Excretory System and Urinary Physiology

Vocabulary flashcards covering the key terms and definitions from the Excretory System lecture notes.

Excretion

Removal of wastes from the body; helps maintain the internal environment (homeostasis).

Homeostasis

Maintenance of stable conditions inside the body, including water and solute balance.

Nitrogenous wastes

Waste products containing nitrogen, mainly ammonia, urea, and uric acid.

Ammonotelic

Animals that excrete ammonia as their primary waste product; requires lots of water.

Ureotelic

Animals that convert ammonia to urea for excretion; uses moderate water.

Uricotelic

Animals that excrete uric acid; conserves water and is common in terrestrial species.

Kidney

Bean-shaped retroperitoneal organ that filters blood and forms urine; consists of cortex and medulla.

Retroperitoneal

Located behind the peritoneum; kidneys are retroperitoneal.

Renal hilum

Indented area of the kidney where vessels, nerves, and ureter enter/exit.

Renal cortex

Outer part of the kidney where renal corpuscles and parts of the nephron reside.

Renal medulla

Inner portion of the kidney containing the renal pyramids.

Renal pyramid

Cone-shaped tissue areas in the renal medulla; contain collecting ducts.

Renal column of Bertin

Extensions of cortical tissue separating renal pyramids.

Renal pelvis

Widened upper end of the ureter within the kidney; collects urine.

Renal capsule

Fibrous outer covering of the kidney.

Ureter

Muscular tube carrying urine from kidney to bladder.

Urethra

Duct through which urine is discharged from the bladder; male and female differences exist.

Urinary bladder

Expandable sac that stores urine before voiding.

Nephron

Functional unit of the kidney; consists of glomerulus, Bowman's capsule, and renal tubules.

Glomerulus

Tuft of capillaries where filtration of blood begins.

Bowman’s capsule

Double-walled cup surrounding the glomerulus; forms glomerular filtrate.

Afferent arteriole

Arteriole delivering blood to the glomerulus; wide in diameter.

Efferent arteriole

Arteriole carrying blood away from the glomerulus; narrower than the afferent.

Podocyte

Visceral epithelial cell of Bowman's capsule with filtration slits.

Proximal convoluted tubule (PCT)

First section of the renal tubule; major site of reabsorption.

Distal convoluted tubule (DCT)

Renal tubule section where selective reabsorption and secretion occur; regulated by hormones.

Loop of Henle

U-shaped portion of the tubule; thin descending limb reabsorbs water, thick ascending limb reabsorbs ions.

Descending limb

Part of the Loop of Henle permeable to water; concentrates filtrate.

Ascending limb

Part of the Loop of Henle impervious to water; reabsorbs NaCl.

Collecting duct

Receives filtrate from nephrons; subject to hormonal control for final urine concentration.

Juxtaglomerular apparatus (JGA)

Structure where distal tubule contacts the afferent arteriole; regulates blood pressure and filtration.

Juxtaglomerular cells

Cells in the afferent arteriole that secrete renin in response to changes in BP or flow.

Macula densa

Cells in the distal tubule that monitor NaCl concentration and signal JGA.

Lacis cells (extraglomerular mesangial cells)

Supportive cells between arterioles and tubules within the JGA region.

Renin

Enzyme released by JG cells; initiates RAAS to raise BP and increase Na+ and water reabsorption.

Angiotensinogen

Liver-produced protein that is converted to angiotensin I by renin.

Angiotensin I

Inactive decapeptide converted to angiotensin II by ACE.

Angiotensin II

Potent vasoconstrictor that stimulates aldosterone release and thirst.

Aldosterone

Mineralocorticoid that increases Na+ and water reabsorption in the distal nephron.

Antidiuretic hormone (ADH, vasopressin)

Hormone that promotes water reabsorption in the distal nephron and collecting ducts.

Glomerular filtration rate (GFR)

Volume of filtrate formed per minute by the kidneys (about 125 ml/min in healthy adults).

Renal blood flow (RBF)

Total blood supplied to the kidneys per minute; approximately 1100 ml/min.

Renal plasma flow (RPF)

Portion of renal blood flow that becomes plasma in the glomeruli (about 650 ml/min).

Filtration membrane

Filtration barrier of the glomerulus comprising endothelial layer, basement membrane, and podocytes.

Endothelial layer

Innermost layer of glomerular capillaries; part of the filtration barrier.

Basement membrane

Glycoprotein layer between endothelium and podocytes; blocks large proteins.

Podocyte layer

Visceral layer of Bowman's capsule with filtration slits.

GFR value

125 ml/min; about 180 L of filtrate formed per day; most is reabsorbed.

Reabsorption

Process of reclaiming water, ions, and nutrients from filtrate back into blood.

Tubular secretion

Active process moving substances from blood into tubules for excretion.

Ultrafiltration

Non-selective filtration of plasma across the filtration barrier into Bowman's capsule.

Peritubular capillaries

Network around renal tubules; important for reabsorption and secretion.

Vasa recta

Straight capillaries in the medulla; participate in counter-current exchange.

Counter-current mechanism

Opposing flow in the loop of Henle and vasa recta that concentrates urine.

Medullary osmotic gradient

Increasing osmolality from cortex to inner medulla; drives water reabsorption in collecting ducts.

Osmolarity

Concentration of solutes in a solution (osmol/L); regulates water movement.

Urea recycling

Urea contributed to medullary osmolarity and reabsorbed in nephron segments.

Atrial natriuretic factor (ANF)

Hormone released from atria that reduces blood pressure by promoting natriuresis and vasodilation.

Autoregulation

Kidneys maintain stable GFR across a range of BP via intrinsic mechanisms.

Osmoreceptors

Receptors that detect changes in body fluid osmolarity and regulate ADH release.

Diabetes insipidus

Condition caused by ADH deficiency leading to polyuria and polydipsia.

Diabetes mellitus

Metabolic disorder with hyperglycemia; glycosuria and polyphagia may occur.

Uremia

Accumulation of urea and other wastes in the blood due to kidney failure.

Renal failure

Kidneys fail to excrete wastes or regulate fluids, leading to oliguria or anuria.

Glomerulonephritis

Inflammation of the glomeruli; can cause proteinuria and hematuria.

Renal calculi (urolithiasis)

Stone formation in kidneys due to deposition of crystals like uric acid or calcium oxalate.

Lungs (excretion)

Excretes carbon dioxide (about 200 ml/min) as a waste product of respiration.

Liver (excretion)

Forms bile containing bilirubin and other wastes; aids excretion of certain metabolites.

Skin (excretion)

Sweat and sebum remove water, salts, and waste products; cooling role of sweat.

Saliva (excretion)

Contains small amounts of urea and uric acid; minor excretory role.

Hemodialysis

Artificial kidney procedure that removes wastes from the blood via dialysis tubing.

Dialysate

Dialysis fluid whose composition mimics plasma to allow diffusion of wastes.

Osmolarity range of human urine

Concentrated urine can reach up to ~1200 mOsm/L under maximal antidiuresis.

Medullary interstitium

Fluid space in the renal medulla with high osmolality aiding urine concentration.

Aldosterone vs ADH action

Aldosterone increases Na+ reabsorption; ADH increases water reabsorption in distal nephron.

Micturition reflex

Reflex causing urine voiding via detrusor contraction and sphincter relaxation.

Detrusor muscle

Smooth muscle layer of the urinary bladder responsible for bladder contraction.

Internal urethral sphincter

Involuntary sphincter at the bladder neck; relaxes during micturition.

External urethral sphincter

Voluntary sphincter controlling urethral opening during urination.

Glomerular filtration rate (GFR) units

Measured in ml/min; rate of filtrate formation by the kidneys.

Renal tubule segments

PCT, Loop of Henle (descending and ascending limbs), DCT, collecting duct.

Osmolarity values (normal plasma)

Approximately 300 mosm/L in a typical individual.

Hyperosmolarity of medullary interstitium

High osmolality in the inner medulla that drives water reabsorption.

Hormonal control of urine concentration

ADH and aldosterone govern water and electrolyte reabsorption in nephron segments.

Inspiration from page 25

Counter-current mechanism operates in loop of Henle and vasa recta to concentrate urine.

Hemodialysis mechanism

Blood passes through semipermeable membranes in contact with dialysate to remove wastes.