4.2.3 Structure of A Nephron

The nephron is the functional unit of the kidney. Each kidney contains about one million nephrons. A nephron consists of a renal corpuscle and a renal tubule. The nephron is responsible for filtering blood, reabsorbing useful substances, and secreting waste products to form urine.

Definition

Nephron: The nephron is the functional unit of the kidney. It consists of a renal corpuscle and a renal tubule. Each kidney contains about one million nephrons.

Renal Corpuscle: A renal corpuscle is composed of a network of capillaries called the glomerulus, which is surrounded by a thin double-walled structure called Bowman's capsule.

Renal Tubule: The renal tubule leads away from the Bowman's capsule and becomes highly coiled. It consists of the proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Main Idea

• Filters blood in the renal corpuscle
• Reabsorbs useful substances in the renal tubule
• Secretes waste products into the tubule
• Concentrates urine in the loop of Henle
• Collects urine in the collecting duct

Core Concept

• Nephron = functional unit of kidney
• Renal corpuscle = glomerulus + Bowman's capsule
• Glomerulus = network of capillaries
• Bowman's capsule = thin double-walled structure
• Proximal convoluted tubule = highly coiled
• Loop of Henle = descending limb + ascending limb
• Distal convoluted tubule = highly coiled
• Collecting duct = receives many nephrons
• Blood circulation = afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → vasa recta → renal vein

Detailed Explanation

Structure of a Nephron

The nephron is the functional unit of the kidney. A nephron consists of a renal corpuscle and a renal tubule.

Renal Corpuscle

• A renal corpuscle is composed of a network of capillaries called the glomerulus.
• The glomerulus is surrounded by a thin double-walled structure called Bowman's capsule.
• The Bowman's capsule is an expansion at the closed end of a renal tubule.

Renal Tubule

The renal tubule leads away from the Bowman's capsule and becomes highly coiled.

Detailed Description of Each Part

• The renal tubule leads away from the Bowman's capsule and becomes highly coiled.
• This coiled portion of the tubule is called the proximal convoluted tubule.

• The proximal convoluted tubule dips toward the renal pelvis into the medulla.
• It forms a sharp loop called the loop of Henle.
• The loop of Henle consists of a descending limb and an ascending limb.

• The ascending limb returns to the region of the renal corpuscle.
• It becomes highly coiled again.
• This is called the distal convoluted tubule.

• The distal convoluted tubule is connected to the collecting duct.
• The collecting duct receives many nephrons.
• Many collecting ducts combine together to form larger collecting ducts.
• These empty into the renal pelvis.

Blood Circulation to Nephron

The renal artery within the kidney gives rise to branches that project into the cortex and give rise to afferent arterioles.

• Afferent arterioles supply blood to the glomerular capillaries of the renal capsule.
• Efferent arterioles arising from the glomeruli give rise to a plexus of capillaries called the peritubular capillaries around the proximal and distal tubules.
• Specialized part of the peritubular capillaries called vasa recta course into the medulla along with the loops of Henle and then back toward the cortex.
• The peritubular capillaries drain into the renal vein.
• The renal vein exits the kidney and connects to the inferior vena cava.

Summary Table of Nephron Structure

Intermediate Level

Structure of Nephron

Blood Circulation to Nephron

Comparison of Cortical and Juxtamedullary Nephrons

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Nephron is the functional unit of the kidney.
• 2. Each kidney contains about one million nephrons.
• 3. Nephron consists of renal corpuscle and renal tubule.
• 4. Renal corpuscle = glomerulus + Bowman's capsule.
• 5. Glomerulus is a network of capillaries.
• 6. Bowman's capsule is a thin double-walled structure.
• 7. Proximal convoluted tubule is highly coiled.
• 8. Loop of Henle has descending and ascending limbs.
• 9. Distal convoluted tubule is highly coiled.
• 10. Collecting duct receives many nephrons.
• 11. Collecting ducts combine to form larger ducts.
• 12. Larger ducts empty into renal pelvis.
• 13. Afferent arteriole brings blood to glomerulus.
• 14. Efferent arteriole takes blood from glomerulus.
• 15. Peritubular capillaries surround tubules.
• 16. Vasa recta course into medulla.
• 17. Peritubular capillaries drain into renal vein.
• 18. Renal vein connects to inferior vena cava.
• 19. Cortical nephrons are 70–80%.
• 20. Juxtamedullary nephrons are 20–30%.

Remember

• - Nephron = functional unit of kidney
• - One million = nephrons per kidney
• - Renal corpuscle = glomerulus + Bowman's capsule
• - Glomerulus = network of capillaries
• - Bowman's capsule = thin double-walled structure
• - Proximal convoluted tubule = highly coiled
• - Loop of Henle = descending limb + ascending limb
• - Distal convoluted tubule = highly coiled
• - Collecting duct = receives many nephrons
• - Afferent arteriole = brings blood to glomerulus
• - Efferent arteriole = takes blood from glomerulus
• - Peritubular capillaries = around tubules
• - Vasa recta = course into medulla
• - Renal vein = exits kidney

Common Mistakes

• 1. Confusing afferent and efferent arterioles — Afferent brings blood to glomerulus; efferent takes blood away.
• 2. Thinking the glomerulus is in the medulla — The glomerulus is in the cortex.
• 3. Confusing Bowman's capsule and glomerulus — Bowman's capsule surrounds the glomerulus.
• 4. Mixing up the parts of the loop of Henle — Descending limb and ascending limb.
• 5. Thinking the collecting duct is part of the nephron — The collecting duct receives many nephrons.
• 6. Confusing peritubular capillaries and vasa recta — Peritubular capillaries surround tubules; vasa recta course into medulla.
• 7. Forgetting the number of nephrons — About one million per kidney.
• 8. Mixing up the types of nephrons — Cortical (70–80%) and juxtamedullary (20–30%).
• 9. Thinking the renal vein brings blood to the kidney — The renal vein carries blood away.
• 10. Believing the nephron only filters blood — It also reabsorbs and secretes.

Quick Revision

The nephron is the functional unit of the kidney. Each kidney contains about one million nephrons. A nephron consists of a renal corpuscle and a renal tubule. A renal corpuscle is composed of a network of capillaries called the glomerulus, which is surrounded by a thin double-walled structure called Bowman's capsule. The Bowman's capsule is an expansion at the closed end of a renal tubule. The renal tubule leads away from the Bowman's capsule and becomes highly coiled. This coiled portion is called the proximal convoluted tubule. The proximal convoluted tubule dips toward the renal pelvis into the medulla forming a sharp loop called the loop of Henle. The loop of Henle consists of a descending limb and an ascending limb. The ascending limb returns to the region of the renal corpuscle, where it becomes highly coiled again, and is called the distal convoluted tubule, which is connected to the collecting duct. The collecting duct receives many nephrons. Many collecting ducts combine together to form larger collecting ducts which empty into the renal pelvis. The renal artery within the kidney gives rise to branches that project into the cortex and give rise to afferent arterioles. The afferent arterioles supply blood to the glomerular capillaries. Efferent arterioles arising from the glomeruli give rise to a plexus of capillaries called the peritubular capillaries around the proximal and distal tubules. Specialized part of the peritubular capillaries called vasa recta course into the medulla along with the loops of Henle and then back toward the cortex. The peritubular capillaries drain into the renal vein. The renal vein exits the kidney and connects to the inferior vena cava.

60-Second Revision

• Nephron = functional unit of kidney
• One million = nephrons per kidney
• Renal corpuscle = glomerulus + Bowman's capsule
• Glomerulus = network of capillaries
• Bowman's capsule = thin double-walled structure
• Proximal convoluted tubule = highly coiled
• Loop of Henle = descending limb + ascending limb
• Distal convoluted tubule = highly coiled
• Collecting duct = receives many nephrons
• Afferent arteriole = brings blood to glomerulus
• Efferent arteriole = takes blood from glomerulus
• Peritubular capillaries = around tubules
• Vasa recta = course into medulla
• Warning: Afferent brings blood to glomerulus; efferent takes it away

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