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What is Gas Exchange?

What is Gas Exchange?. Gas exchange -> supplies oxygen for cellular respiration -> disposes of carbon d ioxide Gases diffuse down pressure gradients in the lungs and other organs b/c of differences in partial pressure . Ok… but what is Partial Pressure?

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What is Gas Exchange?

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  1. What is Gas Exchange? • Gas exchange-> supplies oxygen for cellular respiration -> disposes of carbon dioxide Gases diffuse down pressure gradients in the lungs and other organs b/c of differencesinpartial pressure. Ok… but what is Partial Pressure? • Partial pressure ->the pressure exerted by a particular gas in a mixture of gases • A gas diffuses from a region of higher partial pressure to a region of lower partial pressure • In the lungs and tissues -> O2 and CO2diffuse from areas of higher partial pressure to lower partial pressure

  2. Where does an organism’s O2 come from? • Respiratory Media • Animals can use air or water as a source of O2, or respiratory medium. • In a given volume, there is less O2 available in water than in air. • So… • Obtaining O2 from water requires greater efficiency than air breathing.

  3. What are respiratory surfaces? • Large, thin, moist tissue used for gas exchange • Gases diffuse across respiratory surfaces

  4. How do cnidarians perform gas exchange? • Cnidarians (i.e. jellies) -> gas exchange occurs in all cells -> no specific respiratory tissue

  5. What about annelids? • Gas exchange performed through the skin • Hemoglobin present in circulatory system

  6. Gills -> outfoldingsof the body that create a large surface area for gas exchange Coelom Gills Gills Tube foot Parapodium (functions as gill) (a) Marine worm (c) Sea star (b) Crayfish

  7. Ventilationmoves the respiratory medium(i.e. air or water) overthe respiratory surface. • Aquatic animals move through water or move water over their gills for ventilation. • Fish gills ->countercurrent exchange -> is when blood flows inopposite directionto water passing over gills -> blood always has less O2than the water moving over it

  8. How do fish gills work? Fluid flow through gill filament Oxygen-poor blood Anatomy of gills Oxygen-rich blood Gill arch Lamella Gill arch Gill filament organization Blood vessels Water flow Operculum Water flow between lamellae Blood flow through capillaries in lamella Countercurrent exchange PO2 (mm Hg) in water 150 120 90 60 30 Gill filaments Net diffusion of O2from water to blood 110 80 50 20 140 PO2 (mm Hg) in blood

  9. How do insects do gas exchange? • Tracheal system->tiny branching tubes that penetrate the body. • Tracheal tubes supply O2 directly to all body cells Also… • Respiratoryandcirculatory systemsare separate. • Larger insects must ventilate their tracheal system to meet O2demands, i.e. in flight

  10. Air sacs Tracheae = air tubes External opening: spiracles Tracheoles Mitochondria Muscle fiber Body cell Air sac Tracheole Trachea Air external openings spiracles Body wall 2.5 µm

  11. How do terrestrial vertebrates do gas exchange? • The circulatory system (open or closed) transports gases between the lungs and the rest of the body. • Lungs=infolding of body surface • Size and complexity of lungs increases with organism’s metabolic rate.

  12. How about mammals, specifically? • System of branching ducts/air tubes conveys air to the lungs. • Air inhaled through the nostrils --> pharynx --> larynx --> trachea --> bronchi --> bronchioles --> alveoli= site of gas exchange. • Alveoli-> sacs of thin epithelium wrapped in capillaries • Exhaled air passes over the vocal cordsto create sounds.

  13. Human Respiratory System Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Terminal bronchiole Nasal cavity Pharynx Larynx Alveoli (Esophagus) Left lung Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM Colorized SEM 50 µm 50 µm

  14. How does breathing ventilate the lungs? • Amphibians -> positive pressure breathing, ->forces air down the trachea. • Mammals -> negative pressure breathing, ->pulls air into the lungs by varying volume/air pressure. • Lung volume increases as the rib muscles and diaphragmcontract. • Tidal volume-> volume of air inhaled/breath • Maximumtidal volume -> vital capacity. • Residual volume-> volume of air that remains in the lungs after exhalation

  15. Negative pressure breathing: H --> L Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air inhaled Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) Volume increases Pressure decreases Air rushes in EXHALATION Diaphragm relaxes (moves up) Volume decreases Pressure increases Air rushes out

  16. How do birds breathe? • Eight-nine air sacsfunction as bellows that keep air flowing through the lungs. • Air passes through the lungs in one direction only. Also… • Every exhalation completely renews the air in the lungs.

  17. The Avian Respiratory System Air Air Anterior air sacs Trachea Posterior air sacs Lungs Lungs Air tubes (parabronchi) in lung 1 mm EXHALATION Air sacs empty; Lungs Fill INHALATION Air sacs fill

  18. How do humans control their breathing? • Breathing control-> two regions of the brain, medullaoblongata & pons • Medulla -> regulates the rate and depth of breathing in response to pH changes: CO2levels in the cerebrospinal fluid -> adjusts breathing rate and depth to match metabolic demands • Pons -> regulates the tempo

  19. Also… • Sensors in the aortaand carotid arteriesmonitorO2 and CO2 concentrations in the blood -> secondary control over breathing

  20. Automatic control of breathing Cerebrospinal fluid Pons Breathing control centers Medulla oblongata Carotid arteries Aorta Diaphragm Rib muscles

  21. How are gases transported in the circulatory system? • In many organisms, blood must transport large amounts of O2 and CO2 • Blood arriving in lungs -> low O2, high CO2 relative to air in alveoli • In the alveoli->O2 diffuses into the blood and CO2 diffuses into the air. • In tissue capillaries -> partial pressure gradients favor diffusion of O2 into the fluid around cells(interstitial fluid)and CO2 into the blood.

  22. Loading and unloading of respiratory gases Alveolus Alveolus PCO2 = 40 mm Hg PO2 = 100 mm Hg PO2 = 40 PCO2 = 46 PCO2 = 40 PO2 = 100 Circulatory system Circulatory system PO2 = 40 PO2 = 100 PCO2 = 40 PCO2 = 46 PO2 ≤ 40 mm Hg PCO2 ≥ 46 mm Hg Body tissue Body tissue (a) Oxygen (b) Carbon dioxide

  23. What are respiratory pigments? • Respiratory pigments->proteins that transport oxygen • Greatly increase the amount of oxygen blood can carry • Arthropods and many molluscs have hemocyanin-> copper = oxygen-bindingcomponent. • Most vertebrates and some invertebrates use hemoglobin-> iron = oxygen-binding component contained within erythrocytes.

  24. How does hemoglobin work? • 1 hemoglobin carries 4 O2 • Hemoglobin dissociation curve-> shows that a small change in the partial pressure of oxygen can result in a large change in delivery of O2 • Bohr Shift -> CO2produced during cellular respiration lowers blood pH and decreases the affinity ofhemoglobin forO2

  25. Hemoglobin  Chains Iron Heme  Chains

  26. 100 O2 unloaded to tissues at rest 80 O2 unloaded to tissues during exercise 60 O2 saturation of hemoglobin (%) Hemoglobin Dissociation Curves (37ºC) 40 20 0 0 20 40 60 80 100 Tissues during exercise Tissues at rest Lungs PO2 (mm Hg) (a) PO2 and hemoglobin dissociation at pH 7.4 100 pH 7.4 80 pH 7.2 Hemoglobin retains less O2 at lower pH (higher CO2 concentration) 60 O2 saturation of hemoglobin (%) 40 20 0 0 20 40 60 80 100 PO2 (mm Hg) (b) pH and hemoglobin dissociation

  27. How is carbon dioxide transported? • Hemoglobin -> helps transport CO2 -> assists in buffering • CO2diffuses into the blood&is transported either in blood plasma, bound to hemoglobin, or as bicarbonate ions (HCO3–.)

  28. Body tissue CO2 transport from tissues CO2 produced Interstitial fluid CO2 CO2 Capillary wall Plasma within capillary CO2 H2O Carbon dioxide transport in the blood Hemoglobin picks up CO2 and H+ Red blood cell H2CO3 Hb Carbonic acid HCO3– Bicarbonate H+ + HCO3– To lungs CO2 transport to lungs HCO3– HCO3– H+ + Hemoglobin releases CO2 and H+ Hb H2CO3 H2O CO2 CO2 CO2 CO2 Alveolar space in lung

  29. How has gas exchange evolved? • Evolutionary adaptations in gas exchange help animals do extraordinary things. • Pronghorn Antelope -> runs extremely fast for long distances b/c of increased O2 consumption • Deep-diving air breathers-> stockpile O2 and deplete it slowly. • Weddell seals-> high blood/ body volume ratio -> can store oxygen in their muscles in myoglobinproteins.

  30. Inhaled air Exhaled air Lungs - Alveolar Air Spaces GAS EXCHANGE Alveolar epithelial cells CO2 O2 Summary CO2 O2 Alveolar capillaries of lung Pulmonary veins Pulmonary arteries Systemic veins Systemic arteries Heart Systemic capillaries O2 CO2 O2 CO2 Body tissue - GAS EXCHANGE

  31. What is cystic fibrosis? • Genetic disease -> autosomal recessive • Faulty gene for a protein that pumps Na+ in lung cells • Causes mucous buildup in respiratory tract • Symptoms include: delayed growth, weight loss, fatigue, nausea, frequent pneumonia, coughing/sinus pressure due to mucous • Diagnosed through blood test or sweat chloride test • Currently no cure, average lifespan 37 years • Treated through specialized diet, frequent exercise, clearing mucous multiple times daily

  32. What is bronchitis? • Inflammation of the bronchi -> main air tubules to lungs • Can be acute, i.e. due to viral infection, or chronic • Symptoms include: cough, chest pain, shortness of breath, fatigue • Treatment -> acute goes away on its own in 1 week -> chronic doesn’t usually go away, but smoking cessation can help

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