Gas exchange

Key concepts Gas exchange occurs across specialized respiratory surfaces Gills in aquatic animals Tracheal systems in insects Lungs Breathing ventilates the lungs Amphibian breathing Bird breathing Control of breathing in humans Respiratory pigments bind and transport gases Diffusion and partial pressure Respiratory pigments O2 and CO2 transport

Vocabulary words ventilation lungs vocal cords bronchioles diaphragm respiratory surface tracheal system larynx bronchi (bronchus) breathing vital capacity partial pressure dissociation curve for hemoglobin ventilation lungs vocal cords bronchioles diaphragm residual volume respiratory pigments Bohr shift countercurrent exchange gills trachea alveoli (alveolus) tidal volume breathing control centers hemoglobin carbon dioxide transport

Respiratory surfaces and gas exchange Gas exchange – uptake of O2 from environment and discharge of CO2 Mitochondria need O2 to produce more ATP, CO2 is the by-product C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP Diffusion rate α SA  large α 1/d2  thin Moist so gases are dissolved first DIFFUSION

Respiratory surfaces and gas exchange Size of organism Habitat Metabolic demands Unicellular organisms Entire surface area for diffusion Simple invertebrates Sponges, cnidarians, flatworms diffusion

Respiratory surfaces and gas exchange More complex animals Thin, moist epithelium Separates medium from capillaries Entire outer skin  small, long, thin organisms Specialized respiratory organs that are extensively folded and branched

Gills in aquatic animals Outfoldings of the body surface suspended in water Sea stars Segmented worms or polychaetes Molluscs and crustaceans Fishes Young amphibians Total surface area is greater than the rest of the body

Water as a respiratory medium Just keep swimming swimming swimming! Surfaces are kept moist O2 concentrations in water are low Ventilation – increasing flow of respiratory medium over the surface Countercurrent exchange – process in which two fluids flow in opposite directions, maximizing transfer rates Why are gills impractical for land animals?

Air as a respiratory medium Air has a higher concentration of O2 O2 and CO2 diffuse much faster in the air  less ventilation Difficulty of keeping surface moist Solution: respiratory infolding inside the body Tracheal system of insects – network of tubes that bring O2 to every cell Spiracles

Lungs Heavy vascularized invaginations of the body surface restricted to one location Found in spiders, terrestrial snails, vertebrates Amphibians supplement lung breathing with skin Turtles supplement lung breathing with moist surfaces in mouth and anus

Mammalian respiration

Lung ventilation through breathing Positive pressure breathing in frogs “Gulping in” air Negative pressure breathing in reptiles and mammals Rib muscles and diaphragm change lung volume and pressure

Lung volumes Factors Tidal volume Vital capacity Sex Height Volume of air inhaled and exhaled with each breath Vital capacity Maximum volume inhaled and exhaled during forced breathing Residual volume Air left in alveoli after forced exhalation Factors Sex Height Smoking Physical activity Altitude

Avian breathing Air sacs act as bellows to keep air flowing through the lungs.

Control centers in the brain regulate breathing

Gases diffuse down pressure gradients concentration and pressure drives the movement of gases into and out of blood

Respiratory pigments O2 transport Low solubility of O2 in H2O Respiratory pigments are proteins with metal atoms Hemoglobin – Fe Hemocyanin – Cu Allow reversible binding of O2 Drop in pH results in a lowered affinity of hemoglobin for O2

Respiratory pigments CO2 transport 7% in plasma 23% bound to hemoglobin 70% as HCO3- buffer Respiratory pigments

Fetal hemoglobin HbF has greater affinity to O2 than Hb low O2% by time blood reaches placenta fetal Hb must be able to bind O2 with greater attraction than maternal Hb

Deep-diving mammals Seals, whales, dolphins are capable of long underwater dives Weddell seal  5% O2 in lungs, 70% in blood Huge spleen stores huge volumes of blood Large concentrations of myoglobin in muscles Heart rate and O2 consumption rate decrease Blood is redirected from muscles to brain spinal cord and eyes