Pneumonia is an infection/inflammation of the lung parenchyma (alveoli and surrounding tissue), causing the alveoli to fill with fluid (exudate) or pus, impairing gas exchange. Causes: Bacterial (most common - Streptococcus pneumoniae/pneumococcus), Viral (Influenza, COVID-19, RSV), Fungal (immunocompromised patients). Symptoms: fever, cough with sputum, chest pain, breathlessness. Diagnosis: Chest X-ray (shows consolidation/white opacity). Treatment: antibiotics (for bacterial), supportive care. Prevention: pneumococcal and influenza vaccines.

The Heimlich Manoeuvre is formally called the Abdominal Thrust technique. It is used when someone is choking (airway obstructed by a foreign body). The rapid upward thrust on the abdomen compresses the diaphragm, suddenly increasing pressure in the thoracic cavity and forcing air through the trachea - acting like an artificial cough to dislodge the obstruction. For infants, back blows and chest thrusts are used instead of abdominal thrusts. For self-choking, the person can perform self-Heimlich using a chair back. CPR is used for cardiac arrest - different from Heimlich.

The Epiglottis is a leaf/flap-shaped elastic cartilage attached to the base of the tongue and top of the larynx. During swallowing (deglutition), the epiglottis folds down over the glottis (opening of the larynx) to prevent food and liquids from entering the trachea and lungs. During normal breathing, the epiglottis is upright, keeping the airway open. If food accidentally enters the trachea (aspiration), a cough reflex is triggered to expel it. Epiglottitis is a dangerous infection of the epiglottis that can obstruct the airway.

The nasal cavity performs three crucial functions for conditioning inhaled air: Filtration (nasal hairs/vibrissae filter large particles; mucus traps smaller particles and microorganisms; cilia sweep trapped material toward the throat), Warming (rich blood supply in the nasal turbinates/conchae warms cold air to body temperature 37 degrees C), and Humidification (mucous membranes add moisture - air reaches nearly 100% humidity before entering the lungs). These functions protect the delicate lung tissue from damage by cold, dry, or contaminated air.

A hiccup (singultus) is caused by an involuntary, sudden spasm of the diaphragm followed by rapid closure of the vocal cords (glottis), producing the characteristic 'hic' sound. Triggers: eating too quickly, swallowing air, alcohol, sudden temperature changes, excitement. The hiccup reflex arc involves the phrenic and vagus nerves. Most hiccups are self-limiting (last a few minutes). Persistent hiccups (>48 hours) or intractable hiccups (>1 month) may indicate serious underlying conditions like CNS disorders, metabolic disturbances, or gastric pathology.

The right lung has 3 lobes: Superior (upper) lobe, Middle lobe, and Inferior (lower) lobe. These are separated by the horizontal fissure (between superior and middle lobes) and the oblique fissure (between middle and inferior lobes). The left lung has only 2 lobes (Superior and Inferior) separated by one oblique fissure. The left lung is smaller to accommodate the heart in the left side of the chest (cardiac notch and lingula).

The Pharynx (throat) is a muscular funnel-shaped tube approximately 13 cm long that serves as the common passageway for both food and air. It has three parts: Nasopharynx (behind nasal cavity; air only; contains adenoids and Eustachian tube openings), Oropharynx (behind mouth; food and air; contains palatine tonsils), and Laryngopharynx (behind larynx; food and air; leads to oesophagus for food and larynx for air). The epiglottis ensures food goes to the oesophagus and air goes to the larynx.

Partial pressures drive gas exchange by diffusion (gases move from high to low partial pressure): Atmospheric O2: PO2 = 159 mmHg (21% of 760 mmHg). Alveolar O2: PO2 = 104 mmHg (lower due to mixing with residual air and water vapour). Pulmonary capillary (venous) blood: PO2 = 40 mmHg. Arterial blood (after exchange): PO2 = ~100 mmHg. O2 diffuses from alveoli (104 mmHg) into blood (40 mmHg). For CO2: PCO2 in venous blood = 45 mmHg, in alveoli = 40 mmHg, CO2 diffuses from blood into alveoli and is exhaled.

The Pleura is a double-layered serous membrane that surrounds each lung. Visceral pleura directly covers the surface of the lung. Parietal pleura lines the inner wall of the thoracic cavity. Between them is the pleural cavity containing a thin film of pleural fluid that reduces friction during breathing and creates surface tension that keeps lungs expanded. Conditions: Pleuritis/Pleurisy = inflammation of pleura (painful breathing), Pleural effusion = excess fluid in pleural cavity, Pneumothorax = air in pleural cavity causing lung collapse.

Haemoglobin (Hb) in red blood cells transports gases: Oxygen - Hb + O2 = Oxyhaemoglobin (HbO2), O2 binds to the iron (Fe2+) in haem groups, each Hb molecule carries 4 O2 molecules, about 98.5% of O2 is carried this way; 1.5% dissolved in plasma. Carbon Dioxide - about 23% of CO2 binds to haemoglobin forming Carbaminohaemoglobin. Most CO2 (70%) is transported as bicarbonate ions (HCO3-) in plasma. 7% dissolved in plasma. Carbon monoxide (CO) binds haemoglobin 200x more strongly than O2 - forms carboxyhaemoglobin - prevents O2 transport - CO poisoning.