Control and abnormalities of body water

Question 1

Define Hyponatraemia

Answer 1

When water content has increased and decreased the original sodium ion concentration

Hyponatremia (usually) means hypo-osmolality body fluids

Question 2

Define Hypernatraemia

Answer 2

When water content has decreased and increased the original sodium ion concentration

Hypernatremia always means hyperosmolality

Question 3

Where are osmoreceptors found and what do they sense?

Answer 3

Osmoreceptors: sensory receptors located in hypothalamus sense changes in osmolality of ECFV

Question 4

What does an increase in osmolarity stimulate?

Answer 4

Thirst

Secretion of vasopressin (ADH)

Question 5

Describe the mechanism of action of ADH

Answer 5

On image

Question 6

What does a large arteriole drop in blood pressure secrete (clue: a hormone)

Answer 6

However, a large drop in arterial pressure is also a powerful stimulus for release

Question 7

Describe the pathway of neurones that leads to the secretion of ADH

Answer 7

On image

Question 8

How and where is angiotensin produced?

Answer 8

On image

Question 9

Define Hyperosmotic thirst

Answer 9

If PLASMA OSMOLARITY INCREASES YOU BECOME THIRSTY

Question 10

Define Hypovolemic thirst

Answer 10

IF YOU LOSE A LOT OF BLOOD YOU BECOME THRISRTY

Question 11

Define solute load

Answer 11

Kidney must excrete significant amount of metabolic waste product in solute form: solute load

Estimated as 10 x BW in kg (e.g., 600 mOsmol for 60 kg person)

If max urine concentration is 1200 mOsmol L-1, then 0.5 L is required to excrete this load

If min urine concentration is 50, then 12 L would be required to excrete the same load

Question 12

What 2 limits can the kidneys control water excretion

Answer 12

Dehydration

Over-hydration

Question 13

Describe the abnormalities of excess water intake and water depletion

Answer 13

Water excess:
Excessive water intake
Impairment in renal water excretion

Water depletion:
Insufficient water intake
Impairment in renal water reabsorption

Question 14

What can Continued water intake with failure to suppress ADH lead to?

Give some examples

Answer 14

water overload and hyponatremia

Some examples
Vomiting, diarrhoea
Certain drugs (MDMA, ‘ecstacy’ promotes ADH secretion)
Ectopic secretion of ADH (syndrome of inappropriate ADH secretion, SIADH)
Hypocortisolism
Primary adrenal insufficiency (Addison’s disease)

Question 15

What is a syndrome of inapprotiorate ADH secretion?

Answer 15

1. Excessive ADH reduces urinary excretion of water

Causes:

Low plasma soidum
Low plasma osmolarity
High urine osmolairty

Question 16

What causes SI ADH?

Answer 16

Tumour - ectopic production of ADH: small cell carcinoma of the lung

CNS disturbance - enhanced ADH release, stroke, trauma, infection

Drugs - enhanced release of ADH or response to ADH, carbamazepine, prozac

Question 17

What people does dehydration occur in?

Answer 17

infants

elderly

people in coma

people with no access to water

Question 18

What conditions can cause dehydration?

Answer 18

Diabetes mellitus

impairment in ADH release

Question 19

What causes central diabetes insipidus?

What causes nephrogenic DI?

Answer 19

1. Lack of secretion of ADH

Genetic mutations
Head trauma
The disease of the hypothalamus/ pituitary

2. Impaired response to ADH

Mutation of ADH receptor
Mutation of ADH-dependant H2O- channels
Drugs e.g lithium