PHGY 209 Lecture Notes - Homeostasis, Phospholipid, Electrochemical Gradient
Document Summary
*milieu interieur (claude bernard): we have internal uniformity to deal with external changes. *homeostasis (walter canon): process used to actively maintain stable conditions necessary for survival. *homeostasis and milieu interieur are similar since they both need to exchange molecules (salts, nutrients, gases and wastes in and out the body and between cell layers) *capillary walls: regulates flow between isf and plasma. Kidney for urea disposal and ion retention. Gi tract: waste disposal and nutrient influx. Important to control flow of gases, co2 , o2, waste and lactic acid. Permeable to water, dissolved gases and uncharged small molecules. Less permeable to larger molecules and charged molecules. Total membrane thickness is 6 - 10 nm. Phospholipids in water organize this way naturally. Phospholipids are amphipathic: one charged end (polar/hydrophilic) and one uncharged end (nonpolar/hydrophobic) Half the weight of the cell membrane are phospholipids. Reduces packing of fatty acid tails and increases membrane fluidity at cool temperatures and rigidifies membrane at warm temperatures.
