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Anatomy & Physiology: Urinary System and Renal Physiology

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  • Primary functions of the urinary system
    Excretion of organic wastes, elimination of waste products, and homeostatic regulation of blood plasma volume and solute concentration.
  • Organs of the urinary system
    Kidneys (produce urine), ureters (paired tubes), urinary bladder (muscular sac), and urethra (exit tube).
  • Four homeostatic functions of the urinary system
    1. Regulates blood volume and pressure, 2. Regulates plasma ion concentrations, 3. Stabilizes blood pH, 4. Conserves valuable nutrients.
  • Location and size of typical adult kidney
    Located on either side of vertebral column; about 10 cm long, 5.5 cm wide, 3 cm thick; weighs ~150 g.
  • Renal cortex and medulla
    Renal cortex is the superficial, reddish-brown granular layer; renal medulla contains 6-18 renal pyramids separated by renal columns.
  • Nephron structure
    Consists of renal corpuscle (glomerulus and Bowman's capsule) and renal tubule (PCT, loop of Henle, DCT).
  • Functions of the renal tubule
    1. Reabsorb useful organic nutrients, 2. Reabsorb over 90% of water, 3. Secrete waste products missed by filtration.
  • Difference between cortical and juxtamedullary nephrons
    Cortical nephrons have short loops mostly in cortex; juxtamedullary nephrons have long loops extending deep into medulla.
  • Role of the juxtaglomerular complex (JGC)
    Endocrine structure that secretes erythropoietin and renin; formed by macula densa and juxtaglomerular cells.
  • Three basic processes of urine formation
    Filtration, reabsorption, and secretion.
  • Filtration at the glomerulus
    Hydrostatic pressure forces water and small solutes through capillary pores; larger solutes and cells are retained.
  • Functions of the proximal convoluted tubule (PCT)
    Reabsorbs organic nutrients, ions, water; secretes wastes; reabsorbs 60-70% of filtrate volume.
  • Role of aldosterone in the kidney
    Hormone from adrenal cortex that stimulates Na+ pumps and channels in DCT and collecting duct, reducing Na+ loss in urine.
  • Effect of antidiuretic hormone (ADH) on urine concentration
    Increases water permeability in DCT and collecting ducts by adding water channels, concentrating urine.
  • Normal composition of urine
    Clear, sterile solution with yellow pigment urobilin; contains dissolved nitrogenous wastes like urea, creatinine, uric acid.
  • Autoregulation of glomerular filtration rate (GFR)
    Maintains stable GFR by adjusting diameters of afferent and efferent arterioles and glomerular capillaries.
  • Renin–angiotensin system effects
    Renin release triggers angiotensin II formation, causing vasoconstriction, aldosterone secretion, ADH release, and increased thirst.
  • Role of atrial natriuretic peptides (ANP and BNP)
    Released by heart to dilate afferent arterioles, constrict efferent arterioles, increasing GFR and promoting sodium and water loss.
  • Micturition reflex
    Stretch receptors in bladder activate parasympathetic neurons causing detrusor muscle contraction and relaxation of urethral sphincters.
  • Fluid balance in the body
    Balance between water gained (eating, drinking, metabolism) and lost (urine, feces, perspiration); regulated by kidneys and hormones.
  • Electrolyte balance importance
    Maintains equal gains and losses of ions; sodium and potassium balance critical for cell function and fluid distribution.
  • Acid–base balance role of kidneys
    Secrete hydrogen ions, reabsorb bicarbonate, and generate buffers to maintain blood pH between 7.35 and 7.45.
  • Carbonic acid–bicarbonate buffer system
    Most important ECF buffer; carbonic acid dissociates into H+ and bicarbonate to stabilize pH; depends on respiratory function.
  • Respiratory compensation in acid–base balance
    Adjusts pH by changing respiration rate to alter CO2 levels, which shifts carbonic acid equilibrium.
  • Renal compensation in acid–base balance
    Adjusts secretion or reabsorption of H+ and HCO3- in response to plasma pH changes to maintain homeostasis.
  • Common acid–base disorders
    Acidosis (pH <7.35) and alkalosis (pH >7.45), affecting nervous and cardiovascular systems.
  • Age-related changes in urinary system
    Decline in nephron number, reduced GFR, decreased ADH sensitivity, and impaired micturition reflex causing incontinence or retention.