A nephron is microscopic structural and functional unit of kidney. Each human kidney contains approximately 800,000 to 1.5 million nephrons. They are responsible for filtering blood, reabsorbing essential nutrients, and excreting metabolic waste products as urine.
Structure of a Nephron
A nephron is consists of two primary components: Renal Corpuscle and Renal Tubule.
1. Renal Corpuscle
This is filtering area of nephron, located in renal cortex.
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Glomerulus: A high-pressure capillary network that acts as a mesh.
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Bowman’s Capsule: A cup-shaped structure surrounding glomerulus that collects filtered fluid (filtrate).
2. Renal Tubule
A long, convoluted duct where composition of filtrate is modified.
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Proximal Convoluted Tubule (PCT): The first section where majority of reabsorption (glucose, amino acids, salts) occurs.
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Loop of Henle: A U-shaped tube that extends into renal medulla. It consists of a descending limb (permeable to water) and an ascending limb (permeable to salt), important for concentrating urine.
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Distal Convoluted Tubule (DCT): Responsible for selective secretion of ions and reabsorption of water under hormonal control.
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Collecting Duct: Receives processed filtrate from multiple nephrons and performs final water reabsorption before emptying into renal pelvis.
Functions of the Nephron
I. Glomerular Filtration
Blood enters glomerulus under high pressure. Water and small solutes (electrolytes, glucose, urea) are forced across capillary walls into Bowman’s capsule. Large molecules like proteins and blood cells remain in bloodstream.
II. Tubular Reabsorption
As filtrate moves through the tubules, body restore useful substances.
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PCT: Reabsorbs 100% of glucose and amino acids, and about 65% of water and sodium.
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Loop of Henle: Establishes an osmotic gradient to conserve water.
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DCT: Maintain balance of sodium and calcium.
III. Tubular Secretion
This is opposite of reabsorption. Tubule cells extract waste materials (such as H+ ions, K+ ions, and certain drugs) from surrounding blood and add them to filtrate to maintain blood pH and electrolyte balance.
Summary of function
| Part | Primary Function |
| Glomerulus | Filters small solutes from blood. |
| Proximal Tubule | Reabsorbs nutrients, ions, and water. |
| Loop of Henle | Reabsorbs water (descending) and salt (ascending). |
| Distal Tubule | Regulates K+, Na+, and pH. |
| Collecting Duct | Final concentration of urine via water reabsorption. |