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Block 1 Week 2 > Principles of Epithelial Transport > Flashcards

Principles of Epithelial Transport Flashcards

1
Q

ECR environment? How does disease effect it?

A

ECF=extracellular fluid

  • rich in Na, poor in K
  • volume & ionic composition constant & stable in healthy people due to homeostatic mechanisms
    • thirst response/kidneys
  • DISEASE can cause malfunction of homeostatic mechanisms
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2
Q

ICF environment? How maintain the ionic gradient?

A

Intracellular Fluid

  • rich in K poor Na
  • continuously differs in ion concentration
  • steep cation gradient which serves as energy source to perform cell functions
  • dissipation of cation gradient happens constantly, but the Na/K pump offsets it
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3
Q

What does the cation gradient provide/help with? What does each gradient do specifically(Na and K)?

A 
-provides energy so the cell can perform variety of functions 
Inward Na gradient:
1)  used to pull AA into cell
2) extrude protons via Na/H exchanger 
3)depolarize membrane potential
4) remove Ca from cell 
5) Bring in salt via Na/salt

Outward K gradient:

1) polarize cell
2) co-transport with chloride to move salt out of the cell

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4
Q

How is the dissipation of the cation gradient fixed?

A

PUMP LEAK HYPOTHESIS

  • dissipation occurs constantly, but the Na/K pump works to offset the cation leaks
  • in steady state: movement of ions through leak pathways is equivalent to the movement of ions via the pump
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5
Q

Volume of a cell and how it changes?

A 
1/3= solid stuff (organelles, solutes etc)
3/4= water
  • from moment to moment, amount of solid doesn’t change but amount of H20 can change remarkably
  • can either dilute or concentrate solutes depending on amount of water in cell at a given time
  • WATER content determines volume of the cell
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6
Q

What does water change/effect in the cellular processes?

A
  • amount of water in cell can dilute/ concentrate its solutes
  • effects kinetic & thermodynamics of every rxt in the cell since changing conc. of enzymes, products & reactants
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7
Q

Osmosis

A
  • passive diffusion of H20 across a semipermeable membrane

- down it’s concentration gradient therefore, moves toward side with MORE solute

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8
Q

When will osmosis stop? When will the water stop moving?

A
  • will move until conc. of water solutes on both sides is equal
  • until osmotic pressure due to the hydrostatic gradient is equal
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9
Q

Why does free water move toward the side with MORE solute?

A

-the more solute that is present, the more free water molecules are displaced. Therefore the conc. of water molecules decreases to make room for the solute particles

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10
Q

What does it mean when say osmosis is colligative?

A
  • that it is based on the ratio of the number of solute to solvent particles in solution
  • NOT dependent on the nature of the particles (size, charge, polarity etc.)
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11
Q

osmotic pressure

A

the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis,

-when hydrostatic pressure reaches a point where no more water can flow into a chamber

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12
Q

What happens if have a fixed environment? Like plant cell that can’t expand due to rigid cell wall?

A

-as osmosis adds to the cell the hydrostatic pressure increases, volume stays the same

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13
Q

How do we oppose osmosis?

A

-by keeping the volume fixed so we increase hydrostatic pressure until it reaches its maximum point and no more water can flow in (this= the OSMOTIC pressure)

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14
Q

How does osmosis alter animal cells?

A
  • animal cells are flexible
  • so osmosis alters internal VOLUME not internal PRESSURE
  • osmotic gradient wouldn’t last very long
  • no hydrostatic pressure gradient would ever exist
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15
Q

why osmotic gradient not last a long time in animal cells?

A
  • because H2O is freely permeable into animal cells via aquaporins
  • so any conc. gradient or addition of solute would be rapidly adjusted by the flow of H2O into/out of the cell
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16
Q

What causes a cell to swell (hyperosmotic) and shrink (hyposmotic)?

A

changes in external osmolarity (fluid outside the cell)

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17
Q

Hyposomotic?

A

-if add H2O outside the cell, will cause H20 conc to increase (diluting solute particles), H2O will flow down gradient into the cell via osmosis, causing it to swell

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18
Q

Isosmotic?

A

normal osmotic pressure, no H20 gradient across membrane

  • same osmotic pressure into the cell and outside
  • 290mOsm osmolarity is isosmotic for animal cells
19
Q

Hyperosmotic?

A

-if add SOLUTE to the cell medium, will decrease the H2O conc; H2O will flow DOWN gradient from cell –> to ECF causing cell to shrink

20
Q

what is osmolarity of mammal fluids normally? Cation vs anion content?

A

~290mOsm

  • cation in human plasma= 145mmolar; anion= 145mmolar
    • together= 290mOsm
  • need SAME # of anions and cations due to net neutrality law
21
Q

How check if any solution is isosmotic?

A

-check osmotic pressure, if its 290mOsm then is isosmotic

22
Q

Isotonic vs. isosmotic?

A
  • tonic is whether the salt conc. is the same in solution as is in body
  • osmotic: means the OSMOTIC Pressure is the same inside vs outside the cell
23
Q

Isotonic?

A
  • any solution that causes cell to neither shrink/swell

- any solution that has equal solute inside vs outside cell

24
Q

Why is something (like urea/ethanol) hypotonic?

A
  • Hypotonic means causes the cell to swell
  • because urea is permeable to the membrane, will continuously enter the cell down its gradient.
  • H2O follows the urea…diluting it…causes MORE urea to enter and MORE water to follow
  • eventually volume gets too much–> cell lysis
25
Q

What contributes to extracellular tonicity?

A
  • ONLY non-penetrating solutes effect ECF tonicity

- penetrating solutes effect ICF tonicity

26
Q

Tonicity vs osmosis?

A
  • osmosis is about osmotic pressure, movement of water down gradient due to external solute conc.
  • tonicity is about movement of solutes into the cell w/ water NOT due to osmosis which causes cell to shrink/swell
27
Q

What happens when sweat 1L?

A

1) sweat=pure H20 from ECF
- whenever loose/gain H2O ALWAYS from ECF
2) have increased Na conc. in ECF increasing ECF osmotic pressure & tonicity
3) osmotic gradient H20 moves ICF–>ECF
4) cells shrink

28
Q

How do changes to internal osmolarity cause cells to swell/shrink?

A

1) increase Intracellular solute, H20 will flow in
2) decrease intracellular solute, H20 will flow out
* only has osmotic pressure gradient for short time since aquaporins allow rapid movement of h20 into cell to alleviate the pressure gradient*

29
Q

Threat of external osmotic changes?

A
  • minor, kidneys & thirst good at regulating osmolarity of ECF
  • rarely experience large external osmotic changes
  • exceptions= diseases like diabetes or dehydration
30
Q

Threat of internal osmotic changes?

A
  • VERY high, very dangerous
  • cell has mechanisms to prevent it
  • dangerous because the processes that could affect intracellular solute concentrations are really important for cell life & shouldn’t be malfunctioning
31
Q

What is cell volume regulation?

A

-mechanism cells use to regulate their volume (tonicity)

32
Q

RBC in HYPOTONIC SOLUTION (3 steps)

A

RBC in HYPOTONIC SOLUTION:

1) osmotic phase: cell swell’s as water rushing in to dilute solute con. inside cell
2) Regulation Volume decrease phase: cell actively releases solute to remove the extra water (vol decrease)
3) OVERSHOOT phase: if transfer back to native medium (isotonic) cell volume will be too shrunken since removing solute & H20 from hypotonic medium experience

33
Q

RBC in HYPERTONIC SOLUTION (3 steps):

A

1) Osmosis phase: lots of solute outside, so water rushes out of cell (shrivels, vol dec.)
2) Volume Regulation Increase: cell takes up solute + H20 to regain size
3) Overshoot: put back in normal medium, have overshot healthy mark, so now too big need to loose solute and H20 to get to normal size

34
Q

How vol. regulate up and down?

A

Cell shrinkage activates:
1) transporters NaKCC1, H/Na and HCO/Cl1 to uptake solutes

Cell swelling activates:
1) K & Cl channels
2) K/Cl co-transporter
both remove solutes and push water out of cell

35
Q

how does cell perceive change in volume?

A
  • series of protein kinases that operate in a cascade

- each is sensitve to subtle changes in cel volume

36
Q

Epithelial functions?

A

1) Barrier: body from external world
2) Regulate composition & vol. of body compartments (make solute gradients/ aiborsob or secrete fluid)
3) metabolism via enzymes on cell surface
4) transmit luminal signals to the body

37
Q

kidney nephron & gut epithelium?

A
  • similar but different systems
    1) both epithelial cell’s absorb, solutes, water and are highly permeable in early part of system, (LEAKY EPITHELIUM) then slows down a lot at end (TIGHT Epithelium)
    2) Tansepithelial gradients & voltage is opposite, tight at first then Leaky
38
Q

How get epithelial tight or leaky?

A
  • is dependent on their tight junctions and how tight they are
  • the epithelial forms defines function
39
Q

Kidney nephron Proximal tubule?

A
  • rapid isosmotic absorption
  • has surface microvilli that amplify absorptive surface
  • tons of mito; need ATP to absorb solute
  • loose tight junctions, beginning of nephron*
40
Q

Thin Descending limb

A
  • no active secretions/ absorption
  • water permeable tubule only
  • very thin epithelial cells, no mito since needs no energy
  • no microvilli/ surface amplification
  • medium tight junction, middle of nephron*
41
Q

Distal tubulle

A
  • slow, powerful absorption since have a lot of time w/ this tubule
  • slow, concentrated, active transport
  • lots of mito. is energetically exspensive
  • few microvilli since not absorbing H2O
  • transports across gradient, since absorbing last of the nutrients, very small amounted absolved here

tight tight junctions…at end of nephron

42
Q

What need to have functional epithelium?

A
  1. Transport pathways (kinetics); move solute across epithelium
  2. Driving force to make transport directional (thermodynamics); needs to be energetically feasible
43
Q

How epithelial cell solve problems?

A
  1. Places diff transporters in apical and basal lateral membranes
  2. energy requiring step is the first in the process, which then drives the process in it’s entirety
44
Q

apical vs basal lateral membrane?

A
  • apical= faces toward ECF (lumen
  • basal membrane faces toward ICF

-both border inside of the epithelial cell

Block 1 Week 2 (9 decks)

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