HY USMLE Q#18 Resp/Biochem Step 1
HY USMLE Q#18 GIT ( Step 1 inspired from MEHLMAN instagram)
A 46-year-old female has right upper quandrant pain following a meal, which has occurred 5 times this month. She has no past medical history. She has 4 kids. BMI is 35 kg/m^2. Which of the following best describes the hormones responsible for the patient’s presentation ?
A. Secreted S cells
B. Secreted by enteroendocrine cells of the small bowel
C. Causes increased tone of the sphincter of oddi
D. Causes the pancreas to secrete isotonic fluids with some bicarbonate
E. Secreted in response to protons entering the duodenum
✅ Correct Answer: B
Educational Objective:
Cholecystokinin is a hormone secreted by the enteroendocrine cells located in the small intestine. The condition being diagnosed is cholelithiasis, characterized by intermittent pain in the right upper quadrant (RUQ) after meals.
This patient exhibits the classic presentation: fat, female, around forty years old, fertile, using fibrates and fair. Estrogen up-regulates HMG-CoA reductase, which increases cholesterol synthesis and leads to augmented cholesterol secretion into the bile. Fair = Genetic variations in cholesterol metabolism and bile composition may contribute to an increased risk.
Cholecystokinin is specifically secreted by I cells. The term "Chole" refers to bile, "Cysto" refers to the bladder, and "Kinin" means to move. Therefore, cholecystokinin literally means "move the gallbladder," as it stimulates the gallbladder to contract and release bile.
It’s important to note that "I cells" do not stand for anything specific. It doesn’t stand for Intestinal or inhibitory it was named by the enteroendocrine cells alphabetically ( K cells, L cells and S cells).
Cholecystokinin has 3 main functions
1. Gallbladder contraction —> increase bile release
2. increase pancreatic enzyme secretion
3. sphincter of oddi relaxation
❌ A. Secretin is secreted by S cells of the small bowel. These are also enteroendocrine cells just like I cells secrete Cholecystokinin.
❌ C. Cholecystokinin causes decrease toke of the sphincter of oddi.
❌ D. This refers to vasoactive intestinal peptide. This causes the pancreas to secrete a lot of water, even though in reality the fluid is isotonic with bicarbonate meaning it has the same osmolarity as the blood.
❌ E. Secretin secreted in response to H+ in the dudodenum from the stomach. Secretin causes the secretion of bicarbonate rich fluid.
