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Urinary System

Urinary System. An overview. Functions of the Urinary System. Functions of the Urinary System. Produces, excretes urine Essential for homeostasis Keeps volume of bodily fluids constant Keeps levels of essential chemicals constant Electrolytes, water, acid/base balance

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Urinary System

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  1. Urinary System An overview

  2. Functions of the Urinary System

  3. Functions of the Urinary System • Produces, excretes urine • Essential for homeostasis • Keeps volume of bodily fluids constant • Keeps levels of essential chemicals constant • Electrolytes, water, acid/base balance • “Clears” (cleans) blood of waste products produced by cellular metabolism (e.g. nitrogenous wastes) • Uremia- toxic buildup of metabolic wastes • Blood pressure regulation

  4. Characteristics of Urine

  5. Structures of the urinary system (Macroscopic)

  6. Major structures of the urinary system • Kidney • Retroperitoneal • Ureters • Urinary Bladder • Urethra

  7. Urinary Bladder • Accumulates, stores urine • Stretchable epithelium, w/ smooth muscle (detrusor) • Internal urinary sphincter • Involuntary, circular muscle • Keeps ureter closed • Can hold up to 1 liter of urine • Stretch receptors signal need to void (micturate) when 20% of bladder capacity reached

  8. Urethra • Single, muscular tube • Controlled by external urethral sphincter • Voluntary • Longer in males • More prone to infection in females

  9. Voiding • Urination = micturition • Innervated by reflex arc; voluntary control gained as one ages • Incontinence – loss of voluntary control • Anuria – lack of urine production • Urinary retention – failure to expel urine • Oliguria – decreased urine production • Polyuria – excessive urine production

  10. The Kidney • Renal cortex – Outer “bark” • Renal medulla – Inner • Renal pyramids • Triangular divisions • Renal columns – • Extension of cortex • Divide pyramids • Renal papilla • Narrow, innermost point of a pyramid • Renal pelvis • Expanded end of upper end of ureter • Calyx • Division of renal pelvis

  11. Microscopic Structure of the Kidney

  12. Microscopic Structure of the Kidney

  13. Functional Unit: Nephron • > 1 million in a kidney • Can be cortical (most) or juxtamedullary • “Tiny funnel” with a very long stem • Highly convoluted (many bends) • 2 principal components: • Renal corpuscle • Renal tubule

  14. Renal corpuscle components • Bowman’s capsule • Cup/sac-like-shaped top of a nephron • Glomerulus • Ball of capillaries, lined with podocytes • Found in Bowman’s capsule • Afferent, efferent arterioles

  15. Renal Tubule • Composed of: • Proximal convoluted tubule (PCT) • Loop of Henle (longer in Juxtamedullary) • Distal convoluted tubule (DCT) • Collecting tubule

  16. Formation of Urine

  17. Formation of Urine: Overview • Filtration • Secretion • Reabsorption • All occur within the functional unit of the kidney, the nephron

  18. Filtration • Of water, dissolved substances out of blood into Bowman’s capsule • Occurs in “renal corpuscles” • Contains larger afferent, smaller efferent arterioles • Creates high pressure in glomerulus • Filters blood across fenestrated capillaries, lined w/ podocytes • Hold in proteins, cells • Lose water, ions = ultrafiltration

  19. Glomerular Filtration Rate • 120 ml/minute = 180 liters/day! • Must maintain a minimum blood pressure for kidneys to filter • Hemorrhage, etc., can cause kidney function (and urine output) to cease

  20. 180 L of urine a day? • No… • Luckily, most of the fluid that leaves blood during filtration returns to the blood during reabsorption…

  21. Reabsorption • Movement of substances out of renal tubules into the blood (into peritubular capillaries) • Water • Glucose • Other nutrients • Sodium, other ions • Begins in proximal convoluted tubule, continues in loop of Henle, distal convoluted tubule, and collecting tubule • Reabsorb ~178 L/day (97-98% of water)

  22. Mechanism? Several… • Active transport • Active transport of sodium ions from tubule into interstitial fluid • Passive Transport • Creates high concentration of sodium, which diffuses into bloodstream • Sodium (Na+) in blood attracts negative ions (Cl-, (PO4)3-), which diffuse into blood

  23. Another Mechanism? Osmosis! (Flow of water from High to Low) • Attracted to blood due to ion flow

  24. Another, another Mechanism? Facilitated Diffusion • Amino acids • Glucose • Cotransported/symported with sodium • Almost all glucose reabsorbed (340 mg/min) • Exceptions exist! • Diabetes mellitus – too much sugar in bloodstream, exceeds ability of kidney tubule cells to reabsorb (not enough Na+ to cotransport) • glycosuria (glucose in blood) • Water is lost along with glucose transport… most people with diabetes mellitus urinate excessively!

  25. Loop of Henle • Descending loop: • Reabsorbs water (20%), large ions and molecules • Ascending loop: • Active transport of Na, Cl ions

  26. Water reabsorption • 90% passive thru osmosis in PCT, descending Loop of Henle, DCT • 10% occurs in last parts of DCT, collecting ducts

  27. Secretion • Substances move into urine in distal, collecting tubules from blood in capillaries around tubules • “Reabsorption in reverse” • Urea, H+, K+ ions, ammonia, drugs • (Bold = active transport; non-bold = diffusion)

  28. Regulation of Urine Formation

  29. Regulation • Regulated by hormones • Antidiuretic hormone (ADH) – increases water reabsorption from collecting duct into bloodstream • Angiotensin II – constricts efferent, systemic arterioles – alters filtration rate, increases pressures • Aldosterone – Produced by adrenal cortex; retains sodium, excretes potassium – raises blood pressure by incr. water absorption in DCT, Collecting duct • Affected by other substances • Diuretic (causes great outflow of urine) • Caffeine –decreases Na+ absorption, causing diuresis • Lasix – works on Loop of Henle, producing massive diuresis

  30. Concentration

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