HSEB Notes on Structure of Kidney and Nephron
Lesson : Excretion and Osmoregulation
Class : 12
A pair of kidneys located on either side of back bone in the abdominal cavity. The left kidney is positioned higher than the right one. At anterior end of kidney adrenal gland is present. Each kidney is bean shaped, about 10 cm long and 6 cm wide and weighs about 150 gm. At the concave side, there is a depression called hilum from where renal artery enters and renal vein and ureters pass out.
Internal structure
Renal cortex outer region is towards convex surface. It contains Bowman’s capsule, glomerulus, proximal convoluted tubule, distal convoluted tubule and collecting tubules of nephron. Renal medulla It is region just inner to renal cortex. It contains loop of Henle and Collecting ducts inside the renal pyramid. The conical pyramid mass projects into renal pelvis. Urine is drained into renal pelvis through minute openings at the apices or papillae of pyramids. Renal pelvis large funnel shaped space behind medulla. Urine is collected and is passed down to the ureters.
Each kidney consists of large number of filtering units called nephrons. A kidney has about 1.2 million nephrons. Each nephron is about 3 cm long, tiny, delicate and coiled tubule which originates in the cortex region and extends into medulla region.
Structure of nephron
Nephron or uriniferous tubule is the functional unit of kidney. Each works as as independent unit and produce miniscule amount of urine. The urine collected by various ducts from all nephrons is finally poured into renal pelvis.
Nephron consists of
1. Renal corpuscle or malpighian body
- Bowman’s capsule
- Glomerulus
3. Loop of Henle
- Descending limb of loop of Henle
- U shaped part
- Ascending limb of loop of Henle
4. Distal convoluted tubule or DCT
5. Collecting tubule
Renal corpuscle or malpighian body is formed by Bowman’s capsule and Glomerulus together. Bowman’s capsule it is cup shaped hollow structure. In the hollow cup there is a network of capillaries called Glomerulus. Bowman’s capsule has inner and outer epithelial layers. Between these layers there is a cavity of Bowman’s capsule. The inner layer is closely applied to walls of Glomerulur capillaries.
Glomerulus It is network of capillaries in the hollow of Bowman’s capsule. It receives the blood through afferent arteriole which breaks up into capillary network. The blood leaves the glomerulus through efferent arteriole. The efferent arteriole is narrower and longer vessel than the afferent. The efferent arteriole breaks up into network of capillaries surrounding whole of PCT, loop of Henle and DCT. At loop of Henle, there is parallel arrangement of capillaries called vasa recta. These capillaries join and return blood to renal vein.
PCT First coiled tubule just behind renal corpuscle. It is lined by cuboidal ciliated epithelium. It transports glomerular filtrate (GF) from Bowman’s capsule into loop of Henle. Loop of Henle form U shaped loop. Descends down into medulla and again returns back. Descending limb is thin and long freely permeable to water. It is lined by flat epithelial Cells. Ascending limb is thicker and impermeable to water. It is lined by cuboidal epithelial cells.
DCT second coiled tubule is relatively shorter. It is permeable to water and under the control of Anti diuretic hormone (ADH) Collecting tubule short and straight opens into collecting duct. It passes down to medulla from cortex. Duct of Bellini many collecting ducts join to form larger duct of Bellini . it ultimately opens into renal pelvis draining all urine collected from various nephrons.
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