5.24 Urinary System

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susaneers
ID:
53678
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5.24 Urinary System
Updated:
2010-12-07 00:39:40
Tags:
Kidneys Ureters Urinary Bladder Urethra Micturation
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Description:
The Urinary System and its associated organs
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  1. The Urinary System
    Important functions of the kidneys: get rid of nitrogenous waste products (urea, uric acid, creatinine)

    Maintains the chemical consistency of blood

    Filters many liters of fluid from blood

    Sends toxins, metabolic wastes, and excess water out of the body

    Organs: kidneys, ureters, urinary bladder, urethra
  2. Location and External Anatomy of the Kidneys
    Located retroperitoneally (behind the parietal peritoneum)

    Hilium: located on the concave surface, where vessels and nerves enter and exit the kidneys

    • Fibrous capsule surrounds the kidneys
    • - Perirenal fat - external to renal capsulle
    • - Renal fascia - external to perirenal fat

    *ptosis: kidneys droop without fibers and fat to hold it in place
  3. Internal Gross Anatomy of the Kidneys
    • Frontal Section through the kidney
    • - Renal cortex (outer part)
    • - Medulla (inner part, darker brown) contains Renal pyramids
    • - Renal columns: extensions of the cortex, in between pyramids
    • - Renal pelvis: extension of ureters
    • - major calyx branch into minor calyx (both collect urine)
  4. Gross Vasculature of Kidneys
    • Renal arteries branch into segmental arteries
    • Segmental arteries branch into interlobar arteries
    • Interlobar arteries branch into arcuate arteries

  5. Mechanisms of Urine Production
    Filtration: filtrate of blood leaves kidney capillaries (filtrate = water, ions, glucose, amino acids, urea)

    Reabsorption: most nutrients, water, and essential ions reclaimed (~99%)

    Secretion: active process of removing undesirable molecules

    *renal clearance (urine) = filtration - reabsorption + secretion
  6. The Nephron: Renal Corpuscle
    • The functional unit of the kidney (produces urine)
    • Consists of glomerulus and renal tubule

    Blood --(nephron)-->---(minor calyx)-->--(major calyx)-->--(ureter)-->--(bladder)-->--(urethra)-->Urine

    • Glomerulus: tuft of capillaries (capillaries are fenestrated; allows filtering, large proteins stay in blood)
    • Glomerular (Bowman's) Capsule surrounds glomerulus
    • - parietal layer : simple squamous epithelium
    • - visceral layer : consists of podocytes/pedicles that help make it "leaky"

    Renal corpuscle (glomerulus + capsule)
  7. The Nephron: Renal Tubule
    Filtrate proceeds to renal tubules from glomerulus

    • Proximal convoluted tubule: 80% of reabsorption occurs here
    • *Thirst triggers pituitary gland to secrete anti-diuretic hormone to make the PCT more porous, allowing more reabsorption
    • Nephron loop (of Henle): descending limb,thin segment, thick segment
    • Distal convoluted tubule:
    • Collecting ducts: retrieve urine from several nephrons; play an important role in conserving body fluids
    • Classes of Nephron:
    • cortical nephrons: 85% of nephrons
    • juxtamedullary nephrons: 15% of nephrons
  8. Blood Vessels Associated with Nephrons
    • Nephrons associate closely with two capillary beds
    • 1. Glomeruli: produce filtrate that becomes urine; fed and drained by arterioles (afferent and efferent arterioles)
    • *efferent arteriole has smaller diameter than afferent arteriole
    • **generates 1L of fluid every 8min, 99% of which is reabsorbed by tubules

    2. Peritubular capillaries in cortical nephrons or vasa recta in juxtamedullary nephrons
  9. Juxtaglomerular Apparatus
    • Functions in regulating blood pressure
    • Granular cells: modified smooth muscle cells with secretory granules
    • - contain the hormone renin (secreted in response to falling BP in afferent arteriole)

    • Macula densa: end of nephron loop; adjacent to granular cells; tall, closely packed epithelial cells
    • - monitors solute concentration in the filtrate; signals granular cells to secrete renin; initiates renin-angiotensin mechanism
  10. Ureters
    • Carries urine from the kidneys to the urinary bladder
    • Oblique entry into bladder prevents backflow of urine

    • Histology of ureter:
    • Mucosa composed of transitional epithelium
    • Muscularis: two layers; inner longitudinal layer and outer circular layer
    • Adventitia: typical connective tissue
  11. Urinary Bladder
    • -A collapsible muscular sac
    • -Stores and expels urine
    • -Full bladder is spherical; expands into the abdominal cavity
    • -Empty bladder lies entirely within the pelvis
  12. Histology of Bladder
    • Urinary bladder is composed of three layers
    • 1. Mucosa: transitional epithelium
    • 2. Detrusor muscle: thick muscle layer
    • 3. Fibrous adventitia
  13. Urethra
    Thin walled tube that drains urine from the bladder

    Females: 3-4cm

    • Males: 20cm; three regions:
    • 1. prostatic urethra: passes through the prostate gland
    • 2. membranous urethra: through the urogenital diaphragm
    • 3. spongy (penile) urethra: passes through the length of the penis

    • Two sphincter muscles control the outflow of urine from the bladder
    • 1. Internal urethral sphincter: involuntary smooth muscle
    • 2. External urethral sphincter: voluntarily inhibits urination; relaxes when one urinates

    *incontinence: lack of control of external urethral sphincter

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