Transcript Respiration #3 - Eastern Michigan University

Control of Ventilation
• Respiratory control center
– Receives neural and humoral input
• Feedback from muscles
• CO2 level in the blood
– Regulates respiratory rate
Location of Respiratory Control Centers
Neural Input to the Respiratory
Control Center
• motor cortex - impulses from cortex may
“spill over” when passing through medulla
on way to heart and muscles
• afferent - from GTO, muscle spindles or
joint pressure receptors
• mechanoreceptors in the heart relay changes
in Q
Humoral Input to the Respiratory
Control Center
• central chemoreceptors - respond to changes
in CO2 or H+ in CSF
• peripheral chemoreceptors - aortic bodies
and carotid bodies
– both similar to central receptors, carotids also
respond to increases in K+ and decreases in
PO2
Ventilation vs. Increasing PCO2
Ventilation vs. Decreasing PO2
Ventilatory Control During
Exercise
• Submaximal exercise
– Linear increase due to:
• Central command
• Humoral chemoreceptors
• Neural feedback
• Heavy exercise
– Exponential rise above Tvent
• Increasing blood H+
Respiration Control during Submaximal
Exercise
Respiratory Control during
Exercise
• Central commmand initially responsible for
increase in VE at onset
• combination of neural and humoral
feedback from muscles and circulatory
system fine-tune VE
• Ventilatory threshold may be result of
lactate or CO2 accumulation (H+) as well as
K+ and other minor contributors
Effect of Training on Ventilation
• Ventilation is lower at same work rate
following training
– May be due to lower blood acidity
– Results in less feedback to stimulate breathing
Training Reduces Ventilatory Response
to Exercise
Final Note
• the pulmonary system is not thought to be a
limiting factor to exercise in healthy
individuals
• the exception is elite endurance athletes
who can succumb to hypoxemia during
intense near maximal exercise
Acid-Base Balance
Acids and Bases
• Acid - compound that can loose an H+ and
lower the pH of a solution
– lactic acid, sulphuric acid
• Base - compound that can accept free H+
and raise the pH of a solution
– bicarbonate (HCO3-)
• Buffer - compound that resists changes in
pH
– bicarbonate (sorry)
pH
• pH = -log10 [H+]
– pH goes up, acidity goes down
• pH of pure water = 7.0 (neutral)
• pH of blood = 7.4 (slightly basic)
• pH of muscle = 7.0
Acidosis and Alkalosis
Acid Production during Exercise
• CO2 - volatile because gas can be
eliminated by lungs
– CO2 + H2O <--> H2CO3 <--> H+ + HCO3-
• The next point is erroneous
• Lactic acid and acetoacetic acid - CHO and
fat metabolism respectively
– termed organic acids
– at rest converted to CO2 and eliminated, but
during intense exercise major load on acid-base
balance
• Sulphuric and Phosphoric acids - produced
by oxidation of proteins and membranes or
DNA
– called fixed because not easily eliminated
– minor contribution to acid accumulation
Sources of H+
Buffers
• maintain pH of blood and tissues
• accept H+ when they accumulate
• release H+ when pH increases
Intracellular Buffers
•
•
•
•
proteins
phosphates
PC
bicarbonate
Insert table 11.1
Extracellular Buffers
• bicarbonate - most important buffer in body
remember the reaction
hemoglobin - important buffer when
deoxygenated
picks up H+ when CO2 is being dumped
into blood
proteins - not important due to low conc.
Buffering Capacity of Muscles vs. Blood
Respiration and Acid-Base
Balance
• CO2 has a strong influence on blood pH
• as CO2 increases pH decreases (acidosis)
CO2 + H2O > H+ + HCO3• as CO2 decreases pH increases (alkalosis)
• so, by blowing off excess CO2 can reduce
acidity of blood
Changes in Lactate, Bicarb and pH vs.
Work Rate
Lines of Defense against pH Change during
Intense Exercise