Localised control of circulation and capillary exchange Flashcards
why do the kidneys produce erythropoeiten when blood pressure drops?
allows more RBCs to be made, increases blood volume, increases venous return, more blood to and from heart, BP increases
why do the kidneys release renin when BP drops?
leads to angiotensin II activation, increase in BV, increase in BP
what is the mechanism of Angiotensin II activation?
Angiotensin is released by the liver, the kidney releases renin which interacts with angiotensin to make angiotensin I
Angiotensin I reacts with ACE (angiotensin converting enzyme) released from the capillary endothelium in the lungs to make Angiotensin II
what does Angiotensin II do?
- binds to Angiotensin II receptors in Blood vessels to cause vasoconstriction
- binds to angiotensin II receptors in adrenal glands to cause aldosterone secretion
what does Aldosterone do?
causes absorption of Na+ ions into the blood, water follows (osmosis), blood volume increases, therefore BP increases
what does the heart do when BP increases?
heart acts as an endocrine gland and releases peptides which act upon different tissues to reduce BP
give 4 features of the capillaries
- thin walls
- slow blood flow
- fenestrated
- 2 way exchange of materials
what is capillary hydrostatic pressure?
high blood pressure applies force to the walls of the capillaries and tends to push water and solutes out of the capillaries into the interstitial fluid
what opposes capillary hydrostatic pressure?
Osmotic forces
if the osmotic potential of interstitial fluid is greater than that of the the fluid in the capillaries (hydrostatic pressure)…
it tends to pull water in
what 2 forces determine net filtration pressure?
hydrostatic and osmotic pressure
how do you calculate net filtration pressure?
Net filtration pressure= net hydrostatic pressure- net colloid osmotic pressure
How does blood pressure change from the arteriole to the venule end of the capillary bed?
it decreases
how is net hydrostatic pressure calculated?
capillary hydrostatic pressure (CHP)- Hydrostatic pressure of interstitial fluid (IHP)
when calculating net hydrostatic pressure, why is hydrostatic pressure of interstitial fluid ignored?
it’s negligible
what values does the capillary hydrostatic range from?
35mmHg (arteriole end) to 18mmHg (venous end)
How is net colloid osmotic pressure calculated?
Blood colloid osmotic pressure (BCOP)- interstitial fluid colloid osmotic pressure (ICOP)
when calculating the net colloid osmotic pressure, why is ICOP ignored?
it’s negligible
of the fluid that is pushed out of the capillaries at the arteriole end of the capillaries, what happens to it?
90% pulled back into capillaries at the end
10% goes into the lymphatic system
How does high blood pressure cause Oedema?
Hydrostatic pressure outstrips colloid osmotic pressure so the fluid is pushed out of the capillaries and into the tissues and can’t return to the capillaries so causes fluid build up in tissues (swelling/oedema)
does the pulmonary circulation have a high or low perfusion rate?
high
is pulmonary arterial BP higher or lower than systemic BP?
lower
why is pulmonary arterial BP lower than systemic BP?
resistance is very low- arterioles and wider and shorter and arteries are thinner walled with less elastic
what does it mean by a vessel having high distensibility?
the vessel can readily accommodate increased cardiac output without significant increases in pressure
