Respiratory System Introduction Flashcards

Organization and Functional Divisions of the Respiratory System

General Anatomy and Guidance
- Comprehensive understanding requires focusing on the anatomical organization of the respiratory system and its primary physiological concepts as outlined in the textbook.
- The respiratory system is categorized into two main anatomical sections: the Upper Respiratory Tract and the Lower Respiratory Tract.
General Functions of the Respiratory Tract
- The respiratory tract serves as the primary passageway for air.
- Optimal Conditions for Air: The system ensures that air is properly humidified and warmed before reaching the deeper structures. This is necessary for the respiratory tract to function at its peak efficacy.
- Homeostasis and Blood Chemistry: The respiratory system is a critical site for gas exchange. This process directly impacts the chemical composition of the blood, maintaining homeostatic targets.
The Respiratory Zone
- The Respiratory Zone includes any part of the respiratory tract actually involved in the exchange of gases.
- There are only three specific parts that constitute the respiratory zone:
  1. Respiratory bronchioles.
  2. Alveolar ducts.
  3. Alveoli.

Epithelial Histology and Structural Protection

Alveolar Epithelium
- The cells of the alveoli are characterized as simple squamous epithelium.
- Morphology: These are single layers of flattened cells.
- Physiological Rationale: The flattening occurs because of the pressure exerted by air pushing against the alveolar walls. The use of a single, thin layer facilitates the easy passage of substances during gas exchange.
Protective Epithelium in High-Friction Areas
- In areas where the airway is subject to rubbing, friction, or abrasion (such as swallowing food), a thicker epithelium is required for protection.
- In these regions, the tissue is stratified (multiple layers) rather than simple.
- Specific Locations:
  - Oropharynx: Subject to friction during the swallowing of food.
  - Laryngopharynx: Subject to friction from swallowing and vibrations from speech/sound.
Anatomic Protective Mechanisms
- The Epiglottis: This structure serves to close off the larynx during the act of swallowing, preventing food or liquid from entering the lower airway.

Mechanics of Pulmonary Ventilation

Definition of Ventilation
- Ventilation is defined as the physical movement of air. It is driven by changes in volume within the intrapulmonary space.
- Because the volume of the atmosphere cannot be changed by the body, the body must change its internal thoracic volume to create necessary pressure gradients.
Muscle Involvement in Quiet Respiration
- Primary Muscles: The two muscles used for quiet (normal) respiration are the Diaphragm and the External Intercostals.
- Classification: These are skeletal muscles, which means they are under voluntary control, though they often function automatically.
- Accessory Muscles: Any other muscles listed in textual resources are considered accessory muscles. These are only recruited during forced respiration (either forced inhalation or forced expiration).
The Process of Inspiration (Quiet)
- This is an active process because it requires muscle contraction.
- Diaphragm Action: The diaphragm contracts, moves downward (descends), and flattens its dome shape.
- Rib Cage Action: The rib cage moves sideways (widens), as well as upward and forward (anteriorly/posteriorly).
- Volume and Pressure Relationship:
  1. The volume of the thoracic cavity increases.
  2. The pleural membranes pull the lungs along with the expanding thoracic wall.
  3. The intrapulmonary space expands in three dimensions: length, width, and depth.
  4. As volume increases, the internal pressure drops (P < P_{atm}).
  5. Once the internal pressure is lower than the atmospheric (barometric) pressure, air moves into the lungs along the path of least resistance.
The Process of Expiration (Quiet)
- 1. The brain removes the stimulus for muscle contraction.
- 2. The muscles relax.
- 3. Elastic Recoil: Due to the natural elasticity of the lung tissue, the structures tend to return to their original, smaller shape.
- 4. The rib cage moves down and in; the diaphragm moves up.
- 5. The volume of the thoracic cavity decreases.
- 6. As volume decreases, the internal pressure increases (P > P_{atm}), forcing air out of the lungs.

Dimensions of Thoracic Change

The thoracic cavity changes in three specific dimensions:
- Length: Primarily regulated by the flattening and descent of the diaphragm during contraction.
- Width and Depth: Regulated by the intercostal muscles that elevate and depress the ribs and sternum.
- Metaphors for Movement:
  - Bucket Handle: The elevation of the ribs increasing the width of the thoracic cavity.
  - Pump Handle: The anterior and superior movement of the sternum increasing the depth of the thoracic cavity.

Stages of Respiration

Pulmonary Ventilation: The physical act of inhaling to fill the alveoli with air.
External Respiration: The exchange of gases between the alveoli and the blood. Oxygen ( $O_2$ ) diffuses into the blood while carbon dioxide ( $CO_2$ ) diffuses into the alveoli.
- Respiratory Membrane: Composed of the alveolar epithelium and the blood vessel (capillary) epithelium fused together.
Gas Transport: The movement of oxygen and carbon dioxide throughout the body via the bloodstream.
Internal Respiration: The exchange of gases at the tissue level. Oxygen leaves the blood to enter the tissues, and carbon dioxide leaves the tissues to enter the blood.

Chemical and Neural Control of Breathing

The Primary Stimulus for Respiration
- Carbon Dioxide ( $CO_2$ ): The level of $CO_2$ in the blood is the main stimulus for respiration.
- Hypoxia vs. Hypercapnia: While low oxygen levels ( $O_2$ ) can stimulate breathing, the oxygen must drop to dangerously low levels before it triggers the medullary respiratory centers. In contrast, even small rises in $CO_2$ will trigger a change in breathing patterns.
- High $CO_2$ as a Toxin: Elevated $CO_2$ levels indicate the accumulation of waste and potential toxicity, requiring immediate expulsion through increased ventilation.
Chemoreceptors and pH
- Chemoreceptors detect chemical changes in the blood, specifically focusing on pH levels.
- The $CO_2$ and pH Relationship:
  - High concentrations of Hydrogen ions ( $H^+$ ) result in a more acidic environment (Lower pH).
  - Low concentrations of $H^+$ result in a more basic or alkaline environment (Higher pH).
  - Higher $CO_2$ levels lead to an increase in $H^+$ production, lowering blood pH.
Metabolic Demand
- During exercise, the demand for $O_2$ increases, which simultaneously increases the production of $CO_2$ waste.
- This rise in $CO_2$ serves as the stimulus to breathe faster (Supply and Expulsion mechanism).
Brain Centers of Control
- Reflexive Control: Occurs at the brain stem level. It is a preprogrammed, automatic response to chemical levels (specifically $CO_2$ ).
- Higher Center Control: Located in the higher brain (cerebral cortex). This allows for conscious control such as:
  - Voluntarily breathing faster.
  - Holding one's breath (e.g., under water).
  - Meditating to slow respiratory rate.
  - Influence of anxiety, stress, or panic on breathing rate.
- Override Limits: Conscious control can only override the automatic reflex to a point. Once $CO_2$ levels rise high enough in the blood, the brain stem will force the individual to breathe.

Partial Pressure and Gas Movement

Understanding Partial Pressure
- Air is a mixture of gases including Nitrogen ( $N_2$ ), Oxygen ( $O_2$ ), and Carbon Dioxide ( $CO_2$ ).
- Each gas exerts a partial pressure based on its concentration within the total space.
- Gradient-Driven Movement: Gases move from areas of higher partial pressure to areas of lower partial pressure.
- Example: If $O_2$ partial pressure is higher in the alveoli than in the blood, $O_2$ will move into the blood.

Assessing Respiratory Function

Spirometry
- Respiratory function is measured using a device called a spirometer.
- Students must be able to describe and identify various respiratory volumes and capacities (e.g., Tidal Volume, Vital Capacity) by their written descriptions, as graphs may not always be provided for matching labels during assessments.
Ventilation Variations
- Hyperventilation: Excessive ventilation leading to low levels of $CO_2$ in the blood.
- Hypoventilation: Insufficient ventilation often caused by issues like airway obstruction, leading to high levels of $CO_2$ and increased hydrogen ion ( $H^+$ ) acidity.