4.3. Regulation of Extra-Cellular Volume - Aldosterone and Atrial Natriuretic Peptide

Question 1

What controls the regulation of Distal Tubule Na+ reabsorption?

Answer 1

Aldosterone

Question 2

What is aldosterone?

Answer 2

An Adrenal Cortical Steroid Hormone

Question 3

What is distal tubule Na+ reabsorption important for?

Answer 3

The long term regulation of Na+, and therefore ECF volume

Question 4

What controls Aldosterone secretion?

Answer 4

Reflexes involving the Juxtaglomerular Apparatus

Question 5

What does the Juxtaglomerular Apparatus produce?

Answer 5

Renin

Question 6

What is the Juxtaglomerular Apparatus made up of?

Answer 6

1. Juxtaglomerular Cells

2. The Macula Densa

Question 7

What are special about the Juxtaglomerular Cells?

Answer 7

Smooth muscle of the afferent afferent arteriole’s media (pre-glomeruli) has become specialized, containing large epithelial cells with plentiful granules

Question 8

What is the Macula Densa?

Answer 8

A histologically specialised loop of the distal tubule

Question 9

What causes an increase in Renin production from the Juxtaglomerular Apparatus?

Answer 9

1. Blood pressure decreases at the Juxtaglomerular Cells (Renal Baroreceptors)
2. Sympathetic Nerve Activity increases (Via the Beta-1 effect)
3. NaCl delivery decreases at the Macula Densa (NaCl delivery is inversely proportional)

Question 10

What is Renin?

Answer 10

A Proteolytic Enzyme

Question 11

What does Renin act on? And where does it do this?

Answer 11

Angiotensinogen to form Angiotensin I - in the plasma

Question 12

Is Angiotensinogen or Renin constantly present in the blood?

Answer 12

Angiotensinogen

Question 13

As Angiotensinogen is always present in the plasma, what is the rate limiting step of the production of Angiotensin I?

Answer 13

The production of Renin

Question 14

What converts Angiotensin I into Angiotensin II?

Answer 14

Angiotensin Converting Enzyme (ACE)

Question 15

Where is Angiotensin Converting Enzyme (ACE) most commonly found?

Answer 15

In the pulmonary capillary endothelium

Question 16

What does Angiotensin II stimulate?

Answer 16

1. Aldosterone Secreting Cells in the Zona Glomerulosa of the Adrenal Cortex
2. ADH secreting cells in the Hypothalamus
3. Arteriole Vasocontriction
4. Cardiovascular Response Centres in the Medulla

Question 17

What does the stimulation of the Aldosterone Secreting Cells (in the Zona Glomerulosa of the Adrenal Cortex) cause?

Answer 17

An increase in Aldosterone being released and therefore an increase in Na reabsorption

Question 18

What does the stimulation of ADH secreting cells (in the Hypothalamus) cause?

Answer 18

1. An increase in ADH being released

2. The feeling of Thirst

Question 19

What does the stimulation of Arteriole Vasoconstriction cause?

Answer 19

An increase in Blood Pressure

Question 20

What does the stimulation of the Cardiovascular Response Centres (in the Medulla) cause?

Answer 20

An increase in cardiovascular response, leading to an increase in Blood Pressure

Question 21

What does an increase in Na reabsorption (due to the increase Aldosterone Secretion), and the increase in ADH secretion result in?

Answer 21

1. An increase in the volume of plasma

2. Maintenance of Osmolarity

Question 22

What does an increase in he plasma volume and maintenance of Osmolarity result in?

Answer 22

An increase in blood pressure

Question 23

What happens if Aldosterone is give to a normal subject, on an adequate Na diet?

Answer 23

1. 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

Question 24

What happens in time, to normal subjects who are given Aldosterone, secondary to the volume expansion?

Answer 24

Spontaneous Diuresis - although K is still lost (via Aldosterone) due to the increased K secretion

Question 25

What happens as a result of an increased blood volume?

Answer 25

1. There is an increased Atrial Stretch

2. Myocardial Cells Stretch and produce Atrial (or Brain) Natriuretic Peptide

Question 26

What does Atrial (or Brain) Natriuretic Peptide stimulate?

Answer 26

1. A decrease in Aldosterone release (from the Adrenal Cortex)
2. A decrease in ADH release from the Pituitary (by acting on the Hypothalamus)
3. A decreased blood pressure (by acting on the Medulla)
4. An increased GFR and Reduced Renin production (by acting on the kidneys)

Question 27

What do all of the actions of the Atrial (or Brain) Natriuretic Peptides result in?

Answer 27

An increase in NaCl and H2O secretion