Which of these is most associated with villi?

Answer Explanation

A. plicae circulares

- Correct: The small intestine possesses permanent folds along its length known as plicae circulares, also called circular folds or valvulae conniventes. These folds are permanent transverse ridges of the mucosa and submucosa that project into the lumen of the small intestine. They increase the surface area for absorption and digestion by slowing the passage of chyme and increasing contact between chyme and the intestinal lining, facilitating nutrient absorption.

B. haustra

- Incorrect: Haustra are pouches or sacculations formed by the muscularis externa of the colon (large intestine), not the folds of the small intestine.

C. villi

- Incorrect: Villi are finger-like projections of the mucosa of the small intestine that extend into the lumen. While villi increase the surface area for absorption, they are not permanent folds along the length of the small intestine.

D. intestinal crypts

- Incorrect: Intestinal crypts, also known as crypts of Lieberkühn, are invaginations of the epithelium located between villi in the mucosa of the small intestine. They contain stem cells that continuously divide and give rise to new epithelial cells, helping to replenish the epithelial lining of the intestine. Crypts are not permanent folds along the length of the small intestine.

Answer Explanation

d. all of the above

- Correct: All of the statements are true regarding the stomach:

a. muscles churn and mix the food with acids and enzymes: The stomach has muscular walls that contract and relax to mechanically churn and mix food with gastric juices, including hydrochloric acid and various enzymes (such as pepsin) that aid in the digestion of proteins.

b. glands make 3 quarts of digestive juices each day: The gastric glands in the lining of the stomach produce gastric juice, which contains hydrochloric acid, enzymes (such as pepsinogen), mucus, and intrinsic factor. These glands collectively secrete about 2 to 3 liters (quarts) of gastric juice per day.

c. food leaves as a thick liquid called chyme: After mixing with gastric juices and undergoing partial digestion in the stomach, food is transformed into a semi-liquid mixture called chyme. Chyme is then gradually released from the stomach into the small intestine for further digestion and absorption.

Therefore, all of the statements accurately describe processes that occur in the stomach.

Answer Explanation

C. jejunum

- Correct: Most of the nutrient absorption along the alimentary canal occurs in the jejunum, which is the middle segment of the small intestine. The jejunum has a highly folded inner surface covered with finger-like projections called villi and even smaller microvilli. These structures greatly increase the surface area available for absorption. The epithelial cells lining the villi contain numerous transport proteins and enzymes responsible for absorbing nutrients such as carbohydrates, proteins, fats, vitamins, and minerals into the bloodstream for distribution to the body's cells.

A. ascending colon

- Incorrect: The ascending colon is part of the large intestine (colon) where water and electrolytes are primarily absorbed, but it is not a major site of nutrient absorption.

B. stomach

- Incorrect: While some substances, such as water, electrolytes, alcohol, and certain drugs, can be absorbed in small amounts in the stomach, the stomach is not a major site of nutrient absorption. Its main function is to begin the digestion of proteins and store food temporarily.

D. ileum

- Incorrect: The ileum is the final segment of the small intestine, and while it does participate in nutrient absorption, the majority of nutrient absorption occurs in the jejunum, which precedes the ileum along the alimentary canal. The ileum primarily absorbs bile salts, vitamin B12, and some remaining nutrients not absorbed in the jejunum.