Rucete ✏ Biology In a Nutshell
1. Purpose of the Respiratory System
- Delivers oxygen (O₂) to internal cells
- Removes carbon dioxide (CO₂) waste
- Enables gas exchange between the body and environment
2. Gas Exchange Mechanisms in Animals
a) Direct with Environment
- Occurs in Platyhelminthes (flatworms)
- Diffusion across body surface due to large surface area
b) Through Skin
- Found in Annelids (segmented worms)
- Use circulatory system and moist skin for gas exchange
c) Gills
- Evaginated structures that extend outward
- Common in aquatic animals
d) Tracheae
- System of air tubes used by insects
e) Lungs
- Invaginated structures (cavities) inside the body
- Used by land animals, including humans
3. Human Respiratory Tract Pathway
- Nose →
- Pharynx →
- Larynx →
- Trachea (lined with cartilage to prevent collapse and block solids/liquids) →
- Bronchi →
- Bronchioles →
- Alveoli (tiny air sacs surrounded by capillaries; main site of gas exchange)
4. Steps of Gas Exchange in Humans
- Diffusion of O₂ from alveoli to capillaries
- Bulk flow of oxygen through blood to body cells
- Diffusion of O₂ from blood into cells
- Diffusion of CO₂ from cells into blood
- Bulk flow of CO₂ in blood to lungs
- Diffusion of CO₂ from blood into alveoli
- Bulk flow of air into and out of the lungs (ventilation)
- Respiratory control regulated by the brain based on CO₂ levels
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Biology in a nutshell