Gas Exchange Chapter 22

The Air Up There Air is a fixed ratio of partial pressures (Px) Air thins with increasing altitude Gas in same ratio, but less of 3000 m 1/3 less O2 Sherpas, athletic training, and blood doping Mountain sickness

Revisiting Respiration Gas Exchange Breathing Organismal level O2 in CO2 out via diffusion Cellular level Use O2 to produce CO2 and ATP Cellular Respiration Exchange Application

Respiratory Surfaces Thin Diffusion distance Speed Moist Gases dissolved in solution Large SA to volume ratio Energy demands

Respiratory Mediums Water Air Pro Con Pro Con Direct contact of respiratory surface to medium Con Less O2 warm and salty even less O2 diffusion slower More energy to ventilate Larger structures Water supports weight Pro High concentration of O2 Less dense O2 diffusion faster Con Desiccation of respiratory surface Small openings externally Indirect contact of respiratory surface to medium

Gill Systems Aquatic organisms Convoluted extensions of body surface (pink) Ventilation varies between organisms Move respiratory medium across respiratory surfaces Inefficient on land Desiccation Tissue Mass Mollusks, annelids, arthropods, echinoderms, fish, and amphibians

Countercurrent Exchange Exchange between 2 oppositely flowing currents Maximizes O2 diffusion out of H2O Concentration gradient maintained entire length Compare to concurrent

‘Skin Breathers’ Earthworms and some amphibians Skin is respiratory surface Circulatory system to distribute (hemoglobin assists) Lower invertebrates without Moist environments

Tracheal System Insects Internal branched tube system Direct exchange Connect all cells to environment Prevents desiccation Direct exchange Open circulatory system Hemolymph = nutrients only Body movements assist

Lungs Branched internal sacs Pigmented, closed circulatory system Moist epithelium Pigmented, closed circulatory system Nutrient and gas transport Most terrestrial vertebrates Elaboration with movement to land Variations between classes Amphibians: positive, others negative

Lung Adaptation Amphibians Birds Mammals O2 via positive pressure into small sacs Skin also for exchange Birds 1 way flow increases efficiency 2 cycles to complete Mammals Negative pressure Incomplete removal Myoglobin content varies

Mammalian Respiratory System Upper respiratory system Nasal cavity Warms air Smells Pharynx Larynx Vocal cords tensed to create sound Lower respiratory system Trachea Cartilage rings Bronchi (2) Bronchioles Alveoli Diffusion with capillaries through interstial fluid

Respiratory Cycle Inhale Exhale Rib muscles (up) and diaphragm (down) contract Chest cavity increases Lowers air pressure in alveoli Rib muscles (down) and diaphragm (up) relax Chest cavity decreases Increases air pressure in alveoli

Respiratory Disruptions Smoking Inhibit cilia movement causes ‘smoker’s cough’ Thicken bronchioles and reduce elasticity Alveoli rupture Stopping allows cilia and alveoli damage to reverse Premature birth (37 weeks or less) Surfactant production incomplete Keeps alveoli from collapsing Each breath requires large effort Emphysema Bronchi swell, tearing alveoli Reduced SA for gas exchange Pneumonia Fluid in alveoli Bronchitis inflames of bronchioles

Respiratory Gas Transport Blood circulates to all cells Hemoglobin binds/carries Protein bound to a metal Carry 4 O2 molecules, some CO2 too PO2 and PCO2 vary within the circulatory system Blue and red vessels Lungs: high O2, low CO2 Body tissues: low O2, high CO2 Pressure gradient facilitates gas exchange in tissue capillaries (purple)

Control of Human Breathing Most is involuntary Control centers in brain Medulla: inhalation signaling Pons: smoothes out rhythm and depth Driven by [CO2] in blood Reactions CO2 + H2O H2CO3 (carbonic acid) H2CO3 H+ + HCO3 CO2 levels increase pH in blood/CSF lowered Respiratory centers signaled Carotid arteries and aorta monitor O2 also Severe deficit, i.e high altitude Increase rate and depth

Human Fetus Amniotic sac in uterus Placental role Lungs are fluid filled Placental role Blood exchange with mother Fetal hemoglobin Birth stops gas exchange pH drop, why? First breath