Introduction to excretory  system
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Introduction to excretory system

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Introduction to excretory  system Introduction to excretory system Presentation Transcript

  • INTRODUCTION TO EXCRETORY SYSTEM Dr.U.Rathnakumari MBBS., MD Physiology I yr PG
  • Gross Anatomy of the Kidney
  • Major Functions of the Kidneys
    • 1. Regulation of HOMEOSTASIS:
    • body fluid osmolarity and volume
    • electrolyte balance
    • acid-base balance
    • blood pressure
    • 2. EXCRETION of
    • metabolic products
    • toxic substances (drugs,pesticides, etc.)
    • excess substance (water, etc)
    • 3. SECRETION of :
    • Erythropoietin
    • 1,25-dihydroxy cholecalciferol
    • vitamin D3 (vitamin D activation)
    • Renin
    • prostaglandin
  • Physiological Anatomy of the Kidney
  • Nephron
    • The functional unit of the kidney
    • Each kidney is made up of about 1 million nephrons
    • Each nephron has two major components:
    • A glomerulus ( a tuft of capillaries )
    • A long tube (tubule)
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  •  
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  • The juxtaglomerular apparatus
    • Where the distal tubule lies against the afferent (sometimes efferent) arteriole
    • Arteriole walls have juxtaglomerular (JG) cells
      • Enlarged, smooth muscle cells
      • Have secretory granules containing RENIN
      • Act as mechanoreceptors
    • Macula densa
      • Tall, closely packed distal tubule cells
      • Lie adjacent to JG cells
      • Function as chemoreceptors or osmoreceptors
    • Mesanglial cells:
      • Have phagocytic and contractile properties
      • Influence capillary filtration
  •  
  • Renin Angiotensin system
  • Renal Tubule
    • Proximal convoluted tubule (PCT)
    • cuboidal cells with numerous microvilli and mitochondria
    • Reabsorbs water and solutes from filtrate and secretes substances into it
    • Loop of Henle – a hairpin-shaped loop of the renal tubule
      • Proximal part is similar to the proximal convoluted tubule
      • followed by the thin segment (simple squamous cells) and the thick segment (cuboidal to columnar cells)
  •  
    • Distal convoluted tubule (DCT)
    • cuboidal cells without microvilli that function more in secretion than reabsorption
    • Collecting Tubules
    • Two important cell types are found here
      • Intercalated cells
        • Cuboidal cells with microvilli
        • Maintainin acid-base balance of the body
      • Principal cells
        • Cuboidal cells without microvilli
        • maintain the body’s water and salt balance
  • Types of nephrons
    • Cortical nephrons – 85% of nephrons; located in the cortex
    • Juxtamedullary nephrons:
      • Are located at the cortex-medulla junction
      • Have loops of Henle that deeply invade the medulla
      • Have extensive thin segments
      • Are involved in the production of concentrated urine
  •  
  • renal blood flow
  • Characteristics of renal blood flow
    • high blood flow .
    • 1200 ml/min, or 21 percent of the cardiac output.
    • 94% to the cortex
    • Two capillary beds
    • High hydrostatic pressure in glomerular capillary (about 60 mmHg) and low hydrostatic pressure in peritubular capillaries (about 13 mmHg)
  • Capillary Beds
    • Vasa recta – long, straight efferent arterioles of juxtamedullary nephrons
  • Functions of the Nephron
          • Filtration
          • Reabsorbtion
          • Secretion
          • Excretion
  • Glomerular filtration
    • First step in urine formation
      • Bulk transport of fluid from blood to kidney tubule
        • Isosmotic filtrate
        • Blood cells and proteins don’t filter
      • Result of hydrostatic pressure
      • GFR = 180 L/day
  • filtration membrane
  • filtration membrane
    • Filter that lies between the blood and the interior of the glomerular capsule
    • It is composed of three layers
      • Fenestrated endothelium of the glomerular capillaries
      • Visceral membrane of the glomerular capsule (podocytes)
      • Basement membrane composed of fused basal laminae of the other layers
  • filtration membrane
  • Glomerular filtration rate (GFR)
    • Amount of filtrate produced in the kidneys each minute. 125mL/min = 180L/day
    • Factors that alter filtration pressure change GFR. These include:
      • Increased renal blood flow -- Increased GFR
      • Decreased plasma protein -- Increased GFR. Causes edema.
      • Hemorrhage -- Decreased capillary BP -- Decreased GFR
  • Tubular Reabsorbtion
      • Process of returning filtered material to bloodstream
      • 99% of what is filtered
      • May involve transport protein(s)
      • Normally glucose is totally reabsorbed
  • Tubular Secretion
      • Material added to lumen of kidney from blood
      • Active transport (usually) of toxins and foreign substances, drugs etc
        • Saccharine
        • Penicillin
  • Mechanisms of Urine Formation
    • involves three major processes
      • Glomerular filtration
      • Tubular reabsorption
      • Secretion
  • QUESTIONS
    • What are the parts of the excretory system?
    • 2 . name the functions of the kidneys.
    • 3.How is the kidney related to hematopoiesis?
    • 4.How does the kidney regulate blood calcium level?
    • 5.What is the total no .of nephrons in the human body?
    • 6.What are the types of nephrons you know?
    • 7.What is a renal corpuscle?
    • name its parts.
    • 8.Describe the epithelium of PCT.
    • 9.Name the parts of JGA- The juxtaglomerular apparatus.
    • 10.Define GFR. what is its normal value?
    • 11.What is the normal volume of urine excreted in one day?
    • what is ‘POLKISSEN’?
  •