Design and Organization of Cardiovascular System Flashcards
Capillaries
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.
Pre-capillary arterioles
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)
What regulates input flow? Output flow?
Input flow: pre-capillary sphincteric action
Output flow: venous muscular tone and systemic venous pressure
Capacitant chambers (right and left atria)
Thin walled
Easily distensible
Minimally contractile
Roughly spherical
Muscular band (right and left ventricle)
Continuous band of muscle fibers, attached with fibers aligned linearly
Functions as syncitium
Runs from beginning of pulmonary artery to base of aorta
Cardiovascular circuit (path of blood flow)
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
Circulations in series
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
Rt = R1 + R2…
Flow through each level of system is the same
Pressure decreases progressively
Cardiac output
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
Venous return
Rate at which blood is returned to atria from veins
(VR to right = VR to left)
VR = CO
AV valves vs. Semilunar valves
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
Change of blood flow to an organ system
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
Arteries
Thick walled
Elastic tissue, smooth muscle and connective tissue
Volume in arteries called “stressed volume”
Largest artery is the aorta
Arterioles
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)
Venules
Thin-walled
Smaller than veins
After capillary and before vein
Veins
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”
Velocity of blood flow (v)
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
Ohm’s Law (for flow)
Q = delta P/R
Q = Flow (mL/min)
delta P = Pressure difference (mmHg) = MAP - MVP
R = Resistance (mmHg/mL/min)
Poiseuille equation
R = (8nl)/(pir4)
R = Resistance
n = Viscosity of blood
l = Length of blood vessel
r = radius of blood vessel
Circulation in parallel
Organ systems function in parallel via arteries so blood simultaneously delivered to brain, kidneys, etc.
1/Rt = 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
Blood distribution in circulation
14% in arteries (20% in pulmonary arteries)
6% in capillaries (40% in pulmonary capillaries)
64% in veins (6% in pulmonary veins)
S1
Mitral and tricuspid valves close
Right before systole
Heard loudest at mitral area
S2
Aortic and pulmonary valve close
Right before diastole
Heard loudest at left sternal border
S3
VOLUME
During rapid ventricular filling of diastole
Increased filling pressure and when you have dilated ventricles
S4
STIFF WALL
“atrial kick”
During late diastole when atria contract, blood is ejected into stiff ventricular wall
Associated with ventricular hypertrophy
a wave of JVP
Atria contract
Push some pressure back into jugular vein
c wave of JVP
RV contracts
Closed tricuspid valve bulges back into RA and pushes pressure back into jugular vein
v wave of JVP
Filling of RA against closed tricuspid
Increases RA pressure, back to jugular vein
S2 splitting
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
