VIEWS: 63 PAGES: 4 POSTED ON: 12/3/2011
BIO338: Mammalian Physiology L32: High Altitude Adapation UNC-Asheville, s2011 High Altitude Physiology and Adaptation ENVIRONMENTAL PHYSIOLOGY Stressors Vary in duration and intensity Severe Acute Chronic Mild Village of Kibber, India (~15,000 ft) Short-term Physiological Responses to Stressors HIGH ALTITUDE Stressors Habituation • stress w/in tolerable limits, lose response to same stimulus Short-term physiological adjustments • quick responses (local, neural, endocrine) • response stops when stress removed or homeostasis achieved • Lower total atmospheric pressure Acclimatization • Cold • long-term changes, including alteration of phenotype • Intense UV radiation • involves gene induction (hormone-mediated; bio-mechanical) • Difficult terrain • reversible; goes away once stress removed (time varies) • Limited vegetation Phenotypic Plasticity • long-term morphological and/or physiological changes • usually response to stresses during development • permanent – not lost when stress removed Genetic Adaptation • heritable genetic changes in a population (natural selection) • present regardless of stress or environment Life-long Effect of Altitude on Atmospheric Gas Concentrations 30,000 ft P = 226 PO2 = 47 O2 Sat = 20% Highest elevation reached without extra O2 (natives) Death in unacclimated humans 20,000 P = 349 PO2 = 73 O2 Sat = 70% Highest Human Villages (unconsciousness in unacclimated humans) (highest Andean Villages) (highest Himalayan Villages) 10,000 Colorado ski resorts P = 523 PO2 = 110 O2 Sat = 90% (Rocky Mtn ski resorts) Mt. Mitchell (Mt. Mitchell) Asheville (Asheville) Sea Level P = 760 PO2 = 158 O2 Sat = 98% 1 BIO338: Mammalian Physiology L32: High Altitude Adapation UNC-Asheville, s2011 Effect of Altitude on Alevolar Gas Concentrations At high altitude, further relative decrease in % O2, N2 (1) PH2O water is constant (body temp) Ptotal PN2 PO2 PCO2 PH2O (2) CO2 is being constantly produced sea level 760 596 104 40 47 800 (75%) (14%) (5%) (6%) 700 PN2 20,000 ft 349 238 40 24 47 (68%) (11%) (7%) (14%) 600 PH20 PCO2 500 PO2 Less air (Ptotal) at high altitudes. 400 CO2 constantly produced by metabolism, stays high. 300 Colder air holds less water (clouds). 200 PH20 in alveoli depends on body temp, which is constant. 100 0 Sea Level 20,000 50,000 “Acute Mountain Sickness” Initial physiological responses to high altitude (short-term adjustments) • Headache; Malaise; Disturbed sleep • Loss of appetite; Nausea, vomiting Individual new to high altitude • Cyanosis • Peripheral edema Primary Stressor? • Pulmonary edema (HAPE) • Hypoxia: low oxygen deliver to cells • Cerebral edema (HACE) (due to low alveolar PO2) Detected through chemoreceptors (carotid body) Physiological adjustments? • increase ventilation (breathing rate & depth) • increase heart rate Hyperventilation Cycle ↑HR and ↑BP needed to provide constant O2 to brain (and other tissues) hypoxia chemoreceptor reflex Can lead to pulmonary edema and cerebral edema ↑PCO2, ↓ pH ↑ ventilation and heart rate Inhibits respiratory centers ↑blood PO2, but ↓PCO2 and heart rate = Higher pH (dizzy phase) Respiratory Alkalosis High alkalinity (pH) prevents sustained hyperventilation. ∴ changing breathing patterns is not sufficient to meet O2 demands. 2 BIO338: Mammalian Physiology L32: High Altitude Adapation UNC-Asheville, s2011 Acclimatization to high altitude Acclimatization to high altitude Phenotypic and biochemical responses ↑ 2,3 BPG (bisphosphoglycerate) Gene induction Produced in RBCs to ↑ O2 delivery has higher affinity for deoxygenated Hb; helps unload O2 to tissues [shifts dissociation curve right] Acclimatization to high altitude Aerobic athletes often train at high elevation to take • ↑ RBC, Hb production (↑ hematocrit) advantage of acclimatization responses. able to carry more O2 • Capillary growth (capillarization) • ↑ myoglobin synthesis in muscle • heart will enlarge; ↑ lung capacity All reversible – effects will be lost within a few weeks after returning to low altitude Genetic Adaptations to high altitude Genetic Adaptations to high altitude Very difficult to sort from acclimatization Acclimatization • Heritability studies Developmental Acclimatization • Comparative studies (phenotypic plasticity) Natural Selection 3 populations that have lived at high altitude (genetic adaptation) Andes Himalayas Genetic Drift Ethiopian highlands 3 BIO338: Mammalian Physiology L32: High Altitude Adapation UNC-Asheville, s2011 Genetic Adaptations to high altitude: Genetic Adaptations to high altitude: Quechua (Andes) Tibetans (Himalaya) Higher blood [Hb] = ↑ O2 saturation • worse O2-saturation; normal Hb Higher birth weight: • Larger lung capacity, larger hearts ↑O2 delivery to placenta, ↑ placenta size (barrel chest) • lower pulmonary BP “hematological adaptations” better blood flow (NO release) Higher birth weight ↑ Blood flow to placenta “respiratory adaptations” Ethiopian Highlanders HIGH ALTITUDE Adaptations ??? llama [neither respiratory or hematological adaptations human have been documented] Other mammals Llama – Hb has higher affinity for O2 than other mammals Also large blood volume; lungs Fetal circulation Fetal Hemoglobin No working lungs; gets O2 from placenta Pulmonary circuit by-passed: • ductus arteriosus (arteries) • foramen ovale (L-R atria) Placenta is part of systemic circuit for both mom and fetus 4
"High Altitude Physiology and Adaptation"