Autacoids and Histamine Overview

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Questions and Answers

What are the primary actions mediated by H1 receptor activation?

Bronchoconstriction and sedation

Bronchoconstriction, vasodilation, increased vascular permeability, pruritus, and pain (correct)

Decreased heart rate and increased gastric acid secretion

Vasoconstriction and decreased vascular permeability

Which of the following is NOT a therapeutic use for first-generation antihistamines?

Gastric acid reduction (correct)

Treatment of urticaria

Management of allergic rhinitis

Motion sickness

Which antihistamine is known for causing significant sedation due to its ability to cross the blood-brain barrier?

Cimetidine

Ranitidine

Burimamibe

Promethazine (correct)

What is a major side effect associated with first-generation antihistamines?

Dry mouth and urinary retention Signup and view all the answers

H2 receptors primarily mediate which of the following physiological processes?

Heart rate increase and gastric acid secretion Signup and view all the answers

Which antihistamine is specifically mentioned as blocking H2 receptors?

Cimetidine Signup and view all the answers

Which of the following is a characteristic of H4 receptors?

Facilitates chemotaxis of mast cells towards inflammation Signup and view all the answers

What effect do H1 receptor antagonists have on the central nervous system?

They induce sedation and drowsiness Signup and view all the answers

What is the main therapeutic action of H2 receptor antagonists like ranitidine and famotidine?

Block the H2 receptor to reduce gastric acid secretion Signup and view all the answers

Which receptors do histamine bind to in allergic rhinitis, causing the symptoms associated with this condition?

H1 receptors on nasal mucosa Signup and view all the answers

What physiological processes are affected by histamine in asthma?

Bronchoconstriction and increased mucus production Signup and view all the answers

Which of the following adverse effects is NOT commonly associated with H2 receptor antagonists?

Nausea Signup and view all the answers

What role does histamine play in peptic ulcer disease?

It stimulates gastric acid secretion Signup and view all the answers

Which immune cells are primarily involved in the release of histamine during allergic reactions?

Mast cells and basophils Signup and view all the answers

In urticaria, which receptors does histamine bind to in order to cause the characteristic skin symptoms?

H1 receptors on the skin Signup and view all the answers

How does histamine contribute to airway inflammation in asthma?

By causing bronchoconstriction and mucus secretion Signup and view all the answers

What distinguishes autacoids from hormones?

Autacoids act locally at the site of synthesis. Signup and view all the answers

Which of the following is NOT a type of histamine receptor?

H5 Signup and view all the answers

Which physiological response is primarily mediated by H1 receptors?

Spasm in smooth muscle. Signup and view all the answers

In which scenario would antihistamines NOT be beneficial?

Asthma attacks Signup and view all the answers

Histamine is stored in which type of cells in the body?

Mast cells and basophiles Signup and view all the answers

Which of the following is a primary role of histamine in the body?

Causing inflammation response. Signup and view all the answers

How does histamine affect blood vessels?

Causes vasodilatation and increased permeability. Signup and view all the answers

Which of the following correctly describes the synthesis of histamine?

Created from decarboxylation of histidine by a decarboxylase enzyme. Signup and view all the answers

What is the primary mechanism of action of H2 receptor antagonists?

They inhibit the production of gastric acid by blocking H2 receptors. Signup and view all the answers

Which medication is commonly used in the treatment of anaphylaxis?

Epinephrine Signup and view all the answers

Which of the following is a second-generation antihistamine?

Loratadine Signup and view all the answers

How do mast cell stabilizers function in the treatment of allergic conditions?

They stabilize mast cells, preventing histamine release. Signup and view all the answers

What is one of the primary uses of corticosteroids in relation to histamine-related diseases?

To suppress the immune system and reduce inflammation. Signup and view all the answers

Which H2 receptor antagonist is known for its use in treating peptic ulcer disease?

Ranitidine Signup and view all the answers

What type of symptoms do antihistamines primarily target?

Allergic reactions and inflammation. Signup and view all the answers

What defines the effectiveness of H2 receptor antagonists in treating GERD?

Their function in blocking histamine from binding to H2 receptors. Signup and view all the answers

Study Notes

Autacoids

Autacoids are substances with diverse biological activity that act locally, at the site of synthesis and release.
They are produced by various cells, especially in response to injury or immune challenge, and can act as neurotransmitters or modulators in the nervous system.
They differ from hormones in that they act locally and are not transported through blood to distant targets.

Examples of Autacoids

Histamine
Hydroxytryptamine (5-HT, serotonin)
Prostaglandins
Leukotrienes
Kinins

Histamine

Histamine is a chemical released from mast cells and basophils in response to allergens or other stimuli.
It is derived from the amino acid histidine.
It is concentrated in the lung, skin and gastrointestinal tract (GIT).

Histamine Receptors

There are four types of histamine receptors (H1, H2, H3, and H4).
All of them are G-protein coupled receptors.

H1 Receptors

Found in: smooth muscle, endothelium, and central nervous system.
They mediate: bronchoconstriction, vasodilation, increased vascular permeability, pruritus, and pain.

H2 Receptors

Found in: gastric parietal cells, heart, and blood vessels.
They mediate: gastric acid secretion, increased heart rate, and vasodilation.

H3 Receptors

Found in: presynaptic neurons.
They regulate histamine release.

H4 Receptors

Found in: haematopoietic cells, spleen, thymus, and colon.
They increase chemotaxis of mast cells and leukocytes to sites of inflammation.

Actions of Histamine

H1 Receptor Actions
- Smooth muscle: causes spasm in the intestine, uterus, and bronchi.
- Blood vessels: causes vasodilation, leading to a drop in blood pressure and increased capillary permeability, resulting in edema.
- Sensory nerve endings: causes itching.
H2 Receptor Actions
- Stomach: increases gastric HCl secretion.
- Blood vessels: causes vasodilation and a drop in blood pressure, increased capillary permeability, with edema.
- Heart: causes positive inotropic and chronotropic actions.

Antihistamines

First Generation Antihistamines
- Examples: Diphenhydramine, Chlorpheniramine, Promethazine.
- They block the actions of histamine on H1 receptors.
- Cross the blood-brain barrier, causing sedation, drowsiness, and other central nervous system side effects.
Second Generation Antihistamines
- Examples: Loratadine, Cetirizine, Fexofenadine.
- They have fewer central nervous system side effects.

Allergic Rhinitis
- Allergic rhinitis is an inflammatory response of the nasal mucosa to allergens that triggers histamine release.
- Histamine binds to H1 receptors on nasal mucosa, resulting in vasodilation, increased vascular permeability, and mucus secretion, causing symptoms like congestion, sneezing, itching, and rhinorrhea.
Urticaria (Hives)
- Urticaria is a skin condition caused by histamine release from mast cells, leading to itchy, raised, red, or white bumps on the skin.
- Histamine binds to H1 receptors on skin, causing vasodilation and increased vascular permeability, resulting in hives.
Asthma
- Histamine in the airways triggers bronchoconstriction and mucus secretion, contributing to asthma symptoms.
- Histamine binds to H1 receptors on bronchial smooth muscle, causing bronchoconstriction, and to H2 receptors on airway epithelial cells, leading to increased mucus production.
Peptic Ulcer Disease
- Histamine stimulates gastric acid secretion, contributing to the development of peptic ulcers.
- Histamine binds to H2 receptors on gastric parietal cells, leading to the activation of the proton pump and the production of hydrochloric acid, which can damage the gastric mucosa.

Antihistamines: Block the H1 receptor, reducing the symptoms of allergic reactions.
H2 Receptor Antagonists: Block the H2 receptor, reducing gastric acid secretion.
Mast Cell Stabilizers: Stabilize mast cells and prevent histamine release.
Epinephrine: Stimulates adrenergic receptors to reverse the effects of histamine in severe allergic reactions (anaphylaxis).
Corticosteroids: Suppress the immune system and reduce inflammation.

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Description

Explore the fascinating world of autacoids and their role in biological activity. Learn about histamine, its receptors, and how these substances act locally in response to various stimuli. This quiz will test your understanding of these important biochemical compounds and their functions in the body.