Design and Organization of Cardiovascular System

Question 1

Capillaries

Answer 1

6um diameter

Single layer of endothelial cells

Thin wall, non-muscular

Nutrients, gases, water, solutes exchanged btwn blood and tissues

Not all capillaries perfused with blood at all times (depends on dilation/constriction of precapillary sphincters and arterioles)

In metabolically active tissue (heart, kidney, lung) there is essentially no diffusion distance of interstitum between capillary and cell. Can be 4 to 6 capillaries next to every cell.

Question 2

Pre-capillary arterioles

Answer 2

Small muscular (30-40um diameter)

Can vasoconstrict using pre-capillary sphincters

Constriction has large effect on vascular resistance, and thus flow

(Constriction of arteries has small effect on flow)

Question 3

What regulates input flow? Output flow?

Answer 3

Input flow: pre-capillary sphincteric action

Output flow: venous muscular tone and systemic venous pressure

Question 4

Capacitant chambers (right and left atria)

Answer 4

Thin walled

Easily distensible

Minimally contractile

Roughly spherical

Question 5

Muscular band (right and left ventricle)

Answer 5

Continuous band of muscle fibers, attached with fibers aligned linearly

Functions as syncitium

Runs from beginning of pulmonary artery to base of aorta

Question 6

Cardiovascular circuit (path of blood flow)

Answer 6

1) Lungs
2) Pulmonary vein
3) LA
4) Mitral valve (bicuspid)
5) LV
6) Aortic valve
7) Aorta
8) Body
9) Vena cava
10) RA
11) Tricuspid valve
12) RV
13) Pulmonary artery
14) Lungs

Question 7

Circulations in series

Answer 7

Left heart and right heart function in series (left to systemic circulation to right to pulmonary circulation)

Blood vessels within a given organ are in series

R_t = R₁ + R₂…

Flow through each level of system is the same

Pressure decreases progressively

Question 8

Cardiac output

Answer 8

Rate (flow) at which blood is pumped from either ventricle

CO = HR x SV

CO is L/min

(CO of left ventricle = CO of right ventricle)

CO = VR

Question 9

Venous return

Answer 9

Rate at which blood is returned to atria from veins

(VR to right = VR to left)

VR = CO

Question 10

AV valves vs. Semilunar valves

Answer 10

AV valves: between atria and ventricles (mitral and tricuspid); chordae tendineae connected to papillary muscles which prevent backflow of blood

Semilunar valves: from ventricle to artery (aortic and pulmonary); scoop-like flaps w/no chordae tendinae or papillary muscles

Question 11

Change of blood flow to an organ system

Answer 11

1) CO constant but blood flow redistributed by selective alteration of arteriolar resistance
2) CO increases or decreases but percentage distribution of blood flow among organ systems constant (everything affected)
3) Combination of the first two: CO and percentage distribution of blood flow altered

Question 12

Arteries

Answer 12

Thick walled

Elastic tissue, smooth muscle and connective tissue

Volume in arteries called “stressed volume”

Largest artery is the aorta

Question 13

Arterioles

Answer 13

Smallest branches of arteries

Have highest resistance to blood flow

Site where resistance can be changed by alterations in sympathetic nerve activity

Smooth muscle innervated by sympathetic alpha1-adrenergic receptors (vasoconstriction) and beta2-adrenergic receptors (vasodilation)

Question 14

Venules

Answer 14

Thin-walled

Smaller than veins

After capillary and before vein

Question 15

Veins

Answer 15

Endothelial cell layer and some elastic tissue, smooth muscle and connective tissue (but less than arteries)

Large capacitance (capacity to hold blood) and contain largest percentage of blood in cardiovascular system

Smooth muscle innervated by sympathetic nerve fibers

Volume of blood in veins called “unstressed volume”

Question 16

Velocity of blood flow (v)

Answer 16

v = Q/A

v = velocity of blood flow (cm/sec)

Q = flow (mL/sec)

A = cross-sectional area (cm²)

Note: use cross-sectional area of ALL capillaries added up; now you see that blood flows faster through aorta than through capillaries

Question 17

Ohm’s Law (for flow)

Answer 17

Q = delta P/R

Q = Flow (mL/min)

delta P = Pressure difference (mmHg) = MAP - MVP

R = Resistance (mmHg/mL/min)

Question 18

Poiseuille equation

Answer 18

R = (8nl)/(pir⁴)

R = Resistance

n = Viscosity of blood

l = Length of blood vessel

r = radius of blood vessel

Question 19

Circulation in parallel

Answer 19

Organ systems function in parallel via arteries so blood simultaneously delivered to brain, kidneys, etc.

1/R_t = 1/R₁ + 1/R₂…

Flow through each organ system is different (a percentage of the total

Pressure is the same as it started and in each organ system

Question 20

Blood distribution in circulation

Answer 20

14% in arteries (20% in pulmonary arteries)

6% in capillaries (40% in pulmonary capillaries)

64% in veins (6% in pulmonary veins)

Question 21

S1

Answer 21

Mitral and tricuspid valves close

Right before systole

Heard loudest at mitral area

Question 22

S2

Answer 22

Aortic and pulmonary valve close

Right before diastole

Heard loudest at left sternal border

Question 23

S3

Answer 23

VOLUME

During rapid ventricular filling of diastole

Increased filling pressure and when you have dilated ventricles

Question 24

S4

Answer 24

STIFF WALL

“atrial kick”

During late diastole when atria contract, blood is ejected into stiff ventricular wall

Associated with ventricular hypertrophy

Question 25

a wave of JVP

Answer 25

Atria contract

Push some pressure back into jugular vein

Question 26

c wave of JVP

Answer 26

RV contracts

Closed tricuspid valve bulges back into RA and pushes pressure back into jugular vein

Question 27

v wave of JVP

Answer 27

Filling of RA against closed tricuspid

Increases RA pressure, back to jugular vein

Question 28

S2 splitting

Answer 28

Aortic valve closes before pulmonic

Inspiration increases difference because decreased thoracic pressure increases venous return to right heart, so fills more and takes longer for pulmonic valve to close