The autonomic system of the PNS controls involuntary processes such as breathing. The process of breathing is under the direction of the peripheral nervous system (PNS).

Oxygen in arterial blood diffuses from the blood into cells. Carbon dioxide diffuses from cells into blood and is transported to the heart by veins. This is accomplished through cardiovascular circulation. Gaseous waste products of cellular respiration such as carbon dioxide must be removed. Oxygen used by cells and tissues must be replaced. The oxygen-rich blood is then transported to the heart where it is pumped out to the rest of the body.Ī similar exchange of gases takes place at body tissues and cells. At the same time, carbon dioxide diffuses from the blood into the alveoli sacs and is exhaled through air passages. As a result, oxygen diffuses across the thin endothelium of the alveoli sacs into the blood within the surrounding capillaries. Oxygen levels within the alveoli sacs is at a higher concentration than oxygen levels in the capillaries surrounding the alveoli. Lung alveoli are coated with a moist film that dissolves air. These arteries form smaller blood vessels called arterioles which send blood to capillaries surrounding millions of lung alveoli. Pulmonary arteries transport oxygen-depleted blood containing carbon dioxide to the lungs. This air fills tiny air sacs in the lungs called alveoli. When the diaphragm relaxes again, space within the chest cavity decreases and the air is forced out of the lungs.Īir is brought into the lungs from the external environment contains oxygen needed for body tissues. The lower air pressure in the lungs causes air to be drawn into the lungs through the nasal passages until the pressure differences equalize. These actions increase volume in the chest cavity and lower air pressure within the lungs. As the diaphragm contracts, the diaphragm moves downward and the intercostal muscles move outward. This shape reduces the volume in the chest cavity. The diaphragm is shaped like a dome and is at its maximum height when it is relaxed. All of these factors must be under strict control and the respiratory system must able to respond to changing demands when necessary.Īir is brought into the lungs by actions of respiratory muscles. Gases must be able to be exchanged between the air and blood, as well as between the blood and body cells. Air must be able to flow into and out of the lungs. There are a number of facets involved in breathing.

Abdominal muscles: aid in faster exhalation of air.īreathing is a complex physiological process that is performed by respiratory system structures.Intercostal muscles: several groups of muscles located between the ribs that help to expand and shrink the chest cavity to aid in breathing.It contracts and relaxes to enable breathing. Diaphragm: muscular partition that separates the chest cavity from the abdominal cavity.Pulmonary veins: blood vessels that transport oxygen-rich blood from the lungs back to the heart.Pulmonary arteries: blood vessels that transport oxygen-depleted blood from the heart to the lungs.Alveoli: bronchiole terminal sacs that are surrounded by capillaries and are the respiratory surfaces of the lungs.Bronchioles: smaller bronchial tubes within the lungs that direct air to small air sacs known as alveoli.Bronchial tubes: tubes within the lungs that direct air into bronchioles and lets air out of the lungs.Lungs: paired organs in the chest cavity that enable gas exchange between the blood and the air.Trachea (windpipe): splits into left and right bronchial tubes that direct air to the left and right lungs.Larynx (voice box): directs air to the windpipe and contains vocal cords for vocalization.Pharynx (throat): directs air from the nose and mouth to the larynx.Nose and Mouth: openings that allow outside air to flow into the lungs.These structures are typically grouped into three main categories: air passages, pulmonary vessels, and respiratory muscles. Respiratory system structures help to bring air from the environment into the body and expel gaseous waste from the body.

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