4.3 Nephron

Introduction

The nephron is the structural and functional unit of the kidney. Each kidney contains about one million nephrons. The nephron is responsible for filtering blood and producing urine. This topic explains the structure of the nephron and its parts.

Definition

The nephron is the structural and functional unit of the kidney. Each kidney, in a human, contains about one million nephrons.

Main Idea

The nephron consists of a long tubule. Each nephron is composed of:

• Renal corpuscle — consists of glomerulus and Bowman's capsule
• Renal tubule — consists of proximal convoluted tubule, loop of Henle, and distal convoluted tubule

Core Concept

Parts of a Nephron

Detailed Explanation

1. Renal Corpuscle

The renal corpuscle consists of:

(a) Glomerulus:

• A network of capillaries.
• Located in the Bowman's capsule.
• Receives blood from the afferent arteriole.
• Blood leaves through the efferent arteriole.

(b) Bowman's capsule:

• A cup-shaped structure that surrounds the glomerulus.
• Collects the filtrate (fluid that leaves the blood).
• The filtrate is called glomerular filtrate.

Simple explanation: The renal corpuscle is like a filter. The glomerulus is a ball of capillaries, and Bowman's capsule is a cup that collects the filtered fluid.

Function:

• Filtration of blood.
• Small molecules (water, nutrients, salts, wastes) move from the glomerulus to the Bowman's capsule.
• Blood proteins and blood cells are too large to be filtered, so they remain in the blood.

2. Renal Tubule

The renal tubule consists of:

(a) Proximal Convoluted Tubule (PCT):

• Coiled tubule in the renal cortex.
• Connected to Bowman's capsule.
• Site of most reabsorption.

Function:

• Reabsorption of water, glucose, amino acids, and salts.
• About 99% of water and most solutes are reabsorbed.

Simple explanation: The PCT is the first part of the tubule. It reabsorbs useful substances back into the blood.

(b) Loop of Henle:

• U-shaped loop that extends into the renal medulla.
• Has a descending limb and an ascending limb.

Function:

• Descending limb: Reabsorption of water.
• Ascending limb: Reabsorption of salts.

Simple explanation: The loop of Henle helps concentrate urine by reabsorbing water and salts.

(c) Distal Convoluted Tubule (DCT):

• Coiled tubule in the renal cortex.
• Connected to the loop of Henle.

Function:

• Reabsorption of water.
• Secretion of ions (K⁺, H⁺), drugs, and waste products.

Simple explanation: The DCT fine-tunes the composition of urine by reabsorbing water and secreting waste.

(d) Collecting Duct:

• Straight tube in the renal medulla.
• Collects urine from several nephrons.
• Passes urine to the renal pelvis.

Function:

• Collects urine.
• Final concentration of urine.

Simple explanation: The collecting duct is like a drain that carries urine to the renal pelvis.

Summary of Nephron Structure

Intermediate Level

The nephron is the structural and functional unit of the kidney.

Parts:

Key points:

• Each kidney has about one million nephrons.
• The renal corpuscle filters blood.
• The renal tubule reabsorbs useful substances and secretes waste.
• Urine is formed in the nephron.

Important Points

• - The nephron is the structural and functional unit of the kidney.
• - Each kidney, in a human, contains about one million nephrons.
• - The nephron consists of a long tubule.
• - Each nephron is composed of renal corpuscle and renal tubule.
• - The renal corpuscle consists of glomerulus and Bowman's capsule.
• - The glomerulus is a network of capillaries.
• - Bowman's capsule is a cup-shaped structure that surrounds the glomerulus.
• - The renal tubule includes proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.
• - The proximal convoluted tubule is in the cortex.
• - The loop of Henle extends into the medulla.
• - The distal convoluted tubule is in the cortex.
• - The collecting duct is in the medulla.

Remember

• - Nephron = structural and functional unit of kidney
• - Each kidney = about 1 million nephrons
• - Renal corpuscle = glomerulus + Bowman's capsule
• - Renal tubule = PCT + loop of Henle + DCT + collecting duct
• - Glomerulus = filtration
• - Bowman's capsule = collects filtrate
• - PCT = reabsorption
• - Loop of Henle = water and salt reabsorption
• - DCT = reabsorption and secretion
• - Collecting duct = collects urine

Common Mistakes

• 1. Confusing the glomerulus and Bowman's capsule.
• - Glomerulus = capillary network.
• - Bowman's capsule = cup-shaped structure surrounding the glomerulus.
• 2. Thinking the nephron is the same as the kidney.
• - The nephron is the functional unit of the kidney. Each kidney has about one million nephrons.
• 3. Mixing up the PCT and DCT.
• - PCT = proximal convoluted tubule (first part).
• - DCT = distal convoluted tubule (last part).
• 4. Forgetting the role of the loop of Henle.
• - The loop of Henle reabsorbs water (descending limb) and salts (ascending limb).
• 5. Thinking the collecting duct is part of the renal corpuscle.
• - The collecting duct is part of the renal tubule.
• 6. Believing the nephron only filters blood.
• - The nephron also reabsorbs useful substances and secretes waste.
• 7. Confusing the afferent and efferent arterioles.
• - Afferent arteriole = brings blood to the glomerulus.
• - Efferent arteriole = takes blood away from the glomerulus.

Quick Revision

60-Second Revision

• Nephron = structural and functional unit of kidney
• Each kidney = about 1 million nephrons
• Renal corpuscle = glomerulus + Bowman's capsule
• Renal tubule = PCT + loop of Henle + DCT + collecting duct
• **Glomerulus** = filtration
• Bowman's capsule = collects filtrate
• **PCT** = reabsorption
• Loop of Henle = water and salt reabsorption
• **DCT** = reabsorption and secretion
• Collecting duct = collects urine
• Warning: Do not confuse the glomerulus (capillary network) with Bowman's capsule (cup-shaped structure).