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Renal system anatomy and physiology
Proximal convoluted tubule
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proximal convoluted tubules p. 611
in proximal convoluted tubules p. 611
ischemia susceptibility p. 210
in ATN p. 626
defects in p. 610
diuretics and p. 631, 633
dopamine secretion by p. 613
glucose clearance and p. 608
physiology of p. 609
relative concentrations in p. 611
renal cell carcinoma and p. 623
If we take a cross-section of the kidney, there are two main parts, the outer cortex and the inner medulla.
If we zoom in, there are millions of tiny tubes called nephrons which go from the outer cortex down into the medulla and back out into the cortex again.
Nephrons filter out harmful substances in the blood so that we can excrete them into the urine.
Red blood cells and proteins are large and stay in the capillaries whereas blood plasma and smaller particles get filtered out.
This filtrate, called tubular fluid, collects in a cup shaped structure containing the glomerulus called the Bowman's capsule.
Together, the glomerulus and the Bowman’s capsule make up the renal corpuscle.
The Bowman’s capsule is connected to the renal tubule which has a few segments: the proximal convoluted tubule, the U- shaped loop of Henle with a descending and ascending limb, and the distal convoluted tubule which empties into the collecting duct, which collects the urine.
So the proximal convoluted tubule comes right after the glomerulus and it’s where most of the reabsorption happens in the kidney. It’s called “convoluted” because it has a twisting path.
Zooming in on the proximal convoluted tubule, it’s lined by tubule cells which are also known as brush border cells.
On one side is the apical surface which faces the tubular lumen and is lined with microvilli.
Microvilli are tiny projections that increase the cell’s surface area to help it reabsorb more solutes or water.
On the other side is the basolateral surface, which faces the interstitium or the space between the tubule and the peritubular capillaries.
Various solutes like Na+, K+, Ca2+, Cl-, and Mg2+ get reabsorbed in the proximal convoluted tubule, and sodium is one of the most important ones because it helps during the reabsorption of other solutes as well as water.
The proximal convoluted tubule (PCT) is a segment of the renal tubule responsible for the reabsorption and secretion of various solutes and water. The PCT is located in the renal cortex, the outer part of the kidney, and is the first segment of the renal tubule, where it receives the filtrate from the renal corpuscle.
The main function of the PCT is to reabsorb water and solutes like sodium, which is continuously pumped into the interstitium to create a gradient that allows many other solutes and even water to be reabsorbed by tubule cells. Certain metabolic byproducts and medications are also secreted into the tubular fluid by the proximal convoluted tubule and excreted in urine.
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