Microanatomy of the Urinary System

Flashcards reviewing microanatomy of the urinary system of domestic animals, covering functions, relevance, kidney microanatomy, ureter, bladder, urethra, and renal development.

What are the primary functions of the urinary system?

Excrete nitrogenous waste, conserve body fluids and electrolytes, reabsorb solutes and water, convey urine to bladder, store urine, expel urine.

What are the specific functions of the kidneys?

Filtration of cellular wastes, selective reabsorption, regulation of fluid balance, maintenance of electrolyte and acid-base balance, excretion of waste, production of hormones, regulation of blood pressure, and activation of vitamin D.

How do clinical signs of renal diseases relate to microanatomy and kidney function?

Relates to abnormal urine content, color, volume, primary renal diseases by site of injury (glomeruli, tubules, blood vessels), ascending infections, renal neoplasia, renal infarction, or renal failure.

What are the main structural components of the kidney?

Capsule, renal lobe/pyramid, outer cortex, inner medulla, papillae/crest, calices, pelvis, and renal hilus.

How do kidney lobe structures vary among domestic animal species?

Unilobar (carnivores), multilobar (large ruminants, pigs), with varying degrees of lobe fusion and presence/absence of a renal pelvis.

What are the important tissues found in the different regions of the kidney?

Capsule (collagen fibers, smooth muscle, blood vessels), cortex (renal corpuscles, convoluted tubules), medulla (loop of Henle, collecting duct), and pelvis (urothelium, submucosa, smooth muscle, adventitia).

How do nephrons contribute to osmoregulation?

Filtration of water and small molecules, and selective reabsorption of water and other filtered molecules.

Which structures are located in the renal cortex?

Renal corpuscles, proximal tubules, distal convoluted tubules, collecting tubules, and peritubular capillary plexuses.

Which structures are located in the renal medulla?

Loops of Henle, collecting ducts, and vasa recta.

What are the components of the renal corpuscle?

Glomerulus and Bowman’s capsule; includes glomerulus (fenestrated capillaries), Bowman’s capsule (visceral podocytes, glomerular basement membrane, urinary space, parietal squamous cells), vascular pole, urinary pole, and mesangial cells.

Which blood vessels are associated with the vascular pole of the glomerulus?

Afferent arteriole (blood enters), efferent arteriole (blood exits).

How is ultrafiltration achieved at the glomerulus?

Blood pressure forces blood through the filtration barrier (fenestrated endothelium, glomerular basement membrane, podocyte foot processes) to produce ultrafiltrate into the urinary space; ultrafiltrate enters the proximal convoluted tubule.

What are the three components of the filtration barrier?

Endothelium of glomerular capillaries, glomerular basement membrane (lamina rara interna, lamina densa, lamina rara externa), and podocytes with pedicels.

How is urine formed?

Primary glomerular filtrate is produced by ultrafiltration of blood in the renal corpuscle; reabsorption of water, Na+, glucose, amino acids; tubular secretion of K+, H+, NH4+, bile salts, drug metabolites.

What are the functions of mesangial cells?

Phagocytic, contractile, and provide support.

What are the three main regions of the renal tubules?

Proximal tubule, thin descending and thick ascending limb of Henle’s loop, and distal convoluted tubule.

What are the key characteristics of the proximal convoluted tubule?

Single layer of cuboidal epithelial cells with microvilli, basement membrane, highly metabolically active with mitochondria, Na+/K+ pumps, aquaporins, peroxisomes, endosomes and lysosomes

What substances are resorbed in the proximal convoluted tubules?

Resorb glucose, Na+/H2O, amino acids, peptides, and low molecular weight proteins.

What types of epithelium line the Loop of Henle?

Cuboidal epithelium (thick descending/ascending) and squamous epithelium (thin segment).

What are the key characteristics of the distal convoluted tubule?

Site of action of aldosterone and contains specialized chemoreceptor cells of the macula densa.

What are the main features of the collecting ducts?

Connect distal convoluted tubule to renal papillae/crest; site of action of antidiuretic hormone (ADH).

What is the function of the two cell types found within the collecting ducts?

Principal cells reabsorb Na and H2O, while intercalated cells participate in acid-base balance.

What are papillary ducts?

Terminal portion of collecting ducts that empty at the area cribrosa of the renal crest or papilla.

Describe the renal vasculature.

Renal artery, interlobar artery, arcuate artery, interlobular artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, vasa recta, intralobular vein, interlobular vein, arcuate vein.

What are the two components of the juxtaglomerular apparatus?

Macula densa cells (DCT) sense Na+ concentrations, juxtaglomerular cells (afferent/efferent arteriole) detect blood pressure variations and secrete renin.

What are the general layers of tubular organs?

Lamina mucosa/epithelium, lamina propria, lamina muscularis, tunica submucosa, tunica muscularis, tunica serosa/adventitia.

What are the layers of the ureters?

Tunica mucosa (transitional epithelium), tunica submucosa (lamina propria), tunica muscularis (3 smooth muscle layers), tunica adventitia.

What are the layers of the urinary bladder?

Tunica mucosa (urothelium/transitional epithelium), tunica submucosa, tunica muscularis (3 smooth muscle layers), tunica serosa/adventitia.

What are the three stages of renal development?

Pronephros (regresses), mesonephros (forms nephrons early, mesonephric duct retained in males), metanephros (forms adult kidney).