The Respiratory System

• The respiratory system oversees gas exchanges between the blood and the external environment.
• Gases exchange in the alveoli within the lungs.
• Passageways purify, warm, and humidify air going to the lungs.

Air Pathway

• Air enters the nose through the nostrils.
• Air enters the nasal cavity, which the nasal septum divides.
• Mucus lines the nasal cavity, which moistens, warms, and traps debris.
• The olfactory (smell) receptors are located on the cavity's superior surface
• Walls have fleshy projection called conchae to increase surface area.
• The pharynx is a muscular passage from the nasal cavity to the larynx.
• Three regions of the Pharynx:
  • The nasopharynx is the superior region behind the nasal cavity.
  • The oropharynx is the middle region behind the mouth.
  • The laryngopharynx is the inferior region attached to the larynx.
• The oropharynx and laryngopharynx are common passageways for air and food.
• Tonsils (clusters of lymphatic tissue) of the pharynx include:
  • Pharyngeal tonsils (adenoids) in the nasopharynx.
  • Palatine tonsils in the oropharynx.
  • Lingual tonsils at the base of the tongue.
• The larynx or voice box protrudes anteriorly (Adam's apple).
• The superior glottis (lumen or opening of the larynx) has an epiglottis.
• Epiglottis routes air into the trachea and food into the esophagus.
• The Larynx contains vocal cords and plays a role in speech.
• The trachea is the windpipe, which connects the larynx with the bronchi.
• The Trachea is lined with ciliated mucosa.
• Ciliated mucosa beats continuously in the opposite direction of incoming air.
• Ciliated mucosa expels mucus loaded with dust and other debris away from the lungs.
• The trachea's walls are reinforced with C-shaped hyaline cartilage rings.
• Primary bronchi is formed by the division of the trachea.
• The bronchi enter the lung.
• The right bronchus is wider (larger), shorter, and straighter than the left and collects more foreign debris.
• Bronchi subdivide into smaller and smaller branches:
  • Secondary bronchi
  • Tertiary bronchi
• The bronchiole is the smallest branch of the bronchi.
• Terminal bronchiole.

Lungs

• Lungs occupy most of the thoracic cavity.
• The apex is near the clavicle, the superior portion.
• The base rests on the diaphragm, the inferior portion.
• Each lung is divided into lobes by fissures.
  • The left lung has two lobes.
  • The right lung has three lobes.
• Coverings of the lungs:
  • Pulmonary (visceral) pleura covers the lung surface.
  • Parietal pleura lines the walls of the thoracic cavity.
  • Pleural fluid fills the area between the layers of pleura to allow gliding.

Respiratory Zone in the Lungs

• The respiratory zone includes the respiratory bronchiole, alveolar duct, and alveoli.
• Gas exchange occurs within the alveoli in the respiratory membrane.
• A thin squamous epithelial layer lines alveolar walls.
• Pulmonary capillaries cover the external surfaces of alveoli.
• Gas crosses the respiratory membrane of the alveoli by diffusion (movement of materials from higher to lower concentration).
  • Oxygen enters the blood from the alveoli.
  • Carbon dioxide enters the alveoli from the blood.
• Macrophages add protection.
• Surfactant coats gas-exposed alveolar surfaces to keep them from collapsing after exhalation.

Events of Respiration

• Pulmonary ventilation moves air in and out of the lungs; it has two phases.
• Inspiration: Flow of air into the lung.
• The diaphragm and intercostal muscles contract.
• The size of the thoracic cavity increases.
• External air enters the lungs due to a drop in pressure inside the thoracic cavity caused by increased size.
• Expiration: Air leaving the lung.
• As muscles (diaphragm and intercostal muscles) relax, the size of the thoracic cavity decreases.
• The decreased size builds pressure in the cavity, which pushes out the air.
• External respiration exchanges gas between pulmonary blood and alveoli in the lungs.
  • Oxygen movement: The alveoli always has more oxygen than the blood, therefore oxygen diffuses into the capillary blood.
  • Carbon dioxide movement: Blood returning from tissues has higher concentrations of carbon dioxide than air in the alveoli, therefore CO₂ diffuses into alveoli.
• Respiratory gas transport: Oxygen and carbon dioxide transport via the bloodstream.
• Oxygen transport: Travels inside red blood cells attached to hemoglobin (oxyhemoglobin [HbO₂]); a small amount is carried in the plasma.
• Carbon dioxide transport: Most is transported in the plasma as bicarbonate ion (HCO₃-); a small amount is carried inside red blood cells on hemoglobin but at different binding sites than those of oxygen.
• Internal respiration exchanges gas between blood and body cells away from the lungs.
• Carbon dioxide diffuses out of tissue to blood, but oxygen diffuses from blood into tissue.

Respiratory Volumes and Capacities

• Respiratory capacity is affected by a person's size, sex, age, and physical condition.
• Tidal Volume (TV): Normal breathing moves about 500 ml of air with each breath.
• Residual volume of air: After exhalation, about 1200 ml of air remains in the lungs.
• Dead space volume: Air that remains in the conducting zone and never reaches alveoli for gas exchange.
• Inspiratory reserve volume (IRV): Amount of air that can be taken in forcibly over the tidal volume, which is usually between 2100 and 3200 ml.
• Expiratory reserve volume (ERV): Amount of air that can be forcibly exhaled that is approximately 1200 ml.
• Vital capacity: The total amount of exchangeable air when Votal capacity = TV + IRV + ERV.
• Respiratory capacities are measured with a spirometer.

Respiratory Sounds

• Sounds are monitored with a stethoscope.
• Bronchial sounds are produced by air rushing through the trachea and bronchi.
• Vesicular breathing sounds are soft sounds of air filling the alveoli.