BIO 3302 Lecture 11: LECTURE 11 – CONTROL OF VENTILATION
13 Dec 2016
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LECTURE 11 – CONTROL OF VENTILATION
Control of Ventilation
• Two components
• Generation of rhythmic breathing movements
• Adjustment of breath frequency and size to meet physiological needs
• Rhythmic breathing movements
• Central pattern generator in medulla sends output to appropriate muscles
• Modulation by various inputs
o Higher brain centres - brain sends signals to muscles to contract to breathe
▪ Conscious control
o Chemoreceptors - detect blood O2 and CO2 levels and pH and adjust ventilation to
keep these levels at set point
▪ Differ quite dramatically between fish and mammals
•
• Mammalian chemoreceptors
• Central
o Main determinant of ventilatory responses
o Located in brainstem
o Sensitive to H+ but respond to blood PCO2 (blood brain barrier)
▪ pH → frequency and/or amplitude
▪ Respond indirectly to CO2 via H+
▪ Protos do’t pass lood rai arrier easily ut CO2 does lipid solule ad
reacts with water to form H.
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• Changes in PCO2 in blood, result in changes in proton levels in fluid in
brain and those changes are detected by chemoreceptors.
• RESPOND TO PCO2, pH falls, PCO2 rises, H rises, drives you to breathe.
• Peripheral
o Located in carotid and aortic bodies
▪ Glomus cells - located in carotid body
▪ More responsive to CO2 and pH.
o Sensitive to O2, CO2 and H+
▪ Greater sensitivity to CO2/pH than O2
▪ Oxygen levels fall on mt Everset, the peripheral chemoreceptors are detecting it
not center.
•
• Fish chemoreceptors
• Ventilation keyed primarily to O2, but CO2 responses present
• No central chemoreceptors
• Peripheral
o Located on gills - neuroepithelial cells
o Thought to be homologous to glomus cells, located on gill arches
o In mammals, blood vessels to brain derived from same blood vessels that go to gills in
fish
▪ Match in placement.
o Sensitive to blood and/or water
o Sensitive to O2 and/or CO2 (but probably not pH)
▪ More responsive to O2 than CO2
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•
• Discuss in groups:
• Why is ventilation keyed to O2 in water breathers, but CO2/pH in air breathers?
• In mammals, brain sensitive to CO2 and animal increases frequency of blah and go up -
hyperventilation
• Fish, main sensors are linked to o2 found in gills and detect water and/or blood.
o Respond to gall of blood o2 levels and water o2 envts.
• Ventilation linked to o2 in water breathers, and CO2/pH in air breathers.
• WATER BREATHERS
o Water is o2 poor medium - to extract enough o2 in water is prob
o Water is variable in o2 levels, fish need to sense water o2 levels for efficient breathing
▪ Major constraint
▪ PCO2 = 4 Torr
• AIR BREATHERS
o High CO2 levels in blood
o Water is oxygen poor medium and air is oxygen rich medium, same rate of o2
consumption so less frequent ventilation for air breathers
o Convection requirement for o2 uptake relieved in air, resulting in higher CO2 levels
▪ Lower convection requirement in air breathers 40 torr of PCO2
o High levels of co2 in air breather in comparison to water breathers
o Easier to get rid of CO2 in water
▪ Have peripheral sensors for backup if climbing huge mountain that can drive
respiration.
Diving and divers → respiratory and cardiovascular adjustments
• Problems
• Absence of ventilation
o Exercise on restricted O2 supplies
• The bends (high pressure)
• (Temperature – maintenance of high Tb in an infinite heat sink)
• Solutions
• Reflect opportunistic nature of natural selection
• Natural selection operates on something that is already present in the envt
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Document Summary
Fish chemoreceptors: ventilation keyed primarily to o2, but co2 responses present. Peripheral: located on gills - neuroepithelial cells, thought to be homologous to glomus cells, located on gill arches. In mammals, blood vessels to brain derived from same blood vessels that go to gills in fish: match in placement, sensitive to blood and/or water. In mammals, brain sensitive to co2 and animal increases frequency of blah and go up - hyperventilation. Fish, main sensors are linked to o2 found in gills and detect water and/or blood: respond to gall of blood o2 levels and water o2 envts, ventilation linked to o2 in water breathers, and co2/ph in air breathers. Water breathers: water is o2 poor medium - to extract enough o2 in water is prob, water is variable in o2 levels, fish need to sense water o2 levels for efficient breathing, major constraint, pco2 = 4 torr.
