Lecture 39: Renal Systems 4

Question 1

What can cause low plasma volume?

Answer 1

Dehydration, blood loss, vomiting or diarrhoea

Question 2

Describe what happens when plasma volume drops:

Answer 2

1. ↓ arterial pressure and GFR and ↑ renal sympathetic nerve activity
2. Low [NaCl] at macula densa cells
3. Triggers release of renin from the juxtaglomerular cells
4. Angiotensin II synthesis
5. Synthesis of aldosterone in adrenal cortex
6. ↑ ENaC on CD
7. ↑ sodium and water re-absorption in the CD

Question 2

What can cause high plasma volume?

Answer 2

Hyperhydration

Question 2

What organ is responsible for the main excretion of water?

Answer 2

Kidneys - 2/3 water from diet and metabolism

Question 3

Describe what happens when plasma volume increases:

Answer 3

1. ↑ distension in heart
2. Release of atrio-natriuretic peptide (ANP) in atria
3. ↑ plasma ANP
   - ↓ plasma aldosterone
   - dilate afferent and constrict efferent arterioles ↑ GFR
   - ↓ Na+ reabsorption and ↑ Na+ excretion over several hours

Question 4

Where does water reabsorption occur in the nephron?

Answer 4

1. PCT (66%)
2. tDLH (25%)
3. CCT (2 - 8%)

Question 5

Describe water absorption across PCT epithelia:

Answer 5

• Leaky epithelia
• Paracellular Cl- and Na+ absorption provides gradient for trans and paracellular absorption of water

Question 6

What transporter is used for the absorption of water in the PCT?

Answer 6

AQP1

Question 6

Describe the counter-current system for water reabsorption in the TAL and tDLH:

Answer 6

• TAL reabsorbs Na+ into interstitium via NKCC2
• tDLH is leaky - water reabsorbed via aquaporins and paracellular pathway

Question 6

Describe the changes of osmolarity of urine along the nephron:

Answer 6

• PCT: isotonic (300mosmol/L)
• tDLH: hypertonic - water reabsorption
• TAL: hypotonic - Na+ reabsorption
• CD: hypertonic - anti-diuretic conditions

Question 7

Where is vasopressin/ADH secreted from?

Answer 7

Posterior pituitary gland

Question 8

What is the stimulus for the release of ADH?

Answer 8

Low blood pressure - baroreceptors
High blood osmolarity - osmoreceptors

Question 9

Describe water reabsorption in the CD:

Answer 9

• Transcellular
• Regulated by vasopressin - targets principle cells in CD
• Vasopressin binds to its receptor to facilitate AQP2 insertion to increase water reabsorption

Question 10

What results when no ADH is present?

Answer 10

Diuresis - 8% filtered water is excreted

Question 11

What results when ADH is present?

Answer 11

Anti-diuresis - 0.5% filtered water is excreted

Question 11

How does the kidney control blood pH?

Answer 11

By changing HCO3- or H+ secretion or re-absorption

Question 12

What is alkalosis?

Answer 12

Decrease of arterial H+ - pH > 7.4

Question 12

What is acidosis?

Answer 12

Increase of arterial H+ - pH < 7.4

Question 13

What happens during respiratory acidosis?

Answer 13

• ↑ CO2 - hyperventilation
• ↑ HCO3- reabsorption in kidney

Question 14

What happens during metabolic acidosis?

Answer 14

• Diabetes mellitus, diarrhea
• ↑ ventilation in lungs

Question 14

What happens during metabolic alkalosis?

Answer 14

• Vomiting
• ↓ ventilation
• If NOT: HCO3- secretion in CCT of kidney

Question 15

What happens during respiratory alkalosis?

Answer 15

• ↓ CO2 - hyperventilation
• HCO3- secretion in CCT of kidney