Functional units of the organ systems

cardiac muscle

a branching network of cells that contracts to push blood from our atria to our ventricles and out to the rest of the body

capillaries

blood vessels of the circulatory system that are skinny enough for O2, CO2, hormones, monomers from food, and wastes like urea to diffuse into or out of them in the appropriate places in the body

smooth muscle

contracts in waves to push food along our digestive track or constricts our blood vessels to regulate blood flow

neurons

nervous system cells that transmit action potentials down their axons and then release neurotransmitters to diffuse across a synapse to the dendrites of the next neuron

glands

organs that secrete hormones into the bloodstream to trigger longer term changes in the body (growth, development, thirst, blood sugar regulation, etc.)

skeletal muscle

organs that work in flexor/extensor pairs and move our skeleton by contracting, pulling on tendons which cause our bones to move in our joints.

villi

small fingerlike projections in the small intestine that increase the surface area where broken down food molecules can be absorbed

nephron

the repeating series of capillaries and tubes in the kidney that filters small substances from the blood and then reabsorbs the good substances, leaving urea and some water to be excreted.

alveoli

tiny sacs in the lung that provide the surface area for O2 to diffuse into the blood and CO2 to diffuse out