Renal Physiology: Loop of Henle and Collecting Ducts Function

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Questions and Answers

Which hormone directly regulates the amount of water excreted by the kidneys?

Angiotensin II (correct)

Aldosterone

Renin

ADH

In the late segment of the distal tubule and collecting duct, what term collectively refers to their responsiveness to aldosterone?

Principal cells (correct)

ADH-sensitive cells

ENaC cells

ATPase cells

What enzyme directly activates ENaC channels by proteolysis?

Renin

Sgk

CAP1 (correct)

Na-K-2Cl cotransporter

Which mechanism is involved in enhancing NaCl reabsorption across principal cells in the ASDN?

Increasing ENaC expression Signup and view all the answers

Which hormone stimulates K secretion by the late segment of the distal tubule and collecting duct?

Aldosterone Signup and view all the answers

What signaling pathway elevates serum glucocorticoid–stimulated kinase (Sgk) levels, leading to increased expression of ENaC?

PI3K-Akt pathway Signup and view all the answers

Which proteins are part of the filtration slit diaphragm between foot processes of podocytes?

Nephrin, NEPH-1, podocin Signup and view all the answers

Which cells in the renal corpuscle utilize phagocytic activity to remove macromolecules from the mesangium?

Mesangial cells Signup and view all the answers

Which substances are secreted by mesangial cells in the renal corpuscle?

Prostaglandins and proinflammatory cytokines Signup and view all the answers

What role do cilia play in nephron cells?

Mechanosensation and chemosensation Signup and view all the answers

Which components of the renal corpuscle provide structural support for the glomerular capillaries?

Mesangial cells Signup and view all the answers

What is the main function of mesangial cells in regulating glomerular filtration rate (GFR)?

Influence blood flow through glomerular capillaries Signup and view all the answers

Which of the following is the primary mechanism by which ADH increases water permeability in the principal cells?

Insertion of water channels in the luminal membrane of the principal cells Signup and view all the answers

How does ADH influence the activity of the Na-K-2Cl cotransporter in the thick ascending limb?

ADH increases the activity of the Na-K-2Cl cotransporter Signup and view all the answers

What is the primary effect of ADH on urea permeability in the collecting ducts?

ADH increases urea permeability only in the inner medullary collecting ducts Signup and view all the answers

What is the consequence of the increase in cAMP levels in the principal cells in response to ADH?

Activation of protein kinase A and phosphorylation of intracellular structures Signup and view all the answers

In the absence of ADH, what is the water permeability of the principal cells?

The principal cells are impermeable to water Signup and view all the answers

Study Notes

Hormones and Kidney Function

AVP (Antidiuretic Hormone) is the only major hormone that directly regulates the amount of water excreted by the kidneys.
Angiotensin II stimulates NaCl and water reabsorption in the proximal tubule, thick ascending limb of the Henle loop, distal tubule, and collecting duct.

Aldosterone and Sodium Reabsorption

Aldosterone is synthesized by glomerulosa cells of the adrenal cortex and stimulates NaCl reabsorption in the thick ascending limb of the Henle loop, late segment of the distal tubule, and collecting duct.
Aldosterone-sensitive distal nephron (ASDN) refers to the late distal tubule and collecting duct.
Aldosterone stimulates K secretion by the late segment of the distal tubule and collecting duct.

Mechanisms of Aldosterone Action

Aldosterone enhances NaCl reabsorption across principal cells in ASDN by:
- Increasing Na-K-ATPase in the basolateral membrane
- Increasing expression of the epithelial sodium channel (ENaC) in the apical cell membrane
- Elevating serum glucocorticoid-stimulated kinase (Sgk) levels, which increases ENaC expression
- Stimulating channel-activating protease (CAP1), which directly activates ENaC channels

Renal Corpuscle Structure

The filtration barrier consists of the capillary endothelium, basement membrane, and foot processes of podocytes.
The filtration slit diaphragm is composed of proteins including nephrin, NEPH-1, podocin, and others.
Mutations in these genes cause nephrotic syndrome, associated with proteinuria and renal failure.

Mesangium and Mesangial Cells

Mesangial cells provide structural support for glomerular capillaries, secrete the extracellular matrix, exhibit phagocytic activity, and secrete prostaglandins and proinflammatory cytokines.
Mesangial cells may influence glomerular filtration rate (GFR) by regulating blood flow or altering capillary surface area.

ADH and Water Reabsorption

ADH increases water permeability in collecting ducts, allowing water reabsorption.
In the absence of ADH, principal cells are impermeable to water.
ADH binds to V2 receptors on principal cells, activating adenylyl cyclase, which increases cAMP and activates protein kinase A, leading to phosphorylation of intracellular structures.

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Description

Test your knowledge on the mechanisms that regulate countercurrent multiplication and corticopapillary osmotic gradient in the kidney. Explore the roles of Na-K-2Cl cotransporter and urea permeability in the loop of Henle and collecting ducts.