Kidneys

The kidneys are complex organs that have numerous biological roles. Their primary role is to maintain the homeostatic balances of bodily fluids and secreting metabolites (such as urea) and minerals from the blood and excreting them, along with water, as urine. The kidneys are important regulators of blood pressure, glucose metabolism, and erythropoeisis (the process by which red blood cells (erythrocytes) are produced). The medical field that studies the kidneys and diseases of the kidney is called nephrology. The prefix nephro- meaning kidney is from the Ancient Greek word nephros; the adjective renal meaning related to the kidney is from Latin rēnēs, meaning kidneys.

In humans, the kidneys are located in the posterior part of the abdomen. There is one on each side of the spine. The right kidney sits just below the liver, the left one is located below the diaphragm and adjacent to the spleen. Above each kidney an adrenal gland is. The asymmetry within the abdominal cavity caused by the liver results in the right kidney being slightly lower than the left one, while the left kidney is located slightly more medial.

The kidneys are approximately at the vertebral level T12 to L3. The upper parts of the kidneys are partially protected by the eleventh and twelfth ribs, and each whole kidney is surrounded by two layers of fat, which help to cushion it.

In a normal human adult, each kidney is about 10 cm long, 5.5 cm in width and about 3 cm thick, weighting 150 grams. Together, the kidneys weight about 0.5% of a person’s body weight.

The two kidneys together receive between 20% and 25% of the total cardiac output. Each kidney receives its blood supply from the renal artery, two of wich branch from the abdominal aorta. Upon entering the hilum of the kidney, the renal artery divides into smaller interlobar arteries situated between the renal papillae. At the outer medulla, the interlobar arteries branch into arcuate arteries, which course along the border between the renal medulla and cortex, giving off still smaller branches, the cortical radial arteries. Branching of these cortical arteries are the afferent arterioles supplying the glomerular capillaries, which drain into efferent arterioles. Efferent arterioles divide into peritubular cappilaries that provide an extensive blood supply to the cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the renal vein. Efferent arterioles of glomeruli closest to the medulla send branches into the medulla, forming the vasa recta (intestinal artery). Blood supply is intimately linked to blood pressure.

Ex. 25. Answer the following questions:

1. What is the major role of the kidneys? 2. Are the kidneys important regulators of blood pressure, glucose metabolism, and erythropoeisis? 3. Why is the right kidney slightly lower than the left one? 4. How do the kidneys receive blood supply?

Ex. 26. Describe the structure of kidney using the following figure:

Parts of Kidney

Parts of the kidney: 1. Renal pyramid; 2. Efferent vessel; 3. Renal artery; 4. Renal vein; 5. Renal hilum; 6. Renal pelvis; 7. Ureter; 8. Minor calyx; 9. Renal capsule; 10. Inferior renal capsule; 11. Superior renal capsule; 12. Afferent vessel; 13. Nephron; 14. Minor calyx; 15. Major calyx; 16. Renal papilla; 17. Renal column.