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Human Physiology 1 > Unit 2b: Cell Membrane Dynamics > Flashcards

Unit 2b: Cell Membrane Dynamics Flashcards

1
Q

intracellular fluid (ICF

A

2/3 of fluid in the body

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2
Q

Extracellular fluids (ECF

A

1/3 of the fluid in the body

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3
Q

Interstitial fluid (ISF)

A

ECF
– surrounds the cells of a tissue; makes
up 75% of ECF volume

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4
Q

Intravascular fluid (IVF)

A

– includes blood plasma and lymph which make up 25% of ECF volume

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5
Q

All body fluids are

A

a solution consisting of a solvent (water) that contains solutes (ions, nutrients, gases, proteins, wastes
like urea, etc)

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6
Q

osmotic equilibrium

A

ECF and ICF are in this

meaning there is no
net movement of water because the two compartments have
the same concentration of solutes.

The concentration of
solutes is equivalent to a 0.9% NaCl solution, or 290 mOsm

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7
Q

How are the ECF and ICF in a chemical and electrical disequilibrium?

A

While the overall concentration is equal between
compartments, the composition and proportion of
different solutes is NOT the same

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8
Q

Which compartment has the highest concentration of protein? In which
compartment are proteins absent?

A

highest= blood plasma and ICF
ISF= lowest

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9
Q

concentration gradients

A

, some solutes are more concentrated in
certain compartments than others. This sets up

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10
Q

What does it mean for solutes to “ move down their concentration gradient”

A

from an area of high
concentration to an area of low concentration

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11
Q

What does it mean for solutes to “ move against their concentration”

A

from an area of
low concentration to an area of high concentration

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12
Q

Passive processes

A

move solute or solvent molecules
down their concentration gradient until equilibrium is
reached and do not require energy.

For example
moving Na+ from the ECF into the ICF; or movement of
water molecules

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13
Q

Describe what net movement means

A

molecules cross a
semipermeable membrane in both directions, but overall more are moving from the area on the left (high concentration) to the area on
the right (low concentration).

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14
Q

Active processe

A

move solute molecules against their
concentration gradients or move large molecules that
would otherwise be unable to cross the membrane
(vesicular transport).

All active transport processes require
the use of energy, which is usually obtained from ATP.

Ø For example moving Na+ from the ICF into the ECF.
Ø Na+ has a low concentration (15 mM) in the ICF, and a high
concentration (145 mM) in the ECF. In order to move Na+
against its concentration gradient, energy is required.

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15
Q

Describe the relative concentrations of key substances (ions, etc.) in the plasma, interstitial fluid, and cytoplasm inside of a cell

A

Blood plasma= high Na+ low K+ high Cl- high protein high HCO3-

ICF= low Na+ high K+ low Cl- high protein low HCO3-

ISF= high Na+ low K+ high Cl- low protein high HCO3-

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16
Q

List what is able to freely pass thru the membrane

A

hydrophobic lipid soluble molecules small polar molecules

ex; o2 co2 water urea

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17
Q

List what isn’t able to freely pass thru the membrane

A

large polar molecules; glc proteins amino acids

charged ions; Na+ K+ Cl-

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18
Q

How do large polar molecules and charged ion enter the cell?

A

require transport proteins

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19
Q

Name the types of transport proteins

A

a. channel proteins

b. carrier proteins

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20
Q

channel proteins

A

Ø is a water filled pore that can be open to both sides.

Ø each channel protein is specific for a particular solute (e.g. Na+
channel, K+ channel, .etc).

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21
Q

aquaporins

A

Channels specific for water

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22
Q

List the different types of channel proteins

A
  1. open channels
  2. gated channels
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23
Q

Open channels (pores)

A

always open (like a doorway with no
door)

Also called “leak channels”, as they allow the solute they
are specific for to continuously leak into/out of the cell

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24
Q

Gated channels

A

can open and close in response to a stimulus
(signal). Each gated channel type has a specific stimulus:

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25
Q

Describe the different types of gated channels

A

i. Chemically gated channels – open in response to a
chemical signal (e.g. a hormone or neurotransmitter)

ii. Voltage-gated channels – open in response to to a
change in the electrical state of the cell.

iii. Mechanically gated channels – respond to physical forces
(temperature or pressure

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26
Q

Carrier proteins

A

Never form an open channel between the ECF and ICF. Are open
to one side at time.

Ø Solute enters carrier protein and binds to it causing a
conformational change (change in protein shape) that cause the
protein to close on one side and open on the other. The solute is
then released

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27
Q

List and describe the different types of carrier proteins

A

a. Uniport – transport only one type of solute e.g. glucose transporters (GLUT) in red blood cells.

b. Symport – transports 2 or more types of solute in the same direction. E.g. Na+/glucose transporters (SGLT) in cells of the
small intestine that absorb glucose from the digestive tract.

c. Antiport – transports two or more types of solute in the
opposite directions. E.g. Na+/K+ - ATPase pump – carries 3 Na+ out of the cell and 2 K+ into the cell.

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28
Q

Osmosis

A

passive process

Movement of water molecules (solvent) down
their own concentration gradient due to kinetic
energy of water molecules.

Ø From an area of high [H2O] (lots of water molecules) to an an area of low [H2O] (few water molecules)

Adding solutes to pure water lowers the
concentration of water molecules. So the more
solute in a solution the less concentrated the water is
in that solution.

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29
Q

How does H20 get across the cell membrane

A

Movement of water molecules occurs directly
across the cell membrane OR through cell
membrane protein channels call aquaporins

30
Q

osmotic pressure

A

Movement of water can cause pressure

The pressure/force required to stop the flow of water
from one solution/compartment to another

31
Q

Osmolarity

A

(mOsm/ L)

The concentration of a solution based on the total number of solute particles
per liter (includes both penetrating and non-penetrating solutes)

32
Q

What is a penetrating solute vs a non penetrating solute?

A

Penetrating solutes – are capable of freely crossing cell membranes
Ø Small, polar and non-polar
molecules
Ø E.g. urea, glycerol, ethanol

Non-penetrating solutes – cannot freely cross cell membranes
Ø Ions and larger polar (hydrophilic)
molecules that cannot cross the hydrophobic region of the
phospholipid bilayer
Ø E.g. Na+, glucose, amino acids

33
Q

Isosmotic

A

have the same osmolarity as another solution

34
Q

hyperosmotic

A

have a higher osmolarity than another solution

35
Q

Hypoosmotic

A

have a lower osmolarity than another solution

36
Q

crenation

A

Movement of water out of the cell causes it to shrink/shrivel

37
Q

tonicity

A

how a solution will affect the volume of a cell

compares a solution to a cell’s intracellular
solution.

Specifically tells you whether or not a cell will swell or shrink

Depends ONLY on the concentration of non-
penetrating solutes

  • Water will always go to high non penetrating solute
38
Q

Hypertonic

A

causes cell to lose water and shrink

( higher concentration of water inside the cell than outside and lower concentration of non penetrating solutes)

39
Q

Isotonic

A

does not change cell shape (no net osmosis)

40
Q

Hypotonic

A

causes cell to swell and may burst.

(higher concentration of water outside the cell than inside and lower concentration of non penetrating solutes outside)

41
Q

Hyposmotic solutions are always…..

A

hypotonic

42
Q

What is diffusion?

A

Movement of solutes down a concentration gradient
(from an area of high concentration to an area of low concentration)

Ø Does not require energy.

Ø Occurs as a result of the kinetic energy (random motion) of
ions/molecules.

Ø Process continues until equilibrium is reached.

Ø Fast over short distances, slow over long distances.
Ø The time it takes to get from A to B is a “distance squared”
relationship. If the distance travelled doubles from 1 to 2, then the
time it takes for diffusion to occur quadruples from 1 to 4 (=2^2 )

Ø Rate of diffusion is faster at high temperatures (increases kinetic
energy/random motion of molecules)

Ø Rate of diffusion is slower across a membrane

43
Q

List the different types of diffusion

A

simple diffusion
facilitated diffusion

44
Q

simple diffusion

A

molecules pass directly through the phospholipid bilayer

  • lipophilic substances can pass right thru
45
Q

What does Fick’s Law of Diffusion say

A

the diffusion rate increases with increasing SA concentration gradient and mem. permeability

46
Q

i

A

a. Surface area of membrane: ↑ surface area = ↑ rate of diffusion
(basically there is more space over which diffusion can occur)

b. Concentration gradient: ↑ gradient = ↑ rate of diffusion
Ø the larger the gradient the more molecules will move
into/out of the cell in an attempt to establish equilibrium

47
Q

What does the permeability of the cell membrane to the molecule depend on?

A

i. Size (and shape) of molecules. ↑ molecular size = ↓ permeability

ii. Lipid solubility of the molecule. ↑ lipid solubility= ↑
permeability

iii. Composition of the membrane
Ø Relative proportions and types of phospholipids,
sphingolipids affect rate as does the amount of
cholesterol.
Ø For example ↑ cholesterol = ↓ permeability
(cholesterol gets in between fatty acid tails and
blocks movement of molecules through the
membrane)

48
Q

Facilitated diffusion

A

protein mediated transport

Ø Movement of a molecule across the cell membrane via a channel protein or a
carrier protein.

The protein facilitates diffusion of the solute down its concentration gradient.

ØDoes not require ATP

ØThis process alone cannot accumulate a solute against a concentration gradient

49
Q

channel-mediated facilitated diffusion

A

Ø uses a channel protein to move the solute down its concentration gradient.
Ø E.g. Na+ leak channels

50
Q

Carrier-mediated facilitated diffusion

A

Ø uses a carrier protein to move the solute down its concentration gradient
.
Ø E.g. facilitated diffusion of glucose into skeletal muscle or liver cells via glucose
transporters (GLUT)

Ø Low concentration of glucose inside of cell are maintained because any glucose entering the cell is immediately converted to glucose-6-phosphate. Prevents equilibrium from being reached.

51
Q

Primary Active Transport

A

Directly uses ATP (i.e. the transport protein that breaks
down ATP is the same protein that will transport the
solute)

b. Establishes concentration gradients.

c. Carrier proteins involved are sometimes called pump

52
Q

Give an example of active transport

A

Na+/K+ ATPase is the most widely known example (found in all cells).

Ø Pumps 3 Na+ out of the cell and 2 K+ into the cell (antiport).

  • CREATES THE NA+ AND K+ GRADIENT THAT EXISTS BETWEEN ECF AND ICF

Ø Carrier protein hydrolyzes ATP and undergoes several
conformational changes

53
Q

Secondary Active Transport

A

Indirectly uses ATP

Ø the transport protein that breaks down ATP creates a concentration
gradient of one solute (solute A).

Ø The kinetic energy stored in this concentration gradient is then used to
move another solute (solute B) against its concentration gradient using a
separate carrier protein.

54
Q

Give an ex of 2 active transport

A

Example: Na+-glucose secondary active transporter (SGLT-protein)
used to absorb glucose from lumen of intestine into intestinal cells.

i. Na+ binds to SGLT carrier protein (moving down its concentration gradient)

ii. Na+ binding creates a high-affinity site for glucose

iii. Glucose binding changes the conformation of the protein so that protein is
open to the inside of the cell.

iv. Na+ is released moving down its concentration gradient

v. Release causes decreases affinity of glucose binding site

vi. Glucose is released into the cytosl

55
Q

Specificity

A

The transporter is specific for a particular
substrate/solute or a particular group of related substrates/solutes

ØE.g. GLUT proteins are specific for 6-carbon sugars, with a preference for
glucose (but can also move galactose and fructose

56
Q

Competition

A

several substrates/solutes compete for the binding
sites on the carrier. This reduces the transport rate.

E.g. glucose and
galactose compete for the same binding sites, so when both are
present, the transport of glucose decreases.

Some competitors are
not transported across the membrane, but simply block the binding
site of the preferred solute (competitive inhibitor)

57
Q

Saturation

A

if there are not enough carriers for the amount of
substrate/solute, the binding sites become saturated

At this point the
rate of transport cannot increase with any further increase in
substrate/solute concentration and so a transport maximum is
reached

ØCells can avoid reaching the transport maximum by building new protein
carriers and inserting them in the membrane.

ØE.g. Insulin acts on muscle cells to increase the number of GLUT4 protein
carriers in their membranes

58
Q

List the different types of active transport

A

primary
secondary
vesicular

59
Q

Vesicular transport

A

Used for large molecules that cannot be transported by membrane
channels or carriers

60
Q

Phagocytosis

A

movement of a very large particle (e.g. bacterium) into
the cell in a large vesicle. ”Cell-eating”

Ø Cell uses cytoskeleton (microfilaments made of actin) and myosin motor
proteins to extend the cell membrane and wrap it around the particle.

Creates a membrane bound space within the cell called a phagosome

Ø E.g. a white blood cell surrounding a bacterium

61
Q

Endocytosis

A

movement of large particles into the cell in small vesicles

Ø Cell membrane surface indents and forms vesicles

62
Q

Pinocytosis

A

a on-selective form of endocytosis (cell takes in all particles – water and solutes – in the area where the vesicle forms). “Cell-drinking”.

63
Q

Exocytosis

A

movement of large particles OUT of the cell in small
vesicles

Ø Intracellular vesicles move to membrane and merge with it (vescicle
membrane becomes part of cell membrane,; vesicle contents exit the cell).

Ø Transport of large lipophobic molecules (e.g. some proteins)

Ø Requires ATP

Ø Usually triggered by an increase in cytosolic Ca++ concentration

64
Q

Absorption

A

transport from the outside of the body to the
inside.

65
Q

Secretion

A

transport from the inside of the body to the outside

66
Q

Apical surface

A

f aces the outside of the body (e.g. the
lumen of the intestine or the lumen of a kidney tubule
(nephron)).

Common location for SLGT proteins in intestinal
cells.

67
Q

Basolateral surface/membrane

A

aces the ISF,. Common
location for Na+/K+ ATPase pumps

68
Q

Paracellular transport

A

Through junctions between adjacent cells

69
Q

Transcellular transport

A

Through cells themselves – substance being absorbed or secreted
must pass through two membranes

Ø Involves a combination of active and passive transport processes

70
Q

Describe transcellular transport of glucose and Na+, including direction of movement, relevant membrane proteins, additional ions, and concentration gradients.

A

a. A Na+/Glucose symporter (SGLUT) in the apical membrane that
moves glucose into the cell using the concentration gradient for Na+
(secondary active transport).

b. GLUT transporter that transports glucose out of the cell into the ECF
(first into the ISF, then into the plasma) using carrier mediated
facilitated diffusion (passive).

c. Na+/K+ ATPase pump in the basolateral membrane that pumps Na+
out of the cell in exchange for K+, thereby keeping [Na+] low inside
the cell (allows for (a) to keep happening). – primary active transport

Human Physiology 1 (16 decks)

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