19. Answer in datail II

Explain the structure of kidney and the steps involved in the formation of urine.

 

a. The kidneys are reddish brown coloured -shaped organs that are found in the abdominal cavity, connected to the dorsal body wall on either side of the vertebral column.

 

b. Each kidney measures approximately  cm in length, 5 cm in width, and 3 cm in thickness. A sheet of fibrous  tissue, renal capsules, adipose capsule, and a fibrous membrane enclose the kidneys.

 

c. The internal structure of kidney consists of an outer dark area called the  and an inner lighter region called the . Both these regions consists of uriniferous tubules or nephrons that are known as the functional units of kidneys.

 

d. The medullary region of the kidneys is made up of multitubular conical masses called medullary pyramids or , which have their bases next to the cortex. A notch called the  is present on the inner concave side of each kidney. Through this notch the blood vessels and nerves enter inside the kidney and the urine leaves through the ureter.

 

e.  are thin muscular tubes that emerge from the hilum. Urine reaches the ureter from the renal pelvis and is brought along by the ureter's walls' peristaltic motions.

 

f.  is a sac-like organ found in the pelvic cavity of the abdomen. It stores urine temporarily.

 

g.  is a membranous tube that transports the urine to the outside. The urethral sphincters keep the urethra closed and only open when micturition (urination).

 

h. The first step in the production of urine is , where the filtration of blood through the epithelial walls of the glomerulus and Bowman's capsule takes place. The filtrate produced is called as  filtrate.

 

i. In , glucose, amino acids, vitamins, sodium, potassium, bicarbonates, and water found in the proximal convoluted tubule are absorbed back into the blood by a process of selective reabsorption.

 

j. In , substances such as $H^{+}\mathit{or}{K}^{+}$ ions are secreted into the tubule. This final tubular filtrate is hypertonic in man and is known as urine. Finally, urine enters the pelvic collecting ducts before passing through the ureter and into the urinary bladder. When the urinary bladder is full the urine is expelled out through the urethra. This is known as micturition.