
## Summary
<ul>
  <li>Histamine is stored in most tissues and metabolised in the liver by histaminase</li>
  <ul>
    <li>Excreted in urine</li>
  </ul>
  <li>
    Histamine modulates the inflammatory response, particularly type I hypersensitivity reactions
  </li>
  <li>Mast cells contain histamine and release it in hypersensitivity reactions</li>
  <li>IgE mediates allergen-induced hypersensitivity</li>
  <li>Histamine is also a neurotransmitter&nbsp;</li>
  <ul>
    <li>There are three common G-protein coupled receptors for histamine</li>
    <li>H1 receptors are found in bronchial muscle and in the CNS</li>
    <ul>
      <li>Activation of phospholipase C</li>
      <li>Affinity with cetirizine</li>
      <li>Activation increases intracellular calcium</li>
      <li>Increased vascular permeability</li>
      <li>Arteriolar dilatation</li>
      <li>Smooth muscle contraction</li>
      <li>Bronchospasm</li>
      <li>CNS arousal</li>
      <li>Note: H1 receptors mediate the type I hypersensitivity reaction</li>
    </ul>
    <li>H2 receptors are found in the stomach, heart and uterus</li>
    <ul>
      <li>Affinity with cimetidine</li>
      <li>Activations stimulates adenyl cyclase and a second messenger cascade, increases cAMP</li>
      <li>Increased pepsin and gastric acid secretion</li>
      <li>Increased myocardial stroke volume (positive chronotrope too)</li>
    </ul>
    <li>H3 receptors: expressed in CNS and mediate neurotransmitter release.</li>
  </ul>
</ul>

## Antihistamines
<ul>
  <li>H1 antihistamines</li>
  <ul>
    <li>Prevent bronchial smooth muscle contraction and vascular permeability in these tissues</li>
    <li>Antiemetic effect on CNS tissue</li>
    <li>Sedative</li>
    <li>Anticholinergic&nbsp;</li>
    <li>
      <span className="font-semibold">Olopatadine</span>: selective H1-receptor antagonist (rapid onset) and inhibitor of
      mast cell degranulation (and prolonged duration of action)
    </li>
  </ul>
  <li>H2 antihistamines</li>
  <ul>
    <li>Decrease gastric acid secretion</li>
    <li>Inhibit cytochrome p450: decrease metabolism of some drugs</li>
  </ul>
</ul>


Summary Histamine is stored in most tissues and metabolised in the liver by histaminase Excreted in urine Histamine modulates the inflammatory response,…

Pharmacology

Histamine

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

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance