1 - Introduction to CVS Flashcards
Where does blood travel to from the left heart?
The body - systemic circulation
Why do we need a cardiovascular system?
Most cells are too far away from the surface to rely on diffusion alone. Allows nutrients and oxygen to be carried closer to the tissues so that diffusion can then occur.
Where does blood travel to from the right heart?
The lungs - pulmonary circulation
Is blood oxygenated or deoxygenated when it leaves the right ventricle?
Deoxygenated
Where does diffusion between the blood and tissues occur?
The capillaries
Which properties of molecules allow direct diffusion through the bilayer?
Hydrophobic/lipophilic
E.g. O2 and CO2
Give examples of molecules that have to diffuse through pores. Why?
Glucose, amino acids, lactate. Hydrophilic.
What does diffusion rate depend upon?
- Area - the larger the area, the faster diffusion is
- Diffusion resistance - the lower the resistance, the faster diffusion is
- Concentration gradient - the greater the gradient, the faster diffusion is
What determines diffusion exchange area in the CVS? Is it usually high or low?
Depends on capillary density
Exchange area between capillaries and tissues usually high, and capillary density is greater in metabolically active tissues
What 3 things influence diffusion resistance?
- Nature of molecule - i.e. size and hydrophilic/phobic. Smaller molecules diffuse faster, e.g. glucose
- Nature of the barrier - i.e. number and size of pores. Larger/more = faster
- Path length - distance between the 2 surfaces. Smaller = faster
A substance diffusing into a tissue is at lower concentration in the capillary than the artery, and lower still in the tissue. What determines how MUCH lower?
Rate of use by the tissue, which affects rate of flow through the capillary, or “perfusion rate”.
Low rate of use by the tissue means low perfusion rate. This reduces the concentration in the capillary, but it must still be higher than in the tissue to allow diffusion to occur.
Discuss the metabolic needs of the brain
Constant metabolic need, met by blood flow of around 750ml/min.
Extremely intolerant of flow interruption.
Discuss the metabolic need of the heart.
During exercise, blood flow may increase four fold.
Extremely intolerant of inadequate flow.
Discuss the blood flow to the kidney
Requires a high, constant blood flow
Discuss blood flow to the gut
During digestion, blood flow is markedly increased
Short term flow reduction is tolerable, however
Discuss blood flow to the skin
Not very metabolically active, so does not need high blood flow
However, may increase a large amount for thermoregulation (vasodilation)
Within what limits is blood flow in an average 70kg man maintained?
5L/min at rest and 25L/min during exercise.
Blood flow to the brain must be maintained at 750ml/min
What are the 5 components of the CVS?
- A pump - the heart
- A distribution system - the arteries
- An exchange mechanism - capillaries
- Flow control - arterioles and pre-capillary sphincters (resistance vessels)
- Capacitance - veins
Why are resistance vessels an important part of the cardiovascular system?
Cardiac output must be distributed throughout the body. By restricting blood flow to parts of the body it is easy to perfuse, via resistance vessels, it then drives blood to areas which are not as easy to get blood to.
Which component of the CVS allows the system to cope with changes in the cardiac output? Explain.
Capicitance.
The veins have thin walls that can distend or collapse - i.e. they can contain varying amounts of blood. Thus they act as a reservoir of blood that can be used to correct imbalances between the amount of blood returning to the heart, and the amount it is required to pump out.
Describe the distribution of blood volume at rest.
Blood volume of around 5L is distributed as follows:
- 11% in arteries and arterioles
- 5% in capillaries
- 17% in heart and lungs
- 67% in veins
Which vessels are under the highest pressure, and which are under the lowest?
Highest = arteries Lowest = veins
