Which of the following neurotransmitters plays an excitatory role in neuromuscular transmission?

A. The spleen is a key component of the lymphatic system. It filters blood, removes old or damaged blood cells, and plays a role in immune function by storing white blood cells that fight infection.

B. The thyroid gland is an endocrine gland involved in regulating metabolism through the production of thyroid hormones, but it is not part of the lymphatic system.

C. The adrenal glands are also endocrine glands responsible for producing hormones like adrenaline and cortisol. They are not part of the lymphatic system.

D. The pancreas is an organ involved in digestion and blood sugar regulation through insulin production. It does not function within the lymphatic system.

A. The tricuspid valve has three leaflets and is located between the right atrium and right ventricle. It closes during ventricular contraction (systole) but does not have two leaflets.

B. The pulmonic valve has three leaflets and controls blood flow from the right ventricle to the pulmonary artery. It is closed during the systolic phase but is not the correct answer for having two leaflets.

C. The aortic valve has three leaflets and controls blood flow from the left ventricle into the aorta. It also closes during systole, but it does not have two leaflets.

D. The mitral valve, also known as the bicuspid valve, has two leaflets and is located between the left atrium and left ventricle. It closes during systole to prevent backflow of blood into the left atrium.