L11

Question 1

how is water distributed in the body?

Answer 1

55% of body is water but varies with sex, age, mass:
- 2/3 intracellular fluid (ICF)
- 1/3 extracellular fluid (ECF): 75% interstitial fluid, 25% plasma

Question 2

what are the average daily water gains and losses?

Answer 2

water gain:
- intake (2.2 L/day)
- metabolic production (0.3 L/day)

water loss:
- output (2.5 L/day)

Question 3

how is water taken in?

Answer 3

food, drink

Question 4

how is water lost from the body?

Answer 4

urine (1.5 L/day), skin (sweat), lungs (breath), [0.9 L/day], feces (0.1 L/day)

Question 5

excessive water loss

Answer 5

• disease (hypotension/shock)
• excessive water loss -> less extracellular fluid -> decreased blood pressure
• confused, chest pain, very low blood pressure, make no urine

Question 6

excessive water intake

Answer 6

• backs up in the lungs, legs, abdomen
• difficulties in breathing, walking

Question 7

how is urine formed?

Answer 7

by the nephron by filtration, reabsorption, secretion

Question 8

amount of solute excreted =

Answer 8

amount filtered - amount reabsorbed + amount secreted

Question 9

—- L of blood flows to the kidneys/day

Answer 9

1584

Question 10

—- L of filtrate formed/day

Answer 10

180 (99% reabsorbed)

Question 11

—- L of urine excreted / day

Answer 11

1.8 (1% excreted)

Question 12

the nephron/kidney is responsible for:

Answer 12

• excreting waste
• regulating blood volume
• controlling electrolytes
• blood pH
• Vitamin D (via PTH)

Question 13

define the nephron

Answer 13

the functional unit of the kidney

Question 14

4 steps of urine formation in the nephron (filtration, reabsorption, secretion)

Answer 14

1. isosmotic fluid leaving the proximal tubules becomes progressively more concentrated in the descending limb.
2. removal of solute in the thick ascending limb of the Loop of Henle creates hyposmotic fluid
3. permeability to water and solutes is regulated by hormones in the collecting duct
4. urine osmolarity depends on reabsorption in the collecting duct

Question 15

define osmolarity

Answer 15

the concentration of a solution expressed as the total number of solute particles per litre

Question 16

functions of vasopressin, aldosterone, atrial natriuretic peptide

Answer 16

vasopressin
- increased H2O reabsorption
aldosterone
- increased Na+ reabsorption
- increased K+ secretion
atrial natriuretic peptide
- decreased Na+ and H2O reabsorption
- increased K+ reabsorption

Question 17

vasopressin =

Answer 17

antidiuretic hormone, ADH

Question 18

where is vasopressin synthesised/secreted

Answer 18

synthesised in the hypothalamus
secreted from the posterior pituitary

Question 19

primary function of vasopressin

Answer 19

to increase water reabsorption in the kidneys:
- conserve body water
- water balance and fluid homeostasis
- increases blood volume and blood pressure
- regulates permeability of cells in kidney (increased permeability = increased reabsorption and low urine output)

Question 20

what are the two main stimuli for vasopressin release?

Answer 20

• detected by reduced stretch of walls of atria of the heart and aortic/carotid arteries
• detected by osmoreceptors in the hypothalamus

Question 21

what is the most potent stimulus for vasopressin release?

Answer 21

plasma osmolarity

Question 22

process behind vasopressin decreasing urine production

Answer 22

1. travels from blood and binds to receptors on collecting duct cells
2. this binding causes a signal cascade
3. signal cascade leads to insertion of aquaporin-2 water pores into the membrane between the collecting duct cell and the collecting duct lumen
4. more water is absorbed and returned to the blood

Question 23

define aldosterone

Answer 23

a steroid synthesised in the adrenal cortex (Zona Glomerulosa) that regulates therefore water homeostasis

Question 24

3 main functions of aldosterone

Answer 24

1. Na+ reabsorption (to retain water)
2. K+ secretion
3. acts on distal tubule and collecting duct

Question 25

what is aldosterone controlled by?

Answer 25

negative feedback, both simple (K+, osmolarity) and complex (renin-angiotensin II)

Question 26

two stimulators of aldosterone

Answer 26

1. high [K+]plasma 2. angiotensin II (via blood pressure)

Question 27

inhibitor of aldosterone

Answer 27

high osmolarity (extracellular fluid)

Question 28

what two locations does aldosterone act on?

Answer 28

the distal tubule and collecting duct

Question 29

5 steps of aldosterone function

Answer 29

1. aldosterone combines with a cytoplasmic receptor 2. hormone-receptor complex initiates transcription in the nucleus 3. translation and protein synthesis makes new protein channels and pumps 4. aldosterone-induced proteins modulate existing channels and pumps 5. result is increased Na+ reabsorption and K+ secretion - prevents degradation of apical Na+ channel - increases expression of Na+ and K+ channels and Na+/K+ channels and Na+/K+ ATPase

Question 30

renin

Answer 30

an enzyme secreted by the renal juxtaglomerular cells when blood pressure falls

Question 31

where are the renal juxtaglomerular cells located?

Answer 31

in the walls of the afferent arterioles, at the entrance to the glomerulus

Question 32

Renin-Angiotensin - Aldosterone Pathway

Answer 32

1. A drop in blood pressure, blood volume, sodium concentration, or an increase in sympathetic activity is detected by the kidney. Juxtaglomerular cells of the kidney release renin. 2. Renin cleaves angiotensinogen (a plasma protein made by the liver) into angiotensin I. 3. As blood passes through the lungs and other vascular beds, angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II. Angiotensin II has multiple actions: - Causes systemic vasoconstriction, raising blood pressure. - Stimulates the adrenal cortex (zona glomerulosa) to release aldosterone. - Stimulates the posterior pituitary to release antidiuretic hormone (ADH). - Activates the hypothalamus to increase thirst. - Enhances sympathetic nervous system activity. 4. Aldosterone acts on the distal tubule and collecting duct of the nephron to: - Increase sodium reabsorption (water follows sodium osmotically). - Increase water retention, expanding blood volume. - Promote potassium secretion. 5. The combined effects of vasoconstriction, sodium and water retention, and increased thirst restore blood pressure and blood volume. 6. Once homeostasis is reached, negative feedback decreases renin release.

Question 33

role of Angiotensin II

Answer 33

- increases vasopressin - stimulates thirst - potent vasoconstrictor - increases proximal tube Na+ retention

Question 34

describe the family of natriuretic peptides secreted by secondary endocrine glands

Answer 34

- ANP: atria (myocardial cells), neurons - BNP: ventricles (myocardial cells), neurons - CNP: brain, pituitary, vessels, kidneys

Question 35

what do ANP and BNP stand for?

Answer 35

atrial natriuretic peptide and brain natriuretic peptide

Question 36

what is the stimulus for the release of ANP and BNP?

Answer 36

sense the stretching of the heart, which suggest too much pressure

Question 37

effects of ANP and BNP

Answer 37

- decreased Na+ and H2O reabsorption (lowers blood pressure) - increased K+ absorption - dilates blood vessels to decrease blood volume - increases renal secretion - suppresses renin, aldosterone, vasopressin

Question 38

draw a flow chart for ANP release and function