Breathing and Gas Exchange

• The thoracic cavity's size variations during breathing influence pressure and airflow, playing a crucial role in respiration.

Breathing Mechanics

• The diaphragm and intercostal muscles contract and relax to facilitate inhalation and exhalation.
• Inhalation involves contraction of the external intercostal muscles and diaphragm, increasing thoracic volume and decreasing pressure, leading to airflow into the lungs.
• Exhalation involves relaxation of the diaphragm and possible contraction of internal intercostal muscles, decreasing thoracic volume and increasing pressure, pushing air out of the lungs.
• The medulla oblongata controls the rhythm of breathing, based on CO₂ levels detected by chemoreceptors.

Gas Exchange

• Hemoglobin in the blood carries most of the oxygen, binding to O₂ depending on the partial pressure of oxygen and the presence of CO₂.
• High partial pressure of O₂ in the lungs leads to hemoglobin saturation.
• Low O₂ pressure in tissues causes hemoglobin to release O₂, especially with high CO₂ concentrations.
• Carbon dioxide is transported as bicarbonate ions (HCO₃⁻), dissolved in plasma, and bound to hemoglobin as carbaminohemoglobin.
• Carbonic anhydrase in red blood cells catalyzes the reaction between CO₂ and water to form bicarbonate.

Breathing Process

• Inspiration (quiet breathing) involves contraction of external intercostals and diaphragm; increasing lung volume and decreasing pressure, which allows air to flow in.
• Expiration (quiet breathing) is passive, with the diaphragm and external intercostals relaxing, decreasing lung volume, increasing pressure, and forcing air out.
• Forced breathing uses additional muscle groups like internal intercostals and abdominal muscles to increase the force of expiration.

Lung Volumes and Capacities

• Tidal Volume (TV) represents the air volume during normal breathing.
• Inspiratory Reserve Volume (IRV) is the additional air volume that can be inhaled after normal inhalation.
• Expiratory Reserve Volume (ERV) refers to the additional air volume that can be exhaled after normal exhalation.
• Residual Volume (RV) is the air volume remaining in the lungs post-maximal exhalation, preventing alveolar collapse.
• Vital Capacity (VC) is the total air amount exhaled after a maximal inhalation, calculated as VC = IRV + TV + ERV.
• Total Lung Capacity (TLC) is the total lung volume, calculated as TLC = VC + RV.

Common Respiratory Diseases

• Bronchitis involves airway inflammation, increased mucus, coughing, and shortness of breath, treated by quitting smoking and medication.
• Asthma is characterized by airway inflammation and narrowing, with wheezing and difficulty breathing, treated with inhalers
• Emphysema results from long-term irritant exposure, causing alveoli destruction, reduced gas exchange, chronic cough, and shortness of breath; treatment includes smoking cessation and pulmonary rehabilitation.
• Pneumonia involves infection-causing inflammation of alveoli and fluid accumulation, with chest pain, cough, and fever; treated with antibiotics or antivirals.
• Cystic Fibrosis is a genetic disorder causing thick mucus in the lungs, recurrent infections, and breathing difficulties; treatments focus on symptom management.

Neural and Chemical Regulation

• The brainstem's respiratory center (medulla oblongata) regulates breathing rate and depth based on CO₂ levels and blood pH.
• Chemoreceptors in the aorta and carotid arteries monitor blood pH and O₂ levels, stimulating the respiratory center to adjust breathing.
• The phrenic nerve impulses sent to the diaphragm and intercostal nerves stimulate the intercostal muscles, coordinating breathing.

Effects of high altitude

• Lower O₂ levels at high altitudes stimulate increased breathing rates.
• Adaptations in the body enhance O₂ delivery, such as increased red blood cell production.
• Long-term exposure to high altitudes may lead to physiological changes improving the efficiency of gas exchange and O₂ transport.