Anatomy & Physiology (Respiratory System)

Nostrils

The external openings of the nasal cavity that admit air.

Nasal Hairs

Hairs inside the nostrils that filter and trap large airborne particles.

Nasal Septum

The partition of bone and cartilage dividing the nasal cavity into halves.

Nasal Conchae

Bony ridges in the nasal cavity that increase surface area and warm air.

Respiratory Mucosa

The ciliated membrane lining the airway that traps debris and moves mucus.

Lacrimal Glands

Glands that secrete tears to lubricate the eyes.

Lacrimal Puncta

Small openings at the inner corners of the eyelids that drain tears.

Nasolacrimal Duct

The canal that drains tears from the lacrimal sac into the nose.

Paranasal Sinuses

Air-filled spaces in cranial bones that lighten the weight of the skull.

Choana

The funnel-shaped posterior opening of the nasal cavity leading to the pharynx.

Pharynx

The muscular throat passage connecting the nasal cavity to the larynx.

Nasopharynx

The uppermost division of the pharynx, located behind the nasal cavity.

Oropharynx

The middle division of the pharynx, located behind the mouth.

Laryngopharynx

The lowest division of the pharynx, opening into the larynx and esophagus.

Hard Palate

The bony anterior portion of the roof of the mouth.

Soft Palate

The flexible posterior muscle portion of the roof of the mouth.

Epiglottis

The elastic cartilage flap that guards the glottis during swallowing.

Glottis

The vocal apparatus of the larynx, consisting of the vocal cords and opening.

Larynx

The cartilaginous organ containing the vocal cords; also called the voice box.

Thyroid Cartilage

The largest laryngeal cartilage, commonly known as the Adam's apple.

Vocal Cords

Folds of tissue in the larynx that vibrate to produce sound.

Trachea

The windpipe; a cartilaginous tube extending from the larynx to the bronchi.

Carina

The anatomical ridge at the bifurcation of the trachea into primary bronchi.

Primary Bronchi

The two main branches of the trachea leading directly into the lungs.

Mediastinum

The central cavity of the thorax between the two lungs.

Visceral Pleura

The inner serous membrane layer adhering directly to the surface of the lungs.

Parietal Pleura

The outer serous membrane layer lining the thoracic cavity wall.

Pleural Cavity

The fluid-filled space between the visceral and parietal pleural layers.

Intrapleural Fluid

Lubricating fluid in the pleural cavity that reduces friction during breathing.

Nasal Conchae vs. Airflow

The conchae create turbulence, forcing air to bounce off the warm, moist respiratory mucosa.

Nasolacrimal Drainage Pathway

Tears flow from lacrimal glands to puncta, then drain into the nasal cavity.

Choana Boundary Zone

The transitional gateway connecting the posterior nasal cavity to the nasopharynx.

Hard Palate vs. Soft Palate Boundaries

The hard palate separates nasal/oral cavities; the soft palate seals the nasopharynx during swallowing.

Epiglottis Glottis Guarding Mechanism

During swallowing, the larynx rises, forcing the epiglottis down to seal the glottis.

Vocal Cord Volume vs. Pitch

Volume is determined by air quantity; pitch is determined by vocal cord tension.

Visceral vs. Parietal Pleura

Visceral pleura covers the lung surface; parietal pleura lines the thoracic cavity wall.

Intrapleural Fluid Function

Reduces friction between pleural layers and creates surface tension that holds the lungs open.

Negative Intrapleural Pressure Dynamics

Subatmospheric pressure prevents lung elastic recoil from causing alveolar collapse.

Bronchial Tree Surface Area Trend

As airways branch from primary bronchi to bronchioles, cross-sectional area increases dramatically.

Alveolar Elastic Tissue Role

Provides the passive stretch and recoil necessary for expiration without muscle energy.

Respiratory Membrane Composition

Alveolar squamous epithelium, capillary endothelium, and their shared fused basement membrane.

Phrenic Nerve Diaphragm Innervation

Motor nerves arising from C3-C5 that stimulate diaphragmatic contraction for inspiration.

Thoracic Volume and Pressure Relationship

Increasing thoracic volume lowers intrapulmonary pressure, drawing air into the lungs.

Quiet vs. Forced Expiration

Quiet expiration is passive elastic recoil; forced expiration requires active accessory muscle contraction.

Non-Respiratory Diaphragmatic Function

Contraction increases abdominal pressure to assist in expelling vomit, feces, or urine.

Alveolar Fluid Dissolution Step

Gases must dissolve in the thin alveolar fluid layer before diffusing across membranes.

Chloride Shift Mechanism

Bicarbonate ions diffuse out of RBCs; chloride ions enter to maintain electrical neutrality.

Medulla Oblongata vs. Pons in Breathing

Medulla sets the basic respiratory rhythm; pons smooths out the transitions between breaths.

Chemoreceptor Reflex Override

High carbon dioxide or low oxygen levels trigger involuntary breathing, overriding conscious breath-holding.

Metabolic Feedback Loop (Lactic Acid)

Lactic acid lowers blood pH, stimulating brainstem chemoreceptors to increase ventilation.

Hypoxic Ventilatory Response

Peripheral chemoreceptors detect low arterial oxygen at high altitudes, triggering hyperventilation.

Periodic Breathing Etiology

Extreme hyperventilation drops CO₂ levels below the threshold needed to stimulate the respiratory drive.

Functional Residual Capacity (FRC) Calculation

Expiratory Reserve Volume (ERV) plus Residual Volume (RV).

Inspiratory Capacity (IC) Calculation

Tidal Volume (TV) plus Inspiratory Reserve Volume (IRV).

Vital Capacity (VC) Calculation

Inspiratory Reserve Volume plus Tidal Volume plus Expiratory Reserve Volume.

Total Lung Capacity (TLC) Calculation

Inspiratory Reserve Volume plus Expiratory Reserve Volume plus Tidal Volume plus Residual Volume.

Alveolar Ventilation Calculation

(Tidal Volume minus Dead Space) multiplied by Respiratory Rate.

Dead Space vs. Alveolar Ventilation

Dead space ventilation measures wasted airflow; alveolar ventilation measures air reaching gas-exchange surfaces.

Swallowing soft palate movement

The soft palate moves reflexively upward to seal off the nasopharynx, preventing food from entering the nasal cavity.

Epiglottis guarding mechanism

During swallowing, the larynx rises and the epiglottis folds down, directing food to the esophagus and sealing the glottis.

Vocal pitch regulation mechanism

Alteration of vocal fold tension; higher tension increases pitch, while lower tension decreases pitch.

Vocal volume regulation mechanism

Adjustment of air quantity; greater force of expired air increases sound volume.

Intrapleural pressure dynamic

Negative pressure relative to atmospheric pressure acts like a vacuum, keeping the lungs inflated against chest wall recoil.

Ciliary mucus movement mechanism

Ciliated cells in the respiratory mucosa beat in unison, sweeping dirty mucus upward toward the pharynx for swallowing.

Active inspiration process

Diaphragm and external intercostals contract, expanding thoracic volume, lowering pressure, and drawing air in.

Passive quiet expiration process

Inspiratory muscles relax, and the elastic recoil of lung tissue drives air out without active muscle contraction.

Active forced breathing mechanism

Voluntary contraction of internal intercostals and abdominal muscles to rapidly decrease thoracic volume and expel air.

Non-respiratory diaphragmatic expulsion

Contraction of the diaphragm and abdominal muscles to increase intra-abdominal pressure, expelling vomit, feces, or urine.

Systemic gas exchange: Step 1 (Dissolution)

Oxygen dissolves in the thin layer of alveolar fluid lining the inner surface of the alveolus.

Systemic gas exchange: Step 2 (Diffusion)

Oxygen diffuses across the respiratory membrane down its partial pressure gradient into the pulmonary capillary blood.

Systemic gas exchange: Step 3 (Plasma entry)

Oxygen crosses the capillary endothelium and enters the blood plasma.

Systemic gas exchange: Step 4 (Oxyhemoglobin binding)

Oxygen diffuses into red blood cells and binds reversibly to hemoglobin, forming oxyhemoglobin.

Systemic gas exchange: Step 5 (Tissue delivery)

In systemic capillaries, oxygen dissociates from hemoglobin and diffuses out of blood into tissue cells.

Systemic gas exchange: Step 6 (CO₂ elimination)

Carbon dioxide diffuses from tissues into blood, is transported to the lungs, and diffuses into alveoli for exhalation.

The Chloride Shift mechanism

Bicarbonate ions diffuse out of red blood cells, while chloride ions shift in to maintain electrical neutrality.

Unconscious breathing control process

The medulla oblongata sets the basic rhythm, while the pons smooths the transition between inspiration and expiration.

Conscious breathing control process

The cerebral cortex sends direct motor signals to respiratory muscles, temporarily bypassing brainstem control.

Chemoreceptor reflex override mechanism

Sensory receptors detect high CO₂ or low pH, overriding voluntary breath-holding and forcing inspiration.

Metabolic feedback loop (Anaerobic exercise)

Lactic acid builds up, lowering blood pH; brainstem chemoreceptors detect this acidity and increase ventilation rate.

Hypoxic ventilatory response mechanism

At high altitudes, peripheral chemoreceptors detect low arterial PO₂ and trigger hyperventilation.

High altitude acclimatization: Initial phase

The body increases resting pulse rate, cardiac output, and stroke volume to maintain tissue oxygenation.

High altitude acclimatization: Late phase

Heart rate, cardiac output, and stroke volume drop back toward normal as red blood cell count increases.

Periodic breathing mechanism

Hyperventilation drops blood CO₂ below the threshold needed to stimulate breathing, causing temporary apnea.

Coughing reflex mechanism

A deep inhalation is followed by closure of the glottis and forceful contraction of expiratory muscles, opening the glottis to blast air outward.

Sneezing reflex mechanism

An irritation in the nasal cavity triggers a reflex that directs a blast of forced air upward through the nose and mouth.

Carbon monoxide poisoning mechanism

CO binds to hemoglobin with 200 times the affinity of oxygen, blocking oxygen transport without triggering standard hypoxia warnings.

Oxygen toxicity mechanism

Inhaling pure oxygen at high pressure generates excess free radicals, damaging central nervous system and pulmonary tissues.

Clinical example of active inspiration in practice

A patient deep-breathing during a lung exam, contracting the diaphragm and external intercostals.

Application of passive quiet expiration

Healthy, effortless exhalation at rest, driven entirely by elastic recoil of lung tissue.

Clinical sign of active forced breathing

An asthma patient visibly contracting internal intercostals and abdominal muscles to push air out.

Example of non-respiratory diaphragmatic pressure

A person straining during defecation or vomiting by contracting abdominal muscles against a closed glottis.

Practical scenario of the Chloride Shift

Bicarbonate leaving red blood cells in systemic capillaries while chloride ions enter to maintain charge.

Example of unconscious breathing control override

The medulla oblongata forcing a breath when a swimmer tries to hold their breath too long.

Example of conscious breathing control

A singer deliberately regulating their breath and vocalizing using the cerebral cortex.

Real-world trigger of the chemoreceptor reflex

An accumulation of carbon dioxide in the blood triggering rapid breathing during a sprint.

Example of metabolic feedback loop activation

Lactic acid buildup during a heavy workout lowering blood pH and increasing breathing rate.

Clinical presentation of hypoxic ventilatory response

A traveler arriving in high-altitude Peru and immediately hyperventilating to compensate for low oxygen.

Physiological sign of high altitude acclimatization

An athlete's elevated heart rate gradually returning to normal baseline after weeks at high elevation.

Clinical trigger for periodic breathing

A sudden drop in blood carbon dioxide levels that temporarily turns off the brain's respiratory drive.

Diagnostic use of spirometry

Having a patient blow hard into a tube to evaluate chronic obstructive pulmonary disease.