Capillaries and regulation

What is the function of capillaries?

site of exchange between blood and tissues for gases, nutrients and wastes

How are capillaries arranged?

into beds, blood supply can be controlled via precapillary sphincters

How do precapillary sphincters and arterioles act together?

Together they regulate blood flow, opening of capillaries is controlled by local metabolic changes (C02 or 02)

Why are capillaries good for diffusion?

Small diffusion distance due to thin walls, small diameter and they have a large network

Large surface area

Slow blood flow

How are gases diffused into interstitial fluid?

lipid-soluble substance pass through the endothelial cells

How are proteins moved into interstitial fluid?

Vesicular transport

How do water-soluble substances go into interstitial fluid?

through the pores

What is bulk flow?

Continuous flow of fluid and solutes between capillaries and interstitial fluid

Driven by hydrostatic and osmotic pressure

What is capillary hydrostatic pressure (HCP)?

The blood pressure in the capillaries, hydrostatic pressure of blood flowing into capillaries, higher at arteriolar end than venular end

What is blood colloid osmotic pressure (BCOP)?

Plasma proteins too large to exit capillary, more solutes in the capillary than the interstitial fluid, osmosis draws the fluid back into the capillary

What is net filtration pressure (NFP)?

the difference between the capillary hydrostatic pressure and the blood colloid osmitic pressure

Positive NFP favours filtration

Negative NFP favours reabsorption

What happens to extra fluid?

Extra fluid is returned to the cardiovascular system via lymphatics

How is blood pressure regulated?

Endocrine mechanisms - long term

Neural mechanisms - shorter term

What is the role of the cardiovascular control centre?

Located in medulla oblongata, receives sensory info via baroreceptors, regulates sympathetic and parasympathetic activity to heart and vessels

Where are baroreceptors located?

carotid sinuses and aortic arch - they are mechanorecptors that respond to stretch

What is the capillary hydrostatic pressure?

The blood pressure in the capillaries