The human excretory system consists of the following parts:
- A pair of kidneys
- A pair of ureters
- A urinary bladder
- A urethra
Kidneys are bean shaped structures located on either sides of the backbone and protected by the last two ribs. Each human adult kidney has a length of 10-12 cm, a width of 5-7 cm and weighs around 120-170g. The kidneys have an inner concave structure. At the centre of which there is a notch called hilum. Through this, Human Excretory System enter the kidney. Towards the inner surface of the hilum, there is a broad funnel shaped space called renal pelvis with projections called calyces.
The outer layer is a capsule. Inside the kidney, there are two zones- the outer zone is cortex and the inner one is medulla. The cortex extends in between the medullary pyramids as renal columns called columns of Bertin.
Nephrons are the functional units of the kidney. Each kidney has millions of such structures. Now each nephron has two parts- glomerulus and renal tubule. Glomerulus consists of a bunch of capillaries formed by afferent arterioles. Blood from glomerulus is carried away by efferent arterioles. The renal tubule starts with a cup like structure called Bowman’s capsule and this encloses the glomerulus. Malpighian body consists of glomerulus and Bowman’s capsule. The highly coiled structure in the tubule next to the Bowman’s capsule is the proximal convoluted tubule.
The next part of the tubule is Henle’s loop which has an ascending and a descending limb. The ascending loop continues as distal convoluted tubule. The distal convoluted tubules of many nephrons open into the collecting duct. The cortical region of the kidney comprises of malpighian corpuscle, proximal convoluted tubule and distal convoluted tubule whereas the medullary region contains loop of Henle.
There are two types of nephrons – cortical and juxtamedullary. In case of cortical, the loop of henle is very short and extends only a little into the medulla. In juxtamedullary, the loop of henle is very long and runs deep into the medulla.
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