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Unlock This CourseThe kidneys are amazing organs that filter your blood to remove waste products and excess substances. Each kidney contains about a million tiny filtering units called nephrons. These microscopic structures are where the real work of excretion happens!
Key Definitions:
Before diving into nephrons, let's understand where they fit. Each kidney is bean-shaped and about the size of your fist. The kidneys are located at the back of your abdomen, one on each side of your spine. Blood enters the kidney through the renal artery and leaves via the renal vein. Urine exits through the ureter to the bladder.
The kidney has three main regions:
Nephrons are vital because they:
Without properly functioning nephrons, waste products would build up in your blood, leading to serious health problems.
Each nephron is a tiny tube about 3cm long but only visible under a microscope. The structure of a nephron is perfectly designed for its filtering function. Let's explore the different parts:
The nephron begins with a cup-shaped structure called the Bowman's capsule. Inside this capsule sits a ball of tiny blood vessels called the glomerulus. Together, they form the renal corpuscle.
The glomerulus is a special network of capillaries with:
The Bowman's capsule has:
After the Bowman's capsule, the nephron continues as a long, winding tube with different regions. Each region has a specific structure and function:
Structure:
Structure:
Structure:
The final part of the nephron is the collecting duct. Multiple nephrons connect to a single collecting duct, which then joins with other ducts to form larger ducts that eventually empty into the renal pelvis.
One of the most important features of the nephron is the filtration barrier in the renal corpuscle. This barrier determines what gets filtered from the blood into the nephron.
The filtration barrier consists of three layers:
This three-layer system allows water, ions, glucose, amino acids and waste products like urea to pass through, but prevents proteins and blood cells from entering the nephron.
The filtration barrier is selective based on:
This means:
When nephrons are damaged by disease, the kidneys can't filter blood properly. Dialysis machines act as artificial nephrons. In haemodialysis, blood passes through tubes made of partially permeable membranes surrounded by dialysis fluid. This fluid has the same concentration of substances as normal blood except for waste products. By diffusion, waste products move from the blood into the dialysis fluid, cleaning the blood much like nephrons would.
Modern dialysis machines can filter about 120-150ml of blood per minute, compared to healthy kidneys which filter about 125ml per minute. However, while dialysis can keep people alive, it requires regular treatments (typically 3-4 hours, three times a week) and can't perform all the complex functions of real nephrons, such as producing hormones that regulate blood pressure and red blood cell production.
The nephron has a unique blood supply system that supports its filtering function:
Unlike most organs, the kidney has two capillary networks in series:
Blood flow follows this path:
Renal artery → Afferent arteriole → Glomerular capillaries → Efferent arteriole → Peritubular capillaries → Venules → Renal vein
This arrangement is crucial for the nephron's function, allowing for both filtration and reabsorption processes.
The nephron's structure is perfectly adapted for its role in excretion:
Understanding the structure of nephrons helps us appreciate how our bodies efficiently remove waste while conserving valuable resources. In the next lesson, we'll explore in more detail how these structures work together in the processes of filtration, reabsorption and secretion.