waves

32 of 62

How do you measure BP?

Use sphygmomanometer and stethoscope to listen to Korotkoff sounds (listen to pulse over radial artery, make a note of when the pulse is first heard and when the there is no sound whilst deflating the cuff - gives systolic and diastolic pressure)

33 of 62

Which blood vessels offer the highest resistance to the flow of blood?

Arterioles (resistance vessels), control flow of blood, also has the largest pressure drop

34 of 62

Describe features of resistance in series combination

System with resistances added up in series (additive), gives total resistance, series combination (CV system as a whole)

35 of 62

Describe features of resistance in parallel combination

Individual organs/vascular beds in parallel. Regulation of flow in any compartment can lead to being able to maintain pressure (in/out). Changed resistance can be counteracted. Change flow. No large drop in BP (narrow). Flow/pressure balance

36 of 62

What is the advantage for organs being arranged in parallel?

Alterations in flow in one organ doesn't greatly affect the system as a whole

37 of 62

What does Poiseuille's Law show?

Resistance is proportional to the inverse of the radius to the power 4. Small change in diameter can cause a large change in resistance and flow. Reducing r by 10% reduces flow by 50% (with everything else being constant)

38 of 62

Outline the process of auto-regulation for active hyperaemia (respond to increase in metabolic activity e.g. exercise)

Increase metabolic activity of organ, decrease O2 tension, increase metabolites in organ interstitial fluid, arteriolar dilation in organ, increase blood flow to organ

39 of 62

Outline the process of flow auto-regulation

Decrease arterial pressure in organ, decrease blood flow to organ, decrease O2, increase metabolites, decrease vessel-wall stretch in organ, arteriolar dilation in organ, restoration of blood flow toward normal in organ

40 of 62

Outline the process of myogenic response

Increase arterial pressure in organ, increase blood flow to organ, myogenic response (vessel wall stretch), arteriolar constriction in organ, restoration of blood flow toward normal in organ

41 of 62

Describe features of auto-regulation

Blood flow maintained within narrow range over large range of perfusion pressure. Increasing perfusion pressure of vascular bed initially increases flow but arterioles constrict to regulate flow back towards original value

42 of 62

Describe features of perfusion pressure in the different blood vessels

Aorta and arteries (pulse pressure), BP drops towards arterioles and capillaries (largest change in resistance), continuous flow in venules and veins

43 of 62

Describe features of the myogenic response

Artery in organ bath, change perfusion pressure. Internal diameter increases then decreases as artery constricts. Response to vascular smooth muscle to stretch

44 of 62

Describe what would happen to flow in active hyperaemia

Build up of metabolites, cause dilatation, blood flow increases to a maximum, then flow decreases

45 of 62

Describe what would happen to flow in reactive hyperaemia

Similar mechanism, occurs in ischaemia, inflate cuff to prevent blood flow, build up of metabolites/no flow to allow wash out of metabolites, release cuff (washout/dilatation), increases in blood flow

46 of 62

What is hyperaemia?

Increased blood flow, caused by accumulation of metabolites which can occur as a result of increased activity (active) or in reaction to a period of under perfusion (reactive)

47 of 62

Describe features of blood flow in a brachial artery measured using ultrasound

Occlusion of artery leads to drop in BP. After occlusion BP returns to normal - example of reactive hyperaemia

48 of 62

How can arteriolar BP be regulated by neural controls?

Vasoconstrictors (sympathetic nerves) and vasodilators (neurones release nitric oxide)

49 of 62

How can arteriolar BP be regulated by hormonal controls?

Vasoconstrictors (NA, angiotension II, vasopressin) and vasodilators (adrenaline, atrial natriuretic hormone)

50 of 62

How can arteriolar BP be regulated by local controls (auto-regulation)?

Vasoconstrictors (internal BP, myogenic response, endothelin-1) and vasodilators (decrease O2, K+, CO2, H+, osmolarity, adenosine, eicosanoids, bradykinin, substances released during injury, nitric oxide)

51 of 62

Describe features of the renin–angiotensin–aldosterone system

Control BP, anti-hypertensives. Angiotension I released using ACE (front-line drugs ACE inhibitors for BP control). Aldosterone released from cortex/medulla of kidney, increase Na/H2O retention, increase blood volume (use of aldosterone-antagonists)

52 of 62

Describe how to the sympathetic neurones regulate blood flow in skeletal muscles

Release NA, NA in extracellular fluid, vasoconstriction, alpha receptor, alter arteriolar radius. Or adrenal medulla secrets epinephrine into blood, increase plasma epinephrine, vasodilation, beta receptors, alter arteriolar radius in smooth muscle

53 of 62

Describe features of sympathetic vasoconstrictor fibre

NA (and ATP), distribute to most organs and tissue, tonically active, central control in brainstem, major role in baroreceptor reflex, very important role in BP homeostasis, duration of effect mostly well sustained

54 of 62

Describe features of sympathetic vasodilator fibre

ACh (and VIP), distribute to sweat glands in humans, skeletal muscle in primates, not tonically active, central control in forebrain, no role in baroreceptor reflex, unimportant role in BP homeostasis, duration of effect transient

55 of 62

Describe the process of sympathetic neuromuscular transmission

NA binds to postsynaptic a1/a2 receptors. a2 receptors for vasodilators, inhibit cAMP production, Ca 2+ opening, vesicle release. Angiotensin receptors promote more transmitter release per action potential. ATP as co-transmitter

56 of 62

Describe the process of endothelium mediated relaxation

Ca 2+ into endothelium. NO synthase converts arginine to NO. Guanylyl cyclase converts GTP to cGMP to PKG which results in relaxation (activates ACh)

57 of 62

Describe the significance of endothelial cells in relaxation of arterial smooth muscle by ACh (1)

Arteries were pre-constricted with NA then treated with increased doses of ACh. Without endothelium (removed by rubbing), ACh causes small additional constriction by direct action on smooth muscle

58 of 62

Describe the significance of endothelial cells in relaxation of arterial smooth muscle by ACh (2)

With endothelium in place (unrubbed) ACh causes relaxation because it stimulates release of NO from endothelium

59 of 62

What kind of drugs can inhibit the endothelium mediated relaxation mechanism?

PDE5 antagonists e.g. sildenafil (increase cGMP)

60 of 62

What are pre-capillary sphincters?

Bands of smooth muscle to adjust blood flow into capillaries mainly in the mesenteric microcirculation

61 of 62

Describe how blood from veins in the legs flows back towards the heart

Skeletal muscle contracts which squeezes the veins. Blood is pumped back to the central pool by a combination of skeletal muscle activity and the presence of valves in the veins (prevent back flow)

62 of 62

Get Revising

Circulation

Other cards in this set

Card 2

Front

Back

Card 3

Front

Back

Card 4

Front

Back

Card 5

Front

Back

Comments

Similar Pharmacy resources:

Other cards in this set

Card 2

Front

Back

Card 3

Front

Back

Card 4

Front

Back

Card 5

Front

Back

Comments

Related discussions on The Student Room

Similar Pharmacy resources: