The ventricle has thicker, more muscular walls than the atria. relate this difference in wall structure to the functions of the 2 types of heart chamber.

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.

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