L18: ADH & the control of osmolality

Question 1

2 properties under physiological control

Answer 1

1) Volume
2) Osmolality

Question 2

Define osmolality

Answer 2

Ability of solutes to lower the concentration of water

Question 3

3 osmolality terms

Answer 3

1) Hyperosmotic (hypertonic solution)

2) Isoosmotic (isotonic) solution

3) Hypoosmotic (hypotonic) solution

Question 4

Define hyperosmotic

Answer 4

Higher osmolality than another solution

Question 5

Define isoosmotic solution

Answer 5

Same osmolality as another solution

Question 6

Define hypoosmotic

Answer 6

Lower osmolality than another solution

Question 7

What happens to a ‘cell’ placed in an isoosmotic solution?

Answer 7

No change

Question 8

What happens to a ‘cell’ placed in an hyperosmotic solution?

Answer 8

Shrink

Question 9

What happens to a ‘cell’ placed in an hypoosmotic solution?

Answer 9

Expand

Question 10

Function of the proximal convoluted tubule

Answer 10

Has microvilli-specialised for absorption

Question 11

Function of the loop of henle

Answer 11

Essential to the ability to conserve H2O & control extracellular osmolality

Question 12

How is osmolality of extracellular fluid controlled?

Answer 12

Produce a range of urine concentrations (hypoosmotic to hyperosmotic)

Question 13

Where is solute in the lumen of the tubule actively reabsorbed into?

Answer 13

Medullary intersititum

• Active reabsorption of H2O

Question 14

Features of the descending limb

Answer 14

Freely permeable to H2O
Not permeable to solute
- Passive reabsorption

Question 15

Describe the countercurrent multiplier

Answer 15

Energy is used to create an osmotic gradient that enables the reabsorption of tubular fluid, so urine can be concentrated
- Nothing is multiplied

Question 16

Describe urea ‘trapping’

Answer 16

1) 5% of filtered urea is reabsorbed into the medullary capillary system
2) Urea is freely filtered in the glomerulus
3) 50% is reabsorbed in the PCT
4) 30% reabsorbed in the DCT & collecting duct
5) 70% down the collecting duct
6) 15% filtered urea excreted

Question 17

Descending limb permeable to

Answer 17

Water

Question 18

Ascending limb permeable to

Answer 18

Solutes

Question 19

What does the medullary capillary system (vasa recta) consists of?

Answer 19

Straight loops; run parallel to the loop of Henle

Question 20

Production of hypoosmotic urine

Answer 20

Hypoosmotic filtrate flows down the collecting duct, then released as hypoosmotic urine

Question 21

Production of hyperosmotic urine

Answer 21

Aquaporins are inserted into the membranes of the medullary collecting duct
- H2O reabsorbed into hyperosmotic intersittium
- Filtrate becomes hyperosmotic as it flows down the collecting duct

Question 22

What does ADH secretion cause?

Answer 22

Insertion of aquaporins into the collecting duct membrane

Question 23

What is ADH release controlled by?

Answer 23

Osmoreceptors

Question 24

What is the rate of ADH secretion when there is an increase in plasma osmolality?

Answer 24

Increase rate of ADH secretion

Question 25

What is the rate of ADH secretion when there is an decrease in plasma osmolality?

Answer 25

Decrease rate of ADH secretion

Question 26

Is plasma osmolality proportional to the rate of ADH secretion?

Answer 26

YEs

Question 27

How is ADH release controlled by osmoreceptors?

Answer 27

ADH neurons in the supraoptic & paraventricular nuclei receive input from central osmoreceptors - they detect changes in plasma osmolality

Question 28

What is ADH released into the blood by?

Answer 28

Posterior pituitary

Question 29

How is ADH released into the blood?

Answer 29

ADH is synthesised by neurons in the supraoptic & paraventricular nuclei of the hypothalamus - It is released by neuronsinto capillaries of the posterior pituitary