Respiratory System

Why Do Cells Need Oxygen?

For cellular respiration to produce ATP (energy)

Two Major Respiratory Challenges

Obtaining enough O₂ and removing CO₂

Where Gas Exchange Occurs in Lungs

Alveoli (tiny air sacs surrounded by capillaries)

What Drives Gas Exchange?

Diffusion based on concentration (partial pressure) gradients

Gas Exchange in Lungs vs Tissues

Lungs: O₂ into blood, CO₂ out
Tissues: O₂ out to cells, CO₂ into blood

Fick’s Law – 3 Optimized Factors

Increase surface area, increase concentration gradient, decrease distance

Gas Exchange in Small/Unicellular Organisms

Gases diffuse directly

Gas Exchange in Fish

Occurs in gills; water flows over gills for diffusion

Trachea

Main airway (windpipe) leading to lungs

Bronchi

Large branches from trachea into each lung

Bronchioles

Smaller branches inside lungs

Alveoli

Tiny sacs where gas exchange occurs

Bird Unidirectional Air Flow (Step 1)

Inhale → air enters posterior air sacs

Bird Air Flow (Step 2)

Exhale → air moves into lungs

Bird Air Flow (Step 3)

Inhale → air moves to anterior air sacs

Bird Air Flow (Step 4)

Exhale → air exits body

How Air Enters Lungs

External intercostal muscles + diaphragm contract → increase volume → decrease pressure → air flows in

Inhalation (Volume & Pressure)

Volume increases, pressure decreases

Exhalation (Volume & Pressure)

Volume decreases, pressure increases

Tidal Volume

Normal air moved in/out during resting breathing

Vital Capacity

Maximum air exhaled after a deep inhale

Inspiratory Reserve Volume

Extra air that can be inhaled after normal inhale

Expiratory Reserve Volume

Extra air that can be exhaled after normal exhale

Residual Volume

Air remaining in lungs after full exhalation

Total Lung Capacity

Vital capacity + residual volume

How Oxygen Is Carried in Blood

Bound to hemoglobin in red blood cells

Factors Affecting Hemoglobin Affinity

pH and temperature

Effect of Low pH / High CO₂

Decreases hemoglobin affinity → releases O₂ to tissues

How CO₂ Is Transported

Mostly as bicarbonate (HCO₃⁻), some bound to hemoglobin, some dissolved in plasma

Obstructive Lung Diseases (Examples)

Asthma, emphysema, COPD

Sickle Cell Anemia Effect on Oxygen Binding

Worse (reduces effective oxygen transport)