The smallest units of an element that retain the properties of the element.
Units of two or more atoms of the same or different elements bonded together.
The basic structural and functional units of living things.
Discrete structures composed of more than one tissue that perform a specialized function.
Chemical messengers that are produced in one location in the body, released into the blood, and travel to other locations, where they elicit responses.
The process by which food is broken down into components small enough to be absorbed into the body.
The process of taking substances from the gastrointestinal tract into the interior of the body.
Body waste, including unabsorbed food residue, bacteria, mucus, and dead cells, which is eliminated from the gastrointestinal tract by way of the anus.
Protein molecules that accelerate the rate of specific chemical reactions without themselves being changed.
A watery fluid that is produced and secreted into the mouth by the salivary glands. In contains lubricants, enzymes, and other substances.
A piece of elastic connective tissue that covers the opening to the lungs during swallowing.
Coordinated muscular contractions that move material through the GI tract.
A semiliquid food mass formed in the stomach
An enzyme that breaks down starches into sugars.
An enzyme that breaks down proteins.
An enzyme responsible for breaking fats down into fatty acids.
A digestive fluid made in the liver and stored in the gall bladder that is released into the small intestine, where it aids in fat digestion and absorption.
The unassisted diffusion of a substance across the cell membrane.
The unassisted diffusion of water across the cell membrane.
Assisted diffusion of a substance across the cell membrane.
The transport of substances across a cell membrane with the aid of a carrier molecule and the expenditure of energy.
A foreign substance that, when introduced into the body, stimulates and immune response.
Proteins, released by a type of lymphocyte, that interact with and deactivate specific antigens.
A substance that causes an allergic reaction.
A burning sensation in the chest or throat caused when acidic stomach contents leak back into the esophagus.
Gastroesophageal Reflux Disease (GERD)
A chronic condition in which acidic stomach contents leak into the esophagus, causing pain and damaging the esophagus.
Open sores in the lining of the stomach, esophagus, or upper small intestine.
Small, thin walled blood vessels through which blood and the body's cells exchange gases and nutrients.
Lymph vessels in the villi of the small intestine that pick up particles containing the products of fat digestion.
A high-energy molecule that the body uses to power activities that require energy.