P: Circulatory system Flashcards
Whats the % of blood volume in system circulation and in heart + lungs at rest?
- Systemic circulation = 84% (64 in veins, 13 in arteries, 7 in arterioles + capillaries)
- Heart and lungs = 16% (7 in heart, 9 in pulm vessels)
Name and describe the 3 tunics of blood vessel walls
- Tunica externa: outer layer, connective tissue
- Tunica media: middle layer, smooth muscle
- Tunica interna: elastin, basement membrane, innermost simple squamous epithelium
What are elastic arteries (conduits) vs muscular arteries (resistance vessels)?
- 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
Describe capillaries
- 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)
What are veins described as?
Capacitance vessels (blood vessels)
What is Ohm’s law?
F = ΔP/R
- F: rate of blood flow
- ΔP: driving force for blood flow
- R: resistance
What are the major regulators of blood flow? What’s the name of the law related to this?
- Vascular blood vessel diameter (radius = most important parameter in Poiseuille’s law)
- Mean arterial pressure
- Blood viscosity
- Poiseuille’s Law
If radius of a vessel doubles, what’s the consequence on resistance and blood flow?
Resistance = 1/16 R
Blood flow = 16 F
What happens to viscosity if heamatocrit = 60 (polycythaemia)?
- Viscosity can reach >7 (normal is ~3)
- Resistance increases and flow through blood vessels can be compromised
What determines blood viscosity and what is its normal blood vs severe anaemia levels compared to water viscosity?
RBC content determines blood viscosity
- Normal blood viscosity = 3x water viscosity
- Severe anaemia: blood viscosity = 1,5x water viscosity
- Decreased resistance of blood –> ____ rate of peripheral blood flow, ____ venous return, ____CO
- ____ also causes blood dilation –> ____ CO
- Sustained ____ in pumping workload of heart
- 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
What does mean pressure fall to as blood flows through the systemic circulation and why?
Progressively falls to about 0 mmHg due to resistance to blood flow mainly in arterioles
How can pressure drop (ΔP) be increased?
Increase in flow or resistance (ΔP = F x R)
What is blood vessel compliance/capacitance + equations?
- Volume of blood that can be stored in a blood vessel for each mmHg pressure raise
- Ca = ΔV/ΔP
- Compliance = distensibility x volume
What are distensibility + compliance determined by?
- Quantity of elastin fibers in vessel wall
- Wall thickness
While ventricular ejection is ____, blood flow in vasculature is ____
- pulsatile
- continuous
What replaces elastin content in large arteries with age?
Collagen –> aorta can’t expand as much to accommodate SV
As blood is ejected, arteries ___ and the increased pressure caused by SV is “___” into arterial walls
- distend
- absorbed
Compliant arteries ___ the workload of the heart
Reduce
Rigid arteries ____ the workload of the heart
Increase
Average blood pressures (systolic/diastolic)
120/80 or 140/90
Mean arterial pressure (MAP) equation + values
MAP = diastolic pressure + 1/3 (systolic - diastolic pressure)
93 mmHg = 80 + 1/3(40)
Why is the value of MAP closer to diastolic pressure?
Because diastole lasts twice as long as systole
Define hypertension
Chronically elevated blood pressure
Types of hypertension
- 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
What are the long-term consequences of hypertension and why?
- 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
What is pulse pressure + equation?
- 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)
Blood pressure wave: name of wave that’s visible during diastolic phase + what it’s caused by?
Dicrotic wave caused by:
- Recoil of blood from closed aortic valve
- Reflection of systolic pressure wave back from small arteries in lower body
