Anatomy of the Cornea
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Anatomy of the Cornea

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Questions and Answers

What is the main substrate for glucose metabolism in the cornea?

  • Glucose (correct)
  • Fatty acids
  • Amino acids
  • Glycogen
  • What is the byproduct of anaerobic oxidation of glucose in the cornea?

  • CO2 and Water
  • Pyruvate and ATP
  • Lactic acid and ATP (correct)
  • Ethanol and ATP
  • What is the location of the necessary enzymes for aerobic oxidation of glucose in the cornea?

  • Epithelium only
  • Stroma only
  • Endothelium only
  • Mitochondria of epithelium, endothelium, and keratocytes (correct)
  • What is the primary function of the pentose phosphate pathway in the cornea?

    <p>Biosynthesis of macromolecules</p> Signup and view all the answers

    What is the primary factor influencing diffusion of oxygen, water, and nutrients across the cornea?

    <p>Corneal permeability</p> Signup and view all the answers

    What is the mechanism of passive permeability in the cornea?

    <p>Diffusion through intercellular pores</p> Signup and view all the answers

    What is the primary function of the endothelial sodium pump in the cornea?

    <p>Regulation of corneal hydration</p> Signup and view all the answers

    What is the characteristic of the normal cornea?

    <p>Avascular</p> Signup and view all the answers

    What is the mechanism of corneal sensitivity?

    <p>Free nerve endings</p> Signup and view all the answers

    What is the characteristic of corneal sensitivity in the horizontal meridian?

    <p>More sensitive than the vertical meridian</p> Signup and view all the answers

    Study Notes

    The Cornea

    • The cornea is the anterior 1/6 of the outer coat, acting as a covering lens, and is avascular and transparent.

    Biochemistry

    • Epithelium:
      • High activities of enzymes of glycolysis, Kreb's cycle, and ATPase pump.
      • High concentration of acetyl choline and choline esterases.
    • Stroma:
      • Low enzymatic activity.
      • Collagen fibrils and glycosaminoglycans occupy the interfibrillar space.
      • Fibrils prevent scattering of light, and swelling of fibrils increases light scatter with a hazy appearance of the cornea.

    Glucose

    • Main substrate.
    • Stored glycogen in epithelium.
    • Glucose metabolism:
      • Anaerobic oxidation (glycolysis): 1 molecule of glucose gives 2 molecules of lactic acid and 2 ATP.
      • Aerobic oxidation (Kreb's cycle): 1 mole of glucose is burnt into CO2, water, and 38 ATP.

    Pentose (HMP) Shunt

    • Extramitochondrial oxidation of glucose.
    • Energy produced is not stored in ATP, but in NADPH2.
    • Energy is used in biosynthesis.
    • 35% of glucose is oxidized in this shunt.

    Corneal Permeability

    • Influences diffusion of oxygen, water, and nutrients from bathing fluids.
    • Regulates corneal hydration.
    • Determines transport of drugs across the cornea.

    Passive Permeability

    • Diffusion: molecules move across semi-permeable membranes (epithelium or endothelium).
    • Molecules achieve equal concentration on the two sides of the membrane.
    • They pass through intercellular pores.
    • Solubility is more important than molecular size.

    Phase Solubility

    • Fatty phase in the epithelium and endothelium: permeable to fat-soluble substances.
    • Watery phase in the stroma: permeable to water-soluble substances.
    • Biphasic substances (both fat and water soluble) are more permeable.

    Active Mechanism

    • Endothelium sodium pump:
      • (Na-K)ATP-ase enzyme.

    Corneal Vascularisation

    • Normal cornea is avascular.
    • Compactness of stroma prevents vascularization.
    • Stromal edema precedes vascularization.

    Corneal Sensitivity

    • Touch, cold, and pain receptors.
    • Pain receptors are very sensitive, increasing from periphery to center.
    • More sensitive in the horizontal meridian than the vertical.
    • More sensitive in the temporal half than the nasal.

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    Description

    Learn about the structure and functions of the cornea, the outermost layer of the eye. This quiz covers its location, characteristics, and importance in vision.

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