A nephron is the basic functional and structural unit of a kidney. Each human kidney has more than eight lakh nephrons. A nephron is made up of renal corpuscles and kidney tubules or renal tubules. Let’s understand in detail the structure and function of the nephron.
Nephron is the structure that produces urine during the excretion of waste. It is done in the process of removing waste and the excess substances present in the blood. There are around a million nephrons present in each human kidney. The primitive form of nephrons is found in the kidneys or pronephros of primitive fishes, larvae of amphibians, and also in the embryos of higher vertebrates. The nephrons found in mesonephros or the kidneys of amphibians and most fish, in late embryos of the higher vertebrates differ slightly in structure. The advanced forms of nephrons occur in the adult kidneys which are termed as the metanephros. It is present in land vertebrates such as birds, reptiles, and mammals.
Structure of Nephron
Every nephron that is found in the kidneys of mammals is a long tubule or a fine long tube measuring about 30-35 mm i.e. 1.2 to 2.2 inches long. The one end of the tube is closed and folded in a cuplike structure. This folded structure is called the Bowman’s capsule which is also called the renal corpuscle capsule. It encloses a cluster of blood vessels or capillaries which are known as the glomerulus. This capsule and the blood capillaries make the renal corpuscle. Blood flows in and out of the way from the glomerulus through tiny arteries called the arterioles. These leave the glomerulus through an opening presentation at the end of the capsule. In the renal corpuscles, the fluid is filtered out from the blood. This is done through the inner wall of the capsule into the nephron tubule. The composition of this filtrate is altered by the secretion of substances, addition of other constituents, and also due to the reabsorption of water selectively. The final product is called the urine which is transferred through the collecting tubules and into the renal pelvis.
In mammals, a nephron structure is extended into a U-shaped loop called the loop of Henle. The only difference between the nephron in mammals and that in other vertebrates is the loop.
Let’s explain the structure of the nephron in detail:
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The extension of the Bowman’s capsule forms the proximal convoluted tubule or PCT.
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The PCT is extended to form the loop of Henle which opens further into the distal convoluted tubule.
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The distal convoluted tubule opens into the collecting duct.
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From the collecting duct, everything is drained out into the urinary bladder.
Different parts of the nephron structure are made up of distinct cell types that help in water absorption and retention of water molecules in the renal tubules. The arrangement of the cells in the structure of a nephron is in a manner that cells with more concentrated substances are placed at the bottom and cells containing less concentrated substances are placed at the top. High concentration cells reabsorb the maximum amount of water as possible from the ultrafiltrate before it is drained into the urinary bladder.
Image: Structure of Nephron
Function of Nephron
The main functions of the nephron include blood filtration, reabsorption of water, and other essential smaller molecules from the ultrafiltrate. Another important function of the nephron is the secretion of glutamate. Let’s look at each function of the nephron in points:
Ultrafication:
Under this process, the working of the nephron is as follows:
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A nephron is the regulator of the entire waste removal process from the blood in the body.
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It separates the different components in the blood for its filtration.
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It removes the toxic and waste substances from the blood and adds the required molecules to the blood.
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Ultrafication occurs when the water molecules and other smaller molecules are forced out of pores in the capillary walls due to blood pressure.
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This liquid that passes out is called ultrafiltrate.
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The ultrafiltrate moves through the tubules of the nephron and collects into the collecting duct before moving onto the bladder.
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The ultrafiltrate does not have red blood cells and other essential giant molecules.
Helps in the Functioning of the Kidney
Another critical nephron function is the working of the kidney. The nephron has a special set of capillaries that help in the functioning of a kidney. Only the vertebrates have a well-developed and fully functional kidney. A single kidney in the vertebrates consists of hundreds of millions of nephrons. Each nephron helps in the process of urine formation and its collection in the urinary bladder.
Glutamate Secretion:
The nephron helps in the secretion of glutamate which is a neurotransmitter that plays an important role in sending excretory function signals.
Reabsorption and Urine Formation
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The Bowman’s capsule is lined by different layers, separating it from the glomerulus.
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One of these layers is known as the basement membrane. It is made up of collagen and fibers consisting of glycoproteins that form a net or a mesh to filter the blood through the process of ultrafiltration. The mesh acts as a filter and allows only the smaller molecules to pass through
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During the process of blood filtration, several important solutes like glucose also get filtered. They are later reabsorbed from the glomerular filtrate. Hence, the process of reabsorption is extremely important.
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The filtered liquid is contained in the proximal tubule and is reabsorbed in the peritubular capillaries.
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At this stage, the important solutes that were earlier filtered out are added to the blood.
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This increases the solute concentration in the blood and it is balanced by an equal amount of water absorption from the proximal tubule.
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The fluid now collects into the distal convoluted tubule and from there it moves into the collecting duct.
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In the collecting duct, this fluid undergoes another round of ultrafiltration and drains into the bladder through the uterus.
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From the urinary bladder, the urine passes out of the body.