Lecture 19- Gas transport and respiratory control

Question 1

How is oxygen carried in the blood?

Answer 1

In two forms:

• Dissolved O2 in the plasma
• Bound to haemoglobin in RBCs

Question 2

What form of transporting oxygen is more efficient?

Answer 2

Bound as oxygen does not dissolve easily

Question 3

How does oxygen bind to haemoglobin?

Answer 3

Each haemoglobin has 4 protein subunits with a heme unit attached. Within these heme units is an iron which binds to oxygen. Therefore each haemoglobin can bind to 4 oxygen molecules. This forms what is known as oxyhemoglobin.

Question 4

What is meant when it is said that oxygen binding is easily reversible?

Answer 4

Means that oxygen can bind to haemoglobin when required and then is released again dependent on need.

Question 5

What is a O2-haemoglobin saturation curve?

Answer 5

Shows the percentage of heme units containing bound oxygen at any given moment/ partial pressure of oxygen – haemoglobin saturation

Question 6

What shape is a typically haemoglobin saturation curve?

Answer 6

• Haemoglobin curve is sigmoidal in shape not linear
• The curve is steep at the start in active muscle tissue/ systemic capillaries. Then begins to flatten out to show when the blood is leaving the peripheral tissues. Finally it is fully flat when representing the blood entering the systemic circuit/ in the pulmonary capillaries.

Question 7

Why does the sigmoidal shape of the curve help
haemoglobin to deliver oxygen to tissues that need it
most?

Answer 7

• When the slope is steep a very small change in the partial pressure of oxygen will result in a large change in the amount of oxygen bound to haemoglobin and thus released. Allows fast delivery to tissues dependent on need. This is in the systemic capillaries. Here we want to offload oxygen. The steep curve allows peripheral tissues to upload a large amount of oxygen with only a small change in the partial pressure of oxygen.
• When slope is flat this act as a buffer of sorts. In the lungs we want to load oxygen so if arterial or alveolar partial pressure of oxygen were to fall too far below normal, there will only be a small reduction in Hb saturation and the total amount of oxygen transported in the blood will remain relatively stable.

fluctuation is prevented meaning the delivery of oxygen is maintained regardless of change to the partial pressure of oxygen

Question 8

How does Bohr effect (pH, temperature, carbon dioxide and H+) affect binding curve?

Answer 8

Right shift in curve is as a result of:
-reduced pH
-increase H+
-increase partial pressure of carbon dioxide
-increased temperature
Means that more oxygen is released from haemoglobin into the tissue as haemoglobin loses its infinity to bind to oxygen (happens in active tissues)

Left shift in curve is as a result of:
-increase pH
-decrease H+
-decrease partial pressure of carbon dioxide
-reduced temperature
Means that less oxygen is released from haemoglobin into the tissue as haemoglobin wants to hold onto oxygen (happens in lungs- favours loading)

Question 9

How is the effect of pH and temperature on haemoglobin helpful during exercise?

Answer 9

• In exercise pH drops as more carbon dioxide is produced
• Temperature also increases
• This means a decrease in the infinity for hemoglobin to bind to oxygen and so more oxygen is released to the tissue

Question 10

Emily goes to the gym and runs on the treadmill, pushing herself to her aerobic limit. Which of the following statements is most likely to be CORRECT as she is exercising?
A. Her alveolar ventilation is decreased.
B. Her breathing frequency is decreased.
C. Her tidal volume is decreased.
D. Her haemoglobin affinity for oxygen near her skeletal muscle is decreased.
E. Her respiratory minute volume is decreased.

Answer 10

D. Her haemoglobin affinity for oxygen near her skeletal

muscle is decreased.

Question 11

What are the three ways carbon dioxide can be transported in the blood?

Answer 11

1. Dissolved in plasma - 20 times more soluble than O2 (~7%)
2. As bicarbonate (70%= most common way)
3. Combined with proteins as carbamino compounds (23%) - bind to haemoglobin

Question 12

What does haemoglobin have more of an infinity to bind to (carbon dioxide or oxygen)?

Answer 12

Oxygen

Question 13

How does bicarbonate form?

Answer 13

• First carbon dioxide and water combine mediated by the enzyme carbonic anhydrase to form carbonic acid
• Carbonic acid is not stable so dissociates immediately into a hydrogen ion and bicarbonate
• Bicarbonate then moves into the plasma in exchange for a chloride ion and is taken back to the alveoli
• The hydrogen ion binds to haemoglobin and is also transported back to the alveoli (it is the Hydrogen ion that effects the pH)

Question 14

What do we need to maintain for metabolic and biochemical stability?

Answer 14

Normal levels of O2 and CO2, example would be maintaining pH

Question 15

What is something that has to be overcome in order for oxygen and carbon dioxide levels to remain stable? and how is this generally done?

Answer 15

• Usage and production of both is quite variable

- Therefore, need tight control of ventilation

Question 16

What part of the brain is the central controller for keeping carbon dioxide and oxygen levels stable?

Answer 16

Pons, medulla, other part of brain

Question 17

What sends afferent signals about carbon dioxide and oxygen levels to the central controller?

Answer 17

Sensors e.g. chemoreceptors, baroreceptors, lung stretch receptors, protective reflexes

Question 18

Where do efferent signals about carbon dioxide and oxygen levels from the central controller get sent to?

Answer 18

Effectors i.e. the muscles of respiration

result is to increase or decrease ventilation

Question 19

What are the three different levels of respiratory control?

Answer 19

• Higher centers
• Apneustics and pneumotaxic centers in the pons
• Respiratory rhythmicity centers

Question 20

What is the role of the respiratory rhythmicity centers?

Answer 20

Role is to generate cycles of contraction and relaxation in the diaphragm, establishing pace of respiration; modify activity in response to chemical and pressure signals

Question 21

What are the three groups of neurons that are together called the respiratory rhythmicity centers?

Answer 21

• Inspiratory center of the dorsal respiratory group (sends signals to the inspiratory center muscles e.g. diaphragm and external intercostals)
• Ventral respiratory group sends signals to the inspiratory centers to activate accessory inspiratory muscles and to the expiratory centers to activate accessory expiratory muscles.
• Pre-Botzinger complex which is the pace maker/ rhythm generator

Question 22

What does the pneumotaxic center do in regards to the Apneustics center?

Answer 22

Inhibition

Question 23

What are the three higher centers?

Answer 23

• Cerebral cortex
• Limbic system
• Hypothalamus

Question 24

What do chemoreceptors do? Where are they found?

Answer 24

• Detect change in carbon dioxide levels, feed back to the brain in order to result in a change (restore homeostasis)
• Located in periphery (arteries- carotid sinus) and in the medulla oblongata (ventral surface)
• They sense a change to the hydrogen ion levels as a result of increased/ decreased carbon dioxide in the blood

Question 25

What is hypercapnia?

Answer 25

Increase in the partial pressure of carbon dioxide in the blood

Question 26

What is Hypocapnia?

Answer 26

Decrease in partial pressure of carbon dioxide in arteries

Question 27

What is the function of baroreceptors within the respiratory system?

Answer 27

-They are blood pressure sensors, this effects the respiratory system
- When arterial BP goes down there is reduced flow.
This is sensed by the baroreceptors. Respiratory minute volume goes up and so there is an increased uptake of air
-When arterial BP goes up there is increased flow. This is sensed by the baroreceptors. Respiratory minute
volume goes down and so there is a decreased uptake of air

Question 28

What are inflation/ deflation reflexes?

Answer 28

-As the lungs inflate or deflate, they send afferent
input from stretch receptors located in alveoli walls
-The brain then sends efferent output preventing
them from stretching too far either way!

Question 29

What are protective reflexes?

Answer 29

-Receptors detect irritation e.g. debris in airway
-Brain sends efferent signal that triggers a sneeze or
cough