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UT BIO 311D - Circulation and Gas Exchange (Part IV)
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Lecture 17 BIO 311D 1st EditionOutline of Last Lecture I. Blood ComponentsII. Partial Pressure Gradients in Gas ExchangeIII. Respiratory SurfacesIV. How other animals breatheV. LungsVI. Pathway of the Respiratory SystemVII. Control of Breathing in HumansOutline of Current Lecture I. HemoglobinII. Carbon Dioxide TransportIII. Respiratory AdaptationsIV. The Immune SystemVI. Barrier DefensesVII. Inflammatory ResponsesCurrent LectureHemoglobin• A single hemoglobin molecule can carry four molecules of O2, one molecule for each iron- containing heme group• Higher affinity for carbon dioxide and carbon monoxide• The hemoglobin dissociation curve shows that a small change in the partial pressure of oxygen can result in a large change in delivery of O2• CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called the Bohr shifCarbon Dioxide Transport• Hemoglobin also helps transport CO2 and assists in buffering the blood• CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin, or as bicarbonate ions (HCO3–)Fully oxygenated hemoglobin arriving in capillaries near active muscles, where PO2 is about 40 mm Hg, would likely unload ___ of its O2 at that pointA. 10%B. 30 %C. 50 %D. 70 %E. 90 %Respiratory Adaptations of Diving Mammals• Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats– For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour– For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours• These animals have a high blood to body volume ratio• Deep-diving air breathers stockpile O2 and deplete it slowly• Diving mammals can store oxygen in their muscles in myoglobin proteins• Diving mammals also conserve oxygen by– Changing their buoyancy to glide passively– Decreasing blood supply to muscles– Deriving ATP in muscles from fermentation once oxygen is depletedInnate immunity is presentA. Only in mammalsB. Only in vertebratesC. Only in animalsD. In eukaryotes but not in prokaryotesE. In all three domains of life, including eubacteria and AchaeaThe Immune System:• Innate immunity is present before any exposure to pathogens and is effective from the time of birth• It involves nonspecific responses to pathogens• Innate immunity consists of external barriers plus internal cellular and chemical defenses• Adaptive immunity, or acquired immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances• It involves a very specific response to pathogensIn innate immunity, recognition and response rely on traits common to groups of pathogens• Innate immunity is found in all animals and plants• In vertebrates, innate immunity is a first response to infections and also serves as the foundation of adaptive immunity• In insects, an exoskeleton made of chitin forms the first barrier to pathogens• The digestive system is protected by a chitin-based barrier and lysozyme, an enzyme that breaks down bacterial cell walls• Hemocytes circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria• Hemocytes also secrete antimicrobial peptides that disrupt the plasma membranes of fungi and bacteriaInnate Immunity of Invertebrates• The immune system recognizes bacteria and fungi by structures on their cell walls• An immune response varies with the class of pathogen encountered• The immune system of mammals is the best understood of the vertebrates• Innate defenses include barrier defenses, phagocytosis, antimicrobial peptides• Additional defenses are unique to vertebrates: natural killer cells, interferons, and the inflammatory responseBarrier Defenses• Barrier defenses include the skin and mucous membranes of the respiratory, urinary, andreproductive tracts• Mucus traps and allows for the removal of microbes• Many body fluids including saliva, mucus, and tears are hostile to many microbes• The low pH of skin and the digestive system prevents growth of many bacteria• Pathogens entering the mammalian body are subject to phagocytosis• Phagocytic cells recognize groups of pathogens by TLRs, Toll-like receptors• A white blood cell engulfs a microbe, then fuses with a lysosome to destroy the microbe• There are different types of phagocytic cells• Neutrophils engulf and destroy pathogens• Macrophages are found throughout the body• Dendritic cells stimulate development of adaptive immunity• Eosinophils discharge destructive enzymes• Cellular innate defenses in vertebrates also involve natural killer cells• These circulate through the body and detect abnormal cells• They release chemicals leading to cell death, inhibiting the spread of virally infected or cancerous cells• Many cellular innate defenses involve the lymphatic systemAntimicrobial Peptides and Proteins• Peptides and proteins function in innate defense by attacking pathogens or impeding their reproduction• Interferon proteins provide innate defense, interfering with viruses and helping activate macrophages• About 30 proteins make up the complement system, which causes lysis of invading cells and helps trigger inflammationInflammatory Responses• The inflammatory response, such as pain and swelling, is brought about by molecules released upon injury of infection• Mast cells, a type of connective tissue, release histamine, which triggers blood vessels to dilate and become more permeable• Activated macrophages and neutrophils release cytokines, signaling molecules that enhance the immune response• Pus, a fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues• Inflammation can be either local or systemic (throughout the body)• Fever is a systemic inflammatory response triggered by pyrogens released by macrophages and by toxins from pathogens• Septic shock is a life-threatening condition caused by an overwhelming inflammatory responseEvasion of Innate Immunity by Pathogens• Some pathogens avoid destruction by modifying their surface to prevent recognition or by resisting breakdown following phagocytosis• Tuberculosis (TB) is one such disease and kills more than a million people a


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