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FRCEM Primary > Physiology - Basic cellular physiology > Flashcards

Physiology - Basic cellular physiology Flashcards

1
Q

Coagulation cascade - Intrinsic pathway
Activated by
Uses what
Final complex

A

Damage to vessel walls
12,11,9
Tenase - 9a + 8a

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2
Q

Coagulation cascade - Extrinsic pathway
Activated by
Uses what
Final complex

A

Damage to extravascular cells
3,7
Tenase - 7a+3

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3
Q

Coagulation cascade - final common pathway

A 
10 with cofactor 5
activates prothrombin to thrombin (2)
activates fibrinogen to fibrin (1)
with cofactor 13 makes
cross linked clot
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4
Q

Which cofactor binds von willibrand factor

A

8

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5
Q

In homeostasis how do receptors, comparators and effectors work in a negative feedback loop?

A

Receptors receive a signal and comparators compare it to a set point that triggers effectors to turn something off.

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6
Q

What is a set point in homeostasis

A

A narrow range of values within which normal function occurs

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7
Q

Why are there oscillations in a feedback loop

A

Due to the lag time in feedback

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8
Q

What is a positive feedback loop for and what are the risks with it?

A

It is an amplification process and it risks uncontrolled, unstable amplification

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9
Q

How does homeostasis protect proteins?

A

It keeps them at a particular temperature and pH, outside of which they denature.

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10
Q

Define osmosis

A

Diffusion of water across a semi permeable membrane down a concentration gradient

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11
Q

Define isotonic

A

Same distribution of solute in both fluids

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12
Q

Define Hypotonic.

What happens to a cell immersed in a hypotonic fluid?

A

Lower concentration of solute.

A cell will swell and rupture - cytolysis

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13
Q

Define Hypertonic.

What happens to a cell immersed in a hypertonic fluid?

A

High concentration of solute.

A cell will lose fluid and become wrinkled - crenation

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14
Q

What is osmolality

A

It measures osmoles of solute per weight of solute

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15
Q

What is osmolarity

A

It measures solute per litre of solution

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16
Q

What are the different fluid spaces and their relative distributions?

A

Intracellular - 60%
Extracellular - 40%

Of extracellular:
60% Interstitial
40% Intravascular

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17
Q 
Cationic concentration differences between ECF and ICF
Na+
K+
Ca2+
Mg2+
Cl-
A 
Na ECF: 145   ICF: 10
K ECF:4    ICF: 159
Ca2+ ECF: 3    ICF: 1
Mg2+ ECF: 2    ICF: 40
Cl- ECF: 117   ICF: 3
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18
Q

What does the Na+/K+ ATPase channel pump do?

A

Pumps cations across cell membranes to maintain different concentrations in each compartment using active transport. 1 molecule of ATP pumps 3 Na+ out of the cell and 2K+ into the cell against the concentration gradient to maintain the electrochemical gradient across the cell membrane and allow facilitated diffusion of other substances.

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19
Q

What is the Gibbs-Donnan equilibrium?

A

Small anions like Cl- are able to cross membranes more easily because small cations like Na and K are pulled back, attracted by large plasma proteins which have a negative charge.

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20
Q

What is oncotic pressure?

A

The osmotic pressure exerted by colloids in solution. Plasma proteins displace some water in the blood, so the proteins pull water into that compartment as osmosis tries to equalise the water in the blood and the interstitial fluid.

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21
Q

What do mitochondria do?

A

Produce energy for cells using aerobic respiration. 36 ATP molecules are made from 1 glucose molecule.

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22
Q

What does the nucleus do?

A

Produces DNA, RNA and controls cell functions. Regulates gene expression. The nuclear envelope containing nuclear pores allows selective movement of proteins and RNA. The outer membrane is continuous with ER and the inner membrane provides a structure for chromosomes. The nucleolus as the site of RNA transcription and regulates the cell cycle

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23
Q

What is the role of the endoplasmic reticulum?

A

Rough endoplasmic reticulum has ribosomes attached to the outside. Amino acids from the nucleus are combined into polypeptides at the ribosome and in the ER they undergo folding.
The smooth endoplasmic reticulum synthesises triglycerides, phospholipids and steroids which form complexes with the proteins in the ER to form lipoproteins. Proteins and lipids leave the ER in transition vesicles and move to the golgi apparatus

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24
Q

What does the golgi apparatus do?

A

Modifies structures made by the ER and packages them into vesicles. The cis side facing the the ER receives the transition vesicle and modifies the structure. The trans side that faces the cell membrane releases the vesicle towards the cell membrane.

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25
Q

What do lysosomes do?

A

Contain 50 different digestive enzymes that can break down any macromolecule in the body.
Primary lysosomes contain digestive enzymes made from Golgi apparatus
Secondary lysosomes contain enzymes and their substrates.

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26
Q

Describe cell membrane structure

A

Lipids arranged in a bilayer with hydrophobic ends facing in and hydrophilic ends facing out. The membrane has transport proteins embedded in it.

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27
Q

Describe G protein coupled receptors

A

When activated GDP becomes GTP causing the alpha subunit to uncouple from beta and gamma subunits and move into the cell to cause an effect.

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28
Q

What two ways are ion channels controlled?

A

Electrical (voltage) gated or ligand (molecule) gated.

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29
Q

Explain cell membrane permeability

A

Cell membranes contain channels that allow them to be selectively permeable. Permeability coefficient depends on cell membrane thickness and lipid solubility of a substance. Diffusion rates across the membrane depend upon concentration gradient and electrochemical gradient.

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30
Q

What determines tube flow? What has the biggest effect

A

Poiseuille’s Law.
Movement of a fluid through a vessel depends on the radius of the vessel, the viscosity of the fluid, the length of the vessel and the pressure difference across the vessel. Radius has the biggest effect on flow rate.

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31
Q

Explain laminar and turbulent flow

A

Blood usually travels smoothly via laminar flow. It flows in layers, all in the same direction. Fluid at the surface walls travels slower than fluid in the centre. Flow is proportional to pressure.
When flow is disrupted it becomes turbulent and is chaotic, multidirectional and travels at different speeds in the vessel. Flow is inversely proportional to pressure. This occurs where the diameter is large and flow is fast like in the aorta, or where there is stenosis across valves.

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32
Q

Explain wall tension and clinical implications

A

Blood flowing through a vessel creates tension on a wall. Laplace’s Law states that wall tension depends on the radius of the vessel, the pressure across the vessel wall and the thickness of the vessel wall. Damage to vessel walls allows distension, increasing the radius and decreasing the thickness allowing rupture.

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33
Q

Normal Hb level

A

Hb - 120-170

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34
Q

Normal haematocrit

A

36-54

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35
Q

Normal platelet count

A

150-400

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36
Q

Normal WBC count

A

4.5-11

37
Q

What is the key component of a RBC

A

Haemoglobin

38
Q

What stimulates production of red blood cells and where is this made?

A

Erythropoietin from the kidneys

39
Q

Life cycle of the red blood cell

A

Made in the red marrow, lives 120 days and then is sequestered in the spleen and broken down into component parts.
Haem to iron and biliverdin. Iron recycled. Biliverdin reduced to bilirubin and bound to albumin. Transported to the liver and excreted as bile salts in the small intestine.

40
Q

The 2 types of white blood cell and their key role

A

Granulocytes (neutrophils, eosinophils and basophils).
Agranulocytes (monocytes, lymphocytes)
They attack foreign substances by phagocytosis, antibody release, neutralisation of toxins, chemical messenger release and enzyme production.

41
Q

What is the main binding protein in plasma?

A

Albumin

42
Q

Platelet role following vessel wall damage

A

Endothelial damage releases ADP which attracts platelets that clump and become activated when exposed to collagen. Activated platelets are sticky and attract more platelets. They release ADP, serotonin and thromboxane A2. Activated platelets anchor in to collagen to stabilise clot formation and stimulate clotting cascade.

43
Q

What do serotonin and thromboxane A2 do when released from platelets?

A

Serotonin increases activation of more platelets. Thromboxane A2 causes vasoconstriction.

44
Q

What do fibrin and thrombin do?

A

Prothrombin is activated to form thrombin which activates fibrinogen to become fibrin. Fibrin forms a network of filaments that trap blood contents to form a clot. After the vessel is repaired plasmin breaks down the fibrin links.

45
Q

What is a membrane potential?

A

The electrical chemical difference across a cell membrane - at rest, usually -70mV, caused by asymmetric distributions of Na and K.

46
Q

What is an action potential?

A

A property of excitable tissues - an action potential is the propagation of a signal along a cell. A change in the membrane potential stimulates cellular components to either conduct the signal onwards or stimulate a cellular function.

47
Q

Ionic basis of the action potential - depolarisation

A

Stimulated either mechanically by stretch or chemically by Ach, the Na channels open and there is an influx of Na, causing a positive charge in the cell that breaches the membrane threshold (-50mV) and depolarises the cell, creating the action potential.

48
Q

Explain threshold potential

A

Going from a charge of -70 to -50 is slow, but then the cell rapidly allows more Na in so -50 to +30 is very quick. Signal strength come from frequency of depolarisation.

49
Q

Ionic basis of the action potential - repolarisation

A

After depolarising K flows out of the cell to repolarise it.

50
Q

Explain absolute and relative refractory period.

A

The period of time when the cell is unable to be depolarised is the refractory period. If Na channels are completely inactive the is an absolute refractory period. In a relative refractory period some Na channels are reset but the signal must be stronger than before to generate an action potential.

51
Q

What is saltatory conduction?

A

Conduction of an action potential down a neuron or axon covered in myelin and spaced by nodes of Ranvier. The myelin insulates the axon and movement of Na cannot happen under it. At the ends of the sheath the axon is exposed to the extracellular fluid which depolarises and sends the signal down.

52
Q

What does myelin do to conduction of the action potential?

A

Increases speed and efficiency. Speed is determined by the distance between the nodes.

53
Q

What is the relation between nerve size and conduction speed?

A

The larger the diameter of the axon the faster the conduction speed due to the reduction in resistance facing the ion flow.

54
Q

What role does the autonomic nervous system play in homeostasis?

A

It is the effector component.

55
Q

What are neurotransmitter vesicles and what do they do?

A

When an action potential arrives at the bouton the pre-synaptic membrane is depolarised and the voltage gated Ca2+ channel opens, allowing an influx of Ca2+. This causes vesicles containing neurotransmitters to bind to the pre-synaptic membrane and release their contents into the cleft to bind on the post-synaptic membrane and have an effect.

56
Q

Post-synaptic excitatory receptors

A

Neurotransmitter release causes Na channels to open increasing chance of depolarisation. Magnitude of effect depends on amount of neurotransmitter released.

57
Q

Pre-synaptic inhibitory receptors

A

Neurotransmitter release causes ion channels to open or close making the membrane potential more negative (hyperpolarised) and therefore harder to depolarise.

58
Q

Role of cholinesterase in synaptic transmission

A

Cholinesterase on the postsynaptic membrane breaks down the acetylcholine neurotransmitter into acetate and choline to be reabsorbed.

59
Q

Role of MAO in synaptic transmission

A

Monoamine oxidase breaks down noradrenaline, serotonin, dopamine, adrenaline and phenylethylamine. It is found in the terminal bouton and acts on NA that has been pumped back in.

60
Q

Role of COMT in synaptic transmission

A

Catechole-o-methyltransferase inactivates noradrenaline at the post synaptic membrane. It also breaks down dopamine and adrenaline.

61
Q

Sympathetic effect on eyes

A

Dilates pupils

62
Q

Parasympathetic effect on eyes

A

Constricts pupils

63
Q

Sympathetic effect on skin

A

Sweat glands increase secretion, hairs stand erect.

64
Q

Sympathetic effect on heart

A

Heart rate and contractility increases

65
Q

Parasympathetic effect on heart

A

Heart rate and contractility decreases

66
Q

Sympathetic effect on respiratory system

A

Airways increase in diameter, secretions decrease, respiratory rate increases

67
Q

Parasympathetic effect on respiratory system

A

Airways decrease in diameter, secretions increase, respiratory rate decreases

68
Q

Sympathetic effect on digestive system

A

Activity decreases, blood supply decreases, glycogen is broken down and glucose is synthesised and released.

69
Q

Parasympathetic effect on digestive system

A

Activity increases, blood supply increases, glycogen is synthesised.

70
Q

Sympathetic effect on kidneys

A

Decreased urine production. Sphincter constricts and bladder relaxes.

71
Q

Parasympathetic effect on kidneys

A

Increased urine production. Bladder contracts and sphincter relaxes

72
Q

Functional purpose of skeletal muscle

A

Striated muscle under voluntary control. Anchored by tendons to the skeleton. Provides short bursts of contraction followed by relaxation

73
Q

Functional purpose of cardiac muscles

A

Involuntary control. Provides repeated contractions that alter in rate and force.

74
Q

Functional purpose of smooth muscle

A

Found in the splanchnic organs (GI, bronchi, uterus, blood vessels). Involuntary control. Allows long and sustained contractions

75
Q

Composition of skeletal muscle

A

Muscle cell fibres comprised of multiple myofibrils, are surrounded by endomysium arranged longitudinally as a fascicle, bundled together by perimysium to form fasciculi.

76
Q

What is a functional unit of muscle?

A

A sarcomere - a section of the muscle fibre separated by z lines. Comprised of Half the I band from Z line on either side, the whole A band, an H zone and an M line

77
Q

What is the sarcolemma?

A

A cell membrane that surrounds multiple myofibrils. It contains T tubule invaginations which penetrate the muscle fibre and lie adjacent to the terminal cisternae of the sarcoplasmic reticulum. The T tubules carry the action potential into the muscle fibre

78
Q

What is the sarcoplasmic reticulum?

A

A membrane bound structure that forms a network of tubules wrapping around myofibrils.
They store calcium. They have enlarged areas called terminal cisternae where they abut a t tubule.

79
Q

What is the I band

A

The zone where thin actin filaments don’t overlap thick myosin filaments.

80
Q

What is the H zone

A

The centre of the sarcomere ending at the start of the actin filaments. The area where thick myosin is not overlapped by thin actin.

81
Q

What is the M line

A

A disc of filaments in the middle of the H zone that holds the myosin filament in place so that each one is surrounded by six actin filaments

82
Q

What is the A band

A

The whole length of the myosin filament

83
Q

How does contraction occur in a muscle?

A

Myosin heads form cross bridges that overlap onto thin filaments. During contraction they pull against each other and reduce the length of the A band. The degree of shortening depends on the amount of overlap.

84
Q

What is excitation-contraction coupling?

A

An electrical signal is transformed into a mechanical action.

  • An action potential causes Ach release at the NMJ
  • Ach binds nicotinic receptors and the ion channels open
  • The action potential generated on the myocyte membrane travels down the T Tubule to the sarcoplasmic reticulum causing calcium to be released.
  • Ca2+ binds Troponin C on actin, causing tropomyosin to be removed from the myosin heads allowing cross-bridge formation.
  • Myosin pulls actin filaments, shortening it, powered by ATP hydrolysis at the myosin head.
  • Ca2+ is actively removed from the cytoplasm allowing tropomyosin to block the actin site.
85
Q

What is temporal summation?

A

Repeated stimulation increases Ca2+ release and decreases the refractory period allowing summation of signals to increase the force of contraction

86
Q

What is spatial summation?

A

A weak signal stimulates weak muscle cells spanning larger units. As nerve impulses increase larger muscle cells are stimulated and force of contraction increases. As more motor nerves are stimulated more muscle units are recruited and more muscle contraction occurs.

87
Q

Difference in electrical-conduction coupling in cardiac muscles

A
  • Ca2+ is released from the endoplasmic reticulum and causes further Ca2+ release into the cytoplasm.
  • The action potential arises from the AV or SA node and spreads through cardiac myocytes through gap junctions
88
Q

How is Ca2+ removed?

A

Na/Ca exchanger

89
Q

Relation between length and tension (Starling relation) in cardiac muscle.

A

Myocyte stretching increases the affinity of Troponin C with Ca2+, increasing the number of crossbridges and increasing contractile force. Muscle stretch depends on ventricular blood volume at diastole and therefore cardiac output increases with venous return.

FRCEM Primary (32 decks)

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