MCAT Biology : Stomach and Small Intestine

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Stomach And Small Intestine

Which answer choice incorrectly matches the type of digestion with the location in the body?

Possible Answers:

Mechanical digestion of food—mouth

Chemical digestion of fats—small intestine

Chemical digestion of protein—stomach

Chemical digestion of carbohydrates—small intestine

Chemical digestion of proteins—mouth

Correct answer:

Chemical digestion of proteins—mouth

Explanation:

Digestion in the mouth involves the mechanical chewing of food and the action of salivary amylase, which breaks down starch. Proteins do not start getting digested until they are in the stomach, where pepsin breaks them down. Fats and carbohydrates are broken down in the small intestne by lipases and other enzymes like lactase.

Example Question #72 : Excretory And Digestive Systems

The stomach secretes large quantities of acid (HCl) into its lumen. What protects the epithelial cells that line the stomach from being broken down by the strong acid?

Possible Answers:

The epithelial cells lining the stomach have specialized defensive properties against stong acids

Mucous found within the stomach

The stomach's epithelial cells are defenseless against stong acids

The stomach has a pH of 7 when digestion isn't taking place

Correct answer:

Mucous found within the stomach

Explanation:

A layer of mucous forms between the epithelial cells of the stomach and the acid within the stomach. This mucous is secreted by mucous cells lining the stomach. When the mucous layer is broken down, certain complications can take place (e.g. stomach ulcers).

Example Question #2 : Stomach And Small Intestine

What peptide hormone, produced by D cells in the antrum of the stomach, inhibits the release of acid from the stomach parietal cells?

Possible Answers:

Somatostatin

Gastrin

Histamine

Ghrelin

Correct answer:

Somatostatin

Explanation:

D cells in the antrum of the stomach are neuroendocrine cells that secrete somatostatin, a neuropeptide that increases stomach pH by decreasing gastric acid secretion from fundal parietal cells. In a negative feedback mechanism, when the stomach pH falls too low, hydrogen ions (H+) will stimulate D cells to secrete somatostatin. This somatostatin blocks histamine release from enterochromaffin-like (ECL) cells in the stomach, preventing the stimulation of parietal cells to release hydrochloric acid.

Histamine is released by ECL cells, stimulating acid secretion from parietal cells. Gastrin is released by G cells, also stimulating acid secretion from parietal cells. Ghrelin is a neurohormone that stimulates hunger.

Example Question #3 : Stomach And Small Intestine

The low pH of the stomach is important in many digestive processes of macro- and micro-nutrients, including the conversion of zymogens into active enzymes by the high hydrogen ion concentration, and acid-base reactions with many ingested micronutrients such as vitamins and minerals. The absorption of which metal, important especially in red blood cell function, requires reduction in the stomach?

Possible Answers:

Iron

Zinc

Copper

Calcium

Correct answer:

Iron

Explanation:

Iron, usually ingested in the Fe3+ form (ferric iron), must be reduced to Fe2+ (ferrous form) in order to be absorbed in the duodenum of the small intestine. The iron undergoes an oxidation-reduction reaction in the stomach, facilitated by the low pH of the stomach lumen.

Example Question #75 : Excretory And Digestive Systems

Gastric emptying (the passage of stomach contents to the small intestine) is regulated by which sphincter of the gastrointestinal system?

Possible Answers:

Pyloric sphincter

Ileocolic sphincter

Lower esophageal sphincter

Upper esophageal sphincter

Correct answer:

Pyloric sphincter

Explanation:

The pyloric sphincter, between the antrum of the stomach and the duodenum of the small intestine, regulates the passage of chyme from the stomach to the small intestine. The antrum has rhythmic contractions that force chyme against the pyloric sphincter, allowing approximately five milliliters to flow through every contraction; thus, the pyloric sphincter allows for the gradual but continual digestion of gastric contents.

The upper and lower esophageal sphincters are involved in the process of swallowing, while the ileocolic sphincter joins the small intestine and large intestine.

Example Question #4 : Stomach And Small Intestine

A patient who complains of acid reflux is given a drug which raises the pH of the stomach. Which macromolecule's digestion will be affected by this drug?

Possible Answers:

All macromolecules will be affected by the drug

Proteins

Carbohydrates

Fatty acids

Correct answer:

Proteins

Explanation:

A low pH in the stomach is necessary in order to activate pepsinogen, the zymogen form of pepsin. Pepsin is necessary for breaking down proteins into smaller polypeptides. In a stomach with a higher pH (less acidic), pepsin production will be decreased, and proteins will not be digested as well.

Example Question #5 : Stomach And Small Intestine

Which of the following is a function of the stomach in digestion?

Possible Answers:

All of the answers are functions of the stomach

Mechanical digestion of food

Secrete pepsinogen

Aid in the absorption of Vitamin B

Correct answer:

All of the answers are functions of the stomach

Explanation:

The lining of the stomach secretes hydrochloric acid, pepsinogen, and intrinsic factor. Intrinsic factor binds to vitamin B and allows for its absorption. Hydrochloric acid cleaves the zymogen pepsinogen to create the active enzyme pepsin, which helps with the preliminary chemical digestion of proteins.

The contraction of the stomach causes the breakdown of food. Only food that has been broken down into small boluses can pass through the pyloric sphincter and enter the small intestine. The stomach is thus responsible for the mechanical modification of food, breaking it into small enough particles that it can pass to the next segment of the digestive tract. The majority of chemical digestion and absorption then occurs in the small intestine.

Example Question #78 : Excretory And Digestive Systems

A patient is recovering from a bacterial toxin that has damaged a large majority of the microvilli in their small intestine. Which is the most immediate issue they should be concerned about?

Possible Answers:

Nutrient absorption

Structure and support of the intestine

Blood loss

Enzyme secretion

Mechanical digestion

Correct answer:

Nutrient absorption

Explanation:

The patient should be most concerned with nutrient absorption. Microvilli provide additional surface area to the small intestine, allowing for nutrient absorption. If the lining of the intestine were completely smooth, nutrients would pass too quickly through the digestive system. Enzyme secretion is primarily provided by the liver and pancreas.

Example Question #6 : Stomach And Small Intestine

The majority of enzymatic digestion occurs in which section of the digestive system?

Possible Answers:

Mouth

Pancreas

Stomach

Small intestine

Large intestine

Correct answer:

Small intestine

Explanation:

The small intestine is the location of where the majority of enzymatic digestion occurs because enzymes from the pancreas are incorporated into the digestive process at this point. It is important to begin the enzymatic breakdown of food as early as possible to maximize nutrient absorption through the intestinal system.

The large intestine is responsible for water absorption and waste removal. The mouth begins enzymatic digestion with salivary amylase, and the stomach introduces pepsin, but these do not constitute the majority of enzymatic activity in the digestive tract.

Example Question #7 : Stomach And Small Intestine

At what point in the small intestine are pancreatic secretions and bile mixed with chyme?

Possible Answers:

Jejunum

Ileum

The pancratic secretions and bile are added before food reaches the small intestine

Colon

Duodenum

Correct answer:

Duodenum

Explanation:

The duodenum is the first part of the small intestine. This is where the acidic chyme from the stomach mixes with pancreatic secretions and bile. The pancreatic secretions and bile contain bicarbonate, which helps to neutralize the acidic chyme. 

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