Correct Answer: D

Rationale: The correct answer is the Sinoatrial (S
A) node. The SA node is known as the natural pacemaker of the heart as it initiates the electrical impulses responsible for the heartbeat. The other choices, such as the Atrioventricular (AV) nodes, Bundle of His, and Purkinje fibers, are involved in conducting the electrical signals generated by the SA node to coordinate the heart's contractions.
Therefore, they do not serve as the primary origin of the heartbeat.

Correct Answer: A

Rationale: Weight loss is a common symptom of hyperthyroidism, which is characterized by an excess secretion of thyroid hormone. This increased metabolic rate can lead to weight loss despite normal or increased appetite. Bradycardia (slow heart rate), cold intolerance, and lethargy are more commonly associated with hypothyroidism, where there is an insufficient production of thyroid hormone.
Therefore, choices B, C, and D are incorrect in the context of hypersecretion of thyroid hormone.

Correct Answer: B

Rationale: The correct function associated with the dermal layer of the skin is to provide support and structure to the skin. The dermis is the thickest layer of the skin and is responsible for maintaining the skin's integrity and firmness.

Choices A, C, and D are incorrect as sensory perception, protection from UV rays, and insulation are functions associated with other layers of the skin, such as the epidermis and subcutaneous tissue.

Correct Answer: D

Rationale: The correct answer is Parathyroid glands. The parathyroid glands are responsible for regulating calcium levels in the blood by secreting parathyroid hormone (PTH). PTH helps increase calcium levels in the blood when they are too low. The other glands listed, such as the Hypothalamus, Thyroid, and Pituitary glands, do not directly control calcium concentration in the blood.

Correct Answer: C

Rationale: The correct answer is C: Store and concentrate bile, a fluid produced by the liver that helps with fat digestion. The gallbladder stores bile produced by the liver and releases it to aid in the digestion of fats.
Choice A is incorrect as the liver, not the gallbladder, filters blood and detoxifies harmful substances.
Choice B is incorrect because the production of enzymes primarily occurs in the pancreas, not the gallbladder.
Choice D is incorrect as the gallbladder's main role is not to further digest food but to store and release bile.