Cards (29)

  • What are the five major stages of urine formation?
    1. Glomerulus: filtration of blood
    2. Proximal tubule: reabsorption of filtrate; secretion into tubule
    3. Loop of Henle: concentration of urine
    4. Distal tubule: modification of urine
    5. Collecting duct: final modification
  • What are the 3 major functions of the nephron?
    1. Filtration: of blood to produce a filtrate
    2. Reabsorption: of water, ions and organic nutrients from filtrate
    3. Secretion: of waste products into tubular fluid
  • What are the characteristics of Filtration as a basic renal process?
    in glomerulus
    force for filtration:
    • blood pressure
    • different diameter of afferent and efferent arterioles
    Glomerular Filration Rate (GFR): rate at which glomerular filtrate is produced
    Can be measured clinically and used as an indicator of renal function
  • How does glomerular filtration work?
    Filtrate passes through:
    1. Pores in glomerular capillary endothelium
    2. Basement membrane of Bowman's capsule
    3. Epithelial cells of Bowman's capsule (podocytes) via filtration slits into capsular space
  • What are the forces acting on glomerular filtration?
    Push fluid out of glomerulus:
    • PGC: glomerular capillary hydrostatic pressure
    • πBS: Bowman's space oncotic pressure (almost 0)
    Oppose ultrafiltration:
    • PBS: Bowman's space hydrostatic pressure
    • πGC: Glomerular capillary oncotic pressure
  • By the end of the glomerular capillary, Net filtration pressure reduced to almost 0.
  • GFR generally remains constant even when systemic BP changes.
  • Why does GFR generally remain constant even when systemic BP changes?
    autoregulation of renal blood flow
  • What is Autoregulation of Renal Blood Flow (RBF)?

    local effect (not neuronal/hormonal)
    Two hypotheses:
    • Myogenic: due to response of renal arterioles stretch (Starling's law)
    • Metabolic: renal metabolites modulate arteriolar contraction, eg adenosine, NO
  • What does GFR depend on?
    diameters of afferent and efferent arterioles
    Eg:
    • Afferent artery dilates, efferent artery constricts: increased GFR
    • eg via Prostaglandins, ANP, dopamine, NO, kinins
    • Afferent artery constricts, efferent artery dilates: decreased GFR
    • eg via Noradrenaline, endothelin, adenosine
  • How can changes in GFR alter systemic blood pressure?
    drop in filtration pressure → drop in GFRless Na enters proximal tubule → mascula densa senses the change → stimulate juxtaglomerular cells → release RENINangiotensin II (vasoconstrictor) → increased BPincreased filtration pressure → normal GFR
  • What happens in the proximal tubule?
    reabsorption
  • What is the driving force for reabsorption in proximal tubule?
    Na / K ATPase
  • What does the brush border allow?
    more surface area for reabsorption
  • How is the Na concentration of peritubular cells?
    low
    due to Na/K ATPase pumping Na out
  • How is the charge of PT cells overall?
    negative
    due to presence of intracellular proteins
  • How does reabsorption occur in the PT?
    Na/K ATPase → Na pumped into capillarylow Na conc in cell → Na diffuses into PT cell from lumenCl follows Na → water follows through aquaporin channels (AQP)
  • How does the transcellular flow of water occur?
    through aquaporins (AQPS) in cell membrane
  • What are the 4 major renal AQPs?
    AQP-1 : proximal tubule
    AQP-2 : collecting duct, expression controlled by ADH
    AQP-3&4 : basolateral surface of tubular cells
  • How does glucose reabsorption from PT occur?
    co-transported with Na
  • What does glucose reabsorption in PT occur through?
    two systems:
    S1 (PCT):
    • into PCT cells: SGLT2
    • out of PCT cells (into blood): GLUT2
    S3 (proximal straight tubule PST):
    • into PST cells: SGLT1
    • out of PST cells into blood: GLUT1
  • Glucose is co-transported into PT cell with Na very efficiently so very little is excreted.
  • How can glucose be present in urine in diabetics?
    glucose transporters become saturated
    so some glucose can't be reabsorbed and escapes into urine
  • What does Tm mean in the glucose titration curve?
    maximum transport capacity of glucose (transport maxima)
    urinary excretion of glucose indicates diabetes
  • How do SGLT2 inhibitors work in diabetes and what are some examples?
    inhibit SGLT2 transporters so glucose isn't reabsorbed into blood
    excreted in urine
    leading to overall hypoglycaemic effect
    examples: Flozins (dapagliflozin, canagliflozin, empagliflozin)
  • What is a major side effect of SGLT2 inhibitors?
    increased risk of developing UTIs
    as glucose in urine
    bacteria use glucose for growth
  • How does protein reabsorption from PT occur?
    pinocytosis (independent of Na)
    vesicle → cell → degraded by lysosomesamino acids returned to blood
    low Tm
    proteinuria: sign of glomerular damage and impending renal failure
  • What is secretion?
    pushing substances from peritubular capillaries into the PT
    two kinds of pumps:
    • for organic acids (eg uric acid, diuretics, antibiotics)
    • for organic bases (eg creatinine, procainamide)
  • What is PAH?
    para-amino hippurate
    secreted into PT from blood
    used as a tool to measure tubular secretion