Localised control of circulation and capillary exchange

Question 1

why do the kidneys produce erythropoeiten when blood pressure drops?

Answer 1

allows more RBCs to be made, increases blood volume, increases venous return, more blood to and from heart, BP increases

Question 2

why do the kidneys release renin when BP drops?

Answer 2

leads to angiotensin II activation, increase in BV, increase in BP

Question 3

what is the mechanism of Angiotensin II activation?

Answer 3

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

Question 4

what does Angiotensin II do?

Answer 4

• binds to Angiotensin II receptors in Blood vessels to cause vasoconstriction
• binds to angiotensin II receptors in adrenal glands to cause aldosterone secretion

Question 5

what does Aldosterone do?

Answer 5

causes absorption of Na+ ions into the blood, water follows (osmosis), blood volume increases, therefore BP increases

Question 6

what does the heart do when BP increases?

Answer 6

heart acts as an endocrine gland and releases peptides which act upon different tissues to reduce BP

Question 7

give 4 features of the capillaries

Answer 7

• thin walls
• slow blood flow
• fenestrated
• 2 way exchange of materials

Question 8

what is capillary hydrostatic pressure?

Answer 8

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

Question 9

what opposes capillary hydrostatic pressure?

Answer 9

Osmotic forces

Question 10

if the osmotic potential of interstitial fluid is greater than that of the the fluid in the capillaries (hydrostatic pressure)…

Answer 10

it tends to pull water in

Question 11

what 2 forces determine net filtration pressure?

Answer 11

hydrostatic and osmotic pressure

Question 12

how do you calculate net filtration pressure?

Answer 12

Net filtration pressure= net hydrostatic pressure- net colloid osmotic pressure

Question 13

How does blood pressure change from the arteriole to the venule end of the capillary bed?

Answer 13

it decreases

Question 14

how is net hydrostatic pressure calculated?

Answer 14

capillary hydrostatic pressure (CHP)- Hydrostatic pressure of interstitial fluid (IHP)

Question 15

when calculating net hydrostatic pressure, why is hydrostatic pressure of interstitial fluid ignored?

Answer 15

it’s negligible

Question 16

what values does the capillary hydrostatic range from?

Answer 16

35mmHg (arteriole end) to 18mmHg (venous end)

Question 17

How is net colloid osmotic pressure calculated?

Answer 17

Blood colloid osmotic pressure (BCOP)- interstitial fluid colloid osmotic pressure (ICOP)

Question 18

when calculating the net colloid osmotic pressure, why is ICOP ignored?

Answer 18

it’s negligible

Question 19

of the fluid that is pushed out of the capillaries at the arteriole end of the capillaries, what happens to it?

Answer 19

90% pulled back into capillaries at the end

10% goes into the lymphatic system

Question 20

How does high blood pressure cause Oedema?

Answer 20

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)

Question 21

does the pulmonary circulation have a high or low perfusion rate?

Answer 21

high

Question 22

is pulmonary arterial BP higher or lower than systemic BP?

Answer 22

lower

Question 23

why is pulmonary arterial BP lower than systemic BP?

Answer 23

resistance is very low- arterioles and wider and shorter and arteries are thinner walled with less elastic

Question 24

what does it mean by a vessel having high distensibility?

Answer 24

the vessel can readily accommodate increased cardiac output without significant increases in pressure