Summary
Highlights
The respiratory system, also known as the human breathing system, is responsible for taking in oxygen and expelling carbon dioxide from the body. It enables us to breathe.
The respiratory system includes the nose and mouth (entrance for oxygen), nasal cavity (warms, moistens, and cleans air), pharynx (throat), larynx (voice box), trachea (windpipe), lungs (main organs), bronchi (tubes connecting trachea to lungs), bronchioles (hair-like tubes connecting to alveoli), and alveoli (where gas exchange occurs).
During inhalation, oxygen enters, ribs move out, chest space increases, and the diaphragm contracts (moves down). During exhalation, carbon dioxide exits, ribs move in, chest space decreases, and the diaphragm relaxes (moves up).
The circulatory system, also known as the cardiovascular system, is the life support structure that nourishes cells and delivers materials throughout the body, working with other body systems.
The major parts of the circulatory system are the heart (pumps blood), blood vessels (carry blood), and blood (transports materials). There are three types of blood vessels: arteries (carry blood away from the heart), veins (carry blood towards the heart), and capillaries (smallest vessels where gas and nutrient exchange happen).
The heart has four chambers: two atria (receiving chambers: right atrium and left atrium) and two ventricles (pumping chambers: right ventricle and left ventricle). Valves between atria and ventricles prevent blood from flowing backward.
Deoxygenated blood enters the right atrium, goes through the tricuspid valve, into the right ventricle, through the pulmonary valve, and exits to the pulmonary artery to the lungs. Oxygenated blood from the lungs enters the left atrium via the pulmonary vein, passes through the bicuspid valve, into the left ventricle, through the aortic valve, and exits to the aorta to the rest of the body.
Air enters the lungs, then goes to the left side of the heart, which pumps oxygenated blood throughout the body. Oxygen helps process nutrients in cells to release energy, producing carbon dioxide. The blood carries carbon dioxide back to the right side of the heart, which pumps it to the lungs for exhalation.
There are three types of circulation: pulmonary circulation (movement of blood from the heart to the lungs and back), coronary circulation (movement of blood through the tissues of the heart only), and systemic circulation (movement of blood from the heart to the rest of the body, excluding the lungs).