BIOB34 Module 5 - Respiration Lecture Slides PDF

Diversity of digestive systems Direct absorption sugars, amino acids, etc. Endocytosis (cellular phenomenon) larger food digested particles intracellularly...

Diversity of digestive systems Direct absorption sugars, amino acids, etc. Endocytosis (cellular phenomenon) larger food digested particles intracellularly © K. Welch – Do Not Distribute 1  Diversity of respiratory systems If small, diffusion is sufficient If larger, need for both conductive/diffusive and convective (bulk flow) steps © K. Welch - Do Not Distribute 2 Respiratory systems can interface with circulatory system Lungs or gills designed with lots of surface area for exchange Exchange is with a delivery fluid (blood) and circ. system © K. Welch - Do Not Distribute 3 Closed (e.g. Mammalian) circulatory system Lower pressure Thick, elastic walls Thoracic duct Higher pressure Thick, muscular, Stiffer walls Thinner, compliant walls © K. Welch - Do Not Distribute 4 Open (e.g. insect) circulatory system and tracheal system Hemolymph is pumped, but not just strictly through vessels In most insects, tracheal system is the main respiratory system © K. Welch - Do Not Distribute 5  Circulatory fluid Vertebrates Invertebrates RBCs – where resp. pigments are In many insects, doesn’t provide Also carry other nutrients, hormones, O2/CO2 delivery role etc. Tracheal system does (IF present) Resp. pigments in plasma E.g. some crustaceans, other arthropods, some worms Also carries other nutrients, hormones, etc. Contains hemocytes Role in immune response, like WBCs © K. Welch - Do Not Distribute 6  Circulatory fluid Vertebrates - fractionated Plasma Buffy coat RBCs © K. Welch - Do Not Distribute 7  Hemoglobin (Haemoglobin - Hb) ≈98.5 % of the O2 in blood is bound to hemoglobin Found inside red blood cells (RBCs) α - subunit ß - subunit H+ and CO2 bind heme group to certain amino acids O2 O2 O2 O2 O2 heme ß - subunit group oxyhemoglobin α - subunit deoxyhemoglobin © K. Welch - Do Not Distribute 8 O2 delivery via circulatory system (the typical vertebrate example) Convection Convection Mitochondria Myoglobin Hemoglobin © K. Welch - Do Not Distribute 9  Respiratory pigments P50 = Partial pressure at which pigment is 50% saturated Sigmoidal versus hyperbolic shape Cooperativity! What is the significance of differing P50 values? Hemoglobin Myoglobin © K. Welch - Do Not Distribute 10  Hemocyanin Respiratory pigment found in some Arthropods (Chelicerates) Does NOT contain a heme group Copper-containing Floats freely in the plasma Harvesting horseshoe crab blood to extract “coagulogen” (a marvelous protein that coagulates to trap bacteria) © K. Welch - Do Not Distribute 11  Hemocyanin Many monomer units bound together (into octamers, dodecamers, etc.) e.g. horseshoe cab What do you predict the shape of the hemocyanin-O2 binding curve is? © K. Welch - Do Not Distribute 12  Other respiratory pigments Hemerythrin/myohemerythrin Contains iron, but not a heme group Found in some marine inverts, single annelid worm genus Colorless when deoxygenated, pink-violet when oxygenated Chlorocruorin Found in plasma of many annelids (especially polychaete worms) Composed of multiple monomers Contains “abnormal” heme group Incidentally, some Nematodes and Arthropods have Hb floating in plasma (or even inside nerves or muscle fibers – kind of similar to role of myoglobin in us) © K. Welch - Do Not Distribute 13  Integrated effects on % O2 saturation Effectors of P50: e.g. Bohr shift → (the following lower affinity = ↑P50) ↑ Temp. ↑ levels (more binding of…) 2,3-DPG (e.g. mammals) ATP, GTP, (e.g. fishes) IP5 (birds) ↓ pH ↑ CO2 (carbamino-hemoglobin formation: HbCO2) © K. Welch - Do Not Distribute 14  Polycythemia Normal Anemia Partial pressure of oxygen (mmHg) In all 3 conditions the O2-hemoglobin saturation reaches 100% of its capacity but the total O2 content differs © K. Welch - Do Not Distribute 15 CO2 and pH (and H2O) are related: HCO3- + H+ Ratio at 1,000 1 20,000 slow fast pH 7.4 CO2 + H2O H2CO3 H+ + HCO3- Carbonic Bicarbonate Spontaneous or enzyme catalyzed acid ≈0 HCO3- H+ + CO32- Carbonate ion Note degree of change between arterial and venous blood Lots of HCO3- Buffers blood near pH = 7.4 © K. Welch - Do Not Distribute 16  The challenge of elevation Partial pressure of all gases (incl. O2 and CO2) are lower This has different effects on two diffusion gradients Relative [gas] partial pressure Elevation Lumen of lung Lung capillaries Diffusion gradient O2: High O2: Low O2: High in Low CO2: Low CO2: High CO2: High out High O2: Lower O2: Same O2: Lower in (change in…) CO2: Even lower CO2: Same CO2: Higher out © K. Welch - Do Not Distribute 17  Acclimatization to high elevation Behavioural response to lower PO2: Mammals in a hypoxic hyperventilation environment (high Called the “Hypoxic Ventilatory Response” elevation) (HVR) Hyperventilation (increased convective flow) enhances O2 AND CO2 exchange But it’s already easier to lose CO2 Lowering of CO2 levels in blood leads to slight increase in pH Now, remember Bohr effect Lower P50 for O2 encourages uptake by Hb at lungs, but discourages release at tissues © K. Welch - Do Not Distribute 18  Acclimatization to high elevation After a few days, there is increased Mammals in a hypoxic release of 2,3-DPG into circulation environment (high As shown several slides ago, this elevation) increases P50 (offsetting effects of pH change) Over similar/slightly longer time frame, body responds with increased EPO This encourages erythropoeisis © K. Welch - Do Not Distribute 19 Evolution of Fish and amphibians: mechanics of buccal oscillations ventilation (or ram ventilation in some fish) 1. Floor of the mouth is lowered; buccal cavity is expanded; air flows through the Glottis nares (nostrils) into the bottom of the mouth. 2. Glottis opens; air flows from the lungs across the top of the mouth and out of the nares. 3. Floor of the mouth is raised; buccal cavity is compressed; air is pumped into the lungs; the glottis closes. © K. Welch - Do Not Distribute 20 Evolution of Reptiles, birds, and mammals: Inspiration creates negative pressure in lungs because pleural space mechanics of (between ribs and lungs) cannot axial expand (fluid filled) musculoskeletal ventilation oscillations Quiet breathing – exhalation is passive (system elasticity) © K. Welch - Do Not Distribute 21  Quantification of ventilation Anatomical dead space: vol. of non-respiratory portion Physiological dead space: vol. not involved in gas transfer (incl. less perfused alveoli) © K. Welch - Do Not Distribute 22  Fick’s equation and mass diffusive flux The rate of mass diffusion (Q - e.g. in moles of dissolved gas) per unit time t is: Q D × A × ∆C = t x where D is the permeation (or diffusion) coefficient A is the cross-sectional area across which diffusion takes place ΔC is the concentration difference (C2 – C1) x is the distance over which diffusion takes place  Greater surface area enhances mass diffusion  Longer diff. distances retard mass diffusion So, it’s no surprise most resp. exchange systems feature lots of surface area and little distance between compartments (i.e. close assoc. of capillaries & alveolae) © K. Welch - Do Not Distribute 23  (Very) high elevation populations People of the Tibetan plateau © K. Welch - Do Not Distribute 24 Hypoxic Pulmonary Vasoconstriction (HPV) Arterioles feeding areas of lung that are hypoxic constrict, reducing blood flow to that area Normally, this helps match lung perfusion to pulmonary blood delivery Think of physiological dead space In hypobaric hypoxia at high elevation, all of pulmonary circulation gets constricted (lung uniformly hypoxic) This increased resistance to flow raises pressure, possibly leading to pulmonary edema Tibetans show blunted HPV response © K. Welch - Do Not Distribute 25  Adaptation to high elevation At high elevation Tibetans tend to show lower increase in hematocrit than lowlanders Is this counter-adaptive? Why not? © K. Welch - Do Not Distribute 26  Concurrent (model approximates mammals) vs. Countercurrent (e.g. fish) ↑ diffusion distance → ↓ diffusive flux © K. Welch - Do Not Distribute 27  Cross-current Resp. exchange surfaces – exchange in birds air capillaries in parabronchii Pulm. blood flow Large anatomical dead space Airsacs and ventilation pattern create large flow rate ACROSS resp. exchange surfaces (not tidal/bidirectional like mammal lungs) © K. Welch - Do Not Distribute 28 © K. Welch - Do Not Distribute 29  Curious cases: air breathing and Dr. Giulia S. Rossi NSERC & L’Oréal-UNESCO for Women in Science Postdoctoral Fellow amphibious fishes (now @ McMaster U) © K. Welch - Do Not Distribute 30 © K. Welch - Do Not Distribute 31 © K. Welch - Do Not Distribute 32