What is Nephron?

Nephrons are the structural and functional unit of the kidney. Nephrons are present in millions of numbers per kidney. Nephrons are responsible for the filtration of blood which helps in the removal of highly toxic nitrogenous waste. Nephrons are microscopic structures that also help in various physiological processes of the body. In this article, we will study the structure, functions, and types of nephrons.

What is Nephron?

The word ‘Nephron’ is derived from the Greek word ‘Nephros’ which means ‘Kidney’ in Greek. The nephron is the basic structural and functional unit of the kidney that carries out filtration and processing of blood to form urine. The urine that is produced by the nephrons is excreted outside of the body with the help of the excretory system.

In every kidney, there are around 1 million nephrons present. There are two kidneys in humans which means there are nearly 2 million nephrons present in the human body. The human kidney internally can be divided into two parts, cortex and medulla. The cortex is the outermost region of the kidney & the medulla is the innermost region of the kidney. Nephrons are usually embedded in between these two divisions.

Definition of Nephron

Nephron is the basic structural and functional unit of the kidney, which is responsible for the filtration of blood and the formation of urine.

Types of Nephron

Depending upon the size, location & availability, the nephrons are divided into two groups. They are;

Cortical Nephrons

This is the most common type of nephron i.e. around 80%. They are short and are located primarily in the outer region of the renal cortex. Cortical nephrons play an important role in the reabsorption of water, ions, and essential substances from the filtrate, regulate blood pressure, and maintain the body’s internal environment.

Juxtamedullary Nephrons

It consists of long loops of Henle that extend deep into the medulla. The long loops of Henle in juxtamedullary nephrons create and maintain the concentration gradient in the medulla. This concentration gradient enables the kidneys to produce concentrated urine, helping conserve water and maintain proper hydration. In the human body, 20% of Nephrons fall under this category.

Diagram of Nephron

The structure of the nephron with the diagrammatic representation is as follows;

Structure of Nephron

A nephron is around 4-5 cm long and the total length of all the nephrons is approximately around 60 km long. The structure of the Nephrons can be divided into two parts; the renal corpuscles, and the renal tubules.

Renal Corpuscles

It is also known as the Malpighian body. It consists of blood vessels surrounded by a capsular structure. It forms the part of the cortex region of the kidney, where urine formation takes place. It consists of:

• Glomerulus: The glomerulus is a tuft of capillaries surrounded by the Bowman’s capsule. The blood pressure forces water, ions, and small solutes out of the blood and into the Bowman’s capsule to form the filtrate.
• Bowman’s Capsule: The Bowman’s capsule is a cup-shaped structure that surrounds the glomerulus. It collects the filtrate formed during blood filtration and transfers it to the renal tubules. It is made up of three layers; the outer parietal layer (made of epithelial cells with pores), the middle basement layer (a selectively permeable layer), and inner visceral layer (consists of podocytes, and podocel).

Renal Tubules

The renal tubule is a long, convoluted tube connected to the Bowman’s capsule, where resorption and secretion of filtrate take place. The renal tubule is divided into several parts; the proximal convoluted tubule, the Henle’s loop, the distal convoluted tubule, and the collecting duct.

Proximal Convoluted Tubule (PCT)

The PCT forms the first part of the nephron and is located near the Bowman’s capsule. It carries out the reabsorption of essential substances such as water, glucose, amino acids, and ions into the bloodstream from the filtrate. They are lined by simple cuboidal epithelial cells having a brush border surface that helps in the secretion and reabsorption of substances.

The Henle’s Loop

It is the middle part of the nephrons and is U-shaped. It is divided into a descending limb and an ascending limb. It maintains the concentration gradient of the solute. Its primary function is to produce concentrated urine by making the interstitial fluid hypotonic. The descending limb is permeable for water whereas the ascending limb is permeable for solute.

Distal Convoluted Tubule (DCT)

This is the last part of the Nephron. After Henle’s Loop, this structure is present. It regulates the body’s acid-base balance and electrolyte levels. They are lined by cuboidal epithelium cells that help in secretion and absorption to maintain the concentration gradient of ions. This region is very much regulated by the action of the aldosterone hormone.

Collecting Duct

After passing through the DCT, the filtrate becomes urine and enters the collecting duct. It is continuous with DCT but it is not a part of the nephron. Each collecting duct is connected with multiple nephrons. They are made of simple cuboidal epithelial cells that help in the concentration of urine by absorbing excess water into the body. Several collecting tubules empty the concentrated urine into the minor calyx and then into the major calyx finally emptying the urine into the renal pelvis.

Mechanism of the Excretion

Excretion is a multistage process. Every part of the Nephrons contributes to the mechanism. The Excretion process is a combination of three sub-processes. These subprocesses are Filtration, Re-Absorption, return, and secretion. These sub-processes are performed by the different parts of the Nephrons.

• Processes performed by the Renal Corpuscles: Here, first, the blood comes to the Glomerulus by the Afferent Vessels. The walls of the Glomerular blood vessels are very thin. Due to the difference in the diameter of the Afferent and Efferent Blood Vessels, high blood pressure forms in the Glomerulus. Due to the high blood pressure, the impure blood that comes to the Nephrons is filtered by the Filtration process and the impurities go into the Bowmen’s Capsule. The impurities along with the water will remain in the Bowmen’s Capsule for a while. Then the impurities will be further transported through the walls of the Capsule and will enter the Renal Tubule. Then the pure blood will come out by the Efferent Vessels.
• Processes performed by the Proximal Convoluted Tubule (PCT): Through the Filtration process, the impurities will come inside the Nephrons. But still, there are some necessary products present and they should not get filtered along with filtrate. For this purpose, Re-Absorption takes place. As these products are very necessary for the body, they will be reabsorbed and will be returned to the blood. In the PCT, some products are being re-absorbed. These products like NaCl, Glucose, Water, Amino Acids, etc. Here, in the PCT, nearly 70% NaCl, 98% Glucose, 70% Water & 97% Amino acids are being re-absorbed.
• Processes performed by Henle’s Loop: The function of Henle’s Loop is different in its different limbs. Through the ascending limb of Henle’s Loop, water can’t be moved out and only some particular substances like 25% Sodium, 25% Calcium, 20% Potassium, and 55% Magnesium can be removed in a small percentage of Re-Absorption takes place here. Whereas in the descending limb, only water is removed. In this part of the Nephron, concentrated urine is formed.
• Processes performed by Distal Convoluted Tubule (DCT): In this part of the Nephron, the final step of excretion is performed. Some amount of Re-Absorption takes place as some amount of Sodium or calcium is being Re-Absorbed. Besides it, the Secretion also takes place. Some important impure substances are Secreted from the DCT like Hydrogen, Potassium & Ammonium ions, and some amount of urea and uric acid. These substances will mix up with the Urine.

Hence, in this way, the excretion process is completed. This urine formed will then come to the Collecting Duct. All the excreted liquid comes to the common Collecting Duct and is ready to be ejaculated outside of the body.

Types of Transporters in Nephron

The Transporter are the structures by which different elements get exchanged through the membrane. The processes of Filtration, Re-Absorption, and Secretion are also completed with the help of these transporters present in the membrane of the Renal Tubules.

1. Uniporter: In this type, an element can move in the opposite direction through the membrane. No exchange of substances takes place while transferring. Active transport mechanisms and diffusion take place to complete such purposes. The Filtration process is completed by such transporters.
2. Symporter: This type of transporter uses a secondary active transport mechanism. In such cases, two or more two elements can go through the membrane at a time. But the movement of such elements should be in the same direction. Also, in these cases, there is no need to exchange any element. The Re-Absorption process is completed by such transporters.
3. Antiporter: Here, two elements move in the opposite direction of each other. This means that transporting, two substances will take the help of an exchange mechanism. One element will move outside of the cell and will collect an element from here. The Secretion process is completed by such transporters.

Functions of the Nephron

The functions of the nephron are as follows:

1. Waste Excretion: The main function of the Nephrons is to filter and excrete the waste products outside of the body. It generally produces urine for all upper-level animals. All types of impurities in the blood are being thrown out of the body. Nephrons produce urine in the Kidney and hence it is ejaculated outside of the body.
2. The pH Maintenance: Nephrons maintain the pH of the body. It resorbs the NaCl salt to the blood. Hence, it controls the salt balance in the body. Salt is the balancer of the pH in the body. According to the condition of the body, Nephrons regulate the salt absorption in the Renal Tubules.
3. Blood Pressure Regulator: Nephrons are not complete influencers for a blood pressure regulator. But still, with the help of the ADH hormone, Nephrons can regulate blood pressure. If necessary, the Nephrons can regulate the blood pressure in the Glomerulus. Hence, it also helps to regulate the blood pressure in the body.
4. Reabsorption of Essential Substances: Water and various other essential substances like glucose, amino acids, etc. from the filtrate are also reabsorbed via the nephron.
5. Maintains the Homeostasis: By secreting and reabsorbing various wastes and essential substances the homeostatic pressure of the body is also maintained.
6. RBC Production: With the help of peritubular cells of this kind the nephrons indirectly stimulate the production of RBC in the bone marrow.

FAQs on Nephron

1. What is a Nephron?

Answer:

A nephron is the basic functional unit of the kidney that is responsible for filtering blood and producing urine. They are microscopic structures that are embedded in the kidney.

2. How many Nephrons are in Each Kidney?

Answer:

The number of nephrons in each kidney can vary among individuals, but on average, there are approximately one million nephrons in each kidney and in total around 2 million nephrons per healthy normal person.

3. Where are Nephrons Located?

Answer:

The nephrons are located in the kidneys, with some nephrons located in the outer region called the renal cortex, and others positioned closer to the border of the cortex and the inner region called the renal medulla.

4. What are the Two Main Parts of the Nephron?

Answer:

The two main parts of the nephron are; the renal corpuscle which consists of the glomerulus & Bowman’s capsule, and the renal tubule which consists of the PCT, Henle’s loop, and the DCT. Also, there is the collection duct after the DCT.

5. What are the Main Functions of the Nephron?

Answer:

The functions of the nephron include filtering waste products and excess substances from the blood to form urine, maintaining the body’s fluid and electrolyte balance, regulating blood pressure, maintaining the pH and conserving water as needed.