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9 Cards in this Set
- Front
- Back
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Small Intestine transport |
Glucose has to crossthe epitehlia plasma membrane. Its transported by a Na/Glusoe symporter. Sodium conc. kept low so rather than establish a concentrationgradient, sodium is actively pumped out via the Na ATPase pump. To move intobloodstream, glucose moves across the plasma membrane via GLUT2. In order tomaintain osmolairty, as Sodium move into the cell, water moves with it via aquaporins
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Parietal Cells in the Stomach |
Parietal Cells which are found in thelining of the stomach. In the stomach, most of the food is digesting usingproteases. The acid in stomach arises because of active pumping of protons fromparietal cells into lumen of the stomach. This is done using H/K ATPase. Thecell would get more alkaline as OH are left behind. To balance the pH upset,CO2 can diffuse form blood into the cell where it reacts with OH to formbicarbonate using carbonic anhydrase. HCO is pumped out via CL-/HCO3 antiporterso Cl- enter. Cl- then leave the cell. |
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Nernst Equation |
I membrane isimpermeable the ions, and there is no net flow, then there is no netdifference. If membrane is permeable to Na, it will move down its concentrationgradient until it reaches equilibrium. This causes an increase of + inside ofthe cell. This creates an electrostatic repulsion of more Na fromentering. This is recognize in theNernst equation. The membrane is now only permeable to K. K moves towardestablishing an equal concentration on either side. This is effected by theelectrostatic repulsion which is also created. The polaritites switch frombefore bevcause charge is no outside of the cell.
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establishing eletropotential across cells |
SO K establishes the electro potentialdifference across most cells. This is mediated by resting potassium channel. Inorder for K to flow, the K must have a gradient which is established by Na/KATPase. The movement of Na allows K to flow to establish the electrostaticdifference.
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Resting Potassium Channel |
Only allows K to flow through. This is dueto conformation and pore of channel (vestibule). K and Na are hydrate inwater, where O atom can coordinate with each of the ions. When ions movethrough channel, the water molecules are replaced by carbonyl oxygen's (sidechains of residues present in vestibule). The K channel is structured so thatonly K can be coordinated by 4 carbonyl oxygen and not Na, so this is how K isselectively able to pass through, but not Na. |
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Generation and Propagation of ActionPotentials |
Nerve cells exist in a steady states, wherevoltage across membrane is established by resting K channels (-60mV netinside). On the inside because K flows out, the amount of positive charge isless on the inside than on the outside. To establish an electrical signal down anerve, the resting potential is disrupted, by events allowing influx of ionsinto cell and change the voltage across membrane. This establishes electricalcurrent which moves down nerve cell. Depolymerisations denotes that the polarity of electro potentialdifference changes from -60 to +59. There must be an influx of positive chargefrom outside to the inside. It only stays like this for a while and negative isrestored. This happens in the body along neurons andin the brain. |
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Motor Neurons andAction Potentials
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At axon termini, there are voltage gated ion channels which can sense the voltage across the membrane. The channels senses depolaristaionand Na floods in. Membrane potential aprroaches +60mv. The resting potential is re established by voltage gated K+ channel. |
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How does channel work? |
Depolarization is sensedby nearby channels which have a charged residue. The depol. induces a movementof residues through change in electrostatic environment. The alpha helices as aresult move which triggers opening of channel through which Na can flow. Following this is themovement of blob to plug pore. This is an intrinsic mechanism to allow tempopening of channel. Eventually thechannel returns to ground state where it can be opened again after a lag. the lag ensures that propagation of the signal is unidirectional and that channels only open at one end. |
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Muscle Contraction |
1. Nerve impulse converted to chemical signal 2. Neurotransmitter released into synapse 3. NT binds to surface on receptor cells allowing Na channels to open. 4. Signal is converted to intracellular effector- Calcium. As it uses T-Tubule to move out from ER. |
