Cellular Physiology (Chapters 1, 2, 4, 25, & 31) Flashcards
What is homeostasis?
maintenance of nearly constant conditions in the internal environment
What are examples of homeostasis?
Lungs provide oxygen to the extracellular fluid to replenish oxygen used by cells
Kidneys maintain constant ion concentration
What is a state of disrupted homeostasis?
Body still tries to regulate function in disease state which can make it difficult to distinguish between primary cause of disease and compensatory response
What is an example of disturbed homeostasis?
Impaired ability of kidney to excrete salt and water may lead to high blood pressure which initially is compensatory to return blood pressure to normal but can in turn cause many other problems instead
How do control systems of the body work?
Many control systems operate within the organs to control functions of individual parts of the organs whereas others operate throughout the entire body to control the interrelations between organs
What is an example of control system of the body?
Oxygen-buffering function of hemoglobin: hemoglobin combines with O2 as the blood passes through the lungs and then as blood passes through the capillaries hemoglobin (due to strong affinity for O2) does not release O2 if there is already enough there – only releases it if it needs to
If a higher than normal concentration of CO2 is in the blood this excites the respiratory center causing a person to breath rapidly and deeply (negative control)
What is negative feedback?
If some factor becomes excessive or deficient, a control system initiates negative feedback, a series of changes that return the factor toward a certain mean value, thus maintaining homeostasis
What is positive feedback?
When the initiating stimulus causes more of the same
Positive feedback is better known as a “vicious cycle,” but a mild degree of positive feedback can be overcome by the negative feedback control mechanisms of the body and the vicious cycle fails to develop.
What is an example of negative feedback?
When the arterial pressure rises too high, the baroreceptors (bifurcation of carotid arteries in neck and arch of aorta) send barrages of nerve impulses to the medulla of the brain. Here these impulses inhibit the vasomotor center, which in turn decreases the number of impulses transmitted from the vasomotor center through the sympathetic nervous system to the heart and blood vessels. Lack of these impulses causes diminished pumping activity by the heart and also dilation of the peripheral blood vessels, allowing increased blood flow through the vessels.
Conversely, a decrease in arterial pressure below normal relaxes the stretch receptors, allowing the vasomotor center to become more active than usual, thereby causing vasoconstriction and increased heart pumping. The decrease in arterial pressure thus initiates negative feedback mechanisms that raise arterial pressure back toward normal.
How is the degree of effectiveness with a control system is determined?
The degree of effectiveness with which a control system maintains constant conditions is determined by the gain of the negative feedback. Gain = correction/error. (Gain = sensitivity of the system), error is due to not being perfect, i.e. blood pressure can still be elevated from baseline even when feedback is trying to return it from elevated state
What are examples of positive feedback?
When a blood vessel is ruptured and a clot begins to form, multiple enzymes called clotting factors are activated within the clot itself. Some of these enzymes act on other inactivated enzymes of the immediately adjacent blood, thus causing more blood clotting. This process continues until the hole in the vessel is plugged and bleeding no longer occurs (this process is part of a larger negative-feedback mechanism, the stopping of bleeding and maintenance of normal blood volume)
When uterine contractions become strong enough for the baby’s head to begin pushing through the cervix, stretch of the cervix sends signals through the uterine muscle back to the body of the uterus, causing even more powerful contractions
To generate an action potential, there is slight leakage of sodium ions through sodium channels which then change the membrane potential which in turn opens more sodium channels so that a small leak can become an explosion of sodium entering the cell
What is feed-forward control?
Often used for muscle contractions when these movements need to occur so rapidly that there is not enough time for nerve signals to travel to the brain and back
What is an example of feed-forward control?
Sensory nerve signals from the moving parts apprise the brain whether the movement is performed correctly. If not, the brain corrects the feed-forward signals that it sends to the muscles the next time the movement is required. Then, if still further correction is necessary, this process will be performed again for subsequent movements. This process is called adaptive control
What is adaptive feedback in context of feed-forward control?
Adaptive feedback corrects itself after feed forward: delayed negative feedback
Describe the difference between the different G-protein coupled receptors and identify how their signaling pathways work
G protein-coupled receptors transmit information through the trimeric G proteins.
G-αs vs. G-αi
Different hormone stimulate different receptors which activate different kinds of G-Proteins.
The main difference is the α-subunit which can be stimulatory (G-αs) or inhibitory (G-αi)
G-αq
Causes PIP2 to be cleaved (by PLC) to IP3 and DAG
IP3 stimulates calcium release from the SR
G-αt
At interacts with phosphodiesterase (PDE) and causes a reduction in cGMP in cells
Common in the visual pathways of the photoreceptor cells
What is the lipid bilayer?
Constitutes a barrier against movement of the water molecules and water-soluble substances between the extracellular and intracellular fluid compartments; fluid mosaic model; formed by phospholipids with cholesterol in between (stiffens membrane and prevents transport through)
What is intracellular fluid?
Contains a large amount of potassium and only a small amount of sodium
Contains very few chloride ions
Significantly higher concentration of phosphates and proteins than the extracellular fluid
What is extracellular fluid?
Contains a large amount of sodium and only a small amount of potassium
Contains many chloride ions
What interrupts the continuity of the lipid bilayer? What is the purpose of this disruption?
Protein molecules interrupt the continuity of the lipid bilayer generating an alternative way through the cell membrane
Transport proteins, channel proteins, carrier proteins
Channel and carrier proteins are usually selective for the types of molecules or ions that are allowed to cross the membrane
What is diffusion?
Passive random molecular movement of substances molecule by molecule either through intermolecular spaces in the membrane or in combination with a carrier protein
What is active transport?
Movement of ions or other substances across the membrane in combination with a carrier protein in such a way that the carrier protein causes the substance to move against the energy gradient
What is the major difference between active transport & diffusion?
Diffusion does NOT require extra energy - energy for this process is through normal kinetic motion of matter
Active transport DOEs require an additional source of energy besides kinetic energy
What is diffusion through the plasma membrane?
The movement of all molecules and ions in the body fluids that consists of greater motion at a greater temperature so that more intermolecular interactions occur
What is simple diffusion?
Kinetic movement of molecules or ions occurs through a membrane opening or through intermolecular spaces without any interaction with carrier proteins in the membrane
How is the rate determined for diffusion?
The rate is determined by the amount of substance available, the velocity of kinetic motion, and the number and sizes of openings in the membrane through which the molecules or ions can move
What factors govern the rate of diffusion through the lipid membrane?
If a substance is lipid soluble (O2, N2, CO2, alcohol, etc) then it can diffuse directly through the lipid bilayer
If more lipid soluble the substance is, the faster it can diffuse through
If a substance is not lipid soluble but still smaller enough it can diffuse through large transport proteins
Aquaporins: selectively permit passage of water through the membrane
As substances get larger, their ability to diffuse falls off (ex. Urea is bigger than H2O and its penetration is drastically less)
What is facilitated diffusion?
Requires interaction of a carrier protein that aids passage of the molecules or ions through the membrane by binding chemically with them and shuttling them through the membrane
What do ion channels do?
Protein pores and channels allow various substances in and out of the cell membrane however the diameter and electrical charge of a pore permit selectivity of certain molecules
How do ion channels work?
Ex: The potassium channel permits passage of K+ ions across the cell membrane about 1000 times more readily than Na
The ability of K+ to pass through but not Na+ which has a slightly smaller diameter can be explained by the structure of the protein
What is the structure of an ion channel?
Tetrameric structure: consists of four identical protein subunits surrounding a central pore with pore loops that form a narrow selectivity filter lined with carbonyl oxygens
What occurs with potassium movement in the ion channel?
When hydrated potassium ions enter the selectivity filter, they interact with the carbonyl oxygens and shed most of their bound water molecules, permitting the dehydrated potassium ions to pass through the channel. The carbonyl oxygens are too far apart, however, to enable them to interact closely with the smaller sodium ions, which are therefore effectively excluded by the selectivity filter from passing through the pore
How does a sodium channel work?
Inner surface of channel is lined with amino acids that are strongly negatively charged and can pull small dehydrated sodium ions into these channels therefore pulling the ions away from their hydrating water molecules
What are gated channels?
Gatelike extensions of the transport protein molecule which can close or open by conformational change of the shape of the protein molecule itself
How does voltage-gated channels work?
Molecular conformation of gate responds to the electrical potential across the cell membrane
What is an example of volage gated channels?
If charge is strongly negative on inside the outside sodium gates will remain shut because this is the desired charge across the membrane but if the inside suddenly loses charge then the gates would open to allow Na+ into the cell
K+ channels are located closer to the inside of the membrane while Na+ channels are located closer to the outside of the membrane
Opening K+ channels are responsible for terminating an action potential
What is chemical (ligand) gating?
Binding of a ligand causes a conformational change that opens or closes the gate
Ex. Acetylcholine Channel: binding of Ach opens this channel
What are the different states of ion channels?
Channels conduct current in an all or nothing fashion
At one specific voltage potential, a channel may be closed all the time whereas at another voltage potential a channel may be open all the time
At in between voltages, gates tend to snap open and closed intermittently resulting in average current flow somewhere between the minimum and maximum
What is facilitated diffusion?
Substance diffuses through the membrane with the help of a specific carrier protein
What uses facilitated diffusion?
Glucose and amino acids uses this type of diffusion and GLUT4 is the glucose transporter sensitive to changes in insulin level
How does simple & facilitated diffusion differ?
Simple diffusion increases proportionately with the concentration of the diffusing substance, but in facilitated diffusion the rate of diffusion approaches a maximum, called Vmax, as the concentration of the diffusing substance increases
How does facilitated diffusion work?
In facilitated diffusion the molecule to be transported is bound and the carrier protein undergoes a conformational change so the pore now opens to the opposite side of the membrane. Because the binding force of the receptor is weak, the thermal motion of the attached molecule causes it to break away and be released on the opposite side of the membrane. The rate at which molecules can be transported by this mechanism can never be greater than the rate at which the carrier protein molecule can undergo change back and forth between its two states
What is osmosis?
Net movement of water caused by concentration difference across a membrane – water moves towards the higher concentration of solute
How is osmotic pressure calculated?
What are the indicators of fluid compartments in the indicator dilution method? Why are these selected?
- Total Body Water: Antipyrine is a soluble lipid and can rapidly penetrate cell membranes and distribute itself uniformly between intracellular and extracellular compartments
- Extracellular Fluid: can use any of several substances that disperse in the plasma and interstitial fluid but do not permeate the cell membrane
- Radioactive sodium may diffuse into cells in small amounts so using this indicator is measuring the “sodium space” or “inulin space” rather than true extracellular fluid volume
- Intracellular Fluid: this compartment cannot be measured directly but can be calculate (equation in chart)
- Plasma Volume: must use a substance that does not readily penetrate capillary membranes but remains in vascular system after injection
- Blood Volume: can be measured in hematocrit is known (equation in chart) or RBCs can be labelled with radioactive substance
- Interstitial Fluid: this compartment cannot be measured directly but can be calculate (equation in chart)
What is the diagnostic table for abnormalities?
