Answers to ‘Revise as you go’
1. Define ‘venous return’ and describe the mechanisms that help maintain venous return during exercise.
VR = Venous blood returning to the heart
Five mechanisms help maintain Venous Return:
Pocket valves
One-way valves, called pocket valves, in the veins prevent backflow of blood and direct blood flow back towards the
heart.
Muscle pump
Veins are situated between skeletal muscle which when contracting and relaxing helps push/squeeze blood through
the veins back towards the heart.
Respiratory pump
During exercise, breathing becomes deeper/faster. This causes pressure changes to occur in the thorax and
abdomen. This increases the pressure in the abdomen causing the large veins in that area to be squeezed/sucked.
This forces the blood back to the heart.
Smooth muscle
Contraction and relaxation of smooth muscle within the middle layer of the veins’ walls also helps to push blood
through the veins and back towards the heart.
Gravity
Blood from the upper body, above the heart, is aided by gravity, which helps blood flow back to the heart.
2. How does maintaining venous return affect performance?
VR determines SV and Q.
Starling’s Law, SV/Q dependent upon VR so if VR increases, SV/Q increases:
increase in SV/Q increases blood/oxygen transport to the working muscles increasing their ability to contract/work
aerobically;
exercise intensity/duration can be increased;
more significant in prolonged aerobic-based exercise, dependant upon oxygen supply;
also increases anaerobic performance as good VR speeds up recovery allowing performers to work anaerobically for
longer.
3. Sketch a diagram to summarise the redistribution of cardiac output from rest and during exercise. What is
this process of blood redistribution called?
See diagram on p.85 Fig 3.2.5
Process of blood redistribution is called the vascular shunt mechanism.
4. Explain how oxygen is transported in the blood and how this aids performance during physical activity.
Oxygen transport
97% is transported within the protein, haemoglobin, packed with red blood cells, as oxyhaemoglobin (HbO2)
3% is transported within blood plasma.
Efficient O2 transport:
prolongs the duration of anaerobic and, especially, aerobic activity;
delays anaerobic threshold, which
increases the possible intensity/work rate for the activity, and
speeds up recovery during and after exercise.
5. What are the benefits of a warm-up to the vascular system of an athlete prior to them engaging in
physical activity?
Increases blood flow/Q due to the vascular shunt mechanism via:
 Vasoconstriction of arterioles/pre-capillary sphincters to organs
 Vasodilation of muscle arterioles/precapillary sphincters
 Increased body/muscle temperature which:
o increases transport of the enzymes required for energy systems and muscle contraction
o decreases blood viscosity, improving blood flow to working muscles
o increases the dissociation of oxygen from haemoglobin in muscle tissues
 Decreased OBLA (onset of blood lactate accumulation) due to the early onset of anaerobic work when a
warm-up is not carried out.
6. How does smoking affect oxygen transport?
Cigarette smoke contains carbon monoxide (CO).
Haemoglobin has a higher affinity (240+ times) to CO, so Hb combines with CO in preference to O 2.
Reduces HbO2 association in lungs and maximal O2 uptake.
Blood O2 transport is reduced, reducing O2 supply to the working muscles and the lactate threshold which decreases
optimal performance, especially in aerobic activities.
7. Provide values to help explain the difference between blood pressure and hypertension.
Bp = ‘pressure exerted by blood against the (arterial) blood vessel walls’
Bp is normally expressed as: Systolic/Diastolic
The average resting Bp is 120/80 mmHg
Hypertension is long term, enduring, high blood pressure.
Hypertension = Bp exceeding 140/90mmHg, but 160/95 is more commonly regarded as real hypertension.
8. List
1.
2.
3.
4.
5.
the risk factors associated with developing coronary heart disease (CHD).
Physical inactivity
High blood pressure
Smoking
High Blood Lipids/Cholesterol (mg/dl)
Obesity (high BMI)
9. Outline the main coronary heart diseases (CHD), and explain how participation in physical activity protects
us from CHD.
Arteriosclerosis
Arteriosclerosis relates to a loss of elasticity, thickening/hardening of the arteries, which reduces their efficiency
to vasodilate/constrict.
Atherosclerosis
Atherosclerosis is a form of arteriosclerosis that leads to a progressive narrowing (diameter) of the lumen (the
space within the vessel) which increases the likelihood of blood clots forming.
Angina
Angina is a partial blockage of the coronary artery causing intense chest pain which occurs when there is an
inadequate O2/blood supply to the heart muscle wall, normally to a smaller area of the heart
Heart Attack
A heart attack is a more severe/sudden or total restriction in O2/blood supply to a part of the heart muscle wall,
usually causing permanent damage.
10. Describe how the vasomotor centre regulates the redistribution of cardiac output during exercise.
The vascular shunt mechanism is controlled by:
the Vasomotor Control Centre located in the medulla oblongata of the brain which stimulates the sympathetic
nervous system to either vasodilate or vasoconstrict the pre-capillary sphincters and arterioles that control the
supply of blood to muscles and organs.
The VCC receives information from:
 Chemoreceptors in muscles, aorta and carotid arteries; these inform the VCC that lactic acid and CO 2 levels
have increased and O2 and pH levels have decreased.
 Baroreceptors in aorta and carotid arteries; these inform the VCC that systolic blood pressure has
increased/decreased.
Sympathetic nervous system
The VCC responds by sending messages via the sympathetic nervous system to:
Organ arterioles and pre-capillary sphincters
 Increasing sympathetic stimulation which vasoconstricts the arterioles and pre-capillary sphincters,
decreasing Q and distributing blood flow away from the non-essential capillaries of the organs.
Muscles arterioles and pre-capillary sphincters
 Decreasing sympathetic stimulation which vasodilates the arterioles and pre-capillary sphincters, increasing
the distribution of Q to the capillaries of the working muscles.