Respiratory and Circulatory Systems: Structure, Function, and Gas Exchange

Vocabulary terms and key definitions covering the structures, pathways, and mechanisms of gas exchange and transport in the human respiratory and circulatory systems.

Alveoli

Tiny air sacs in the lungs where oxygen enters the blood and carbon dioxide leaves it.

Capillaries

The smallest blood vessels, featuring walls that are only one cell thick, which connect arteries and veins and form a mesh around the alveoli.

Diaphragm

The dome of muscle located beneath the lungs that contracts and flattens to pull air into the lungs and relaxes to push air out.

Diffusion

The movement of molecules or particles from a region where they are crowded (high concentration) to where they are sparse (low concentration).

Hemoglobin

The oxygen-carrying protein packed inside red blood cells that oxygen binds to for transport and that gives red blood cells their color.

Trachea

The tubular airway that directs air from the nose or mouth down toward the lungs before splitting into two bronchi.

Bronchi

The two main branches of the airway that split from the trachea, one entering each lung, which repeatedly branch into smaller tubes.

Bronchioles

Smaller branching tubes within the lungs that lead directly to the alveoli.

Concentration Gradient

The difference between a crowded area of high concentration and a sparse area of low concentration across which particles drift.

Passive Transport

The movement of substances driven solely by the random motion of particles without requiring cellular energy, pumps, or carrier proteins.

Arteries

Elastic blood vessels that carry blood away from the heart.

Veins

Blood vessels that transport blood back toward the heart.

Plasma

The liquid component of blood in which carbon dioxide travels mostly dissolved as waste returning to the lungs.

Heart

A muscular organ with four chambers that serves as a pump running two simultaneous circulatory circuits through the body.

Lungs

Two air-filled organs that bring in fresh air and allow the transfer of oxygen into the bloodstream.

Right Side of the Heart

The side of the heart that pumps oxygen-poor blood to the lungs.

Left Side of the Heart

The side of the heart that pumps oxygen-rich blood out to the rest of the body.