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A&P Ch. 5
Terms in this set (82)
fluid concentrations are equal on the inside and outside of the cell
overall concentrations of the ECF and ICF are equal but some solutes more concentrated in one compartment than the other
Which ions are more concentrated in extracellular fluid?
Which ions are more concentrated in intracellular fluid?
Where do many cells store Ca2+?
inside organelles such as the endoplasmic reticulum and mitochondria
negative ions in intracellular fluid, positive ions in extracellular fluid
Describe the equilibrium state of the ICF vs. ECF compartments of the body.
ICF and ECF are in osmotic equilibrium, but in chemical and electrical disequilibrium. These are the steady states.
a protein that creates special water channels to allow water to move freely in and out of the cell
movement of water across a membrane in response to a solute concentration gradient (relies on aquaporins); water moves to dilute the more concentrated solution
the pressure that exactly opposes a given concentration gradient
Why do we use osmolarity instead of molarity when describing biological solutions?
Osmolarity expresses the number of particles per liter of solution, which is more relevant than the number of molecules because some molecules dissociate into ions when they dissolve in a solution.
Concentration expressed as osmoses of solute per kilogram of water. Can be used interchangeably with osmolarity in physiology.
two solutions contain the same concentration (300 mOms)
higher osmolarity (greater than 300 mOsm)
lower osmolarity (less than 300 mOsm)
how the solution affects the volume of the cell
If the cell gains water at equilibrium and swells, the solution is hypotonic to the cell (environment is more dilute so water moves into the cell to dilute it)
If the cell loses water and shrinks at equilibrium, the solution is hypertonic (cell is more dilute so water moves out of the cell to dilute the environment)
cell in solution does not change size at equilibrium
penetrating vs. nonpenetrating solutes
tonicity depends on the concentration of nonpenetrating solutes because penetrating solutes will diffuse themselves
What are 3 examples of penetrating solutes?
glucose, urea, alcohol
a pressure gradient causes fluid to flow from regions of higher pressure to regions of lower pressure; fluids are gases and liquids
does not require the input of energy other than the potential energy stored in a concentration energy
requires the input of energy from some outside source, such as ATP
To what kinds of molecules is the membrane permeable?
oxygen, carbon dioxide, lipids
To what kinds of molecules is the membrane impermeable?
ions, most polar molecules, and very large molecules (such as proteins)
What two properties of a molecule (particle) influence its movement across cell membranes?
size of the molecule and its lipid solubility
the movement of molecules from an area of higher concentration to an area of lower concentration
What are the 7 properties of diffusion?
1. Diffusion is a passive process (uses only the kinetic energy possessed by all molecules).
2. Molecules move from higher to lower concentration.
3. Net movement of molecules occurs until the concentration is equal everywhere.
4. Diffusion is rapid over short distances but much slower over long distances.
5. Diffusion is directly related to temperature (molecules move faster at higher temperatures).
6. Diffusion rate is inversely related to molecular weight and size.
7. Diffusion can take place in an open system or across a partition that separates two compartments.
a difference in the concentration of a substance between two places (aka chemical gradient)
What things allow for diffusion through the membrane faster?
-Membrane's surface area is larger
-Membrane is thinner
-Concentration gradient larger
-Membrane is more permeable to the molecule
What is Fick's law of diffusion?
rate of diffusion = surface area x concentration gradient x membrane permeability
What does membrane permeability equal?
Lipid solubility/molecular size
What are the four functions of membrane proteins?
1. structural proteins
3. membrane receptor proteins
4. transporters for particles that can't pass the membrane
What 3 roles do structural proteins of membranes have?
1. Create cell junctions that hold tissues together
2. Connect membrane to cytoskeleton to maintain cell shape
3. Attach cells to extracellular matrix
What do membrane enzymes do?
catalyze chemical reactions that take place either on the cell's external surface or inside the cell
What are 2 types of transport proteins and what do they do?
Channel proteins: create water-filled passageways that directly link the intracellular and extracellular compartments
Carrier proteins: bind to the substrates that they carry but never form a direct connection between the ICF and ECF
What are the 7 different types of channel proteins?
Water channels: aquaporins
Ion channels: Na+ channels, K+ channels, nonspecific monovalent (one-charge) cation channels
Open channels: usually gate open, allowing ions to move back and forth without regulation
Gated channels: usually closes, regulate movement of ions
Chemically gated channels: gating is controlled by intracellular messenger molecules or extracellular ligands that bind when the channel opens
Voltage-gated channels: open and close when electrical state of the cell changes
Mechanically gated channels: respond to physical forces (increased temperature, pressure)
What are the 3 different types of carrier proteins?
uniport carriers: move only 1 kind of molecule
symport carriers: transports molecules in the same direction
antiport carriers: molecules are being carried in opposite directions
highest rate something could move across the membrane
Primary (direct) active transport
uses the energy of ATP to push molecules against their concentration gradient
Secondary (indirect) active transport
uses potential energy stored in the concentration gradient of one molecule to push other molecules against their concentration gradient
What are the 3 properties of carrier-mediated transport?
specificity: specific to what they're carrying
competition: one molecule binds and takes up space where another molecule should be (fighting for living binding site)
saturation: carriers working at transport maximum
Na+/K+ ATPase Pump
-primary active transport
-Na+ out, K+ in
-stores potential energy inside the cell
-maintain concentration gradient so sodium-dependent transporters work and use ATP
-secondary active transport
-brings Na+ into the cell WITH glucose
1. Na+ binds to carrier.
2. Na+ binding creates a high-affinity site for glucose.
3. Glucose binding changes carrier conformation so that binding sites now face the ICF.
4. Na+ is released into cytosol, where [Na+] is low. Release changes glucose-binding site to low affinity. Glucose released.
move glucose and related hexose sugars across membranes
-protein-mediated transport in which no outside source of energy except a concentration gradient is needed to move molecules across the cell membrane
-brings glucose into cell down its concentration gradient using a GLUT transporter
Give an example of competition within a GLUT transporter.
Maltose is a competitive inhibitor that binds to the GLUT transporter but is not itself carried across the membrane
-for bigger molecules, when diffusion won't work
-fold over membrane, form a bubble to draw stuff in
-vesicles created by the cytoskeleton
-cell engulfs bacterium or other particles into phagosome (large bubble)
endocytosis (What kind of process is it?)
-membrane surface indents and forms vesicles
-active process that can be nonselective (pinocytosis) or highly selective
receptor-mediated endocytosis (Where does it take place?)
-a ligand binds to a membrane receptor protein to activate the process
-takes place in coated pits in the membrane (indentations where the cytoplasmic side of the membrane has high concentrations of protein)
most common protein found in coated pits
small flask-shaped indentations
-some endocytosis uses this rather than clathrin to concentrate and bring receptor-bound molecules into the cell
-releases hormones into the blood stream
-intracellular vesicles move to the cell membrane, fuse with it, and then release their contents to the ECF
-surface of the epithelial cell that faces the lumen of an organ
-often folded into microvilli that increase its surface area
-below tight junctions, the three surfaces of the cell that face the ECF
Where is the Na+/K+ -ATPase found?
only in the basolateral membrane
Where is the Na+-glucose symporter found?
only in the apical membrane
What does the polarized transporting cells allow for?
allows the one-way movement of certain molecules across the epithelium
through junctions between adjacent cells
-through the epithelial cells themselves
-use both active and passive transport (cross 2 membranes)
absorption vs. secretion
absorption: lumen to ECF
secretion: ECF to lumen
What 3 transport systems are involved in transepithelial movement of glucose?
1. sodium glucose mediated secondary active transport of glucose with Na+ from lumen into cell at apical membrane, followed by Na+ and glucose out of cell on separate transporters
2. glucose leaves the cell by facilitated diffusion on GLUT carriers
3. sodium moves out via Na+-K+ -ATPase
combination of endocytosis, vesicular transport across the cell, and exocytosis
-molecule brought into cell via receptor-mediated endocytosis
-resulting vesicle attaches to microtubules in the cell's cytoskeleton and moved across the cell via vesicular transport
-at the opposite side of the epithelium, the contents of the vesicle are expelled into the interstitial fluid by exocytosis
What is the purpose of transcytosis?
makes it possible for large proteins to move across an epithelium and remain intact
body is electrically neutral, but there is a chemical disequilibrium between ICF and ECF
-ICF has net negative charge (proteins and anions)
-ECF has net + charge (Na+)
-Na+ wants to get inside the cell where it's negative
K+ leak channel
-allows K+ to leave the cell down its concentration gradient
-anions cannot follow K+ out of the cell because the cell is impermeable to anions
-negative charge inside cell begins to attract K+ back into the cell
a difference in the net charge between two regions
combination of electrical and concentration gradients
membrane potential that opposes the concentration gradient
How is the equilibrium potential (Eion) calculated?
How is membrane potential measured?
micropipette: filled with liquid that conducts electricity
voltmeter: measures the electrical difference
What mostly causes the resting potential in cells?
What 2 factors influence a cell's membrane potential?
1. concentration gradients of different ions across the membrane
2. permeability of the membrane to those ions
when the potential difference between the inside of the cell and the outside is less
return to the resting membrane potential
resting potential becomes more negative
When is insulin secreted?
When the blood sugar rises, energy (glucose) is stored and insulin is released. Glucose is then let into the cell.
What happens in terms of insulin secretion when the beta cell is at rest?
Low glucose levels in blood, metabolism slows, ATP decreases, ATP-gated K+ channels (KATP) open, cell at resting potential and no insulin is released
What happens when the beta cell secretes insulin?
High glucose levels in blood, metabolism increases, ATP increases, KATP channels close, cell depolarizes and calcium channels open, Ca2+ entry acts as an intracellular signal, Ca2+ signal triggers exocytosis and insulin is secreted
How does insulin help in transporting glucose?
Glucose can't pass the membrane so it needs the trigger from insulin to be available to transport the glucose through the GLUT transporter.
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