The Structure of a Kidney Nephron
Kidney nephrons are the functional units of the kidneys.
There are normally approx. one million (0.8 - 1.5 million) kidney nephrons in each of the two kidneys in the body.
This page follows the diagram of the gross anatomy of the kidney and is related to the summary of the blood filtration processes within the kidney. It includes a simple diagram of a kidney nephron followed by short descriptions of the parts of the kidney nephron.
Simple Diagram of a Kidney Nephron:
Anatomy: Descriptions of the Parts of a Kidney Nephron:
There are two parts of a kidney nephron: the renal corpuscle, and the renal tubule.
The renal corpuscle is the part of the kidney nephron in which blood plasma is filtered.
The word "corpuscle" means "tiny" or "small" body. The renal corpuscle of each kidney nephron has two parts - they are the Glomerulus, which is a network of small blood vessels called capillaries, and the Bowman's Capsule (also known as the Glomerular Capsule), which is the double-walled epithelial cup within which the glomerulus is contained.
Within the glomerulus are glomerular capillaries that are located between the afferent arteriole bringing blood into the glomerulus and the efferent arteriole draining blood away from the glomerulus. The (outgoing) efferent arteriole has a smaller diameter than the (incoming) afferent arteriole. This difference in arteriole diameters helps to raise the blood pressure in the glomerulus.
The area between the double-walls of the Bowman's Capsule is called the capsular space. The cells that form the outer edges of the glomerulus form close attachments to the cells of the inner surface of the Bowman's Capsule. This combination of cells adhered to each other forms a filtration membrane that enables water and solutes (substances that are dissolved in the water / blood) to pass through the first wall of the Bowman's Capsule into the capsular space. This filtration process is helped by the raised blood pressure in the glomerulus - due to the difference in diameter of the afferent and efferent arterioles.
In the renal corpuscle blood is forced through the glomerular capillaries at higher pressure than the pressure at which the blood generally travels around the body (and also into the kidney itself). Helped by the increased pressure in the glomerular capillaries, a filtration process occurs in which some blood fluid is forced out of the glomerulus and into the capsular space of the Bowman's Capsule.
The fluid that is filtered into the Bowman's Capsule is called the glomerular filtrate.
The renal tubule is the part of the kidney nephron into which the glomerular filtrate passes after it has reached the Bowman's capsule. The first part of the renal tubule is called the proximal convoluted tubule (PCT), which is shown on the right-hand side of the diagram above.
The water and solutes that have passed through the proximal convoluted tubule (PCT) enter the Loop of Henle, which consists of two portions - first the descending limb of Henle, then the ascending limb of Henle. In order to pass through the Loop of Henle, the water (and substances dissolved in it) pass from the renal cortex into the renal medulla, then back to the renal cortex. When this fluid returns to the renal cortex (via the ascending limb of Henle) it passes into the distal convoluted tubule (DCT), which is shown on the left-hand side of the diagram above.
The distal convoluted tubules of many individual kidney nephrons converge onto a single collecting duct. The fluid that has passed through the distal convoluted tubules is drained into the collecting duct (far left-hand-side of the diagram above). Many collecting ducts join together to form several hundred papillary ducts. There are typically about 30 papillary ducts per renal papilla (the renal papillae being the tips of the renal pyramids - which point towards the centre of the kidney). At each renal papilla the contents of the papillary ducts drain into the minor calces - the channels through which the fluid passes, via the major calyx, into the centre of the kidney - called the renal pelvis.