IB Biology - Topic 6.4 - Gas exchange

Alveoli

Alveoli

air sacs that constitute the gas exchange surface of the lungs.

Antagonistic muscle

a muscle that opposes the action of another.

Bronchi

the two main branches of the trachea that go into the lungs; this then further divides into the bronchioles and alveoli.

Bronchioles

any of the fine, thin-walled, tubular extensions of a bronchus.

Capillary

one of the minute blood vessels that connect arterioles and veins where the interchange of various substances occur.

Concentration gradient

the gradient resulting from an unequal distribution of ions across the cell membrane.

Diaphragm

a dome-shaped muscular partition separating the thorax from the abdomen. It plays a major role in breathing as its contraction increases the volume of the thorax and so inflates the lungs.

Emphysema

a chronic respiratory disease where there is over-inflation of the air sacs (alveoli) in the lungs causing a decrease in lung function and often breathlessness.

Epidemiology

the study of the incidence and causes of disease.

Expiration

when the muscles of the thorax contract to cause the volume to decrease, this increases the pressure in the lungs and air moves from the higher pressure inside the lungs to the lower pressure outside the body.

Inspiration

when the air moves from a higher pressure (outside the body) to the lower pressure (inside the lungs).

Intercostal muscles

muscles found between the ribs. They are mainly involved in the mechanical aspect of breathing.

Pneumocyte

one of the cells lining the alveoli (the air sacs) in the lung that assists in gas exchange and in the secretion of pulmonary surfactant.

Spirometer

an instrument for measuring the volume of air entering and leaving the lungs.

Surface tension

the force that causes the molecules on the surface of a liquid to be pushed together and form a layer.

Surfactant

a substance composed of lipoprotein that is secreted by the alveolar cells of the lung and serves to maintain the stability of pulmonary tissue by reducing the surface tension of fluids that coat the lung.

Tidal volume

the volume of air inspired or expired in a single breath during regular breathing.

Trachea

thin-walled, cartilaginous tube descending from the larynx to the bronchi and carrying air to the lungs.

Ventilation rate

the volume of air passing into and out of the lungs per minute.

Inhalation

diaphragm contracts and flattens; abdominal muscles relax external intercostal muscles contract; internal intercostals relax; volume in thoracic cavity increases; pressure in lungs drops below atmospheric pressure; air flows into lungs along a pressure gradient.

Exhalation

diaphragm relaxes and curves upwards; abdominal muscles contract; internal intercostal muscles contract; external intercostals relax; volume in thoracic cavity is decreased; pressure in lungs rises above atmospheric pressure; air flows out of lungs along a pressure gradient.