BI0005 - Lecture 17 - Changes of exercise
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What two main forms does exercise take?
- -E.g. walking: rhythmic movement involving flexing of joints as well as rhythmic contractions and relaxations of skeletal muscles
- - E.g. Weight lifting: no external work, specific muscles maintain contractions for a period of time (isometric contractions)
What happens to blood flow and oxygen uptake during exercise and rest?
- During rest, there is a blood flow of about 5 litres per minute.
- During severe exercise there is a blood flow of about 25 litres per minute.
- During rest there is an O2 uptake of about 250ml per minute.
- During severe exercise there is an O2 uptake of about 2000ml per minute
During severe exercise blood flow greatly increases to the muscles, increases to the skin, increases to the heart, and decreses to the kidneys and other organs (stays same to brain).
How does the whole body respond to the stress of exercise?
The relative proportion of aerobic and anaerobic metabolism varies with the severity and duration of exercise.
Oxygen consumption does not rise immeditately to match energy requirements, so there is an oxygen deficit.
Blood lactate levels rise rapidly as the anaerobic threshold is reached.
After exercise ATP and creatine phosphate are resynthesized, and excess lactate is resynthesized into glucose and glycogen.
What happens to the heart rate?
At rest, the parasympathetic control keeps resting heart rate at 70 bpm.
Exercise reduces vagal activity
Excercise increases sympathetic activity - positive chronotropic (changes to heart rate) effect
What cardiovascular changes occur?
The stroke volume increases
Contraction of the veins
Increase in cardiac contractility
What is the stroke volume?
In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from one ventricle of theheart with each beat
What is cardiac contractility?
Myocardial contractility represents the intrinsic ability of the heart / myocardium to contract.
What happens to cardiac output?
Cardiac output in litres per minute = stroke volume (mls) x heart rate (beats per minute)
In moderate levels of exercise CO increases due to increased SV and increased HR.
Approaching severe levels of exercise, CO increases due to increased HR
What happens to blood pressure?
Blood pressure (mmHg) = Cardiac output (lpm) x Total peripheral resistance.
Intrisinc and Extrinsic factors affect resistance:
Increased metabolites results in vasodilation, which decreases TPR
Increased sympathetic activity releases noradrenaline which causes vasoconstriction, and thus increases TPR
Increased sympathetic activity releases adrenaline which results in vasodilation, thus decreasing TPR
Overall, there is a decrease in TPR
Systolic pressure increases as the increase of cardiac output is greater than the decrease of TPR
What regulates the changes during exercise?
'Central command center'
Reflexes- afferent activity from joints, chemoreceptors, metabolites
What difference is there in fitness of athletes and sedentary students ?
At a similar heart rate, endurance athletes recieve about twice as much oxygen (~4.8 compared to ~2.2 L.min)
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