Regulation of ECFV and Blood Volume

Question 1

what is the main determinant of ECFV?

Answer 1

[Na]

Question 2

what is a normal western diet Na intake? what is necessary?

Answer 2

120 mEq. less than 1% is necessary

Question 3

how is most salt excreted?

Answer 3

90% urine, 7% feces, 3% sweat

Question 4

describe how the body senses blood volume

Answer 4

2 types of sensors- high and low pressure

high pressure-
afferent arterioles JGA- monitor long term blood volume changes w/ stretch receptors. they do not adapt over time
carotid and aortic sinus- sense short term changes to ensure adequate brain perfusion, but adapt over days d/t muscle wall thickening

low pressure-
cardiac atria, vena cava, pulmonary arteries- low pressure vessels where stretch is related to volume. result in intermediate changes. these do undergo adaptation over time.

Question 5

effective circulating volume

Answer 5

total blood volume - pooled blood

Question 6

what is the main natriuretic?

Answer 6

ANP (Na secretion)

Question 7

what are the primary anti-dantriuretic mechanisms?

Answer 7

RAAS and sympathetic renal innervation (Na Reabsorption)

Question 8

what are the major effects of angiotensin 2

Answer 8

1. increase Na/H exchanger in PT
2. constricting efferent arterioles, increasing reabsorption
3. reducing medullary flow, increasing the [ ] gradient
4. aldosterone stimulation
5. vasoconstrictor
6. stimulate thirst

Question 9

what is the most important hormone is Na reabsorption? what are its effects

Answer 9

aldosterone

1. main stimulator of reabsorption in CT and DT (epithelial Na channels)
2. enhances reabsorption in colon and sweat glands
3. stimulates salt appetite
4. increases sensitivity of taste buds to salt
5. decreases Na in saliva

Question 10

how is renin release regulated?

Answer 10

1. stretch receptors from BP in afferent arterioles
2. sympathetic fibers- stimulation = release
3. granular cells receive input from macula densa for release w/ low NaCl load
4. pressor hormones- AII inhibits renin

Question 11

how is aldosterone synthesis regulated?

Answer 11

by AII

Question 12

how does sympathetic innervation increase reabsorption besides the renin system

Answer 12

increases Na reab in the proximal tubule

Question 13

describe the effects of ANP

Answer 13

1. reduce contractility
2. vasodilate resistance vessels and veins, decreasing preload and afterload
3. increase capillary permeability to decrease BV
4. increases GFR
5. increases medullary flow
6. inhibits Na reab, especially in CD
7. inhibits aldosterone and renin production
8. inhibits ADH

Question 14

what is pressure natriuresis?

Answer 14

kidneys have an intrinsic ability to increase rate of Na in response to an increase in perfusion pressure

Question 15

what cells release EPO?

Answer 15

fibroblasts from the kidney interstitium

Question 16

why is the kidney a good place for EPO monitoring?

Answer 16

b/c of the constant pO2 in the tissues d/t the constant A-V difference. The A-V difference remains constant because the supply of blood creates the demand for energy. thus Po2 can be monitored to see if changes are needed in the EPO secretions