What is a Nephron?
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:
The glomerulus is a set of a net of blood capillaries contained in a capsule-shaped structure called the glomerular capsule or the Bowman’s capsule.
The extension of the Bowman’s capsule forms the proximal convoluted tubule or PCT.
The PCT is extended to form the loop of Henle which opens further into the distal convoluted tubule.
The distal convoluted tubule opens into the collecting duct.
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:
A nephron is the regulator of the entire waste removal process from the blood in the body.
It separates the different components in the blood for its filtration.
It removes the toxic and waste substances from the blood and adds the required molecules to the blood.
Ultrafication occurs when the water molecules and other smaller molecules are forced out of pores in the capillary walls due to blood pressure.
This liquid that passes out is called ultrafiltrate.
The ultrafiltrate moves through the tubules of the nephron and collects into the collecting duct before moving onto the bladder.
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
The Bowman’s capsule is lined by different layers, separating it from the glomerulus.
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
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.
The filtered liquid is contained in the proximal tubule and is reabsorbed in the peritubular capillaries.
At this stage, the important solutes that were earlier filtered out are added to the blood.
This increases the solute concentration in the blood and it is balanced by an equal amount of water absorption from the proximal tubule.
The fluid now collects into the distal convoluted tubule and from there it moves into the collecting duct.
In the collecting duct, this fluid undergoes another round of ultrafiltration and drains into the bladder through the uterus.
From the urinary bladder, the urine passes out of the body.
FAQs on Nephron - Renal Tubules and Function of Nephron
1. What are the functions of nephrons?
The nephron is the main and basic structural and functional unit of kidneys. They regulate the water present in our body and also the soluble substances that are present in the blood. This is done by filtering the blood and reabsorbing all the necessary substances required by the body again, excreting out the waste. The waste is called urine. The nephrons also have their functions in the homeostasis of blood volume and pressure, the osmolarity of the plasma. This is regulated by the neuroendocrine systems present in the body. The hormones are antidiuretic hormone or vasopressin, parathyroid hormones, and aldosterone.
2. What is glomerulus?
Glomerulus can be defined as the tuft of capillaries that is required to receive blood from the afferent arteriole in the renal circulation. In this, the solutes and fluids are filtered out from the blood and are transferred into the Bowman’s capsule. Juxtaglomerular apparatus or JGA is a group of specialized cells that are located in the afferent arteriole that then enters the renal corpuscle. JGA secretes the enzyme renin which is mainly involved in the homeostasis of blood volume. The Bowman’s capsule is present around the glomerulus which is composed of visceral or inner and parietal or outer layers. These are made of simple squamous cells of the epithelium.
3. What is the loop of Henle and what is its function?
This is a loop that is shaped as U and consists of a descending loop as well as an ascending one. It helps in the transportation of fluids from the proximal tube to the distal tube. The descending limb has a high permeability to water but is not permeable or impermeable to ions. This causes a large amount of water to be reabsorbed and increases the osmolarity of fluid. The ascending loop, on the other hand, is impermeable to water but has a high permeability to ions. This causes a decrease in the osmolarity of fluid in the loop.
4. What is the distal convoluted tube?
The distal convoluted tube along with the collecting duct can be defined as the site or place where the reabsorption process occurs in the nephron. Here, the permeability of the tube to water is variable and depends on various factors. It depends on the stimulus given by various hormones which in turn, leads to the regulation of blood osmolarity, pressure, and pH. Vasopressin or antidiuretic hormones act on the tubule to increase the permeability of the distal convoluted tubule to water leading to an increase in water reabsorption. This in turn, results in an increase in blood pressure and volume. Other hormones also act on the tubule which causes its homeostasis.
5. What is the collecting duct and what is its function?
The function of the collecting duct is similar to the distal convoluted tube i.e. it functions in the regulation of homeostasis which is in response to the stimuli provided by the hormones. However, it must be noted that they differ in histology. The osmolarity of these two ducts is variable and highly depends on the stimulus provided by the hormones. After the fluid passes through the collecting duct, it is brought back to the ureter which moves out from the kidney as urine.
6. What are the excretory materials in different animals?
The excretory materials in different animals are:
Ammonia- Amphibians and early forms of vertebrates
Aves and Reptiles- Uric acid which has a high concentration of ammonia
Mammals- Urea
7. How does the camel survive in the desert with the help of the Ultrafiltrate?
In mammals, the excretory material is urea. To prevent water loss from the body and to retain as much of it as possible in the body, the water molecules in the urea are absorbed to create concentrated urea in the urine. This helps in the water reabsorption process from the ultrafiltrate. It enables water retention in the body and helps animals like camels who live in dry and arid regions. They can survive for long without water as they can store water in their bodies. Camels can filter out most of the water present in the blood and can use it multiple times.
8. Why are nephrons the most important unit in waste removal from the body?
Although the body performs many functions and uses several mechanisms to remove the waste from the body, an important role is played by nephrons. They help in waste removal from the body and in the filtration of blood. The kidneys are the main organs that are involved in this process and their failure to perform these functions can prove fatal. They perform critical functions for the body and the nephrons help in the smooth functioning of the kidney. It is why the nephrons are the most important unit in waste removal from the body.
