Regulation of Osmolarity

Question 1

What type of hormone is ADH?

Answer 1

Peptide hormone - neurohormone

Question 2

Where is ADH synthesised?

Answer 2

Supraoptic and Paraventricular nuclei of the hypothalamus

Question 3

Where is ADH secreted?

Answer 3

Posterior pituitary

Question 4

What is the half life of ADH?

Answer 4

10 minutes

Question 5

Why is the half life of ADH so short?

Answer 5

so can rapidly be adjusted depending on the body’s needs for H2O conservation

Question 6

What is the primary control of ADH secretion?

Answer 6

Plasma osmolarity

Question 7

How does increased osmotic pressure effect ADH secretion?

Answer 7

Increased supraoptic/paraventricular nuclei discharge causing increased ADH release

Question 8

Where are neuronal discharge changes mediated?

Answer 8

Osmoreceptors in the anterior hypothalamus

Question 9

Where is thirst mediated?

Answer 9

Lateral hypothalamus

Question 10

How do osmoreceptors detect increased osmolarity?

Answer 10

↑ H2O outflow from cell
Cell shrinks → stretch sensitive ion channel activated
↑ neural discharge
↑ ADH secretion

Question 11

How do osmoreceptors detect decreased osmolarity?

Answer 11

H2O enters cells
Cells swell
↓ Neural discharge
↓ ADH secretion

Question 12

What is the effect on ADH when osmoreceptors detect a stretch?

Answer 12

Increased H2O levels, decreased ADH secretion

Question 13

What is the normal plasma osmolarity?

Answer 13

280-290mOsm/kg

Question 14

2.5% increase in osmolarity causes what increase in ADH?

Answer 14

10x increase

Question 15

Why does urea concent not effect osmolarity?

Answer 15

Urea passes freely with water through membranes

Question 16

What is the maximum concentration of urine?

Answer 16

1200-1400mOsm

Question 17

Why does ingestion of hypertonic solutions cause dehydration?

Answer 17

The increased solute load increases urine flow as more H2O is needed to excrete than was ingested with it

Question 18

Where is the main site of water regulation in the kidney?

Answer 18

Collecting duct

Question 19

Via what mechanism does ADH cause increased water absorption?

Answer 19

ADH binds with basolateral membrane
Vesicles containing aquaporins exocytose onto brush border membranes membranes
Increased permeability to water

Question 20

ADH levels affect aquaporins where?

Answer 20

On the brush border membrane of the collecting duct

Question 21

What is the effect of ADH on aquaporin levels on the basolateral membrane of the collecting duct?

Answer 21

None - aquaporins here are constant

Question 22

What is the collecting duct concentration if ADH is present?

Answer 22

Proportional to the cortical interstitium (300mOsm), then with the hypertonic medullary interstitial gradient

Question 23

What is the collecting duct concentration if ADH levels are at maximum?

Answer 23

Contents equilibrates with medullary interstitium via osmotic efflux and become highly concentrated at the tip

Question 24

How would urine present with maximal [ADH]?

Answer 24

Small volume, highly concentrated

Question 25

How is H2O reabsorbed in the presense of Maximal [ADH]?

Answer 25

Via oncotic pressure of the vasa recta which will be high in the presence of a H2O deficit

Question 26

How would urine present with absent ADH? What osmolarity?

Answer 26

Large volume Very dilute 30-50mOsm

Question 27

Why are urea concentrations high in the presence of ADH?

Answer 27

Water leaves the collecting duct and urea remains

Question 28

How does urea permeability vary in the collecting ducts?

Answer 28

More permeable to urea towards the medullary tips

Question 29

What is the role of urea reabsorbed into the interstitium from the collecting ducts?

Answer 29

Acts to reinforce the interstitial gdt in the region of the thin ascending loops of Henle

Question 30

What happens to urea during maximum anti-diuresis?

Answer 30

Urea is retained to save water and reinforce the medullary gradient in the thin ascending limb

Question 31

Why is the reabsorption of urea important in maximal ADH?

Answer 31

Too much urea in the collecting duct would have an osmotic effect and impede potential rehydration Conservation of H2O more important than Urea excretion

Question 32

What is the effect of increased extracellular fluid volume on ADH?

Answer 32

Increased ECF volume = decreased ADH

Question 33

What is the effect of decreased extracellular fluid volume on ADH?

Answer 33

Decreased ECF volume = increased ADH

Question 34

Why does low blood volume cause increased ADH secretion?

Answer 34

Low blood volume = low stretch receptor afferent discharge = increased ADH secretion

Question 35

Where are the low pressure receptors located?

Answer 35

L and R atria | Great veins

Question 36

Where are the high pressure receptors located?

Answer 36

Carotid | Aortic arch baroreceptors

Question 37

Moderate decreases in ECF volume primary affect what?

Answer 37

Atrial - low pressure receptors

Question 38

How do atrial receptors effect ADH release?

Answer 38

Presence of reduced ECF volume Decreased discharge (via vagus nerve) Increased ADH release

Question 39

When do carotid/aortic baroreceptors engage to contribute to ADH secretion?

Answer 39

When volume changes are significant enough to affect MBP

Question 40

What type of cells secrete ADH?

Answer 40

Neurones

Question 41

What stimuli can increase ADH?

Answer 41

Pain, emotion, stress Exercise Nicotine, morphine Surgery

Question 42

What stimuli can decrease ADH?

Answer 42

Alcohol

Question 43

What is the effect of Alcohol on ADH?

Answer 43

Suppresses ADH release

Question 44

Why is ADH an important factor post-surgery?

Answer 44

Surgery causes inappropriate ADH secretion - monitor H2O intake

Question 45

An osmolarity above what will trigger vasopressin secretion?

Answer 45

280mOsM

Question 46

Changes in blood pressure are detected where?

Answer 46

Carotid/aortic baroreceptors

Question 47

Changes in blood volume are detected where?

Answer 47

Atrial stretch receptors

Question 48

How do messages from the hypothalamic osmoreceptors reach the hypothalamus?

Answer 48

Interneurons to hypothalamus

Question 49

Changes in osmolarity are detected where?

Answer 49

Hypothalamic osmoreceptors

Question 50

ADH acts where?

Answer 50

Collecting duct epithelium

Question 51

What is central Diabetes insipidus?

Answer 51

ADH deficiency

Question 52

What factors can cause diabetes insipidus?

Answer 52

Meningitis Tumours Surgery

Question 53

What is peripheral diabetes insipidus?

Answer 53

Collecting ducts insensitive to ADH

Question 54

How are diabetes insipidus characterised?

Answer 54

Polyuria (>10L/day) | Polydipsia

Question 55

How is central diabetes insipidus treated?

Answer 55

Give patient ADH

Question 56

What is the typical cause of peripheral diabetes insipidus?

Answer 56

Hypercalcaemia | Hypokalemia

Question 57

What is the genetic cause of diabetes insipidus?

Answer 57

Gene for aquaporins | Gene for ADH receptors

Question 58

What is the normal fluid osmolarity in the bowmens capsule?

Answer 58

300mOsM

Question 59

What is the normal fluid osmolarity at the end of the proximal tubule?

Answer 59

300mOsM

Question 60

What is the normal fluid osmolarity at the end of the loop of henle?

Answer 60

100mOsM

Question 61

What is the normal fluid osmolarity at the end of the collecting duct?

Answer 61

50-1200mOsM

Question 62

How much fluid passes the bowmans capsule a day?

Answer 62

180L

Question 63

How much fluid passes the ends of the proximal tubules a day?

Answer 63

54L

Question 64

How much fluid passes the ends of the loop of henle a day?

Answer 64

18L

Question 65

How much fluid passes the ends of the collecting ducts a day?

Answer 65

1.5L (average)