What are the 3 layers of arterial and venous walls? Briefly describe each
Tunica interna (intima) - endothelial layer that lines the lumen of all vessels
Tunica media - smooth muscle the elastic fibre layer, regulated by sympathetic nervous system (controls vasoconstriction and vasodilation)
Tunica externa - contains collagen fibres protect and reinforce the vessels
What is the lumen?
Central blood-containing space surrounded by tunics
What are capillaries composed of?
Endothelium with a sparse basal lamina
What is blood flow?
The actual volume of blood flowing through a vessel, organ, or the entire circulation (tissue) in a given period of time. (equivalent to CO) (ml/min)
Rate of blood flow per given mass of tissue (ml/min/g)
What is blood flow velocity?
A measurement of the rate of which blood flows through a particular vessel (cm/min)
What is laminar flow? What causes it?
When blood flows in streamlines. Caused by the outside layers in contact with the wall adhering and the inner layers slipping over each other
What causes turbulent blood flow?
This occurs when blood is passing an obstruction, makes a sharp turn or increases in velocity
What does Q represent in terms of the hydrodynamics of fluid flow?
Q = flow
What does P represent in terms of the hydrodynamics of fluid flow?
Difference in pressure
What does R represent in terms of the hydrodynamics of fluid flow?
Resistance to pressure
What is the equation for fluid flow according to hydrodynamics?
Q = P/R
What is the formula Q = P2-P1 = P? Describe what it means.
Flow = Pressure 2 (pressure at the start of the vessel) - Pressure 1 (pressure at the end of the vessel) = Difference of pressure
It means the pressure difference between 2 end of the vessel creates flow along pressure gradient
What does SPR mean?
Systemic peripheral resistance
What does TPR mean?
Total peripheral resistance
What are the 4 main factors that impact resistance?
- Amount of fluid in the system (CO)
- Blood viscosity
- Vessel length
- Vessel diameter
How does vessel length impact resistance?
The longer the vessel the greater the resistance
How does the amount of fluid in the system (CO) impact resistance?
The more fluid in the system, the greater the resistance
What resistance factors remain relatively constant?
Blood viscosity - stickiness of the blood
Blood vessel length
What does TR = 1/R1 + 1/R2 + 1/R3 mean?
It means the total resistance of the system is the sum of the reciprocals of the individual resistances.
By how much does resistance vary with vessel radius?
The resistance varies inversely with the fourth power of vessel radius. e.g. If the radius is doubled, the resistance is 1/16 as much
What blood vessels does the sympathetic nervous system act on?
What is the rate of flow through the system at rest normally? (assuming CO is 6l/min)
What is vascular compliance? What is the formula for it?
The total quantity of blood able to be stored in a given portion of the circulation for each mmHg rise. vascular compliance = increase in volume = increase in pressure
How much more vascular compliance do systemic veins have compared to its corresponding artery?
What is systemic blood pressure measured in?
What is systems blood pressure?
The force exerted by blood against any unit area of blood vessel wall.
Where is systemic pressure highest?
What is the systemic blood pressure in the right atrium?
Where does the steepest change in systemic blood pressure occur?
In the arterioles
What is systolic pressure?
Pressure exerted on arterial walls during ventricular contraction
What is diastolic pressure?
The lowest level of arterial pressure during a ventricular cycle
What is pulse pressure?
The difference between systolic and diastolic pressure
What is mean arterial pressure? What is its formula?
The average pressure through each cycle of the heart beat
MAP = CO x TPR
What values does the capillary blood pressure range between?
What factors increased venous return?
Increased blood volume
Increased large vessel tone
Dilation of the arterioles
What is the venous pressure at the feet when a person is standing? (approx)
What factors aid venous return?
Respiratory pump - pressure changes created during breathing suck blood towards the heart by squeezing local veinsMuscular pump - contraction of muscles push blood towards heart