BIOL1108 UNIT 4 HOMEOSTASIS October 31 How are molecules exchanged between the different systems What common feature of animal tissues enhances this exchange of molecules Biological systems are primarily based on diffusion in which gases salts water etc all move from areas of high concentration to low concentrations by way of passive transport The diffusion of materials is facilitated by a high surface area to volume ratio SA V Homeostasis Values of variables fluctuate around the set point to establish a normal range of values Set point the ideal normal value of a variable What is the set point for body temperature A homeostatic system has three functional components A receptor thermometer A control center thermostat An effector heater Feedback loop The principle of a feedback loop is based on the fact that the outputs of a system can act as inputs for another system which in turn loops back to the original system Negative feedback loop The production of A yields the production of B but the production of B diminishes the amount of A Self monitoring Positive feedback loop The production of A yields the production of B which yields more production of A etc Will not stop unless something breaks it Population True whether a population is increasing or decreasing In animals the ideal outcome for a properly functioning homeostatic system is for the system to remain at or near the set point What are some homeostasis examples in animal systems Temperature glucose blood pressure pH water calcium oxygen toxin levels ITN10 What is the secret that enables the people of Tibet to survive at very high altitudes Just like the circulatory system plays the principal role in delivering the hormones of the endocrine system and the glucose models of the digestive system it is the carrier of gases of the respiratory system It does so not by having the gases directly dissolved in the fluid of the blood but rather carried on hemoglobin filled erythrocytes Hemoglobin bound to it The heme molecule changes shape depending on whether or not oxygen is There is iron at the center of each heme molecule which is how things like anemia are measured If an individual does not have enough iron they don t have enough hemoglobin and cannot get enough oxygen During their lifetime humans make two types of hemoglobin Adult hemoglobin two alpha subunits two beta subunits Fetal hemoglobin two alpha subunits two gamma subunits Fetal hemoglobin has a greater affinity for oxygen molecules than adult hemoglobin Why Stealing mom s oxygen The circulatory systems of both mother and fetus are separate but come in close contact with each other in the placenta the fetal blood must take oxygen nutrients and other needed components from the mother s blood At the time of birth a newborn s blood contains about 50 adult hemoglobin and 50 fetal hemoglobin By eight months of age it is nearly all adult hemoglobin Some individuals have an allele for the beta subunit of hemoglobin that codes for a Valine at position 6 instead of the normal Glutamate amino acid This one minor change results in a hemoglobin molecule that can clump together and in doing so change the shape of the erythrocytes Such individuals have a condition known as Sickle Cell Disease Capillaries get smaller and smaller as they go into certain tissues and erythrocytes normally can squeeze through these capillaries However sickle cells clump up in these capillaries and cause blockages Humans have relatively poor gas exchange compared to other mammals Birds have passive exchange So do dinosaurs Insects have special tissues that require a lot of oxygen They don t have lungs so oxygen must be dense for passive transport Higher concentrations of oxygen on the outside allow the gas to move into the body of the insect Gas exchange What about the people of Tibet Most of Tibet is in the very high or extreme altitude range What if we compare the physiology of the average American the average Tibetan and the average of another group of people that live at very high altitudes the Aymara people in the Andes The study measures the concentration of hemoglobin The hypothesis was that the Tibetans and the Aymarans had comparable amounts of hemoglobin but this was not the case Aymarans have higher concentrations of hemoglobin compared to Tibetans Women of Tibet give birth to babies that weigh more than babies born to Han Chinese women another example of being more equipped to give birth at high altitude When a woman is pregnant she will sometimes move to a lower elevation for the duration of her pregnancy to help with oxygen levels Han women cannot successfully give birth at elevations higher than 12 500 feet while Tibetan women can give birth at high altitudes Han women are also at a much greater risk for preeclampsia For those living at high altitudes Tibetans have more blood vessels than others In terms of mitochondrial volume both high altitude Tibetans and Andeans have less mitochondrial volume than those living at low altitudes Since oxygen is a limiting material having more ways for it to move through the body is very advantageous Since there is less oxygen they have adapted to do less cellular respiration to not use as much oxygen leading to less mitochondria A haplotype refers to a set of DNA variants along a single chromosome that tend to be inherited together They tend to be inherited together because they are close to each other on the chromosome and recombination between these variants is rare You can take these haplotypes and compare them to form a The Tibetans are profoundly different genetically than all other phylogenetic tree people on earth The closest relative is the Denisovans The Denisovans are a group of hominins that were contemporary with the Neanderthals that settled in eastern Asia This haplotype is only found in Denisovans and Tibetans surprisingly other groups have haplotypes that are the same as Denisovans The people of Melanesia The Inuit people of the north Evidence that the Denisovans successfully reproduced with Homo sapiens Endothelial PAS domain containing protein 1 EPAS1 A protein that in humans is encoded by the EPAS1 gene It is a type of hypoxia inducible factor a group of transcription factors involved in the body s response to oxygen levels The variant of the EPAS1 gene found in Tibetan people is unique among all races This allele may allow Tibetans to live in a reduced oxygen atmosphere with the same amount of hemoglobin as North Americans living at