cellular physiology I and II

Question 1

what is the interstitial water?

Answer 1

the extracellular water outside the blood and bathes the cells

Question 2

Is body water found in the lymphathic system?

Answer 2

Yes, a small amount

Question 3

how much intracellular water is there in liters?

Answer 3

28L

Question 4

how to calculate body fluid volume?

Answer 4

mass (in grams)/concentration

Question 5

total body water can be measured using what chemical substances?

Answer 5

3H2O or 2H2O

Question 6

which dye can be used to measure the plasma volume and how does it work?

Answer 6

using Evans Blue; it has high affinity for serum albumin

Question 7

how can extracellular fluid be measured?

Answer 7

using a plant polysaccharide Inulin.

Question 8

what does the intracellular space fluid consist of?

Answer 8

connective tissue, collagen and proteoglycan filaments together with an ultrafiltrate of plasma.

Question 9

how does the body prevent fluid from flowing downwards due to gravity?

Answer 9

the water from the interstitial fluid hydrates the proteoglycan filaments to form a gel and in normal tissues there is little free flow of fluid.

Question 10

exchange of water and solutes occur by diffusion; how does exchange between interstitial fluid and the capillaries or lymphatics occur?

Answer 10

by bulk flow

Question 11

how can the amount of water in each fluid compartment be determined?

Answer 11

by diluting specific markers. For accurate measurement, the markers have to be evenly distributed throughout the body and must be physically inert. i.e. should not be metabolized or alter any physiological variable.

Question 12

how do O2 and CO2 cross the plasma membrane?

Answer 12

they are lipid soluble molecules that cross the membrane freely because they can dissolve in the lipid bilayer.

Question 13

what is osmotic pressure?

Answer 13

The pressure that is

just sufficient to prevent the uptake of water is known as the osmotic pressure of the solution

Question 14

what determines total body water?

Answer 14

a known amount of radioactive water 3H2O or deuterium oxide 2H2O, injected, and allowed sufficient time for complete distribution.

Question 15

Extracellular volume requires a substance that freely pass between the circulation and the interstitial fluids but does not go into the cells; what substances can meet these requirements?

Answer 15

inulin or mannitol.

Question 16

what are examples of hydrophilic substances?

Answer 16

glucose, Na+, K+, ethanol and many proteins

Question 17

what are examples of hydrophobic substances?

Answer 17

lipid, fats, waxes and cholesterol

Question 18

what are amphiphilic substances? what are the examples?

Answer 18

substances that have mixed properties-one part is hydrophilic and another part is hydrophobic. examples are long chain fatty acids, bile salts and the phospholipids.

Question 19

what factors determine rate the diffusion?

Answer 19

temperature, magnitude of the concentration gradient and the area over which diffusion can occur. large molecules diffuse slower than smaller ones.

Question 20

The molecular characteristics of the solute and solvent also affect the rate of diffusion. these characteristics are reflected in a physical constant known as the?

Answer 20

diffusion coefficient.

Question 21

Define the Fick’s law of diffusion.

Answer 21

Amount moved=diffusion coefficient X Area X concentration gradient
J= -D X A X dC/dX
the negative sign indicates that diffusion occurs from a high to low concentration gradient.
the diffusion coefficient becomes smaller as the molecular size increases so that large molecules move slower.

Question 22

what is osmotic pressure?

Answer 22

A hydrostatic pressure sufficient to stop the flow of osmosis (movement of water or other solvent through a semipermeable membrane that permits the passage of the water but not the solute particles).

Question 23

How do we calculate the osmotic pressure?

Answer 23

osmotic pressure (Pi) = MRT
M=molarity, R=the universal gas constant 0.31 J/K/mol, 
T=the absolute temperature (310 K at normal body temp)

Question 24

what does the osmotic pressure depend on?

Answer 24

the number of particles present per unit volume of solvent and not on their chemical makeup. salts like sodium chloride will exert twice its molecular concentration.

Question 25

define osmolarity

Answer 25

moles solute particles per litre of a solution.

Question 26

define osmolality

Answer 26

moles solute particles per kilogram of a solution. The total osmolality of a solution is the sum of the osmolality due each of the constituents of the solution.

Question 27

what osmolality does blood plasma have?

Answer 27

300 mosmol/L. the principle ions like Na+, K+, Cl-, HCO3-, contribute most of this, around 290 mosmol/L
Glucose and other small molecules < 10 mosmol/L
Proteins contribute only about 1 mosmol/L, only 0.5% of total plasma osmolality.

Question 28

two solutions with the same osmolality are said to be

Answer 28

iso-osmotic

Question 29

Fluids which are isotonic are also iso-osmotic; however not all iso-osmotic solutions are isotonic. Give an example:

Answer 29

iso-osmotic solutions of urea cause cells to swell

Question 30

define hypotonicity

Answer 30

extracellular concentration of solvents higher than intracellular concentration, causes swelling of the cell.

Question 31

define hypertonicity

Answer 31

extracellular concentration of solvent lower than intracellular concentration. causing water to be drawn out of the cell.

Question 32

blood plasma is isotonic with red blood cells. true of false

Answer 32

true

Question 33

which three factors determine the electrochemical transport?

Answer 33

the concentration gradient, the charge of the molecule or ion and the membrane potential

Question 34

which substances are abundant in the ICF?

Answer 34

K+, proteins such as enzymes and structural proteins, and the small organic molecules that are involved in metabolism or signalling ATP etc.

Question 35

which substances are abundant in the ECF?

Answer 35

Na+ and Cl-

Question 36

proteins facilitate the translocation of water soluble molecules to cross the membrane by which channels?

Answer 36

ion channels and carrier channels

Question 37

characteristics of ion channels:

Answer 37

have a central pore for ion diffusion down their electrochemical gradient;
diffusion through pore is passive;
are selective for particular ions;
generally have a high capacity for transport;
can be leak channels or gated channels;

Question 38

the capacity of a cell to transport a molecule is limited by what?

Answer 38

both the number of transmembrane carriers and the number of molecules each carrier is able to translocate.

Question 39

carrier proteins are subdivided into three groups of carriers. what are they?

Answer 39

uniport-bind to a specific molecule at one side and transport it to another side;
cotransport-substances transported only in association with a 2nd molecule or ion, and a symport is when both molecules or ions move in the same direction;
antiport-ion move into the cell is coupled with a 2nd ion/molecule out of the cell

Question 40

define active transport

Answer 40

occurs when ions/molecules move against their concentration gradients and requires cell to expand metabolic energy. the activity of the carrier proteins need metabolic energy derived from the hydrolysis of ATP

Question 41

secondary active transport is:

Answer 41

the transport of a substance can occur against its electrochemical gradient by coupling its uphill movement to the downhill movement of sodium into the cell. it depends on the ability of the sodium pump to keep the IC concentration of sodium significantly lower than that of the ECF.

Question 42

Cells often use carriers in combination to regulate the IC concentration of certain ions. Thus, the IC concentration of calcium ions is regulated by what?

Answer 42

by sodium-calcium exchange and by a calcium pump

Question 43

how is the IC concentration of hydrogen ions regulated?

Answer 43

regulated by

1. sodium-hydrogen exchange–antiport: H+ ions move up the [] gradient out of the cell and Na+ move down their [] gradient into the cell;
2. sodium-bicarbonate co-transport to increase IC HCO3-: bicarbonate transported against their electrochemical gradient, bind to the H+ ions to form carbonic acid which is in equilibrium with CO2 that can cross the membrane by diffusion. For each CO2 that leaves the cell, one H+ molecule is used up to form one molecule of water;
3. Chloride-bicarbonate exchange- provides a means of defence against a fall int he IC H+ ion concentration, freely reversible and plays an important role in the carriage of CO2 in red cells.

Question 44

The sodium pump balances two ions, what are they?

Answer 44

IC sodium ions and EC potassium ions against their [] gradients. Requires ATP.

Question 45

Hydrolysis of ATP is tightly bound to the coupling of efflux of Na+ and influx of K+ in such a way that:

Answer 45

for each molecule of ATP hydrolyzed, 3 Na+ pumped out and 2 K+ pumped in. The sodium potassium pump can be inhibited by a glycoside called ouabain that binds to the EC face of the protein.

Question 46

the secondary AT is particularly important for the transport of amino acids and glucose across sheets of?

Answer 46

epithelia; lining in the intestine or kidney

Question 47

The epithelia has two layers of membrane: the apical membrane (lumen) and the baso-lateral membrane (blood). What types of carriers or channels do they have?

Answer 47

The apical membrane close to the lumen has a symport called SGLT1 (sodium-linked glucose transporter 1) that binds both sodium and glucose.
The baso-lateral membrane close to the blood has a different type of glucose carrier, a uniport called GLUT2, that permits the movement of glucose from the cell interior down its [] gradient into the space surrounding the baso-lateral surface.

Question 48

define secretion.

Answer 48

cells release molecules they have synthesized into the extracellular environment; In some cases occur by simple diffusion through the plasma membrane–the secretion of steroid hormones by the cells of adrenal cortex. This method is only for those that can penetrate the lipid bilayer.

Question 49

define exocytosis

Answer 49

polar molecules are packaged in membrane bound vesicles which can fuse with the plasma membrane and release their contents into the extracellular space

Question 50

Exocytosis can occur via two pathways. What are they and make short notes on them.

Answer 50

1. constitutive secretion which is continuous; common to all cells and is the mechanism by which cells are able to insert new proteins to the membrane such as carriers.
2. regulated secretion is secretion is response to a specific signal; all exocrine and endocrine cells use regulated secretion to control the timing and rate of release.

Question 51

Regulated secretion is controlled by EC signals. What is the universal trigger?

Answer 51

an increase in Ca2+ concentration in the cytosol

Question 52

Regulated secretion occurs in two processes, what are they?

Answer 52

1. entry of calcium through calcium channels in the plasma membrane
2. release of calcium from IC stores (mainly ER)

Question 53

Cells in the exocrine glands provide a clear example of zonation of polarized secretory cells–one part of the membrane is specialized to receive signal while another region is adapted to permit the fusion of secretory vesicles. what are these type of cells called?

Answer 53

acinar cells

Question 54

Where does the baso-lateral surface receive chemical signals from?

Answer 54

circulating hormones and nerve endings

Question 55

what does the signal going to the baso-lateral surface do?

Answer 55

activate receptors that control the secretory response

Question 56

define pinocytosis

Answer 56

it is called cell-drinking, when during formation of vesicles the membrane pinches off and contains a little bit of ECF.

Question 57

define phagocytosis

Answer 57

specialized cells engulf foreign particles and cell debris which is triggered when receptors on the cell surface recognizes specific proteins on the surface of the foreign particle. The ingested material is digested in specific vacuoles called phagosomes.

Question 58

Does co-transport require metabolic energy?

Answer 58

Yes, it requires indirect metabolic energy. solutes move in the same direction as Na+ as either coupled or symported.

Question 59

what is the equilibrium potential?

Answer 59

the potential at which the tendency of the ion to move down its [] gradient is exactly balanced by the membrane potential is known as the equilibrium potential for that ion so that at the EP at the rate at which ions enter the cell is exactly balanced at which they leave.

Question 60

How do we calculate the resting membrane potential?

Answer 60

By The Ernst Equation. E= RT/zF X ln X [c]o/[c]i
ln=natual log
[c]0 and [c]i = EC [] and IC []
R=gas constant 8.31 J/K/mol
T=absolute temp =310 K under normal temp
z= the charge of the ion (+1 for Na -1 for Cl)
F= Faraday Constant 96487 C/mol
At 37% the term RT/F=26.7

Question 61

what is the modified form of the Ernst equation and what does it do?

Answer 61

The Goldman equation; explain dynamic aspects of membrane potential behavior. The equation takes into account not only the ionic gradients that exist across the membrane but also the permeability of the membrane to the different ions.

Question 62

The best characterized route for endocytosis mechanism is called:

Answer 62

clathrin-mediated endocytosis

Question 63

How does the mechanism for endocytosis work?

Answer 63

the structure of the cytoplasmic domain of a cell-surface receptor changes when it binds its specific ligand. this is followed by recruitment of adaptor proteins which connect the membrane receptor to the clathrin scaffold. The adapter proteins then recruit clathrin which forms a molecular scaffold for inward budding of the cell membrane. As the clathrin assembles into a mesh work, the membrane buds into the cell to form a clathrin-coated pit, after which dynamin and its associated proteins act to cut the membrane off from the plasma membrane. The endocytosed membrane is now a clathrin coated vesicle. Once separated from the the plasma membrane, chemical changes in the membrane cause the dissolution of the clathrin complex, leaving an endocytic vesicle which is then trafficked by the appropriate pathway.