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biology final test help
Terms in this set (68)
The law of mass Balance
that if the amount of a substance in the body is to remain constant, any gain must be offset by and equal loss.
) of substance x in the body = intake + production - excretion - metabolism
the elimination of material from the body, and it usually takes place through the urine, feces. lungs, or skin.
second output option for maintaining mass balance
- nutrients that enter body become different substance but in doing so creates a new mass balance disturbance by adding more of the metabolite to the body
Excretion Clears Substances from the body
rate at which molecule disappears from the body by excretion, metabolism, or both
- kidney and liver involved in clearing materials especially xenonbiotics.
- hepatocytes: liver cells metabolize hormones and drugs
- saliva, sweat, breast milk, and hair contain solutes cleared from the body
- lungs clear volatile lipid soluble materials from the blood
-expressed in blood plasma cleared of x per unit of time.
= concentration x volume flow
Homeostasis Does Not Mean Equilibrium
stay in dynamic disequilibrium
the total amount of solutes per volume of fluid is equal on the two sides of the cell membrane
certain solutes are more concentrated in one of the two body compartments than in the other
ionic imbalance, changes in the disequilibrium create electrical signals
fluids within a compartment
gases and liquids - diff: gases are compressible because their molecules are so far apart in space
- pressure gradient causes fluid to flow from regions of higher pressure to regions of lower pressure
lipid and protein composition of a given cell membrane determines which molecules will enter the cell and which will leave
allows substances to pass
does not allow substance to pass
what are two properties that influence movement across cell membranes?
size and its lipid solubility
does not require input of energy
requires input of energy from some outside source such as the high energy phosphate bond of ATP
movement of molecules from an area of higher concentration of the molecules to an area of lower concentration of molecules.
1. Diffusion is a passive process . By passive, we mean that diffusion does not require the input of energy from some outside source. Diffusion uses only the kinetic energy possessed by all molecules.
2. Molecules move from an area of higher concentration to an area of lower concentration. A difference in the concentration of
a substance between two places is called a
aka chemical gradient . rate depends on concentration gradient. The larger the concentration difference,the faster diffusion takes place.
3. Net movement of molecules occurs until the concentration is equal everywhere. Once molecules of a given substance have distributed themselves evenly, the system reaches equilibrium and diffusion stops. Individual molecules are still moving at equilibrium, but for each molecule that exits an area, another one enters.The dynamic equilibrium state in diffusion means that the concentration has equalized through out the system but molecules continue to
4. Diffusion is rapid over short distances but much slower over
5. Diffusion is directly related to temperature. At higher temperatures, molecules move faster. Because diffusion results from molecular movement, the rate of diffusion increases as temperature increases.
6. Diffusion rate is inversely related to molecular size. Einstein calculated that diffusion is inversely proportional to the radius of the molecule: the larger the molecule, the slower its diffusion through a given medium.
7. Diffusion can take place in an open system or across a partition that separates two systems.
- ions do not move by diffusion move by electrochemical gradients
diffusion directly across the phospholipid bilayer
1.The rate of diffusion depends on the ability of the diffusing molecule to dissolve in the lipid layer of the membrane
2. The rate of diffusion across a membrane is directly proportional to the surface area of the membrane .
3. The rate of diffusion across a membrane is inversely proportional to the thickness of the membrane.
Ficks law of diffusion
3 major roles.
(1) connect the membrane to the cytoskeleton to maintain the shape
(2) create cell junctions that hold tissues together
(3) to attach cells to the extracellular matrix by linking cytoskeleton fibers to extracellular collagen
catalyze chemical reactions that take place either on the cell's external surface or just inside the cell.
part of chemical signaling system
- binding of receptor with ligand usually triggers another event at the membrane, such as activation of an enzyme
moves molecules across membranes
create water filled passageways that directly link the intracellular and extracellular compartments
bind to the substrates that they carry but never form a direct connection b/w the intracellular fluid and extracellular fluid.
channel allow more rapid transport across the membrane but generally are limited to moving small ions and water. carriers can move larger ones
made from protein called aquaporin
specific for one ion or may allow ions of similar size and charge to pass
selectivity of a channel is determined by the diameter of its central power and by the electrical charge of the amino acids that line the channel
spend most of their gate open allowing ions to move back and forth across the membrane without regulation
-leak channels, pors, water pores
spend most of their time in a closed state which allows these channels to regulate the movement of ions through them
solutes cross membrane with help from proteins
If mediated transport is passive and moves molecules
down their concentration gradient, and if net transport stops when concentrations are equal on both sides of the membrane,
transport requires energy from ATP and moves against the concentration gradient
chemically gated channels
gating is controlled by intracellular messenger molecules or extracellular ligands that bind to the channel protein
voltage gated channels
open and close when the electrical state of the cell changes
mechanically gated channels
respond to physical forces such as increased temperature or pressure that puts tension on the membrane and pops the channel gate open
move only one kind of molecule
carrier that moves more than one kind of molecule at one time
molecules being transported are moving in the same direction, whether into or out of the cell
molecules carried in opposite directions
-bind with specific substrates and carry them across the membrane by changing conformation
differ from channel proteins: never create a continuous passage between the inside and outside of the cell
-like revolving doors allow movement between inside and outside without ever creating an open hole
move glucose and related hexose sugars across membranes.
- transported molecules move down their concentration gradient, the process requires no input of energy and net movement stops at equilibrium
primary (direct) active transport
energy to push molecules against their concentration gradient comes directly from ATP
- known as
hydrolyze ATP to ADP- sometimes called pumps
secondary (indirect) active transport
uses potential energy stored in the concentration gradient of one molecule to push other molecules agains their concentration gradient
-ultimately depends on primary active transport because the concentration gradients that drive secondary transport are created using energy from ATP
- use the kinetic energy moving down its concentration gradient to push other molecules against their concentration gradient
Na+ -glucose secondary active transporter (SGLT)
sodium and glucose bind to the SGLT protein on the extracellular fluid side. (1) sodium binds first then glucose. (2) protein changes conformation again and opens its channel to the ICF side
-only move into the cells
Carrier Mediated Transport Exhibits Specificity, Competition, Saturation
ability of a carrier to move only one molecule or only a group of closely related molecules
related members of a substate compete with one another for the binding sites on the transporter
substrate transport depends on both the substrate concentration and the number of carrier molecules, a property that is shared by enzymes. fixed number of carriers= substrate concentration increases, the transport rate increases up to maximum point at which all carriers are said to have reached saturation. =
Phagocytosis Creates Vesicles Using the Cytoskeleton
- is the actin mediated process by which a cell engulfs a bacterium or other particle into a large membrane bound vesicle called
- pinches off from the cell membrane and moves to the interior of the cell where it fuses with a lysosome, destroy the bacterium
-requires energy from ATP for the movement of the cytoskeleton and for the intracellular transport of vesicles
Endocytosis Creates Smaller Vesicles
- large molecules or particles move into cells.
- membrane surface indents rather than pushes out
- vesicles formed from endocytosis are much smaller
- some constitutive
-requires energy from ATP
allowing extracellular fluid to enter the cell
Receptor Mediated Endocytosis
indentations where the cytoplasmic side of the membrane has high concentrations of protein. most common protein found in coated pits is clathrin
- ligands receptors may be reused in
receptors moves to the cell membrane and fuses with it then moved to membrane by exocytosis
Potocytosis and Caveolae
distinguished from receptor mediated endocytosis by the fact that potocytosis uses
(little caves) rather than clathrin coated pits
-caveolae are membrane regions with lipid rafts, membrane receptor proteins and a coat of membrane proteins named cave-ins. look like small indented pockets
- functions: to concentrate and internalize small molecules, to help in the transfer of macromolecules across the capillary endothelium and to participate in cell signaling.
Exocytosis Releases Molecules Too Large for Transport Proteins
opposite of endocytosis
- intracellular vesicles move to the cell membrane, fuse with it, and then release their contents into the extracellular fluid.
- to export large lipophobic molecules such as proteins synthesized in the cell and to get rid of wastes left in lysosomes from intracellular digestion.
- from ECF =
- ECF to lumen = *secretion
Epithelial Transport May Be Paracellular or Transcellular
movement across an epithelium may take place either through the junctions between adjacent cells (
)or through the epithelial cells themselves (
). In tight epithelia the cell-cell junctions act as barriers to minimize the unregulated diffusion of material between the cells, so there is very little paracellular transport.
Transcellular Transport of Glucose Uses Membrane Proteins
- Transepithelial movement of glucose involve three transport systems: SGLT mediated secondary active transport of glucose with Na+ from the lumen into the epithelial cell at the apical membrane, followed by the movement of both Na+ and glucose out of the cell into the ECF on the basolateral side of the cell. Sodium moves out by primary active transport via a Na+ -K+ -ATPase, and glucose leaves the cell by facilitated diffusion on GLUT carries
- requires input of energy
Transcytosis Uses Vesicles to Cross an Epithelium
- combination of endocytosis, vesicular transport across the cell and exocytosis.
- molecule brought to epithelial cell via receptor mediated endocytosis or potocytosis- attaches to microtubules in the cell's cytoskeleton and it transported across cell by
contents expelled into the interstitial fluid by exocytosis
movement of water across a membrane in response to a solute concentration gradient
-moves to thin a more concentrated solution
pressure that must be applied to the piston to exactly oppose the osmotic movement into a compartment
number of particle per liter of solution
- particles may be ions, uncharged molecules, or a mixture of both
molarity(mol/L) x number of particles/ molecule = osmolarity (osmol/L)
concentration expressed as osmoses of solute per kilogram of water.
- used in clinical situations
Comparing Osmolarities of Two Solutions
two solutions contain the same number of solute particles per unit volume
- A is higher than B. A is
- B is fewer than A. B is
-depends strictly on the number of particles per liter of solution
- permeable to water = hyposmotic -> hyperosmotic
Tonicity of a Solution Describes the Volume Change of a Cell Placed in That Solution
physiological term used to describe a solution and how that solution affects cell volume.
- cell gains water
- cell looses water
- cell does not change size
How is Tonicity different from osmolarity?
1. Osmolarity describes the number of solute particles dissolved in a volume of solution. It has units, such as osmoles/ liter. The osmolarity of a solution can be measured by a machine called an osmometer. Tonicity has no units; it is only a comparative term.
2. Osmolarity can be used to compare any two solutions, and
the relationship is reciprocal (solution A is hyperosmotic to solution B; therefore, solution B is hyposmotic to solution A). Tonicity always compares a solution and a cell, and by convention, tonicity is used to describe only the solution for example, Solution A is hypotonic to red blood cells.
3. Osmolarity alone does not tell you what happens to a cell placed in a solution. Tonicity by definition tells you what happens to cell volume when the cell is placed in the solution.
solute particles can cross the cell membrane
particles that cannot cross the cell membrane
- depends on the concentration of non penetrating solutes only
rules for predicting tonicity
1. If the cell has a higher concentration of nonpenetrating solutes than the solution, there will be net movement of water into the cell. The cell swells, and the solution is hypotonic.
2. If the cell has a lower concentration of nonpenetrating solutes than the solution, there will be net movement of water out of the cell. The cell shrinks, and the solution is hypertonic.
3. If the concentrations of nonpenetrating solutes are the same in thecellandthesolution, therewillbenonetmovementof water at equilibrium. The solution is isotonic to the cell.
important principle when you deal with electricity in physiological systems.
the law of conservation of electrical charge
states that the net amount of electrical charge produced in any process is zero. This means that for every positive charge on an ion, there is an electron on another ion. Overall, the human body is electrically neutral.
2. Opposite charges are attracted to each other, but two charges of the same type repel each other. The protons and electrons in an atom exhibit this attraction.
3. separating positive charges from negative charges requires energy. For example, energy is needed to separate the protons and electrons of an atom.
4.if separated positive and negative charges can move freely toward each other, the material through which they are moving is called a conductor. Water is a good
of electrical charge. If separated charges are unable to move through the material that separates them, the material is known as an
.The phospholipid bilayer of the cell membrane is a good insulator,as is the plastic
coating on electrical wires.
- electricity comes from Greek word elektron meaning "amber"
input of energy to transport ions across the membrane
- a difference in the net charge between two regions.
Separation of Electrical Charge
cell membrane acts as an insulator to prevent free movement of ions between intracellular and extracellular compartments
combination of electrical and concentration gradients
-cell remains in osmotic equilibrium because water can move freely across the membrane in response to solute movement
resting membrane potential difference/ membrane potential
-electrical gradient between the extracellular fluid and the intracellular fluid.
1. The resting part of the name comes from the fact that this electrical gradient is seen in all living cells, even those that appear to be without electrical activity. steady state not changing
2. potential part, electrical gradient created by active transport of ions across the cell membrane is a form of stored, or protein, energy, just as a concentration gradients are a form of potential energy. the work done by electrical energy includes opening voltage-gated membrane channels and sending electrical signals
3. difference part of the name is to remind you that the membrane potential reps a difference in the amount of electrical charge inside and outside the cell.
Resting Membrane Potential is Due Mostly to Potassium
- the loss of positive ions from the cell creates an electrical gradient,
however. Because opposite charges attract each other, the negative proteins inside the cell try to pull K+ back into the cell. At some point in this process, the electrical force attracting K+
into the cell becomes equal in magnitude to the chemical concentration gradient driving K+ out of the cell. At that point, net movement of K+ across the membrane stops. The rate at which K+ ions move out of the cell down the concentration gradient is exactly equal to the rate at which K+ ions move into the cell down the electrical gradient.
-basically the force of concentration gradient pulling out the K+ is equal to the membrane potential(electrical gradient) pulling the K+ back into the cell =
- dealing with one ion
- cannot be used to calculate membrane potential
considers concentration gradients of the permeable ions and the relative permeability of the cell to each ion.
Changes in Ion Permeability Changes the Membrane Potential
influences of membrane potential (1) concentration gradients of different ions across the membrane and (2) the permeability of those ions
-depolarize, less negative membrane potential
-repolarization, return to the resting membrane potential
- hyperpolarization, becomes more negative
What causes changes in membrane potential?
-response to movement of one of four ions: Na+(sodium) Ca+(calcium) Cl+ (chloride) K+ (potassium)
- entry of Ca+ or Na+ depolarizes the cell
- entry of Cl- hyper polarizes the cell
-most cells permeable to K+ = leaking
- the concentration gradient does not have to reverse to change the membrane potential
Integrated Membrane Process
- process of beta cells release insulin
- beta cells of pancreas synthesize insulin and store it in cytoplasmic secretory vesicles.
- when blood glucose increase = release of insulin by exocytosis, then insulin directs other cells of body to take up and use glucose bringing blood concentration back down
How does beta cell know that glucose levels have gone up and that it needs to release insulin?
has two channels:
voltage gated Ca2+ channel
closed at resting membrane potential and
ATP-gated K+ channel
usually open and closes when ATP binds to it.
-less glucose=less ATP = less ATP to bind to K+channel = open gates allowing K+ to leak out.
- at rest voltage gated Ca2+ channel are closed and no insulin secretion
-glucose levels increase = reach beta cells +GLUT transporters to move into cells = increased glucose = stimulation of metabolic pathways of glycolysis and citric acid cycle = more ATP = ATP binds to K+ channels and the gate closes preventing leakage of K+ = depolarization of cell = voltage gated Ca2+ channell to open = calcium ions move in from the ECF moving down electrochemical gradient = Ca2+ to bind to proteins that initiate exocytosis of the insulin containing vesicles and the insulin is released into the extracellular space.
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