Week 3 - F - Physiology 6(b) - Aldosterone and ANP

Question 1

What are the 3 sections of adrenal cortex? (outer to inner) and what do they secrete?

Answer 1

Zona glomerulosa - secretes mineralocorticoids - aldosterone Zone fasiculata - secretes glucocorticoids - cortisol Zona reticularis - secretes androgens (and glucocorticoids)

Question 2

Which hormone is secreted in response to In response to 1.rising [K+] or falling [Na+] in the blood 2. activation of the renin-angiotensin system ?

Answer 2

Aldosterone

Question 3

If decrease in plasma conc. Of sdoim acts indirectly to cause the RAAs system If increase in potassium, directly acts to cause increase in aldosterone from the zona glomerulsosa of the adrenal cortex What does aldosterone stimulate?

Answer 3

Aldosterone stimulates the reabsroption of sidum in the distal tubules and the secretion of patassium - sodium regulates the blood pressure

Question 4

What happens if there is an over secretion of aldosterone?

Answer 4

This could potentially lead to a life threatneing hypokalaemia

Question 5

Normally, ~90% of K+ is reabsorbed in the early regions of the nephron (mainly the proximal tubule) What happens to potassium levels if aldosterone were absent?

Answer 5

Potassium would be reabsorbed in the distal tubule therefore none in the urine

Question 6

What are the three cells of the juxtaglomerular apparatus?

Answer 6

• 1. Juxtaglomerular cells (granular cells)
• 2. Macula densa
• 3. Extra glomerular mesangial cells (Lacis cells)

Question 7

A decrease in plasma [Na+] promotes the indirect secretion of aldosterone by means of the juxtaglomerular apparatus What are the salt sensitive cells that sense this?

Answer 7

The macula densa cells in the juxtaglomerular apparatus sense the low sodium in the efferent arteriole They send vasoactive mediators to cause dilation of the afferent arteriole and the juxtaglomerular cells (granular cells) secrete renin to start the RAAS process

Question 8

Decreased sodium causes a decreased extracellular fluid volume which causes a decreased arterial blood pressure Describe what happens in the RAAS system and where the hormones come from?

Answer 8

Renin is produced in the granular cells of the kidney Causes the conversion of angiotensinogen produced by the liver to angiotensin 1 (AT1) Angiotensin converting enzyme (ACE) produced mainly by the lungs converts AT1 to AT2 AT2 causes the increased porudction of aldosterone from the zona glomerulosa of the adrenal cortex which then acts on the kidneys

Question 9

Describe the four effects that angiotensin 2 has?

Answer 9

It promotes the secretion of aldosterone from the adrenal cortex It increases fluid intake as you are thirsty Increases vasopressin and increases arteriolar vasoconstriction

Question 10

What effect does aldosterone have?

Answer 10

It causes the increased reabsorption of sodium and chlorine (passively) This osmotic gradient absorbs more H20

Question 11

Renin release from the granular cells in the JGA is controlled by severeal factors As the kidneys is controlled by sympathetic innervation, what does an increase in sympathetics cause? What relfex to low blood volume would cause an increase in sympathetics?

Answer 11

Causes an increase in renin production Baroreceptor reflex to low blood volume would cause an increased sympathetic flow

Question 12

Macula densa cells sense the amount of NaCl in the distal tubule If NaCl reduced, more renin released, more Na+ reabsorbed If the blood pressure in the afferent arteriole is decreased what happens?

Answer 12

Aldosterone increases Na+ reabsorption in the distal and collecting tubule

Question 13

Aldosterone increases Na+ reabsorption in the distal and collecting tubule What channels does it bind to, to cause this effect?

Answer 13

Binds to the sodium potassium pump at the basolateral membrane to increase the expression and activity of the channel Also increases the expression of sodium channels at the apical membrane

Question 14

a failing heart will mean decreased cardiac output which will increase RAAS system to increase plasma volume, this produces more load on failing heart which makes the cycle What is the treatment of heart failure? (diet and drugs)

Answer 14

Low salt diet Also have loop diuretics to get rid of excess fluid retention And have first line ACE inhibitor and BBlocker to lower heart rate and contraction)

Question 15

Which drug causing ulcers is contraindicated in use with ACEinhibitors and why?

Answer 15

ACE inhibitors cause vasodilation of the efferent arteriole therefore decreasing GFR NSAIDs cause vaosconstriction of the afferent arteriole therefore decreasing GFR In combination could have a drastic decreasing effect on the GFR

Question 16

Just some info Changes in Filtration Pressure * Changes in afferent arteriole resistance is the most common physiological regulator of GFR * Increase in afferent resistance (vasoconstriction) decreases GFR * Decrease in afferent resistance (vasodilation) increases GFR

Answer 16

Jus some info * Changes in efferent arteriole resistance * Vasoconstriction of the efferent arteriole increases the hydrostatic pressure in the capillaries of the glomerulus as it acts like a dam, and GFR increases * Dilation of the efferent arteriole decreases glomerular capillary hydrostatic pressure, therefore GFR decreases

Question 17

Where in the heart is Atrial natriuretic peptide (ANP) produced?

Answer 17

It is produced in the atiral cells of the heart

Question 18

ANP has the opposite action on the kidneys compared to aldosterone ANP is released when these cells are mechanically stretched due to an increase in the circulating plasma volume What does ANP cause?

Answer 18

It causes an increase in sodium excretion to lower the blood pressure

Question 19

Once the kidneys have produced urine it is temporarily stored in the bladder Micturation happens as a filling and voiding phase The filling phase activates strect receptors what cause the micturition reflex. What happens during the micturition reflex?

Answer 19

Stretch receptors sense the increase in bladder volume causing the parasympathetic fibres from the pelvic splachnic nerves to cause contraction of the detrusor muscle and the opening of the internal urethral sphincter (it is closed under control from sympathetic)supply

Question 20

Voluntary control overirides the micturition reflex What nerve causes voluntary control to what sphincter?

Answer 20

The pudendal nerve (S2,3,4) causes the voluntary control to opening/closure of the external urethral sphincter

Question 21

In water diuresis there is an increased urine flow but not an increased solute excretion How does this differ from osmotic diuresis?

Answer 21

In osmotic direiss there is an increased primary salt excretion resulting in a water excretion as the plasma omsolarity has not increased for there to be more ADH production E.g. failure of normal Na+ reabsorption causes both increased sodium and increased water excretion)

Question 22

What is the substance produced in the kidneys that leads to the formation of red blood cells in the bone marrow? (erythropoesis)

Answer 22

Erythropoietin - stimulates eyrthropoiesis (formation of RBC)