Topic 40 - Basic physiological functions of the kidney: filtration, reabsorption, secretion, excretion Flashcards

1
Q

Words to include in filtration

A
  • Permability of the barriers
  • Capillary Filtration Coefficient (CFOC)
    • Ultrafiltration
    • Renal glomerulus
    • Lamina densa of the basal membrane
      • Negatively charged
    • Mesangial cells containing myogen elements
      • Size of filtrating surface
  • Effective filtration pressure (EFP)
    • Ultrafiltration
    • Pressure gradient
    • Ratio:
      • Hydrostatic blood pressure
      • Tissue pressure
      • Colloid osmotic pressure
    • Components of EFP:
      • Hydrostatic pressure of the glomerulus (GP)
      • Bowman-sheath’s pressure (CP)
      • Colloid-osmotic pressure of the plasma (GCP)
    • EPF = GP - (CP + GCP)
    • Oncotic pressure
    • Vas eferent
    • Vas afferent
    • Protein concentration

Anatomic basis of glomerular filtration

  • Filtration barrier layers
    • Fenestrated endothelium
    • Glomerular basement membrane (GBM)
    • Podocyte foot processes (outermost)
  • Size-selective filter
  • Plasma macromolecules
    • Negatively charge molecules (filtered in smaller amounts)
    • Negative < neutral < positive
  • Type IV collagen
  • Nidogen
  • Laminin
  • Proteoglycan (glycosaminoglycans)
    • Negative charge
    • Anion filtration barrier
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2
Q

Words to include in reabsorption

A
  • 90% of filtrated amount is reabsorbed
  • Pathways of the reabsorption of the ultrafiltrate
    • Paracellular
    • Transcellular
  • Reabsorption maximum (Tm)
    • Tm (Transfer Maximum)
      • Upper limit of reabsorption
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3
Q

Words to include in secretion

A
  • Directly from the blood vessel
  • Plasma
  • Glomerulus
  • Efferent arteriole
  • Tubular lumen
  • Peritubular capillaries
  • Can occur:
    • Transcellular
    • Paracellular
  • Nephrons
  • Secreting maximum
  • Active cellular work
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4
Q

Words to include in excretion

A
  • Result of:
    • Filtration
    • Reabsorption
    • Secretion
  • End of tubular system
  • Secondary filtrate of urine
  • Rate of excretion = urine of seleced material excreted
  • Filtration + secretion = excretion

Autoregulation of renal circulation

  • Independent of blood pressure (midpressure)
    • Autoregulation of renal perfusion
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5
Q

Filtration

A
  • The rate of filtration is determined by:
    • Effective Filtration Pressure (EFP)
    • Permability of the barriers
  • Proteins are not filtrated
  1. Capillary filtration coefficient
    • ​​The degree of ultrafiltration taking place in the renal glomerulus is a hundred times higher than in any other capillary areas
    • Most important factor: lamina densa of the basal membrane
      • ​Negatively charged
    • The size of the filtrating surface is regulated by the mesangial cells containing myogen elements
    • Total filtration: 180-200 liter/100 kg bwt/day
  2. Effective Filtration Pressure (EFP)
    • ​The extent of ultrafiltration depends on the pressure gradient
    • Depends on the ratio of:
      • Hydrostatic blood pressure
      • Tissue pressure
      • Colloid osmotic pressure
    • Components of EFP:
      • Hydrostatic pressure of the glomerulus (GP)
      • Bowman-Sheath’s pressure (CP)
      • Colloid-osmotic pressure of the plasma (GCP)
    • EFP = GP - (CP + GCP)
    • The oncotic pressure increases in the direction of the vas efferent, as the protein content increases due to ultrafiltration

Anatomic basis of glomerular filtration

  • The filtration barrier consists of three layers:
    1. Fenestrated epithelium
    2. Glomerular basement membrane (GBM)
    3. Outermost epithelial podocyte foot processes
  • Behaves as a size-selective filter that restricts the passage of plasma macromolecules based on their size, shape, and charge
  • Negatively charged molecules are filtered in smaller amounts than neutral molecules of comparable size, and the traversal of positively charged molecules is actually facilitated.
    • Negative < neutral < positive
  • Molecular scaffold:
    • Independent structural networks of type IV collagen and laminin
    • Linked through nidogen
    • The role of negatively charged proteoglycans (glycosaminoglycans) is to serve as an anionic filtration barrier
    • The GBM therefore can restrict the traversal of large plasma proteins
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6
Q

Give the valuse for the vas afferent and vas efferent occuring in effective filtration pressure

A
  • Vas afferent:
    • GP: 60 mmHg
    • CP: 20 mmHg
    • GCP: 28 mmHg
    • EFP: 12 mmHg
  • Vas efferent:
    • GP: 60 mmHg
    • CP: 20 mmHg
    • GCP: 36 mmHg
    • EFP: 4 mmHg
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7
Q

Reabsorption

A
  • The extremely large filtration rate could mean a fatal loss of fluid, if it appeared in full amount in the urine
    • Only a small fraction of it (0,5-1%) becomes urine, made possible by reabsorption
  • More than 90% of the filtrated amount is reabsorbed
  • Two main pathways for the reabsorption of the ultrafiltrate:
    • Paracellular
    • Transcellular
  • Reabsorption maximum (Tm):
    • Tm (Transfer maximum)is theupper limit of reabsorption
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8
Q

Secretion

A
  • Some substances are either secreted:
    • after filtration and reabsorption
    • Directly from the blood vessel
  • Secretion: From the plasma leaving the glomerulus through the efferent arteriole further substances can get into the tubular lumen at the site of the peritubular capillaries
  • Can occur:
    • Transcellular
    • Paracellular
  • Above certain plasma concentration, the secretion becomes constant
  • All of the nephrons participating in secretion reaches the secreting maximum
  • Proves that the secretion is a active cellular work
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9
Q

Excretion

A
  • As a result of the filtration, reabsorption and secretion by the end of the tubular system the secondary filtrate of urine is formed
  • Rate of excretion = the urine or selected material excreted
  • Average excretion rate of urine is 2-3 ml/min/100 kg bodyweight
  • Filtration + secretion = excretion
  • Phases of excretion:
    1. ​Linear phase
    2. SDL phase (Self depression limit)
    3. Saturation phase
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10
Q

Figure to draw in the essay

A
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