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CardioRespiratory Year 1 > Carriage of Oxygen in the Blood > Flashcards

Carriage of Oxygen in the Blood Flashcards

1
Q

What is the job of the cardiovascular system

A
  1. to supply oxygen and metabolic fuel such as glucose to the tissues and take away the waste products of metabolism such as carbon dioxide
  2. maintain defences against invading micro-organsims-organisms
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2
Q

why is the carriage of oxygen a problem

A
  • oxygen is a powerful oxidising agent and this causes damage to molecules
  • erythrocytes are designed to carry the oxygen
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3
Q

What is the definition of oxidation

A

oxidation is the loss of electrons

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4
Q

what do oxidising agents do

A
  • they combine with other atoms and remove electrons from the oxidised molecule
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5
Q

What does oxidation do

A
  • simplified the electronic structure of the substrate and decreases the free energy in the system
  • this releases energy in the form of heat
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6
Q

What is the definition of reduction

A

this is the addition of electrons

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7
Q

What does reduction do

A
  • builds more complex molecules from simpler ones, therefore decreasing the free energy in the environment
  • this requires energy
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8
Q

write an example of oxidation

A

Fe2+ = Fe3+ + e-

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9
Q

when oxidation releases a ….

A

large amount of energy it is irreversible whereas if the electron transfer only involves a small amount of energy the reaction is revertive

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10
Q

Name an example of a reduction and oxidation reversible reaction

A

NAD

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11
Q

what is the equation of the NAD system

A

NAD+ + H+ + 2e- = NADH

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12
Q

How do anaerobic organisms create oxidising agents

A
  • use other oxidising agents other than oxygen such as sulphate, nitrate, sulphur and live in poor oxygen
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13
Q

what is haemoglobin

A
  • a molecule that is in erythrocytes that can combine rapidly and reversible with oxygen without becoming oxidised
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14
Q

What is the structure of a normal erythrocyte

A
  • biconcave discs
  • 7um in diameter
  • 2um thick
  • volume of 90cu mm
  • contains 270 million haemoglobin molecules
  • no nucleic or mitochondria as they are easily damaged by high oxygen levels found in erythrocytes
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15
Q

What is microcytic anaemia

A

this is when the red blood cell is smaller than usually, this means that it is harder to get oxygen into the tissue

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16
Q

What is microcytic anaemia

A
  • this is when the red blood cell is larger than normal, t his causes the red blood cells to break apart when damaged
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17
Q

what are immature red blood cells called

A

reticulocytes

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18
Q

how much of circulating red blood cells do reticulocytes make up

A
  • 1-2% of the circulating red blood cells in normal person
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19
Q

When do reticulocytes turn into normal red blood cells

A
  • change into mature red blood cells about a day after entering circulation
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20
Q

why are reticulocytes called reticulocytes

A
  • they have a reticular network of ribosomal RNA that is visible under a microscope with methylene blue stain
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21
Q

what can mature red blood cells not do

A
  • have a lack of nucleic and organelles therefore they cannot divide or repair themselves and cannot survive for long
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22
Q

what do actin filaments do in erythrocytes

A
  • they hold the biconcave discs in place
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23
Q

how do red blood cells produced ATP

A
  • they have no mitochondria so they produced ATP by glycolysis - they cause glucose to turn to pyruvate and then this is converted into lactic acid but this is less efficient that aerobic metabolism
  • red blood cells have a low pH
  • they have a Glut-1 facilitated uniport diffusion channel that allows them to uptake glucose for glycolysis this is not regulated by insulin
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24
Q

what does vitamin C do

A
  • it is an antioxidant
  • protects the red blood cells against oxidative damage
  • take form the blood via glut-1
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25
Q

what happens to red blood cells over a period of time

A
  • they are progressively damaged by oxygen that they carry the haemoglobin are progressively converted to methamgolbin
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26
Q

how long is the life time of a red blood cell

A
  • lifetime of 120 days
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27
Q

why do red blood cells have a short lifetime

A
  • this is because they have a lack of repair ability
  • erthryocytes undergo changes in its plasma membrane and makes it susceptible to recognition by phagocytes and therefore phagocytosis in the spleen, liver and bone marrow
  • formation of methaemoglobin - some red blood cells gradually accumulate methaglobin and cannot carry oxygen any more, some repair can be done by the enzyme methaemoglobin reductase
28
Q

what does the ability of haemoglobin to transport oxygen dependent on

A
  • ability to transport oxygen without being oxidised depends on the ability of the iron atom to be hexavalent
29
Q

what is it called when the iron atom forms 6 bonds

A

hexavalent

30
Q

describe the structure of the ferrous iron

A
  • atom has 6 unpaired D orbital electrons therefore it can form 6 bonds with 6 electrons from other atoms
  • 4 are in plane
  • 2 are above and below the plane
31
Q

how are the 4 electrons in plane held together

A
  • they are held together by 4 covalent bonds to nitrogen atoms in a porphyrin ring
32
Q

what is a haem group

A
  • the porphyrin ring together with its ferrous iron centre is called a ham group
33
Q

what is the group underneath the porphyrin ring called

A
  • a histidine group

- this binds to the 5th iron electron and leaves one electron which can react with the other molecules such as oxygen

34
Q

describe how oxygen binds to haemoglobin

A
  • haemoglobin oxygen forms a weak reversible bond with the 6th ferrous electron
35
Q

why is the bond between the ferrous ion and the oxygen weak in haemoglobin

A
  • it is weak as the oxygen molecule cannot get close enough to the iron to fully remove the electron due to steric hinderance from other parts of the haemoglobin molecule
36
Q

what is the structure of haemoglobin

A
  • teratemer - made up of 4 subunits
  • each subunit has a ham and prosthetic group attached
  • polypeptides chains are bound to each other by salt bridges, hydrogen bonds and hydrophobic interactions
  • 3d folding creates steric hindrance
37
Q

what is steric hindrance

A
  • this is when the oxygen molecule cannot get physically close enough to the iron to remove the electron so therefore the oxygen is attached but is not close enough to oxidise it
38
Q

what happens when the partial pressure of oxygen is high

A
  • when the partial pressure is high the oxygen binds and forms oxyhemoglobin, this happens in the lungs
39
Q

what happens when the partial pressure of oxygen is low

A
  • when the partial pressure of oxygen is low oxygen dissociates and deoxyhaemoglobin is formed, this happens in the tissues
40
Q

what happens when steric hindrance does not work

A
  • iron ion is oxidised and changed into its ferric stat
  • haemoglobin with ferric iron is called methamoglobin and cannot carry oxygen as the ferric iron no longer has the 6th electron to attract the oxygen molecule
41
Q

what is metaemoglobin

A
  • this is haemoglobin with its ferric ion

-

42
Q

what happens to methaemoglobin in newly formed red blood cells

A
  • most of the methaemoglobin formed is converted back to haemoglobin by NADH deponent enzyme methaemoglobin reductase which is found inside the cells but the amount of methaemoglobin increases over time
43
Q

what can an increase in methaemoglobin be due to

A
  • exposure to various chemicals such as methaemoglobinaemia
  • genetics - cogentianl deficiency of methaemoglobin reductase - this usually happens in Alaskan Inuit people - these people compensate by making more red blood cells this is called polycythemia so the total oxygen carrying capacity of the blood is increased
44
Q

how much percentage of a persons haemoglobin is methaemoglobin

A

1-2%

45
Q

what is adult haemoglobin made up of

A
  • two alpha and 2 beta
46
Q

what is foetal haemoglobin made up of

A
  • two alpha and 2 gamma
47
Q

what does the amount of steric hindrance vary upon

A
  • varies depending on the mix of subunits in a particular molecule such as if the haemoglobin has alpha or beta subunits
48
Q

foetal haemoglobin has a …

A
  • higher affinity for oxygen then adult haemoglobin
  • this means it can remove it from the placental blood
  • left of the curve
49
Q

what is 2,3- DPG

A
  • it is a small separate molecule that is bound loosely to the haemoglobin molecule
50
Q

what does 2,3-DPG do

A
  • when beta subunits start to deoxygenate it binds to them more tightly and moves into the centre of the haemoglobin increasing the rate of oxygen release
  • it therefore enhances the ability of red blood cells to release oxygen in hypoxic tissues
51
Q

how do you measure percent saturation

A
  • use a pulse oximeter
52
Q

what is percent satruation

A
  • this is the proportion of haemoglobin that is bound to oxygen
  • should be above 94%, healthy individuals show between 96% and 99%
53
Q

What is hypoxaemia

A
  • this is when the oxygen saturation valve is below 90%
54
Q

describe the oxygen saturation curve

A
  • the upper flat part of the curve means that haemoglobin is more than 90% saturated by oxygen over a wide range of oxygen in the lungs
  • steep middle part of the curve means that haemoglobin releases large amounts of oxygen for a small decrease in partial oxygen pressure over the range 20-40 mmHg
55
Q

What factors cause the oxygen dissociation curve to change

A
  • Heat

- acid

56
Q

What does heat do to the saturation of oxygen

A
  • metabolising tissue heats up whereas tissue that is not metabolising slows down
  • heat causes Hb curve to move to the right therefore it is unloading more oxygen at any given partial pressure
  • cold moves the curve to the left - cold limb can become hypoxic
57
Q

what does acid do to the saturation of oxygen curve

A
  • heavy metabolising tissue generates more carbon dioxide and therefore becomes more acidic
  • lower pH moves curve to the right - therefore more oxygen is unloaded at any given partial pressure
  • this is called Bohr shit
58
Q

what is myoglobin

A

this is a form of haemoglobin that is found in the muscle

59
Q

what is the difference between myoglobin and haemoglobin

A
  • myoglobin is a single subunit whereas haemoglobin has 4 subunits
  • myoglobin has a greater affinity for oxygen than haemoglobin which means as the blood travels through muscle capillaries oxygen is transferred to myoglobin
60
Q

what happens when myoglobin is released from damaged muscle tissue

A
  • the process is called rhabdomyolysis
  • release myoglobin is filtered by the kidneys but is toxic to the renal tubular epithelium so can cause acute renal failure
61
Q

what is haematocrit

A

this is the percentage of blood which is red cells-

- normally 45%

62
Q

what determines the amount of oxygen carried

A

haematocrit

63
Q

what controls the haematocrit concentration

A

erythropoietin EPO

64
Q

describe how EPO controls haematocrit

A
  • EPO is released from the interstitial cells in the kidney
  1. haematocrit falls
  2. renal hypoxia
    3 EPO production increases
  3. red blood cell production in bone marrow is stimulated
  4. normal 45% haematocrit is restored
  • negative feedback loop
65
Q

what is EPO used to treat

A
  • available as a therapeutic agent in treating anaemia which results from chronic kidney disease, from the treatment of cancer and from other critical illnesses
66
Q

Describe how red blood cells carry carbon dioxide

A
  1. carbon dioxide combines with water
  2. carbonic anhydrase converts it to bicarbonate and hydrogen ions
  3. most of the bicarbonate that is formed is then expelled into the plasma and carried in the venous blood to the lungs
  4. in order to keep the red blood cells at a neutral charge chloride ions diffuses in to the red blood cells as bicarbonate diffuses out this is called a chloride shift

in the lungs

  • bicarbonate enters the red blood cells and is converted back to carbon dioxide which is then released into the alveoli
  • chloride leaves to balance the electrical change when the bicarbonate enters
67
Q

what happens to carbon dioxide in the blood

A
  • majority is transported by red blood cells as bicarbonate
  • some is soluble in the water
  • some binds to haemoglobin and forms carboaminohaemoglobin - this displaces oxygen in acidic condition

CardioRespiratory Year 1 (28 decks)

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