Cardiovascular Physiology 2 (9/18b) [Biomedical Sciences 1]

Question 1

What physical principles influence how blood flows through the system?

Answer 1

Pressure (P)
Flow (Q)
Resistance (R)

Question 2

How are pressure, flow, and resistance related?

Answer 2

Q = ΔP / R

Q= flow (L/min)
ΔP= pressure gradient (P1-P2)
R= resistance

Question 3

What factors affect resistance?

Answer 3

Viscosity
Vessel length
Vessel radius

Remember resistance ~ 1/radius^4

Question 4

Pressure circuits in the CV system

Answer 4

Systemic system and pulmonary system

Pressure and resistance are much less in pulmonary circuit

Pulse pressure avg 80-120 mmHg

Question 5

Pressures in the circuits

Answer 5

Large arteries: systemic 90-100 mmHg, pulmonary 15 mmHg

Arterioles: systemic 50 mmHg, pulmonary n/a

Capillaries: systemic 20 mmHg, pulmonary 10 mmHg

Large vein: systemic 4 mmHg, pulmonary 8 mmHg

Atrium: systemic 0-2 mmHg, pulmonary 2-5 mmHg

Question 6

Cardiac Output equation

Answer 6

CO = BP / TPR

CO = cardiac output (L/min)
BP = blood pressure (mmHg)
TPR = total peripheral resistance

(Similar to Q = ΔP / R)

Rearrange to get BP = CO * TPR

Question 7

Pressure across the arterioles

Answer 7

Arterioles are the greatest source of resistance to flow in the cardiovascular system and a key determinant of TPR

Biggest pressure drop happens (~50 mmHg drop) across arterioles

Question 8

Flow through one system is (less/greater/equal to) flow through the other system?

Answer 8

Equal to (=)

Question 9

How does the vasculature regulate flow?

Answer 9

By regulating arteriole smooth muscle contraction since arterioles control how much blood an organ gets

Contraction = vasoconstriction
Relaxation = vasodilation

Through local and distant mechanisms

Question 10

Regulating Flow - Local Mechanisms

Answer 10

Tissue metabolites (dilation)

Myogenic (dilation/constriction)

Endothelial 
factors (dilation/constriction)

Question 11

Local Mechanisms - Metabolites and Endothelial

Answer 11

Metabolites → Increase in blood flow in response to:

1) Active hyperemia
2) Reactive hyperemia

Question 12

Active hyperemia

Answer 12

increase in tissue metabolic activity (exercise)

Tissue metabolism → release of metabolites → vasodilation
K+, phosphate, adenosine, prostaglandins, etc

Question 13

Reactive hyperemia

Answer 13

period of occlusion

Shear of blood flow against vessel wall → releases vasodilator substance from endothelium → vasodilation

Question 14

Local Mechanisms - Myogenic

Answer 14

Autoregulation - intrinsic property of vascular smooth muscle allows the vessel to adjust diameter to maintain constant flow despite changes in BP

Dilates to maintain flow in response to decrease BP

Constricts to maintain flow in response to increase BP

Question 15

Regulating Flow - Distant Mechanisms

Answer 15

Neural sympathetic (constriction)

Humoral (dilation/constriction)

Question 16

Distant Mechanisms

Answer 16

Blood vessels innervated by sympathetic nervous system
-Norepinephrine acts on alpha-1 receptors → vasoconstriction

SNS also stimulates adrenal cortex
-Releases epinephrine into bloodstream (circulating catecholamines)

Kidneys release hormones that regulate vessel contractions and resistance
-Important for long term maintenance of BP

Question 17

Circulating catecholamines

Answer 17

epinephrine and norepinephrine flowing in the bloodstream

Question 18

Baroreceptor Reflex (neural mechanism)

Answer 18

Key for SHORT term management of BP

Sensors detect change in pressure, processor develops response, effector carries out response

If arterial pressure decreases

1) increase cardiac output
- Parasympathetic withdrawal → increased HR
- Sympathetic activity → increased HR, increased SV

2) increase TPR via sympathetically-mediated vasoconstriction
3) Sympathetic constriction of veins to increase venous return

Question 19

Renin-Angiotensin-Aldosterone System (humoral mechanism)

Answer 19

Key for LONG term management of BP

Decreased mean arterial pressure leads to decreased perfusion pressure in the kidneys

Increased release of renin

Question 20

Renin

Answer 20

produced in kidneys, catalyzes angiotensinogen to angiotensin I

Question 21

Angiotensin converting enzyme (ACE)

Answer 21

converts angiotensin I to angiotensin II (increase BP, vasoconstrictor)

Question 22

3 Targets for Pharmacologic Management of Hypertension

Answer 22

Decrease cardiac output

Decrease total peripheral resistance

Decrease fluid volume

Question 23

Pharmacologic Management of HTN - Decreased CO

Answer 23

Calcium channel blockers (diltiazem)
-Block influx of Ca2+ during plateau of cardiac action potential, thereby decreasing cardiac contractility and SV

Beta blockers (propranolol)
-Block SNS stimulation of HR and SV, leading to decreased CO

Question 24

Pharmacologic Management of HTN - Decreased TPR

Answer 24

Angiotensin converting enzyme (ACE) inhibitors

-Prevent formation of angiotensin II

Question 25

Pharmacologic Management of HTN - Decreased Fluid Volume

Answer 25

Diuretics (furosemide)

-Increase production of urine by kidneys

Question 26

Systemic circulation has ___ pressure gradient, while pulmonary circulation has ___ pressure gradient

Answer 26

High

Low