Which of the following organs has 3 layers of smooth muscle in its muscularis externa?

Answer Explanation

a. nutrients

- Correct: The digestive system breaks down food into nutrients. These nutrients include carbohydrates, proteins, fats, vitamins, minerals, and water, which are essential for various physiological functions in the body. Once broken down into nutrients through mechanical and chemical digestion, these substances are absorbed by the intestines and transported via the bloodstream to cells throughout the body for energy production, growth, repair, and other metabolic processes.

b. amylase

- Incorrect: Amylase is an enzyme involved in the digestion of carbohydrates. It is produced by salivary glands in the mouth and by the pancreas and helps break down complex carbohydrates into simpler sugars. While amylase is an important component of the digestive process, it is not the end product of digestion.

c. saliva

- Incorrect: Saliva is a fluid secreted by salivary glands in the mouth. It contains water, electrolytes, mucus, and enzymes such as amylase. Saliva helps moisten food, initiate the digestion of carbohydrates, and facilitate swallowing, but it is not the end product of digestion.

d. sphincters

- Incorrect: Sphincters are ring-like muscles that control the movement of materials through various parts of the digestive tract by opening and closing. While sphincters play a crucial role in regulating the flow of food and waste through the digestive system, they are not the end products of digestion.

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 listed stimuli activate sensors in the walls of digestive organs:

a) Breakdown products of digestion: The presence of breakdown products, such as nutrients and smaller molecules resulting from digestion, can activate sensors in the walls of digestive organs. These sensors help regulate various digestive processes and signal the release of digestive enzymes and hormones.

b) Distension: Distension, or stretching of the walls of the digestive organs, is a stimulus that activates sensors. It occurs as the volume of the digestive tract increases due to the presence of ingested food, and it triggers reflexes that coordinate muscular contractions for propulsion and mixing.

c) pH of chyme: The pH of the chyme (the semi-liquid mixture of food and digestive juices in the stomach and small intestine) is another stimulus that activates sensors. Changes in pH can signal the need for adjustments in the secretion of digestive enzymes and the regulation of gastric and intestinal functions.

Therefore, all of the mentioned stimuli play a role in activating sensors and regulating digestive processes in response to the specific conditions within the digestive organs.