Download Proximal convoluted tubule

Renal Tubule
Renal tubule consists of :
1-proximal convoluted tubule(PCT).
2-Loop of Henle(LH).
3-Distal convoluted tubule(DCT).
Renal corpuscle, PCT,DCT lie in the renal cortex. Loop of henle
extends in to the renal medulla makes a hairpin turn and then
return to the renal cortex. In a nephron, the loop of Henle connects
PCT and DCT. the first portion of loop of henle dips in to the
renal medulla and called descending limb of loop of Henle ,then
bends in a U shaped and returns to the renal cortex as ascending
limb of loop of Henle. The DCT of several nephrons empty in to
a single collecting duct.
Proximal convoluted tubule: is lined by cuboidal epithelium
with numerous apical microvilli which give a brush border
appearance. The basolateral membrane of the cell is highly folded
and this area contains plenty of mitochondria. 65% of water and
100% of some solutes like glucose and amino acids in the filtrate
are absorbed in the PCT. Organic acids, bases like drugs and drug
metabolites are secreted in the PCT.
Distal convoluted tubule and collecting duct: they are lined by
cuboidal epithelium with few microvilli. Two types of cells are
present in DCT and collecting duct:
1- Principal cells: which respond to ADH and aldosterone.
2- Intercalated cells: Which secrete hydrogen ions.
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Juxtaglomerular apparatus:
In each nephron, the ascending limb of loop of Henle makes
contact with the afferent arteriole of its own renal corpuscle. The
cells of the renal tubule in this region are tall and crowded
together and that part is known as macula densa. These cells
monitor the Na+ and Cl˗ concentration of fluid in the tubular
lumen.
The wall of afferent arteriole contains modified smooth
muscle fibers of tunica media, called Juxtaglomerular cells. the
granules in the Juxtaglomerular cells store renin. Between the
afferent and efferent arterioles in this area are present Lacis cells,
Juxtaglomerular cells, Lacis cells and macula densa together
constitute Juxtaglomerular apparatus.
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Function of Juxtaglomerular apparatus:
JGA helps to regulate arteriole blood pressure, Na+
conservation, K+ excretion and rate of formation of glomerular
filtrate by the kidney.
Glomerular filtration:
Glomerular filtration occurs across the glomerular membrane.
The Mechanism is similar to tissue fluid formation. Since the
pressure in the glomerular capillary is very high, water and
solutes which are ˂ 4nm are forced through the glomerular
membrane in to the capsular space. This fluid is called
glomerular filtrate which is an ultra filtrate of plasma. About 180
L of filtrate enter the capsular space each day. Out of this 178179L return to circulation by tubular reabsorption. Only 1-2L are
excreted as urine.
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