The loose-fitting sac around the heart is the:

This is because it is an example of a positive feedback loop, which amplifies the change and moves the system away from its normal state.
A negative feedback loop is a mechanism that reverses a deviation from the set point and maintains homeostasis.
Choice A is wrong because increasing heart rate and force of contraction when blood pressure falls is a negative feedback loop that restores blood pressure to normal.
Choice B is wrong because secreting insulin after a meal to return blood sugar concentration toward normal is a negative feedback loop that regulates glucose levels.
Choice D is wrong because shivering when body temperature falls below normal is a negative feedback loop that increases heat production and raises body temperature.
Normal ranges for blood pressure are 90/60 mmHg to 120/80 mmHg, for blood glucose, are 70 mg/dL to 140 mg/dL, and for body temperature are 36.5°C to 37.5°C or 97.7°F to 99.5°F.

The pancreas is an organ that has both endocrine and exocrine functions.
As an endocrine gland, it secretes hormones such as insulin and glucagon that regulate blood sugar levels.
As an exocrine gland, it releases substances that neutralize stomach acid and digestive enzymes that break down proteins, fats, and carbohydrates.
Choice A is wrong because the thyroid gland is only an endocrine gland.
It secretes hormones such as thyroxine and calcitonin that regulate metabolism and calcium levels.
Choice C is wrong because the anterior pituitary is only an endocrine gland.
It secretes hormones such as growth hormone, prolactin, and adrenocorticotropic hormone that regulate growth, lactation, and stress response.
Choice D is wrong because the liver is mainly an exocrine gland. It produces bile that helps digest fats and detoxifies the blood.
The liver also has some endocrine functions, such as producing insulin-like growth factor 1 and angiotensinogen, but these are not its primary roles.