Breathing (lol)

Overview of the Respiratory System

• Primary Function: The respiratory system is responsible for exchanging gases between the human body and the external environment.

• Gases Exchanged:

  • Oxygen ($O_2$): Inhaled from atmospheric air into the body and transferred into the bloodstream.

  • Carbon Dioxide ($CO_2$): Produced as waste by body tissue, transferred from the blood into the lungs, and exhaled into the air.

• Core Respiratory Actions:

  • Inhalation (Breathe In): Air enters through the nose; oxygen from the air moves into the blood.

  • Exhalation (Breathe Out): Air leaves through the nose; carbon dioxide from the blood moves into the air and is released.

• Composition of Breathed Air:

  • Nitrogen: Makes up the majority of atmospheric air at $78\%$.

  • Oxygen: Makes up approximately $21\%$.

  • Other Gases: Represent the remaining $1\%$.

Anatomical Structure of the Respiratory Tract

The respiratory tract defines the path air follows as it enters, traverses, and leaves the body:

• Nostrils & Nasal Cavity: Air enters via the nostrils into the nasal cavity, which warms and moistens incoming air before it proceeds deeper into the system.

• Pharynx: The throat passage situated behind the nasal cavity and mouth, leading down toward the larynx.

• Larynx (Voice Box): Located beneath the pharynx. As air passes outward through the larynx, it vibrates vocal cords, enabling speech.

• Trachea (Windpipe): A main cartilaginous tube conducting air downward from the larynx into the chest region.

• Bronchi (plural; singular: Bronchus): The base of the trachea splits into two primary tubes called bronchi, with one bronchus entering the right lung and the other entering the left lung.

• Bronchioles: Inside each lung, each bronchus branches progressively into smaller and narrower bronchial tubes known as bronchioles.

• Alveoli (plural; singular: Alveolus): Microscopic air sacs attached at the terminal ends of each bronchiole. They create an exceptionally large surface area required for gas exchange with surrounding blood vessels.

Respiratory Support Structures and Musculature

• Epiglottis: A flap of cartilage located at the back of the throat. During swallowing, it folds down to seal off the top of the trachea, preventing food and liquids from entering the respiratory tract and lungs.

• Ribs: Curved bony structures forming a protective skeletal cage around the lungs and thoracic cavity.

• Intercostal Muscles: Muscles situated between adjacent ribs that contract and relax to move the rib cage during respiration.

• Diaphragm: A dome-shaped sheet of muscle attached to the lower ribs and spine that forms the floor of the chest cavity.

• Sternum: The central chest bone (breastbone) to which the ribs anchor anteriorly.

Microscopic Gas Exchange in the Alveoli

• Alveolar Structure & Capillary Network:

  • Alveoli provide an extensive surface area inside the lungs for maximum exchange efficiency.

  • Each alveolus is wrapped in a dense mesh of microscopic blood vessels called capillaries.

• Mechanism of Diffusion:

  • Definition of Diffusion: The movement of matter from an area of higher concentration to an area of lower concentration.

  • Oxygen Transfer: Oxygen ($O_2$) concentration inside the inhaled alveolar air is higher than in the deoxygenated capillary blood returning from the body. Oxygen diffuses across the thin alveolar wall into the blood.

  • Carbon Dioxide Transfer: Carbon dioxide ($CO_2$) concentration in returning capillary blood is higher than in the air within the alveoli. Carbon dioxide diffuses out of the blood into the alveolar space to be exhaled.

Mechanics of Breathing (Ventilation)

• Inability of Lungs to Move Independently: Lungs contain no muscle tissue and cannot expand or contract on their own. Breathing relies entirely on changes in chest cavity volume and air pressure driven by external muscles.

• Inhalation (Inspiration):

  • Intercostal Muscles: Contract, lifting the rib cage upward and outward.

  • Diaphragm: Contracts, moves downward (descends), and flattens out.

  • Volume & Pressure: These muscular actions expand the thoracic cavity, increasing internal volume and dropping internal air pressure below atmospheric pressure.

  • Air Movement: Higher atmospheric pressure outside forces external air to rush into the lower-pressure environment inside the lungs.

• Exhalation (Expiration):

  • Intercostal Muscles: Relax, allowing the rib cage to drop downward and inward.

  • Diaphragm: Relaxes, moves upward (ascends), and returns to its curved dome shape.

  • Volume & Pressure: These actions reduce thoracic cavity volume, compressing air inside the lungs and elevating internal air pressure above atmospheric pressure.

  • Air Movement: Higher internal pressure forces air out of the lungs into the environment.

Checks for Understanding & Review Questions

• Check for Understanding 1: Respiratory System Overview

  • Question: What is the respiratory system responsible for?

  • Answer: Exchanging two primary gases—oxygen and carbon dioxide—between the human body and the environment.

  • Question: Which two gases are exchanged?

  • Answer: Oxygen ($O_2$) and carbon dioxide ($CO_2$).

  • Question: How is inhalation different to exhalation?

  • Answer: Inhalation draws atmospheric air into the lungs to deliver oxygen to the bloodstream, whereas exhalation expels air from the lungs to remove carbon dioxide waste from the bloodstream.

• Check for Understanding 2: Respiratory Tract

  • Question: What is the respiratory tract?

  • Answer: The complete pathway air travels within the body during breathing.

  • Question: How does air get into the respiratory system?

  • Answer: Air is inhaled through the nostrils into the nasal cavity, flowing down through the pharynx, larynx, and trachea.

  • Question: When the trachea splits, what does it become?

  • Answer: Two branches called bronchi (singular: bronchus).

  • Question: How are bronchioles different to the bronchi?

  • Answer: Bronchi are the two primary main stem tubes branching off the trachea, whereas bronchioles are smaller branch tubes extending off the bronchi throughout the interior of the lungs.

• Check for Understanding 3: Support Organs and Alveoli

  • Question: What is the epiglottis?

  • Answer: A flap of cartilage located at the back of the throat that covers the entrance to the trachea during swallowing to prevent food from entering the airway.

  • Question: What is the function of the alveoli?

  • Answer: To provide a massive surface area inside the lungs for efficient gas exchange with the bloodstream.

  • Question: What surrounds each alveolus?

  • Answer: A network of microscopic blood vessels known as capillaries.

  • Question: What role does blood play in gas exchange?

  • Answer: Blood carries carbon dioxide waste to alveolar capillaries to be released into the lungs and collects oxygen from alveoli to deliver to body tissue.

• Check for Understanding 4: Mechanics of Breathing

  • Question: Why are the lungs unable to move on their own?

  • Answer: The lungs contain no muscle tissue.

  • Question: Which muscles work together to allow the body to breathe?

  • Answer: The diaphragm and intercostal muscles working alongside rib movements.

  • Question: How is the body able to move air into and out of the lungs?

  • Answer: By using muscle contractions and relaxations to change thoracic space and create air pressure differences between the inside of the chest and the external atmosphere.

• Skill Closure Practice:

  • Prompt 1: Explain how inhaling and exhaling happens. Include the ribs, intercostal muscles, and the diaphragm in your answer.

  • Answer: Inhaling occurs when intercostal muscles contract to lift the ribs up and out while the diaphragm contracts and flattens downward. This expands chest volume, lowers internal air pressure, and draws external air in. Exhaling occurs when intercostal muscles relax to lower the ribs down and in while the diaphragm relaxes back into a dome shape upward. This shrinks chest volume, increases internal air pressure, and pushes air out.

  • Prompt 2: What two gases are exchanged by the respiratory system? Explain how they are exchanged.

  • Answer: Oxygen ($O_2$) and carbon dioxide ($CO_2$) are exchanged through diffusion across alveoli and blood capillaries. Oxygen diffuses from high concentration in inhaled air within alveoli into blood capillaries. Carbon dioxide diffuses from high concentration in capillary blood into alveolar spaces to be expelled during exhalation.