HUBS192 Lecture 19 - Gas Transport and Respiratory Control

Question 1

what are the 2 forms oxygen is carried in the blood?

Answer 1

1) dissolved O2

2) bound to haemoglobin in red blood cells (RBC’s)

Question 2

is oxygen soluble or insoluble and why?

Answer 2

oxygen is poorly soluble therefore it dissolves poorly, especially because blood is warm

Question 3

how much oxygen can dissolve in warm blood?

Answer 3

only about 3mL of O2 per litre of blood and because the body has approx. 5 litres of blood –> about 15mL total

Question 4

how much oxygen do we require MINIMUM per minute in mL?

Answer 4

about 250 mL/min

Question 5

what is the predominant form to carry oxygen in the blood?

Answer 5

bound to haemoglobin in RBC’s

Question 6

what are 4 functions and characteristics of red blood cells (RBC’s, erythrocytes)?

Answer 6

1) contains large amounts of haemoglobin
2) 1/3 weight of the RBC
3) uses iron as part of the heme structures (left, red) to bind oxygen
4) four heme units, so each haemoglobin can bind four O2 molecules

Question 7

what is the relationship between the first O2 binding to a heme unit and the affinity for O2?

Answer 7

the hardest O2 to bind is the first O2 but with each bound O2 the affinity for the next bound oxygen becomes much greater
- more oxygen bound –> tightly binds the O2

Question 8

what is the relationship between the % of heme sites that are occupied at increasing oxygen levels? (in terms of a graph)

Answer 8

the relationship is sigmoidal due to cooperative binding of oxygen molecules

Question 9

what are the features of the haemoglobin binding curve graph?

Answer 9

-pressure of oxygen increases along the x-axis (increase gas concentration)

Question 10

what is the oxyhemoglobin % saturation?

Answer 10

percent saturation of oxygen that is bound to haemoglobin

- 100% = each haemoglobin has a full complement of 4 bound oxygens

Question 11

what is oxygen binding to haemoglobin?

Answer 11

cooperative binding

Question 12

what is the lowest part of the sigmoidal curve of the haemoglobin binding curve and describe this?

Answer 12

-PO2 in the active muscle tissues (skeletal muscle during exercise)
at the part with the lowest oxygen bound to haemoglobin % saturation

Question 13

what is the middle part of the sigmoidal curve of the haemoglobin binding oxygen curve and describe this?

Answer 13

-average PO2 of blood leaving peripheral tissues
where binding becomes cooperative and affinity ‘sky rockets’ by binds quickly and easily
-tissue at rest, with low metabolic demand

Question 14

what are the 3 parts of the sigmoidal curve of the haemoglobin binding curve?

Answer 14

1) average PO2 of blood entering the systemic circuit (highest % saturation)
2) average PO2 of blood leaving peripheral tissues (middle % saturation)
3) PO2 in active muscle tissue (lowest % saturation)

Question 15

what is highest part of the sigmoidal curve of the haemoglobin binding oxygen curve and describe this?

Answer 15

-average PO2 of blood entering the systemic circuit
binding curve starts to slow down as most of the binding sites are occupied. The additional oxygen molecule that wants to bind to haemoglobin has trouble to find an open spot, therefore slowing binding down to a plateau

Question 16

what are the 2 ends of the gas delivery system?

Answer 16

1) external respiration

2) internal respiration

Question 17

what happens during external respiration

Answer 17

delivering low oxygen blood to the lungs for it to participate in gas exchange with the alveoli across the blood air barrier
-ultimately enriching the blood with oxygen

Question 18

what happens during internal respiration?

Answer 18

delivering high oxygen blood to the various tissues of the body
-because the tissues consume oxygen they will have a lower oxygen content and haemoglobin in the blood will release some of the oxygen so it can diffuse into the tissues

Question 19

how is oxygen distributed?

Answer 19

oxygen is distributed to the tissues that need it most

Question 20

why can the relationship of the haemoglobin binding curve not be linear?

Answer 20

• because it would release to much oxygen to the resting tissues (more than it needs)
• very small difference in oxygen delivery between the resting tissue (average PO2 of blood leaving peripheral tissues) and the active tissue (PO2 in active muscle tissue)

Question 21

is the haemoglobin binding curve fixed?

Answer 21

no the curve is not fixed, it can shift around depending on localised conditions

Question 22

what happens when there is a rightward shift of the sigmoidal curve caused by pH?

Answer 22

extra oxygen will be released from haemoglobin and will be available to diffuse into the tissue
-affinity between oxygen and haemoglobin has dropped and that makes it easier to relate more oxygen into the tissue

Question 23

what is the relationship between shifting of the haemoglobin binding curve and pH?

Answer 23

moves to the right (rightward shift) as pH falls

-the lower the pH the more the curve shifts to the right (more acidic)

Question 24

what happens when there is a rightward shift of the sigmoidal curve caused by temperature?

Answer 24

when temperature of the tissue increases there will be rightward shift of curve therefore a reduced oxygen affinity making it easier to bind

Question 25

what are the 2 ways haemoglobin is caused to release more oxygen?

Answer 25

1) lower pH

2) higher temperature

Question 26

what is the effect of exercise in terms of pH and temperature of tissues?

Answer 26

exercise causes pH to drop (more acidic) and temperature to rise in skeletal muscle
-pushing the haemoglobin binding curve to the right

Question 27

what are the 3 forms carbon dioxide (CO2) transported in?

Answer 27

1) dissolved in plasma (7%) - partially soluble
2) bound to haemoglobin (23%)
3) converted to bicarbonate (70%)

Question 28

how is carbon dioxide converted into carbonic acid?

Answer 28

converted by the enzyme carbonate anhydrase (H2CO3)

Question 29

what happens to carbon dioxide after it has been converted to carbonic acid?

Answer 29

immediately dissociates (falls apart) and forms bicarbonate and an H+ proton

Question 30

what happens to the bicarbonate once formed?

Answer 30

shipped out of the RBC and back into the plasma

Question 31

is bicarbonate soluble or insoluble and what does this mean?

Answer 31

highly soluble in plasma (water) and then can be transported in the blood as dissolved bicarbonate to the right side of the heart into the pulmonary circuit and ends up at the blood air barrier of the alveoli. There it is reconverted to carbon dioxide and is exchanged the alveoli to be exhaled out of the body

Question 32

what is the process of the formation of bicarbonate?

Answer 32

• carbon dioxide and water combine to form carbonic acid
• carbonic acid dissociates not bicarbonate and a hydrogen ion
• this lowers the pH… the blood gets more acidic

Question 33

what is the effect of the H+ proton formed?

Answer 33

lowers the pH in the area it is being formed (makes it more acidic)

Question 34

what is the function of maintaining normal levels of O2 and CO2?

Answer 34

maintain normal levels of O2 and CO2 for metabolic and biochemical stability (e.g pH)

Question 35

is O2 usage and CO2 production variable?

Answer 35

O2 and CO2 production are quite variable depending on the need of each individual tissue in the body (different tissues produce more CO2 and use more O2 at different times)

Question 36

how does the brain control breathing?

Answer 36

brain communicates with the respiratory system to regulate gas exchange levels and takes action via signalling pathways to change the rate of breathing

Question 37

what are the 4 receptors that monitor our respiratory state?

Answer 37

1) chemoreceptors
2) baroreceptors
3) lung stretch receptors
4) protective reflexes

Question 38

what happens if there something that goes wrong when controlling breathing?

Answer 38

the sensors will send an afferent signal to the brain (pons, medulla, other part of brain) and then the brain will send an efferent signal out to the effectors

Question 39

what are effectors of the respiratory system?

Answer 39

various structures that control respiratory function

Question 40

what is the function of the sensors of the respiratory system?

Answer 40

monitors the changes from the effectors to see whether the change has solved the problem or if more action needs to be taken (did this have the desired effect?)

Question 41

what is the most important respiratory receptor and why?

Answer 41

chemoreceptors because they send the most important afferent signalling to the brain and get the strongest efferent response

Question 42

what is the function of chemoreceptors?

Answer 42

to monitor carbon dioxide levels (mostly)

Question 43

what is an example of how chemoreceptors work while holding your breath?

Answer 43

after holding your breath for a while you will begin to experience extreme discomfort, this discomfort is from the build up of carbon dioxide within your system, the chemoreceptors notice this and send an afferent signal to the brain which sends an efferent signal back out to make you very uncomfortable and force you take a breath

Question 44

what are baroreceptors and where are they located?

Answer 44

stretch receptor located mainly in the aortic arch and the carotid artery that monitor blood pressure

Question 45

what do the baroreceptors do when arterial BP goes down?

Answer 45

• when arterial BP goes down, flow is reduced
• this is sensed by baroreceptors
• then respiratory minute volume goes up and there is an increased uptake of air

Question 46

what do the baroreceptors do when arterial BP goes up?

Answer 46

• when arterial BP goes up, flow is increased
• this is sensed by baroreceptors
• then respiratory minute volume goes down and there is a decreased uptake of air

Question 47

what is the function of the lung stretch receptors?

Answer 47

• as the lungs inflate or deflate, they send afferent input from stretch receptors
• the brain then sends efferent output preventing them from stretching too far either way

Question 48

what is the function of the protective reflexes?

Answer 48

• receptors that detect irritation

- brain sends efferent signal that triggers a sneeze or cough