Respiratory System Functions

• Ventilation involves the movement of gases from the outside to the inside of the body.

Respiratory Functions

• Gas exchange occurs between the atmosphere and the blood.
• Homeostatic regulation of body pH is maintained.
• Protection is provided from inhaled pathogens and irritants.
• Vocalization happens via vocal cords and sinus cavities.

Respiratory System Bulk Flow

• Flow happens from higher to lower pressure regions.
• A muscular pump, the diaphragm, creates pressure gradients.
• Airflow resistance depends on the diameter of the tubes.

External Respiration

• Oxygen and carbon dioxide are exchanged between the lungs and the blood.
• Oxygen and carbon dioxide are transported by the blood.

Internal Respiration

• Gases are exchanged between the blood and the cells.
• Capillaries are made of simple squamous cells, which increases diffusion.
• Serous fluid between membranes reduces friction and holds lungs tight against the thoracic wall.
• The pleura sac is a thin, double-walled serous membrane around the lungs.

Nasal Cavity

• Temperature regulation
• Humidification
• Filtration
• Nasal plasticity involves gradual adaptation to mouth breathing.
• The GI tract consists of epithelial tissue.
• The pharynx consists of stratified squamous tissue due to torsion and nonkeratinized mucus production.
• The trachea has C-shaped hyaline cartilage.
• The trachea, bronchi, and bronchioles contain pseudostratified ciliated columnar cells.
• Cilia are short, hair-like projections for movement against ventilation, moving mucus toward the pharynx to remove pathogens.
• Bronchioles lack cartilage to increase permeability and diffusion capacity.
• Alveoli and capillary beds have simple squamous epithelium for maximum diffusion capacity.
• Pleuritis involves inflammation of the pleura, causing respiratory issues.

Alveolar Cells

• Type I: Gas exchange, simple squamous
• Type II: Surfactant production for decreasing surface tension
• Type III: Wandering macrophages
• Alveoli are the site of gas exchange with connective tissue (elastin and collagen), closely associated with capillaries, and have low-pressure pulmonary circulation.

Pulmonary Circulation Pathway

• Right ventricle -> Pulmonary trunk -> Pulmonary arteries -> Lungs -> Pulmonary veins -> Left atrium
• The pulmonary circuit has low pressure.
• Goblet cells secrete mucus.
• Mucinex inhibits mucus secretion.

Gas Laws

• Dalton's Law
• Boyle's Law
• Standard atmospheric pressure is 1 ATM or 760 mmHg at sea level.
• Dalton’s Law: The total pressure of a gas mixture equals the sum of individual pressures.
• Boyle’s Law: Pressure is inversely proportional to volume.

Types of Lung Volumes

• Tidal Volume
• Inspiratory Reserve Volume
• Expiratory Reserve Volume
• Residual Volume
• Tidal volume (Vt) is the air volume during one breath during quiet breathing.
• Inspiratory reserve volume (IRV) is the additional volume forcefully inhaled above tidal volume during forced breathing.
• Expiratory reserve volume (ERV) is the volume forcefully exhaled after normal expiration during forced breathing.
• Residual volume (RV) is the air volume remaining after maximum exhalation.

Lung Capacity

• Vital Capacity
• Total Lung Capacity
• Inspiratory Capacity
• Functional Residual Capacity
• Vital Capacity (VC) = IRV + ERV + RV.
• Total Lung Capacity (TLC) = Vt + IRV + ERV + RV.
• Inspiratory Capacity = Vt + IRV.
• Functional Residual Capacity = RV + ERV.
• Lung capacity indicates respiratory capacity.
• During inspiration, the diaphragm contracts and elevates the thoracic cavity, increasing volume and decreasing pressure.
• During expiration, the diaphragm relaxes and depresses the thoracic cavity, decreasing volume and increasing pressure.
• Interpleural pressure drops during inspiration and returns to normal during expiration.
• Pneumothorax leads to a collapsed lung.
• Hemothorax is blood accumulation in the pleural space, increasing lung pressure and collapse.
• Normal negative pressure for sub-atmospheric intrapleural pressure is -3 mmHg.
• Surfactant decreases surface tension in alveoli, reducing breathing effort by disrupting water's cohesive force, with higher concentrations in smaller alveoli, containing proteins and phospholipids.
• Without surfactant, increased friction can collapse alveoli because closely placed alveoli with hydrogen bonds prevent alveolar expansion.
• Newborn Respiratory Distress Syndrome (NRDS) occurs when premature babies have inadequate surfactant.
• Not all air leaves the lungs during expiration to prevent collapse.
• Hyperventilation involves increased respiratory rate/volume without increased metabolism.
• Hyperpnea involves increased respiratory rate/volume with increased metabolism.
• Respiratory acidosis occurs due to obstructive and restrictive lung diseases.

Obstructive Lung Disease

• Able to inspire, struggles to expire
• O2 in and O2 can't leave
• Increased CO2
• Increases Airway Resistance
• Asthma, Obstructive sleep apnea, COPD

Restrictive Lung Disease

• Struggle to Inspire; able to expire
• No O2 in and increased CO2
• Reduced Lung Compliance
• Pulmonary Fibrosis (Increase Elastins, Decrease Compliance)
• Forced Vital Capacity is the forced expiration volume in 1 second and the FEV/FVC ratio distinguishes obstructive and restrictive lung diseases.
• Total Pulmonary Ventilation is the volume of air moved in/out of lungs per minute (ventilation rate x tidal volume).
• Alveolar Ventilation is the accurate measurement (ventilation rate x [Vt - dead space]).
• Hypoxia is too little oxygen.
• Hypercapnia is increased carbon dioxide.
• The body responds to oxygen, carbon dioxide, and pH levels.
• Breathing is the bulk flow of air into and out of the lungs.
• Individual gases diffuse along partial gradients until equilibrium is reached.
• Total pressure of mixed gas is the sum of partial pressures of individual gases.
• In alveoli and blood gas exchange, alveolar Po2 > blood Po2, and blood Pco2 > alveolar Pco2.
• In blood and tissue gas exchange, blood Po2 > tissue Po2, and tissue Pco2 > blood Pco2.
• Lower alveolar Po2 decreases oxygen uptake.
• Inspired air with abnormally low oxygen results in low alveolar Po2, and higher altitude decreases Po2.
• Low alveolar Po2 results from inadequate alveolar ventilation (hypoventilation).
• Decreased lung compliance (e.g., asbestosis), increased airway resistance (e.g., COPD), and CNS depression are all examples of alveolar ventilation.
• CNS depression includes alcohol poisoning and drug overdose, and affects the respiratory center in the brainstem.

Pathologies That Cause Hypoxia

• Emphysema
• Fibrotic Lung Disease
• Pulmonary Edema
• Asthma
• Emphysema involves the destruction of alveoli which means less surface area for gas exchange.
• Fibrotic Lung Disease involves thickened alveolar membranes and slows gas exchange, and the loss of lung compliance may decrease alveolar ventilation.
• Pulmonary Edema occurs when fluid in the interstitial space increases diffusion distance, and arterial Pco2 may be normal due to higher carbon dioxide solubility in water.
• Asthma involves increased airway resistance decreases alveolar ventilation.
• Gas entering into the capillaries first dissolves in the plasma.
• Hemoglobin binds to oxygen that obeys the law of mass action.
• Inc. Po2 shifts reaction to R (Hb + O2 -> HbO2) - In Lungs Dec. Po2 Shifts reaction to L (HbO2 -> Hb + O2) - In active tissues
• Blood pH, temperature, and Pco2 affect oxygen binding.

Medulla

• Rhythm generation
• Innervates diaphragm- phrenic nerves
• Innervates intercostal muscles
• Receives sensory input from central and peripheral chemoreceptors regarding primarily CO2 blood levels and to a lesser extent O2 levels and pH.
• Pontine Respiratory Groups output to the medulla to ensure a smooth respiratory rhythm.

Ventral Respiratory Group

• Prebotzinger complex: basic pacemaker activity
• Other regions control muscles involved for active expiration/ greater than normal inspiration (Labored Breathing)
• Innervate muscles of the larynx, pharynx, and tongue to keep these airways open during breathing

Chemoreceptors

• Peripheral: Located in carotid bodies (located in carotid arteries)
• Sense changes in Po2, pH and Pco2
• Dec. Po2 and Inc Pco2 initiate increase in ventilation
• O2 must fall below 60 mmHg to trigger reflex
• Central: Located in CNS (on ventral surface surface of medulla)
• Respond to changes in Pco2 in CSF
• Arterial Inc. Pco2, CO2 diffuses into CSF
• CO2 is converted to bicarbonate and H+
• H is actually detected CO2+H2O —> H2CO3 —> HCO3- + H+

GI System Anatomy

• Oral Cavity
• GI Tract
• The oral system consists of the mouth and pharynx.
• The GI Tract consists of the esophagus, stomach, small intestine, and large intestine.
• Gut refers to stomach through anus and is primarily involved in digestion (chemical and mechanical).
• Accessory glandular organs (salivary glands, pancreas, liver) secrete materials to aid in digestion.
• Chyme is a mixture of food and secretions.
• Digestion products are absorbed across the epithelium into interstitial fluid, then to blood/lymph.
• Waste is excreted from the GI tract through the anus.
• Digestion begins in the oral cavity via chewing and salivary glands.

Digestive System Pathway

• Oral Cavity -> Esophagus -> Stomach: Fundus -> Body -> Antrum -> Pylorus with pyloric valve -> Small intestine: Duodenum -> Jejunum -> Ileum -> Large Intestine: Colon -> Rectum -> Anus with external anal sphincter -> Feces
• The pharynx has nonkeratinized stratified squamous epithelium.