4.3. Regulation of Extra-Cellular Volume - Aldosterone and Atrial Natriuretic Peptide Flashcards
What controls the regulation of Distal Tubule Na+ reabsorption?
Aldosterone
What is aldosterone?
An Adrenal Cortical Steroid Hormone
What is distal tubule Na+ reabsorption important for?
The long term regulation of Na+, and therefore ECF volume
What controls Aldosterone secretion?
Reflexes involving the Juxtaglomerular Apparatus
What does the Juxtaglomerular Apparatus produce?
Renin
What is the Juxtaglomerular Apparatus made up of?
- Juxtaglomerular Cells
2. The Macula Densa
What are special about the Juxtaglomerular Cells?
Smooth muscle of the afferent afferent arteriole’s media (pre-glomeruli) has become specialized, containing large epithelial cells with plentiful granules
What is the Macula Densa?
A histologically specialised loop of the distal tubule
What causes an increase in Renin production from the Juxtaglomerular Apparatus?
- Blood pressure decreases at the Juxtaglomerular Cells (Renal Baroreceptors)
- Sympathetic Nerve Activity increases (Via the Beta-1 effect)
- NaCl delivery decreases at the Macula Densa (NaCl delivery is inversely proportional)
What is Renin?
A Proteolytic Enzyme
What does Renin act on? And where does it do this?
Angiotensinogen to form Angiotensin I - in the plasma
Is Angiotensinogen or Renin constantly present in the blood?
Angiotensinogen
As Angiotensinogen is always present in the plasma, what is the rate limiting step of the production of Angiotensin I?
The production of Renin
What converts Angiotensin I into Angiotensin II?
Angiotensin Converting Enzyme (ACE)
Where is Angiotensin Converting Enzyme (ACE) most commonly found?
In the pulmonary capillary endothelium
What does Angiotensin II stimulate?
- Aldosterone Secreting Cells in the Zona Glomerulosa of the Adrenal Cortex
- ADH secreting cells in the Hypothalamus
- Arteriole Vasocontriction
- Cardiovascular Response Centres in the Medulla
What does the stimulation of the Aldosterone Secreting Cells (in the Zona Glomerulosa of the Adrenal Cortex) cause?
An increase in Aldosterone being released and therefore an increase in Na reabsorption
What does the stimulation of ADH secreting cells (in the Hypothalamus) cause?
- An increase in ADH being released
2. The feeling of Thirst
What does the stimulation of Arteriole Vasoconstriction cause?
An increase in Blood Pressure
What does the stimulation of the Cardiovascular Response Centres (in the Medulla) cause?
An increase in cardiovascular response, leading to an increase in Blood Pressure
What does an increase in Na reabsorption (due to the increase Aldosterone Secretion), and the increase in ADH secretion result in?
- An increase in the volume of plasma
2. Maintenance of Osmolarity
What does an increase in he plasma volume and maintenance of Osmolarity result in?
An increase in blood pressure
What happens if Aldosterone is give to a normal subject, on an adequate Na diet?
- There is an increase in Na retention and K loss.
2. This results in weight gain because of the H2O retention associated with the Na retention
What happens in time, to normal subjects who are given Aldosterone, secondary to the volume expansion?
Spontaneous Diuresis - although K is still lost (via Aldosterone) due to the increased K secretion
What happens as a result of an increased blood volume?
- There is an increased Atrial Stretch
2. Myocardial Cells Stretch and produce Atrial (or Brain) Natriuretic Peptide
What does Atrial (or Brain) Natriuretic Peptide stimulate?
- A decrease in Aldosterone release (from the Adrenal Cortex)
- A decrease in ADH release from the Pituitary (by acting on the Hypothalamus)
- A decreased blood pressure (by acting on the Medulla)
- An increased GFR and Reduced Renin production (by acting on the kidneys)
What do all of the actions of the Atrial (or Brain) Natriuretic Peptides result in?
An increase in NaCl and H2O secretion
