Flashcards in CVS 1 Deck (65)
Describe the structure of capillaries
Single layer of endothelial cells surrounded by a basal lamina.
How can small hydrophilic molecules, like glucose, pass out of capillaries into interstitial tissue space?
Through small aqueous pores in between the endothelial cells lining the capillary. Except in the brain where there is tighter junctions between endothelial cells (blood-brain barrier).
State factors that affect the rate of diffusion
1. Concentration gradient
2. Diffusion distance
3. Diffusion resistance - usually low
4. Surface area available for exchange
What affects the diffusion resistance?
1. Nature of molecule - lipophilic, hydrophilic, size
2. Nature of barrier - pore size, number of pores for hydrophilic molecules
3. Path length - depends on capillary density, path length is shorter in more active tissues
How does the rate of blood flow through the capillary bed affect the concentration gradient?
If it is too slow, the concentration gradient will dissipate. Therefore the blood flow must be matched to the rate of use by tissues.
What is the perfusion rate?
the rate of blood flow through the capillaries per unit mass of tissue, expressed in milliliters per minute per 100 g
Which organs receive a steady blood flow?
Brain and kidneys
What is the cardiac output at rest of a 70kg man?
During exercise the cardiac ouput can increase from 5l/min to ...
What are the 4 components of the cardiovascular system?
1. Pump - heart
2. Distribution system - vessels and blood
3. Exchange mechanism - capillaries
4. Flow control - arterioles and pre-capillary sphincters
Why is resistance an essential component of the cardiovascular system?
In order to regulate blood flow so that it doesn't only perfuse those areas which are easiest (e.g. not against gravity). By reducing the ease of blood flow in some areas you direct it to areas that are more difficult to perfuse.
What component of the cardiovascular system provides a temporary store of blood, which can be returned to the heart at a different rate?
The veins. They have thin, distensible walls and therefore easily distend and collapse acting as temporary reservoirs.
The distensibility of blood vessels located within the body; it is inversely proportional to elasticity. Therefore, the greater the amount of elastic tissue in a blood vessel, the greater the elasticity, and the smaller the compliance.
What determines the direction of blood flow around the circulatory system?
Flow travels from higher pressure to lower pressure.
Where is the largest proportion of blood found in the cardiovascular system?
Where is blood flow the fastest?
Where the total cross-section is the least
In which vessels is blood flow the slowest?
What are the major elastic arteries of the body?
Right and left pulmonary arteries
Left carotid artery
Left subclavian artery
Left and Right common iliac arteries
Where are the semi-lunar valves found?
Aortic and pulmonary valves
Where is a bi-cuspid valve found?
Mitral valve - left atrio-ventricular valve
Where is a tri-cuspid valve found?
Right atrio-ventricular valve
What essential function do elastic arteries have during diastole?
They act as pressure reservoirs - they store elastic energy during systole and release it (recoil) during diastole maintaining blood pressure.
Why are pulses only found in arteries and to as lesser extent arterioles?
Because these are elastic vessels which are stretching and recoiling during systole and diastole respectively.
What are the three major types of arteries?
1. Elastic conducting arteries (widest)
2. Muscular distributing arteries (intermediate diameter - most of the named arteries)
3. Arterioles - narrowest
What three layers make up the walls of arteries and veins?
Tunica adventitia - usually connective tissue
What are vasa vasorum? Where are they found?
They are 'vessels of the vessels' - small blood vessels that supply the walls of large vessels such as elastic arteries, muscular arteries and large veins.
What type of cell produces the elastin, collagen and extracellular matrix found in the tunica media?
smooth muscle cells
What is aortic dissection?
The separation of elastic llamelae by high pressure blood forcing its way in e.g. aortic dissection.
Why are individual's with Marfan's syndrome at high risk of aortic dissection?
Marfan's syndrome is a genetic syndrome. A defect in the fibrillin-1 gene (a glycoproteins which forms elastic fibres in connective tissue), weakens elastic fibres, such as those found in the tunica media of elastic arteries. This makes them more vulnerable to damage by the high pressure blood flow in these vessels.