Respiration Overview and Anatomy

Respiration Overview

• Respiration is the process of acquiring oxygen and eliminating carbon dioxide.
• Three steps occur in the human body:
  • Pulmonary ventilation: Gas exchange between the atmosphere and lung tissues.
  • External respiration: Gas exchange between lung tissues and blood.
  • Internal respiration: Gas exchange between blood and body tissues.
• Functions of the respiratory system:
  • Exchanging gases.
  • Regulating blood pH.
  • Allowing for vocal sounds and the sense of smell, filtering inhaled air, and excreting wastes during exhalation.
  • The scientific and medical study of the respiratory system is called otorhinolaryngology.
• Cells require oxygen for aerobic cellular respiration.

Anatomy of the Respiratory System

• The respiratory system is structurally divided into upper and lower respiratory systems.
• The upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures.
• The lower respiratory system includes the larynx, trachea, bronchi, and lungs.
• Functionally, the respiratory system can be divided into a conducting zone and a respiratory zone.
  • The conducting zone directs air towards the respiratory zone, filtering, warming, and humidifying the air.
  • The respiratory zone is the site of gas exchange.

Upper Respiratory System

• Nose: Composed of bone, cartilage, and connective tissues containing the nasal cavity. Air enters through the external nares (nostrils).
• Nasal Cavity: Bounded by oral cavity and nasal bones. Structure keeps passages unobstructed. Divided by the nasal septum. Contains:
  • The paranasal sinus (mucus membranes that vibrate to permit speech).
  • Nasal conchae (swirl inhaled air).
  • Olfactory epithelium (sensory receptors for smell, no goblet cells).
• Pharynx: A tube of skeletal muscle lined with a mucous membrane, connecting to the cricoid cartilage.
  • Divided into nasopharynx (superior), oropharynx (intermediate), and laryngopharynx (inferior).

Larynx

• Nine rings of cartilage form the larynx.
  • Thyroid cartilage (Adam's apple): Hyaline cartilage forming the anterior surface of the larynx. Larger in males.
  • Epiglottis: A flap of elastic cartilage that covers the larynx opening during swallowing.
  • Cricoid cartilage: Ring of hyaline cartilage at the inferior portion of the larynx, a landmark for tracheotomies.
• Vocal folds (true vocal cords): Folds of non-keratinized stratified squamous epithelium forming elastic ligaments. Vibrate with air to produce sound. Muscles and cartilage control tension to change pitch.
• Vestibular folds (false vocal cords): Superior folds that come together when holding breath.

Trachea

• A 2.5 cm wide x 12 cm long tube.
• 16-20 rings of hyaline cartilage connected by dense connective tissue to keep it patent.
• Anterior to the esophagus.
• Lined with ciliated pseudostratified epithelium.

Bronchi

• The trachea bifurcates into the right and left bronchi.
  • Carina: Ridge at branchpoint, sensitive, triggers cough reflex.
• Branches into progressively smaller tubes called the bronchial tree that end in terminal bronchioles.
• The supporting cartilage and proportion of smooth muscle changes throughout the bronchial tree

Lungs

• Wrapped in pleural membrane (two serous membranes with a pleural cavity containing fluid to reduce friction).
• Lungs are separated by the mediastinum and its organs.
• Extend from the clavicles to the diaphragm.
• Separated into lobes by fissures (oblique and horizontal).
  • Lobar bronchi (e.g., superior, middle, inferior) and segmental bronchi (13 in the right lung, 8 in the left lung) direct air into the individual bronchopulmonary segments, further subdivided into lobules.
  • Each lobule contains a terminal bronchiole, arteriole, venule, lymphatic vessel and surrounding elastic connective tissue.
• Respiratory bronchioles are microscopic bronchial branches that lead to alveolar ducts, with the alveoli (air sacs) for gas exchange.
• Alveoli structure: Type I cells (simple squamous epithelium, thin for diffusion), Type II cells (non-ciliated cuboidal, secrete surfactant to prevent sticking).
• Respiratory membrane: The very thin membrane (0.5 μm) separating alveoli and capillaries.

Blood Supply to Lungs

• Pulmonary arteries: Bring deoxygenated blood to be oxygenated.
• Bronchial arteries: Branch from the aorta, deliver oxygenated blood to lung tissue.

Gas Exchange and Ventilation

• Pulmonary ventilation (inhalation and exhalation) leads to gas exchange at the alveoli.
• Regulated by pressure changes in the thoracic cavity requiring respiratory muscle contraction.
• Inhalation (inspiration):
  • Lungs expand, decreasing pressure below atmospheric pressure causing air to flow in down its partial pressure gradient.
  • The diaphragm contracts and the external intercostal muscles contract , increasing the volume of the thoracic cavity.
• Exhalation (expiration): A passive process. relaxation of muscles, stretches elastic lungs, increasing pressure, causing air to flow out.

Factors Affecting Pulmonary Ventilation

• Surfactant: Essential for ventilation, helps prevent alveolar collapse.
• Lung compliance: Distensibility of lung tissue, resistance to change in volume.
• Airway resistance: Affected by airway diameter and smooth muscle activity.

Lung Volumes and Capacities

• Lung volumes are specific measures of air movement.
• Lung capacities are sums of lung volumes.

Mechanisms of Gas Exchange

• Gases move down their partial pressure gradients (high to low).
• External respiration (alveoli to blood, PO2 in alveoli lower, PO2 in blood in high, thus the gradient is in favor for oxygen moving into the blood).
• Internal respiration (blood to tissues, PO2 in the blood is high and PO2 in tissues is low, thus the gradient is in favor for oxygen moving out of the blood into the tissues).

Oxygen Transport

• Most oxygen is transported bound to hemoglobin (Hb) in red blood cells.
• Saturation of Hb is affected by factors like PO2, blood acidity, PCO2, temperature, and type of Hb.

Carbon Dioxide Transport

• CO2 is transported dissolved in blood, bound to Hb, or as bicarbonate.
• The chloride shift maintains electrical balance.

Regulation of Breathing

• The respiratory center in the medulla oblongata and pons regulates breathing.
  • Medullary respiratory group (DRG) and (VRG) regulate breathing.
  • Pontine respiratory group influences normal breathing rate.
• Chemoreceptors sense changes in blood gases and pH, influencing respiratory rate.
  • Central chemoreceptors located near medulla oblongata monitor PCO2+H+ in cerebrospinal fluid.
  • Peripheral chemoreceptors in aortic and carotid bodies monitor blood-PCO2+pH, affecting respiratory rate adjustments.
• The inflation reflex provides feedback to moderate breathing.
• External factors influence respiratory rate.

Homeostatic Imbalances

• Smoking can impair respiratory function.

Exercise and Respiration

• Exercise increases pulmonary perfusion & ventilation.