week 4: Flashcards
what is exercise a challenge to
homeostasis
muscle blood flow and exercise intensity relationship
directly proportional until saturation point has been hit
reasons for saturation point
opened up as many blood vessels as you can
can’t increase exercise intensity anymore
cardiac output= (litres per minute)
heart rate x stroke volume
stroke volume
volume ejected by ventricle per beat
bradycardic
less than 60bpm
tachycardic
over 90bpm
fox’s formula
max heart rate = 220-age
more recent max heart rate formula
211- (0.64) x age
relationship between heart rate and the amount of work being performed
very positive correlation
r=0.99
peak heart rate often hit when
peak oxygen transport hit (V02 max)
Karvonen heart rate reserve method
max hr- resting hr = HRR
moderate = 60-70% HRR
how much can cardiac output increase by during exercise
normally 4-6 fold
( from 4-8 litres per min- 20-25)
stroke volume increase during exericse
30% increase compared to at rest
80ml per beat - 120/140ml per beat
heart rate increase during exercise
2-3 fold
60 bpm- 180bpm
what does exercise anticipation activate
sympathetic neurons in hypothalamus
what nerve switches off during exercise and what nerve becomes activated
vagal (parasympathetic) nerves switches off
sympathetic nerve becomes activated
what does sympathetic nerve becoming activated cause
SA nodes intrinsic firing frequency accelerates
faster heart rate
gets stronger until peak HR reached
what does sympathetic nervous stimulation of adrenal medulla release
epinephrine
effects of epinephrine
delivered by blood
accelerates SA nod discharge
dilates coronary vessels
increases myocardial metabolism
what do efferent sympathetic fibers increase
heart rate
myocardial contractility
dilate coronary arteries
changes in muscle during exercise
elevated temp
decreased local O2
elevated local CO2
falling local pH
increasing local adenosine
increased nitric oxide
elevated local K+
what do all of these local factors do
open up blood vessels
why does pH fall
H+ is accumulated as a product of elevated metabolism due to producing and breaking lots of ATP
more acidotic
relaxes blood vessel walls
why does adenosine increase
lots of ATP breakdown releases adenosine
effect of nitric oxide
smooth muscle in blood vessels relax
why does blood prefer to go to places which are more metabolically active
blood vessels a these places have been triggered to relax
effect of adrenaline on alpha receptors
vasoconstriction
exercise increases adrenaline however more blood flows to muscles needed
as adrenaline goes up it restricts blood flow
competition between metabolically active tissue and adrenaline
what happens when muscle is activated by a somatomotor nerve
releases vasodilator stimuli
what does active sympathetic nerve cause
vasoconstrictor stimuli
why is good blood flow important
ensure active muscle is getting oxygen and nutrients
sympatholytic effect
vasodilator stimuli overpowers sympathetic input
blood will get to where required
where muscle isn’t active, blood flow shut down to these areas (diversion of blood to where its required)
group III and group IV nerves embedded in skeletal muscles
directly responsive to temp, muscle tension, acidosis
send signal back to medulla (to say how well muscles are coping?)
perception of effort
effect of signals from group III and group IV nerves
increase sympathetic output to encourage greater diversion
shutting off splanchnic blood vessels
diverting blood away from guts/ kidneys/ liver
enhanced capacity to supply muscle blood
syncope
fainting/ passing out
affect of higher blood pressure during exercise
bigger pressure gradient between arteriole side and venule side
greater rate of flow maintained through skeletal muscle
effect of exercise on diastolic and systolic blood pressure
systolic: increases
diastolic: remains same
why does diastolic pressure stay same
if it was too fall, it would mean arteries were relaxing during exercise
if it was to rise, not beneficial as heart would be doing a lot more work
VO2 max=
cardiac output max x a-v O2 difference
why is VO2 max one one legged exercise 75%-80% of two legged- exercise
higher blood flow can be achieved to activate muscles in one-legged exercise
if both legs were dilated to the same extent as in one-legged exercise, blood pressure would fall
what is responsible for making sure pressure goes up and demnads are met
ensuring enough blood goes into heart to maintain good stroke volume
must also ensure not to elevate the resistance to which the heart is working, if diastolic pressure increases it would oppose blood flow out of heart
increase contractility of heart to ensure as much blood as possible leaves per beat
how to ensure heart is filling with blood to allow efficient stroke volume during exercise
increase blood volume
increase return
how to increase blood volume
contract spleen
constrict splanchnic supply
constrict capacitance veins
how to increase return
constrict veins
constrict supply to other tissues
muscle pump
deep veins sit within skeletal muscle
when skeletal muscles activated they contract, pressure around skeletal muscle increases,
skeletal muscles push on veins reducing their volume and elevating the pressure within the veins, helps pump blood back towrds heart
what is muscle pump facilitated by
valves within the large veins
prevents backflow
blood can only go towards heart
what does negative pressure in thorax increase
venous return
what creates negative pressure in thorax
breathing
exercise presser reflex
baroreceptor input inhibited
allowing bp to increase
