Lecture 36: Renal Systems 1

Question 1

Is absorptive and secretory epithelia leaky or tight?

Answer 1

BOTH

Question 2

What is the sodium specific channel for sodium and water absorption in tight epithelium?

Answer 2

ENaC

Question 3

What type of water absorption is found in tight epithelia?

Answer 3

Transcellular

Question 4

What are salivary glands?

Answer 4

• Acinar cells of the salivary gland are leaky secretory epithelium
• Produce an isotonic primary fluid that flows into the mouth

Question 5

Other than salivary glands, give 5 examples of secretory epithelia:

Answer 5

1. Sweat glands
2. Lacrimal (tear) duct
3. Stomach
4. Small intestine
5. Pancreas

Question 6

Describe the secretion of chloride:

Answer 6

1. Na+/K+-ATPase - transport of Na+ out of cell generates gradient for Na+ to enter the cell from basolateral side
2. Na+/K+/2Cl- enter the cell through the co-transporter (NKCC1, basolateral)
3. Chloride is secreted apically via a chloride channel

Question 7

What happens to the K+ and Na+ that was brought into the cell, when chloride is secreted?

Answer 7

• Sodium is absorbed on the basolateral side by the Na+/K+-ATPase
• Potassium is absorbed by a basolateral K+ channel

Question 8

What are the effects of chloride secretion on sodium secretion?

Answer 8

• Cl- secretion results in a -ve lumen and a +ve interstitium driving paracellular Na+ secretion in leaky epithelium
• Water will follow down its osmotic gradient

Question 9

Describe the secretion of water:

Answer 9

• Movement of ions makes the basolateral side hypotonic and leads to water secretion both trans- and para-cellularly

Question 10

What happens if the chloride channel is defective and what can cause this defect?

Answer 10

Water secretion is severely
decreased
* Caused by genetic changes in the CFTR/cystic fibrosis gene

Question 11

Compare leaky and tight epithelia:

Answer 11

1. Leaky epithelia
   *Na+-coupled solute transport e.g SGLT1
   *High rates of Na+
   re-absorption (bulk absorption)
   *High water permeability (trans and para-cellular)
2. Tight epithelia
   * Na+ channel (ENaC)
   *Low rates of Na+
   re-absorption for fine-tuning
   *Low water permeability (only trans-cellular, AQP2)

Question 12

What hormone regulates renal epithelia?

Answer 12

AVP - vasopressin

Question 13

Which parts of the nephron are not hormone regulated?

Answer 13

• Leaky (water permeable): PCT, PST and tDLH
• Tight (water impermeable): tALH up to CNT

Question 14

Which parts of the nephron are hormone regulated?

Answer 14

Tight (water permeability is facilitated by AVP): CCT, OMCD and IMCD

Question 15

What are 8 functions of the kidney?

Answer 15

1. Water homeostasis
2. Reabsorption of nutrients
3. Salt/ion homeostasis
4. Excretion drugs
5. pH regulation
6. Gluconeogenesis
7. Metabolism
8. Hormone production erythropoietin

Question 16

What is expected to be in normal urine?

Answer 16

• ~1.5L/day
• 95-98% water
• Creatinine
• Urea
• H+, NH3 (ammonia)
• Na+, K+
• Drugs (anti-viral, diuretics)

Question 17

What is expected to be in pathologic/abnormal urine?

Answer 17

• Glucose (glucosuria, diabetes)
• Protein (proteinuria)
• Blood (erythrocytes, haematuria)
• Haemoglobin (haemoglobinuria)
• Leucocytes
• Bacteria (infection)

Question 18

What give urine a yellow colour?

Answer 18

Pigments from breakdown of haemoglobin

Question 19

What is the colour scale of urine and what does it mean?

Answer 19

Estimate total body water
* Above bar = enough water: clear to pale yellow
* Below bar = need more water

Question 20

How does normal urine look, taste and smell?

Answer 20

Look: clear, light, or dark amber
Taste: acidic (pH:5-6)
- Veggies up to 7.2
- Meat eater 4.8
Smell: unremarkable

Question 21

How does pathologic/abnormal urine look, taste and smell?

Answer 21

Look: golden, red, brown, blue
Taste: sweet
Smell: fruity (ketosis, diabetes, alcohol) or rotten (infection, tumour)