Biology Chapter: Specialized Exchange Surfaces

The Need for Specialized Exchange Surfaces

• Multicellular organisms have lower surface area to volume ratios than single-celled organisms, necessitating specialized exchange surfaces
• Specialized exchange surfaces provide efficient transport of gases, nutrients, and waste products

Features of an Efficient Exchange Surface

• Large Surface Area: Increases the area for diffusion, examples include root hair cells and folded membranes in mitochondria
• Thin: Reduces the distance over which substances need to diffuse, allowing for quicker exchange
• Good Blood Supply/Ventilation: Maintains a steep concentration gradient to facilitate diffusion

Mammalian Gaseous Exchange System

• Lungs: Composed of two structures within the chest cavity with a large surface area
• Rib Cage: Protects the lungs
• Lubricating Substance: Prevents friction between the rib cage and lungs during breathing
• Intercostal Muscles: External muscles raise the rib cage during inhalation, internal muscles lower the rib cage during exhalation
• Diaphragm: Separates the lungs from the abdominal area, contracts to flatten during inhalation and relaxes to dome upwards during exhalation
• Airways: Include the nose, trachea, bronchi, and bronchioles, facilitating air passage
• Alveoli: Tiny sacs filled with air where gas exchange occurs

Structures and Functions of Mammalian Gaseous Exchange System

• Cartilage: Provides support to the trachea and bronchi, prevents collapse during exhalation
• Ciliated Epithelium: Lines the bronchi, bronchioles, and trachea, moves mucus towards the throat to prevent lung infections
• Goblet Cells: Produce mucus to trap bacteria and dust, reducing infection risk
• Smooth Muscle: Contracts to constrict airways, regulating airflow to and from alveoli
• Elastic Fibres: Stretch during inhalation and recoil during exhalation, assisting airflow

Ventilation

• Inspiration (Inhalation): External intercostal muscles contract, diaphragm flattens, increasing thorax volume and decreasing pressure, drawing air into the lungs
• Expiration (Exhalation): Internal intercostal muscles contract, diaphragm relaxes, decreasing thorax volume and increasing pressure, forcing air out of the lungs

Spirometer

• Purpose: Measures lung volume
• Function: A person breathes into an airtight chamber, causing it to move up and down, producing a trace on a graph for analysis
• Vital Capacity: Maximum volume of air inhaled or exhaled in one breath
• Tidal Volume: Volume of air breathed in and out at rest
• Breathing Rate: Number of breaths per minute, determined by counting peaks or troughs on the spirometer trace
• Residual Volume: Air always present in the lungs
• Inspiratory Reserve Volume: Additional volume of air that can be inhaled beyond tidal volume
• Expiratory Reserve Volume: Additional volume of air that can be exhaled beyond tidal volume

Ventilation and Gas Exchange in Bony Fish

• Fish Adaptations: Small surface area to volume ratio, impermeable skin necessitate specialized gas exchange systems
• Gills: Four pairs of gills supported by arches
• Gill Filaments: Projections along each arch containing lamellae for gas exchange
• Countercurrent Flow: Water and blood flow in opposite directions across the lamellae, maximizing gas exchange efficiency
• Ventilation: Requires continuous unidirectional water flow
• Buccal Cavity: Fish open their mouths and lower the buccal cavity floor to draw water in, then raise the floor to increase pressure and force water over the gills
• Operculum: Acts as a valve and pump, regulating water flow

Ventilation and Gas Exchange in Insects

• Lack of Transport System: Oxygen must be transported directly to respiring tissues