Nephron Function

Kidneys are the vital organs of the human body, responsible for a multitude of important functions. These bean-shaped organs are a part of the urinary system and play a key role in eliminating the harmful waste, toxins, and excess water from the body.

They also help in maintaining fluid balance within the body. Nephron function as the structural and functional units of the kidney, and are involved in almost all its activities. Each kidney contains approximately one million nephrons.

Nephrons are thin, long, tubular structures present in the kidneys. They are made of intricately-woven thin capillaries and drainage canals to filter toxic wastes and ions from the blood into the urine. Each nephron contains two main parts, the renal tubule and the renal corpuscle.

Renal corpuscle is the initial filtering component of the nephron, composed of two structures, a glomerulus and the Bowman's capsule. Glomerulus is a small intertwined group of thin blood vessels that receives blood from the renal circulation. 

The blood pressure in the glomerulus provides the driving force for solutes to be filtered into the space made by Bowman's capsule. Damage to the glomerulus can result in a condition known as glomerulonephritis. The Bowman's capsule is a cup-shaped, double membrane that surrounds the glomerulus.

Also known as the glomerular capsule, the Bowman's capsule is composed of a thin visceral layer made of specialized cells called podocytes and a parietal outer layer made of simple squamous epithelium.

They are the ducts that begin from Bowman's capsule in the cortex, loop through the renal medulla, then return to cortex and connect to collecting duct system. Each renal tubule is further divided into a proximal tubule, loop of Henle and distal convoluted tubule. Proximal tubule has microvilli, a brush border, which increases surface area for absorption.

Nephrons are classified into 2 classes - cortical and juxtamedullary, based on location of the renal corpuscles associated with them. Renal corpuscles of the former are present in the superficial renal cortex, whereas, those of latter lie near the renal medulla. Any damage to these nephrons can affect their function and result in serious kidney diseases.

The function in the kidney is mainly concerned with filtration, reabsorption, and secretion of various solutes, carbohydrates, and glutamate. The blood that enters the glomerulus is separated by the space in the Bowman's capsule by two cell layers and a basement membrane. The basement membrane is composed of glycoprotein and collagen fibers. 

Mesh-like structure of the collagen fibers filters the blood by a process known as ultrafiltration. Most of the small molecules in blood can pass through the membrane, however, it prevents large molecules such as proteins and blood cells from passing through. About 70% of water and solutes are removed from blood plasma when it passes through glomerulus. 

Many useful substances, like glucose and amino acids are also filtered by this process. Now, these molecules are absorbed back in the body by a process known as selective reabsorption to maintain the electrolyte levels of the body.

The filtered fluid enters the proximal tubule, and is reabsorbed in the peritubular capillaries. All the essential substances, including glucose, vitamins, amino acids and ions are actively transported back into the blood. The microvilli provide a large surface area, and thus facilitate effective absorption.

Now, the solute concentration of the blood in the capillaries surrounding the nephrons increases, as these substances are added back to them. To balance the electrolyte levels, a large amount of water passes back into the blood in the proximal tubule by a process known as osmosis.

The function of the loop of Henle is to concentrate the salts that will be excreted in the urine. It creates an area of high solute concentrate in the medulla. The limbs of the loop of Henle are permeable to certain ions, and solutes and water is reabsorbed from the collecting ducts that pass through this area. 

The ascending limb is more permeable to salts as compared to water, and the active absorption of salts causes more water to be pushed out through the descending limb, resulting in the formation of concentrated urine. It is drained into the distal convoluted tubule, which maintains the pH levels of urine and blood.

The fluid is then passed into the collecting duct where ultrafiltration takes place again. It is then passed to the ureters and bladder to be eliminated out of the body.

This was all about nephron function in the kidney. These tiny tubules are capable of performing complex functions of the body to keep it running smoothly. Damage to any of these structures can result in various renal diseases.

Disclaimer: This is for informative purposes only, and should not be used as a replacement for expert medical advice.