17 Metabolism and exercise Flashcards
how many minutes per week should a healthy adult be active?
150 mins (at least 10 mins per day)
why does heart rate increase immediately with exercise?
incr. in adrenaline secretion
incr. in stimulation of the sympathetic NS
incr. anticipatory response –> release of NT (e.g. adrenaline and noradrenaline)
–> increases proportional to exercise until plateau/max h.r. reached
how does vasodilation of arterioles in skeletal muscles occur?
secretion of nitric oxide by arteriolar endothelium
in response to fall in O(2) levels
why does stroke volume increase with exercise?
more blood returns to left atrium
∴ larger volume of blood filling ventricle in diastole
∴ greater volume of blood pumped out in systole
why does breathing rate + tidal volume increase with exercise?
more air into alveoli –> incr. in concentration gradient ∴ O(2) can diffuse into the blood more easily
∴ incr. rate of aerobic respiration ∴ more CO(2) produced ∴ more H(2)CO(3) produced
incr. in blood acidity detected by chemoreceptors - sends impulses to respiratory centre in medulla
incr. in rate and extent of contractions of diaphragm and intercostal muscles
what are the long term effects of exercise on the circulatory system?
incr. VO2 max
incr. heart size (hypertrophy of cardiac muscle –> incr. in wall thickness)
decr. resting h.r.
incr. stroke volume
decr. recovery time
what are the long term effects of exercise on the respiratory system?
incr. max b.r.
incr. tidal volume
incr. vital capacity
incr. capillary density –> decr. b.r. at rest
what are the long term effects of exercise on the skeletal system?
incr. in cross-sectional area of slow twitch muscle fibres
incr. in size/number of mitochondria in muscle fibres
incr. capillary network surrounding muscle fibres
incr. efficiency of lipid metabolism
incr. Mb and glycogen stores
what is the definition of aerobic fitness?
a measure of the ability of the heart and lungs to respond to the demands of aerobic exercise
what are three indicators of aerobic fitness?
efficiency of GES/CVS
extent of aerobic respiration without fatigue
efficiency of respiration
how is aerobic fitness achieved?
20 mins of exercise
3 x per week
increasing in intensity to 50-55% of VO2 max
give four factors that affect aerobic fitness
age
gender
smoking
malnutrition
motivation
programme
alcohol consumption
stimulants
depression
give four health benefits of regular aerobic exercise
strengthened skeletal muscle
improved circulatory efficiency
reduced blood pressure
improved mental health
reduced risk of diabetes
stimulate bone growth
how can aerobic exercise be improved?
increase:
- Frequency
- Intensity
- Type
- Time (i.e. duration)
how is aerobic fitness measured?
decr. resting h.r.
decr. recovery time
incr. VO2 max
how does a successful training programme bring improved aerobic fitness?
successful training = stressor
body adapts
progressive overload –> prevents plateau
what is the definition of VO2 max?
the maximum rate at which oxygen can be taken in, transported and utilised, as measured by/during incremental exercise
what units is VO2 max measured in?
absolute rate = dm^3 min-1
relative rate = ml kg-1 min-1
what is the function of the Bruce treadmill test?
to check the development of general endurance
can check nerve impulses from SAN if coronary heart disease is suspected
how is VO2 max calculated for men and women?
men: VO2 max = 14.8 - (1.379 x T(1)) + (0.451 x T(2)) - (0.012 x T(3))
women: VO2 max = 4.38 x T - 3.9
{where T = minutes on treadmill}
what is directly measured in the Bruce treadmill test?
ventilation rate
oxygen concentration of inhaled air
CO(2) concentration of exhaled air
when is VO2 max reached?
when O(2) consumption remains steady despite increased workload
what is excessive post-exercise oxygen consumption (EPOC)?
the increased volume of oxygen consumed following vigorous exercise
how is EPOC calculated?
oxygen consumed during recovery period - total oxygen consumed
why is oxygen required after exercise?
reoxygenate Hb and Mb
balance hormones
replenish glycogen stores in skeletal muscles
carry out cell repairs
regenerate ATP
convert lactate to glucose/glycogen
meet demands of incr. metabolic rate
what are the advantages of high intensity interval training?
incr. resting metabolic rate
improved VO2 max
how does erythropoietin enhance athletic performance?
recombinant human erythropoietin (RhEPO)
EPO normally secreted from cells in renal cortex of kidneys
incr. erythrocyte production in bone marrow
incr. RBC count
how is RhEPO produce?
GE bacteria
detectable ∴ random tests given
what are the advantages of RhEPO and blood doping?
incr. RBC count
incr. Hb concentration
incr. oxygen-carrying capability of the blood
incr. VO2 max
incr. performance
what are the disadvantages of RhEPO?
unethical
illegal
can cause severe cardiovascular problems
can lead to renal failure
how does blood doping enhance athletic performance?
remove ~ 1 dm^3 several months before competition
extra EPO secreted naturally
RBC count increases to normal
blood reintroduced a few days before the competition
what are the disadvantages of blood doping?
unethical
illegal
dangerous
- incr. blood viscosity –> clotting/pulmonary embolism
difficult to detect
how do steroids enhance athletic performance?
stimulate anabolic reactions
cause transcription of specific genes
artificial anabolic steroids can be used to increase muscle mass
what are the advantages of steroids?
incr. muscle size and strength
more aggressive
what are the disadvantages of steroids?
unethical
can cause liver damage
decr. natural testosterone production
decr. immune response
how does carbohydrate loading enhance athletic performance?
incr. stored glycogen in skeletal muscles (more a. glucose)
carbodepletion - CBH intake reduced
carbloading - high CBH diet for days before competition –> incr. a. glucose
what is the advantage of carbohydrate loading?
more a. glucose ∴ more aerobic respiration ∴ can work for longer
what are the disadvantages of carbohydrate loading?
weight gain
digestive issues + bloating
around how many molecules of haemoglobin (Hb) are there per RBC?
~ 280 million
how many O(2) molecules can each Hb molecule transport?
4
{accounts for 98% of O(2) in blood)
what is the prosthetic group of a Hb molecule?
haem (Fe2+)
binds cooperatively (allosteric conformational change makes it easier for the next O(2) to bind)
what is the definition of a respiratory pigment?
a specialised molecule that is capable of binding reversibly with oxygen
what is the function of Hb?
to transport O(2) as oxyHb to all respiring cells, where is acts as the final e- acceptor in the eTC
what is association?
the binding uptake of O(2) by Hb to form oxyHb
what is dissociation?
the ability of oxyHb to release O(2) from haem groups
what is the oxygen dissociation curve (ODC)?
a graph that shows the relationship between the partial pressure of oxygen (PO(2)) and % saturation of Hb
how is PO(2) calculated?
volume of gas/total volume = pressure of gas/total pressure
what is the oxygen binding capacity?
1.34 cm^3 of O(2) per g-1 of Hb
what is the appearance of the ODC for adult Hb (aHb)?
{sigmoidal curve - coop binding}
at high PO(2), little/no change in % saturation of Hb (i.e. plateau)
∴ O(2) is still taken up by Hb in capillaries
steep part = active skeletal muscles
∴ small changes in PO(2) –> large change in % saturation
what is the appearance of the ODC for foetal Hb (fHb)?
fHb has higher affinity for O(2) than aHb
∴ at any PO(2), fHb has higher % saturation than aHb
∴ fHb can obtain (O(2)) from maternal Hb via placenta
what is the quaternary structure of fHb?
2 alpha and two gamma p.p.c.
haem prosthetic groups
what is the quaternary structure of myoglobin (Mb)?
1 a. helix p.p.c.
1 haem prosthetic group
when does Mb release O(2)?
at low PO(2)
~ 0.5 kPa
why can Mb not bind cooperatively?
only 1 prosthetic group
Mb + O(2) MbO(2)
what is the appearance of the ODC for Mb?
a hyperbolic curve
what are the three ways in which CO(2) is transported in the blood?
dissolved in the blood plasma (5%)
reacts with terminal amine groups in haem p.p.c. to form carbaminohaemoglobin (10%)
reacts with water to form carbonic acid (85%)
which enzyme is required to turn CO(2) and H(2)O into carbonic acid (H(2)CO(3))?
carbonic anhydrase
can also catalyse the reverse reaction
how does the reaction between CO(2) and H(2)O in the blood decrease blood pH?
dissociation of H(2)CO(3) into H+ and HCO(3)-
H+ combines with Hb to form haemoglobinic acid (H.Hb)
what is the Bohr shift?
an decrease in blood pH due to the presence of CO(2) causes more O(2) to dissociate from Hb in erythrocytes
respiring tissues require more oxygen for more aerobic respiration to produce more ATP
more CO(2) is produced ∴ less Hb can combine with O(2) ∴ it is released more easily
what does the Bohr shift look like on a graph?
shift of ODC to right at same PO(2)
what happens to the HCO(3)- ions produced? what is their effect?
diffuse out of RBCs into plasma
Cl- diffuse in to balance change in charge
how is CO(2) reformed from H(2)CO(3) in the lungs and exhaled?
carbonic anhydrase catalyses the reverse reaction
releasing CO(2) and H(2)O
CO(2) diffuses down concentration gradient into the alveolar space and is exhaled
give three features of cardiac muscle
striated
myogenic
has intercalated discs
what is the purpose of intercalated discs?
cells membranes fuse and form gap junctions
free diffusion of ions for action potential movement
give three types of cardiac muscle
walls of atria
walls of ventricles
specialised conductive and excitatory muscle fibres
give three features of smooth muscle
tires easily
not under conscious control
has circular and longitundinal bundles for peristalsis
how is smooth muscle used in the iris?
circular bundles: contraction –> constriction of pupil
radial bundles: contraction –> dilation of pupil
give three features of skeletal muscle
multinucleated
striated
under conscious control of motor cortex
muscle –> ……… –> sarcomere
muscle
muscle bundle
fascicle
muscle fibre (cell)
myofibril
sarcomere
name the three proteins that make up actin
troponin (globular)
tropomyosin (‘string’)
G-actin (where myosin binds)
what enzyme can a myosin head function as?
ATPase
sliding filament theory: outline the formation of the cross bridge
myosin head has ADP + P(i) bound to it
E from hydrolysis of ATP activates myosin to ‘cocked’ position
Ca2+ released from sarcoplasmic reticulum and bind to tropomyosin
troponin undergoes allostery causing tropomyosin to move and expose mysosin binding sites on G-actin
myosin binds, forming cross bridge
P(i) released –> bridge strengthened
sliding filament theory: outline the power stroke
ADP is released from myosin head
head pivots and slides actin filament towards centre of sarcomere
sliding filament theory: outline the cross bridge detachment
another ATP binds to the myosin head
cross bridge weakens and myosin detaches
sliding filament theory: outline the reactivation of the myosin head
ATP is hydrolysed by myosin kinase
E released activates myosin head to ‘cocked’ position
why is Ca2+ required in muscle contraction?
causes troponin to undergo an allosteric change
which moves tropomyosin
exposing actin binding sites for the myosin heads
how is a nerve impulse converted into a muscle contraction?
a.p. arrives at synaptic end bulb of axon
synaptic transmission of ACh (see chap. 26)
ACh binds to receptors on motor end plate, opening Na+ channels
t tubules carry Na+ to centre of muscle fibre, spreading a.p. through the muscle
Ca2+ released and spread to actin filaments
outline the differences between slow and fast-twitch muscle fibres
slow:
- ATP production in aerobic respiration
- lots of mitochondria for KC and OP
- high Mb conc.
- small diameter
- high capillary density
fast:
- anaerobic respiration
- few mitochondria
- low Mb conc.
- large diameter
- low capillary density
