4.4B. Control of body fluid volumes and extracellular fluid osmolality.

Question 1

I. Osmoreceptors
1. What is the role of Osmoreceptors?

Answer 1

Osmoreceptor cell in the hypothalamus detect changes in osmotic status when they swell/shrink depending on the hyper/-hypoosmotic nature of their surrounding ECF

Question 2

I. Osmoreceptors
2. What are definitions of hyperosmotoc and hypo osmotic?

Answer 2

• Hyperosmotic = water moves out of the cell (cell shrinks)
• Hypoosmotic = water moves into the cell (cell swells)

Question 3

I. Osmoreceptors
3. What happen when there is a hyperosmotic activity?

Answer 3

When there is a hyperosmotic activity, we feel thirst
- To eliminate that, we can increase water-intake

Question 4

I. Osmoreceptors
4. Why does the normalization of the osmotic environment take time?

Answer 4

Since the main hypothalamic osmoreceptors are located in the hypothalamus, the normalization of the osmotic environment will take time
- The peripheral (GI) osmoreceptors located in the mouth, stomach, intestine and liver can signal the hypothalamus to ‘’turn off’’ the feeling of thirst upon detection of ingested fluid
=> This prevents overcorrection (over-hydration)

Question 5

I. Osmoreceptors
5. What is the role of peripheral (GI) osmoreceptors?

Answer 5

The peripheral (GI) osmoreceptors located in the mouth, stomach, intestine and liver can signal the hypothalamus to ‘’turn off’’ the feeling of thirst upon detection of ingested fluid
=> This prevents overcorrection (over-hydration)

Question 6

II. Hyperosmosis
1. How does our body response to Hyperosmosis?

Answer 6

Hyperosmosis -> (-) water balance
- The osmoreceptor cells in the hypothalamus are located very close to the supraoptic
nucleus and the paraventricular nucleus

• The osmoreceptor cells regulate the secretory activity of these nuclei, which have long axons travelling to the posterior neurohypophysis
• If there is hyperosmosis (osmoreceptor cells shrink)ADH secretion
  +) ADH increases water-reabsorption from kidney = less water-excretion
  => Contributes to (+) water balance (=retention)

Question 7

III. How does our body respond to changes in blood volume?

Answer 7

• The circulating blood volume is measured indirectly
  => We instead measure the circulating BP at different locations to estimate the circulating blood volume