Anatomy of the renal system

 

The urinary system consists of

-        Two kidneys

-        Two ureters

-        Urinary bladder

-        Urethra

 

Kidneys

Kidneys are bean shaped paired organs. The weight of each kidney is approximately 150 grams. The right kidney is lower than the left, because it is crowded by the liver. Kidney lies on posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum and below the diaphragm. Kidneys are extended from 12^th thoracic vertebra to 3^rd lumber vertebra.

There are three areas can be distinguished in a longitudinal section of the kidney.

-        Fibrous capsule, which is surrounding the kidney

-        The cortex, outer reddish-brown layer of tissue

-        The medulla, pale innermost layer

 

Hilum is the concave medial border of the kidney. Renal blood vessels, lymph vessels, ureter and nervous enter to the kidney at the hilum. Renal pelvis is a funnel shaped structure, it continuous inferiorly with ureter.it has a number of distal branches, called as calyces, surrounds the apex of a renal pyramid.

 

The nephron is the functional unit of the kidney. There are around one million nephrons per one kidney. The nephron consists of ,glomerular capsule ( Bowman’s capsule), which almost completely encloses the glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, which are leading to a collecting duct.

The collecting ducts combine to develop larger ducts that empty into the minor calyces. The cortex consists of most of the glomeruli, proximal tubules and distal tubules. The medulla, divides into renal pyramids, the apex extends towards the renal pelvis forming papillae. Medullary rays connect the kidney cortex with the medulla, they are composed of descending (strait proximal) and ascending (straight distal) thick limbs of Henle and collecting ducts.

Glomerulus are projects into Bowman’s capsule. Glomerular capillaries are supplied by an afferent arteriole and drained by slightly smaller efferent arteriole. There are two cellular layers separating the blood from the glomerular filtrate in Bowman’s capsule. The capillary endothelium and the specialized epithelium of the capsule made up of podocytes overlying the glomerular capillaries. These layers are separated by basal lamina. Mesangial cells are located between the basal lamina and the endothelium. Bowman’s capsule forms the beginning of the tightly coiled, proximal convoluted tubule which on its progress toward the renal medulla becomes strained and is then called pars recta. The glomerulus and its Bowman’s capsule called as renal corpuscle.

Juxtaglomerular apparatus is where the ascending loop of Henle passes very close to the Bowman’s capsule of its own nephron, the cells of the tubule and the afferent arteriole show regional specialization. The tubules form macula densa and the arteriolar cells are filled with granules. This area is called the juxtaglomerular apparatus.

Proximal convoluted tubule composed of simple cuboidal epithelium with numerous microvilli and mitochondria. The proximal part of the loop of Henle similar to the proximal convoluted tubule. Proximal part is followed by the thin segment (squamous cells), and the thick segment (cuboidal cells). Distal convoluted tubule composed of cuboidal cells without microvilli. Collecting duct composed of columnar epithelium cells.