Histology of Kidney

Histology is the study of microscopic structures, such as tissues and cells of animals and plants. The histology of the kidney incorporates the detailed study of various microscopic parts and tissues of the kidney.

The kidney is bean shaped and has two sides, the renal cortex and renal medulla. The renal cortex is the outer convex part, while the renal medulla is concave in shape. Inside the medulla are conical bodies known as renal pyramids. The renal pelvis joins the concave part of the kidney with the ureter. Around one million nephrons are present in every kidney. These tube-like structures carry out the filtration of blood.

The Medulla
The medulla of the kidney is formed of pyramidal structures known as renal pyramids. The medulla lies near the concave side of the kidney. The apex of a pyramid is known as papilla. The papilla meets the calyx, a branch of the renal pelvis. The basal portion of the pyramidal structures elongate and expand as they grow towards the cortex. The spaces between the renal pyramids are known as renal columns.

Cortex
The cortex of the kidney is composed of two different types of tissues, the medullary rays and the 'labyrinth of Ludwig' or 'cortical substance proper'. The medullary rays, also known as 'Henle' are cylindrical in shape and are aligned parallel to each other. The medullary rays are the extensions of pyramidal structures, while the cortical substance proper is interspersed between them. The labyrinth of Ludwig contains small structures known as glomeruli or Malpighian tubules.

The space between the cortex and medulla contains blood vessels which form an arcade shape. These blood vessels run parallel to the surface of the cortex.

Renal Pelvis or Artery
The renal artery enters the concave side of the kidney through the hilum. The renal pelvis branches out as it moves towards the cortical portion of the kidney. The artery branches out in right angles or in an oblique manner. The branches at the base of the renal pelvis are known as major calyx; while, those smaller in diameter and away from it, are the minor calyx.

Connective Tissues
The material present between the main parts of the kidney is formed of blood vessels, stroma and collecting tubules. These parts of the kidney appear more like a colloidal substance altogether.

Renal Tubules
The renal tubules are small tubes which have a diameter of 0.2mm. The tubes either follow a straight path or twist around themselves. Every renal tubule originates from a sac-like structure present around the glomerulus. The structure is known as the Bowman's capsule.

Nephrons
Nephrons are important units of the kidney that filter the blood to control and regulate the concentration of substances, such as water and the salts of sodium. The renal tubules in the nephrons excrete waste materials, while the renal corpuscles (in nephrons) reabsorb the necessary substances. The nephrons regulate blood pressure and blood volume. They are controlled by the endocrine system. The hormones such as aldosterone, parathyroid hormone and antidiuretic hormone help in the regulation of the functioning of nephrons. Cortical nephrons and juxtamedullary nephrons are the two types of nephrons.

The kidney is a vital organ in the functioning of the human body. It is probably, the second-most important part, after the heart. It carries out the purification of blood. Kidney stone and kidney failure are some serious diseases related to the organ.