The anatomy of the kidney

The kidneys receive oxygenated blood through the renal arteries.

This blood is filtered in the kidneys, and the resulting urine passes into the ureters, which transport it to the bladder. Urine is stored in the bladder and eventually removed from the body via the urethra.

The renal vein returns the filtered blood to the heart via the vena cava.

The internal structure of the kidney includes:

• Fibrous capsule - An outer membrane that surrounds and protects the kidney.
• The renal cortex - The outer region that contains Bowman's capsules, convoluted tubules, and blood vessels.
• The renal medulla - The inner region with structures called pyramids that contain loops of Henle, collecting ducts, and blood vessels.
• The renal pelvis - The funnel-shaped cavity that collects urine into the ureters.

The structure and function of nephrons

Each kidney contains approximately one million nephrons, which are responsible for filtering blood, reabsorbing useful substances back into the blood, and removing wastes from the blood. A nephron is the basic structural and functional unit of the kidney.

The material that is initially filtered from blood that moves through the nephron is called filtrate.

Filtrate moves through the structures in a nephron in the following order:

1. Bowman's capsule (renal capsule) - This surrounds a capillary ball known as the glomerulus, from which filtrate is formed, and contains cells called podocytes in its inner layer.
2. Proximal convoluted tubule (PCT) - This section reabsorbs useful substances, including water, glucose, and salts, into surrounding capillaries and the epithelial cells in its wall have microvilli to increase their surface area.
3. Loop of Henle - This long, hairpin loop extends from the cortex into the medulla and then back into the cortex, and creates a high solute gradient in the medulla, helping with the reabsorption process.
4. Distal convoluted tubule (DCT) - This part fine-tunes the water balance by reabsorbing water into surrounding capillaries, influenced by antidiuretic hormone. It is surrounded by fewer capillaries than the PCT.
5. Collecting duct - This tube collects filtrate from multiple nephrons and further fine-tunes the water balance, before the urine formed is passed to the bladder.

The blood vessels associated with the nephron

There are several different blood vessels that are associated with each nephron.

These blood vessels include:

• The afferent arteriole - This supplies the glomerulus with blood.
• The glomerulus - Fluid is forced out of the blood within this mass of capillaries into the Bowman’s capsule through ultrafiltration.
• The efferent arteriole - This carries blood away from the glomerulus.
• The capillaries around the proximal and distal convoluted tubules and the loop of Henle - These absorb salts, glucose, and water.