The excretory system in humans comprises of a urinary bladder, a urethra, and a urethra. Kidneys are situated between the levels of last thoracic and third lumbar vertebra. It is close to the dorsal inner wall of the abdominal cavity.
Kidneys are bean-shaped structure and are reddish brown in color. The outer layer of a kidney is comprised of a tough capsule. A notch called helium is present at an inner concave surface of the kidney through which nerves, blood vessels, and ureter enter. The renal pelvis is broad funnel-shaped space that is present inner to the hilum. The inner medulla and the outer cortex are the two zones present inside the kidney.
Nephrons are complex tubular structures which form functional units of the kidney. Each nephron comprises of two parts. The renal tubule and the glomerulus. The renal tubule double walled cup-like structure known as Bowman’s capsule. The tubule further forms a highly coiled network. A hairpin-shaped Henle’s loop is the next part of the tubule which comprises of an ascending and descending limb. The ascending limb further forms a coiled tubular region called distal convoluted tubule – DCT. The loop of Henle in nephrons too short and extends only very little into the medulla. Such nephrons are termed as cortical nephrons. Blood from the glomerulus is carried away by an efferent arteriole. A glomerulus is a tuft of capillaries formed by the afferent arteriole.
Urinary bladder comprises of two parts.
Trigon: It is triangular in structure. The two sphinctors are present at the lower end of trigon. They include Internal and External sphincter. The internal sphincter is made up of unstriated muscles and External sphincter is made of striated muscles.
Body: It is made of involuntary muscles known as detrusor muscle.
Urinary bladder has a capacity of seven hundred to eight hundred ml. When it is filled up to three hundred to four hundred ml of urine then stretch receptors present on the wall of the urinary bladder, are stimulated and impulse is formed. the impulse that is formed is carried through a pelvic nerve. When there is a contraction of the detrusor muscle and relaxation of internal sphincter occurs, This causes urine come out. The process is called micturation because external sphincter is made of striped muscles. Diaphragm and Abdominal muscles helps in micturation.
The urinary bladder leads into the urethra. In a male urethra is much longer, about 20 cm and carries urine as well as spermatic fluid. In the female, it is quite short, only about 3 to 5 cm long, and carries only urine.