Question

3) Describe the location, structure, and functions of the components of the urinary system, beginning at the kidney and ending at the urethra.

Answer 1

Ans- The urinary system also known as renal system or urinary tract consists of the kidneys, ureters, bladder and urethra. The purpose of urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites and regulate blood pH.

Kidneys- The kidneys are bean shaped organs (about 11cm X 7cm X 3cm) which are located in the upper abdominal area against the back muscles. They are opposite to one another , the right and left kidney but right kidney is slightly lower than the left to accomodate the liver.

It has a conves and concave border and the recessed area on the concave border is known as hilum where renal artery enters the kidney and renal vein and ureter leaves the kidney. The kidney is sorrounded by a tough fibrous tissue called renal capsule which is sorrounded by perirenal fat, renal fascia and pararenal fat. The anterior of these tissues is the peritoneum while posterior is the transversal is fascia. The functional area of kidney is divided into two major structures: outer renal cortex and inner renal medulla. There are around eight to eighteen cone shaped renal lobes called renal pyramids. Between renal pyramids are projections of renal cortex called renal columns. Nephrons which are the functional unit of kidney are present which cover cortex and medulla, has initial filtering portion called renal corpuscle , located in cortex. Followed by this is renal tubule which passes from cortex to deel into medullary pyramids. Part of renal cortex, medullary ray is collection of renal tubules which drain into single collecting duct. The tip or papilla of each pyramid empties urine into minor calyx which empties into major calyx which further empties into renal pelvis. This becomes the ureter.

The main function of kidneys is to excrete variety of waste materials produced by metabolism in urine. It participates in the whole body homeostasis regulating acid base balance, electrolyte concentration, extracellular fluid volume and blood pressure.

Ureters- There are two ureters from each kidney which arises in the pelvis of kidney and passes down the side of kidney and enters the back of bladder.

Each ureter is a small tube about 25 cm long that carries urine from renal pelvis to urinary bladder. The wall of ureter consists of three layers- the outer layer is the fibrous coat, is a supporting layer of fibrous connective tissue , the middle layer is the muscular coat which consists of inner circular and outer longitudinal smooth muscle and the inner layer is the mucosa which is a transitional epithilium that is continuous with the lining of renal pelvis and urinary bladder. The main function of middle layer is peristalsis while inner layer secretes mucous which coats and protects the surface of cells.

The main function of ureter is to carry urine away from kidney to the urinary bladder which is the temporary reservoir of the urine.

Urinary bladder- It is located in the lesser pelvis when empty and extends into abdominal activity when full. In children, the bladder is located in the abdomen and does not completely descend into the pelvis until puberty.

When full, bladder is oval in shape while it is flattened by overlying bowel when empty. It consists of an apex which is located superiorly, pointing towards the pubic symphysis . It is connected to the umbilicus by median umbilical ligament. The body is the main part of the bladder which is located between the apex and fundus. Fundus or base is located posteriorly which is triangular shaped with the tip of the triangle pointing backwards. The neck is formed by the convergence of the fundus and two inferolateral surfaces. Urine enters the bladder through ureters and leaves via urethra. Internally, these orifices are marked by a trigone- a triangular area located within the fundus. In contrast to rest of the internal bladder, trigone has smooth muscles . The wall of the bladder consists of detrusor muscle whose fibres are oriented in multiple directions, this retaining structural integrity when stretched.

The main function of the bladder is to temporary store the urine . It can accomodate around 300-400 ml of urine in healthy adult. The musculature of bladder contracts during micturition , with simultaneous relaxation of sphincters.

Urethra--

Male urethra- It is approximately 15-20 cm long.The male urethra runs through the prostate eccentrically, with most of the prostatic tissue in a posterior and inferior location. It is divided into three parts-

(i). Prostatic urethra- It begins as a continuation of bladder neck and passes through the prostate gland. It is the widest part and recieves the ejaculatory ducts.

(ii). Membranous duct- It is the narrowest part and passes through pelvic floor and deep perineal pouch .It is sorrounded by external urethral sphincter which provides voluntary control of micturition.

(iii). P_e_n_i_l_e (bulbous) urethra- It passes through the bulb and corpus spongiosum of the p_e_n_i_s ending at the external urethral meatus and recieves the bulbourethral gland proximally. In the glans p_e_n_i_s, the urethra dialtes to form the navicular fossa.

The male urethra is the common passage of urine and ejaculation from the the male body.

Female urethra- In human females, the urethra is about 4.8 cm to 5.2 cm long and exits the body between c_l_i_t_o_r_i_s. and the v_a_g_i_n_a, extending from internal to external urethral orifice . The meatus is located below the c_l_i_t_o_r_i_s.

The urethra begins at the neck of bladder, and passes inferiorly through the perineal membrane muscular pelvic floor. The urethra opens directly onto the perineum, in an area between labia minora known as vestibule. Within the vestibule, urethral orifice is located anterior to the v_a_g_i_n_a_l opening and 2-3 cm posterior to the clitoris. The distal end of the urethra is marked by the presence of two mucous glands that lie either side of urethra called Skene's glands. They are homologous to make prostate.

The function of female urethra is to expell urine out of the body.