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Foundations of Medicine > Physiology > Flashcards

Physiology Flashcards

1
Q

Who is the father of physiology?

A

Claude Bernard

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2
Q

Why are membranes important?

A

The cell (plasma) membrane forms an outer boundary of every cell
Selectively permeable
Controls the entry of nutrients and exit of waste (and secretory) products
Maintains differences in ion concentration inside and outside the cell
Participates in the joining of cells to form tissues and organs
Enables a cell to respond to changes (signals) in the cell’s environment

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3
Q

What are the two principal constituents of the cell membrane?

A

Lipid and protein

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4
Q

What is the membrane primarily composed by?

A

Phospholipids

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5
Q

What are the components of the head and tail of the phospholipid?

A

Head: Ethanolamine and phosphate
Tail: Glycerol and fatty acid

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6
Q

What are the charges and polarity of both the head and tail of the phospholipid?

A

Head: Negatively charged, polar and hydrophilic.
Tail: Uncharged, non-polar, and hydrophobic.

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7
Q

What role does cholesterol have in the membrane?

A

Cholesterol aids in stiffening the membrane, therefore enforcing its stability. And it can flip easily.

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8
Q

What are six common membrane lipids?

A

Phosphatidylinositol
Phosphatidylserine
Phosphatidylcholine
Sphingomyelin
Galactocerebroside
Cholesterol

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9
Q

The lipid bilayer is ideally suited to separate what?

A

Two aqueous compartments

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10
Q

What is the phospholipid bilayer permeable and impermeable to?

A

-Pure phospholipid bilayer membranes are extremely impermeable to almost any water-soluble substance
E.g. ions, proteins, and sugars are insoluble in the hydrophobic membrane core
-In contrast, small uncharged polar molecules can cross fairly freely
E.g. O2, CO2, NH3 and water itself

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11
Q

What are the three important functions the bilayer forms?

A
  1. It forms the basic structure of the membrane.
  2. Its hydrophobic interior serves as a barrier
    The cell can maintain differences in solute composition and concentrations inside/outside the cell
  3. It is responsible for the fluidity of the membrane
    Enables cells to change shape
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12
Q

What can membrane proteins be regarding the phospholipid membrane?

A

Membrane proteins can belong to either of two broad classes: peripheral or integral

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13
Q

How are membrane proteins attached to the phospholipid membrane?

A

Not embedded within the membrane
Instead, they adhere tightly to the cytoplasmic or extracellular surfaces of the PM

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14
Q

Integral membrane proteins are intimately associated with the lipid bilayer in any of 3 ways:

A
  1. Some proteins span the lipid bilayer once or several times – transmembrane proteins
  2. Some are embedded but do not cross the bilayer
  3. Some are linked to a lipid component of the membrane or a fatty-acid derivative that intercalates into the membrane
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15
Q

Seven functions of integral membrane proteins

A
  1. Ligand-binding receptors
  2. Adhesion molecules
  3. Pores and channels
  4. Carriers
  5. Pumps
  6. Integral membrane proteins can also be enzymes
  7. Integral membrane proteins can participate in intracellular signaling
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16
Q

Example of ligan-binding receptors?

A

Hormone receptors

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17
Q

What are adhesion molecules and what are they important for?

A

Form physical contact with the surrounding extracellular matrix or with cellular neighbors
Important in regulating cell shape, growth, and differentiation, allowing the cell to adapt to its immediate surroundings

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18
Q

Define integrins

A

Cell-matrix adhesion molecules

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19
Q

What do pores and channels do?

A

Serve as conduits that allow water or specific ions to flow passively through the lipid bilayer

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20
Q

What do carriers do?

A

Either facilitate the transport of a specific molecule or couple the transport of a molecule to that of other solutes

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21
Q

What do pumps do?

A

Use the energy that is released through the hydrolysis of ATP to drive the transport of substances into or out of cells against energy gradients

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22
Q

What are Docking-marker acceptors, where can you locate them how does it interact?

A

Located on the inner membrane surface
Interact with secretory vesicles leading to exocytosis of the vesicle contents

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23
Q

What is sugar coating regarding membranes?

A

A small amount of membrane carbohydrate is located on the outer surface of cells.

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24
Q

What are short carbohydrate chains bound to and what do they form?

A

Glycoproteins and glycolipids, forming the glycocalyx

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25
Q

What are the short carbohydrate chains on the outer membrane surface for?

A

Self-identity markers that enable cells to identify and interact with one another

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26
Q

What are the three specialized cell junctions?

A
  1. Tight junctions
  2. Desmosomes
  3. Gap junctions
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27
Q

Two properties that influence whether a particle can permeate the plasma membrane without assistance:

A

Solubility of the particle in lipid
Size of the particle

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28
Q

What are two elements required for movement across a membrane?

A

Pathway and a driving force

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29
Q

What can driving forces be divided into?

A

Passive and Active

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30
Q

Molecules and ions that can penetrate the membrane are passively driven across the membrane by two forces:

A

Diffusion down a concentration gradient, &/or
Movement along an electrical gradient

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31
Q

What is the point of diffusion?

A

Make a balance within both aqueous spaces.

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32
Q

What is Fick’s Law?

A

Fick’s law states that the rate of diffusion of a substance across unit area is proportional to the concentration gradient.

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33
Q

Five factors in addition to the concentration gradient influence the rate of the net diffusion across the membrane and collectively make up Fick’s law of diffusion:

A
  1. The magnitude of the concentration gradient
  2. The surface area of the membrane across which diffusion is taking place
  3. The lipid solubility of the substance
  4. The molecular weight of the substance
  5. The distance through which diffusion must take place
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34
Q

What is Fick’s formula?

A

Q= ΔC x A x P

Q (Net rate of diffusion)
ΔC (Concentration gradient of substance)
A (Surface area of membrane)
P (Permeability)

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35
Q

What two things affect ion movement?

A

Concentration gradient and electrical gradient

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36
Q

How is an electrical gradient formed?

A

A difference in charge between two adjacent areas generates an electrical gradient that promotes the movement of ions toward the area of opposite charge

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37
Q

What are two ion-specific channel proteins?

A

Leak or gated

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38
Q

Both an electrical and a concentration (chemical) gradient may be acting on a particular ion at the same time
True or False?

A

True

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39
Q

What is the net effect of simultaneous electrical and concentration gradients on this ion called?

A

Electrochemical gradient

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40
Q

What does the electrochemical gradient contribute to??

A

The electrical properties of the plasma membrane

41
Q

Define osmosis

A

Osmosis is the net diffusion of water down its own concentration gradient through a selectively permeable membrane. Water moves by osmosis to the area of higher solute concentration

42
Q

What channels does water use during osmosis?

A

Aquaporins

43
Q

Define osmolarity and what are the units.

A

Osmolarity is the concentration of osmotically active particles present in a solution.
osmoles (Osm) of solute per liter (Osm/l or osmol/l)

44
Q

Define tonicity, its three types, and its units

A

Tonicity is the effect a solution has on cell volume.
Iso-, hypo- or hypertonic
Tonicity has no units

45
Q

What is isotonic saline used as?

A

Vehicle for delivery of drugs intravenously.

46
Q

What happens in isotonic conditions?

A

No net movement of water, no change in cell volume

47
Q

What happens in hypotonic conditions?

A

Water diffuses into cells, cell swell.

48
Q

What happens in hypertonic conditions?

A

Water diffuses out of cells, and cells shrink.

49
Q

What are three passive transport mechanisms and what do they all depend on?

A

Diffusion down concentration gradients (simple diffusion)
Movement along electrical gradients (ion channels)
Osmosis
All depend on lipid solubility or ability to fit through specific channels

50
Q

What are two mechanisms for selective transport?

A

Carrier-mediated transport
Vesicular transport

51
Q

What is carrier-mediated transport?

A

Substance binds onto a specific carrier which undergoes a conformational change (shape change) that transports the substance.

52
Q

Three important characteristics determine the kind and amount of material transferred across the membrane with carrier-mediated transport:

A
  1. Specificity
  2. Saturation
  3. Competition
53
Q

Carrier-mediated transport takes two forms:

A

Facilitated diffusion (not requiring energy)
Active transport (requiring energy)

54
Q

Explain facilitated diffusion

A

Facilitated diffusion uses a carrier to facilitate (assist) the transfer of a substance across the membrane ‘downhill’ from high to low concentration.

55
Q

Explain active transport

A

Active transport requires the carrier to expend energy to transfer a substance ‘uphill’ against a concentration gradient.

56
Q

Tell me the four steps of a model for facilitated diffusion

A
  1. Carrier protein takes conformation in which the solute binding site is exposed to the region of higher concentration.
  2. Solute molecule binds to carrier proteins.
  3. Carrier protein changes conformation so that the binding site is exposed to a region of lower concentration.
  4. Transported solute is released and carrier protein returns to conformation in step 1.
57
Q

What are the divisions of active transport, and do they require energy?

A

-Primary active transport (ATP (e.g. Na+-K+ ATPase))
Energy is directly required to move a substance against its concentration gradient.
-Secondary active transport (ion coupled (Na+)
Energy is required, but it is not used directly to produce an ‘uphill’ movement.
The carrier does not split ATP – instead, it moves a molecule ‘uphill’ by using secondhand energy stored in the form of an ion concentration gradient (usually a Na+ gradient)

58
Q

Tell me the five steps of the model for simple active transport.

A
  1. Carrier protein splits ATP into ADP plus phosphate. The phosphate group binds to the carrier, increasing the affinity of its binding site for ions.
  2. Ion to be transported binds to the carrier on the low-concentration side.
  3. In response to ion binding, the carrier changes conformation so that the binding site is exposed to the opposite side of the membrane. The change in shape also reduces the affinity of the site for ions.
  4. Carrier releases ions to the side of higher concentration. The phosphate group is also released.
  5. When the binding site is free, carrier reverts to its original shape
59
Q

Tell me the five steps of the model for simple active transport.

A
  1. Carrier protein splits ATP into ADP plus phosphate. The phosphate group binds to the carrier, increasing the affinity of its binding site for ions.
  2. Ion to be transported binds to the carrier on the low-concentration side.
  3. In response to ion binding, the carrier changes conformation so that the binding site is exposed to the opposite side of the membrane. The change in shape also reduces the affinity of the site for ions.
  4. Carrier releases ions to the side of higher concentration. The phosphate group is also released.
  5. When the binding site is free, the carrier reverts to its original shape
60
Q

Na+-K+ ATPase is a more complicated primary active transporter, where is it found and what does it transport?

A

Found in the plasma membrane of all cells.
Transports 3x Na+ out of the cell for every 2x K+ in.

61
Q

What are the three important roles of the Na+-K+ pump:

A

-Helps establish Na+ and K+ concentration gradients across the plasma membrane of all cells.
-Helps regulate cell volume by controlling the concentration of solutes inside the cell.
-The energy used to drive the pump indirectly serves as the energy source for secondary active transport.

62
Q

Define the secondary active transport

A

The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (typically Na+)

63
Q

Secondary active transport occurs by one of two mechanisms:

A

–Symport (co-transport)
The solute and Na+ move in the same direction.
E.g. glucose absorption at the apical membrane of enterocytes

–Antiport (exchange or countertransport)
The solute and Na+ move in opposite directions (Na+ into, solute out of the cell).
For E.g. cells exchange Na+ and H+ by means of antiport, important in the regulation of intracellular pH.

64
Q

Does the vesicular transport need energy?

A

Requires energy for vesicle formation and movement within the cell (active).

65
Q

The two divisions of vesicular transport

A

Endocytosis and exocytosis

66
Q

Define depolarization and hyperpolarization

A

Depolarization – the membrane potential becomes less negative (or even positive)
Hyperpolarization – the membrane potential becomes more negative

67
Q

Why does ionic movement happen?

A

Due to changes in membrane potential

68
Q

The direction of the change in potential (i.e. depolarization or hyperpolarization) depends on:

A
  1. The direction of movement of the change in potential (Efflux or influx)
  2. The charge carried by the ion (Negative/Positive)
69
Q

Passive movement of an ion through an ion channel is driven by the…

A

Electrochemical gradient for that ion :P

70
Q

Movement of Na+ is a response to what?

A

Opening of cell membranee sodium selected channels

71
Q

The inward current of Na+ occurs due to the following:

A

Both the concentration and the electrical gradient is inward

72
Q

Numerically, what is usually the membrane potential?

A

-70 mV

73
Q

What is the driving force for Na+ influx?

A

(Vm - ENa). When negative inward movement of Na+ occurs

74
Q

The current carried by Na+ (INa) is given by the expression:

A

I(Na)= g(Na) (Vm-E(Na))
Values: Na+ current, Na+ conductance and driving force

75
Q

What is the movement of K+ a response to?

A

Opening of cell membrane potassium-selective channels

76
Q

Why does potassium cause an outward current?

A

The concentration gradient is outward and has an energy that exceeds that of the electrical gradient, which is inward

77
Q

What is the driving force for K+ efflux?

A

Vm-Ek
When positive, outward movement of K+ occurs

78
Q

The current carried by K+ (IK) is given by the expression:

A

Ik= gK (Vm-Ek)
Values: Potassium current, K+ conductance and driving force

79
Q

What are the usual values for ENa and Ek

A

+60 mV and -90 mV

80
Q

What are ion channels?

A

Ion channels are protein complexes spanning the lipid bilayer forming a central pathway that permits the rapid flow of selected ions

81
Q

There are three types of ion channels that are gated by:

A

Membrane voltage – voltage-gated ion channels (VGICs)
Chemical substances – ligand-gated ion channels (LGICs)
Socal stimuli – e.g., mechanical, thermal

82
Q

The ion channels responsible for the action potential in neurons are VGICs; what are they called, and for what stage are they?

A

voltage-activated Na+ channels (Nav) (depolarizing)
voltage-activated K+ channels (Kv) (hyperpolarizing

83
Q

What are action potentials, and how do they propagate?

A

Action potentials are brief electrical signals in which the polarity of the nerve cell membrane is momentarily (about 2 msec) reversed.
Action potentials propagate along nerve cell axons with constant magnitude and velocity (for a given axon), allowing signaling over long distances.

84
Q

How are Voltage-activated Na+ and K+ channels activated and at what speed?

A

Both are activated by membrane depolarization – Na+ channels rapidly; K+ channels with a slight delay

85
Q

Is the activation of the Na+ channel self-limiting?

A

No, the activation of Na+ channels is self-reinforcing – opening a few channels causes further channels to open, causing further depolarization. This is positive feedback

86
Q

Is the activation of the Na+ channel self-limiting?

A

No, the activation of Na+ channels is self-reinforcing – opening a few channels causes further channels to open, causing further depolarization. This is positive feedback.

87
Q

Is the activation of K+ channels self-limiting?

A

Yes, activation of K+ channels is self-limiting – the outward movement of K+ causes repolarization, which turns off the stimulus for opening.
This is negative feedback.

88
Q

What is the refractory period?

A

The refractory period is the time after an action potential is generated, during which the excitable cell cannot produce another action potential. The Na+ channels enter a non-conducting, inactivated state during maintained depolarization.

89
Q

Define the two divisions of the refractory period

A

-Absolute refractory period – no stimulus, however strong, can elicit a second action potential (all Na+ channels inactivated)
-Relative refractory period – a stronger than normal stimulus may elicit a second action potential (mixed population of inactivated and closed channels, plus the membrane is hyperpolarized)

90
Q

Action potentials allow electrical signals to be conducted over large distances without decaying. True or false?

A

Trueeeee

91
Q

What is contiguous conduction?

A

Ions in each neighboring section of the membrane move through their voltage-gated channels. As the action potential moves along the axons, charges change.

92
Q

What is passive conduction?

A

Current conduction by neurons in the absence of action potentials

93
Q

The leakier the axon, the greater the local current spread. True or false?

A

False, less leaky the axon, the greater the local current spread

94
Q

What increases Action Potential conduction velocity?

A

Greater local current spread

95
Q

Explain simply the physical displacement of the action potentials in the axon.

A

1- inactive region ahead of the AP
2- active region
3- inactive region following the AP

96
Q

What are the two strategies to increase passive current spread?

A

-Increase axon diameter (increases current spread)
-Decrease leak of current across the axon

97
Q

How do you decrease the leak of current across the axon?

A

Adding an insulating material – myelin.

98
Q

What cells make myelin?

A

Provided by Schwann cells in the PNS and oligodendrocytes in the CNS

99
Q

Schwann cells and oligodendrocytes are types of what?

A

Macroglia

Foundations of Medicine (18 decks)

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