Chewing or mastication reflex originates in the ______ and the ability to initiate or stop chewing originates in the ______.

Correct Answer: B

Rationale: The correct answer is B. The chewing reflex originates in the medulla oblongata, which controls basic life functions like breathing and swallowing. The ability to voluntarily initiate or stop chewing comes from the cerebrum, the part of the brain responsible for conscious thoughts and movements. The pons (choice A) is involved in regulating breathing, not chewing. The spinal cord (choice C) is responsible for reflex actions but not specifically chewing. The midbrain (choice D) is more related to sensory processing and motor function, not chewing reflex. Therefore, the correct answer is B based on the roles of the medulla oblongata and cerebrum in chewing.

Correct Answer: C

Rationale: Granular cells, also known as Paneth cells, produce antimicrobial peptides to protect the intestinal epithelium from bacteria. These peptides have antimicrobial properties that help prevent bacterial overgrowth and maintain intestinal homeostasis. Absorptive cells are primarily responsible for nutrient absorption, while goblet cells secrete mucus for lubrication. Endocrine cells produce hormones that regulate various physiological processes. Therefore, the correct answer is C, as granular cells play a direct role in protecting the intestinal epithelium from bacteria.

Correct Answer: D

Rationale: The correct answer is D: chymotrypsin. Chymotrypsin is not part of the enzymatic component of pancreatic juice. Pancreatic juice contains amylase for carbohydrate digestion, lipase for fat digestion, and nucleases for nucleic acid digestion. Chymotrypsin is produced in the pancreas but is not secreted directly into the pancreatic juice. It is released in an inactive form that is activated in the small intestine. Therefore, chymotrypsin is not directly involved in the initial breakdown of nutrients in the pancreatic juice.

Correct Answer: D

Rationale: The correct answer is D: high-density lipoprotein (HDL). HDL is known to have a higher proportion of protein compared to other lipoproteins. In this case, with 45% protein content, it aligns with the typical composition of HDL. HDL is responsible for transporting cholesterol from peripheral tissues back to the liver for excretion, making it crucial for maintaining cardiovascular health. A: Micelle is incorrect as it is a single-layered structure formed by amphipathic molecules in a specific environment like bile salts in the intestines. B: Chylomicron is incorrect as it is primarily composed of triglycerides and is responsible for transporting dietary lipids. C: Low-density lipoprotein (LDL) is incorrect as it typically has higher cholesterol content compared to HDL and is known as "bad cholesterol" due to its role in depositing cholesterol in arteries.

Correct Answer: A

Rationale: The correct answer is A because the absorption of vitamins from the intestine involves various mechanisms. Vitamin E is indeed absorbed by a protein that binds peroxidized fatty acids. Thiamine pyrophosphate and pyridoxal phosphate need to be dephosphorylated before absorption. Oxidized vitamin C is absorbed by a glucose transporter. Therefore, all the options given are correct as they describe different aspects of the absorption process. Each choice provides a unique insight into how different vitamins are absorbed, highlighting the complexity of the absorption process.