Lecture 19 : Physiology of the Renal System IV : Osmolality

Question 1

Notes about ADH

Answer 1

• Synthesised in hypothalamus
• Also known as AVP or vasopressin
• Released from pituitary gland
• Acts on distal tube and collecting duct by increasing AQP2 activation in the walls, which increases water permeability and hence water reabsorption into the blood

Question 2

Osmolality in nephron before vs after ADH

Answer 2

Question 3

Flow rate in nephron before vs after ADH

Answer 3

Question 4

Urea

Answer 4

• Waste product formed in liver from breakdown of amino acids (ammonia)
• Ammonia is toxic so liver converts it to urea
• Helps to maintain osmolality in renal medulla

Question 5

Cells in medulla exposed to harsh environments. How do they overcome it

Answer 5

Question 6

2 Types of diabetes insipidus

Answer 6

Nephrogenic diabetes insipidus
- Loss of sensitivity of kidneys to ADH
- Problem with V2 receptors

Central Diabetes Insipidus
- Or loss of ADH secretion

Both leave kidneys unable to produce concentrated urine, leading to polyuria, dehydration and hypovolemia, leading to polydipsia (drinking too much water).
If fluid intake is inadequate they become hypernatraemic.

Question 7

Central Diabetes Insipidus

Answer 7

Characterised by loss of ADH secretion

Causes :
- head injury
- Tumors
- Infection

Management :
- Demopressin (ADH analogue)
- Thiazide diuretics encourage proximal tubule water reabsorption

Question 8

Nephronergic Diabetes Insipidus

Answer 8

• Loss of sensitivity of kidneys to ADH
• Problem with V2 receptors

Causes :
- Toxicity
- Hypercalcaemia
- Genetic (mutation in V2 or AQP2)

Treatment :
- NOT with desmopressin, kidneys are insensitive to it remember
- Thiazide diuretic
- Low salt diet

Question 9

SIADH

Answer 9

• Show symptoms of very high ADH
• Head injury can cause this, and rare cancers
• urine very concentrated
• Hyponatraemic (very low Na+ conc in blood, due to lots of water in blood, <135 mmol/L)

Treatments :
- Fluid restriction
- Give urea

Question 10

Thirst

Answer 10

When AV3V region detects increase in osmolality of blood plasma.

Hypothalamus then increases thirst.

Question 11

Drinking sea water and newborn’s drinking concentrations

Answer 11

Question 12

Osmolytes

Answer 12

Na+
Cl-
Carbs, fats, proteins

Question 13

Hyperosmolar state

Answer 13