13. which of the following occurs in the cardiac cycle if the impulse triggered at the sinoatrial node never close? a. diastole will shorten in duration b. the ventricles will not contract c. there will be an absence of systole d. the atria will not contract.

What sentence best supports the statement that hormones are involved in the regulation of homeostasis? a. the hormone erythropoeitin increases the production of red blood cells when oxygen levels are low. b. the hormone oxytocin promotes labor contractions of the uterus during childbirth. c. the hormone melatonin induces sleep and its production is slowed by exposure to light. d. the hormone cortisol suppresses the immune system and is produced when the body is under stress.