The human female reproductive cycle is regulated primarily by the
white blood cells of the circulatory system
muscle cells of the skeletal system
enzymes of the digestive system
hormones of the endocrine system

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

b a mature ovary of a plant.