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FM1010 Physiology > Transport Across Cell Membranes > Flashcards

Transport Across Cell Membranes Flashcards

1
Q

How does glucose enter the bloodstream?

A

Leave intestine, enters blood, crosses 4 lipid membranes and interstitial space

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2
Q

What determines whether a molecule/ion/gas will cross the cell membrane?

A

Chemical gradient
Electrical gradient
Permeability

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3
Q

What are the forms of passive transport?

A

Simple diffusion
Simple diffusion through protein channels
Facilitated diffusion

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4
Q

What passes through simple diffusion?

A

Nonpolar molecules

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5
Q

What passes through simple diffusion through protein channels?

A

Inorganic ions and water

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6
Q

What passes through facilitated diffusion?

A

Small organic molecules
Glucose

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7
Q

Explain Brownian Motion.

A

Molecules of a solution are in a constant state of motion as a result of their thermal energy

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8
Q

How do gated channels open when closed?

A

Chemical, mechanical and electrical signals

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9
Q

According to Fick’s Law of Diffusion, what is diffusion rate proportional to?

A

Concentration gradientmembrane permeabilitysurface area/membrane thickness

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10
Q

What is membrane permeability proportional to?

A

Lipid solubility/molecular size

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11
Q

What factors affect the rate of diffusion through cell membranes?

A

Lipid solubility
Molecular size
Cell membrane thickness
Concentration gradient
Membrane surface area
Composition of lipid layer

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12
Q

How do ions passively move through channels?

A

Channels form pores in membranes
Specific for single substance
Flux of ions is passive and is dictated by concentration gradient

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13
Q

How do uniporters work?

A

Bind and transport molecules of one type down concentration gradient
Regulated by insertion/removal of uniporter from membrane

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14
Q

Why does glucose use a transporter rather than a channel?

A

Charge, size and shape
Glucose channel would allow movement of other ions and water
Loss of selectively permeable nature of cell membrane

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15
Q

What is primary active transport?

A

Transport by ion pumps and is ATP dependent

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16
Q

What is secondary active transport?

A

Symporters and antiporters
Uses energy stored in concentration gradients by primary active transport

17
Q

What is the osmolarity of plasma?

A

150 mM Na+
5mM K+
2mM Ca++
130mM other solutes

18
Q

How do you calculate osmolarity in biological fluids?

A

Measure depression of freezing point - affected by total concentration of solution
One mole of solute depresses the freezing points of water by 1.86oC
Depression in freezing point/-1.86 = x Osm = 1000x mOsm

19
Q

What is the solute composition of ECF?

A

150mM Na+
5mM K+
2mM Ca++

20
Q

What is the solute composition of ICF?

A

10mM Na+
150mM K+
0.0004 mM Ca++

21
Q

Is tonicity or osmolarity more physiologically relevant and why?

A

Tonicity as it accounts for cell membrane permeability

22
Q

What is osmolality?

A

The number of solute particles in 1kg of solvent

23
Q

In the case of dehydration, how is blood osmolality regulated?

A

Blood volume decrease and plasma osmolality increase
Osmoreceptors are activated by this increase
Thirst is stimulated, releasing vasopressin
Water retention promoted

24
Q

How does glucose cross epithelial cells and enter interstitial space?

A

ICF [Na+] is reduced by the Na+ pump on the basolateral membrane
Low [Na+] creates a gradient for Na+ to enter, but there are no suitable channels on apical membrane
Na+/Glu symporters harness the energy from Na+ gradient to allow Na+ and glucose to enter
Glucose leaves the basolateral membrane using a glucose uniporter

25
Q

What must be in place on epithelia to make glucose enter blood?

A

Sodium pump must be on basolateral membrane
Na/Glu symporter must be on apical membrane
Glucose uniporter must be on basolateral membrane

26
Q

How do antiporters and symporters move molecules through the plasma membrane?

A

Uses energy stored in concentration gradients established by primary active transport

27
Q

What does the route of water in transport through epithelia depend on?

A

Type of epithelia
Location within the body

28
Q

What is the paracellular pathway of water transport?

A

Leaky tight junctions
Requires osmotic gradient, but essentially a constitutive process

29
Q

How does absorption work?

A

Na+ pump extrudes Na+ via basolateral membrane
Na+/Glu symporter allows Na+ to cross apical membrane
Na+ is pumped out of basolateral membrane and glucose leaves via uniporter

30
Q

How is water absorbed into a cell?

A

Uses the Na+/Glu movement which creates a large osmotic gradient across the cell
Water moves paracellularly from lumen to interstitial space

31
Q

How does oral rehydration therapy work?

A

Increased interstitial fluid [Na+] is required for reabsorption of water
Glucose accelerates absorption of solute and water

32
Q

How is secretion of H2O work?

A

Opposite of absorption
Export Cl-
H2O and Na+ will follow

FM1010 Physiology (12 decks)

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