Rao Objectives- Loop of Henle, DCT, and Collecting Ducts

Question 1

Describe the structure of the Loop of Henle

Answer 1

It consists of the thin descending limb, thin ascending limb, and thick ascending limb.
**Located in the medulla.

Question 2

Describe the structure of the DCT.

Answer 2

IT continues from the LOH into the cortex and forms the JGA when it comes in contact with its own glomerulus.

Question 3

Describe how collecting ducts are connected.

Answer 3

Several nephrons are joined together into collecting ducts that span both the cortex and the medulla.

Question 4

What is the function of the LOH and distal nephron?

Answer 4

1. Coordinates formation of urine
2. Determines the urinary osmolarity, electrolyte composition, and pH.
   * **Epithelial cells are specialized for tight regulatory mechanisms.

Question 5

Describe the thin descending limb of the LOH.

Answer 5

1. Epithelium consists of thin cells with few mitochondria.
2. Interstitial env exhibits an osmolarity gradient increasing from 280 mOsml/L at the cortical end to 1200 mOsml/L at the medullary end.
3. No active transport mechanism.
4. Epi is highly permeable to water.
5. Minimally permeable to NaCl and urea.
6. Water is absorbed from the lumen due to osmotic gradient across the epithelium, resulting in a rise of luminal osmolarity.

Question 6

Describe the thin ascending loop of the LOH.

Answer 6

1. Epithelium is made of thin cells with few mitochondria.
2. No active transport mechanism.
3. Extremely impermeable to water.
4. Highly permeable to NaCl.
   * *NaCl is reabsorbed due to osmotic gradient and impermeability to water.
   * *Luminal osmolarity also drops.

Question 7

Describe the thick ascending limb of the LOH.

Answer 7

1. Epi is made of thick epithelial cells with many mitochondria.
2. Impermeable to water.
3. High NaCl reabsorption takes place due to active transport mechanism.
   * *Channels involved in NaCl reabsorption include: Na+K+Cl- Transporter (NK2C), Na+K+ATPase and chloride channels.
   * *NK2C inhibitors such as furosemide and bumetanide serve as diuretics.

Question 8

Describe sodium transport from the lumen in the DCT and collecting duct.

Answer 8

It is actively transported via two distinct mechanisms involving the electrogenic Na+ channels and electroneutral Na+Cl- cotransporters.

Question 9

How do loop diuretics work?

Answer 9

Loop diuretics such as ameloride and triamptrene inhibit Na+ channels.

Question 10

How do thiazides serve as loop diuretics?

Answer 10

They inhibit Na+Cl- cotransporters.

Question 11

What facilitates potassium secretion?

Answer 11

Sodium absortion via electrogenic Na+ channels generate lumen-negative transepithelial voltage.

Question 12

Describe potassium secretion.

Answer 12

1. High intracellular [K+] caused by the Na+K+ATPase and lumen negative transepithelial voltage drives potassium secretion into the lumen.
2. Factors that increase Na+ delivery into the distal tubular lumen increase K+ secretion (Loop diuretics do this).

Question 13

How does aldosterone regulate Na+ and K+ transport in the distal tubule?

Answer 13

1. It binds to nuclear receptors and alters gene expression.
2. It increases expression of Na+ channel and Na+Cl- cotransporters.
3. It increases the expression of Na+K+ATPase, Krebs Cycle enzymes, and K+ channel.

Question 14

Addison’s Disease

Answer 14

Characterized by complete absence of aldosterone and is associated with increased urinary excretion of NaCl.

Question 15

Liddle’s Syndrome

Answer 15

Characterized by high aldosterone and is associated with increased Na+ reabsorption and K+ secretion.