lecture 19 - gas transport & respiration Flashcards
What are the 2 forms in which oxygen is transported in the blood?
Dissolved, and bound to haemoglobin in red blood cells
Why does oxygen dissolve poorly in the blood?
It has low solubility at physiological partial pressure
What is the equation for haemoglobin and oxygen binding?
O2 + Hb ⇌ HbO2
What is the shape of a haemoglobin-oxygen saturation curve?
Sigmoidal
What does an oxygen-haemoglobin saturation curve show?
oxyhemoglobin (% saturation) vs PO2(mmHg)
What is the advantage of the upper flat part of a oxygen-haemoglobin saturation curve?
Moderate changes in PO2 around the normal value in the lungs (~100mmHg) have only small effects of the %saturation, and therefore the amount of oxygen carried by the arterial blood
What is the advantage of the steep part of a oxygen-haemoglobin saturation curve?
helps in the unloading of O2 to the tissues
What is the Bohr effect?
Haemoglobin has a lower affinity for oxygen when there is an increase in the partial pressure of CO2 and/or a decrease in blood pH
If the binding affinity of oxygen decreases, what direction does the oxygen-haemoglobin saturation curve shift?
Rightwards - higher PO2 is needed to achieve greater saturation
What factors affect oxygen affinity to Hb?
Temperature, PCO2, pH, BPG levels
What is the affect of high temperature on oxygen affinity to Hb?
Reduced affinity
What is the effect of BPG on oxygen binding/affinity to Hb?
Decreases affinity, causes rightward shift of saturation curve
How does exercise affect the affinity of oxygen and Hb?
Causes plasma pH to drop and temperature to rise, causing right ward shift
What are the 3 forms in which CO2 is transported in the blood?
dissolved in plasma, as bicarbonate, combined with protein as carbamino compounds (The latter two are within RBCs)
What percentage of CO2 is in the plasma and in RBCs?
7% in plasma, 93% diffuses into RBCs
In what form is CO2 bind to haemoglobin?
HbCO2 - carbaminohaemoglobin
How is carbon dioxide converted to bicarbonate ions in the blood?
Carbonic anhydrase enzymes convert CO2 + H2O to carbonic acid, which then dissociates into hydrogen ions and bicarbonate ions
What enzyme converts CO2 to carbonic acid in RBCs?
Carbonic anhydrase
What is the equation for the conversion of CO2 to carbonic acid and then bicarbonate ions?
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
What is the chemical formula for the bicarbonate ion?
HCO3-
What happens to the H+ ions in RBCs that are the product of the dissociation of carbonic acid from CO2?
They bind to haemoglobin to form HbH+
What is the product of H+ ions binding to haemoglobin?
HbH+
What happens to the bicarbonate ions (HCO3-) in RBCs that are the product of the dissociation of carbonic acid from CO2?
They move into the plasma in exchange for chloride ions in a process called chloride shift
What is chloride shift?
When bicarbonate ions move into the plasma from RBCs in exchange for Cl- ions
What is the role of the respiratory rhythmicity centres?
Generate cycles of contraction and relaxation in the diaphragm, establishing normal pace of respiration. Modify activity in response to chemical and pressure signals
What are the 3 key respiratory rhythmicity centres?
Inspiratory centre of the dorsal respiratory group (DRG), ventral respiratory group (VRG), Pre-Bötzinger complex
Where are the key respiratory rhythmicity centres located?
The medulla oblongata, in the brain stem
What is the function of the inspiratory centre of the dorsal respiratory group (DRG)?
signals to diaphragm & external intercostals muscles - the essential inspiratory muscles
What is the function of the ventral respiratory group?
Inspiratory centres signal to accessory inspiratory muscles, expiratory centres signal to accessory expiratory muscles
What is the function of the Pre-Bötzinger complex?
Acts as a ‘pulse generator’ (similar to the SA node) to establish the pace/rate of respiration
What is the efferent signal from the medulla in respiratory control?
Contraction signals to the respiratory muscles
What is the afferent signal to the medulla in respiratory control?
sensory information from receptors
What are the types of sensors that provide afferent input to the medulla from sensory control?
chemoreceptors, lung stretch receptors, baroreceptors, protective reflexes
Where are (respiratory) central chemoreceptors located?
In the medulla
What are (respiratory) central chemoreceptors sensitive to?
PCO2, but not to PO2 of blood
How do (respiratory) central chemoreceptors detect PCO2?
When CO2 diffuses out of the cerebral capillaries, it changes the pH of cerebrospinal fluid. Central chemoreceptors can detect this pH change.
Where are (respiratory) peripheral chemoreceptors located?
In the carotid and aortic bodies
What are (respiratory) peripheral chemoreceptors sensitive to?
PO2, little response to PCO2
What are the most rapidly responding type of respiratory chemoreceptor?
Peripheral chemoreceptors
What is the function of lung stretch receptors?
As the lungs inflate or deflate, they send afferent input to the brain to ensure that the lungs do not stretch too much or too little.
How are protective reflexes involved in respiratory control?
Receptors detects irritation from dust and other foreign particles and feedback to the brain stem that can send an efferent signal to trigger a sneeze or cough
