Sperm cells are produced in the _________.

A zygote is created when two __________ unite.

__________ in certain arteries are sensitive to carbon dioxide and pH changes in the blood.

The _________ is a network of membranous channels in the muscle cells that releases calcium ions, causing muscle contractions.

The _________ is a network of membranous channels in the muscle cells that releases calcium ions, causing muscle contractions.

When the distance between the ends of a contracting muscle increases, the isotonic contraction is said to be _____.

The ___________ nervous system regulates the actions of glands, smooth muscles, and the heart.

All of the following are accessory organs of the digestive system except _____.

When the distance between the ends of a contracting muscle increases, the isotonic contraction is said to be _____.

The ___________ nervous system regulates the actions of glands, smooth muscles, and the heart.