What are Kidneys? Renal Cortex, Renal Medulla & Renal Sinus

What are Kidneys? Renal Cortex, Renal Medulla & Renal Sinus

What are Kidneys? Kidney is a dark-red, bean shaped compound tubular gland covered by a connective tissue capsule. A pair of kidneys is present in the human body. Each kidney is 10 cm long, 5 cm wide and 4 cm thick and weighs about 120 grams. They are placed against the back wall of abdominal cavity just below the diaphragm, one on either side of the vertebral column. Concave side of the kidney faces the vertebral column. Right kidney is slight lower in position than the left kidney. There is a depression on the medial border of kidney called hilum. This is the point through which renal arteries, renal veins, sensory nerves, lymphatic vessels and ureters enter and leaves the kidney.

Components of Kidney:

Components of kidneys are arranged in three layers. These are!

  • Renal Cortex.
  • Renal Medulla.
  • Renal sinus

1- Renal Cortex:

Renal Cortex is outer dark and granular portion of kidney. It contains renal corpuscles and convoluted tubules. Cortical tissue penetrates the renal medulla in the form of columns called renal columns or columns of Bertini.

2- Renal Medulla:

Renal Medulla is the inner, pale-red portion of kidney. It consists of:

  • Loop of Henle: It is the long U-shaped structure of the tubule. It conducts urine within each part of nephron of the kidney in reptiles, mammals and birds. The main function of the Loop of Henle is to recover the water and sodium chloride from urine.
  • Renal Pyramids: It contains 8 to 18 cone-shaped tubular and vascular structures arranged in parallel radial lines. These are also known as Malpighian Pyramids. The broad portion of renal pyramids face towards renal cortex and the apex projects in minor calyx. It conducts fluid in to the kidney.

3- Renal Sinus:

Renal Sinus is the third portion of kidney consisting of following structures.

  • Renal Pelvis: This is the upper expanded part of Ureter. It is like funnel-shaped. It works as a pathway, transport fluid to the bladder.
  • Minor & Major Calyx: These are the sub-divisions of Renal Pelvis. These are of small cup-shaped spaces that collect the fluids before it passes to the bladder. A kidney contains 2 or 3 major calyces and about 8 minor calyces.
  • Branches of Nerves
  • Blood vessels
  • Loose Connective Tissues & Fat


A small opening which is located on the inner edge of the kidney may be called as hilum. It curves towards inside to produce its unique bean-like shape. The funnel-shaped part of ureter known as renal pelvis move through the hilum, as well as the:

  • Renal Artery: The renal artery brings oxygenated blood for filtration from the heart to the kidneys.
  • Renal Vein: The renal vein takes the blood which is filtered back from the kidneys to heart.


It is a tube of muscle through which urine passes into the bladder for collection and remains in the body.

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