Renal pelvis (REE-nul PEL-vis): The funnels-shaped expansion of the upper ureter within the kidney's sinus; it collects urine from the major calyces and channels it into the ureter.
Ureter (YOO-rih-ter): A muscular tube lined by transitional epithelium/urothelium that transports urine by peristaltic contractions from the renal pelvis of the kidney to the urinary bladder.
Detrusor muscle (dih-TROO-ser MUS-ul): The thick layer of intermingled smooth muscle fibers that forms the wall of the urinary bladder; its contraction expels urine through the urethra.
Ureteric orifice (yoo-rih-TER-ik OR-ih-fis): The slit-like openings where the left and right ureters empty into the urinary bladder, located at the posterior corners of the trigone.
Trigone (TRY-gohn): A smooth, triangular region on the internal floor of the urinary bladder, defined by the two ureteric orifices and the internal urethral orifice; its mucosa is tightly bound, making it a common site for infection.
Urethra (yoo-REETH-ruh): The tube that conveys urine from the urinary bladder to the exterior of the body; it is lined by various epithelia depending on the segment (transitional, pseudostratified, stratified squamous).
Renal cortex (REE-nul KOR-teks): The outermost, light-colored layer of the kidney; it contains the renal corpuscles, convoluted tubules (proximal and distal), and cortical collecting ducts.
Renal column (REE-nul KOL-um): Columns of tissue that extend inward from the renal cortex, separating adjacent renal medulla (pyramids); these columns are composed of cortical tissue and blood vessels.
Renal medulla (pyramid) (REE-nul muh-DUL-uh): The inner region of the kidney, composed of 8-15 cone-shaped structures (renal pyramids); it contains the straight portions of the nephron (nephron loops) and the collecting ducts.
Renal papilla (REE-nul puh-PIL-uh): The blunt, pointed apex of a renal medulla (pyramid) that projects into the lumen of a minor calyx; it is perforated by the openings of the collecting ducts, allowing urine to enter the calyx system.
Minor calyx (MY-ner KAY-liks): A cup-shaped tube that receives urine directly from the renal papilla; several minor calyces merge to form a major calyx.
Major calyx (MAY-jer KAY-liks): A large cup-shaped tube formed by the union of two or three minor calyces; the major calyces merge to form the renal pelvis.
Perirenal adipose (per-ih-REE-nul AD-ih-pohz): The protective layer of fat (adipose tissue) that immediately surrounds the kidney and fills the renal sinus; it helps cushion and stabilize the organ.
Nephron (NEF-ron): The structural and functional unit of the kidney, responsible for forming urine; it consists of the renal corpuscle and the renal tubule (including proximal and distal convoluted tubules and the nephron loop).
Capsular space (Bowman's space) (KAP-suh-ler spays): The space within the glomerular capsule that receives the primary filtrate squeezed from the glomerulus through the renal filtration barrier.
Glomerulus (gluh-MER-yuh-lus): A tuft of highly convoluted, fenestrated capillaries encapsulated by the glomerular capsule; it is the site of blood plasma filtration.
Efferent arteriole (nephron) (EF-uh-rent ar-TIR-ee-ohl): The small arteriole that drains blood away from the glomerulus; its smaller diameter relative to the afferent arteriole helps maintain the high pressure needed for filtration.
Afferent arteriole (nephron) (AF-uh-rent ar-TIR-ee-ohl): The small arteriole that supplies blood to the glomerulus; it is involved in regulating blood flow and pressure within the glomerulus.
Cortical radiate artery (KOR-tih-kul RAY-dee-ayt AR-tuh-ree): Small arteries that radiate outwards from the arcuate arteries within the renal cortex; they give rise to the afferent arterioles that supply the glomeruli.
Cortical radiate vein (KOR-tih-kul RAY-dee-ayt vayne): Veins that parallel the cortical radiate arteries in the renal cortex; they drain blood from the peritubular capillaries and empty into the arcuate veins.
Proximal convoluted tubule (PROK-sih-mul kon-vuh-LOO-ted TOO-byool): The initial, highly coiled segment of the renal tubule, located in the renal cortex; its cells have abundant microvilli (brush border) and are the main site for reabsorption of water, ions, and nutrients from the filtrate.
Distal convoluted tubule (DIS-tul kon-vuh-LOO-ted TOO-byool): The final, coiled segment of the renal tubule, located in the renal cortex; its cells lack a prominent brush border and are primarily involved in fine-tuning ion and water reabsorption under hormonal control.
Cortical collecting duct (KOR-tih-kul kuh-LEK-ting dukt): The segment that receives filtrate from multiple distal convoluted tubules in the renal cortex; it further adjusts the concentration of urine under the influence of hormones (e.g., ADH).
Proximal straight tubule (PROK-sih-mul strayt TOO-byool): The short, straight continuation of the proximal convoluted tubule that descends into the outer renal medulla; it is part of the descending nephron loop.
Distal straight tubule (DIS-tul strayt TOO-byool): The thick-walled portion of the ascending nephron loop located in the outer renal medulla; it is lined by low cuboidal epithelium and actively transports ions out of the filtrate.
Descending nephron loop (of Henle) (dih-SEN-ding NEF-ron loop): The thin-walled segment of the renal tubule that descends deep into the renal medulla; its thin, simple squamous epithelium is highly permeable to water.
Ascending nephron loop (of Henle) (uh-SEN-ding NEF-ron loop): The segment of the renal tubule that ascends back toward the renal cortex; its thick portion actively pumps ions (Na+, K+, Cl-) out of the filtrate but is impermeable to water.
Renal corpuscle (REE-nul KOR-pus-ul): The initial part of the nephron, located in the renal cortex; it consists of the glomerulus and the glomerular capsule surrounding it, functioning as the site of blood filtration.
Glomerular capsule (Bowman's capsule) (gluh-MER-yuh-ler KAP-sool): A cup-shaped structure composed of an outer parietal layer (simple squamous epithelium) and an inner visceral layer (podocytes); it surrounds the glomerulus and collects the filtrate.
Glomerular space (gluh-MER-yuh-ler spays): Alternate term for the capsular space; the fluid-filled cavity between the parietal and visceral layers of the glomerular capsule that receives the primary filtrate.
Macula densa (MAK-yuh-luh DEN-suh): A specialized patch of columnar epithelial cells in the wall of the distal straight tubule where it abuts the afferent arteriole; it senses the concentration of NaCl in the filtrate and regulates renin release.
Podocyte (PAH-duh-syt): Highly specialized epithelial cells of the inner (visceral) layer of the glomerular capsule; their large cell bodies give off primary processes and small secondary processes (pedicels) that wrap around the glomerular capillaries to form the filtration slits.
Mesangial cell (meh-SAN-jee-ul sell): Modified smooth muscle-like cells found within the matrix between the glomerular capillaries; they provide structural support, contractility to regulate blood flow, and phagocytosis.
Glomerular capillary (gluh-MER-yuh-ler KAP-ih-lair-ee): The tiny blood vessels that make up the glomerulus; they are lined by a fenestrated endothelium and are the site from which blood plasma is filtered into the capsular space.
Renal filtration barrier (REE-nul fil-TRAY-shun BAR-ee-er): The three-layered structure that blood must cross to become filtrate; it consists of the fenestrated endothelium of the glomerular capillary, the glomerular basement membrane, and the filtration slits created by the pedicels of the podocytes.
Fenestra (pl. Fenestrae) (fuh-NES-truh/fuh-NES-tray): Large, open pores or windows in the endothelial cells of the glomerular capillary; these pores allow plasma fluid and solutes to exit the blood but restrict the passage of blood cells.
Glycocalyx (gly-koh-KAL-iks): A thick, negatively charged coat of glycoproteins and proteoglycans (on the endothelial cell surface and within the basement membrane) that forms part of the renal filtration barrier; it limits the filtration of large, negatively charged plasma proteins.
Pedicels (PED-ih-selz): The small, finger-like extensions (foot processes) that arise from the podocytes; they interdigitate and wrap around the glomerular capillaries, leaving narrow filtration slits through which the final filtrate passes.
Umbrella cells (UM-brel-uh selz): The large, specialized, highly differentiated superficial cells that line the lumen of the transitional epithelium/urothelium; they possess a thick, impermeable apical membrane (plaques) that protects the underlying cells from hypertonic urine.
Transitional epithelium/Urothelium (tran-ZISH-un-ul ep-uh-THEE-lee-um yoor-oh-THEE-lee-um): The unique, stratified epithelium that lines most of the urinary tract (renal calyces, renal pelvis, ureter, and urinary bladder); it is characterized by umbrella cells and the ability to stretch significantly without damage.