Notes on the Respiratory System

The Respiratory System

Learning Outcomes

• Role in Homeostasis: The respiratory system maintains homeostasis by regulating oxygen and carbon dioxide levels in the body.

• Inspiration vs. Expiration: Understand the difference between the two phases of ventilation: inspiration (inhalation) brings air into the lungs, while expiration (exhalation) expels air out of the lungs.

• Structures: Identify key anatomical structures involved in respiration.

Overview of the Respiratory System

• Function: Facilitates the exchange of oxygen (O2) and carbon dioxide (CO2).

• Inspiration: Air moves from the atmosphere via cavities and tubes into the lungs.

• Expiration: Air flows from the lungs back to the atmosphere through the same pathways.

Human Respiratory Tract Structures

• Upper Respiratory Tract:

  • Nasal Cavity: Filters, warms, and moistens incoming air.

  • Pharynx: Common passageway for air and food.

  • Glottis: Vocal cords and the space between them.

  • Larynx (Voice Box): Produces sound.

  • Trachea (Windpipe): Conducts air to the lungs.

• Lower Respiratory Tract:

  • Bronchus: Air passage to the lungs; branches into bronchioles.

  • Bronchioles: Small air passageways leading to alveoli.

  • Lungs: Contain alveoli where gas exchange occurs.

  • Diaphragm: Muscle that aids in ventilation.

Ventilation Process

• Ventilation (Breathing): Consists of inspiration and expiration; relies on the cardiovascular system for oxygen transport.

  • External Respiration: Gas exchange between air and blood in the lungs.

  • Transport: Movement of gases to/from lungs and tissues.

  • Internal Respiration: Gas exchange between blood and tissue fluid.

Upper Respiratory Tract Structures and Functions

• Nasal Cavities:

  • Structure: Divided by a septum, lined with mucous membranes to trap particles.

  • Function: Filtration, warming, and moisture of air.

• Pharynx:

  • Structure: Funnel-shaped cavity connecting nasal and oral cavities.

  • Function: Defense against pathogens through tonsils.

• Larynx:

  • Structure: Contains vocal cords, glottis, and the Adam's apple.

  • Function: Sound production; directs air into trachea.

Lower Respiratory Tract Structures and Functions

• Trachea:

  • Structure: Reinforced by C-shaped cartilaginous rings, lined with ciliated epithelium.

  • Function: Transports air; cilia sweep mucus and debris upward.

• Bronchial Tree:

  • Structure: Primary bronchi branch into smaller bronchioles.

  • Function: Airways for air to travel into lungs.

• Lungs:

  • Structure: Right lung has three lobes, left lung has two, due to heart position.

  • Function: Site of gas exchange facilitated by alveoli.

Alveoli and Gas Exchange

• Structure: About 300 million alveoli increased surface area, surrounded by blood capillaries.

• Function: Oxygen enters blood, CO2 exits into alveoli for exhalation. Surfactant reduces surface tension to keep alveoli open.

Mechanism of Breathing

• Ventilation Phases:

  • Inspiration: Active; diaphragm contracts, thoracic cavity expands, lowering alveolar pressure, allowing air to flow in.

  • Expiration: Passive; diaphragm relaxes, ribs move down and inward, air flows out due to increased pressure.

• Boyle's Law: Pressure of a gas decreases as volume increases and vice versa, this governs ventilation.

Control of Ventilation

• Nervous System: The brain’s respiratory control center sends signals for breathing; can be modified voluntarily (e.g., speaking).

• Chemical Control: Chemoreceptors monitor CO2 levels and pH in blood, adjusting the rate and depth of breathing to maintain homeostasis.

Gas Exchange

• External Respiration: O2 from alveoli to capillaries; CO2 from blood to alveoli.

• Internal Respiration: O2 from blood to tissues; CO2 from tissues into blood.

  • Important Enzymes: Carbonic anhydrase assists in CO2 transport in blood.

Disorders of the Respiratory System

• Upper Respiratory Infections: Include colds, sinusitis, tonsillitis, laryngitis.

• Lower Respiratory Disorders: Include bronchitis, pneumonia, asthma, emphysema, and lung cancer.

  • Smoking leads to significant respiratory issues, reducing lung function and capacity.