19. 5-HT Flashcards
Histamine exerts the following actions Except:
A: Dilation of large blood vessels.
B: Dilation of small blood vessels.
C: Stimulation of isolated Guinee pig heart
D: Itching
E: Increased vascular permeability.
Answer: A Dilation of large blood vessels.
Histamine plays an important role in initiating the body’s immune response to the presence of foreign antigens and pathogens. A primary source of histamine released during inflammatory conditions are:
A: B cells.
B: Enterochromaffin-like cells
C: Presynaptic nerve terminals
D: Mast cells.
E: T lymphocytes.
Answer D: mast cells
Site of action for H2 receptor antagonists with respect to acid production inhibition:
A: Parietal cells
B: Chromaffin cells.
C: Mast cells.
Answer A: Parietal Cells
Which type of antibody is associated with an allergic reaction:
A: IgA.
B: IgE.
C: IgM.
D: IgG.
Answer B: IgE
Which of the following enzymes is essential for the conversion of histidine to histamine:
A: Histidine amylase.
B: Histidine hydrolase.
C: Histidine decarboxylase.
D: Histidine phosphorylase.
Answer C: Histidine decarboxylase
Which of the following statements about histamine is correct.
A: Histamine is stored in peripheral nerve endings
B: Histamine is released from mast cells following an allergic challenge.
C: Histamine is a vasoconstrictor.
D: Histamine is an essential amino acid
Answer B: Histamine is released from mast cells following an allergic challenge.
Which of the following activities occurs following stimulation of H2 receptors.
A: Vasodilation
B: Uterine contractions
C: Bronchial smooth muscle contraction
D: Enhanced secretion of hydrochloric acid in the stomach
Answer D: Enhanced secretion of hydrochloric acid in the stomach
Which of the following statements about histamine is not correct?
A: It is a bronchodilator.
B: Large scale release of it may cause a drop in blood pressure.
C: Large scale release of it may cause a fall in blood volume.
D: Histamine release contributes to the symptoms of anaphylaxis
Answer A: It is a bronchodilator
Serotonins effect on platelets:
A: Promotes aggregation.
B: Inhibits aggregation
C: No effects.
Answer A: Promotes aggregation.
Greater than 90% of serotonin is located here:
A: Platelets.
B: Raphe nucleus (brain stem)
C: Enterochromaffin cells of the GI tract
D: Lungs
E: Cerebral cortex.
Answer C: Enterochromaffin cells of the GI tract
Describe 5-Hydroxytrptamine (5-HT)
-known as serotonin.
-found in CNS Gi tract and platelets
-Important neurotransmitter playing important role in GI tract and vascular system.
-both too high and too low can cause symptoms hard to balance.
Describe the synthesis of 5-HT
-Synthesised in CNS and in enterochromaffin cells in the gut
-Tryptophan is hydrolysed by Tryptophan hydroxylase to make 5-hydroxytryptophan
-This is the decarboxylated by l-aromatic acid decarboxylase to make 5-HT
Describe dietary intake of 5-HTs effect
-Dietary intake of 5-HT does not affect body’s pool as it is excreted via urine
Describe Metabolism of 5-HT
-5-HT is oxidised by monoamine oxidise (MAO) and then dehydrogenated by Aldehyde dehydrogenase and can now be excreted by urine.
Describe storage of 5-HT
-90% is stored in the gut
-Is taken up via platelets and stored within granules
Describe three things that can alter 5-HT levels in the body
-Fenfluramine depletes levels in the CNS
-Ecstasy causes release of 5-HT in the CNS
-A carbohydrate rich diet can boost levels of 5-HT.
Describe the general composition of 5-HT receptors and there transducers and name the exceptions
-All are g-protein coupled receptor except 5-HT3 which is a internal cationic channel
-5-HT2 use Ip3/DAG as a transducer instead of cAMP.
Describe 5-HT1 receptors
-Mainly found in the CNS
-Activation of these receptors result in neural inhibition and vasoconstriction
-5-Ht1 receptors are important in mood and behaviour, thermoregulation, feeding and sleep.
Describe 5-HT2 receptors
-5-H2 receptors occur in the CNS and are also widely distributed in the periphery.
Describe 5-Ht role in migraines
-Is known to cause vasoconstriction in cerebral arteries.
-Found in urine of patients with migraine.
Describe 5-Hts role in the gut
5-Ht stimulates Gi motility both directly via 5-Ht2 receptors on the smooth muscle cells and indirectly via 5-HT3 and 5-Ht4 receptors on enteric neurons.
5-HT stimulates fluid secretions and elicits nausea and vomiting by stimulating 5-Ht receptors in the stomach.
Describe the effects of 5-HT in the cardiovascular system
The actions of the 5-Ht in the cardiovascular system depend on the size of the vessel, species and sympathetic activity, can lead to a rise in BP as large vessels constrict followed by a fall as the arterioles dilate. veins strongly constrict leading to pooling in the capillaries.
