Vascular Physiology Flashcards
What are the 3 layers of blood vessels?
Arteries, arterioles, and veins have three layers.
- Inner layer or “tunica intima”-single layer of flattened cells known as the endothelium
- Middle layer or “tunica media”-is smooth muscle that encircles the blood vessels
- Outer layer or “tunica adventitia” -is connective tissue
What is the function of the arteries?
Passageway from heart to organs; pressure reservoir
Thick, highly elastic, walls; large radius
What is the function of the arterioles
Primary resistance vessels; determine distribution of cardiac output
Increase or decrease radius will affect flow through their capillaries
Highly muscular, well-innervated walls; small radius
What is the function of the capillaries?
Site of exchange; determine distribution of extracellular fluid between plasma and interstitial fluid
Very thin walled; large total cross sectional area
What is the function of the veins?
Passageway to the heart from organs; blood reservoir
Thin walled compared to arteries; highly distensible (swelling); large radius
What is the pathway of the vesicular system?
Heart arteries ————(in the organ) small arteries arterioles capillaries venules Small veins ————(in the organ) veins back to the heart (repeat)
How many layers are present in capillaries?
One (very thin) layer. The endothelium.
Process of exchange in the capillaries
O2 and nutrients of the blood diffuse into the ISF (the middle man) which is between the capillaries and the cells
This is done by diffusion so it is down a concentration gradient (from high to low)
O2 and other nutrients from the capillaries diffuse across the ISF to the cell, and the CO2 and other wastes from the cell diffuse across the ISF into the blood or capillaries.
Flow rate
Flow rate is measured in volume/ time (CO is a flow rate)
F=delta P/R
Flow rate depends on the pressure difference
A larger pressure difference means higher flow (assuming the vessels and fluid in the vessels are identical)
This means flow is proportional to pressure difference
—————-
Also need to know resistance (R) to determine flow rate.
R is a measure of the friction that opposes flow
Increased R means decreased flow
What determines Resistance (R)?
Viscosity of blood- a measure of friction of molecules (milk shake is more viscous)
Example: in anemia with decreased RBCs viscosity would decrease, resistance would decrease, and flow would increase
Vessel length- a longer vessel means more friction because more blood would contact the lining of longer vessel versus shorter vessel. (Vessel length does change; basically constant; doesn’t change R)
Vessel radius (has big effect)- what is controlled to control R If you increase tube radius it decreases resistance
How do arteries maintain constant pressure throughout the body?
Arteries have little resistance to flow
when we measure blood pressure in arm artery vs aortic pressure it is essentially equal (pressure doesn’t drop in arteries)
The reason pressure drops in circulatory system is friction (friction dissipates pressure)
How do arteries act as a pressure reservoir?
Do to their elasticity they can maintain blood flow during diastole.
When the heart contracts (during systole) the arteries can expand
When the heart relaxes (during diastole) the arteries can snap back and maintain the pressure.
Arterial pressure
Recorded as systolic pressure/ diastolic pressure
120/80 mmHg
Pulse pressure (PP)
Difference between systolic pressure (SP) and diastolic pressure (DP)
Mean arterial pressure (MAP)
The average pressure driving blood forward into the tissues through cardiac system
More important than systolic and diastolic pressures
MAP is estimated: MAP=DP +1/3 PP
