Nephrons are the functional units of the kidney and play a crucial role in filtering blood and forming urine. Each nephronA nephron is the basic structural and functional unit of the kidney. Its primary role is to filter blood, remove waste products, and regulate water and electrolyte balances in the body. Each nephron consists of a glomerulus for filtration and a tubule system for reabsorption and secretion of various substances. is a tiny, complex structure with several components, each with a specific function. Here’s a detailed look at their structure and functioning:
Structure of Nephrons
A tiny ball of capillaries where blood filtration begins. It’s enclosed in a cup-like structure called Bowman’s capsule.
Surrounds the glomerulus and collects the filtrate produced by the filtration of blood.
Proximal Convoluted Tubule (PCT):
A twisted tube that extends from Bowman’s capsule. It’s lined with microvilli to increase surface area for reabsorption.
Loop of Henle and Collecting Duct
Loop of Henle:
A hairpin-shaped loop that extends into the kidney’s medulla. It has a descending limb that carries fluid down into the medulla and an ascending limb that carries fluid back up toward the cortex.
Distal Convoluted Tubule (DCT):
Similar to the PCT but shorter and with a different cellular structure. It further processes the filtrate.
Multiple DCTs from different nephrons empty into a collecting duct. These ducts pass through the medulla and carry urine to the renal pelvis.
Functioning of Nephrons: Filtration and Reabsorption in the PCT
Blood enters the glomerulus, where high blood pressure forces water, salts, glucose, amino acids, and waste products out of the blood and into Bowman’s capsule, forming the filtrate. Large molecules like proteins and blood cells are too big to pass through and remain in the blood.
Reabsorption in the PCT:
As the filtrate moves through the PCT, most of the water, glucose, salts, and amino acids are reabsorbed back into the blood. This is done through both active and passive transport mechanisms.
Loop of Henle, Reabsorption and Secretion in the DCT
Loop of Henle:
The descending limb is permeable to water but not to salts. As the filtrate moves down, water is reabsorbed into the surrounding blood vessels.
The ascending limb is impermeable to water but allows salts to be reabsorbed. This creates a concentration gradient in the kidney’s medulla, which is important for the kidney’s ability to concentrate urine.
Reabsorption and Secretion in the DCT:
The DCT fine-tunes the composition of the filtrate. Additional ions and water are reabsorbed, and some ions and wastes are secreted into the filtrate.
Collecting Duct and Urine Excretion
The filtrate, now called urine, passes through the collecting duct. The duct’s permeability to water is regulated by the hormone antidiuretic hormone (ADH). In the presence of ADH, water is reabsorbed, concentrating the urine. In its absence, the urine remains dilute.
The concentrated urine is eventually led to the renal pelvis, from where it moves to the bladder for storage before being excreted.
Through these processes, nephrons filter the blood, remove waste products, regulate electrolyte and water balance, and maintain blood pressure. The kidneys contain millions of nephrons, each contributing to the overall function of the kidney in maintaining homeostasis in the body.