The loose-fitting sac around the heart is the:

The endocrine system may have a longer-lasting effect than the nervous system because the hormones it produces can circulate in the bloodstream for a long time and affect many organs and tissues.
The nervous system, on the other hand, uses nerve impulses and neurotransmitters for communication, which are faster but more short-lived.
Choice A is wrong because the endocrine system is essential to life.
It regulates many vital functions such as metabolism, growth, reproduction, mood, sleep, and blood pressure.
Choice B is wrong because the endocrine system takes longer than the nervous system to deliver its messages.
The hormones have to travel through the bloodstream to reach their target cells, while the nerve impulses can travel along the nerve fibers at high speeds.
Choice D is wrong because the endocrine system does use receptors.
The hormones bind to specific receptors on the target cells to trigger a response.

This helps prevent blood pooling and clotting in the lower extremities, which can lead to deep vein thrombosis and pulmonary embolism.
It also reduces the workload on the heart and improves blood circulation throughout the body.
Choice A is wrong because contraction of muscles does not stimulate the arteries to vasodilate, but rather causes vasoconstriction in the inactive tissues to divert blood flow to the active muscles.
Choice B is wrong because the contraction of muscles itself does not increase heart rate significantly unless it is part of an aerobic exercise that elevates the metabolic demand.
Burning calories and keeping the heart strong are benefits of regular physical activity, not occasional muscle contraction.
Choice C is wrong because contraction of the leg muscles does not stimulate baroreceptors, which are pressure-sensitive receptors located in the walls of the arteries.

Baroreceptors respond to changes in blood pressure and signal the autonomic nervous system to adjust heart rate and vascular resistance accordingly.
Contraction of the leg muscles does not affect blood pressure or heart rate directly but rather assists with venous return.