The Respiratory System: Anatomy, Mechanics, and Gas Exchange

Comprehensive vocabulary flashcards covering the human respiratory system, pulmonary anatomy, mechanics of ventilation, lung volumes, gas transport, and cardiorespiratory exercise physiology.

Respiratory System

The organ system consisting of the airways, lungs, and blood vessels responsible for bringing atmospheric air into the lungs, supplying blood with $O_2$, removing $CO_2$ waste, and facilitating voice production.

Three Main Sections of the Respiratory System

The anatomical divisions of the respiratory system consisting of the airways (conducting system), the lungs, and the blood vessels (pulmonary capillaries and vasculature).

Conducting System

The series of air pathways—including the nasal cavity, oral cavity, pharynx, larynx, trachea, and bronchi—that warm, filter, moisten, and transport air deep into the lungs.

Inspiration

The active process of breathing in, during which the intercostal muscles contract (lifting ribs upwards and outwards) and the diaphragm contracts downwards, enlarging the thoracic cavity, lowering pressure in the lungs below atmospheric pressure, and causing air to rush in.

Expiration

The passive process of breathing out at rest, during which the intercostal muscles and diaphragm relax, allowing the ribs to drop and lung volume to decrease, thereby raising intrapulmonary pressure above atmospheric pressure to push air out.

Diaphragm

The major dome-shaped breathing muscle separating the thoracic and abdominal cavities that contracts downward to enlarge thoracic volume during inhalation and relaxes upward during resting exhalation.

Epiglottis

A flexible flap of cartilage situated above the larynx that folds down during swallowing to prevent food and liquid from entering the trachea and lungs.

Trachea

The cartilaginous windpipe that carries air from the larynx down into the chest cavity, where it splits into the left and right primary bronchi.

Alveoli

Microscopic, thin-walled air sacs in the lungs surrounded by dense capillary networks that provide an expansive surface area (equivalent to the size of a tennis court) for gaseous exchange.

Diffusion

The natural movement of gas or solute particles from a region of higher concentration to a region of lower concentration down a concentration gradient.

Gaseous Exchange

The physiological process occurring at the alveoli/capillary and capillary/muscle interfaces where $O_2$ diffuses into blood or cells and $CO_2$ diffuses out down partial pressure and concentration gradients.

Respiratory Rate ($RR$)

The frequency of breathing expressed as the number of breaths taken per minute, averaging $12\text{--}15\text{ breaths/min}$ at rest.

Tidal Volume ($TV$)

The volume of air inhaled and exhaled per breath, averaging $600\,\text{mL}$ in males and $500\,\text{mL}$ in females ($0.5\,\text{L/breath}$ at rest) and peaking sub-maximally during exercise.

Minute Ventilation (Pulmonary Ventilation, $V$)

The total volume of air moved into and out of the respiratory tract each minute, calculated as $V = TV \times RF$ (averaging $6.0\,\text{L/min}$ at rest: $12\,\text{breaths/min} \times 0.5\,\text{L/breath}$).

Inspiratory Reserve Volume ($IRV$)

The maximal extra volume of air that can be inspired into the lungs following the end of a normal tidal inspiration, averaging $45\,\text{mL/kg}$.

Inspiratory Capacity ($IC$)

The maximum volume of air that can be inspired after reaching the end of a normal expiration, averaging $3.8\,\text{L}$ in males and $2.4\,\text{L}$ in females.

Vital Capacity ($VC$)

The total volume of air exhaled following maximal inhalation, averaging $4.8\,\text{L}$ in males and $3.1\,\text{L}$ in females ($60\text{--}70\,\text{mL/kg}$).

Total Lung Capacity ($TLC$)

The total volume of air contained within the lungs following maximal inspiratory effort, averaging $75\text{--}80\,\text{mL/kg}$.

Expiratory Reserve Volume ($ERV$)

The additional volume of air that can be forcefully exhaled from the lungs after the conclusion of a normal tidal expiration, averaging $15\,\text{mL/kg}$.

Residual Volume ($RV$)

The volume of air that permanently remains in the lungs following a maximal, forceful expiration, averaging $1.2\,\text{L}$ in males and $1.1\,\text{L}$ in females ($15\text{--}20\,\text{mL/kg}$).

Functional Residual Capacity ($FRC$)

The volume of air remaining inside the lungs following a normal, resting expiration, averaging $2.4\,\text{L}$ in males and $1.8\,\text{L}$ in females ($30\,\text{mL/kg}$).

Spirometry

The recording and measurement of pulmonary lung volumes and capacities over time across resting breathing and maximal inspiratory/expiratory efforts.

Respiratory Control Centre

The neural structure located in the brain that monitors blood concentrations of $O_2$ and $CO_2$ and adjusts heart rate and respiratory rate to maintain homeostasis.

Haemoglobin ($Hb$)

An iron-based protein located in red blood cells that transports $O_2$ to tissues and $CO_2$ back to the lungs; each molecule binds up to four $O_2$ molecules, allowing $100\,\text{mL}$ of blood to carry approximately $20\,\text{mL}$ of $O_2$.

Oxyhaemoglobin ($HbO_2$)

The chemical complex formed when oxygen chemically binds to haemoglobin molecules within red blood cells.

Myoglobin

An oxygen-binding protein in skeletal and cardiac muscle fibers that accepts oxygen from capillaries, stores it, and delivers it to the mitochondria.

Mitochondria

The specialized intracellular organelles within cells that serve as the site for ATP resynthesis via aerobic respiration.

Arteriovenous Oxygen Difference ($a\text{-}vO_2\text{ diff}$)

The numerical difference in oxygen concentration between arterial and venous blood, which widens during exercise as working muscles extract greater amounts of oxygen from the bloodstream.