Introduction to Respiration and Anatomy

Introduction to Respiration

• Respiration is the process of acquiring oxygen and eliminating carbon dioxide.
• Three steps in the human body:
  • Pulmonary ventilation: Gas exchange between 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:
  • Exchanges gases.
  • Regulates blood pH.
  • Permits vocal sounds and the sense of smell, filters inhaled air, and excretes wastes during exhalation.
  • Oto(rhino)laryngology is the study of the respiratory system.
• Cells need oxygen for aerobic cellular respiration.

Anatomy of the Respiratory System

• Structurally, the respiratory system is divided into:
  • Upper respiratory system: Nose, nasal cavity, pharynx, and associated structures.
  • Lower respiratory system: Larynx, trachea, bronchi, and lungs.
• Functionally, the system is divided into two zones:
  • Conducting zone: Directs air to the respiratory zone, filters, warms, and humidifies the air.
  • Respiratory zone: Site of gas exchange, includes respiratory bronchioles, alveolar ducts, alveolar sacs.
• The nose: Made of bone, cartilage, and connective tissue; air enters through external nares (nostrils).
• The nasal cavity: Interior space of the nose, bounded by the oral cavity and nasal bones. The nasal septum divides it, contains paranasal sinuses (lined with mucous membranes) and nasal conchae (swirls inhaled air), and olfactory epithelium (sensory receptors for smells).
• The pharynx: Tube of skeletal muscle lined with mucous membrane, starts at internal nares and extends to the cricoid cartilage.
  • Nasopharynx (superior): Ciliated pseudostratified columnar epithelium, sweeps mucus into the pharynx.
  • Oropharynx (intermediate): Common passage for air and food, contains tonsils (trap pathogens).
  • Laryngopharynx (inferior): Similar to oropharynx.
• The larynx: Tube with nine cartilages.
  • Thyroid cartilage: Forms the anterior surface (Adam's apple).
  • Epiglottis: Flap of cartilage that covers the entrance to the larynx during swallowing.
  • Cricoid cartilage: Inferior ring of cartilage, landmark for tracheotomies.
  • Vocal folds (true vocal cords): Made of stratified squamous epithelium, vibrate to produce sounds; tension on ligaments changes pitch.
  • Vestibular folds (false vocal cords): Protect the vocal cords.
• The trachea: Tube with 16-20 C-shaped hyaline cartilages, keeps the trachea patent, anterior to the esophagus, lined with ciliated pseudostratified epithelium.
• The bronchi: Trachea splits into right and left bronchi (carina = ridge, triggers cough reflex); branch into smaller tubes (bronchial tree) ending in terminal bronchioles. The mucous membrane changes along the bronchial tree.
• The lungs: Wrapped in pleural membrane (2 serous membranes, pleural fluid reduces friction); separated by the mediastinum and its organs; extend from clavicles to diaphragm, rest on the costal surfaces (ribs).
  • Base: Inferior portion of the lung.
  • Apex: Superior portion of the lung.
  • Hilum: Permits passage of bronchi, blood vessels, nerves, and lymphatic vessels.
  • Cardiac notch: Space for the heart (decreases the size of the left lung).
  • Fissures: Divide the lungs into lobes.
    • Oblique fissure: Separates superior and inferior lobes.
    • Horizontal fissure: Borders the middle lobe of the right lung.
    • Lobar bronchi: Named for the lobes they branch into.
    • Segmental bronchi: Support a bronchopulmonary segment (13 in right lung, 8 in left).
    • Lobules: Small compartments containing a branch of a terminal bronchiole, arteriole, venule, lymphatic vessel, and elastic connective tissue.
  • Respiratory bronchioles: Microscopic branches of bronchi, lined with simple cuboidal epithelium, branch into alveolar ducts.
  • Alveoli: Air sacs where gas exchange occurs.
    • Type I alveolar cells: Simple squamous epithelium, facilitating gas diffusion.
    • Type II alveolar cells: Secrete surfactant (phospholipids + lipoproteins) preventing alveolar collapse.
    • Respiratory membrane: Alveoli and associated capillaries (0.5 µm thick).
• Blood supply to the lungs:
  • Pulmonary arteries: Bring deoxygenated blood from right ventricle.
  • Bronchial arteries: From the aorta, deliver oxygenated blood to lung tissue.

Gas Exchange and Ventilation

• Pulmonary ventilation: Inhalation and exhalation; regulated by pressure changes within the thoracic cavity and respiratory muscle contractions.
• Inhalation (inspiration):
  • Pressure in lungs must decrease below atmospheric pressure to draw air in.
  • Diaphragm contracts, increasing thoracic cavity volume. Intercostal muscles also elevate ribs.
  • Negative intrapleural pressure keeps the pleural membranes adhering to the thoracic cavity wall.
• Exhalation: -Passive process; respiratory muscles relax, thoracic cavity volume decreases.
  • Elastic recoil of lung tissue generates pressure for exhalation.

Factors affecting pulmonary ventilation

• Surfactant: Essential for preventing alveolar collapse.
• Compliance: Distensibility of elastic tissues; high compliance = easier breathing. Low compliance is harder because much more effort is needed.
• Resistance: Airway diameter and smooth muscle constriction affect resistance. Obstruction / collapse of airways increases resistance.

Lung volumes and capacities

• Lung volumes are specific measures of air movement (inhaled, exhaled, or retained).
• Lung capacities are sums of specific lung volumes.

Principles of Gas Exchange

• Gases move from high to low partial pressure.
• Solubility of gases affects rate; CO2 is more soluble than O2, elimination of CO2 is 20x faster than O2 acquisition.
• External Respiration: Gas exchange between alveoli and blood.
• Internal Respiration: Gas exchange between blood and body tissues.

Factors affecting respiration

• Partial pressure gradient: Decreased atmospheric pressure affects O2 gradient, lowering the rate of respiration and oxygen availability.
• Surface area: Large surface area of alveoli enhances gas exchange efficiency.
• Diffusion distance: Thin alveolar walls facilitate efficient diffusion.
• Molecular weight and solubility affect the rate of net elimination of CO2 (20x faster than net O2 acquisition).

Oxygen Transport

• Hemoglobin (Hb) in erythrocytes transports 98.5% of oxygen.
• Hb binds oxygen reversibly.
  • Increased PO2 favors Hb-O2 formation.
  • Factors affecting Hb saturation: partial pressure of oxygen, blood acidity, partial pressure of CO2, temperature, the type of hemoglobin, and intermediate products of glycolysis

Carbon Dioxide Transport

• CO2 is transported as dissolved gas, bound to proteins, and as bicarbonate.
• Chloride shift: maintains electrical balance during CO2 transport.

Regulation of Breathing

• Respiratory center: Cluster of neurons in the medulla oblongata and pons that regulate respiratory muscles.
  • Medullar respiratory group: Dorsal respiratory group (normal breathing), ventral respiratory group (forceful breathing).
  • Pontine respiratory group: Influences normal breathing.
• Cortical influences: Allows voluntary control over breathing.
• Chemoreceptors: Sense changes in blood chemistry.
  • Central chemoreceptors: Located near medulla oblongata; sense PCO2 and H+.
  • Peripheral chemoreceptors: In aortic and carotid bodies; monitor PCO2, PO2, and blood pH.
• Hyperventilation: High breathing rate and depth; response to low blood pH to increase O2 levels. Hypocapnia and hypoxia can result if sustained.
• Inflation reflex: Prevents over-inflation of the lungs.

Other Influences on Breathing

• Emotions, temperature, pain, airway irritation, blood pressure can all influence breathing rate.

Exercise and the Respiratory System

• Exercise increases pulmonary perfusion and ventilation.

Homeostatic Imbalances

• Tobacco smoking can lead to COPD (emphysema, increased mucus secretion) impairing ciliary function and decreasing alveolar surface area.

This quiz explores the fundamental processes of respiration, including gas exchange and the anatomical structures involved in the respiratory system. Understand the significance of pulmonary ventilation, external and internal respiration, and the overall functions of the respiratory system. Delve into the components that make up the upper and lower respiratory systems.