Respiratory System: Exchange of Gases

RESPIRATORY SYSTEM: EXCHANGE OF GASES

Important Information

  • The following slides do not encompass all information in the related textbook chapter (Michael D. Johnson, Human Biology: Concepts and Current Issues, Seventh Edition).

  • Students are responsible for comprehending all material contained in the relevant chapter, as it will be included in assessments.

Respiration Processes

  • Breathing (ventilation): The process of moving air in and out of the lungs.

  • External respiration: This is the gas exchange occurring between air and blood.

  • Internal respiration: Involves the gas exchange between blood and tissues.

  • Cellular respiration: Utilization of oxygen to generate ATP, leading to carbon dioxide production as a waste product.

Respiratory System Overview

  • Pulmonary circulation: Involves the transport of blood between the heart and lungs.

  • Systemic circulation: Refers to the blood flow from the heart to the rest of the body.

  • Capillary networks: Present in the head, limbs, torso, and internal organs.

  • Interstitial fluid: Surrounds cells in tissues and helps facilitate gas exchange.

Oxygen and Carbon Dioxide Levels in Various Environments

  • Systemic veins and pulmonary artery: O2 < 40 mmHg, CO2 > 46 mmHg

  • Pulmonary vein and aorta: O2 100 mmHg, CO2 40 mmHg

  • Alveolar air: O2 104 mmHg, CO2 40 mmHg

  • Moist exhaled air: O2 120 mmHg, CO2 27 mmHg

  • Dry inhaled air: O2 160 mmHg, CO2 0.3 mmHg

Anatomy of the Respiratory System

Components of the Upper Respiratory Tract

  • Nose: For air passage.

  • Mouth: Passageway for food and air.

  • Epiglottis: Flexible cartilage that covers the larynx during swallowing.

  • Pleural membranes: Cover the lungs and line the chest cavity.

  • Lungs: Main organs of gas exchange.

  • Intercostal muscles: Assist in rib movement during respiration.

  • Diaphragm: The main skeletal muscle of respiration.

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

  • Tongue: Aids in swallowing and taste.

  • Pharynx: Common passageway for air, food, and liquid.

  • Larynx (Voice box): Produces sound and protects the trachea against food aspiration.

  • Trachea (Windpipe): Main airway leading to the bronchi.

  • Bronchi: Branching air pathways that lead to the lungs.

  • Alveoli: Air sacs where gas exchange occurs.

Components of the Lower Respiratory Tract

  • Larynx: Contains the epiglottis and vocal cords to maintain airway and produce sound.

  • Trachea: Conducts air to lungs and is supported by C-shaped cartilage rings; lined with mucus-secreting ciliated epithelium for particle trapping.

  • Bronchi: Trachea divides into right and left bronchi; contain ciliated epithelia, smooth muscle, and cartilage.

  • Bronchioles: Smaller branches of bronchi that lack cartilage.

Functions of the Respiratory Tract

Upper Respiratory Tract Functions

  • Acts as a passageway for respiration.

  • Houses receptors for smell.

  • Filters larger foreign material from incoming air.

  • Moistens and warms entering air.

  • Provides resonating chambers for voice production.

Lower Respiratory Tract Functions

  • Facilitates gas exchanges during respiration.

  • Larynx:

    • Contains flexible epiglottis and vocal cords.

    • Ensures an unobstructed airway.

  • Trachea:

    • Conducts air to and from lungs, lined to trap foreign particles.

    • Initiates a cough reflex to expel irritants.

  • Bronchi and Bronchioles:

    • Transport air and condition it (clean, warm, humidify).

    • Cilia's cleansing action is often impaired by smoking (leading to smoker's cough).

Structure and Function of the Lungs

  • The lungs are composed of supportive tissue enclosing bronchi, bronchioles, blood vessels, and alveoli, where gas exchanges occur.

  • Each lung resides in the thoracic cavity, enclosed by two layers of pleural membranes, creating a pleural cavity filled with fluid to minimize friction.

  • The right lung has three lobes, while the left lung has two lobes; they can function independently.

Gas Exchange Mechanisms

  • Oxygen Transport:

    • Bound to hemoglobin in red blood cells (98%) or dissolved in blood plasma (2%).

  • Carbon Dioxide Transport:

    • Dissolved in plasma (10%), bound to hemoglobin (20%), or in the form of bicarbonate (HCO3-, 70%).

Breathing Mechanism: Pressure Gradient

  • Inspiration (inhalation):

    • Diaphragm contracts and moves downward.

    • Intercostal muscles contract, elevating the chest wall and expanding lung volume, decreasing pressure within the lungs to draw in air.

  • Expiration (exhalation):

    • Muscles relax:

    • Diaphragm returns to a dome shape.

    • Intercostal muscles relax, lowering chest volume, thus increasing chest pressure and expelling air.

Measurement of Lung Capacity

  • Lung Volumes (milliliters):

    • Tidal Volume: Average ~ 500 mL — volume of air inhaled/exhaled during normal breathing.

    • Dead Space Volume: ~ 150 mL — air that remains in airways and does not engage in gas exchange.

    • Vital Capacity: ~ 4800 mL — Maximum volume exhaled after maximum inhalation.

    • Inspiratory Reserve Volume: ~ 2100-3200 mL — air inhaled beyond tidal volume.

    • Expiratory Reserve Volume: ~ 1000-1200 mL — air forcibly exhaled beyond tidal volume.

    • Residual Volume: ~ 1200 mL — air remaining in lungs after maximal expiration.

Gas Exchange Process

  • Gas diffusion occurs based on partial pressure gradients during:

    • External Respiration: Between alveoli and blood.

    • Internal Respiration: Between blood and tissue fluids.

Carbon Dioxide Transport Mechanism

  • In venous blood:

    • 20% combines with hemoglobin (Hb).

    • 10% dissolves in plasma.

    • 70% converts to bicarbonate (HCO3-) and diffuses into plasma.

  • In arterial blood, approximately 98% of oxygen is bound to hemoglobin within red blood cells, with the small remainder dissolved in plasma.

Regulation of Breathing: Nervous System Involvement

  • The respiratory center in the medulla oblongata establishes the breathing pattern.

  • Chemical receptors monitor levels of carbon dioxide, hydrogen ions, and oxygen.

  • Medullary centers react to changes in hydrogen ion levels due to CO2 retention.

  • Carotid and aortic bodies also play roles in sensing changes in O2 and CO2 concentrations.

  • Higher brain centers can exercise conscious control over the respiratory process.

Disorders of the Respiratory System

  • Reduced Air Flow Disorders:

    • Asthma

    • Emphysema

    • Bronchitis

  • Infectious Disorders:

    • Pneumonia

    • Tuberculosis

    • Botulism

  • Other Conditions:

    • Lung cancer

    • Congestive heart failure

    • Cystic fibrosis