The DCT and Collecting Duct

What percentage of H₂O is still present in fluid arriving at the DCT?

20%

What percentage of NaCl remains in glomerular fluid arriving at the DCT?

7%

If all fluid arriving at the DCT were excreted, approximately how much urine would be produced per day?

36 L/day

What ions are secreted in variable amounts in the DCT and collecting duct?

H⁺ and K⁺

Which substances are reabsorbed in variable amounts in the DCT and collecting duct?

H₂O and NaCl

Which hormones are reabsorbed and regulated in the DCT and collecting duct?

Aldosterone, Atrial natriuretic peptide, & ADH (Vasopressin)

Aldosterone

The “salt-retaining” hormone, a steroid secreted by the adrenal cortex when blood Na+ concentration falls or when K+ concentration rises.

What is the main effect of aldosterone?

Increases Na⁺ reabsorption

Aldosterone acts mainly on which cells?

Principal cells of the DCT and collecting ducts

Aldosterone increases Na⁺ reabsorption beyond what baseline percentage?

8%

Aldosterone increases Na⁺ reabsorption by inserting more..

Na⁺ leak channels and Na⁺/K⁺ pumps

Where are Na⁺ leak channels located under aldosterone action?

Luminal membrane

Where are Na⁺/K⁺ pumps increased by aldosterone?

Basolateral membrane

What happens to Cl⁻ when Na⁺ is reabsorbed under aldosterone action?

It passively follows Na⁺

What ion secretion is also controlled by aldosterone in the DCT and collecting ducts?

K+

What is the main ionic effect of the outcome of aldosterone?

Reabsorbs Na⁺ and secretes K⁺

What happens to H₂O and Cl⁻ during aldosterone action?

They passively follow Na⁺

What is the net effect of aldosterone on the body in the outcome of Aldosterone?

by the body retaining NaCl and water

How does aldosterone affect blood volume?

Increases blood volume (More H2O in blood)

How does aldosterone affect blood pressure?

Increase blood pressure

What happens to urine volume under the outcome of aldosterone?

it is reduced

What is the characteristic of urine under the outcome of aldosterone?

Urine has an elevated K+ concentration

What is the main effect of ADH (vasopressin) in the renal system?

Makes the collecting duct more permeable to H₂O

How does vasopressin increase water reabsorption?

By inserting water channels (aquaporins) into collecting ducts

What is another name for antidiuretic hormone (ADH)?

Vasopressin

What are diuretics?

Therapeutic agents that cause diuresis (increased urinary output) and promote fluid loss in the body.

In response to what condition is antidiuretic hormone (ADH) released?

Dehydration and rising blood osmolarity

ADH (vasopressin) is secreted from which part of the pituitary gland?

posterior lobe of the pituitary

Where is vasopressin produced before being stored in the pituitary?

supraoptic nucleus of the hypothalamus

What is the role of the posterior pituitary in ADH regulation?

Stores and releases ADH

Where is atrial natriuretic peptide (ANP) secreted from?

Atrial myocardium of the heart

What stimulates the release of ANP?

High blood pressure

What is the overall effect of the four actions of atrial natriuretic peptide (ANP)?

result in the excretion of more salt and water in the urine, reducing blood volume and blood pressure.

What is the effect of ANP on the glomerular arterioles?

Dilates the afferent arteriole and constricts the efferent arteriole.

What is the effect of ANP on GFR?

Increase GFR

ANP inhibits which hormone system?

Renin and aldosterone secretion

What is the effect of ANP on ADH secretion?

Inhibits ADH secretion

What does ANP do to NaCl reabsorption in the collecting duct?

Inhibits NaCl reabsorption