RESPIRATORY SYSTEM

Ventilation and Gas Exchange

Internal Linings with cilia and mucus secreting cells. Pseudostratified columnar epithelium.

Nose: moistens, warms and cleans air. Site of olfactory cells.

Pharynx: connects nasal and oral cavities.

• Nasopharynx: air passage only. Site of auditory tube connection.
• Oropharynx: continuous with oral cavity. Conducts food and air.
• Laryngopharynx: conducts both food and air. Divides into larynx and esophagus.

Larynx: Airway opening with epiglottis. Vocal cords and large cartilages.

Trachea: carries air from larynx to two bronchi. Tracheal cartilage rings for support.

Lungs: paired lobed structures separated by mediastinum.

Right lung has 3 lobes, Left lung has two lobes.

Smaller divisions are called bronchopulmonary segments.

Still smaller division are called lobules.

External Linings: visceral and parietal pluerae. Provide lubrication. Pleural cavity is between these membranes.

Bronchi divide into smaller bronchioles.

Bronchioles end at tiny air sacs called alveoli -- functional units of lung.

Alveoli are where gas exchange occurs -- Interface between circulatory and respiratory systems. Thin, single-cell layer (simple squamous epithelium)

There are 300 million alveoli in the average respiratory system (total surface area = 70 square meters)

Nerve supply:Autonomic nervous system innervates smooth muscles of respiratory tract.
 
Pulmonary Ventilation = inspiration + expiration. Depends upon pressure changes.

Intrapulmonary pressure: varies, but normalizes with atmospheric pressure

Intrapleural pressure: varies, but is negative with respect to intrapulmonary pressure.

Lungs held to thoracic wall:

• Adhesive force of pleural fluid.
• Absorption of gases
• Positive pleural pressure

Forces which would tend to cause lung detachment:

• Elastic recoil
• Surface tension of alveolar fluid film.

Mechanics of Breathing

Pneumothorax: lung collapses due to equilibration of external and internal pressure.

Boyle's Law: pressure of gas varies inversely with volume (P1V1=P2V2). Increase volume of chamber with set amount of gas --> pressure decreases. Decrease volume of chamber --> pressure increases.

Inspiration

Active: due to action of inspiratory muscles (diaphragm and external intercostals)

Diaphragm contracts --> flattens out and moves inferiorly --> thoracic cavity increases.

External intercostal muscles contract --> elevates rib cage --> thoracic cavity increases.Increase in thoracic cavity size decreases intrapulmonary and intraplueral pressure --> atmospheric air enters due to pressure gradient.

Quiet/resting inspiration -- tidal volume of about 500 mls.

Forced inspiration: other muscles recruited (e.g., pectoralis minor, scalenes) to help expand thoracic cavity.

Expiration

Generally passive: relax muscles and thoracic cavity volume decreases --> this increases intrapulmonary pressure --> air forced out. Lungs recoil.
Forced expiration: contraction of abdominal muscles and internal intercostal muscles.

Passageway resistance:

Air flow is inversely proportional to resistance. Regulated by bronchiole diameter.

Asthma: airway restriction due to constriction of bronchioles.

Allergic

Exercise-induced

Treatments:

b-2 agonists (e.g., albuterol ) are bronchodilators (they mimic epinephrine and relax smooth muscle of airways)

steroids (anti-inflammatory action)

Asthma and Lung Function (FEV1/FVC)

Other factors affecting ventilation:

Lung compliance, lung elasticity and alveolar surface tension/surfactant

Lung volumes and capacities: Spirometry

Obstructive vs Restrictive Conditions
Pulmonary Function Tests
Minute respiratory volume: total amount of gas that flows into and out of the respiratory tract in 1 minute.

Gas Exchange in Lung: Determined by partial pressures of oxygen and carbon dioxide, solubilities of gases, and surface factors.

Important Gas Laws Related to Respiration

Dalton's Law of Partial Pressures

Henry's Law of Gas Solubilities

Gas Transport

External respiration

Pulmonary gas exchange

Partial pressure gradients and gas solubilities

Respiratory membrane thickness

Surface area for gas exchange (70 square meters)

Alveolar Airflow - Blood Flow Coupling

Internal respiration

Transport of Oxygen in Blood

• 98% carried by hemoglobin (oxyhemoglobin)

Oxygen-hemoglobin dissociation curve.

High P02, Hemoglobin is more saturated.

Hemoglobin can load or unload large amount of oxygen within narrow range of PO2.

Kinetics of curve affected by temperature and pH.

Transport of Carbon Dioxide
10% dissolved, 60-70% as bicarbonate, and 20-30% as carbaminohemoglobin.

Chloride shift - (exchange of chloride for biocarbonate) important in buffering of carbon dioxide.

Haldane Effect: enhances carbon dioxide uptake from tissues and elimination from lungs.
Carbon monoxide: 200X more affinity for hemoglobin than oxygen.

Breathing is controlled by nervous and chemical reflexes

Neural Control:

Medulla oblongata: medullary rhythmicity area with inspiratory and expiratory centers -- generate basic rhythm.

Pons: influences medullary rhythmicity area.

Stretch reflex (Hering-Breuer)

Hypothalamic and cortical controlChemical Influences:

Increased PCO2 --> increased blood and CSF acidity --> increased ventilation (chemoreceptors in carotid and aortic bodies as well as in medulla).

Increased PO2 --> chemoreceptors can respond to inhibit ventilation. Decreased PO2 can stimulate ventilation.
 
Clinical Conditions

Rhinitis: inflammation of nasal sinuses.

Allergic Rhinitis (e.g., hayfever)

Viral Rhinitis (common cold)

Laryngitis: local infection of larynx.

Bronchitis: inflammation of bronchus with overproduction of mucus

Emphysema: loss of elasticity of alveoli (usually from smoking). Functional surface area decreases. Thoracic cavity increases as muscle use increases.

Pleurisy: Inflammation of visceral or parietal pleura.

Pneumonia: fluid filling of alveoli, usually from infection.

Tuberculosis: bacterial disease that affects the lungs Drug resistant forms increasing.

Lung cancer: usually from cigarette smoking

• 4 types:squamous cell carcinoma; adenocarcinoma; small cell carcinoma, and large cell carcinoma.

Malignant mesothelioma: specific type of lung cancer typically due to long-term asbestos exposure

Hyaline membrane disease: in newborns,especially pre-mature births. Insufficient surfactant.

Cystic fibrosis: genetic defect. More common in whites than non-whites. Chloride transporter is defective --> less chloride transport, less water follows via osmosis, and thus mucus is thicker and more difficult to remove from lungs. Therapies: lung lobe transplants. Future: insertion of normal transporter.