Arachidonic Acid Functions

Questions and Answers

What are the products of the cyclooxygenase pathway?

Epoxides

Prostaglandins and thromboxane (correct)

HETE

Leukotrienes

Which of the following functions is NOT attributed to eicosanoids?

Regulation of blood pressure

Formation of blood clots

Vision regulation (correct)

Smooth muscle contraction

At what concentrations do eicosanoids typically exert their effects?

Moderate concentrations

Very low concentrations (correct)

Very high concentrations

Constant levels

Which component is found in the structure of thromboxanes?

6-membered ring that includes an oxygen atom Signup and view all the answers

Which receptor type is primarily mediated by eicosanoids?

G-protein coupled receptors Signup and view all the answers

Which of the following is NOT a product of the lipoxygenase pathway?

Thromboxane Signup and view all the answers

Which physiological function is directly linked to eicosanoids?

Gastric acid secretion Signup and view all the answers

What characteristic is essential for the structure of prostaglandins?

Hydroxyl group at carbon 15 Signup and view all the answers

Which eicosanoid is known to affect blood flow to specific organs?

Prostaglandins Signup and view all the answers

What is the primary role of arachidonic acid in cellular biochemistry?

It acts as a precursor to key signaling molecules. Signup and view all the answers

Which enzyme is primarily responsible for the release of free arachidonic acid from membrane phospholipids?

Phospholipase A2 Signup and view all the answers

Which type of cells can be stimulated by thrombin to release arachidonic acid?

Platelets and endothelial cells Signup and view all the answers

What determines the rate of product formation in relation to arachidonic acid release?

The amount of free arachidonic acid released. Signup and view all the answers

In which position on the glycerol backbone is arachidonic acid stored in cell membrane phospholipids?

2 position Signup and view all the answers

What is released from phosphatidylinositol by the action of phospholipase C?

Inositol Signup and view all the answers

What is the effect of bradykinin on renal tubular cells regarding arachidonic acid?

It stimulates its release. Signup and view all the answers

What is the function of leukotrienes derived from arachidonic acid?

Mediators of inflammatory responses. Signup and view all the answers

The hydrolysis of arachidonate is primarily facilitated by which enzyme?

Phospholipase A2 Signup and view all the answers

Which of the following is NOT produced from arachidonic acid?

Cholesterol Signup and view all the answers

What is the role of hydroxyl fatty acid derivatives in eicosanoid metabolism?

Exhibit no clear biologic activity Signup and view all the answers

Which eicosanoid formation is primarily affected by NSAIDs?

Cyclooxygenase pathway Signup and view all the answers

Which of the following NSAIDs is NOT mentioned as an example?

Naproxen Signup and view all the answers

What does the subscript in nomenclature denote?

Number of unsaturated bonds Signup and view all the answers

Which substitution positions are identified for hydroperoxy in nomenclature?

5, 12, 15 Signup and view all the answers

What condition may NSAIDs potentially trigger due to increased leukotrienes?

Asthma attacks Signup and view all the answers

Which of the following best describes the structure of hydroperoxy-eicosatetraenoic acid?

Hydroxyl fatty acid derivative with no ring structure Signup and view all the answers

What effect do NSAIDs have on blood clot formation?

Reduce blood flow to the clot site Signup and view all the answers

What type of acid is hydroperoxy-eicosatetraenoic acid derived from?

Arachidonic acid Signup and view all the answers

What is the effect of thromboxane A2 produced by COX-1 in activated platelets?

Encourages thrombus formation Signup and view all the answers

What is a primary function of eicosanoids?

Reducing inflammation Signup and view all the answers

How does prostacyclin (PGI2) influence platelet activity?

It inhibits platelet aggregation and promotes vasodilation Signup and view all the answers

Which of the following is a primary effect of low-dose aspirin therapy?

Decreased risk of stroke and heart attack Signup and view all the answers

What is the primary mechanism of action of aspirin in relation to prostaglandins?

Irreversible acetylation of a specific serine residue Signup and view all the answers

What effect does cortisol have on phospholipase A2?

Decreases the production of thromboxane A2 Signup and view all the answers

Which statement best describes the impact of NSAIDs like aspirin and indomethacin?

They inhibit both COX-1 and COX-2, reducing thrombus formation. Signup and view all the answers

What is the primary biological role of COX-1 in the body?

Maintains healthy gastric tissue and renal homeostasis Signup and view all the answers

Which of the following correctly describes the effect of ibuprofen on PGH synthase?

It blocks the active site of PGH synthase reversibly and noncovalently Signup and view all the answers

Why is acetaminophen considered to have weak anti-inflammatory effects?

It poorly inhibits COX in the presence of elevated peroxides Signup and view all the answers

What is a primary function of leukotrienes in the body?

They participate in allergic responses and inflammation Signup and view all the answers

What is the role of 5-lipoxygenase in the lipooxygenase system?

It facilitates the synthesis of linear hydroxyperoxy acids Signup and view all the answers

Which class of drugs is referred to as selective COX-2 inhibitors?

Celecoxib Signup and view all the answers

How does PGH synthase contribute to the synthesis of PGH2?

By catalyzing the oxidative cyclization of free arachidonic acid Signup and view all the answers

What is one major consequence of elevated PG synthesis mediated by COX-2?

Increased inflammatory response in the body Signup and view all the answers

What effect does high concentrations of peroxides have on acetaminophen's efficacy?

It impedes its ability to inhibit cyclooxygenase enzymes Signup and view all the answers

What essential fatty acid is a precursor to prostaglandins and other related substances?

Linoleic acid Signup and view all the answers

Study Notes

Eicosanoids Function

Derived from arachidonic acid, a 20-carbon polyunsaturated fatty acid.
Not stored but synthesized on demand, responding to cellular signaling.
Mediated by G-protein coupled receptors, influencing various physiological functions.

Functions of Eicosanoids

Reproductive functions including smooth muscle contraction during menstruation and labor.
Modulation of inflammation, resulting in fever and pain responses.
Involvement in blood clot formation and regulation of blood flow to specific organs.
Influence on wake-sleep cycles and responsiveness to hormones like epinephrine and glucagon.
Regulation of gastric acid secretion and blood pressure.

Pathways for Eicosanoid Synthesis

Cyclooxygenase Pathway: Produces prostaglandins and thromboxanes.
Lipoxygenase Pathway: Generates leukotrienes, HETE (Hydroxyeicosatetraenoic acid), and lipoxins.
Cytochrome P450 System: Synthesizes epoxides, HETE, and diHETE.

Prostaglandins

Composed of a 20-carbon fatty acid structure with a 5-membered internal carbon ring and a hydroxyl group at carbon 15.
Nomenclature begins with "PG" followed by capital letters indicating specific substitutions.

Thromboxanes

Feature a 6-membered ring including an oxygen atom.
Nomenclature uses "TX" with capital letters for ring substitutions and subscripts indicating unsaturated bonds.
Function primarily in blood clot formation and reduction of blood flow to injury sites.

Hydroperoxy-eicosatetraenoic Acid (HETE)

Hydroxyl fatty acid derivative of arachidonic acid, lacking a ring structure.
Nomenclature includes hydroperoxy substitutions at positions 5, 12, and 15.

Metabolism of Eicosanoids

Arachidonic acid is a precursor for major eicosanoids, stored as phospholipid esters in cell membranes.
Released by phospholipase A2 when stimulated, influencing the rate of eicosanoid synthesis.
Specific agonists like thrombin and bradykinin stimulate arachidonic acid production.

Synthesis of Eicosanoids

Linoleic acid, an omega-6 fatty acid, is essential for prostaglandin production.
Arachidonic acid is derived from dietary intake of linoleic acid.
Prostaglandin H2 (PGH2) synthesized through oxidative cyclization of arachidonic acid, requiring oxygen and reducing agents.

Inhibition of Eicosanoid Synthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen inhibit cyclooxygenase (COX) enzymes, shifting production to lipoxygenase pathways.
NSAIDs can potentially induce asthma attacks through increased leukotriene synthesis.

Roles of Prostaglandins in Platelet Homeostasis

Thromboxane A2 (TXA2): Promotes platelet aggregation and vasoconstriction; synthesized by COX-1 in activated platelets.
Prostacyclin (PGI2): Inhibits platelet aggregation and promotes vasodilation; produced by COX-2 in vascular endothelium.

Aspirin and Its Effects

Provides antithrombogenic effects by irreversibly acetylating COX enzymes, reducing TXA2 synthesis in platelets while affecting PGI2 synthesis in endothelial cells.
Low-dose aspirin therapy lowers the risk of stroke and heart attacks by decreasing thrombus formation.

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Description

This quiz explores the cellular and tissue functions of arachidonic acid, a key polyunsaturated fatty acid. Learn about its role in smooth muscle contraction and other important physiological processes that occur at low concentrations. Test your knowledge on its production mechanisms and receptor mediation.