PSIO 201 EXAM 1.docx - 1 Define homeostasis and describe...

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1. Define homeostasis and describe the elements that comprise a feedback loop. Identify a representative example of a positive vs. a negative feedback loop:= Homeostasis: relative constancy of the internal environment Physiological Limits: Living systems exist within limits of heat, moisture, pressure, chemical composition, etc Viability: Threshold for keeping the body alive, you can't survive above it Steady State: Constant state maintained through time (homeostasis); energetically expensive (REQUIES energy), far away from equilibrium Equilibrium: Constant state achieved WITHOUT energy expenditure Negative feedback loops: most feedback systems in the body are negative. Original stimulus reversed. (Tries to get back to the set point/normal) o used for conditions that need frequent adjustment (body temperature, blood sugar levels, blood pressure, etc.) o Increased pressure in the aorta triggers mechanisms to lower blood pressure. o a rise in blood calcium levels causes the release of a hormone to lower blood calcium levels. o Increased blood sugar stimulates the release of a hormone from the pancreas that stimulates the liver to remove sugar from the blood. o A decrease in body temperature triggers a neural response that initiates physiological changes to increase body temperature. Positive feedback loop : original stimulus intensified; Changes from the normal point and amplifies it. o Blood clot formation: amplifies chemicals in the clot promote further clotting UNTIL it's sealed o Milk production: as long as baby is nursing. milk will be produced UNTIL babies done o Uterine contractions during childbirth: contractions UNTIL babies out/no more stimulus o Fever : virus/bacteria, body heats self to get rid of it UNTIL the enemy destroyed o a rise in estrogen during the menstrual cycle causes an increase in the number of progesterone receptors in the uterus. 2. Compare and contrast the integral and peripheral membrane proteins. Explain why the amphipathic structure of phospholipids and integral membrane proteins is important in establishing stable membrane structure. Integral proteins: extend into or completely across cell membranes and are amphipathic with hydrophobic portions ‘hiding’ among the phospholipid tails of the lipid bilayer; Act as carriers to move polar substances from one side of a membrane to the other Peripheral proteins : attached to either inner or outer surface of cell membrane and are easily removed from it, provides a framework for the plasma membrane Amphipathic molecule : has a polar ‘head group’ region & non-polar ‘tail’ region capable of spontaneous ‘self- assembly’ 3. Define Diffusion and Osmosis. Predict the direction of net osmotic water flow. Compare and contrast the concepts of Osmolarity and Tonicity.
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