Gas Exchange

• 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

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