BIOL 2420 Lecture Notes - Metabolic Acidosis, Oxidative Phosphorylation, Myocyte
26 Jun 2018
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Human Physiology II
Chapter 25: Integrative Physiology III: Exercise
Metabolism and Exercise
small amount of ATP for muscle contraction present in muscle fibre when contraction begins
as ATP present is used up, transformed into ADP, phosphocreatine transfers energy
from its high-energy bond to ADP, replenishing muscle’s supply of ATP
combination of muscle ATP, phosphocreatine supports 15s of intense exercise
muscle fibers must manufacture more ATP from energy stored in nutrients (from muscle
itself or mobilized from liver, adipose tissue)
carbohydrates, fats primary substrates for energy production
most efficient ATP production through aerobic pathways
glucose, fatty acids metabolized to provide ATP if cell has adequate oxygen for oxidative
phosphorylation
if oxygen requirement of muscle fiber exceeds supply, energy production from fatty acids
decreases, glucose metabolism shifts to anaerobic pathways
when cell lacks oxygen for oxidative phosphorylation, final product of glycolysis
(pyruvate) converted to lactate instead of acetyl CoA
exercise that depends on anaerobic metabolism cannot be sustained for extended period
cells that obtain ATP by anaerobic metabolism of glucose to lactate said to be carrying out
glycolytic metabolism
anaerobic metabolism produces ATP 2.5x faster than aerobic pathways
2 disadvantages:
1. anaerobic metabolism provides 2 ATP per glucose whereas oxidative metabolism
provides 30-32 ATP per glucose
2. anaerobic metabolism contributes to state of metabolic acidosis be producing H+
(although carbon dioxide generated during exercise more significant source of acid)
3 sources of glucose for ATP production:
1. plasma glucose pool
2. intracellular glycogen stores in muscles, liver
3. “new” glucose made in liver through gluconeogenesis
glucose can’t provide enough ATP for endurance athletes, rely on energy stored in fats
aerobic exercise uses both fatty acids, glucose as substrates for ATP production
at lower exercise intensities, most energy for ATP production comes from fats
as intensity increases, ATP consumed faster, muscle fibres use larger proportion glucose
aerobic training increases fat, glycogen stores within muscle fibres
endurance training increases activity of enzymes for -oxidation, converts muscle fibres
from fast-twitch glycolytic to fast-twitch oxidative glycolytic
Hormones Regulate Metabolism during Exercise
plasma concentrations of glucagon, cortisol, catecholamines (epinephrine, norepinephrine),
growth hormone increase during exercise
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cortisol, catecholamines, growth hormone promote conversion of triglycerides to
glycerol, fatty acids
glucagon, catecholamines, cortisol mobilize liver glycogen, raise plasma glucose levels
although plasma glucose concentrations rise, insulin secretion suppressed by sympathetic
input onto beta cells of pancreas
cells other than muscle fibers reduce glucose uptake, sparing glucose for use by muscles
actively contracting muscles not affected by low insulin levels because contraction
stimulates insulin-independent translocation of GLUT4 transporters to muscle membrane,
increasing glucose uptake in proportion to contractile activity
Oxygen Consumption Is Related to Exercise Intensity
Oxygen Consumption (VO2): oxygen consumed during oxidative phosphorylation, when it
combines with hydrogen in mitochondria to form water
measure of cellular respiration, measured in L of oxygen consumed/min
individual’s maximal rate of oxygen consumption (VO2max) indicator of ability to perform
exercise
metabolic hallmark of exercise is increase in oxygen consumption that persists after activity
ceases
when exercise begins, muscle oxygen consumption increases to rapidly that it’s not
immediately matched by oxygen supplied to muscles
during lag time, ATP provided by muscle ATP reserves, phosphocreatine, aerobic
metabolism supported by oxygen stored on muscle myoglobin, blood hemoglobin
use of muscle stores creates oxygen deficit because replacement requires aerobic
metabolism, oxygen uptake
once exercise stops, oxygen consumption slow to resume resting level
Excess Post-Exercise Oxygen Consumption: oxygen used to metabolize lactate, restore ATP,
phosphocreatine levels, replenish oxygen bound to myoglobin
increased body temperature, circulating catecholamines also play role in elevating post-
exercise oxygen consumption
Several Factors Limit Exercise
resistance training depends heavily on anaerobic metabolism
if muscle mitochondria limited in number/have insufficient oxygen supply, muscle fibres
unable to produce ATP rapidly
muscle metabolism influences sub-maximal exercise capacity
ability of cardiovascular system to deliver oxygen, nutrients to muscle at rate that supports
aerobic metabolism major factor in determining max. oxygen consumption
Ventilatory Responses to Exercise
Exercise Hyperventilation/Hypernea: hyperventilation resulting from combination of
feedforward signal from central command neurons in motor cortex and sensory feedback from
peripheral receptors
when exercise begins, mechanoreceptors, proprioceptors in muscles, joints, send info about
movement to motor cortex
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find more resources at oneclass.com
Document Summary
Metabolism and exercise small amount of atp for muscle contraction present in muscle fibre when contraction begins. As atp present is used up, transformed into adp, phosphocreatine transfers energy from its high-energy bond to adp, replenishing muscle"s supply of atp. Combination of muscle atp, phosphocreatine supports 15s of intense exercise. Muscle fibers must manufacture more atp from energy stored in nutrients (from muscle itself or mobilized from liver, adipose tissue) carbohydrates, fats primary substrates for energy production. 3 sources of glucose for atp production: plasma glucose pool. Hormones regulate metabolism during exercise plasma concentrations of glucagon, cortisol, catecholamines (epinephrine, norepinephrine), growth hormone increase during exercise. Cortisol, catecholamines, growth hormone promote conversion of triglycerides to glycerol, fatty acids. Glucagon, catecholamines, cortisol mobilize liver glycogen, raise plasma glucose levels although plasma glucose concentrations rise, insulin secretion suppressed by sympathetic input onto beta cells of pancreas. Cells other than muscle fibers reduce glucose uptake, sparing glucose for use by muscles.
