Lecture 19: O2 and CO2 TRANSPORT Flashcards
How is oxygen carried in the blood?
Dissolved in the plasma and bound to haemoglobin in RBC’s (most effective)
How much oxygen is dissolved in a litre of blood?
3mL so about 15mL in body but we need about 250mL/min
What does oxygen do?
Form an easily reversible combination with Hb to give oxyhaemoglobin
What does binding of oxygen depend on?
The partial pressure of oxygen
What is haemoglobin saturation?
The percentage of heme units containing bound oxygen at any given moment
What is the average partial pressure of oxygen of blood entering the systemic circuit?
High (95-100mmHg)
What is the average partial pressure of oxygen of blood leaving peripheral tissues (venous blood)?
Moderate (40-50mmHg)
What is the average partial pressure of oxygen in active muscle tissue?
Low (10-20mmHg)
What is the shape of the oxygen haemoglobin saturation curve?
Sigmoidal, not linear
What happens when the slope of the saturation curve is steep?
A very small change in partial pressure of oxygen in the blood will result in a large change in the amount of oxygen bound to haemoglobin or released from oxyhemoglobin. oxygen binding affinity is decreased
What happens in the flat part of the saturation curve?
Large changes in partial pressure of oxygen will result in small changes in the percentage of oxyhaemoglobin
What does the curve vary with?
Conditions to improve oxygen uptake and delivery
What shifts the curve right?
Reduced pH (Bohr’s effect), increased partial pressure of carbon dioxide and increased temperature
What shifts the curve left?
Increased pH (Bohr’s effect), decreased partial pressure of carbon dioxide and decreased temperature
How is carbon dioxide transported?
Dissolved in plasma (7%), as bicarbonate (70%) and combined with proteins as carbamino compounds (23%)
What does 70% if carbon dioxide do?
It is converted to carbonic acid by activity of enzyme carbonic anhydrase
What do the carbonic acid molecules do?
Immediately dissociate into a hydrogen ion and bicarbonate ion
What do the hydrogen ions do?
Bind to haemoglobin forming HbH+
What do the bicarbonate ions do?
Move into plasma in exchange for chloride ions (Cl-). Process called the chloride shift
What do we need to maintain?
Normal levels of oxygen and carbon dioxide for metabolic and biochemical stability
What is variable?
Oxygen usage and carbon dioxide production but despite this, oxygen and carbon dioxide are kept within close limits
What is the control centre?
Pons, medulla oblongata and other parts of the brain
What does the control centre receive?
Afferent signals from sensors
What are the sensors?
Chemoreceptors, baroreceptors, lung stretch receptors and protective reflexes
What does the control centre send?
Efferent signals to effectors
What are the effectors?
Muscles of respiration
What can the higher centres do?
Alter the activity of the pneumotaxic centres
Where are the higher centres?
Cerebral cortex, limbic system and hypothalamus
What do the apneustic and pneumotaxic centres do?
Adjust the output of the respiratory rhythmicity centres
What do apneustic centres do?
Promote inhalation by stimulating DRG (dorsal respiratory group)
What do the pneumotaxic centres do?
Inhibit apneustic centres
Where are the apneustic and pneumotaxic centres?
In the pons
What do the respiratory rhythmicity centres do?
Generate cycles of contraction and relaxation in the diaphragm, establishing pace of respiration, modify activity in response to chemical and pressure signals
What does the dorsal respiratory group of neurons (DRG) have?
An inspiratory centre
What does the DRG do?
Send signals to inspiratory muscles (diaphragm and external intercostals)
What is the pre-botzinger complex?
A pace maker/rhythm generator
What does the ventral respiratory group of neurons (VRG) have?
Inspiratory and expiratory centres
What does the VRG do?
Sends signals to accessory inspiratory and expiratory muscles
What respiratory centre can’t be damaged?
Respiratory rhythmic centres
What is part of the respiratory rhythmic centres?
VRG, DRG and pre-botzinger complex
What are the most important receptors in determining respiratory activity?
Carbon dioxide receptors (chemoreceptors)
Where are peripheral chemoreceptors?
Carotid artery and aortic arch
Where are the central chemoreceptors?
Medulla oblongata
What is increasing arterial partial pressure of carbon dioxide called?
Hypercapnia
What also happens in hypercapnia?
Decreased pH
What is decreasing arterial partial pressure of carbon dioxide called?
Hypocapnia
What also happens in hypocapnia?
Increased pH
What is the result of hypercapnia?
Respiratory muscles stimulated, increased respiratory. rate with increased elimination of carbon dioxide at the alveoli
What is the result of hypocapnia?
Respiratory muscles inhibited, decreased respiratory rate with decreased elimination of carbon dioxide at the alveoli
What are baroreceptors?
Blood pressure sensors that also affect respiratory function
What happens when arterial blood pressure goes down?
Reduced flow, sensed by the baroreceptors, respiratory minute volume goes up and increased uptake of air
What happens when arterial blood pressure goes up?
Increased flow, sensed by the baroreceptors, respiratory volume goes down and decreased uptake of air
What do the lung stretch (inflation/deflation) receptors do?
They send afferent input as the lungs inflate or deflate
What does the brain do once it receives afferent input from the lung stretch receptors?
Sends efferent output preventing them from stretching too far either way
What do protective reflexes do?
Detect irritation
What does the brain do once it receives information from the protective reflexes?
Sends efferent signal that triggers a sneeze or cough
