Respiratory System

Four Processes of Respiration

• Pulmonary Ventilation: Movement of air into and out of the lungs (breathing).

• External Respiration: Exchange of gases (O2 and CO2) between lungs and blood.

• Transport of Respiratory Gases: Movement of O2 and CO2 in the blood between lungs and tissues.

• Internal Respiration: Exchange of gases between systemic blood vessels and tissues.

Pathway of Air Movement

• Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

• Inspiration: Air enters through the nasal cavity and travels down to the alveoli for gas exchange.

• Expiration: Air follows the reverse path out of the body.

Functions of the Nasal Cavity and Effect of Smoking

• Functions: Warms, moistens, and filters incoming air; houses olfactory receptors.

• Effect of Smoking: Damages cilia, increases mucus production, impairs filtration, and increases risk of respiratory infections.

Differences in Lungs

• Right Lung: Three lobes (superior, middle, inferior).

• Left Lung: Two lobes (superior, inferior) and a cardiac notch for the heart.

Conducting Zone vs. Respiratory Zone

• Conducting Zone: Includes all respiratory passageways from the nose to the terminal bronchioles; functions as air conduits and in air purification, humidification, and warming.

• Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, and alveoli; site of gas exchange.

• Bronchial Tree Changes: With branching, cartilage decreases, smooth muscle increases, and epithelium changes from pseudostratified to cuboidal.

Pressures in the Thoracic Cavity

• Atmospheric Pressure (Patm): Pressure exerted by air surrounding the body (~760 mmHg at sea level).

• Intrapulmonary Pressure (Ppul): Pressure in the alveoli; fluctuates with breathing but always equalizes with Patm.

• Intrapleural Pressure (Pip): Pressure in the pleural cavity; always negative relative to Ppul.

• Inspiration: Thoracic volume increases, Ppul drops below Patm, air flows in.

• Expiration: Thoracic volume decreases, Ppul rises above Patm, air flows out.

Lung Collapse (Atelectasis)

• Occurs when intrapleural pressure equals or exceeds intrapulmonary pressure, causing the lung to collapse.

• Can result from airway obstruction or pneumothorax (air in pleural cavity).

Diaphragm Movement During Respiration

• Inspiration: Diaphragm contracts and moves downward, increasing thoracic volume.

• Expiration: Diaphragm relaxes and moves upward, decreasing thoracic volume.

Physical Factors Influencing Pulmonary Ventilation

• Airway Resistance: Increased resistance (e.g., asthma) decreases airflow.

• Alveolar Surface Tension: Surfactant reduces surface tension, preventing alveolar collapse.

• Lung Compliance: The ease with which lungs can expand; decreased in fibrosis or edema.

Infant Respiratory Distress Syndrome (IRDS) and Pulmonary Surfactant

• IRDS: Premature infants lack sufficient surfactant, leading to alveolar collapse and difficulty breathing.

• Pulmonary Surfactant: Lipid-protein complex produced by type II alveolar cells; reduces surface tension.

Partial Pressure Gradient and Gas Diffusion

• Gases move from areas of higher partial pressure to lower partial pressure.

• Net Diffusion: The greater the gradient, the faster the diffusion of gases across the respiratory membrane.

• Equation:

Respiratory Membrane

• Composed of alveolar epithelium, fused basement membranes, and capillary endothelium.

• Thin barrier (0.5 μm) for efficient gas exchange.

Emphysema

• Chronic condition characterized by destruction of alveolar walls, reducing surface area for gas exchange.

• Results in decreased lung elasticity and impaired ventilation.

Diffusion and Solubility of O2 and CO2

• O2: Lower solubility in plasma; requires hemoglobin for efficient transport.

• CO2: More soluble in plasma; diffuses more readily across the respiratory membrane.

Transport of O2

• 98.5% bound to hemoglobin (as oxyhemoglobin), 1.5% dissolved in plasma.

• Equation:

CO2 Transport in the Blood

• Transported in three forms:

  • 7-10% dissolved in plasma

  • 20% bound to hemoglobin (as carbaminohemoglobin)

  • 70% as bicarbonate ions (HCO3-) in plasma

• Equation:

Digestive System

Activities in Food Processing

• Ingestion: Taking food into the mouth.

• Propulsion: Moving food through the alimentary canal (includes swallowing and peristalsis).

• Mechanical Digestion: Physical breakdown of food (chewing, churning, segmentation).

• Chemical Digestion: Enzymatic breakdown of food molecules.

• Absorption: Transport of digested nutrients into blood or lymph.

• Defecation: Elimination of indigestible substances as feces.

Peristalsis and Segmentation

• Peristalsis: Involuntary, wave-like muscle contractions that move food along the digestive tract.

• Segmentation: Rhythmic contractions that mix food and increase contact with digestive juices in the small intestine.

Layers of Digestive Organs

• Mucosa: Innermost layer; secretes mucus, enzymes, and hormones; absorbs nutrients.

• Submucosa: Connective tissue with blood vessels, nerves, and lymphatics.

• Muscularis Externa: Smooth muscle responsible for peristalsis and segmentation.

• Serosa: Outermost protective layer (visceral peritoneum).

Digestion in the Mouth and Salivary Glands

• Mouth: Mechanical digestion (chewing); chemical digestion begins with salivary amylase (starch breakdown).

• Salivary Glands: Parotid, submandibular, and sublingual glands secrete saliva containing enzymes and mucus.

Esophagus and Heartburn

• Esophagus: Muscular tube transporting food from pharynx to stomach via peristalsis.

• Heartburn: Caused by gastric acid refluxing into the esophagus, irritating its lining.

Processing of Carbohydrates, Lipids, and Proteins

• Carbohydrates: Digested in mouth (salivary amylase), small intestine (pancreatic amylase, brush border enzymes).

• Lipids: Digested mainly in small intestine (bile emulsifies fats, pancreatic lipase breaks them down).

• Proteins: Digested in stomach (pepsin), small intestine (pancreatic proteases, brush border enzymes).

Stomach: Gastric Secretions, Cell Types, and Functions

• Parietal Cells: Secrete hydrochloric acid (HCl) and intrinsic factor.

• Chief Cells: Secrete pepsinogen (inactive enzyme, activated to pepsin by HCl).

• Mucous Cells: Secrete mucus to protect stomach lining.

• Enteroendocrine Cells: Secrete hormones (e.g., gastrin).

Digestive Processes in the Stomach

• Mechanical mixing of food (chyme formation).

• Chemical digestion of proteins by pepsin.

• Limited absorption (e.g., alcohol, aspirin).

Regulation of Gastric Secretions

• Regulated by neural (vagus nerve) and hormonal (gastrin) mechanisms.

• Three phases: cephalic (before food enters), gastric (food in stomach), intestinal (chyme in duodenum).

Gastric Emptying and Duodenal Monitoring

• Duodenum monitors chyme composition (fat, acidity, hypertonicity) and regulates gastric emptying via hormones (e.g., secretin, cholecystokinin).

Small Intestine: Modifications, Absorption, and Digestion

• Structural Modifications: Circular folds, villi, and microvilli increase surface area for absorption.

• Absorption: Most nutrients absorbed here via active and passive transport mechanisms.

• Digestion: Enzymes from pancreas and brush border complete digestion.

Accessory Organs: Pancreas and Liver

• Pancreas: Produces digestive enzymes (proteases, lipases, amylases) and bicarbonate-rich fluid to neutralize stomach acid.

• Liver: Produces bile, processes nutrients, detoxifies substances, stores glycogen and vitamins.

Function of Bile and Pancreatic Juices

• Bile: Emulsifies fats, aiding in their digestion and absorption.

• Pancreatic Juices: Contain enzymes for digestion of all macronutrients and bicarbonate to neutralize acidic chyme.

Large Intestine: Functions and Digestive Processes

• Absorbs water, electrolytes, and some vitamins.

• Forms and stores feces.

• Propels fecal material toward the rectum via mass movements.

Bacterial Flora in the Large Intestine

• Synthesize vitamins (e.g., vitamin K, B vitamins).

• Ferment indigestible carbohydrates, producing gases.

• Contribute to immune function and prevent growth of harmful bacteria.

Additional info: Academic context and explanations have been expanded for clarity and completeness based on standard Anatomy & Physiology textbooks.