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Physiology Exam 2 > Membrane Transport & The Membrane Potential > Flashcards

Membrane Transport & The Membrane Potential Flashcards

1
Q

__ of our water is within cells in the intracellular component.

A

2/3 (67%)

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2
Q

__ of our water is within cells in the extracellular component.

A

1/3 (33%)

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3
Q

What is extracellular fluid made of?

A
  • Blood plasma: 20%
  • Tissue fluid (interstitial fluid with extracellular matrix): 4/5
  • Lymph
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4
Q

What is the extracellular matrix made of?

A

Consists of connective tissue (protein fibers collagen and elastin), as well as a gel-like ground substance

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5
Q

What is collagen?

A
  • Connective tissue fiber; about 15 kinds
  • In basal lamina
  • Binds to carbohydrates on plasma membrane, the matrix of connective tissue (proteoglycans and glycoproteins; play a role in cell recognition)
  • Binds ET to CT
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6
Q

What is elastin?

A

Connective tissue fiber that plays a big role in anchoring the cell to extracellular

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7
Q

What is ground substance?

A

Highly functional, complex organization of molecules chemically linked to the extracellular protein fibers of collagen and elastin

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8
Q

What is in the hydrated gel of the ground substance?

A

Contains glycoproteins and proteoglycans, composed primarily of polysaccharides and have a high content of bound water molecules

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9
Q

What are integrins?

A 
A class of glycoproteins that extend from the cytoskeleton within a cell, through its plasma membrane, and into the extracellular matrix, glue between cells and extracellular matrix
-relays signals between these compartments
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10
Q

What is the plasma cell membrane selectively permeable to?

A
  • Generally NOT permeable to proteins and nucleic acids

- SELECTIVELY permeable to ions, nutrients and waste

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11
Q

T or F: The plasma cell membrane is a biological interface between the two compartments.

A

TRUE

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12
Q

What does the plasma membrane contain that allows it to function as the site of chemical reactions?

A
  • Enzymes are located in it
  • Receptors: can bond to molecular signals and function in cell recognition
  • Transporter molecules
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13
Q

What do recognition factors allow for?

A

Cellular adhesion

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14
Q

What is carrier mediated transport?

A

Facilitated diffusion and active transport

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15
Q

What is non-carrier mediated transport?

A

Diffusion, osmosis and bulk flow (pressure gradients)

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16
Q

What is vesicle mediated transport?

A

Exocytosis and endocytosis (pinocytosis/phagocytosis)

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17
Q

What is passive transport?

A

The net movement of molecules and ions across a membrane from higher to lower concentration (down its concentration gradient); does not require metabolic energy

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18
Q

What is active transport?

A

The net movement of molecules and ions across a membrane from the region of lower to the region of higher concentration (against a concentration gradient), USES metabolic energy and involves specific carriers

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19
Q

What is diffusion?

A

Random molecular motion

  • Molecules/ions are in constant state of random motion due to their thermal energy
  • Eliminates a concentration gradient and distributes the molecules uniformly
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20
Q

When does diffusion occur?

A

If there is a concentration difference across the membrane and the membrane is permeable to the diffusing substance

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21
Q

What is the cell membrane permeable to?

A

Non-polar molecules (O2)
Lipid soluble molecules (steroids)
Small polar covalent bonds (CO2)
H2O (small size, lack charge)

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22
Q

What is the cell membrane impermeable to?

A

Large polar molecules (glucose)

Charged inorganic ions (Na+)

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23
Q

What 4 things affect the rate of diffusion?

A

1) Magnitude of concentration gradient - driving force of diffusion
2) Permeability of the membrane - neuronal cell membrane is 20x more permeable to K+ than Na+
3) Temperature - higher temp, faster diffusion rate
4) Surface area of the membrane - microvilli increase surface area (20-30x more)

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24
Q

What is osmosis?

A

Net diffusion of H2O across a selectively permeable membrane (water will always travel from high to low concentration of water/to where there is more solute)

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25
Q

What are the 2 requirements for osmosis to occur?

A

1) Concentration difference of a solute on the 2 sides of the selectively permeable membrane
2) Membrane must be impermeable to the solute

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26
Q

What are osmotically active solutes?

A

Solutes that cannot pass freely through the membrane (Na+)

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27
Q

If you have a selectively permeable membrane between 2 solutes (solute 1 = 180 g/L glucose and solute 2= 360 g/L glucose) at what concentration will equilibrium be reached?

A

(360 + 180)/2 = 270 g/L glucose

28
Q

For those 2 solutes (180 g/L glucose and 360 g/L), once equilibrium is reached what fraction of the volume will be in solute 1? Solute 2?

A

M1 V1 = M2 V2
Solute 1 = (M1/M2) = 180/270 = 2/3x
Solute 2 = (M1/M2) = 360/270 = 4/3x

29
Q

What is osmotic pressure?

A

Force required to stop osmosis

-Indicates how strongly the solution “draws” H20 into it by osmosis

30
Q

What is osmolality?

A

The concentration of a solution expressed as the total number of solute particles per kilogram

31
Q

What is molarity?

A

The number of moles per liter of solution

32
Q

What is molality?

A

The number of moles of solute per kilogram of solvent

33
Q

What is the plasma osmolality?

A

300 mOsm/L

34
Q

What is the effect of ionization on osmotic pressure?

A

NaCl ionized when dissolved in H2O forms 1 mole of Na+ and 1 mole of Cl- ; thus has a concentration of 2 Osm

35
Q

What is the osmolality of a 0.9% NaCl solution?

A

0.9 g NaCl/100 mL = 9 g/1000 mL = 9 g/1 L = 9 g/1 kg
mol = mass/GFM = 9 g/58.5 g/mol = 0.154 mol (1000) = 154 mmol
m = moles/kg = 0.154 mol/1 kg = 154 mmol –> dissociates into 154 mmol and 154 mmol –> 308 osmosm total

36
Q

What is the osmolality of a 5% glucose solution?

A

5 g/100 mL = 50 g/1000 mL = 50 g/1 kg
mol = mass/GFM = 50 g/180 g/mol = 0.28 mol = 280 mmol
0.28 moles/1 kg = 280 Osm total (glucose does not dissociate in H20)

37
Q

What is tonicity?

A

The effect of a solution on the osmotic movement of H2O

38
Q

What is isotonic?

A

Equal tension to plasma

-RBCs will NOT gain or lose H2O

39
Q

What is hypotonic?

A

Osmotically active solutes in a lower osmolality and osmotic pressure than plasma
-RBC will hemolyse (cell grows)

40
Q

What is hypertonic?

A

Osmotically active solutes in a higher osmolality and osmotic pressure than plasma
-RBC will crenate (cell shrinks)

41
Q

How is plasma osmolality maintained?

A

Osmoreceptors stimulate hypothalamus -> ADH release and thirst is increased

42
Q

What happens if a person is dehydrated?

A

The blood volume decreases meaning the plasma osmolality increases –> this is detected by the hypothalamus –> sends signals to posterior pituitary to secrete ADH (that goes to the kidneys and increases water retention) and sends signals to increase thirst (that increases water intake)

43
Q

What is carrier-mediated transport?

A

Transport across cell membrane by protein carriers

44
Q

What are some characteristics of protein carriers?

A
  • Specificity: interact with specific molecule only
  • Competition: molecules with similar chemical structures compete for carrier site
  • Saturation: carrier sites filled
45
Q

What is transport maximum (Tm)? How does competition affect it?

A

At Tm carriers have become saturated (zero order kinetics); if molecules X and Y compete for the same carrier Tm is lowered

46
Q

Why would glucose show up in the urine?

A

Tm has been reached

47
Q

What is facilitated diffusion?

A

Passive transport (ATP not needed); powered by the thermal energy of the diffusing molecules and involves net transport from the side of higher to the side of lower concentration

48
Q

What is active transport?

A

Requires ATP; movement of molecules and ions against their concentration gradients (low -> high)
-2 types: primary and secondary

49
Q

What is primary active transport?

A

ATP directly required for the function of the carriers

  • Molecule or ion binds to carrier site
  • Binding stimulates phosphorylation (breakdown of ATP)
  • Conformational change moves molecule to other side of membrane
50
Q

What is the Na+/K+ ATP-ase pump?

A

Carrier protein that is also an ATP enzyme that converts ATP to ADP and Pi
-2 K+ in and 3 Na+ out

51
Q

What 7 steps happen in the Na+/K+ ATP-ase pump?

A

1) 3 Na+ ions and ATP bind to carrier protein
2) ATP breaks into ADP and Pi and releases energy
3) Carrier protein changes shape and Na+ are transported across membrane
4) Na+ diffuse away from carrier protein
5) 2 K+ ions bind to carrier protein
6) Phosphate is released
7) Carrier protein changes shape, transporting K+ across cell membrane and K+ diffuse away from carrier protein. The carrier protein can again bind to Na+ and ATP

52
Q

What is secondary active transport?

A

Coupled transport, does not require ATP directly ; energy needed for uphill movement obtained from downhill transport of Na+

53
Q

What is cotransport (symport)?

A

Secondary active transport; molecule or ion moving in the same direction

54
Q

What is countertransport (antiport)?

A

Secondary active transport; molecule or ion is moved in the opposite direction

55
Q

What is SGLT?

A

Sodium Glucose Lag Transporter (co-transport)

  • sodium goes from high -> low
  • glucose goes from low -> high
56
Q

Glucose transport is an example of what type of transport?

A

Co-transport, primary active transport and facilitated diffusion

57
Q

What is bulk transport?

A

Many large molecules are moved at the same time

-exocytosis and endocytosis

58
Q

What is the membrane potential?

A
  • Proteins and phosphates are negatively charged at normal cellular pH
  • These anions attract positively charged cations that can diffuse through the membrane pores
  • Membrane more permeable to K+ than Na+
  • Na+/K+ ATP-ase pump 3 Na+ out for 2 K+ in
  • All contribute to unequal charge across the membrane
59
Q

What effect do the fixed anions have on the distribution of cations?

A

Membrane is negatively charged inside –> attraction for positive ions –> creates an electrochemical gradient (electrical attraction and certain amount of build up of ions)
-The Na+/K+ pumps help facilitate the electrochemical gradient

60
Q

What is the equilibrium potential?

A

Theoretical voltage produced across the membrane if only 1 ion could diffuse through the membrane

61
Q

What is the potential difference?

A

Magnitude of difference in charge on the 2 sides of the membrane
-potential difference of -90 mV if K+ were the only diffusible ion

62
Q

What is the NERST equation?

A

Membrane potential that would exactly balance the diffusion gradient and prevent the net movement of a particular ion

  • Equilibrium potential for K+ = -90 mV
  • Equilibrium potential for Na+ = +65 mV
63
Q

Calculate the NERST equation for K+

A

Electron motive force = E = -nRT log (Ci/Co)
E = -61 log (155/5)
E = -90 mV

64
Q

Calculate the NERST equation for Na+

A 
E = -61 log (10/145)
E = + 65 mV
65
Q

What is the resting membrane potential?

A

The resting membrane potential is less than Ek because some Na+ can also enter the cell –> the slow rate of Na+ efflux is accompanied by slow rate of K+ influx
= -65 mV

Physiology Exam 2 (4 decks)

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