Glossary

alveolar sacs

Part of the respiratory zone structures, located at the end of the alveolar duct.

apnoea

A temporary cessation of breathing.

Bohr effect

Influence of CO₂ and acidity on the affinity of haemoglobin for oxygen.

bronchi

The two main branches of the windpipe or trachea, leading to the lungs (singular, bronchus).

carbaminohaemoglobin

Haemoglobin that is bound to carbon dioxide (HbCO₂).

cellular respiration

The metabolic process in which living cells obtain energy (in the form of adenosine triphosphate, ATP) from the breakdown of molecules, particularly glucose.

central chemoreceptors

Receptors located on neurons within the medullary and pontine respiratory centres of the brain that detect differences in blood pH.

compliance

The ease with which the lungs and pleura expand and contract based on changes in pressure.

conduction zone

The parts of the lungs that conduct gas to and from the external environment.

deoxyhaemoglobin

Haemoglobin that is not bound to oxygen.

diaphragm

A muscular wall involved in lung ventilation, separating the chest (thoracic) cavity from the abdominal cavity.

external respiration

Exchange of gases in the lung between the blood and the external environment.

forced expiratory volume 1

The amount of air that is forcibly blown out within the first second of a spirometry test.

forced vital capacity

Total volume of air that can be forcefully blown out.

haemoglobin

A globular iron-containing protein present in red blood cells, which binds oxygen at the lungs and transports it to the tissues. Some of the carbon dioxide transported from the tissues to the lungs is also carried by haemoglobin.

Haldane effect

Influence of oxygen on haemoglobin transport of carbon dioxide.

hypopnoea

Reduction in airflow.

intercostal muscles

External and internal muscles between the ribs that are involved in the movement of the ribcage during breathing.

intercostal nerves

Nerves that innervate the intercostal muscles.

lungs

The respiratory organs that are located in the chest cavity; consisting of two elastic sacs with branching airways that allow air to be drawn into the body and expelled by a combination of muscular action and elastic recoil. They provide a large surface area where gaseous exchange occurs between the blood and the air.

nasal cavities

Part of the upper respiratory tract by which air enters and leaves the body.

oxygen–haemoglobin dissociation curve

'S'-shaped curve that dictates how the affinity of haemoglobin for oxygen changes with different partial pressures of oxygen.

oxyhaemoglobin

Haemoglobin bound to oxygen molecules. Oxyhaemoglobin transports oxygen from blood vessels in the lungs to the cells in the rest of the body,

partial pressure

The pressure that one component of a mixture of gases would exert if it were alone in a container.

peak expiratory flow

The maximum rate at which air is forcefully expired (litres per second).

peripheral chemoreceptors

Receptors in the carotid artery (carotid bodies) and aorta (aortic bodies) of the heart that detect and respond to changes in partial pressure of oxygen.

pharynx

The opening at the back of the throat that serves as a common passageway for the digestive and respiratory systems.

phrenic nerve

Nerve originating in the medulla of the brain that innervates the diaphragm.

pleura

The thin membranes lining the fluid-filled cavity (the pleural cavity) between the lungs and the inside of the thoracic (chest) wall (singular, pleura).

resistance

The friction that is generated when the air passes along the structures in the conduction and respiratory zones.

respiratory centres

The areas of the medulla region in the brain that integrate sensory information from chemoreceptors monitoring the level of oxygen and carbon dioxide in the blood. The respiratory centres send out appropriate signals to regulate the rate of contraction of the respiratory muscles (including the diaphragm and intercostal muscles).

respiratory zones

Composed of the bronchioles, alveolar ducts and alveoli in which gas exchange takes place during respiration.

sickle cell anaemia

A genetic disorder linked to abnormal haemoglobin. A point mutation has replaced the amino acid glutamic acid with valine, disrupting the structure of haemoglobin. The abnormal haemoglobin crystallizes when deoxygenated, forming sickle-shaped red blood cells that tend to block capillaries.

spirometry

A test used to measure lung function.

surface tension

Chemical forces that hold liquids in their smallest surface area possible.

surfactant

A phospholipid substance that breaks surface tension of water by attaching to the water molecules and preventing them from interacting with each other.

thalassaemias

A group of inherited autosomal recessive disorders that cause anaemia because of the decreased or absent synthesis of a globin chain of haemoglobin.

trachea

A tube that connects the throat (pharynx) and voice box (larynx) to the lungs, allowing the passage of air. Also known as the windpipe.