Cystic Fibrosis (CF) is the most common life-threatening genetic disorder in Caucasians, caused by mutations in the CFTR (Cystic Fibrosis Transmembrane conductance Regulator) gene on chromosome 7. It is an autosomal recessive condition. Effect on respiratory system: Abnormally thick, sticky mucus clogs airways, Impairs mucociliary clearance, Leads to recurrent bacterial infections (Pseudomonas aeruginosa), and Progressive bronchiectasis and respiratory failure. Also affects pancreas, liver, and reproductive system. Treatment: chest physiotherapy, DNase (dornase alfa), CFTR modulators (Ivacaftor/Lumacaftor), lung transplant in severe cases.

The Larynx (voice box) is a cartilaginous structure located in the anterior neck, between the pharynx and trachea. It contains the vocal cords (vocal folds) which vibrate as air passes through, producing sound. The larynx is composed of 9 cartilages, the largest being the thyroid cartilage (Adam's apple). The epiglottis is a leaf-shaped cartilage that covers the larynx during swallowing to prevent food/liquid from entering the airway. The larynx also controls airflow during breathing.

The correct pathway of air through the respiratory system: Nose/Mouth > Nasal cavity > Pharynx > Larynx > Trachea > Primary bronchi (R & L) > Secondary bronchi > Tertiary bronchi > Bronchioles > Terminal bronchioles > Respiratory bronchioles > Alveolar ducts > Alveolar sacs > Alveoli. The nose filters, warms, and humidifies air. The pharynx is the common passageway for food and air. The larynx connects to the trachea. The trachea divides into bronchi which further divide into smaller bronchioles leading to alveoli.

Respiratory terminology: Eupnoea = normal, easy breathing. Dyspnoea = difficulty in breathing / shortness of breath (SOB). Apnoea = cessation of breathing. Tachypnoea = abnormally rapid breathing (>20/min). Bradypnoea = abnormally slow breathing (<12/min). Orthopnoea = breathlessness when lying flat (relieved by sitting up - common in heart failure). Hyperpnoea = increased depth of breathing. Hypoxia = low oxygen in tissues. Hypoxaemia = low oxygen in blood. Hypercapnia = excess CO2 in blood.

The Trachea (windpipe) is a tube approximately 10-12 cm long that extends from the larynx to the point where it divides into the two primary bronchi (carina). It is reinforced by C-shaped (horseshoe-shaped) rings of hyaline cartilage that keep it open and prevent collapse during breathing. The trachea is lined with ciliated pseudostratified columnar epithelium with mucus-secreting goblet cells that trap and remove foreign particles and pathogens via the mucociliary escalator.

Lung volumes in a healthy adult male (approximate): Tidal Volume (TV) = ~500 mL (air breathed in/out in one normal breath). Inspiratory Reserve Volume (IRV) = ~3000 mL. Expiratory Reserve Volume (ERV) = ~1200 mL. Residual Volume (RV) = ~1200 mL (air remaining after maximum exhalation - cannot be expelled). Total Lung Capacity (TLC) = TV + IRV + ERV + RV = ~6000 mL (6 litres). Vital Capacity (VC) = TV + IRV + ERV = ~4800 mL.

Haemoglobin (Hb) is the iron-containing protein in red blood cells (RBCs) responsible for oxygen transport in the blood. Structure: 4 subunits each containing a haem group (with iron Fe2+) and a globin protein chain. Each molecule can carry 4 oxygen molecules. Normal haemoglobin levels: Males: 13.5-17.5 g/dL, Females: 12-15.5 g/dL. Myoglobin stores O2 in muscle tissue. Bilirubin is the breakdown product of haemoglobin. Low Hb = Anaemia - reduced O2 carrying capacity - fatigue, breathlessness.

The trachea bifurcates (divides) into the right and left primary bronchi at the level of T4-T5 vertebrae, at a landmark called the Carina. This level also corresponds to the Sternal Angle of Louis. The right primary bronchus is wider, shorter, and more vertical - more likely to receive inhaled foreign objects. The left primary bronchus is narrower, longer, and more horizontal.

Tidal Volume (TV) is the volume of air that moves in and out of the lungs in one normal, relaxed breath - approximately 500 mL (0.5 litres) in a healthy adult at rest. Of this 500 mL: About 350 mL actually reaches the alveoli for gas exchange. About 150 mL remains in the anatomical dead space (nose, pharynx, trachea, bronchi) - airways that conduct air but don't participate in gas exchange. During exercise, tidal volume increases significantly as breathing becomes deeper.

During exercise, the muscles require more oxygen for aerobic respiration and produce more CO2 and lactic acid. This leads to: Increased breathing rate (tachypnoea), Increased tidal volume (deeper breaths), Combined effect = Increased minute ventilation (up to 150 L/min during intense exercise vs. 6-8 L/min at rest). The primary stimulus for increased breathing during exercise is rising blood CO2 (hypercapnia) and falling blood pH - detected by chemoreceptors in the medulla and carotid/aortic bodies. Also triggered by muscle/joint mechanoreceptors even before CO2 rises.