The Respiratory System

What are the anatomical divisions of the respiratory tract?

Upper (nose to pharynx), Lower (larynx to lungs).

What are the physiological divisions of the respiratory tract?

Conducting zone (nose to terminal bronchioles), Respiratory zone (respiratory bronchioles to alveoli).

What epithelium lines the conducting zone?

Mostly pseudostratified ciliated columnar with goblet cells; oro-/laryngopharynx has stratified squamous.

What epithelium lines the respiratory zone?

Simple squamous (Type I cells).

What is the role of goblet cells in the respiratory epithelium?

Produce mucus to trap inhaled particles.

What is the role of Type II alveolar cells?

Secrete surfactant to reduce surface tension.

What are the functions of nasal conchae?

Spin air, remove particles, increase mucosal/olfactory contact.

How do the right and left lungs differ?

Right: 3 lobes, 2 fissures (oblique, horizontal). Left: 2 lobes, 1 fissure (oblique), cardiac notch.

What is the primary muscle of respiration?

Diaphragm (contracts to expand thoracic cavity).

Name two accessory muscles of inspiration.

External intercostal muscles, sternocleidomastoid.

What is the role of pleural fluid?

Reduces friction, aids adhesion of pleural membranes via surface tension.

Why is the right main bronchus more prone to foreign object entry?

Wider and more vertical than the left.

What triggers the cough reflex at the carina?

Mechanical stimuli at the last tracheal cartilage.

What is the function of the nasal cavity’s blood vessel plexus?

Warms incoming air.

How does inspiration occur?

Thoracic cavity expands, intrapulmonary pressure decreases, air is drawn in.

What is the primary function of breathing?

Maintain blood gas homeostasis (O₂, CO₂, pH).

What are the two zones of the respiratory tree?

Conducting airways (trachea to non-respiratory bronchioles), respiratory unit (respiratory bronchioles to alveoli).

What muscle is the primary driver of inspiration?

Diaphragm (descends to expand thoracic cavity).

How does quiet expiration occur?

Passive process via elastic recoil of lungs and thorax.

Name two accessory muscles used in strenuous inspiration.

Sternocleidomastoid, alae nasi.

What is the tidal volume at rest?

~500 ml per breath.

What is anatomic dead space?

Air in conducting airways (~150 ml) that does not participate in gas exchange.

How is partial pressure of a gas calculated?

Pgas = Fraction of gas (Fgas) × Barometric pressure (PB).

What is the PO₂ in the trachea after humidification?

150 mmHg (PIO₂ = (760 – 47) × 0.21).

What drives gas exchange in the alveoli?

Diffusion down pressure gradients (O₂: alveoli to blood, CO₂: blood to alveoli).

Why is CO₂ exchange efficient despite a smaller pressure gradient?

CO₂ is more diffusible than O₂.

What is the blood volume in the alveolar-capillary network at rest?

~75 ml (increases to 150–200 ml during exercise).

What is the thickness of the alveolar-capillary membrane?

1–2 μm.

What is the vital capacity?

RV + VT + ERV (~4800 ml).

How long do red blood cells take to pass through pulmonary capillaries?

<1 second (sufficient for gas exchange).

How is O₂ primarily transported in blood?

Bound to haemoglobin (Hb); small fraction dissolved.

What is the O₂ capacity of blood with 150 g Hb/L?

~208 ml O₂/L (150 × 1.39 ml O₂/g Hb) + 3 ml dissolved.

What does the flat portion of the oxyhaemoglobin dissociation curve indicate?

Minimal change in Hb saturation for PO₂ drop from 100 to 60 mmHg.

How is CO₂ primarily transported in blood?

70% as bicarbonate (HCO₃⁻), 23% as carbaminohemoglobin, 7% dissolved.

What is the role of carbonic anhydrase in CO₂ transport?

Catalyzes CO₂ + H₂O → H₂CO₃, which dissociates to H⁺ + HCO₃⁻.

What is the respiratory exchange ratio (RER)?

0.8 (80 CO₂ expired per 100 O₂ consumed).

Where are peripheral chemoreceptors located?

Carotid bodies (glossopharyngeal nerve) and aortic bodies (vagus nerve).

What stimulates peripheral chemoreceptors?

Hypoxia (PO₂ < 60 mmHg).

What stimulates central chemoreceptors?

Hypercapnia (increased PCO₂) or decreased pH.

Why is PCO₂ more critical than PO₂ for moment-to-moment breathing control?

Small PCO₂ changes cause large ventilation increases (central chemoreceptors).

What do mechanoreceptors in the respiratory system detect?

Lung inflation and chest wall movement.

Which nerve carries mechanoreceptor signals to the brainstem?

Vagus nerve (to NTS).

What is the role of the ventral respiratory group (VRG)?

Contains rhythm-generating neurons for inspiration and expiration

Which nerve innervates the diaphragm?

Phrenic nerve (exits C3–C5).

What brainstem region receives chemoreceptor and mechanoreceptor inputs?

Nucleus tractus solitarius (NTS).

What is the primary function of the lungs?

Oxygenate blood via gas exchange in pulmonary capillaries.

Which nerves cause bronchoconstriction in airways?

Parasympathetic nerves (acetylcholine on M3 receptors).

How do sympathetic nerves contribute to bronchodilation?

Adrenaline from adrenal medulla activates β2-adrenoceptors, increasing cAMP.

What do inhibitory NANC nerves release to relax airway smooth muscle?

Nitric oxide (NO) and vasoactive intestinal peptide (VIP).

What structural changes occur in asthma?

Smooth muscle hypertrophy, mucus hypersecretion, oedema, epithelial damage, inflammation.

What are the two phases of an asthma attack?

Immediate (mast cell-driven bronchospasm) and late (Th2/eosinophil inflammation).

What does a normal FEV1/FVC ratio indicate?

80% (FEV1 = 4.0 L, FVC = 5.0 L).

What is the mechanism of β2-agonists like salbutamol?

Activate β2AR, increase cAMP, relax airway smooth muscle.

How do muscarinic antagonists like ipratropium work?

Block M3 receptors, reduce Ca²⁺-mediated bronchoconstriction.

What is the role of glucocorticoids in asthma?

Inhibit prostanoids, leukotrienes, and Th2 cytokines to reduce inflammation.

What is montelukast used for in asthma?

CysLT1 antagonist, relaxes airways, reduces inflammation (oral).

Which biologic targets free IgE in severe asthma?

Omalizumab (Xolair).

What do biologics like mepolizumab target?

IL-5, reducing eosinophil-mediated inflammation.

What is the duration of action for short-acting β2-agonists like salbutamol?

4–6 hours.

How are biologics administered for asthma?

Injection or intravenous drip.