Key Terms

acclimatization

process of adjustment that the respiratory system makes due to chronic exposure to high altitudes

acute mountain sickness (AMS)

condition that occurs a result of acute exposure to high altitude due to a low partial pressure of oxygen

ala

(plural = alae) small, flaring structure of a nostril that forms the lateral side of the nares

alar cartilage

cartilage that supports the apex of the nose and helps shape the nares; it is connected to the septal cartilage and connective tissue of the alae

alveolar dead space

air space within alveoli that are unable to participate in gas exchange

alveolar duct

small tube that leads from the terminal bronchiole to the respiratory bronchiole and is the point of attachment for alveoli

alveolar macrophage

immune system cell of the alveolus that removes debris and pathogens

alveolar pore

opening that allows airflow between neighboring alveoli

alveolar sac

cluster of alveoli

alveolus

small, grape-like sac that performs gas exchange in the lungs

anatomical dead space

air space present in the airway that never reaches the alveoli and therefore never participates in gas exchange

apex

tip of the external nose

apneustic center

network of neurons within the pons that stimulate the neurons in the dorsal respiratory group; controls the depth of inspiration

atmospheric pressure

amount of force that is exerted by gases in the air surrounding any given surface

Bohr effect

relationship between blood pH and oxygen dissociation from hemoglobin

Boyle’s law

relationship between volume and pressure as described by the formula: P₁V₁ = P₂V₂

bridge

portion of the external nose that lies in the area of the nasal bones

bronchial bud

structure in the developing embryo that forms when the laryngotracheal bud extends and branches to form two bulbous structures

bronchial tree

collective name for the multiple branches of the bronchi and bronchioles of the respiratory system

bronchiole

branch of bronchi that are 1 mm or less in diameter and terminate at alveolar sacs

bronchoconstriction

decrease in the size of the bronchiole due to relaxation of the muscular wall

bronchodilation

increase in the size of the bronchiole due to contraction of the muscular wall

bronchus

tube connected to the trachea that branches into many subsidiaries and provides a passageway for air to enter and leave the lungs

carbaminohemoglobin

bound form of hemoglobin and carbon dioxide

carbonic anhydrase (CA)

enzyme that catalyzes the reaction that causes carbon dioxide and water to form carbonic acid

cardiac notch

indentation on the surface of the left lung that allows space for the heart

central chemoreceptor

one of the specialized receptors that are located in the brain that sense changes in hydrogen ion, oxygen, or carbon dioxide concentrations in the brain

chloride shift

facilitated diffusion that exchanges bicarbonate (HCO₃^–) with chloride (Cl^–) ions

conducting zone

region of the respiratory system that includes the organs and structures that provide passageways for air and are not directly involved in gas exchange

cricoid cartilage

portion of the larynx composed of a ring of cartilage with a wide posterior region and a thinner anterior region; attached to the esophagus

Dalton’s law

statement of the principle that a specific gas type in a mixture exerts its own pressure, as if that specific gas type was not part of a mixture of gases

dorsal respiratory group (DRG)

region of the medulla oblongata that stimulates the contraction of the diaphragm and intercostal muscles to induce inspiration

dorsum nasi

intermediate portion of the external nose that connects the bridge to the apex and is supported by the nasal bone

epiglottis

leaf-shaped piece of elastic cartilage that is a portion of the larynx that swings to close the trachea during swallowing

expiration

(also, exhalation) process that causes the air to leave the lungs

expiratory reserve volume (ERV)

amount of air that can be forcefully exhaled after a normal tidal exhalation

external nose

region of the nose that is easily visible to others

external respiration

gas exchange that occurs in the alveoli

fauces

portion of the posterior oral cavity that connects the oral cavity to the oropharynx

fibroelastic membrane

specialized membrane that connects the ends of the C-shape cartilage in the trachea; contains smooth muscle fibers

forced breathing

(also, hyperpnea) mode of breathing that occurs during exercise or by active thought that requires muscle contraction for both inspiration and expiration

foregut

endoderm of the embryo towards the head region

functional residual capacity (FRC)

sum of ERV and RV, which is the amount of air that remains in the lungs after a tidal expiration

glottis

opening between the vocal folds through which air passes when producing speech

Haldane effect

relationship between the partial pressure of oxygen and the affinity of hemoglobin for carbon dioxide

Henry’s law

statement of the principle that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas

hilum

concave structure on the mediastinal surface of the lungs where blood vessels, lymphatic vessels, nerves, and a bronchus enter the lung

hyperpnea

increased rate and depth of ventilation due to an increase in oxygen demand that does not significantly alter blood oxygen or carbon dioxide levels

hyperventilation

increased ventilation rate that leads to abnormally low blood carbon dioxide levels and high (alkaline) blood pH

inspiration

(also, inhalation) process that causes air to enter the lungs

inspiratory capacity (IC)

sum of the TV and IRV, which is the amount of air that can maximally be inhaled past a tidal expiration

inspiratory reserve volume (IRV)

amount of air that enters the lungs due to deep inhalation past the tidal volume

internal respiration

gas exchange that occurs at the level of body tissues

intra-alveolar pressure

(intrapulmonary pressure) pressure of the air within the alveoli

intrapleural pressure

pressure of the air within the pleural cavity

laryngeal prominence

region where the two lamine of the thyroid cartilage join, forming a protrusion known as “Adam’s apple”

laryngopharynx

portion of the pharynx bordered by the oropharynx superiorly and esophagus and trachea inferiorly; serves as a route for both air and food

laryngotracheal

bud forms from the lung bud, has a tracheal end and bulbous bronchial buds at the distal end

larynx

cartilaginous structure that produces the voice, prevents food and beverages from entering the trachea, and regulates the volume of air that enters and leaves the lungs

lingual tonsil

lymphoid tissue located at the base of the tongue

lung

organ of the respiratory system that performs gas exchange

lung bud

median dome that forms from the endoderm of the foregut

meatus

one of three recesses (superior, middle, and inferior) in the nasal cavity attached to the conchae that increase the surface area of the nasal cavity

naris

(plural = nares) opening of the nostrils

nasal bone

bone of the skull that lies under the root and bridge of the nose and is connected to the frontal and maxillary bones

nasal septum

wall composed of bone and cartilage that separates the left and right nasal cavities

nasopharynx

portion of the pharynx flanked by the conchae and oropharynx that serves as an airway

olfactory pit

invaginated ectodermal tissue in the anterior portion of the head region of an embryo that will form the nasal cavity

oropharynx

portion of the pharynx flanked by the nasopharynx, oral cavity, and laryngopharynx that is a passageway for both air and food

oxygen–hemoglobin dissociation curve

graph that describes the relationship of partial pressure to the binding and disassociation of oxygen to and from heme

oxyhemoglobin

(Hb–O₂) bound form of hemoglobin and oxygen

palatine tonsil

one of the paired structures composed of lymphoid tissue located anterior to the uvula at the roof of isthmus of the fauces

paranasal sinus

one of the cavities within the skull that is connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consists of frontal, maxillary, sphenoidal, and ethmoidal sinuses

parietal pleura

outermost layer of the pleura that connects to the thoracic wall, mediastinum, and diaphragm

partial pressure

force exerted by each gas in a mixture of gases

peripheral chemoreceptor

one of the specialized receptors located in the aortic arch and carotid arteries that sense changes in pH, carbon dioxide, or oxygen blood levels

pharyngeal tonsil

structure composed of lymphoid tissue located in the nasopharynx

pharynx

region of the conducting zone that forms a tube of skeletal muscle lined with respiratory epithelium; located between the nasal conchae and the esophagus and trachea

philtrum

concave surface of the face that connects the apex of the nose to the top lip

pleural cavity

space between the visceral and parietal pleurae

pleural fluid

substance that acts as a lubricant for the visceral and parietal layers of the pleura during the movement of breathing

pneumotaxic center

network of neurons within the pons that inhibit the activity of the neurons in the dorsal respiratory group; controls rate of breathing

pulmonary artery

artery that arises from the pulmonary trunk and carries deoxygenated, arterial blood to the alveoli

pulmonary plexus

network of autonomic nervous system fibers found near the hilum of the lung

pulmonary surfactant

substance composed of phospholipids and proteins that reduces the surface tension of the alveoli; made by type II alveolar cells

pulmonary ventilation

exchange of gases between the lungs and the atmosphere; breathing

quiet breathing

(also, eupnea) mode of breathing that occurs at rest and does not require the cognitive thought of the individual

residual volume (RV)

amount of air that remains in the lungs after maximum exhalation

respiratory bronchiole

specific type of bronchiole that leads to alveolar sacs

respiratory cycle

one sequence of inspiration and expiration

respiratory epithelium

ciliated lining of much of the conducting zone that is specialized to remove debris and pathogens, and produce mucus

respiratory membrane

alveolar and capillary wall together, which form an air-blood barrier that facilitates the simple diffusion of gases

respiratory rate

total number of breaths taken each minute

respiratory volume

varying amounts of air within the lung at a given time

respiratory zone

includes structures of the respiratory system that are directly involved in gas exchange

root

region of the external nose between the eyebrows

thoracic wall compliance

ability of the thoracic wall to stretch while under pressure

thyroid cartilage

largest piece of cartilage that makes up the larynx and consists of two lamine

tidal volume (TV)

amount of air that normally enters the lungs during quiet breathing

total dead space

sum of the anatomical dead space and alveolar dead space

total lung capacity (TLC)

total amount of air that can be held in the lungs; sum of TV, ERV, IRV, and RV

total pressure

sum of all the partial pressures of a gaseous mixture

trachea

tube composed of cartilaginous rings and supporting tissue that connects the lung bronchi and the larynx; provides a route for air to enter and exit the lung

trachealis muscle

smooth muscle located in the fibroelastic membrane of the trachea

transpulmonary pressure

pressure difference between the intrapleural and intra-alveolar pressures

true vocal cord

one of the pair of folded, white membranes that have a free inner edge that oscillates as air passes through to produce sound

type I alveolar cell

squamous epithelial cells that are the major cell type in the alveolar wall; highly permeable to gases

type II alveolar cell

cuboidal epithelial cells that are the minor cell type in the alveolar wall; secrete pulmonary surfactant

ventilation

movement of air into and out of the lungs; consists of inspiration and expiration

ventral respiratory group (VRG)

region of the medulla oblongata that stimulates the contraction of the accessory muscles involved in respiration to induce forced inspiration and expiration

vestibular fold

part of the folded region of the glottis composed of mucous membrane; supports the epiglottis during swallowing

visceral pleura

innermost layer of the pleura that is superficial to the lungs and extends into the lung fissures

vital capacity (VC)

sum of TV, ERV, and IRV, which is all the volumes that participate in gas exchange