Why do we need a respiratory system

• Need O2

  • Aerobic cellular respiration

  • Make ATP

• Need CO2 out

  • Waste products from the Krebs cycle

Gas Exchange

• O2 and CO2 exchange between environment and cells

  • Need moist membrane

  • Need high surface area

Optimizing Gas Exchange

• High surface area

  • Maximizing rate of gas exchange

  • CO2 and O2 move across cell membrane by diffusion

    • Rate of diffusion is proportional to surface area

• Moist Membranes

  • Moisture maintains cell membrane structure

  • Gases diffuse only dissolved in water

Evolution of Gas Exchange Structures

• Aquatic organisms

  • External system with lots of surface area exposed to aquatic environment

• Terrestrial

  • Moist internal respiratory tissues with lots of surface area

Counter Current Exchange System

• Water carrying gas flows in one direction, blood flows in the opposite direction

Gas Exchange on Land

• Advantages

  • Air has many advantages over water

    • Higher concentration of O2

    • O2 and CO2 diffuse much faster through air

      • Respiratory surfaces exposed to air do not have to be ventilates as thoroughly as gills

    • Air is much lighter than water and therefore much easier to pump

      • Expend less energy moving air in and out

• Disadvantages

  • Keeping large respiratory surface moist causes high water loss

    • Reduce water loss by keeping lungs internal

Terrestrial Adaptations

• Tracheae

  • Air tubes branching throughout the body

  • Gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system

Alveoli

• Gas exchange across thin epithelium of millions of alveoli

Negative Pressure Breathing

• Breathing due to changing pressures in lungs

  • Air flows from higher pressure to lower pressure

  • Pulling air instead of pushing it

Mechanics of Breathing

• Air enters nostrils

  • Filtered by hairs, warmed, and humidified

  • Sampled for odors

• Pharynx → glottis → larynx (vocal cords) → tracheae (windpipe) → bronchi → bronchioles → air sacs (alveoli)

• Epithelial lining covered by cilia and thin film of mucus

  • Mucus traps dust, pollen, and particulates

  • Beating cilia moves mucus upward to pharynx, where it is swallowed

Autonomic Breathing Control

• Medulla sets rhythm and pons moderates it

  • Coordinate respiratory, cardiovascular systems and metabolic demands

• Nerve sensors in walls of aorta and carotid arteries in the neck detect O2 and CO2 in blood

Medulla Monitors Blood

• Monitors CO2 level of blood

  • Measures pH of blood and cerebrospinal fluid bathing the brain

  • If pH decreases then increase depth and rate of breathing and excess CO2 is eliminated in exhaled air

Breathing and Homeostasis

• Homeostasis

  • Keeping the internal environment of the body balance

  • Need to balance O2 in and CO2 out

  • Need to balance energy production

• Exercise

  • Breathe faster

    • Need more ATP

    • Bring in more O2 and remove more CO2

• Disease

  • Poor lung and heart function

    • Breathe faster

      • Need to work harder to bring in O2 and remove CO2

Hemoglobin

• Why use a carrier molecule

  • O2 is not soluble enough in water for animal needs

    • Blood alone could not provide enough O2 to animal cells

    • Hemocyanin in incest

      • Copper

    • Hemoglobin in vertebrates

      • Iron

• Reversibly binds O2

  • Loading O2 at lungs or gills and unloading cells

Cooperatively in Hemoglobin

• Binding O2

  • Binding O2 to first subunit causes shape change to other subunits

    • Conformational change

  • Increasing attraction to O2

• Releasing O2

  • When first subunit release O2, causes shape change to other subunits

    • Conformational change

  • Lowers attraction to O2

O2 dissociation curve for hemoglobin

• Drop in pH lowers affinity of Hb for O2

• Active tissue lowers blood pH and induces Hb to release for O2

• Increase in temperature lowers affinity of Hb for O2

• Active muscle produces heat

Transporting CO2

• Dissolved in blood plasma as bicarbonate ion

Releasing CO2 from blood and lungs

• Lower CO2 pressure at lungs allow CO2 to diffuse out of blood into lungs

Adaptation for pregnancy

• Mother and fetus exchange O2 and CO2 across placenta tissue

Fetal Hemoglobin

• Fetal hemoglobin had greater attraction to O2 than hemoglobin

  • Low % O2 by time blood reaches placenta

  • Fetal hemoglobin must be able to bind O2 with greater attraction than maternal Hemoglobin