Human and Social Biology: The Respiratory Tract and Breathing Study Guide

Introduction to the Respiratory System

• Definition of the Respiratory System: The respiratory system is comprised of tissues and organs involved in the process of breathing. These components include the diaphragm muscles, intercostal muscles, pleural membranes, rib cage, mouth, nose, larynx, pharynx, bronchi, bronchioles, and alveoli.
• Location of Core Components: The bronchi, bronchioles, and alveoli are specifically located within the lungs.
• Primary Roles:     * The system facilitates taking air into the body to make oxygen available for cells.     * It functions as a waste removal system for gases such as carbon dioxide.
• Key Operating Gas: The human body is operated by oxygen ($O_2$).
• Vital Organ Importance: The lungs are the primary organs of the respiratory system, serving as the site for gas exchange.

Functions of the Respiratory System

• Breathing Process: It facilitates the inhalation (breathing in) and exhalation (breathing out) of air in and out of the lungs.
• Oxygen Delivery: It delivers oxygen directly to the cells throughout the body.
• Waste Removal: It removes carbon dioxide ($CO_2$), which is a byproduct waste gas, from the body.
• Protection: It protects the airways from irritants and potentially harmful substances.
• Sensory and Communication: The system aids in the processes of talking (through the larynx) and smelling (through the nasal cavity).

Anatomy of the Respiratory Tract

The Upper Respiratory Tract

• Nose: Serves as the primary entrance and exit for inhaled and exhaled air.
• Mouth: Can be used as an entrance/exit for air; however, air entering through the mouth is not filtered.
• Nasal Cavity:     * Cilia: Contains small hairs that trap bacteria and dust.     * Goblet Cells: Secrete mucus to provide moisture to the incoming air.     * Blood Supply: Features a rich blood supply that warms the inhaled air.
• Pharynx (Throat): Acts as a shared passageway for both air and food.
• Epiglottis: A leaf-shaped flap made of flexible cartilage. It functions as a valve that prevents food from entering the trachea during swallowing.

The Lower Respiratory Tract

• Larynx (Voice Box): Contains the vocal cords, which vibrate to produce sound.
• Trachea (Windpipe): A tube that allows air to flow from the throat down to the bronchi. It is supported by rings of cartilage that prevent the structure from collapsing.
• Bronchi (Singular: Bronchus): These tubes allow air to flow into and out of each individual lung.
• Bronchioles: Small branches extending from the bronchi that allow air to flow between the bronchi and the alveoli.
• Alveoli (Singular: Alveolus): Located at the terminal ends of the bronchioles. This is the site of gas exchange where oxygen diffuses from the air into the blood, and carbon dioxide diffuses from the blood into the air.
• Diaphragm: A muscle that separates the thoracic cavity from the abdominal cavity and aids in the breathing process.

Conditions Affecting the Lower Respiratory Tract

• Pneumonia: An infection resulting in the inflammation of air sacs in one or both lungs.
• Bronchitis: An inflammation specifically affecting the lining of the bronchial tubes.
• Asthma: A chronic medical condition characterized by the narrowing and inflammation of the airways.
• Tuberculosis: A bacterial infection that typically affects the lungs but can target other parts of the body.

The Mechanism and Pathway of Breathing

Definition of Breathing

• Breathing is the mechanism through which air is taken into and removed from the lungs. The organs facilitating this make up the respiratory system.

Pathway of Inhalation (Breathing In)

1. Entry: Air enters through the nose or mouth.
2. Filtration: In the nostrils, fine hairs called cilia filter out dust particles.
3. Pharynx: Air from the mouth and nose meets at the pharynx (located behind the buccal cavity).
4. Larynx and Trachea: Air passes through the larynx into the trachea.
5. Bronchi and Bronchioles: The trachea splits into two bronchi, leading into the lungs and further into the bronchioles.
6. Alveoli: Each bronchiole delivers air to an alveolus for gaseous exchange.

• Summary Flow: $\\text{Nose/Mouth} \\rightarrow \\text{Pharynx} \\rightarrow \\text{Larynx} \\rightarrow \\text{Trachea} \\rightarrow \\text{Bronchi} \\rightarrow \\text{Bronchioles} \\rightarrow \\text{Alveoli}$

Pathway of Exhalation (Breathing Out)

1. Departure: Air leaves the alveoli and enters the bronchioles.
2. Transport: Air moves into the bronchi and then into the trachea.
3. Exit: From the trachea, air moves through the larynx and pharynx to the mouth or nostrils to exit the body.

• Summary Flow: $\\text{Alveoli} \\rightarrow \\text{Bronchioles} \\rightarrow \\text{Bronchi} \\rightarrow \\text{Trachea} \\rightarrow \\text{Larynx} \\rightarrow \\text{Pharynx} \\rightarrow \\text{Nose/Mouth}$

Detailed Mechanics

• Inhalation:     * Outer intercostal muscles contract; inner intercostal muscles relax.     * The rib cage moves upwards and outwards.     * The diaphragm contracts and flattens.     * The volume of the thoracic cavity increases, causing air pressure to decrease.     * Air is drawn into the lungs.
• Exhalation:     * Outer intercostal muscles relax; inner intercostal muscles contract.     * The rib cage moves downwards and inwards.     * The diaphragm relaxes and curves upwards.     * The volume of the thoracic cavity decreases, causing air pressure to increase.     * Air is forced out of the lungs.

Factors Affecting the Rate of Breathing

• Brain Regulation: The brain monitors concentrations of $O_2$ and $CO_2$ in the blood and the stretch of the lungs to determine the rate and depth of breathing.
• Exercise:     * Increases the rate and depth of breathing.     * Increases the volume of inhaled air.     * Increases the amount of carbon dioxide exhaled.     * Leads to an increased number of capillaries in the lungs and expansion of the alveoli.     * Increases the strength and size of the diaphragm and intercostal muscles.
• Age: Younger individuals generally have higher breathing rates due to higher activity levels.
• Gender: Women tend to have a slightly higher breathing rate than men.
• Health: Better overall health correlates with a lower resting breathing rate.
• Environmental Factors: Poorly ventilated or crowded rooms increase $CO_2$ levels, which increases the breathing rate and induces yawning.
• High Altitudes: Lower oxygen availability in the air at high altitudes increases both the depth and rate of breathing.
• Weight: Obese individuals may experience breathlessness because it is physically difficult for the diaphragm to move downward properly.

Lung Capacities and Volumes

Basic Concepts

• Vital Capacity: The maximum volume of air a person can exhale after a maximum inhalation. It is measured using a spirometer.
• Normal Range: Between $3\\text{ and } 5\\text{ litres}$ for a normal adult.
• Influencing Factors: Age, sex, height, and body mass.
• Measurement Type: Lung volumes are measured directly, while capacities are inferred from those volumes.

Respiratory Volume and Capacity Data

Bell Jar Model Activity

• Model Components: The breathing process can be demonstrated using a bell jar apparatus.     * Bell Jar: Represents the rib cage/chest cavity.     * Glass Tube: Represents the trachea.     * Balloon: Represents the lung.     * Plastic/Rubber Sheet: Represents the diaphragm.
• Volume Changes: When the rubber sheet (diaphragm) is pulled down, the internal volume increases, pressure decreases, and the balloons (lungs) inflate. When pushed up, volume decreases, pressure increases, and balloons deflate.
• Model Limitations: Students are encouraged to suggest reasons why this is not an exact model for human breathing (e.g., the bell jar is rigid unlike the moving rib cage).