The Urinary System (Ch. 23)

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Vocabulary-style flashcards covering key terms and definitions from the urinary system lecture notes.

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70 Terms

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Urinary system

The body system that filters blood, forms urine, and removes wastes.

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Urinary tract

Organs involved in urine production and transport: kidneys, ureters, bladder, urethra (and in males, the prostate).

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Kidney

Primary organ of the urinary system; filters blood and forms urine via nephrons.

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Ureter

Tube that carries urine from the kidney to the bladder through peristaltic movement.

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Urinary bladder

Elastic sac that stores urine before it is excreted.

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Urethra

Duct through which urine exits the body; in males it also carries semen.

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Prostate

Male gland near the urethra contributing to semen; part of the urinary tract in men.

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Nephron

Functional unit of the kidney responsible for filtration and urine formation.

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Glomerulus

Ball of capillaries where blood is filtered to form filtrate.

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Bowman's capsule (Glomerular capsule)

Double-walled capsule surrounding the glomerulus that collects filtrate.

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Renal corpuscle

The glomerulus plus Bowman's capsule—the filtration unit of the nephron.

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Renal tubule

Tubular structure where filtrate is converted to urine via reabsorption and secretion.

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Proximal convoluted tubule (PCT)

Long, highly coiled segment with microvilli; major site of reabsorption.

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Loop of Henle

Nephron loop with descending and ascending limbs; creates medullary osmotic gradient.

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Descening limb

Part of the loop of Henle that is permeable to water, promoting water reabsorption.

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Thin ascending limb

Segment of loop of Henle; relatively impermeable to water; reabsorbs Na+, K+, Cl- via cotransporters.

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Thick ascending limb

Section of loop of Henle that reabsorbs Na+, K+, Cl- but is impermeable to water.

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Distal convoluted tubule (DCT)

Renal tubule segment after the loop; shorter and less coiled; hormonally regulated reabsorption.

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Collecting duct

Receives filtrate from multiple nephrons; concentrates urine; site of ADH action.

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Glomerular filtration rate (GFR)

Rate of filtrate formation in the renal corpuscles; ~125 mL/min in adults; tightly regulated.

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Urine

Fluid expelled from the body containing waste products filtered from the blood.

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Filtration

Movement of fluid from blood into the nephron lumen at Bowman's capsule.

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Reabsorption

Movement of substances from the filtrate back into the blood.

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Secretion

Removal of specific wastes from blood into the filtrate in the tubule.

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Excretion

Elimination of waste products in urine.

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Filtration barrier

Three-layer barrier (fenestrated endothelium, basement membrane, podocytes) that limits filtration by size and charge.

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Fenestrated endothelium

Capillary lining with pores that restrict large molecules from filtration.

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Glomerular basement membrane

Negatively charged, proteoglycan-rich layer that repels large anions and governs filtration.

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Podocytes

Visceral layer of Bowman's capsule with filtration slits that restrict filtration to small molecules.

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Filtration slit

Narrow gaps between podocyte foot processes through which filtrate passes.

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Afferent arteriole

Blood vessel delivering unfiltered blood to the glomerulus; larger diameter.

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Efferent arteriole

Blood vessel leaving the glomerulus; smaller diameter, maintains glomerular pressure.

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Peritubular capillaries

Network surrounding the renal tubules; site of reabsorption and secretion.

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Juxtamedullary nephron

Nephron with a long loop of Henle extending into the medulla; ~15% of nephrons.

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Cortical nephron

Most nephrons with shorter loops; located mainly in the renal cortex.

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Macula densa

Cells in the ascending limb sensing NaCl content to regulate GFR via juxtaglomerular cells.

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Juxtaglomerular cells

Granular cells that secrete renin in response to signals from the macula densa or sympathetic input.

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Renin-angiotensin-aldosterone system (RAAS)

Hormonal cascade regulating blood pressure and GFR; renin → angiotensin II → aldosterone; increases Na+ and water reabsorption.

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Renin

Enzyme released by juxtaglomerular cells; converts angiotensinogen to angiotensin I.

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Angiotensin II

Potent vasoconstrictor that raises blood pressure and preferentially constricts efferent arterioles; stimulates aldosterone, ADH, and thirst.

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Aldosterone

Steroid hormone that increases Na+ and water reabsorption in the collecting ducts.

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Antidiuretic hormone (ADH/vasopressin)

Hormone that increases water reabsorption in the collecting ducts via aquaporins.

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ACE (angiotensin-converting enzyme)

Enzyme that converts angiotensin I to the active angiotensin II.

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ANP (atrial natriuretic peptide)

Hormone from the heart that promotes Na+ and water excretion and reduces renin/aldosterone effects.

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Osmolarity

Measure of solute concentration; expressed in mOsm/L; essential for urine concentration.

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Medullary gradient

Osmotic gradient from cortex to medulla in the kidney, enabling urine concentration.

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Vasa recta

Countercurrent exchange vessels that preserve the medullary osmotic gradient.

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AQP (aquaporin)

Water channels in tubule membranes that facilitate water reabsorption.

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ANP vs RAAS balance

ANP promotes excretion of Na+ and water; RAAS promotes reabsorption to raise BP and GFR.

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PTH (parathyroid hormone)

Hormone that increases Ca2+ reabsorption and decreases phosphate reabsorption in the kidney.

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Urea cycling

Reabsorption and secretion of urea between the loop of Henle and collecting duct to maintain medullary osmolarity.

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Urea recycling

Process where about half of filtered urea is reabsorbed and re-secreted to help maintain gradient.

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Loop of Henle gradient

Generation of a hyperosmotic medullary interstitium via countercurrent multiplication.

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Diabetes insipidus

Condition with excessive urination due to ADH deficiency or renal insensitivity to ADH.

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Diabetes mellitus type 1

Autoimmune destruction of pancreatic beta cells leading to insulin deficiency and hyperglycemia.

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Diabetes mellitus type 2

Insulin resistance with relative insulin deficiency; common cause of hyperglycemia.

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Gestational diabetes

Glucose intolerance first recognized during pregnancy.

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Diabetes mellitus vs diabetes insipidus (DI)

Mellitus: high blood glucose; Insipidus: impaired urine concentration and polyuria not due to lipids or glucose.

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BUN (Blood Urea Nitrogen)

Blood level of nitrogenous wastes; normal ~10–20 mg/dL; high levels indicate azotemia.

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Uric acid

Nitrogenous waste from nucleic acid metabolism; largely reabsorbed with some secretion.

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Creatinine

Waste from muscle creatine phosphate breakdown; used to estimate GFR.

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Filtration fraction

Fraction of renal plasma flow that becomes filtrate, influenced by hydrostatic and oncotic pressures.

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Tm (Transport Maximum)

Maximum rate at which a solute can be reabsorbed or secreted by a transporter.

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Paracellular transport

Movement of substances between adjacent epithelial cells, driven by gradients.

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Transcellular transport

Movement of substances across an epithelial cell, via channels, transporters, or pumps.

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SGLT (Sodium-glucose transporter)

Sodium-glucose cotransporter that reabsorbs glucose from filtrate into tubule cells.

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PAH (para-aminohippurate)

Substance used to measure renal plasma flow; freely secreted by tubules.

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Protein reabsorption in PCT

Proteins are reabsorbed and hydrolyzed into amino acids rather than excreted.

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Autoregulation

Intrinsic ability of kidneys to maintain GFR despite BP changes via tubuloglomerular feedback and myogenic mechanisms.

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Myogenic mechanism

Vascular smooth muscle response to stretch: increases resistance when BP rises to maintain GFR.