When the first heart sound is heard, what is occurring with the heart valves?

A. Maintaining blood glucose concentration: Incorrect (this is a liver function) -the liver stores glycogen and performs gluconeogenesis to regulate blood glucose.
B. Secretion of bile: Incorrect (this is a liver function) -the liver synthesizes and secretes bile.
C. Formation of urea: Incorrect (this is a liver function) -the liver converts ammonia to urea (urea cycle).
D. Secretion of insulin: insulin is produced and secreted by the pancreatic β-cells, not the liver, so this is not a liver function.

A. External jugular vein: the external jugular drains superficial structures of the head and neck (including much of the face and scalp) and empties into the subclavian vein.
B. Superior vena cava: Incorrect (in the direct sense) -the superior vena cava is the large trunk that returns venous blood to the right atrium, but it does not directly drain the face/scalp; it receives blood ultimately via the brachiocephalic veins.
C. Subclavian vein: Partially related but not the primary answer -the subclavian receives blood from the external jugular, but it primarily drains the upper limb; it is a larger trunk rather than the direct superficial drain of face/scalp.
D. Cephalic vein: the cephalic vein is a superficial vein of the lateral upper limb (arm/forearm), not a drain of the head or face.