Into which parts of the human digestive system are digestive enzymes secreted?

Answer Explanation

C) villi

- Correct: The absorptive surface of the small intestine is greatly increased due to the presence of villi. Villi are finger-like projections that line the inner surface of the small intestine. These structures greatly increase the surface area available for absorption. Each villus contains capillaries and lacteals (lymphatic vessels) that absorb nutrients from digested food. The large surface area provided by the villi allows for more efficient absorption of nutrients such as carbohydrates, proteins, fats, vitamins, and minerals.

A) alveoli

- Incorrect: Alveoli are tiny air sacs in the lungs where gas exchange occurs during respiration. They are not found in the digestive system and do not contribute to the absorptive surface of the small intestine.

B) neurons

- Incorrect: Neurons are nerve cells that transmit signals throughout the body, including the digestive system. While neurons play a role in regulating digestion and other digestive processes, they do not directly contribute to the absorptive surface of the small intestine.

D) nephrons

- Incorrect: Nephrons are the functional units of the kidneys responsible for filtering blood and producing urine. They are not part of the digestive system and do not contribute to the absorptive surface of the small intestine.

Answer Explanation

A) liver

- Correct: The liver produces bile, a substance that aids in the mechanical breakdown of fats. Bile is stored in the gallbladder and released into the small intestine when needed. Bile emulsifies large fat globules into smaller droplets, which increases the surface area for the action of digestive enzymes. This process facilitates the breakdown of fats into smaller molecules for digestion and absorption.

B) thyroid gland

- Incorrect: The thyroid gland produces hormones that regulate metabolism but is not directly involved in the mechanical breakdown of fats.

C) testes

- Incorrect: The testes are reproductive organs responsible for the production of sperm in males and do not play a role in the mechanical breakdown of fats.

D) pituitary gland

- Incorrect: The pituitary gland is a master gland that produces and regulates various hormones but is not involved in the mechanical breakdown of fats.

Answer Explanation

A) The stomach - This is an organ of the digestive system. It plays a crucial role in breaking down food through the secretion of gastric juices, which contain enzymes and acids to begin the process of digestion. Therefore, option A is correct.

B) The mouth - The mouth is also an organ of the digestive system. It is where the process of digestion begins, as it is responsible for chewing and breaking down food into smaller pieces. Additionally, saliva produced in the mouth contains enzymes that start the chemical breakdown of food. Therefore, option B is correct.

C) The intestines - Both the small intestine and the large intestine are essential organs of the digestive system. The small intestine is where most of the absorption of nutrients from food occurs, while the large intestine absorbs water and salts from the material that has not been digested. Therefore, option C is correct.

D) The heart - The heart is not an organ of the digestive system. Instead, it is a part of the circulatory system responsible for pumping blood throughout the body. While the circulatory system works in conjunction with the digestive system to transport nutrients absorbed from the intestines to various tissues and organs, the heart itself is not directly involved in digestion. Therefore, option D is incorrect.