Excretory Products and Their Elimination · Lesson 3 of 10
Nephron Structure: Renal Corpuscle, Tubules and Blood Supply
“Follow blood and filtrate through the nephron, including cortical and juxtamedullary forms, peritubular capillaries and vasa recta.”
• Define the nephron and renal corpuscle. • Label afferent/efferent arterioles and the tubular sequence. • Explain why the filtration and tubular blood routes differ. • Distinguish cortical from juxtamedullary nephrons. • Locate peritubular capillaries and vasa recta.
One kidney contains a vast number of small working units
The kidney is built from many repeated microscopic units called nephrons, approximately a million in each adult human kidney. Every nephron joins a blood-filtering component to a long, specialised tubule. Rather than filtering blood and discarding everything in one step, the nephron first creates a relatively large volume of filtrate and then reclaims most of its water and useful solutes. Some additional wastes are secreted into the tubular fluid. This explains why the organ can continuously process substantial blood flow while producing comparatively little final urine.
The microscopic functional unit of a kidney, comprising a renal corpuscle associated with a renal tubule that modifies the filtrate.
The renal corpuscle: where filtration begins
A glomerulus is a tuft of small blood capillaries supplied by an afferent arteriole. Blood leaves that tuft through an efferent arteriole. The glomerulus sits within a double-walled cup called Bowman's capsule. Together, the glomerulus and capsule form a renal corpuscle, also called the Malpighian body. Water and small plasma solutes cross the filtration barrier into the capsular space; blood cells and most plasma proteins normally remain in the circulation.
The distinction between afferent and efferent is directional. Afferent means 'towards' the glomerulus and efferent means 'away from' it. The presence of arterioles on both sides helps regulate pressure in the glomerular capillaries. Blood does not enter Bowman's capsule as whole blood: it remains within capillaries while filtrate forms across their walls.
The renal tubule follows a precise sequence
The capsular space opens into the proximal convoluted tubule (PCT), an extensively coiled segment in the cortex. The PCT gives way to the loop of Henle, which descends from the cortex into the medulla and bends back up. The ascending limb continues toward the cortex and into the distal convoluted tubule (DCT), another coiled segment. DCTs connect to collecting ducts that receive fluid from many nephrons and descend through the medulla towards the kidney's collecting spaces.
The tubule's segments do not perform identical jobs. Their epithelial cells vary in surface area, transport proteins and permeability, allowing one segment to reclaim abundant nutrients while another builds the osmotic gradient necessary for water conservation. A useful structural rule is to trace filtrate separately from blood: filtrate flows through the tubule; blood runs through adjacent capillaries where reabsorbed substances return.
Cortical and juxtamedullary nephrons
Most renal corpuscles lie in the cortex, but nephrons differ in how deeply their loops reach into the medulla. Cortical nephrons have relatively short loops of Henle and predominantly cortical tubular networks. Juxtamedullary nephrons have renal corpuscles near the corticomedullary junction and long loops that descend into deeper medulla. These long loops participate especially in creating the medullary osmotic gradient needed to produce concentrated urine.
Do not mistake the word *juxtamedullary* for the *juxtaglomerular apparatus*: they refer to different features. Juxtamedullary describes a nephron's position and long loop, while the juxtaglomerular apparatus is a local feedback structure near the meeting of a distal tubule and an arteriole. One relates mainly to concentration anatomy and the other to regulation of filtration and blood pressure.
| Feature | Cortical nephron | Juxtamedullary nephron |
|---|---|---|
| Renal corpuscle | Outer/middle cortex | Near corticomedullary boundary |
| Loop of Henle | Usually relatively short | Long, descending deep into medulla |
| Vasa recta | Usually absent or reduced | Well-developed parallel hairpin vessels |
| Functional emphasis | Substantial filtration and tubular recovery | Major contribution to concentrating mechanisms |
What happens to blood after it leaves the glomerulus?
The efferent arteriole divides into fine peritubular capillaries around portions of the renal tubule. These vessels receive reabsorbed water and useful solutes and can supply substances for secretion into the tubule. In juxtamedullary nephrons, long, hairpin-shaped capillaries called vasa recta follow the loops of Henle down and up through medullary tissue. Their paired opposing blood flows help preserve the high concentration of the renal medulla rather than washing it away.
The capillary arrangement creates two functionally linked but distinct steps: the glomerulus filters plasma, while the peritubular network supports reclamation and secretion. This is why a nephron cannot be understood solely as a tube filled with urine. Its architecture includes a carefully organised blood supply whose pressures and solute composition determine renal function.
Blood: afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → renal venous drainage. Filtrate: Bowman's space → PCT → descending loop → ascending loop → DCT → collecting duct.
Quick Quiz
Quiz
What forms the renal corpuscle?
Which vessel brings blood into the glomerulus?
Which structure immediately follows the PCT?
Which nephron type typically has a longer loop of Henle?
Where do most reabsorbed solutes directly enter the blood?
What is the vasa recta?
Practice Problems
- Draw and label the major structures of a nephron in the order of tubular fluid flow.
- How does afferent differ from efferent arteriole in a renal corpuscle?
- Compare cortical and juxtamedullary nephrons and explain why they differ in concentrating capacity.
- Describe the functional significance of the peritubular capillaries.
- Explain why renal corpuscle and nephron are not synonyms.
Bowman's space → PCT → descending loop of Henle → ascending loop → DCT → collecting duct, with glomerulus and arterioles adjacent to the capsule.
Key Takeaways
• The nephron is the functional unit of the kidney and contains a filtering corpuscle and tubular segments. • The renal corpuscle is the glomerulus enclosed within Bowman's capsule. • Filtrate flows from PCT through Henle's loop to DCT and collecting ducts. • Afferent and efferent arterioles bring blood into and away from the glomerulus. • Long loops and vasa recta of juxtamedullary nephrons support urine concentration.