Histology of Kidney

The term 'histology' refers to the study of microscopic structures, such as tissues and cells of animals and plants. The histology of kidney incorporates the detailed study of various microscopic parts and tissues of the kidney. The human body comprises two bean-shaped organs that are located on either side of the body underneath the diaphragm.

The kidneys comprise renal cortex, which is the outer convex part, and the renal medulla, which is the concave-shaped inner part. Inside the medulla are conical bodies known as renal pyramids. The renal pelvis joins the concave part of the kidney with the ureter.

Each kidney contains about one million nephrons, which are tube-like structures that carry out the task of the filtration of blood.

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 the 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.

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 that form an arcade shape. These blood vessels run parallel to the surface of the cortex.

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, whereas the branches that are smaller in diameter and away from it are called minor calyx.

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.

The renal tubules are small tubes which have a diameter of 0.2 mm. 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 are the most important functional 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.

If the kidneys are unable to perform the vital task of purification of the blood, it can have an adverse effect on one's health. Kidney stone and kidney failure are some of the serious diseases related to the organ. One can live a normal life, even if one of the kidneys is functioning. However, serious problems can arise if the functioning kidney also gets affected. Thus, care must be taken to ensure that the kidney function is not affected adversely.