Urinary System

Urinary System
The urinary system consist of the paired kidneys , the paired ureters , which lead form the kidneys to the bladder , and the uretha , which leads form the bladder to the exterior of the body .
1. Kidney
A –Capsule
The capsule is composed of dense irregular collagenous connective tissue . Occasional fibroblasts and blood vessels may be seen .
B – Cortex
The cortex consists of nephrons and collecting tubules are arranged in cortical labyrinths and medullary rays . Additionally , blood vessels and associated connective tissue ( renal interstitium ) are also present .

1. Cortical Labyrinth
Is composed of renal corpuscles and cross- sections of proximal convoluted tubules(constituted of cuboidal cells with borderd brush ) , distal convoluted tubules (constituted of cuboidal cells ) ,and the macula densa region of distal tubules . Renal corpuscles consist of :- parietal ( simple squamous ) and visceral ( modified to podocytes ) layers of Bowman,s capsule , and an associated capillary bed , the glomerulus , as well as the intervening Bowman,s space , which receives the ultrafiltrate . The afferent and efferent glomerular arterioles supply and drain the glomerulus , respectively, at its vascular pole . The macula densa region of the distal tubule is associated with the juxtaglomerular ( modified smooth muscle ) cells of the afferent ( and sometimes efferent ) glomerular arterioles .

2. Medullary Rays
Medullary rays are continuations of medullary tissue extending into the cortex . They are composed mostly of collecting tubules, pars recta of proximal tubules , ascending thick limbs of Henele,s loop , and blood vessels .

C - Medulla
The medulla is composed of renal pyramids that are bordered by cortical columns . The renal pyramids consist of collecting tubules .

D - Pelvis
Subdivided into the minor and major calyces , constitutes the beginning of the main excretory ducts of the kidney. The transitional epithelium of the minor calyx is reflected onto the renal papilla . The calyces are lined by transitional epithelium . The subepithelial connective tissue of both is loosely arranged .The muscularis, composed of inner longitudinal and outer circular layers of smooth muscle . An adventitia of loose connective tissue surrounds the muscularis .


2. EXTERNAL PASSAGES
A. Ureter
The ureter possesses a stellate – shaped lumen that is lined by transitional epithelium. The subepithelial connective tissue ( sometimes said to be subdivided into lamina propria and submncosa ) is composed of a fibroelastic connective tissue . The musclaris is again composed of inner longitudinal and outer circular layers of smooth mucsle, although in its lower portion near the bladder a third , outermost longitudinal layer of smooth mucsle is present . The mucsularis is surrounded by a fibroelastic adventitia .



B. Bladder
The urinary bladder resembles the ureter except that it is a much larger structure and dose not possess a stellate lumen , although the mucosa of the empty bladder is thrown into folds . The lamina propria is fibroelastic in character. The muscularis is composed of three indefinite layers of smooth muscle : inner longitudinal . middle circular , and outer longitudinal . The circular muscle coat forms the internal sphincter at the neck of the bladder . An adventitia or serosa surrounds the bladder .