2.1-2.2

Human Respiratory System

  • Breathing

    • Defined as the process of inhaling and exhaling air by the lungs.

    • The system that facilitates this process is known as the human respiratory system.

  • Functions

    • The primary function of the human respiratory system is to supply oxygen to the body and remove carbon dioxide from the body cells.

Structure of the Human Respiratory System

  • Components include:

    • Nasal cavity

    • Nostrils

    • Pharynx

    • Epiglottis

    • Larynx

    • Trachea

    • Right lung

    • Left lung

    • Diaphragm

    • Intercostal muscles

    • Bronchus

    • Bronchiole

    • Alveolus

Breathing Mechanism

  • Inhalation

    • Pathway of air:

    • Direction: Nostrils → Nasal cavity → Pharynx → Trachea → Bronchus → Bronchiole → Alveolus

    • Process of inhalation involves:

    • Contraction of intercostal muscles which pull the rib cage upward and outward.

    • Contraction of diaphragm which descends and flattens.

    • These actions increase the volume of the thoracic cavity, causing a drop in air pressure within, leading to air being drawn into the lungs.

  • Exhalation

    • Pathway of air:

    • Direction: Alveolus → Bronchiole → Bronchus → Trachea → Pharynx → Nasal cavity → Nostrils

    • Process of exhalation involves:

    • Relaxation of intercostal muscles which causes the rib cage to move downward and inward.

    • Relaxation of diaphragm which curves upwards.

    • These actions decrease the volume of the thoracic cavity, increasing air pressure, and pushing air out of the lungs.

Movement and Exchange of Gases in the Human Body

  • Gas Exchange Process

    • The movement of oxygen and carbon dioxide molecules occurs from areas of higher concentration to lower concentration.

    • In the alveolus:

    • Inhaled air has higher oxygen concentration compared to blood in the capillaries.

    • Oxygen diffuses from the alveolus into the blood capillaries.

    • In red blood cells:

    • Presence of haemoglobin, a dark red compound, which combines with oxygen to form oxyhaemoglobin (unstable, bright red).

    • As blood reaches body cells with low oxygen concentration, oxyhaemoglobin splits back into haemoglobin and oxygen.

    • Oxygen is utilized in cellular respiration, producing carbon dioxide, water, and energy:

    • extGlucose+extOxygen<br>ightarrowextCarbonDioxide+extWater+extEnergyext{Glucose} + ext{Oxygen} <br>ightarrow ext{Carbon Dioxide} + ext{Water} + ext{Energy}

    • Carbon dioxide from cells diffuses into blood capillaries and is transported back to the alveolus for removal during exhalation.

Adaptations of the Alveolar Structure

  • Adaptations enhance the efficiency of gas exchange:

    • Thin walls: Alveoli and blood capillaries have walls comprised of a single layer of cells facilitating diffusion.

    • Large surface area: Millions of alveoli in the lungs provide extensive area for gas exchange.

    • Moist walls: Allows respiratory gases to dissolve and diffuse effectively.

    • Network of capillaries: Compact capillary network increases gas exchange rate between alveolus and blood.

  • Concentration Gradient:

    • Higher concentration differences between gases in the alveoli and blood capillaries enhance diffusion rates.

Key Figures

  • Figure 2.1: Structure of the Human Respiratory System

  • Figure 2.2: Direction of Air in the Breathing Mechanism

  • Figure 2.3: Inhalation Process

  • Figure 2.4: Exhalation Process

  • Figure 2.10: Adaptations of the Alveolar Structure