Secretion of bile into duodenum is stimulated by?

ESIC Nursing Officer 2016 (Shift -2)

Applied Physiology

Easy

Appeared in: ESIC Nursing Officer 2016 (Shift -2)

Explanation

Cholecystokinin (CCK) is a gastrointestinal hormone released from the I-cells of the duodenal and jejunal mucosa.
The primary stimulus for CCK release is the presence of fatty acids and amino acids in the chyme entering the duodenum.
CCK's main functions are to stimulate the contraction of the gallbladder and the relaxation of the sphincter of Oddi.
This coordinated action results in the delivery of bile into the small intestine to emulsify fats, making them accessible to digestive enzymes like lipase.

Option A: Lipase is a digestive enzyme, not a hormone. Its function is to break down fats, a process that is aided by the bile that CCK helps release.
Option C: Pepsin is a proteolytic enzyme that functions in the stomach to digest proteins. It is inactive in the alkaline environment of the duodenum and has no role in bile secretion.
Option D: Amylase is an enzyme that digests carbohydrates. It is secreted by the salivary glands and the pancreas and has no function related to stimulating bile release.

Visual 1: Diagram - A flowchart illustrating the hormonal control of digestion. It should show food (fats, proteins) entering the duodenum, stimulating I-cells to release CCK, which then acts on the gallbladder and sphincter of Oddi to release bile.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormonal regulation of bile secretion as background academic context rather than a clinical decision trigger.
Understanding CCK's function is crucial in diagnosing gallbladder disorders. For example, in a HIDA scan (hepatobiliary iminodiacetic acid scan), synthetic CCK (sincalide) can be administered to assess gallbladder contractility (ejection fraction). A low ejection fraction may indicate chronic cholecystitis.
Patients with gallstones (cholelithiasis) may experience biliary colic, which is severe pain caused by the gallbladder contracting against an obstructed duct, often triggered by a fatty meal that stimulates CCK release.
What if? If a patient has had their gallbladder removed (cholecystectomy), bile is no longer stored and concentrated. Instead, it trickles continuously from the liver into the duodenum. The hormonal signal of CCK still occurs, but it no longer has a gallbladder to act upon.

How to Approach the Question

First, identify the core of the question: what stimulates the secretion of bile into the duodenum.
Differentiate between hormones (signaling molecules) and enzymes (catalysts for digestion). The question asks for a stimulus, which points towards a hormonal regulator.
Analyze the options: Lipase, Pepsin, and Amylase are all digestive enzymes. Cholecystokinin is a hormone.
Recall the function of each substance. CCK's name itself (chole-cysto-kinin) means 'bile-sac-mover', directly hinting at its function of causing gallbladder contraction.
Eliminate the enzymes as they are involved in the chemical breakdown of food, not in signaling for bile release. This leaves Cholecystokinin as the only logical answer.

Concept Tested & Keywords

QrnYgogqjfNet7kNeg2sv8