Week 3 - F - Physiology 6(a) - Anti-diuretic hormone

Question 1

What is the osmolarity of the tubular fluid leaving the ascending loop of Henle and entering the distal tubule?

Answer 1

Concentration - 100mosmol/l

Question 2

What is the surrounding omsolarity of interstitial fluid around the proximal distal convoluted tubule?

Answer 2

300mosmol/l is the omsolarity of the surrounding interstitium

Question 3

The distal tubule then empties into the collecting duct Once it passes from cortex into medulla, what is the collecting duct exposed to?

Answer 3

It is exposed to the corticomedullary gradient of the surrounding interstitium - 300 to 1200 as you go deeper

Question 4

What are the major sites for regulation of ion and water balance in the nephron?

Answer 4

This would be the distal tubule and the collecting duct

Question 5

What is the major site for reabsorption of salt and water?

Answer 5

This is the proximal convoluted tubule

Question 6

What does the rate of fluid flowing into the proximal tubule to leaving change by?

Answer 6

Flows in at 125ml/min and then due to tubular reabsorption leaves at 45ml/min

Question 7

The regulation of the salt and ion concentration is due to hormones, what are the sites that the hormones act on in the nephron?

Answer 7

The distal and the convoluted tubule

Question 8

What are the 4 primary hormones that regulate the ion and water reabsorption in the nephron?

Answer 8

1. ADH (vasopressin) 2. Aldosterone 3. ANP (Atrial-natriuretic hormone) 4. Parathyroid hormone

Question 9

What is the role of ADH in the nephron? What does it cause to the urine?

Answer 9

It promotes the reabsorption of water therefore changing the volume and concentration of urine produced

Question 10

What does aldosterone cause? (one thing reabsorbed, 2 things secreted)

Answer 10

Cause the reabsorption of sodium and the secretion of hydrogen and potassium

Question 11

What does atrial natriuretic hormone cause? What does parthyorid hormone cause in the kidneys?

Answer 11

Causes decreased sodium reabsorption Parathyroid hormone causes increased calcium absorption and decreased phosphate absorption

Question 12

What does parathyroid hormone cause in the gut and bone?

Answer 12

In gut and bone Gut - absorption of calcium and phosphate Bone - increased bone resroption leading to increased calcium and phosphate

Question 13

In the basal state (resting conditions), what is the permability of the distal tubule to urea and water?

Answer 13

Distal tubule has a low permeability to urea and water - Urea is therefore concentrated in the tubular fluid (which helps to establish the osmotic gradient within the medulla

Question 14

The late distal collecting duct has a low ion permability however a high permeability to water What is this permeability to water influenced by?

Answer 14

It is influenced by the circulating levels of ADH

Question 15

Where is ADH synthesised and what is its other name?

Answer 15

ADH is synthesised in the supraoptic and paraventricular nuclei in the hypothalamus ADH is also known as (arginine) vasopressin

Question 16

What other hormone is synthesised in the supraoptic and paraventricular nuclei in the hypothalamus?

Answer 16

Oxytocin

Question 17

Both ADH and oxytocin are transported where to be stored until release?

Answer 17

Transported to the posterior pituitary to be stored until release

Question 18

Once the axon potentials from the hypothalamus are fired to the posterior pituitary, which chemical is the release of ADH (and oxytocin) dependent on?

Answer 18

Calcium dependent release

Question 19

What is the primary reason for the release of ADH?

Answer 19

An increase in plasma omsolarity so that ADH can caused increased water reabsorption in the collecting duct and distal tubule

Question 20

Where are the two vasopressin receptors and which type is where?

Answer 20

Type 1 vasopressin receptor is on smooth muscle Type 2 vasopressin receptor is at the basolateral membrane of the tubular cell

Question 21

Once vasopressin binds to the basolateral V2 receptor, what occurs?

Answer 21

An increase in intracellular cyclic AMP which causes the increased concentration of aquaporins at the apical membrane

Question 22

What does the increased concentration of aquaporins at the apical membrane of the distal tubule cause?

Answer 22

This causes the increased permability of the apical membrane to water

Question 23

High levels of vasopressin increases permability of tubular cells, low levels lowers permeability of tubular cells to water Summarise what happens when there is an increase in plasma omsolarity?

Answer 23

Hypothalamus sends neurons to elicit Ca2+ dependent release of ADH ADH binds to V2 (vasopressin 2) receptors on the basolateral tubular cell membrane This causes an increase in intracellular cyclicAMP which causes an increase in the concentration of aquaporins at the apical membrane The aquaporins increase the permability of the tubular cell to water

Question 24

describe the volumes of urine produced in high and low levels of ADH?

Answer 24

High ADH level - small and concentrated levels of urine Low ADH levels - large volume and dilute levels of urine

Question 25

What does dehydration cause to the ADH production and how?

Answer 25

Dehydration causes a high serum osmolarity leading to an increased production of ADH which will promote the reabsorption of water in the distal convoluted tubule and the collecting duct

Question 26

When there is increased ADH concentration, the tubular lumen is permeable to water, what therefore happens during the corticomedullary gradient as the collecting duct extends into the medulla?

Answer 26

This promotes the omsotic gradient of water into from the tubular cells via aquaporins and into the intersitium

Question 27

What further modification happens to the urine once it reaches the pelvicalcyeal system?

Answer 27

No further modification once the urine has eft the kidneys

Question 28

In presence of minimal levels of ADH, how does the corticomedullary gradient affect the water flow?

Answer 28

Since their is minimal, the distal convoluted tubule / collecting duct is not permable to water and therefore no water flows and a large dilute volume of urine is produced

Question 29

How does the ADH affect the solute concentration of the tubules?

Answer 29

ADH does not have an effect on this concentration

Question 30

What are the cells detecting the change in osmolarity of the plamsa in the hypothalamus known as?

Answer 30

Known as hypothalamic osmoreceptors

Question 31

Hypothalamic osmoreceptors cause increased hypothalmic neurons leading to increase ADH and increased thirst This decreases urinary output overall decreasing plasma omsolarity and increasing plasma volume What does a decrease in ECF volume cause to the blood pressure?

Answer 31

This cause a decrease in arterial blood pressure

Question 32

Left atrial volume receptors only kicks in a significant arterial BP drop (aka someone with a bad haemorrhage) In response to a significant decrease in ECF volume, this is picked up by stretch receptors in the left atrium of thee heart and this will signal to hypothalamic neurones to promote secretion of ADH What does the ADH cause to smooth muscle of arteriole and what does this cause?

Answer 32

ADH binds to V1 (vasopressin) receptors on smooth muscle causing contraction and this leads to an increased TPR of arterioles

Question 33

What is Vessel resistance equal to?

Answer 33

The vessel resistance is resistance is proportional to the length of vessel and viscosity of the blood but inproportional to the radius of the vessel to the power of 4 - therefore when there is vasoconstriction causing constricted arterioles this increases TPR causing increased MABP

Question 34

Name the condition where there is a continual excess diuresis due to water loss? What are the two types?

Answer 34

This is Diabetes insipidus (cranial or nephrogenic)

Question 35

HowDiabetes insipidus is diagnosed by a water deprivation test How can you tell from cranial and nephrogenic?

Answer 35

Give a vasopressin test If cranial, this will cause a water reabsorption If nephrogenic there will be no change in urine production

Question 36

What is the treatment of cranial diabetes insipidus? What is the treatment of nephrogenic diabetes insipidus?

Answer 36

Cranial - desmopressin Nephrogenic - give thiazide diuretics (has a paradoxical effect causing increased reabsorption of water in the proximal tubule)

Question 37

What drug prescribed for bipolar disorder can cause it if on this treatment long term?

Answer 37

Lithium

Question 38

What in cigarretes stimulates ADH release? What (say on nights out) inhibits ADH release?

Answer 38

Nicotine stimulates, alcohol inhibits