

## Platelets
<ul>
  <li>4 layered</li>
  <li>Peripheral zone:</li>
  <ul>
    <li>Rich in glycoproteins and platelet factor 3 for adhesion and aggregation</li>
  </ul>
  <li>Sol-gel zone</li>
  <ul>
    <li>Microtubules and microfilaments to maintain discoid shape</li>
  </ul>
  <li>Organelle zone</li>
  <ul>
    <li>
      Alpha granules and others containing mediators of clotting (factor VIII related antigen,
      factor V, fibrinogen, fibronectin, platelet-derived growth factor, chemotactics)
    </li>
  </ul>
  <li>Inner membrane zone</li>
  <ul>
    <li>Dense tubular system for contractility and prostaglandin synthesis</li>
  </ul>
</ul>

## Thrombosis
<ul>
  <li>
    Endothelial collagen and fibrin exposure leads to platelet adhesion to endothelium via
    glycocalyx signalling
  </li>
  <li>
    Calcium is released from platelets dense tubular system leading to their{' '}
    <strong>degranulation </strong>(releasing factor V and fibrinogen which form thrombin via the
    coagulation cascade)
  </li>
  <li>Aggregation is stimulated by ADP and thrombin: platelets form a clump</li>
  <ul>
    <li>Note: aggregation is stimulated by thromboxane A2 and inhibited by prostaglandin I2.</li>
  </ul>
  <li>Inhibition of thrombosis:</li>
  <ul>
    <li>Protein C: vitamin-K dependent inhibitor of factors Va and VIIIa.</li>
  </ul>
</ul>
<ClinicalCorrelate>
  <>
    <p>Diseases of protein C function</p>
<div>
    <ul>
      <li>Protein C deficiency is autosomal dominant trait</li>
      <li>
        Factor V Leiden leads to resistance of factor V to activated protein C (may contribute to
        12% of patients with CRVO)
      </li>
    </ul>
    <ul>
      <li>Protein S and phospholipid are cofactors in factor Va and VIIIa deactivation.</li>
      <ul>
        <li>Protein S deficiency is autosomal dominant</li>
      </ul>
      <li>Antithrombin III inhibits numerous activated coagulation factors</li>
    </ul>
    <ul>
      <li>Thrombi may:</li>
      <ul>
        <li>Break and form emboli</li>
        <li>Be lysed by plasmin</li>
        <li>
          Persist and organise (flow may be re-established by collateralisation/recanalisation)
        </li>
      </ul>
    </ul>
</div>
  </>
</ClinicalCorrelate>

## Retinal emboli
<ul>
  <li>Most commonly originate from an atheromatous plaque at the carotid bifurcation</li>
  <li>Cholesterol (Hollenhorst plaque)</li>
  <li>Calcium: tend to cause more extensive pathology: BRAO, CRAOs</li>
  <li>Platelets: fibrin-platelet emboli cause TIAs</li>
  <li>Bacteria/vegetations: infective endocarditis</li>
</ul>

## Atherosclerosis
<ul>
  <li>Endothelial damage</li>
  <li>Platelet adherence to injured endothelium</li>
  <li>Intimal smooth muscle proliferation in response to platelet-derived growth factor</li>
  <li>
    Lipid accumulation intra- (macrophages become foam cells) and extracellularly (lipid within the
    arterial wall)
  </li>
</ul>


Platelets 4 layered Peripheral zone: Rich in glycoproteins and platelet factor 3 for adhesion and aggregation Sol-gel zone Microtubules and microfilaments…

Pathology

Thrombosis / Atherosclerosis

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

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Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

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Endocytosis

Glycosaminoglycans

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Eye Movements

Accomodation

Vision

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Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Cell Growth

Neoplasia

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Nystagmus

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Immunology

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Genetics

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Mitosis

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Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance