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Guyton > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

Higher intra/extracellular?
Sodium, potassium, chloride, phosphate, protein

A

Intra - potassium, phosphate, protein
Extra - Sodium, chloride

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2
Q

What type of molecules can diffuse freely through the cell membrane?

A

Lipid

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3
Q

Name examples of substances that dissolve directly through the lipid bilayer (4)

A

Oxygen, nitrogen, C02 and alcohols

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4
Q

How do simple and facilitated diffusion compare/contrast?

A

Simple diffusion dependent on lipid solubility of substance, linear relationship with concentration
Facilitated diffusion depends on Vmax of substance, normally faster initially, then plateaus - limited by maximum rate of conformational change of carrier protein

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5
Q

What is the formula for net diffusion?

A

Net diffusion is proportional to the concentration of a substance outside a membrane, minus the concentration of the substance inside the membrane

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6
Q

What is the Nernst potential?

A

The electrical difference that will balance a given concentration difference of univalent ions at normal body temperature

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7
Q

What is the Nernst equation?

A

EMF(mV) = +/-(61/z) x (logC1/C2)
z = electrical charge of ion

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8
Q

What factors effect net diffusion?

A

Concentration, electrical potential, pressure

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9
Q

What determines osmotic pressure?

A

The number of particles per unit volume

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10
Q

How does the Na-K pump work? What is it’s main function?

A

3xNa+ pumped out of cell in exchange for 2xK+
Regulates cell volume

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11
Q

Describe the electrogenic nature of the Na-K pump

A

Because 3 Na and removed from the cell in exchange for 2 K+, there is a net positivity outside the cell and negativity inside the cell

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12
Q

How does calcium concentration compare inside/outside the cell? How is it maintained?

A

Intracellular calcium concentration very low
2 calcium pumps, one pumps calcium outside the cell, the other pumps into intracellular organelles (SR in muscle, mitochondria other cells)

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13
Q

Name 2 examples of primary active transport of hydrogen ions?

A

Gastric glands of the stomach
Late distal tubules and cortical collecting ducts in kidneys (intercalated cells)

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14
Q

If it takes 1400 calories to concentrate 1 osmole of a substance 10-fold, how much would be needed to concentrate it to (a) 100-fold and (b) 1000-fold?

A

a) 2800
b) 4200

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15
Q

What is the resting membrane potential of large nerves?

A

-70mV

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16
Q

What factors contribute to the negative resting potential of cells?

A

Increased permeability of cell membrane to K+, allows K+ to leak out - main contributor
The 3Na-2K pump - more sodium removed from cell than potassium in

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17
Q

What are the stages of a neuron action potential?

A

Resting stage
Depolarisation - voltage-gated sodium channels open, membrane becomes permeable to sodium ions, flood in and depolarisation
Repolarisation - sodium channels close, voltage-gated potassium channels open, potassium moves out, repolarisation

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18
Q

Describe the opening, closing and re-opening of voltage-gated Na channels

A

When resting membrane potential becomes less negative, channel is activated. The same increase in voltage causes inactivation a few seconds later
Channel will not re-open until membrane potential returns to near the original level

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19
Q

Describe the opening of the voltage-gated potassium channels

A

Activated when membrane potential rises, however, slight delay so open as sodium channels close

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20
Q

What is the role of calcium in the generation of an action potential?

A

Voltage-gated slow calcium channels - contribute to depolarisation, produce more sustained depolarisation

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21
Q

Where are calcium channels most numerous?

A

Smooth muscle and cardiac muscle

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22
Q

How does the concentration of calcium ions in the ECF effect depolarisation?

A

When there is a deficit of Ca++, sodium channels are opened by smaller increase in membrane potential

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23
Q

Which cells produce myelin?

A

Schwann cells

24
Q

What is the name for the notches in myelin?

A

Nodes on Ranvier

25
Q

What is the function of the nodes of Ranvier and what are the benefits (2)?

A

Allow saltatory conduction
1 - increased velocity of nerve transmission
2 - requires less energy

26
Q

Describe the microscopic structure of skeletal muscle

A

Light bands - actin only - I bands
Dark bands - actin and myosin - A bands
Z disks - actin attach
Region between Z disks = sarcomere
Titin - maintains side-by side relationship of actin/myosin
Space between myofibrils filled with sarcoplasm

27
Q

What is the content of the sarcoplasm?

A

K+, Mg++, PO4-, mitochondria

28
Q

Describe the general mechanism of muscle contraction

A

Action potential travels along motor nerve
ACh secreted
ACh acts on muscle fibre membrane - opens ACh-gated cation channels - Na influx => action potential
Action potential causes sarcoplasmic reticulum to release Ca++

29
Q

Describe the structure of myosin

A

6 polypeptide chains, 2 heavy, 4 light
Heavy chains wrap around each other to form helix, ends folded into head
Light chains form part of head
Myosin molecules bundled together with a twisted axis

30
Q

Describe the structure of actin

A

Backbone - double stranded F-actin, each strand polymerised G-actin
Each G actin molecule has ADP attached - active site for cross bridge interaction
Tropomyosin - wrapped around F actin - lie on top of binding sites in resting state
Troponin - TI - affinity for actin
- TT - affinity for tropomyosin
- TC - affinity for Ca++

31
Q

What activates actin?

A

Ca++

32
Q

Describe the relationship of ATP/ADP and the power stroke of the myosin head

A

ATP binds myosin head - ATPase - ADP + PO4
Binds exposed actin site - power stroke, ADP released
ATP binding causes myosin head detachment
ATP cleaved - head re-cocked

33
Q

What are the 3 sources of energy for muscle contraction?
Which of them need O2
Which is the main contributor to long term muscle contraction?

A

1 - phosphocreatine (O2)
2 - glycolysis
3 - oxidative metabolism (O2) (MAIN CONTRIBUTOR)

34
Q

What are the features of slow muscle fibres?

A

Small, small nerve fibres, extensive blood supply, lots of mitochondria, large amounts of myoglobin

35
Q

Describe ACh secretion in the NMJ

A

Action potential
Voltage-gated Ca++ channels open
Ca++ influx
Ca-calmodulin-dependent protein kinase activation
Phosphorylation of synapsin proteins (anchor ACh vesicles)
Free ACh vesicles dock at release sites and empty via exocytosis

36
Q

What ions are transmitted through ACh channels?

A

Positive only (strong negative charge in channel)
Sodium flows most - negative charge inside cell pulls in

37
Q

How/where is ACh formed?

A

Vesicles formed in Golgi
ACh formed in cytoplasm, immediately transported into vesicles

38
Q

What is ACh split to by acetylcholinesterase? What happens to the substances?

A

Acetate + choline
Choline actively reabsorbed to form more ACh

39
Q

How are vesicles formed for repeated NMJ transmission?

A

After each action potential coated pits appear (formed by contractile proteins - clarithrin) and break away to form new vesicles

40
Q

What is the MOA of neostigmine?

A

Inactivates acetylcholinesterase

41
Q

What is the pathophysiology of myasthenia gravis?

A

Autoantibodies produced that block or destroy ACh-r

42
Q

In what 3 ways do action potentials in skeletal muscle differ from in neurone?

A

Lower resting potential (-80-90mV)
Longer duration
Slower velocity of conduction

43
Q

How do action potentials spread across muscle fibres?

A

Across surface, penetration through transverse (T) tubules

44
Q

How does an action potential lead to calcium release in a muscle fibre?

A

Action potential sensed by dihydropyridine receptor, linked to calcium release channel (ryanodine receptor channel) in the sarcoplasmic reticulum

45
Q

How is calcium concentration in the sarcoplasmic reticulum achieved?

A

SERCA pump - constantly active
Calcium-binding protein in SR - calsequestrin

46
Q

What is the MOA of dantrolene?

A

Antagonises ryanodine receptor, inhibits calcium release from the SR

47
Q

What are the two types of smooth muscle?

A

Multi-unit - eg cilia/iris
Unitary - most viscera in body

48
Q

What is the main difference between smooth and skeletal muscle?

A

No troponin complex in smooth

49
Q

Briefly, how are smooth muscle fibres organised?

A

Actin filaments connected to dense bodies, with myosin fibres interspersed between

50
Q

What are 6 differences between smooth muscle contraction and skeletal?

A

Slow cycling of myosin cross-bridges
Low energy requirement
Slow onset
Greater force of contraction
Latch mechanism
Stress-relaxation

51
Q

How is smooth muscle activated?

A

Smooth muscle contains calmodulin rather than troponin
Ca++ binds to calmodulin
Ca-calmodulin activates myosin light chain kinase
Phosphorylates regulatory myosin head - while phosphorylated capable of repeated binding

52
Q

What is the source of calcium for SM contraction?

A

Extracellular (poorly developed sarcoplasmic reticulum)

53
Q

What regulates the force of SM contraction?

A

Extracellular calcium

54
Q

What causes SM relaxation?

A

Ca pump removes calcium, myosin phosphatase reverses phosphorylation of myosin head

55
Q

What is the action potential of SM?

A

-50-60mV

56
Q

What are the two types of action potential in unitary smooth muscle?

A

Spike potentials
Action potential with plateau

57
Q

How do smooth muscle action potentials differ from skeletal muscle?

A

Far more voltage-gated calcium channels, fewer sodium
Mainly generated by Ca influx, slower to open and remain open longer than Na channels

Guyton (10 decks)

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