Introduction to renal structure

The kidneys are primarily responsible for the maintenance of the internal environment of the human body. They share the following structural features:

1. • They are paired retroperitoneal organs.

2. • They weigh 110–170g each in the adult male, are 10–12cm long, 5–7.5cm wide and 2.5–3cm thick.

3. • They receive 20%–25% of the cardiac output, which corresponds to 1000–1200 ml/minute, but only account for about 10% of the oxygen consumption of the body.

4. • The kidneys thereby receive the highest blood flow per gram of organ weight in the human body, while accounting for only 0.4% of the body weight. The entire plasma volume is cycled through the glomerular system 20 times per hour.

5. • Their internal structure consists of an outer cortex and an inner medulla. The medulla consists of ten pyramids, with their bases near the cortex and apices (papillae) which project into the calyceal sinuses. The pyramids are separated by columnar extensions of the cortex. Ninety per cent of the renal blood supply goes to the cortex.

6. • The cortex comprises glomeruli and proximal convoluted tubules, while the medulla comprises the loops of Henle, the distal convoluted tubules and the collecting ducts.

Functional components of the kidneys

The functional components of the kidney are the nephrons (each kidney contains one million nephrons), collecting ducts and the microvasculature.

A nephron, the structural and functional unit of the kidneys, demonstrates functional segmentation and consists of:

Renal corpuscle, which comprises Bowman's capsule and the glomerular capillary tuft. The glomerular tuft has three cell types: mesangial cells, capillary endothelial cells and podocytes (visceral epithelium of Bowman's capsule).

Renal tubule, which comprises:

Proximal convoluted tubule;

Proximal straight tubule (pars recta);

Descending thin limb of loop of Henle (in long-loop nephrons only);

Medullary thick ascending limb of loop of Henle;

Cortical thick ascending limb of loop of Henle;

Distal convoluted tubule.

The collecting duct system comprises the connecting tubule, cortical collecting duct, outer and inner medullary collecting ducts.