Download Peak Performance

Peak Performance
Topic 7.3
Introduction
• Why is O2 necessary for exercising?
• Regular exercise improves the body’s ability to deliver oxygen
to the muscles.
• What body systems would training improve?
Cardiac Output
• How does our body meet the O2 demands when we
exercise?
•
•
•
•
Breathing rate increases
Breathing deepens
Cardiac output increases
Blood flow is directed to active muscles
• Cardiac output = stroke volume * heart rate
Review of the Heart and
Cardiac Cycle
• What are the three stages of the cardiac cycle?
• Diastole, atrial systole, ventricular systole
• What happens during each stage?
Stroke Volume
• What is stroke volume?
• Volume of blood pushed out of the left ventricle into the aorta
with each beat
• Stroke volume at rest= 50-90cm3
• When does the heart refill with blood?
• During diastole
• Why? Volume of heart increases and pressure decreases,
skeletal muscle contraction pushes blood along the veins and
pressure gradient causes blood to move into the heart
• During exercise more blood enters the heart during diastole =
higher venous return
• This leads to higher stroke volume, as more blood then leaves
during systole
Heart Rate
• What is your pulse?
• The blood being pushed along the arteries by the contraction
of the heart
• Where is the easiest place to take your pulse?
• Wrist or neck
• Take your pulse!
• Average heart rate is about 70-72 bpm: is your heart rate
above or below this?
• Factors that might affect heart rate: Age, body size, size of
heart, fitness level
• Q7.17
• Activity 7.10
Control of Heart Rate
• The heart is myogenic: it can beat without any external
nervous stimulation
• However the contractions must be coordinated
• Your heart’s electrical system animation:
http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_all.html
• The SA node is the pacemaker: it is a small patch of cardiac tissue
which is joined to nerves, these nerves can bring impulses to speed
up or slow down heart rate
• An electrical impulse is generated by the SAN
• This spreads across the atria and causes them to contract
• The impulse can only be transferred to the ventricles by the AVN, as
there is a layer of non-conductive tissue separating the atria and
ventricles
• There is a slight delay (0.13 secs) before the impulse spreads down
and then up the ventricles
• Why is this important?
• The atria need to finish contracting before the ventricles contract to
allow the blood to be pushed in the ventricles first
• Contraction of the ventricles start at the apex and works up: why is
this important?
• To push the blood up and out into the arteries
• Activity 7.11
• Checkpoint Question 7.3
Measuring Heart Activity
• ECG/ EKG are used to show the electrical changes that occur
throughout the cardiac cycle
• Electrodes are attached to the patients skin around the heart
and limbs: these measure electrical impulses
• Most often done at rest, but can also be done during exercise
•
•
•
•
•
•
•
•
P (atrial contraction)
PR interval (delay between atrial and ventricular contraction)
Q, R, S (Ventricular contraction)
T wave (diastole, repolarisation)
How do we determine the length of one cardiac cycle?
Time between QRS complexes
http://library.med.utah.edu/kw/pharm/hyper_heart1.html
Q 7.18
Heart Problems
• Bradycardia: heart rate under 60 bpm: caused by drugs, heart
disease, hypothermia
• Tachycardia: heart rate over 100 bpm: caused fever, drugs,
exercise, fear
• Ischaemia: when the heart muscle does not receive blood due
to blockage of the coronary arteries, atherosclerosis, this can
affect conduction of impulses
• Atrial fibrillation and possibly Wolff-Parkinson White
Syndrome are examples of heart problems:
http://www.nhlbi.nih.gov/health/dci/Diseases/arr/arr_types.h
tml
• Q 7.19-7.21
• Activity 7.12
Nervous Control of Heart Rate
•
•
•
•
•
•
•
•
•
The heart is myogenic: what does this mean?
It does not need external stimulation to beat
Does it always beat at the same rate?
No
Why not?
The oxygen demands of the body vary
Nervous stimulation can increase or decrease heart rate
Do we consciously control our heart rate? No
The cardiovascular control centre in the medulla of the brain
controls heart rate.
Nervous System,
Chain of Events
•
•
•
•
•
•
Stimulus
Detection (receptors)
(sensory neurones)
Coordination (CNS)
(motor neurones)
Response (effectors)
Sympathetic Nervous System
•
•
•
•
Prepares body for action (fight or flight)
Increases heart rate, breathing rate, stroke volume
Decreases digestion
Sympathetic nerve stimulates SAN to speed up heart rate:
Accelerator
• Noradrenaline is the neurotransmitter released when the
impulse reaches the SAN
Parasympathetic Nervous
System
• Controls resting and digesting
• Decreases heart rate, breathing rate, stroke
volume
• Increases rate of digestion
• Vagus Nerve impulse causes SAN to slow the
heart rate down: Decelerator
• The Autonomic Nervous System
• Baroreceptors and chemoreceptors detect changes.
• What triggers the cardiovascular centre (what is the
stimulus) to increase HR?
•
•
•
•
•
Increase in CO2 concentration in the blood
Increase in lactate
(Decrease in O2 concentration)
Sensory receptors detect movement by muscles
Sensory receptors can detect decrease in blood pressure in arteries
• Which of these are detected by chemoreceptors
and which by baroreceptors?
• What triggers the cardiovascular centre (what is the
stimulus) to decrease HR?
• Raised blood pressure (detected in arteries)
• decrease in CO2 and lactate
• (increase in O2 concentration)
Hormones
•
•
•
•
•
•
•
•
•
•
•
Hormones: Chemicals messengers
Testosterone, oestrogen, FSH, LH, growth hormone, ADH
Produced: Endocrine glands
Examples of endocrine glands: Pituitary, adrenal, pancreas, thyroid,
testes, ovaries
Differences between nervous and hormonal control: speed,
duration, means of conduction
Which hormone is released during flight or fight situations?
Adrenaline
Produced: The adrenal glands
Location: Just above the kidneys
The effect on the SAN is similar to stimulation by the sympathetic
nerve.
Q 7.22-7.24
Breating Rate
• Read page 167
• Tidal volume: the volume of air inhaled and exhaled in each
breath
• Vital capacity: the maximum volume of air we can inhale and
exhale
• Minute ventilation: The volume of air entering the lungs per
minute
• = tidal volume X breathing rate
• Equipment we use to measure this: Spirometer
• How spirometer works:
http://athome.harvard.edu/programs/hse/video/hse2_5_mod
ule.html
Aerobic Capacity
•
•
•
•
•
•
•
•
The ability to take in and use O2
VO2= volume of O2 per minute
At rest= 0.2-0.3 litres per minute
VO2 (max) = during maximum aerobic exercise
VO2 (max) is 3-6 litres
VO2 (max) is often measured in ml/ min/ kg
What will effect VO2 (max)?
Lung capacity, heart capacity, efficiency of cardiovascular
system, efficiency of muscles
• Who will have higher VO2 (max)?
• Athletes, people who exercise regularly
• Activity 7.9
• We can calculate the volume of oxygen used up by using soda
lime to absorb the CO2 produced: this causes a drop in
volume, which shows up on the trace
• Q7.25-7.26
• Interactive tutorial
• Activity 7.13
Control of Breathing Rate
• Similar to control of heart rate in that changes occur and these
are detected by receptors and the CNS coordinates a
response.
• These are types of negative feedback
• Breathing rate is controlled by the ventilation centre in the
medulla of the brain.
Inhalation
•
•
•
•
•
•
•
External intercostals muscles contract
Diaphragm contracts
(other muscles may also contract during deep breathing)
Ribs move up and out
Volume increases
Pressure decreases
Mass flow: air moves into the lungs
Exhalation
• Stretch receptors in the bronchiole detect expansion during
inhalation, this inhibits contraction of muscles causing
inhalation
• Internal intercostal muscles contract during deep breathing
• Ribs move down and in
• Volume decreases
• Pressure increases
• Mass flow, air moves out of the lungs
•
•
•
•
•
Is all the air pushed out of the lungs during exhalation?
No
Residual air is what is left
Does the amount of residual air change?
Yes, more air is pushed out during deep breathing, when
exercising
Chemoreceptors and Breathing
• Carbon dioxide concentration in the blood determines
breathing rate
• CO2 reacts with water to produce carbonic acid (H2CO3)
• Since this can dissolves, it disassociates into ions, like all other
acids
• HCO3- and H+ ions are formed
• The higher the concentration of H + ions, the more acidic, the
lower the pH
• Chemoreceptors can detect H + ions
• These receptors are found in the ventilation centre, in the
carotid artery and the aorta
• Signals are then sent to the ventilation centre in the medulla
to either speed up or slow down ventilation rate
• Why is it important to increase ventilation rate when CO2
concentration increases?
• When breathing rate increases, CO2 can be removed more efficiently
by maintaining a high concentration gradient between the alveoli
and the blood= diffusion will happen more efficiently
• Will it have any other effects?
• Yes, O2 will also be absorbed more efficiently due to high
concentration gradient
• During exercise, the motor cortex sends signals to the ventilation
centre
• Stretch receptors in muscles and tendons also send signals to the
ventilation centre to increase breathing rate
• Read did you know, page 171
• Extension 7.3
• Activity 7.3b
Muscle Fibres
• What are the three different types of muscle?
• Skeletal, cardiac and smooth
• Skeletal muscle tissue can be sub divided into 2 different
types, each with a different function
Slow Twitch
•
•
•
•
•
•
•
•
Can contract over long periods of time
Carry out lots of aerobic respiration
Many mitochondria
Lots of myoglobin (similar to haemoglobin: acts as a store for
O2: it only releases it when O2 concentration is very low)
Appearance: darker, red colour
Surrounded by many capillaries = good blood supply
Little sarcoplasmic reticulum
Tire slowly: waste products can be removed
• Read page 172-173 and answer Q 7.30-7.32
• End: Control of Cardiac Cycle Exam Questions
Fast Twitch
•
•
•
•
•
•
•
•
Involved in rapid, intense muscle contraction
Rely mainly on anaerobic respiration
Few mitochondira
Little myoglobin
Appearance: lighter, white colour
Few capillaries
Large network of sarcoplasmic reticulum
Tire quickly due to build up of lactate