Module 1 Lecture 7

Question 1

How is O2 is carried in the blood?

Answer 1

1) it is bound to hemoglobin (Hb) within red blood cells (98% this way)
2) Dissolved in plasma (2% this way)
O2 loading and unloading is very rapid and efficient

Question 2

What is haeoglobin made of?

Answer 2

Haemaglobin is composed of 4 iron-containing heme groups- each haemaglobin molecules can carry 4 oxygen molecules

Question 3

Label the O2-haemoglobin dissociation curve

Question 4

What are loading and unloading regulated by?

Answer 4

• Partial pressure of oxygen (PO2)
• Temperature
• Hydrogen ions (decreased pH)
• Partial pressure of carbon dioxide (PCO2)
• Blood BPG (2,3-bisphosphoglycerate) concentration

Question 5

Influence of other factors on O2 loading and unloading

Answer 5

Temperature, blood H+, partial pressure of CO2 (PCO2), blood BPG
(2,3-bisphosphoglycerate) concentration all ↑ upon greater
metabolic demand (i.e. in systemic capillaries)

Question 6

Increase in any factor and a decrease of Hb to Oxygen =?

Answer 6

increase in oxygen unloading, more oxygen is available for use by local tissues

Question 7

A decrease in any factor and an increase of the binding strength of Hb to Oxygen =?

Answer 7

a decrease in oxygen unloading, meaning less oxygen is available for use by local tissues

Question 8

What are the three ways that Carbon dioxide is carried in the blood?

Answer 8

1. Dissolved in plasma (7-10%)
2. Bound to haemoglobin (Hb) within red blood cells (20%)
3. As bicarbonate ions in plasma (70%)

Question 9

CO2 path?

Answer 9

Carbon dioxide is transported to lungs -> diffuses down partial
pressure gradient from pulmonary capillaries into alveoli & expired

Question 10

Amount of carbon dioxide transported in blood is affected by the
degree of blood oxygenation!

Answer 10

• ↓ PO2 & Hb oxygen saturation = ↑ CO2 transported
• E.g. In systemic tissues, where PO2 is low, CO2 is more readily loaded onto Hb
  to be carried via venous system to the heart, then lungs. In lungs, where PO2
  is high, CO2 is unloaded from Hb & diffused into alveoli

Question 11

Regulation of breathing?

Answer 11

• Respiratory muscles contract only when stimulated by
  nerves
  • Rhythmic breathing is established by cyclic neural
  activity from the brainstem to respiratory muscles
  (although origin of this rhythm not well understood)
  • Maintains breathing & reflex adjustments when
  required
  • Can be voluntarily modified

Question 12

What are the neural mechanisms in the regulation of breathing?

Answer 12

Medullary Respiratory Centre and Pons respiratory Centre

Question 13

What is Medullary respiratory centre and what does it do? LABEL

Answer 13

Medullary Respiratory Centre has two neuronal clusters:
• Ventral respiratory group (VRG) – rhythm generating
• Dorsal respiratory group (DRG) – integrates inputs from
peripheral stretch receptors, chemoreceptors & higher
brain centres à communicates with & modifies VRG
neurons

Question 14

What is the Pons Respiratory Centre and what does it do? LABEL

Answer 14

Pons Respiratory Centre fine-tunes breathing during
activities such as talking, sleeping, exercise - integrates
inputs from peripheral sensory receptors & higher brain
centres à communicate & modifies DRG & VRG neurons

Question 15

How is the depth of breathing determined?

Answer 15

Depth is determined by degree of neuronal stimulation from respiratory
centres: ↑ stimulation of inspiratory neurons ↑ force of respiratory muscle
contraction resulting in greater thoracic expansion

Question 16

What is rate determined by?

Answer 16

Rate is determined by how long the inspiratory neurons are active

Question 17

What are the respiratory centres in the medulla and pons sensitive to excitatory and inhibitory stimuli?

Answer 17

Chemical factors: arterial CO2, H+, O2 via central & peripheral chemoreceptors
– Higher brain centres: hypothalamus (emotions & pain) & motor cortex
(voluntary control)
– Pulmonary irritants: mucus, dust, fumes stimulate bronchiole receptors that
communicate with respiratory centres via vagal nerve afferents – reflex
constriction, cough, sneeze
– Inflation reflex: stretch receptors signal respiratory centres via vagal nerve
afferents to end inspiration & lungs recoil

Question 18

DRAW the chemical cycle

Question 19

Breathing during exercise

Answer 19

Ventilation ↑ 10-20-fold during vigorous exercise due to ↑ tidal
volume & respiratory rate: 4L/min –> 80L/min
• Greater force of contraction of respiratory muscles & activation of
accessory muscles that further ↑ thoracic volume

Question 20

How is breathing regulated during exercise?

Answer 20

• Not due to ↑ PCO2 or ↓ PO2 as ventilation ↑ as soon as exercise
begins & arterial PCO2 & PO2 remain relatively constant (although
capillary & venous levels change)
• Psychological – anticipation of exercise
• Simultaneous cortical motor & respiratory centre activation
• Proprioceptors in active muscles, tendons, & joints stimulate
respiratory centres

Question 21

Why are respiratory systems susceptible toi infection?

Answer 21

Respiratory system susceptible to infections due to open airways

Question 22

What are chronic diseases?

Answer 22

Obstructive: COPD (chronic bronchitis & emphysema usually caused by
inhaled irritants & smoking), asthma (acute respiratory episodes caused by
immune-mediated inflammation)
– Restrictive: TB (infectious disease caused by bacterium), lung fibrosis (e.g.
asbestos)
– Lung cancer (~90% cases due to smoking)

Question 23

What are chronic diseases? p2

Answer 23

Sleep Apnea: temporary pause in breathing during sleep
– Obstructive: collapse of upper airway & obesity is a risk factor
– Central: respiratory centre depressed during sleep