The nephron and its blood supply · Biology Class 11–12 | StemPy Lab
Course 15.1·Lesson 3 of 3
The nephron and its blood supply
The nephron is the working unit of the kidney. It has a glomerulus in a Bowman's capsule and a long tubule, with the proximal tubule, the loop of Henle, the distal tubule and the collecting duct. Two sets of capillaries surround it. This lesson follows the fluid along the nephron and shows how its parts are placed in the cortex and the medulla.
about 30 min1 simulation1 practice question
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The unit that makes the urine
A kidney has about a million nephrons, and each one is a small filter of its own. Learn one nephron well, and you know the kidney. A nephron has two parts: a glomerulus and a renal tubule.
A drawing of one nephron, placed across the line between the cortex above and the medulla below. At the top left, the Bowman's capsule is a double walled cup around the glomerulus, a tuft of capillaries. The afferent arteriole enters the glomerulus and the narrower efferent arteriole leaves it. The tubule leaves the capsule as the proximal convoluted tubule, a coiled part in the cortex. It straightens and dips into the medulla as the descending limb of the loop of Henle, turns in a hairpin, and returns upward as the ascending limb. In the cortex it coils again as the distal convoluted tubule, which joins a collecting duct that runs down through the medulla. Peritubular capillaries surround the coiled parts, and a long U shaped vessel, the vasa recta, runs beside the loop.
The glomerulus and the Bowman's capsule
The glomerulus is a tuft of capillaries. A fine branch of the renal artery, the afferent arteriole, brings the blood into it. The blood leaves it by the efferent arteriole. The afferent arteriole is wider than the efferent one, and this keeps the pressure in the glomerulus high.
The Bowman's capsule is the beginning of the renal tubule. It is a double walled cup, and it encloses the glomerulus. The glomerulus together with the Bowman's capsule is the renal corpuscle, also called the Malpighian body.
The renal tubule
Follow the fluid from the capsule onward.
The proximal convoluted tubule (PCT) is a highly coiled network that comes next. The word proximal means near the capsule.
The loop of Henle is a hairpin shaped part. It has a descending limb that goes down and an ascending limb that comes up.
The ascending limb continues as a highly coiled distal convoluted tubule (DCT).
The DCTs of many nephrons open into a straight collecting duct. Many collecting ducts join and open into the renal pelvis, through the medullary pyramids, in the calyces.
Where each part lies
The Malpighian corpuscle, the PCT and the DCT lie in the cortex.
The loop of Henle dips into the medulla.
The collecting duct runs from the cortex down into the medulla.
This arrangement matters. The parts in the medulla make a salty region, and you will see in the second course how it helps the kidney to make a concentrated urine.
Two kinds of nephron
The loop of Henle is short in some nephrons and long in others. In a cortical nephron, the loop is very short and goes only a little way into the medulla. In a juxtamedullary nephron, the loop is very long and runs deep into the medulla. Most nephrons are cortical.
Two nephrons side by side across the cortex and the medulla. The cortical nephron, on the left, has its corpuscle high in the cortex and a very short loop of Henle that dips only a little into the medulla. It has no vasa recta, or only a small one. The juxtamedullary nephron, on the right, has its corpuscle deep in the cortex next to the medulla and a very long loop of Henle that runs deep into the medulla. A long vasa recta runs beside it. A note says that most nephrons are cortical.
The capillaries around the tubule
The efferent arteriole does not go straight to a vein. It forms a fine network of capillaries around the renal tubule, the peritubular capillaries. A minute vessel of this network runs parallel to the loop of Henle and forms a U shaped loop, the vasa recta. The vasa recta is absent or reduced in cortical nephrons.
So blood passes through two beds of capillaries in turn: the glomerulus, where it is filtered, and the peritubular capillaries, which take back the useful things that the tubule reabsorbs.
Try it in Python
The program lists the parts of the nephron in order with the region of each, and works out how much filtrate one nephron forms in a minute.
Practise with new numbers
Common mistakes
Saying that the glomerulus is a part of the tubule. It is a tuft of capillaries. The tubule begins at the Bowman's capsule.
Putting the loop of Henle in the cortex. It dips into the medulla. The corpuscle, the PCT and the DCT are in the cortex.
Mixing up afferent and efferent. The afferent arteriole brings blood to the glomerulus, and the efferent one takes it away.
Saying that the vasa recta is a part of the tubule. It is a blood vessel, and it runs beside the loop of Henle.
Saying that all nephrons have long loops. Most are cortical, with short loops.