Gas Exchange in Humans

A complete set of vocabulary flashcards covering the structure and function of the human breathing system, gas exchange mechanisms, inhaled vs exhaled air differences, and protective cellular structures according to Cambridge IGCSE Biology standards.

Alveolus

The gas exchange surface in humans, consisting of tiny air sacs where oxygen diffuses into the blood and carbon dioxide diffuses out.

Ribs

Bone structure that protects internal organs such as the lungs.

Intercostal Muscle

Muscles between the ribs which control their movement, causing inhalation and exhalation.

Diaphragm

A sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation.

Trachea

Windpipe that connects the mouth and nose to the bronchi, allowing air to pass into the lungs.

Larynx

Also known as the voice box; structure where sound is produced when air passes across it.

Bronchi

Large tubes branching off the trachea, with one leading into each lung (singular: bronchus).

Bronchioles

Smaller tubes formed when bronchi split inside the lungs, which connect to the alveoli.

Cartilage (in Trachea)

Rings surrounding the trachea and bronchi that support the airways and keep them open during breathing, preventing collapse when internal air pressure drops.

External Intercostal Muscles

Intercostal muscles located on the outside of the ribcage that contract during inhalation to pull the ribcage up and out.

Internal Intercostal Muscles

Intercostal muscles located on the inside of the ribcage that contract during forced exhalation to pull the ribcage down and in.

Inhalation (Inspiration)

The process of breathing in, where external intercostal muscles contract, ribcage moves up and out, diaphragm contracts and flattens, increasing thorax volume and decreasing pressure to draw air into the lungs.

Exhalation (Expiration)

The process of breathing out, where external intercostal muscles relax, ribcage moves down and in, diaphragm relaxes and becomes dome-shaped, decreasing thorax volume and increasing pressure to force air out.

Forced Exhalation

An active process during strenuous activity where internal intercostal muscles pull the ribs down and in to decrease thorax volume further, forcing air out rapidly and forcefully.

Limewater Test

An experimental test for carbon dioxide where clear limewater turns cloudy or milky when carbon dioxide is bubbled through it.

Inspired Air Composition

Inhaled atmospheric air containing approximately $21\%$ oxygen, $0.04\%$ carbon dioxide, $78\%$ nitrogen, and $0.2 - 4\%$ water vapour.

Expired Air Composition

Exhaled air containing approximately $16\%$ oxygen, $4\%$ carbon dioxide, $78\%$ nitrogen, and $1 - 5\%$ water vapour.

Oxygen Debt

The extra volume of oxygen required after exercise to break down lactic acid that accumulated in muscles during anaerobic respiration.

Chemoreceptors

Sensory cells in the medulla oblongata of the brain that detect chemical changes in the body, such as drops in blood pH caused by increased carbon dioxide levels.

Goblet Cells

Specialized cup-shaped cells lining the respiratory tract that produce mucus to trap dust, particles, and pathogens.

Ciliated Epithelial Cells

Cells lining the respiratory passages with tiny hair-like extensions (cilia) that beat to push mucus away from the lungs toward the throat.

Human Breathing System Anatomy

The organ system composed of the lungs, diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, and alveoli.