B3.1 Gas Exchange

Gas Exchange

Absorption of one gas and release of another gas

Properties of gas exchange surfaces

Permeable, large surface area-to-volume ratio, moist, and thin

Ventilation

Air exchange in and out of lungs

What occurs during Inspiration?

• The diaphragm contracts and moves downward

• External intercostal muscles contract → pull ribs up and away from the spine

• increasing the volume in the thorax

• decreased pressure in thorax

What occurs during Expiration?

• Diaphragm relaxes and moves upwards

• Posterior intercostal muscles contract

• Anterior abdominal wall contracts

• volume in thorax decreases

• increased pressure in thorax

Role of concentration gradients in ventilation

Concentration gradients facilitate the movement of oxygen and carbon dioxide between the alveoli and blood, allowing for efficient gas exchange.

Adaptations of the lungs for gas exchange

• All the alveoli combined give the lungs a big surface area

• alveoli and capillary walls are thin

• cells in alveoli secrete surfactant → reduce surface tension and prevent collapse

Direction of CO2 diffusion in ventilation

CO2 moves from blood to air in alveoli

Waxy cuticle

waterproof layer that varies in thickness with low permeability to gases

Epidermis

secretes wax layer that covers the outside of the leaf

Guard cells

Open and close stomata

Palisade mesophyll

Maximize light absorption for photosynthesis

Spongy mesophyll

Network of air spaces that allows CO2 and oxygen to diffuse

Veins

Contain xylem vessels that transport water

Transpiration

Loss of water as vapor from stomata of leaves

Structure of hemoglobin

Hemoglobin has 4 subunits, each with a binding site for oxygen

How does hemoglobin’s affinity for oxygen vary

Depends on the state of hemoglobin

• 1 oxygen molecule at 1 subunit → conformational change → increased affinity for oxygen

R state and T state

R state: Fully saturated

T state: No oxygens bound

Difference between fetal and adult hemoglobin

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin

Effect of carbon dioxide on hemoglobin affinity for oxygen

Increased CO2 concentration reduces hemoglobin’s affinity for oxygen, promoting oxygen release via allosteric binding and lowering blood pH

Bohr effect

Reduction in affinity for oxygen

Partial pressure

Pressure exerted from an individual gas

Type 1 pneumocytes

Carry out gas exchange

Type 2 pneumocytes

Secrete surfactant, which reduces surface tension in the lungs