Biogenic Amines - Histamine and Serotonin Flashcards
Histamine is an essential ______
Essential amino acid
When is histamine derived from?
Histidine
Where is histamine found?
In almost all tissues
What enzyme converts histidine to histamine?
Histidine Decarboxylase
What are the 4 functions of Histamine for NORMAL physiology?
- Tissue growth and regeneration
- Neuromodulation (affects neurotransmission)
- Regulator or microcirculation (smaller vessels)
- Body Defense Mechanisms
Where is histamine STORED?
Mast cells of skin and lungs
Histamine release is part of both a _____ mechanism and a _____ system.
Protective mechanism and a Warning system
What causes histamine to be released following tissue injury?
As part of the inflammatory response to tissue injury, stored histamine is released as part of an ANTIGEN-ANTIBODY interaction
What are the 4 kinds of tissue injuries that would induce histamine release?
- Mechanical (ie scrape)
- Thermal (i.e. burn)
- Radiant (ie sunburn/frost bite)
- Chemical (i.e. acid, drugs, insect venom)
In what 2 ways does histamine serve as a “warning system”?
- Serves to prevent further tissue damage
2. Serves as enhancer of immunological response
What is Histamines MECHANISM OF ACTION
ACTIVATES A RECEPTOR – binds to specific histamine receptors H1 and H2
What are the 4 physiological effects of histamine?
- Vascular
- Neuronal
- Smooth Muscle
- Exocrine secretion
What are the 5 ways in which histamine induces vascular physiological effects?
- Constricts LARGER vessels
- Dilates SMALLER vessels (esp. in head and neck)
- Can cause pooling of blood at injury site
- Causes endothelial cell leakage (edema –> wheal)
- Induces “triple response”
What is the significance of histamine inducing local edema?
Endothelial cell leakage (local edema) serves to increase access of immune cells to site of injury
What is the ‘triple response’ induced by histamine?
- Central red spot = due to vasodilation
- Flare = surrounding the area
- Wheal = swelling due to edema
In what 2 ways does histamine induces neuronal physiological effects?
- Stimulates sensory neurons leading to ITCHING and PAIN
2. In CNS, Increases Alertness
In what 2 ways does histamine induce smooth muscle physiological effects?
- Constricts bronchioles (bronchoconstriction)
2. Constricts intestinal muscles (diarrhea)
In what 2 ways does histamine induce exocrine secretion?
Stimulates bronchiole, salivary, and digestive secretions – helps to dilute and thus wash out bugs
T/f: Histamine plays no role in asthma
TRUE!
What is the MECHANISM of action for ANTI-histamines?
INHIBIT A RECEPTOR – blocks H1 and H2 receptors
What are the 4 physiological targets/effects of H1 blocking antihistamines?
- CNS effects
- Drying of mucous membranes
- PNS effects
- Smooth muscle dilation
How do H1 specific anti-histamines effect the CNS?
- Sedative effect (exception: kids and elderly)
- Anti-nausea
- Anti-emetic
How do H1 specific antihistamines dry out mucous membranes
Blockade of H1 receptors leads to Anti-muscarinic effects
How do H1 specific antihistamines effect the PNS?
Act as a local anesthetic (neuromodulator activity blocks pain)
