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100 Cards in this Set
- Front
- Back
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Physiology
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The study of the normal functioning of a living organism and its component parts.
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Name organ systems that are continuous with the external environment.
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Respiratory, urinary, reproductive, digestive
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Homeostasis
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The ability of the body to maintain a relatively constant internal environment.
A self-regulatory process The body controls homeostasis using negative feedback |
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Homeostasis Fluctuation
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Blood pH: 7.38 - 7.42
Blood Glucose: 4-6 mmol/L before a meal |
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Negative Feedback
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A homeostatic feedback loop designed to keep your body at or near a set point. A change in a controlled variable triggers a response that drives the variable. Once the variable is back at the set point, the response loop shuts off.
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Negative Feedback Picture
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o
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Control Center
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Compares set point to value given by sensory
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Effector
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Performs an action that changes a controlled variable
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Total Body Water for a 70 KG Man
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TBW = 42 L
Intracellular Fluid = 28L Extracellular Fluid = 14L Interstitial = 11L Plasma = 3L |
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Salty Banana
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There is a lot of Na+ and Cl- outside the cell
There is a lot of K+ inside the cell |
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Smooth ER
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Fatty acid lipid synthesis
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Centrioles
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Directs DNA during cell division
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Golgi Apparatus
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Modifies and packages proteins
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Rough ER
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Protein synthesis
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Cytoskeleton
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Provides support and enables mobility
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Mitochondria
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Makes ATP
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Lysosome
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Digests bacteria and old organelles
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Nucleus
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Contains DNA
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Function of the Cell Membrane
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Compositions of interstitial fluid and plasma are the same
Compositions of intracellular fluid and extracellular fluid are different This is because the intracellular fluid is separated from the interstitial fluid by a cell membrane which is selectively permeable. |
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Fatty Acid Chains: Block and pass
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Hydrophobic
Blocks water and water-soluble substances such as ions, glucose, urea, etc. Passes fat soluble substances such as oxygen, alcohol and steroid hormones |
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Phosphate Head
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Polor and hydrophilic
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Fatty Acid Chains
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Non-polar and hydrophobic
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Label the Cell Membrane
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o
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Neurotransmitters
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A chemical signal released by a neuron onto a target cell
Affects only cells with receptors for the chemical |
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Hormones
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Produced by an endocrine cell
A chemical signal secreted into the blood stream Affects only cell with receptors for the chemical |
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Neurohormones
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A chemical signal made by a neuron and secreted into the blood stream
Only affects cells with receptors for the chemical |
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How do cells that are no of endocrine or nervous origin communicate?
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Chemical mediated cell to cell communication
Contact dependent signals Gap junctions |
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Autocrine
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The signal that acts on the cell that made it
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Paracrine
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The signal that acts on neighboring cells
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Cytokine
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A chemical signal made by any type of cell in response to a stimulis
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Contact Dependent Signals
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Surface molecules on one cell membrane bind to a membrane protein of another cell
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Gap Junctions
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Protein channels that make cytoplasmic bridges between adjacent cells
Can directly transfer chemical and electrical signals Made of proteins called connexins |
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The Four Functions of Membrane Proteins
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Ion channels
Enzymes Receptors Membrane carriers |
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How Do Molecules Get Across the Plasma Membrane?
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Endocytosis/exocytosis/pinocytosis
Diffusion through a lipid bilayer (fat soluble molecules) Diffusion through protein channels (water-soluble molecules) Facilitated diffusion Active transport |
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Simple Diffusion
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The movement of molecules from an area of higher concentration to an area of lower concentration due to a molecules random thermal motion
No energy required At equilibrium, concentrations are equal but molecules are moving with no net movement |
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Diffusion of Fat-Soluble Molecules Through the Lipid Bilayer
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Must be lipid soluble
AFFECTED BY: 1. Concentration Gradient: larger = faster 2. Surface Area of Membrane: larger = faster 3. Size of Molecule: smaller = faster 4. Membrane Thickness: thinner = faster 5. Lipid Solubility of a Molecule: more lipid soluble = faster |
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What does lipid soluble mean?
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Non polar and hydrophobic
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Diffusion of Water Soluble Molecules Through Protein Channels
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Ions and water soluble molecules cannot diffuse directly through membrane due to hydrophobic core
Can be selected due to charge/size AFFECTED BY: 1. Concentration Gradient: Larger = faster 2. Molecule size 3. Charge of molecule 4. Number of Protein Channels: more channels = faster |
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Facilitated Diffusion
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AFFECTED BY:
1. Concentration gradient 2. Chemical specificity 3. Competitive inhibition 4. Limited transport capacity |
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Active Transport
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Moves substances against the concentration gradient
Chemical specificity Completely inhibited Carrier mediated transport Limited transport capacity |
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Active Transport Steps
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3 Na+ from ICF bind to transporter
ATP -> ADP + Pi bind to transporter Transporter changes conformation Na+ released into ECF 2 K+ bind from ECF Transporter changes conformation 2 K+ released into ICF |
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Define osmosis
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The net movement of water down a concentration gradient
Water moves to dilute the more concentrated solution |
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What are the three factors that affect osmosis across a cell membrane?
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1. Permeability of the membrane
2. Concentration gradient of solutes 3. Pressure gradient across the cell membrane |
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Osmotic Pressure
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Pressure applied to exactly oppose the osmotic movement of water
Measured in mm Hg Note: Since the amount of osmotic pressure is proportional to the concentration of the solute in numbers of molecules, expressing the solute concentration in terms of mass is of no value in determining osmotic pressure The unit used to express the number of particles is an osmole If a substance dissociates in a solution, the number of osmoles generated from one mole of substance is increased Example: One mole of NaCl would dissociated into Na+ and Cl-, thus generating two osmoles |
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Osmolarity
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The number of particles per litre of solution
Osmol/L Concerned with only the number of particles in solution, NOT size or composition |
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What two factors must we know in order to calculate osmolarity?
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1. The number of moles of substance in solution
2. Whether the substance dissociates in solution |
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Resting Membrane Potential
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The unequal distribution of a few key ions across biological membranes
Since many of the ions contained in the ECF and the ICF are electrolytic , the uneven distribution of these ions results in an electric potential difference across the membrane |
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Draw a cell and indicate where the Na+, K+ and Cl- ions are high and low.
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woot
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Describe the RMP
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A small amount of anions accumulate inside the cell membrane
An equal number of cations accumulate outside the cell membrane This establishes an electrical potential difference across the membrane with the inside negative in respect to the outside This potential difference across the plasma membrane is present in even resting cells |
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What is tonicity?
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The ability of a solution to cause osmosis across biological cell membranes
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What is the osmolarity of body fluids?
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300 mosmoles per kg of solution
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Isotonic
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Same osmolarity as body fluids
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Hypotonic
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Lower osmolarity than body fluids
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Hypertonic
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Higher osmolarity than body fluids
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Chemical Gradient
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Molecules move from areas where they are high in concentration to areas where they are low in concentration
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Electrical Gradient
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Electrically charged molecules (ions) tend to move towards areas of opposite charge
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What happens if the electrical and chemical gradients are in opposite direction?
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The ion will move down is electrochemical gradient until and electrochemical equilibrium is reached
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List the functions of the sodium/potassium pump
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1. Moves sodium out of the cell
2. Moves potassium into the cell Overall: maintains concentration gradients |
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Excitable Cells
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Generate and respond to electrical signals
Includes neurons and muscle cells (cardiac, smooth, skeletal) |
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How do neurons communicate?
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Neurons used electrical signals in the form of action potentials to communicate
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What is the resting membrane potential of a neuron?
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-70mV
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Gated channels
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Control the ion permeability of the neuron
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Mechanically Gated Ion Channels
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Open in response to mechanical stimulus
Example: change in pressure |
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Chemically Gated Ion Channels
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Open in response to a chemical/ligand binding
Example: acetlycholine binding |
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Voltage Gated Ion Channels
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Open in response to a change in voltage of the cell
Example: -70mV to -55 mV |
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Input Zone
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soma/dendrites
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Conducting Zone
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Axon
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Output Zone
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Axon terminal
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Trigger Zone
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Axon hillock
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Graded Potentials
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Occur in the soma or dendrites of a neuron
Depolarizations or hyper-polarizations caused by opening voltage-gated channels Travel only a short distance and the signal loses strength due to current leak and cytoplasmic resistance |
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Why are graded potentials "graded"?
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The amplitude of potential is directly proportional t the stimulus strength
Large stimulus = large potential |
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Action Potential: How is the axon hillock acting like a trigger zone?
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At the axon hillock, if the depolarizing stimulus reaches threshold (-55mV), an action potential will be triggered and shot down the axon
*different from graded potentials |
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The three important things about action potentials
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All or none, unidirectional, amplitude and duration
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All or None
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If a graded potential of -55mV is reached an action potential will fire
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Unidirectional
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Action potentials always flow from the axon hillock to the axon terminals
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Amplitude & Duration
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Always the same amount of depolarization and the same duration
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Axon Potential and Membrane Permeability - sodium
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During the resting state, the permeability of the membrane for potassium is 25 - 100 times greater than that for sodium, due to the greater leakage of potassium ions through the "leak" channels
An action potential triggers the voltage dependent sodium channels to open and increase the membrane permeability for sodium 500 times The sodium gates are then inactivated within a fraction of a millisecond and the sodium permeability goes back to normal. |
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Axon Potential and Membrane Permeability - potassium
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An action potential also causes the voltage dependent potassium gates to open but at a slower rate
Potassium conductance does not reach as high as sodium Potassium gates are slower to close, which returns the membrane potential to normal resting levels AND causes the slight hyper-polarization which follows the action potential |
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Depolarization
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The cell becomes more positive
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Repolarization
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Depolarized membrane (+30mV) returns to resting membrane potential
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Threshold
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-55mV will trigger an action potential in the
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How many ions move through the membrane during one action potential?
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Relatively few
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Define the absolute refractory period
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When no action potentials can be fired due to the sodium inactivation gate being closed
No matter how great the stimulis no action potential will be fired Sodium channels remain closed until the membrane hyperpolarizes |
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What mechanism returns the membrane potential from +35mV to the resting level of -70?
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The loss of potassium through potassium channels.
It is not the sodium/potassium pump. |
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Would it be possible to generate a single action potential immediately after adding a chemical that blocked the sodium/potassium pump?
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Yes... approx 1000 action potentials could be generated because the sodium potassium pump is not directly involved in action potential conduction.
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Describe the mechanism behind voltage dependent sodium and potassium channels
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Exist in plasma membranes
The walls of the channel contain oxygen atoms and the dehydrated sodium and potassium can bind to the oxygen Oxygen configuration determines if potassium or sodium will bind to it. |
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Describe action potential movement
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When there is an action potential the inside of the membrane is positive in respect to the outside
This causes negativity outside of the membrane which draws off positive charges in front and behind the action potential There is current flow from the movement of ions on the inside of the membrane from the region of the action potential towards adjacent regions of the membrane Result = depolarization of the membrane ahead and behind the action potential. |
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List the five steps of action potential propogation
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1. Graded potential reaches axon hillock
2. Sodium voltage gated channels open 3. Positive charge flows into the adjacent parts due to current flow 4. Current flow causes new section to depolarize 5. Unidirectional due to refractory period. Sodium leaves. |
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What happens when a section of the axon depolarizes?
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Positive charges move by current flow into adjacent sections of cytoplasm
On the extracellular region, current flows towards the DEPOLARIZED region |
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What are the factors that affect the speed of an action potential down an axon?
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1. The diameter of the axon: larger diameter leads to faster conduction
2. The resistance of the axon membrane to ion leakage: increased ion leakage = slow action potential |
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What prevents ion leakage?
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Myelin
Multiple layers of cell membrane that wrap around and insulate axons Conduction is faster with myelin so axons can have a smaller diameter |
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Saltatory Conduction
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The leap-frogging of the action potential down myelinated axons from node to node
Does not involve membrane permeability changes along the membrane - only at the nodes |
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What is an advantage of saltatory conduction?
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Smaller axon diameters
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Where does information pass from cell to cell?
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The chemical synapse made up of an axon terminal of the pre-synaptic cell and the plasma membrane of the post-synaptic cell
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List the steps of a chemical synapse
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1.The depolarizing stimulis arrives at the axon terminal
2. Voltage gated calcium channels open and Ca2+ enters the cell 3. Ca2+ causes docking of vesicles with neurotransmitter to membrane 4. Neurotransmitter diffuses into synapse and binds to receptors on post-synaptic cell 5. Response in post-synaptic cell |
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List the ways a neurotransmitter is removed from the synaptic cleft
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1. Returned to axon terminals
2. Enzymes in the synapse inactivate neurotransmitters 3. Neurotransmitters diffuse out of the synaptic cleft |
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Neurotransmitters in the post-synaptic cell
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Induce a rapid response in the post-synaptic cell by opening ion channels
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Neuromodulators
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Slower acting
Act by causing the post-synaptic cell to produce new proteins |
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Depolarization of excitatory post synaptic potential
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More Na+ in
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Hyperpolarization of inhibitory post synaptic potential
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More K+ out or more Cl- in
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