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Urinary System

Urinary System. Chapter 25. Urinary System Organs. 2 Kidneys forms urine 2 Ureters transport urine Urinary bladder stores urine Urethra transports urine. http://findmeacure.com/2008/03/27/hematuria-blood-in-the-urine/. Functions. Primary

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Urinary System

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  1. Urinary System Chapter 25

  2. Urinary System Organs • 2 Kidneys forms urine • 2 Ureters transport urine • Urinarybladder stores urine • Urethra transports urine http://findmeacure.com/2008/03/27/hematuria-blood-in-the-urine/

  3. Functions • Primary • Filters and excretes toxins, wastes, and ions • Regulates blood volume, pressure, & composition • Maintain balance in blood (H20, salt, acids & bases) • Supporting • Gluconeogenesis w/ fasting • Renin and EPO production • Vitamin D activation

  4. Kidney Anatomy (external) • Paired retroperitoneal organs • Right lower b/c liver • Renal ptosis: kidney falls w/ emaciation  kinks ureters • Hydronephrosis w/ resulting urine backup • Adrenalglands on top • Renal hilum for vessel entry http://www.arizonatransplant.com/images/kidney_large_1.JPG

  5. Kidney Anatomy (internal) • Renal capsule • Renal cortex • Renal medulla • Renal (medullary) pyramids w/ papilla • Renal columns • Renal pelvis • Walls are smooth muscle peristalsis • Major and minor calyces • Pyelitis when inflamed • Pyelonephritis all inflamed http://tejatechblog.blogspot.com/2010/06/internal-struture-of-kidney.html

  6. Blood and Nerve Supply • ¼ total CO • 90% of supply enters cortex • Renal plexus off of celiac plexus (SNS)

  7. Nephron • Forms urine from filtrate • Renal corpuscle • Glomerulusis a fenestrated capillaries • Glomerular (Bowman’s) capsule surrounds • Outer sim. squ. & inner podocyte • Renal tubules • PCT: sim. cub. w/ microvilli & mitochondria (cortex) • Increase SA for absorbing H20 & solutes and secretion • Loop of Henle: sim. cub.  sim. squ.  sim. cub/col • Corticalvsjuxtamedullary nephrons • DCT: see PCT, but no microvilli (cortex) • Collecting ducts: sim. cub. (medullary pyramids) • Intercalated cells: abundant microvill and maintain acid/base balance • Principal cells: sparse microvilli and maintain H2O and Na+ balance http://kvhs.nbed.nb.ca/gallant/biology/nephron_structure.html

  8. Nephron Blood Supply • Glomerulus • Afferent artery in from cortical radiate • High BP (wider too) force solute & fluid out • Produces filtrate • Peritubular capillaries • Efferent artery out • Porous & low pressure to reabsorb filtrate (99% to venules) • Modified as vasa recta in juxtamedullary nephrons

  9. Juxtaglomerular (JG) Apparatus • Regulate BP and rate of filtrate formation • Specialized cells • Juxtaglomerular (JG) cells in afferent arteriole • Smooth muscle w/ renin secreting granules • Mechanoreceptors for BP • Macula densain renal tubule • Columnar cells • Chemoreceptors for changing [NaCl] in filtrate http://pclab.cataegu.ac.kr/physiology/Kidney.htm

  10. Filtration Membrane • B/w blood and intercapsular space • Layers • Fenestrated epi. of glomerulus • All, but blood cells pass • Basement membrane (b/w epi and podocytes) • All, but smallest proteins • (-) electrical charge assists repulsion of (-) proteins • Podocyte • Filtration slits b/w feet w/additional slits prevent macromolecule escape

  11. Kidney Physiology (overview) • Steps • Cell and protein free blood into tubules/collecting duct (1) • Vasa recta reclaims needs and excretes rest • All glucose, AA’s, salt, and 99% H2O (2) • Selective addition of other molecules (3) • Terminology • Filtrate is everything in blood, but protein • Urine is metabolic waste & excess substances

  12. Glomerular Filtration (1) • More efficient than other capillaries • High permeability and SA of glomerulus • Glomerular BP higher • Higher net filtration pressure (NFP) • H2O, glucose, AA’s, & nitrogenous waste diffuse • Similar composition of filtrate & blood • Large proteins prevented • Maintain colloid pressure • Prevent all H2O loss from blood • Proteins in blood = imbalance

  13. Net Filtration Pressure (1) • Review chpt 19 • Hydrostatic pressure, fluid force on wall • Filters fluids from cells and proteins • Colloid osmotic pressure • Nondiffusible molecules encourage osmosis • Determines filtrate formation (glomerulus) • Glomerular hydrostatic pressure pushes H2O out into intercapsular space • Colloid osmotic pressure of glomerular blood and capsular hydrostatic pressure opposes • NFP = HPg – (OPg + HPc)

  14. Glomerular Filtration Rate (GFR) (1) • Volume of filtrate made/min (~ 120 -125 ml/min) • Regulation • SA for filtration • Filtration membrane permeability • NFP • Directly proportional to NFP

  15. Intrinsic Regulation of GFR (1) • Myogenic mechanism (JG cells monitor) • Up systemic BP vasoconstrictaff. art.  down flow to glomerulus • Decreased GFR protects glomerulus • Down systemic BP reverses • Tubuloglomerular feedback mechanism (macula densa monitor) • GFR up = insufficent reabsorption = high NaCl vasoconstrictaff. art. = down flow to glomerulus • NFP and GFR down to allow time for filtration • Low NaCl reverses • Adaptable except low BP (< 80 mm Hg) = stops

  16. Extrinsic Regulation of GFR (1) • SNS maintain systemic BP • NE w/ stress vasoconstrictaff. art.  down filtrate formation • Stimulates macula densa and JG cells • Renin – angiotensin mechanism restores blood volume and BP • Renin converts angiotensinogen toangiotensin I • Renin w/ down stretch, activation by macula densa, and Epi receptor stimulation • Angiotensin I to angiotensin II • MAP up (vasoconstriction) • Increase Na+ reabsorbed by PCT • Adrenal cortex release aldosterone

  17. Tubular Reabsorption (2) • All glucose and AA’s • H2O and ions dependent on hormones • Can be active or passive • Transcellular route though renal tubule cells • Lumen and basement membrane  peritubular capillaries • Paracellular route between renal tubule cells • Tight junctions hinder, but in PCT (Ca2+, Mg2+, K+, & Na+)

  18. Na+ Reabsorption(2) • Primary cation in filtrate moved actively • 1° active transport: • Na+-K+ ATPase pumps Na+ into interstitial fluid • Low HP and high OP (undiffusible proteins) into capillaries • 2° active transport • From (-) electrochemical gradient primary set up • Na+ low inside and K+ rapidly leak out • Na+ passively into cells (facilitated diffusion) • Cotransport of glucose, AA’s, lactic acid ,and vitamins

  19. More Reabsorption(2) • Passive tubular transport from 1° and 2° active transport • Aquaporins • Responsible for obligatory H2O reabsorption in PCT • Absent in collecting ducts w/o ADH • Up [solute] in filtrate  solutes diffuse out • Lipid soluble toxins and drugs also • (-) electrochemical gradient  anions diffuse out • Transport maximum (Tm) reflects number of carriers present • Relative to need for molecule • At saturation excess molecules excreted • Diabetes mellitus has increase [glucose] in urine

  20. Renal Tubular Activity (2) • PCT (previously) most active • Loop of Henle • Descending H2O in, but no ascend [aquaporins] • Solutes opposite • Role in dilute vs concentrated urine • DCT • Depends on body needs • ADH adds aquaporins = H2O reabsorption up • Aldosterone (renin-angiotensin) up Na+ reabsorption • H2O follows = BP increase • ANP encourages Na + loss • W/ high atrial pressure to drop blood volume and pressure

  21. Diuretics (2) • Chemicals enhancing urine output • Substances nor reabsorbed • Substances exceeding renal tubules ability to reabsorb • Substances inhibiting Na+ reabsorption • Alcohol inhibits ADH (H2O reabsorption) • Caffeine, drugs, and other Na+ reabsorption inhibitors • Stop obligatory H2O reabsorption

  22. Tubular Secretion (3) • Reabsorption in reverse • PCT mainly, but cortical collecting ducts too • Functions • Eliminate drug bound proteins (not filtered) • Eliminate urea and uric acid (protein metabolism) • Eliminate excess K+ ions • Control blood pH • Up acidity = excess H+ in urine and HCO3- reabsorbed • Down acidity = HCO3- in urine and Cl- reabsorbed

  23. Ureters • Two tubes containing a tri-layered wall • Transitional epi. mucosa (kidney pelvis and bladder too) • Inner longitudinal & outer circular smooth muscle • 3rd external longitudinal layer in lower 1/3 • Fibrous CT adventitia • Urine transport through peristalsis • Stretch signal more than neural • Imbalances • Renal calculi (kidney stones) from Ca2+, Mg2+, or uric acid salts precipitating • Bacterial infections, urine retention, high ion levels, and alkaline pH predispose • Cranberry juice acidifies and H2O dilutes

  24. Urinary Bladder • Ureteral and urethral orifices form trigone • Common site of infections • Similar tri-layer wall as ureters • Middle layer resemble lower 1/3 ureter = detrusor muscle • Walls w/ rugae for distension

  25. Urethra • Trans.  pseudostrat. colum.  strat. sqam. • Internal urethral sphincter @ junction w/ bladder • Contraction opens • External urethral sphincter @ urogenital diphragm • Levatorani assists • External urethral orifice • Males w/ 3 regions • Prostatic, membranous, and spongy • Imbalances • Dysuria (painful urination) • Indicators: up urgency, frequency, and/or presence of blood • UTI’s from bacterial infections • Females predisposed b/c location, intercourse, wiping • Can cause urethritis, cystitis, pyelitis , inflammation of urethra, bladder, or kidney

  26. Urine Characteristics • Color and turbidity • Yellow shades from urochrome, product of Hb breakdown • Higher concentration is darker yellow • Abnormal colors from foods, bile pigments, or blood • Cloudiness could indicate UTI • Odor • Fresh is aromatic, but standing more ammonia b/c bacterial activity • Drugs, vegetables (asparagus & onions), & diseases can alter • pH • Usually ~ 6 • Down w/ acidic diet (high protein, whole wheat) • Up w/ vegetarian diet, prolonged vomiting, and infection • Specific gravity, ratio of urine to dH2O • Higher than 1.0 b/c H2O + solutes • [solutes] determines, 1.001 – 1.035 is normal

  27. Chemical Composition of Urine • 95% water • 5% solutes • Nitrogenous wastes • Urea, uric acid, and creatinine (AA, nucleic acid, & CP breakdown respectively) • Na+, K+, Ca2+, Mg2+, HCO3- also • Abnormal amounts, protein, or WBC presence indicates disease/imbalance

  28. Micturition (Urination) • Voiding of bladder • Distension of bladder walls initiates spinal reflex • Contraction of external urethral sphincter • Inhibit detrusor muscle and internal sphincter (temporarily) • Reflexive control till ~ 2 or 3 years of age (pons) • Incontinence when can’t control • Laughing and coughing up abdominal pressure • Pregnancy stretches muscles • Urinary retention when can’t go • Common after anesthesia or w/ prostate enlargement

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