Introduction To The CVS Flashcards
Why do we need the CVS?
- to pump blood through the lungs and carry oxygen
- to transport nutrients to the muscles and organs
- to circulate hormones and immune mediators
- as a connection to the lymphatic system
- for human reproduction
- for temperature regulation
What is passive diffusion, and what is its relative equation?
Passive diffusion is the random, undirected thermal movement of molecules.
The time needed to diffuse a given distance is proportional to the square of the distance: t ∝ d².
Diffusion is fast in μm but very time consuming over distances over 1 mm and inappropriate for transport throughout the body.
What is the main method of molecule movement within the CVS?
The CVS uses convection, which is the movement by a pressure gradient. It provides fast and directional transport; however, diffusion is still crucial for transport over short distances.
What is the significance of having pressure differences?
The output of blood at high pressure creates a pressure difference with distant blood vessels.
This pressure difference drives blood flow.
Where does cardiac output go? What two areas are of significance in relation to cardiac output distribution?
The blood is distributed to various parts of the body, such as the kidneys, liver and GI, etc.
Two places to take note of are the brain and myocardium (muscular heart tissue). These places are relatively underperfused. They have special mechanisms to overcome this problem; however, whenever there is a problem with blood supply, these two places are at risk (stroke, heart attack, etc.).
What controls cardiac output?
- filling pressure (Starling’s Law)
- sympathetic and parasympathetic autonomic nerves
- chemical factors and hormones (eg. adrenaline)
What is the equation for calculating cardiac output?
Cardiac Output = Heart Rate x Stroke Volume
CO = HR x SV
Why are blood flow and blood pressure important?
Blood flow and blood pressure are critical for correct bodily functioning.
As they are linked in the proper distribution of blood (for eg. if there is poor perfusion of the kidney, it could cause renal failure and death).
What is the equation for calculating blood flow?
Blood flow = (Pa - Pv)/resistance
Pa is the pressure at the artery, while Pv is the pressure at the vein.
Blood flow is:
1) proportional to pressure across the blood vessel
2) inversely proportional to the resistance of the blood vessel
Why does blood slow down in the capillaries?
The velocity of the blood is much slower in the capillaries to allow for gaseous/nutrient exchange to occur.
What is the equation for calculating blood velocity?
Blood velocity (cm/s) = blood flow (cm³/s) / cross-sectional area (cm²)
To calculate cross-sectional area, we do the number of vessels times the πr² per vessel.
Describe how dual circulation can be in parallel or in series.
IN SERIES (PORTAL)
- same blood supply between organs
- lower perfusion pressures
- medically significant if the first organ is being underperfused
IN PARALLEL:
- cardiac output is split up
- safeguards O₂ supply in organs
- most organs are supplied this way
List differences between the structures of arteries and veins.
ARTERIES:
- thicker elastic wall to maintain blood pressure
- have high pressure that ensures blood flows in one direction
VEINS:
- thinner elastic walls
- have valves to ensure no blood backflow
What are the four main functional groups of blood vessels?
ELASTIC VESSELS: ARTERIES
Large arteries accomodate stroke volume and convert intermittent ejection into continuous flow
RESISTANCE VESSELS: ARTERIOLES
Control arterial blood pressure and regulate local blood flow
EXCHANGE VESSELS: CAPILLARIES
Nutrient delivery to cells and tissues for water and lymph formation, and removal of metabolic waste
CAPACITANCE VESSELS: VENULES AND VEINS
Control the filling pressure and provide a reservoir of blood, so the veins can constrict and send blood to the heart if needed
Where is most of the blood volume distributed?
It is mostly found in large and small veins and venules. Systemic veins and venules serve as a reservoir, holding about 65% of the volume.
