Scenario 5 - Respiration Flashcards
what are the two types of alveolar cells? what do they do?
Type I cells - squamous pulmonary epithelium - form continuous lining of wall - MAIN SITE OF GAS EXCHANGE
Type II (Septal) Cells - between the type I cells - rounded cuboidal epithelium - free surfaces contain microvilli - SECRETE ALVEOLAR FLUID
What is the alveolar fluid?
keeps the surface between the cells, and the air, moist
produce surfactant - that maintains airway patency
what are the alveolar macrophages?
found within the wall of the alveolus - phagocytose fine dust and other debris
what is the role of fibroblasts in the alveolar wall?
production of reticular and elastic cells
under the type I pnuemocytes to produce the elastic basement membrane
What is the respiratory membrane?
where gaseous exchange occurs
- alveolar wall (type I and II pneumocytes, macrophages)
- epithelial basement membrane of the alveoli
- capillary basement membrane (usually fused with (2))
- capillary endothelium
What is the pore of Kohn?
collateral ventilation between the alveoli
inter-alveolar
what is the Channel of martin?
interbronchiolar colateral ventilation
what is the channel of Lambert?
bronchioalveolar colateral ventilation
what factors effect the rate of gaseous exchange
Concentration gradient determined by: - partial pressure gradient - solubility of the gases Surface area respiratory membrane thickness
What is the effect of solubility of a gas on rate of exchange?
if dissolved in water, diffusion is more efficient
so more soluble = faster diffusion across the respiratory membrane
what is the percentage of nitrogen in:
(i) dry air
(ii) alveolar air
(i) 79%
(ii) 75%
what is the percentage of oxygen in:
(i) dry air
(ii) alveolar air
(i) 21%
(ii) 14%
what is the percentage of carbon dioxide in:
(i) dry air
(ii) alveolar air
(i) 0.04%
(ii) 5.3%
what is the percentage of water vapour in:
(i) dry air
(ii) alveolar air
(i) 0
(ii) 6.2%
What is the partial pressure of oxygen in the alveoli?
13.3 kPa
what is the partial pressure of carbon dioxide in the alveoli
5.3 kPa
how is oxygen transported?
mainly through binding to haemoglobin
1.5% disolved in plasma
what effects oxygen binding to haemaglobin
partial pressure of oxygen
- when PO2 is high - in the lungs - O2 binds to Hb
- when PO2 is low - in the respiring tissues - O2 dissociates from oxyHb
what does haemoglobin saturation mean?
the amount of haemoglobin with O2 bount
i.e. when Hb is low saturated - not a lot of O2 is bound to Hb
What is affinity of Hb?
the tightness with which Hb binds O2
i.e. high affinity - more tightly bound to O2
low affinity - O2 is released more readily
what does an oxygen dissociation curve show?
how saturated Hb is at different partial pressures of O2
so when PO2 is low, such as in deoxygenated blood - Hb is not very saturated
when PO2 is high - eg. oxygenated blood in systemic circulation, saturation of Hb is high
what is the effect of acidity on the oxygen dissociation curve?
when pH decreases - suggests CO2 in the blood is high
causes Hb affinity for O2 to decrease - so O2 is released more readily
CURVE SHIFTS TO RIGHT
what is normal pH?
7.4
how does the shift caused by acidity help to return pH to normal?
oxy-Hb becomes deoxy-Hb - releasing oxygen
in the process, the oxygen binding site is replaced by binding of H+ ions - thus removing them from circulation and increasing pH
What is the effect of haemaglobin binding CO2?
causes affinity for O2 to decrease - O2 dissociates more readily.
CURVE SHIFTS RIGHT
why would there be a high concentration of H+ ions in circulation?
when CO2 is high, it reacts with H20 in the RBCs forming H2CO3 - which is unstable and forms H+ and HCO3-
HCO3- remains in RBC
H+ moves out into the blood
what is the effect of temperature on oxygen dissosiation?
increased temp - faster chemical reactions - more metabolic products - decreased pH - more O2 disossiation
CURVE SHIFTS RIGHT
What is the effect of BPG on oxygen dissosiation?
BPG formed by RBCs during glycolysis
binds to the beta globin chain go Hb
decreases affinity for O2 - more O2 released
CURVE SHIFTS RIGHT
What would cause the oxygen dissosiation curve to shift lefT?
high pH, low temperature, low [BPG]
what causes the Bohr Shift?
O2 dissosiates readily from Hb at higher PO2 due to acidity or high concentration of CO2.
what are the main ways that CO2 is transported?
Disolved in plasma (7%)
Carboamino compounds (i.e. bound to Hb) - 23%
As bicarbonate ions (70%)
how is carbon dioxide transported as carboamino compounds
CO2 binds to the terminal alpha and beta chains of Hb
particularly when PCO2 is high
How is CO2 transported as bicarbonate ions?
CO2 + H2O –> H2CO3 –> H+ and HCO3-
mainly carried in the RBC as HCO3-
some HCO3- diffuses out in exchange with Cl- (THE CHLORIDE SHIFT) to be transported in plasma
what is the Haldane effect?
the more oxy-Hb in the circulation, the lower the carrying capacity for CO2
if there is high deoxy-Hb, it can:
- bind more CO2
- bind more H+ ions
by binding H+, increases the concentration gradient between RBC and blood - so more H+ can be formed from CO2 in the RBC
NET EFFECT - when oxygen levels are low, ability to transport carbon dioxide is higher.
what is daltons law?
determines partial pressure
a gas exerts its own pressure in a mixture of gases as if no other gases were present
what is the rhythm for normal breathing?
2 second burst for inspiration and 3 second relaxation for exhilation
where is the inspiratory burst initiated?
DRG - sends impulses to diaphragm via phrenic nerve
& sends impulses to external intercostals via intercostal nerves
VRG acts as a pacemaker - sending signals to the DRG to initiate inspiration
where are the DRG and VRG found
in the medullary respiratory centre
what is the role of the VRG
pacemaker to DRG in quiet breakting
send impulses to accessory muscles in forceful inhalation
and in forced exhalation when DRG is not firing
where is the pneumotaxic centre and what is its role?
within the Pons
transmit impulses to the DRG in normal breathing
Modifies the basic rhythm formed by the VRG during complex breathing - e.g. exercise, speaking, sleeping
what is the role of the apneustic centre
increases the length of inspiration when talking by feeding back to DRG - to cause forced inhalation, and VRG to activate accessory muscles.
what is the role of chemoreceptors?
detect pH of the blood - if low, then CO2 must be high
input to VRG - causing forced exhalation to blow off more CO2
where are the central chemoreceptors?
within the medulla - CO2 diffuses into CSF - effects pH - central chemoreceptors feed to VRG directly
80% of response to high CO2
where are the peripheral chemoreceptors
in the carotid and aortic bodies
how do the peripheral chemoreceptors respond?
monitor pH, O2 and CO2
Carotid body –> glossopharangeal nerve –> DRG
Aortic body –> vagus nerve –> DRG
what is the role of stretch mechanoreceptors?
found in smooth bronchiole walls
detect stretching to prevent over inflation of the lungs
feed back to DRG via vagus nerve - causing shorter and shallower breathing
what is the role of J receptors?
found in alveolar and bronchiole walls
respond to lack of movement in the alveoli or bronchi
feed back to DRG via vagus nerve
increase rate and depth of breathing
what is the role of proprioceptors?
within all respiratory muscles except the diaphragm
detect the position and length of the muscles - feed back to DRG to increase rate of breathing if the muscles are excessively stretched - i.e. in exercise
what is the role of cortical control in breathing
higher centres detect anxiety, talking exercise etc.
input to the pons to modulate breathing
what is VO2?
oxygen consumption
the amount of oxygen being used by the tissues per minute
what is DO2?
oxygen delivery
the amount of oxygen being delivered to the tissues per minute
