Distal convoluted tubule

Distal convoluted tubule
	Kidney nephron (labeled as "2nd convoluted tubule", near top)
	Section of cortex of human kidney.
Latin	tubulus contortus distalis
Gray's	subject #253 1223
Precursor	Metanephric blastema
MeSH	Distal+Kidney+Tubule

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The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting duct system.

[edit] Physiology

It is partly responsible for the regulation of potassium, sodium, calcium, and pH.

It regulates pH by absorbing bicarbonate and secreting protons (H⁺) into the filtrate, or by absorbing protons and secreting bicarbonate into the filtrate.

Sodium and potassium levels are controlled by secreting K⁺ and absorbing Na⁺. Sodium absorption by the distal tubule is mediated by the hormone aldosterone. Aldosterone increases sodium reabsorption. Sodium and chloride (salt) reabsorption is also mediated by a group of kinases called WNK kinases. There are 4 different WNK kinases, WNK1, WNK2, WNK3, and WNK4.

It also participates in calcium regulation by reabsorbing Ca²⁺ in response to parathyroid hormone.

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Arginine vasopressin receptor 2 is also expressed in the DCT.

[edit] Clinical significance

Thiazide diuretics inhibit Na⁺/Cl^- reabsorption from the DCT by blocking the thiazide-sensitive Na-Cl cotransporter.

[edit] Histology

The DCT is the final segment of the nephron. It is lined with simple cuboidal cells that are shorter than those of the proximal convoluted tubule (PCT). The lumen appears larger in DCT than the PCT lumen because the PCT has a brush border (microvilli). DCT can be recognized by its numerous mitochondria, basal infoldings and lateral membrane interdigitations with neighboring cells.

The point where DCT contacts afferent arteriole of renal corpuscle is called macula densa. It has tightly packed columnar cells which display reversed polarity and may monitor the osmolarity of blood.

Histologically, cells of the DCT can be differentiated from cells of the proximal convoluted tubule:

Characteristic	PCT	DCT
Apical brush border	Usually present	Not present
Eosinophilicity	More	Less
Cytoplasm	More	Less
Visible nuclei	Less likely	More likely