Human Excretory System:

It consists of a pair of kidneys, a pair of ureters, single urinary bladder and a urethra.

• Kidney: bean shaped organ lies below the diaphragm. It has 3 layers. It is composed of many small tubules called nephrons. These nephrons are held together by capsule of white fibre tissues (1^st layer). This capsule is enclosed by a fatty layer called adipose capsule(2^nd layer) and this fatty layer is further enclosed by renal fascia (3^rd layer). These 3 layers form the protective covering of kidney.

1. Renal Cortex: outer region of kidney, where nephrons are more coiled and that appears dotted is called renal cortex.
2. Renal medulla: Inner region of kidney, where nephrons are less coiled and appears striated, is called renal medulla.
3. Medullary pyramids: Renal medulla is further divided into 15-16 conical masses called renal pyramids.
4. Renal minor calyces: each renal /medullary pyramid opens into a cavity called minor calyces.
5. Major calyces: All minor calyces join to form 2 or 3 major calyces in each kidney.
6. Pelvis: Major calyces open into a single tube like structure, called Pelvis.
7. Columns of Bertini: Between the medullary pyramids, there are column shaped free spaces, where cortex extends into medulla, are called columns of Bertini.
8. The renal papilla is the location where the renal pyramids in the medulla empty urine into the minor calyx in the kidney.
9. Hilum: A depression from where something arises or leave any organ.

Longitudinal section of mammalian kidney

 

• Ureters: It arises from hilum in each kidney. Each ureter runs downward and bends inwards at the end of abdomen cavity and opens into a single urinary bladder. They transfers the urine formed in kidneys to urinary bladder.
• Urinary Bladder: It is a pear shaped hollow structure, lies in the end of abdominal region. Its size changes as the amount of urine changes in it. Its (neck) lower part, leads to urethra. Its neck is regulated by 2 rings called sphincters they only relax when there is an urge for urination.
• Urethra: Starts from urinary, bladder’s lower part and leads to outside of body. It has an aperture at lower part called urinary aperture. It remains close except during urination.