Most of the nutrient absorption along the alimentary canal occurs in the

Answer Explanation

b. esophagus, stomach, and intestines

- Correct: The alimentary canal, or digestive tract, is made up of the esophagus, stomach, and intestines (both small and large). These organs form a continuous tube that extends from the mouth to the anus and is responsible for the digestion and absorption of food and the elimination of waste. The esophagus transports food from the mouth to the stomach through peristaltic contractions, while the stomach and intestines further digest food and absorb nutrients.

a. pancreas, liver, and gallbladder

- Incorrect: While the pancreas, liver, and gallbladder are important accessory organs that produce digestive enzymes and substances involved in digestion (such as bile), they are not part of the alimentary canal itself. Instead, they secrete their products into the alimentary canal to aid in digestion.

c. colon, rectum, and anus

- Incorrect: The colon, rectum, and anus are parts of the large intestine, which is a component of the alimentary canal. However, the alimentary canal is not solely composed of these organs; it also includes the esophagus, stomach, and small intestine.

d. mouth, esophagus, and stomach

- Incorrect: While the mouth, esophagus, and stomach are indeed part of the alimentary canal, they do not represent the entirety of it. The alimentary canal includes additional organs such as the small and large intestines, which are also involved in the digestion and absorption of food.

Answer Explanation

c) Food that distends the stomach initiates long reflexes.

- False: This statement is false. Food that distends the stomach initiates short reflexes, not long reflexes. Short reflexes are local reflexes that are mediated by the enteric nervous system, which consists of a network of neurons within the walls of the digestive tract. When food stretches or distends the stomach, sensory neurons in the stomach wall detect this mechanical stimulus and initiate short reflexes that regulate local gastrointestinal functions, such as gastric motility and secretion.

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.