Lecture 7

Overview of the Human Respiratory System

• The human respiratory system consists of the airways and lung tissue.

• Air enters through the nose or mouth, travels into the trachea, and then into the lungs.

Trachea and Glottis

• Trachea: A large tube supported by cartilaginous rings to prevent collapse, located adjacent to the esophagus (which collapses when not feeding).

• Glottis: The opening of the trachea, controlled by muscles via the vagus nerve (cranial nerve X).

• Epiglottis: A flap that covers the glottis during swallowing to prevent food or liquid from entering the trachea.

Branching of Airways

• The trachea branches into primary bronchi (one for each lung), and further subdivides through 16 to 25 orders of branching into smaller tubes called bronchioles.

• Alveolar Sacs: Tiny sac-like structures at the end of bronchioles made of clusters of alveoli, the site for gas exchange.

Gas Exchange Process

• Alveoli: The site where oxygen is absorbed from inhaled gas into the blood, and carbon dioxide is expelled from the blood into the lungs to be exhaled.

• Importance of Carbon Dioxide (CO2): CO2 levels trigger the breathing cycle, more so than oxygen levels.

Structure of Alveoli

• Alveoli are surrounded by capillaries, which are embedded within alveolar walls, facilitating gas exchange.

• Elastin: A connective tissue protein that allows alveoli to stretch during inhalation and recoil during exhalation.

• Capillary Endothelial Cells: The cells lining blood vessels that interact with the alveolar cells for gas exchange.

Mechanics of Breathing

• Diaphragm: The primary respiratory muscle, innervated by the phrenic nerve originating from cervical vertebrae (C3-C5).

• Upon contraction, the diaphragm moves downwards creating negative pressure, pulling air into the lungs. Intercostal muscles assist in expanding the rib cage.

• Exhalation occurs passively as the lung tissue recoils.

Types of Respiratory Diseases

Obstructive Diseases

• Characterized by difficulty in exhalation, examples include:

  • Asthma: Inflammation and narrowing of airways due to multiple triggers (allergic and non-allergic).

  • Chronic Bronchitis: Excessive mucus production and airway inflammation.

  • Emphysema: Breakdown of alveolar structure leading to decreased gas exchange efficiency.

Restrictive Diseases

• Characterized by reduced lung capacity, examples include:

  • Pulmonary Fibrosis: Fibrous tissue impedes lung expansion and gas diffusion.

COVID-19 Impacts on Respiratory Health

• Causes both obstructive and restrictive problems:

  • Inflammation and mucus in airways leading to obstruction.

  • Fibrosis in alveoli limiting expansion and gas exchange.

Importance of Sleep and Breathing

• Sleep is a cyclic occurrence crucial for well-being.

• Narcolepsy: A condition where REM sleep intrudes into wakefulness, leading to sudden sleep episodes.

• Obstructive Sleep Apnea: Characterized by airway obstruction during sleep, causing drops in oxygen levels and cardiovascular risks.

Case Studies in Respiratory Complications

• Case Study 1: Obstructive Sleep Apnea leading to inefficient lung movements and decreased oxygen levels, causing spikes in blood pressure.

• Case Study 2: Partial paralysis due to nerve injury affecting the diaphragm; reliance on intercostal muscles leads to issues during REM sleep.

• Ondine's Curse: Automatic control of breathing dysfunction during sleep due to neurological damage, emphasizing the importance of brainstem function in respiration.

Summary of Respiratory System Function

• The respiratory system's primary function is to obtain oxygen and eliminate CO2, in concert with the cardiovascular system.

• Hemoglobin in red blood cells plays a crucial role in oxygen transport and CO2 conversion in blood.

• Understanding the respiratory mechanics is vital in diagnosing, managing, and treating various respiratory conditions.