Nephron Function: Reabsorption Mechanisms

Values below 1.0 indicate that the substance is reabsorbed more avidly than ______.

The ______ of Henle is divided into thin descending and thick ascending segments.

The distal tubule is a ______ segment.

Thiazide diuretics act on the ______ tubule.

Principal cells in the late distal tubule and cortical collecting tubule ______ sodium and secrete potassium.

Potassium-sparing diuretics act on ______ cells.

Intercalated cells ______ hydrogen ions and reabsorb bicarbonate and potassium ions.

The medullary collecting duct reabsorbs only ______% of the filtered water and sodium.

The permeability of the medullary collecting duct to water is ______ dependent.

The medullary collecting duct is capable of ______ H ions and plays a key role in acid-base regulation.

Reabsorption Mechanisms

Reabsorption of chloride, urea, and other solutes occurs through passive diffusion, coupled with sodium reabsorption
65% of filtered sodium, chloride, bicarbonate, and potassium, and essentially all filtered glucose and amino acids are reabsorbed by the proximal tubule

Proximal Tubule

Reabsorbs 65% of filtered sodium, chloride, bicarbonate, and potassium, and essentially all filtered glucose and amino acids
Concentrations of solutes along the proximal tubule can be seen in fig 7
Secretes organic acids and bases

Loop of Henle

Composed of three functionally distinct segments: thin descending segment, thin ascending segment, and thick ascending segment
Thick ascending segment reabsorbs sodium, chloride, and potassium (fig 8-B)

Active Transport

Primary active transport linked to hydrolysis of ATP (fig 2)
Secondary active reabsorption through the tubular membrane (fig 3)
Secondary active secretion into the tubules (fig 3)
Pinocytosis: an active transport mechanism for reabsorption of proteins
Transport maximum for substances that are actively reabsorbed (fig 4)

Distal Tubule and Collecting Duct

Forms part of the juxtaglomerular apparatus (JGA)
Diluting segment
Site of action of thiazide diuretics
Principal cells reabsorb sodium and secrete potassium (fig 10)
Intercalated cells avidly secrete hydrogen and reabsorb bicarbonate and potassium ions
Medullary collecting duct reabsorbs only 10% of filtered water and sodium, permeability to water is ADH dependent

Understand how the nephron reabsorbs chloride, urea, and other solutes, including the role of passive diffusion and the proximal tubule. Learn about the mechanisms of reabsorption and secretion along different parts of the nephron.