7.11 - Kidneys - The Nephron

Gross structure of the kidney and the nephron

• Each kidney is part of the urinary system.
• Blood is brought to the kidney by the renal artery and filtered blood leaves by the renal vein.
• Urine produced by the kidney drains out through the ureter, which carries it to the bladder, where it's stored before being released through the urethra.

Connection to the central blood vessels

• The renal artery branches from the aorta - the body's main artery, carrying blood away from the heart.
• The renal vein empties into the vena cava - the body's main vein, returning blood to the heart.
• So both kidneys connect to these large central vessels via their renal arteries and renal veins.

Regions inside the kidney

• Cortex - The outer part of the kidney.
• Medulla - The inner part of the kidney.
• Pelvis - A wide, funnel-shaped region at the top of the ureter (where it meets the kidney) that collects the urine and channels it into the ureter.

The nephron

• Filtering happens in tiny tube-like structures called nephrons (also called kidney tubules). A single kidney contains around a million of them.
• The nephrons run across both the cortex and the medulla.
• A network of capillaries wraps around the tubule alongside the nephron.

Each nephron is made up of the following, in order:

1. Glomerulus (also called the capillary knot) - A ball of capillaries where the nephron begins.
2. Bowman's capsule - A cup-shaped structure that the glomerulus sits inside.
3. Proximal convoluted tubule - The first section of the long, looping tubule leading from the Bowman's capsule.
4. Loop of Henle - The middle looping section of the tubule.
5. Distal convoluted tubule - The final section of the tubule.
6. Collecting duct - Carries the finished urine away towards the ureter.

High pressure in the glomerulus

• The arteriole carrying blood into the glomerulus is wider than the one carrying blood away from it.
• This difference builds up a high pressure inside the glomerulus.