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Urinary System and Kidney Function - Anatomy & Physiology

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  • Main functions of the kidney

    Regulate osmolality, water volume, ion concentration, blood cell formation (erythropoietin), blood pressure (renin), acid-base balance, filter metabolic wastes, activate Vitamin D, and perform gluconeogenesis during fasting.

  • Components of the urinary system

    Kidneys, ureters, urinary bladder, and urethra.

  • Renal hilum

    Opening in the kidney for the ureter, blood vessels, lymphatics, and nerves.

  • Three layers surrounding the kidney

    Renal fascia (superficial, attachment), perirenal capsule (middle, trauma protection), fibrous capsule (deep, infection protection).

  • Regions of the kidney

    Renal cortex (outermost), renal medulla (middle, contains pyramids and columns), renal pelvis (innermost, continuous with ureter).

  • Functional unit of the kidney

    Nephron, consisting of renal corpuscle and renal tubules.

  • Difference between cortical and juxtamedullary nephrons

    Cortical nephrons mostly in cortex with short loops; juxtamedullary nephrons near cortex-medulla junction with long loops and vasa recta.

  • Glomerulus function

    First capillary bed in nephron; filters blood to form filtrate.

  • Afferent vs efferent arterioles

    Afferent arterioles carry blood to glomerulus; efferent arterioles carry blood away to peritubular capillaries or vasa recta.

  • Three processes of urine formation

    Glomerular filtration, tubular reabsorption, and tubular secretion.

  • Filtrate vs urine

    Filtrate is blood plasma without proteins; urine is filtrate with unneeded substances like excess salts and wastes.

  • Filtration membrane components

    Endothelial fenestrations, basement membrane, and filtration slits between podocytes.

  • Outward pressure in glomerular filtration

    Hydrostatic pressure of glomerular capillaries (HPgc) pushes water and solutes out of blood.

  • Inward pressures opposing filtration

    Hydrostatic pressure in capsular space (HPcs) and osmotic pressure in glomerular capillaries (OPgc).

  • Net Filtration Pressure (NFP) formula

    \(\text{NFP} = HP_{gc} - (HP_{cs} + OP_{gc})\)

  • Normal Glomerular Filtration Rate (GFR)

    120-125 ml/min; volume of filtrate formed per minute by all glomeruli.

  • Intrinsic GFR control mechanisms

    Myogenic response (arteriole constriction/dilation) and tubular glomerular feedback via juxtaglomerular complex.

  • Role of macula densa cells

    Monitor NaCl concentration in filtrate and signal afferent arteriole to constrict or dilate to regulate GFR.

  • Renin-Angiotensin-Aldosterone (RAA) system effect on blood pressure

    Renin converts angiotensinogen to angiotensin I; ACE converts to angiotensin II which increases BP by vasoconstriction, aldosterone release, ADH release, and thirst stimulation.

  • How ADH affects urine concentration

    Increases aquaporins in collecting ducts, promoting water reabsorption and reducing urine output.

  • Primary active transport in sodium reabsorption

    Na+/K+ pump moves Na+ out of tubule cells against gradient, creating electrochemical gradient for secondary transport.

  • Secondary active transport types in kidney tubules

    Symporters move Na+ and other molecules in same direction; antiporters move Na+ and H+ in opposite directions.

  • Osmosis in kidney water reabsorption

    Water moves from low solute to high solute concentration areas, mainly through aquaporins by facilitated diffusion.

  • Countercurrent multiplier function

    Creates concentration gradient in medulla by NaCl movement in ascending loop and water movement in descending loop to concentrate urine.

  • Role of vasa recta in urine concentration

    Countercurrent exchanger that preserves medullary gradient and removes reabsorbed water without washing out solutes.

  • Urea recycling in urine concentration

    Urea is reabsorbed and recycled in medulla to maintain high solute concentration and promote water reabsorption when ADH is present.

  • Function of tubular secretion

    Removes substances not filtered at glomerulus, disposes of drugs, wastes, excess K+, and helps regulate blood pH.

  • Effect of aldosterone on kidney function

    Increases Na+/K+ pump activity, promoting sodium reabsorption and increasing blood pressure via RAA system.

  • Micturition control

    Internal urethral sphincter is involuntary smooth muscle; external urethral sphincter is voluntary skeletal muscle.