Blood pressure

Question 1

Describe the arteries

Answer 1

-under high pressure
-blood in arteries is known as ‘stressed volume’
-arteries have lower compliance and capacitance compared to veins

Question 2

Describe arterioles

Answer 2

-tonically active vascular smooth muscle (VSM)
-highest resistance to blood flow

Question 3

In arterioles, resistance to blood flow can change in response to what?

Answer 3

-sympathetic nerved - alpha 1 adrenergic receptors decrease arteriole diameter + increase resistance, beta 2 adrenergic receptors in heart arterioles dilate + relax
-circulating catecholamines (e.g adrenaline)
-other vasoactive substances

Question 4

What pressure is in the capillaries?

Answer 4

Low pressure

Question 5

Describe venules and veins

Answer 5

-low pressure
-large capacitance
-contain largest percentage of blood in CV system - ‘unstressed volume’
-increased activity via alpha 1 adrenergic receptors, causing contraction to reduce capacitance, decreasing the ‘unstressed volume’

Question 6

What is the relationship between velocity and total cross sectional area?

Answer 6

Inverse relationship

Question 7

How do you calculate velocity of blood flow in cm/s?

Answer 7

V = Q (flow-mL/s)/A (cross-sectional area-cm^2)

Question 8

What is blood flow determined by?

Answer 8

-pressure difference between 2 points in a vessel
-resistance

Question 9

What is the significance of the relationship between blood flow, resistance and pressure?

Answer 9

1. blood pressure regulation:
   -vasoconstriction increases resistance, increasing BP
   -vasodilation decreases resistance, decreasing BP
2. blood flow distribution

Question 10

What is total peripheral resistance (TPR)?

Answer 10

Resistance of the entire systemic vasculature

Question 11

How can resistance of a single organ be calculated?

Answer 11

By substituting flow for e.g renal flow

Question 12

How do you calculate blood volume per unit of time in mL/s?

Answer 12

Q (blood vol-mL/s) = delta P (pressure difference-mmHg)/R (resistance-mmHg/mL per min)

Question 13

What is resistance to flow proportional to?

Answer 13

-directly proportional to vessel length and blood viscosity (haematocrit)
-inversely proportional to 4th power of the radius

Question 14

Describe series resistance (within an organ)

Answer 14

-total resistance = sum of individual resistances
-pressure decreases through each sequential component
-largest decrease in pressure in arterioles = largest resistance: delta P = RxQ

Question 15

Describe parallel resistance

Answer 15

-less than any of the individual resistances
-no loss of pressure

Question 16

How does blood pressure vary throughout the cardiovascular system?

Answer 16

-decreases with blood flow as energy lost overcoming frictional resistance
-aorta - pressure high + low compliance
-arteries - pressure high + elastic recoil
-arterioles - low pressure due to high resistance
-capillaries - low pressure due to frictional resistance to flow + filtration
-venules + veins - low pressure + high capacitance

Question 17

Describe arterial pressure (Pa)

Answer 17

-systemic circulation
-oscillations reflect pulsatile heart activity
-diastolic pressure - lowest Pa during ventricular relaxation
-systolic pressure - highest Pa after ventricular blood ejection during contraction

Question 18

Describe venous pressure (Pv)

Answer 18

-systemic circulation
-pressure less than 10mmHg in venules + veins
-result of decreased resistance at each level

Question 19

Is the pressure of pulmonary vasculature lower than systemic?

Answer 19

Vasculature pressure much lower than systemic due to much lower resistance

Question 20

How do you calculate pulse pressure?

Answer 20

Pulse pressure = systolic - diastolic pressure

Question 21

How do you calculate mean arterial pressure?

Answer 21

Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
-average pressure in complete cardiac cycle

Question 22

What are baroreceptors?

Answer 22

-pressure receptors
-found in carotid + aortic sinuses

Question 23

What does the hormonal system regulate (RAAS)?

Answer 23

-blood volume
-electrolyte balance
-systemic vascular resistance

Question 24

In kidneys, what does decreased arterial pressure lead to?

Answer 24

-decreased renal perfusion detected by kidney afferent arteriole mechanoreceptors (prorenin)
-renin released into blood
-helps convert angiotensinogen, then angiotensin I, then angiotensin II

Question 25

What are the effects of angiotensin II?

Answer 25

-increased aldosterone, leads to sodium reabsorption, increasing ECF
-stimulates sodium reabsorption, increasing ECF
-hypothalamus - increased thirst + ADH secretion, leading to increased water reabsorption in collecting ducts
-vasoconstriction of arterioles

Question 26

What are other regulatory mechanisms in BP homeostasis?

Answer 26

-chemoreceptors
-ADH (AVP) secretion from pituitary

Question 27

What can a small increase in BP lead to for someone with hypertension?

Answer 27

Increased risk of morbidity + mortality

Question 28

What are treatments of hypertension?

Answer 28

-lifestyle changes
-diuretics
-angiotensin-converting enzyme (ACE) inhibitors
-angiotensin II receptor blockers (ARBs)
-renin inhibitors
-calcium channel blockers
-beta blockers