A nephron is the functional unit of the kidney responsible for filtering blood and forming urine. Each kidney contains about one million nephrons. Let's understand its structure step by step.

Step 1: Main Components
A nephron consists of two main parts:

Renal Corpuscle: This is where blood filtration begins.
Renal Tubule: This is a long, coiled tube where the filtered fluid is processed to form urine.

Step 2: The Renal Corpuscle
The renal corpuscle is located in the cortex of the kidney and is made up of:

Glomerulus: A network of tiny blood capillaries (arterioles) where blood pressure forces water and small solutes out of the blood.
Bowman's Capsule: A cup-shaped structure that surrounds the glomerulus and collects the filtered fluid, now called filtrate.

Step 3: The Renal Tubule
The renal tubule is a long, winding pathway with several distinct regions, each with a specific function:

Proximal Convoluted Tubule (PCT): The first coiled section after Bowman's capsule. Here, essential nutrients, ions, and water are reabsorbed back into the blood from the filtrate.
Loop of Henle: A U-shaped loop that dips into the kidney medulla. It has a descending limb and an ascending limb. Its primary role is to create a concentration gradient in the medulla, which is crucial for water reabsorption.
- Descending Limb: Permeable to water, so water moves out of the tubule.
- Ascending Limb: Impermeable to water but actively pumps out salts (like NaCl).
Distal Convoluted Tubule (DCT): Another coiled section where fine-tuning occurs. More salts are reabsorbed and certain ions (like potassium and hydrogen) are secreted into the filtrate under hormonal control.
Collecting Duct: This is not technically part of a single nephron, as it receives filtrate from multiple nephrons. It runs through the medulla and is the final site where water reabsorption is regulated by the hormone ADH (Antidiuretic Hormone), determining the final concentration of urine.

Step 4: Associated Blood Vessels
Blood supply is crucial for the nephron's function:

Afferent Arteriole: Brings blood into the glomerulus.
Efferent Arteriole: Takes blood away from the glomerulus. It is narrower than the afferent arteriole, which helps maintain the high pressure needed for filtration in the glomerulus.
Peritubular Capillaries: A network of capillaries that surround the renal tubule (PCT and DCT). They reabsorb the substances and water that the tubule puts back into the blood.
Vasa Recta: A special set of peritubular capillaries that run alongside the Loop of Henle in the medulla. They help maintain the concentration gradient established by the loop.

Final Answer: A Labelled Diagram
While I cannot draw an image, a standard labelled diagram of a nephron would include the following key labels:

Bowman's capsule
Glomerulus
Afferent arteriole
Efferent arteriole
Proximal Convoluted Tubule (PCT)
Descending limb of Loop of Henle
Ascending limb of Loop of Henle
Distal Convoluted Tubule (DCT)
Collecting Duct
Peritubular Capillaries

The diagram would show the renal corpuscle and the highly coiled tubule in the cortex, with the Loop of Henle and Collecting Duct extending down into the medulla.

Related Topics & Formulae

Key Processes in the Nephron:

Filtration: Occurs in the glomerulus. The driving force is the pressure difference across the capillary walls. The rate at which this happens is the Glomerular Filtration Rate (GFR).
Reabsorption: The movement of substances (like water, glucose, amino acids, ions) from the filtrate in the tubule back into the blood in the peritubular capillaries. This occurs primarily in the PCT via active and passive transport.
Secretion: The active movement of substances (like $H^{+}$ ions, $K +$ ions, drugs) from the blood in the peritubular capillaries into the filtrate in the tubule. This is a key way the body eliminates waste and regulates blood pH.

Hormonal Regulation:

ADH (Vasopressin): Increases water reabsorption in the collecting duct, making urine more concentrated.
Aldosterone: Increases sodium reabsorption (and consequently water reabsorption) in the DCT and collecting duct, which also affects blood pressure.