P: Circulatory system

Question 1

Whats the % of blood volume in system circulation and in heart + lungs at rest?

Answer 1

• Systemic circulation = 84% (64 in veins, 13 in arteries, 7 in arterioles + capillaries)
• Heart and lungs = 16% (7 in heart, 9 in pulm vessels)

Question 2

Name and describe the 3 tunics of blood vessel walls

Answer 2

• Tunica externa: outer layer, connective tissue
• Tunica media: middle layer, smooth muscle
• Tunica interna: elastin, basement membrane, innermost simple squamous epithelium

Question 3

What are elastic arteries (conduits) vs muscular arteries (resistance vessels)?

Answer 3

• Elastic arteries (conduits): aorta + larger arteries, elastin fibers expand when blood pressure rises during ventricule systole and recoil when ventricles relax
• Muscular arteries (resistance vessels): arteriole, less elastic and thicker layer of smooth muscle, regulates diameter of lumen

Question 4

Describe capillaries

Answer 4

• Exchange vessels, smallest blood vessels
• Single layer of endothelium and a basement membrane
• Allows exchange of nutrients and wastes between blood and tissue fluid (thin wall)

Question 5

What are veins described as?

Answer 5

Capacitance vessels (blood vessels)

Question 6

What is Ohm’s law?

Answer 6

F = ΔP/R
- F: rate of blood flow
- ΔP: driving force for blood flow
- R: resistance

Question 7

What are the major regulators of blood flow? What’s the name of the law related to this?

Answer 7

• Vascular blood vessel diameter (radius = most important parameter in Poiseuille’s law)
• Mean arterial pressure
• Blood viscosity
• Poiseuille’s Law

Question 8

If radius of a vessel doubles, what’s the consequence on resistance and blood flow?

Answer 8

Resistance = 1/16 R
Blood flow = 16 F

Question 9

What happens to viscosity if heamatocrit = 60 (polycythaemia)?

Answer 9

• Viscosity can reach >7 (normal is ~3)
• Resistance increases and flow through blood vessels can be compromised

Question 10

What determines blood viscosity and what is its normal blood vs severe anaemia levels compared to water viscosity?

Answer 10

RBC content determines blood viscosity
- Normal blood viscosity = 3x water viscosity
- Severe anaemia: blood viscosity = 1,5x water viscosity

Question 11

• Decreased resistance of blood –> ____ rate of peripheral blood flow, ____ venous return, ____CO
• ____ also causes blood dilation –> ____ CO
• Sustained ____ in pumping workload of heart

Answer 11

• Decreased resistance –> increased rate of peripheral blood flow, increased venous return, increased CO
• Hypoxia also causes blood dilation –> further increases CO
• Sustained increase in pumping workload of heart

Question 12

What does mean pressure fall to as blood flows through the systemic circulation and why?

Answer 12

Progressively falls to about 0 mmHg due to resistance to blood flow mainly in arterioles

Question 13

How can pressure drop (ΔP) be increased?

Answer 13

Increase in flow or resistance (ΔP = F x R)

Question 14

What is blood vessel compliance/capacitance + equations?

Answer 14

• Volume of blood that can be stored in a blood vessel for each mmHg pressure raise
• Ca = ΔV/ΔP
• Compliance = distensibility x volume

Question 15

What are distensibility + compliance determined by?

Answer 15

• Quantity of elastin fibers in vessel wall
• Wall thickness

Question 16

While ventricular ejection is ____, blood flow in vasculature is ____

Answer 16

• pulsatile
• continuous

Question 17

What replaces elastin content in large arteries with age?

Answer 17

Collagen –> aorta can’t expand as much to accommodate SV

Question 18

As blood is ejected, arteries ___ and the increased pressure caused by SV is “___” into arterial walls

Answer 18

• distend
• absorbed

Question 19

Compliant arteries ___ the workload of the heart

Answer 19

Reduce

Question 20

Rigid arteries ____ the workload of the heart

Answer 20

Increase

Question 21

Average blood pressures (systolic/diastolic)

Answer 21

120/80 or 140/90

Question 22

Mean arterial pressure (MAP) equation + values

Answer 22

MAP = diastolic pressure + 1/3 (systolic - diastolic pressure)
93 mmHg = 80 + 1/3(40)

Question 23

Why is the value of MAP closer to diastolic pressure?

Answer 23

Because diastole lasts twice as long as systole

Question 24

Define hypertension

Answer 24

Chronically elevated blood pressure

Question 25

Types of hypertension

Answer 25

• Essential hypertension: unclear, multifactorial causes, 95% of cases
• Secondary hypertension: hypertension resulting from another condition (renal disease), chronically elevated salt and water reabsorption in nephron will increase blood volume and chronically raise blood pressure

Question 26

What are the long-term consequences of hypertension and why?

Answer 26

• Heart and kidney damage, risk factor for heart attack
• Ventricles must contract more forcefully to maintain adequate SV –> long term damage to heart muscle (increased afterload)
• High pressure damages endothelial lining of arteries –> formation of atherosclerotic plaques –> increases risk of heart attack or stroke

Question 27

What is pulse pressure + equation?

Answer 27

• LV contraction –> pulse of systolic pressure
• Pulse transmitted through elastic walls of large arteries
• Velocity of transmission of pressure pulse is ~15 times velocity of blood flow
• Pulse pressure = systolic pressure - diastolic pressure (40 mmHg = 120 mmHg - 80 mmHg)

Question 28

Blood pressure wave: name of wave that’s visible during diastolic phase + what it’s caused by?

Answer 28

Dicrotic wave caused by:
- Recoil of blood from closed aortic valve
- Reflection of systolic pressure wave back from small arteries in lower body