Body Fluid Homeostasis

Question 1

What does vasopressin/ADH regulate?

Answer 1

Body fluid osmolality

- conserves H2O

Question 2

Which peptide hormone does ADH share the same pathway as?

Answer 2

Oxytocin

Question 3

Mechanism of ADH secretion

Answer 3

• Change in osmolality is detected by hypothalamic osmoreceptors
• Neurosecretory neurons produce ADH. Cell body lies in hypothalamus axon leads to posterior pituitary gland where ADH is released
• Increases feeling of thirst

Question 4

Which nuclei are stimulated in body fluid homeostasis?

Answer 4

Supra-optic and paraventricular nuclei

Question 5

When is ADH released?

Answer 5

H2O deficiency, decreased blood volume

Question 6

What is osmolality proportional to?

Answer 6

The number of particles per kg of solvent

Question 7

What is osmolarity proportional to?

Answer 7

The number of particles per L of solution

Question 8

Mechanism of vasopressin on principal cell

Answer 8

Binds to V2 receptor on basolateral membrane
activate protein kinase A
Inserts AQP2 channels into apical membrane
takes in more water –> fall I’m osmolality

Question 9

Which receptors does vasopressin bind to?

Answer 9

V2 receptors on basolateral membrane of principal cell

Question 10

What are the two types of diabetes insipidus?

Answer 10

• Central DI

- Nephrogenic DI

Question 11

What is central DI?

Answer 11

No vasopressin release so kidneys can’t regulate how much H2O is excreted

Question 12

What is nephrogenic DI?

Answer 12

The kidney cells have no response to ADH due to a defect in the V2 receptor and aquaporin defect

Question 13

How can the two types of diabetes insipidus be treated?

Answer 13

Central - nasal spray DDAVP (synthetic analogue of ADH)

Nephrogenic - No treatment

Question 14

Where is aldosterone released?

Answer 14

Mineralocorticoid released from the adrenal cortex

Question 15

What does aldosterone regulate?

Answer 15

Na+, K+ and body fluid volume

Question 16

What does aldosterone act on? What effect does it have?

Answer 16

Distal tubule and collecting duct
Increases reabsorption of Na+
Increases secretion of K+ and H+

Question 17

With which system does aldosterone coordinate regulation?

Answer 17

Renin-angiotensin system

Question 18

What is Liddle’s syndrome?

Answer 18

• High Na+ reabsorption - mutation in ENaC
• Low aldosterone
• Increase Na+ channels in principal cell
  leads to hypertension

Question 19

What is pseudohypoaldosteronism?

Answer 19

• Salt loss but high aldosterone
• Loss response to aldosterone
• Mineralocorticoid receptor problem

Question 20

Where is renin released from?

Answer 20

Juxtaglomerular apparatus (JGA)

Question 21

What is the macula densa?

Answer 21

Part of the distal tubule which detects [Na+] - regulates blood pressure and filtration rate

Question 22

Renin-angiotensin cascade

Answer 22

• Decrease ECF volume
• Renin released from JGA
• Angiotensinogen converted to angiotensin I in blood
• Angiotensin-converting eznyme converts to angiotensin II

Question 23

Angiotensin II effects

Answer 23

• aldosterone release
• vasoconstriction
• increases bp
• increases plasma Na+ and ECF volume

Question 24

What happens when you ingest salt?

Answer 24

• Increases plasma Na+ and H2O
• H2O moves out ICF into blood
• Increases ECF volume and osmolality plasma

Question 25

What does a decrease in aldosterone cause?

Answer 25

• Increases Na+ loss
• Increases H2O loss
• Decreases ECF volume

Question 26

What does an increase in vasopressin cause?

Answer 26

• Increases H2O reabsorption

- Decreases osmolality but increases ECF volume