Urinary System Quiz

Urinary System Histology

• The urinary system comprises paired kidneys and ureters, a urinary bladder, and a urethra.
• Kidneys are bean-shaped retroperitoneal organs, formed of stroma (capsule, renal interstitium, CT) and parenchyma (outer cortex, inner medulla).
• The nephron is the functional unit, consisting of a renal corpuscle and tubule (proximal, loop of Henle, distal, collecting).
• The renal corpuscle includes a glomerulus (vascular ball, 200 µm diameter) covered by Bowman's capsule (double-walled epithelial cup).
• The filtration membrane separates blood in the glomerular capillaries from the urinary space in Bowman's capsule.
• The filtration membrane has fenestrated endothelial cells, a continuous basement membrane, and filtration slits with diaphragms.
• Mesangial cells are stellate cells supporting glomerular capillaries and having phagocytic function.
• The juxtaglomerular apparatus (JGA) includes cells from the distal tubule (macula densa), afferent arteriolar smooth muscle cells (juxtaglomerular cells), and lacis cells (extraglomerular mesangial cells).
• Macula densa acts as osmoreceptors sensitive to sodium concentration in the distal tubule.
• Juxtaglomerular cells secrete renin to regulate blood pressure.
• Lacis cells function in supporting the JGA.
• Proximal convoluted tubule (PCT) is lined with simple cuboidal epithelium with a brush border (microvilli). Its functions include active reabsorption of glucose and amino acids, and reabsorption of Na+, Cl-, K+, and H2O.
• Distal convoluted tubule (DCT) is lined with cuboidal epithelium without a brush border. It functions include reabsorption of Na+, K+, and water under aldosterone and ADH influences, and excretion of H2O and NH3.
• Urinary passages include calyces, pelvis, ureter, bladder, and urethra.
• Urinary passages have a mucosa with transitional epithelium, a muscular layer (detrusor muscle), and an adventitia (loose connective tissue).