How Homeostatis Happens

Question 1

/Mechanisms that Maintains Homeostasis of fluid volume

Answer 1

1. The Renin-Angiotensin-Aldosterone-System ( RAAS)
2. The thirst mechanism
3. Atrial Naturietic Hormone (ANP)
4. Brain Natrurietic Hormone (BNP)

1&2 are Angiotensin II AGONIST
3&4 are Angiotensin II Antagonist

Question 2

How Does RAAS happens

Answer 2

Hypovolaemia( which leads to low BP) causes the kidneys especially the Juxtaglomerular cells to Release RENIN into the blood stream.

Anytime there is Renin in the blood the liver responds by activating a substance called ANGIOTENSINOGEN Which later turns to Angiotensin I .

Angiotensin I causes the release of Angiotensin Converting enzymes (ACE) to turn Angiotensin I to ANGIOTENSIN II

NOW , with Angiotensin II, it does the following MAJOR EFFECT on the body:

1. It causes the blood vessels to constrict (vasoconstriction) to retain some of the blood or volume into the system, allowing just small amounts of it to be filtered.
2. It releases ALDOSTERONE which informs the kidneys to retain sodium . Where there is is sodium, there is water! Hence water is retained
3. Informs the Posterior Pituitary Gland to release Antidiuretic hormone which antagonises diuresis hence scanty urine is produced and more water is retained .
   - the release of ADH stimulates thirst mechanism

Question 3

The thirst mechanism

Answer 3

Low blood pressure causes hypovolavemia which means there is high solutes in the system hence high OSMOLALITY.

High osmolality cause the hypothalamus specifically the osmoreceptors to release ANTI DIURETIC HORMONES , remember that ADH is produced in the hypothalamus and it’s been stored and released by the posterior pituitary gland.

When there’s a release of that, the human body senses excessive thirst in response to that water is taken .

As ADH is released, it informs the kidneys specifically the NEPHRONS : distal convoluted tubules and collecting duct to REABSORB water. So instead of the normal filtration process, there is a reverse of that to help retain water , increasing the blood pressure

Question 4

NATRIURETIC PEPTIDES

Answer 4

Call them the ANGIOTENSIN II Antagonists because they keep its work of retaining fluid in check!!

1. ATRIAL NATRIURETIC PEPTIDE (ANP) : this hormone is found in the upper chamber of the heart ( atrium) which is only released when there is an over stretching of the Atrium .
2. BRAIN NATRIURETIC PEPTIDE (BNP) : this hormone is also found in the Lower chamber of the heart (VENTRICLES) and it is also released when there is an over stretch of the ventricle.

Usually these terms are heard when managing patients with heart failure.

When there’s a release of ANP or BNP, it antagonises the effect of ANGIOTENSIN II there by
1. Stopping the effect of vasoconstriction
2. Stops the release of Aldosterone and ADH and the thirst mechanism.

All this will cause the release of excess fluid in the body hence increase in urination