EXSC 510
CASE STUDY ESSAY QUESTION 2
Autoregulation is defined as the continual automatic adjustment or
self-regulation of a biochemical, physiological, or ecological system to
maintain a stable state (Dictonary.com). Autoregulation is used to describe
many different physiological processes. The renal, cardiovascular, and
cerebral circulations are examples of autoregulation. The process of
autoregulation is a crucial component of the regulation of blood flow to
muscle cells during exercise. Autoregulation is an “intrinsic control” process
that allows blood flow to differ based on local metabolites. Metabolic demand
for blood flow is controlled by vasodilators, nitric oxide, prostaglandins,
endothelium-derived hyperpolarization, ATP, and adenosine (Powers &
Howley, 2021). All of these factors interact in order to encourage
vasodilation and the subsequent increase in blood flow to the muscles being
used (Powers & Howley, 2021). During exercise, the body reduces blood flow
to less essential organs like the liver, GI tracts, and kidneys in order to
increase blood flow to crucial cells in the muscles (Powers & Howley, 2021).
There are three aspects that allow the occurrence of autoregulation to
control blood flow: vasodilation, vasoconstriction, and capillary recruitment.
Vasodilation is increasing the diameter or radius of blood vessels as well as
recruiting new capillaries. The blood vessels that go to tissues in need of
more blood flow, oxygen, and nutrients will be vasodilated. This often occurs
at the start of exercise bouts when the body goes from resting to an excited
state or when someone increases exercise intensity (Liberty University,
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Adaptations, 2021). As the body becomes more active, or increases intensity,
more ATP must be made. To make ATP, oxygen is required in the muscle cells
and blood flow is responsible to deliver this oxygen. Vasodilation also
happens when the body enters a “fight or flight” response. As the diameter
increases, blood flow will increase and oxygen delivery increases. The level
of dilation in the blood vessels is determined by exercise intensity and the
number of motor units recruited (Powers & Henley, 2021). A higher intensity
exercise bout recruits more motor units and causes a greater level of
vasodilation than a lower intensity bout.
Vasoconstriction is the opposite of vasodilation and causes the
diameter or radius of blood vessels to decrease in size. This process occurs
during the transition from rest to exercise and before and after the “fight or
flight” response. Tissues and organs that are not in use do not require as
much oxygen as the ones being used for the exercise bout. Therefore, these
cells not in use are not given as much blood through vasoconstriction. Less
blood will flow to the areas in which the blood vessels are constricted. It is
important to note that blood flow to the brain is relatively constant and is not
largely affected by these processes (Liberty University, Adaptations, 2021). The
brain is the master or controller of the body and so must be functioning at
high capacity in almost all circumstances. During a lower body exercise, such
as cycling or squatting, blood flow will increase to the legs via vasodilation
and decrease to the upper body through vasoconstriction. The upper body
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blood flow must be lessened in order to allow more blood to be given to the
working muscles of the legs. It is a give-and-take system.
Capillary recruitment is the third aspect of autoregulation. This is used
in conjunction with vasodilation in order to increase blood supply to tissues in
need of oxygenated blood. During a resting state, the body only has 5-10%
of capillaries open. Comparatively, during exercise 100% of capillaries are
open (Liberty University, Adaptations, 2021). At exercise, the capillaries are open to
the muscles primarily involved in the exercise being performed. The number
of open capillaries to certain muscles changes based on need for oxygen and
nutrients during exercise. Capillaries have sphincters that allow them to
increase and decrease in size (Liberty University, Adaptations, 2021). Sometimes
they are so small that RBCs have to go in a single file line to pass through.
Capillary recruitment influences autoregulation through changes in
metabolites concentrations, oxygen needs of tissues, level of CO2 in blood,
and changes in pH levels (Liberty University, Adaptations, 2021). Capillary
recruitment acts similarly to vasodilation and vasoconstriction in that more
are recruited and vasodilate in a muscle group as more blood flow is needed
to a certain area and other capillaries vasoconstrict to restrict blood flow to
unused muscles.
Aerobic capacity is often measured by VO2max. This measurement is a
great indicator for cardiorespiratory endurance since it measures maximal
oxygen consumption. Someone with a higher VO2max is considered to be in
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better cardiovascular condition than someone with a lower VO2max
measurement. A lower VO2max can be improved through cardiovascular
endurance training in as little as 8-12 weeks. Increased endurance through
training allows the person to last longer during aerobic exercise and get
closer to attaining their true VO2max. As well as a change in VO2max,
someone has the ability to increase stroke volume, increase heart size, and
lower heart rate through an aerobic training program for several weeks
(Liberty University, Cardiovascular and Peripheral Training Adaptations, 2021). Heart size
will increase as the body adapts to allow more blood to be pumped per beat.
The heart is a muscle and repeated contractions during these exercise
sessions allows the heart muscle to grow bigger. The left ventricle size will
subsequently also be increased. This will lead to an increase in stroke volume
(SV) (Liberty University, Cardiovascular and Peripheral Training Adaptations, 2021). Stroke
volume refers to the amount of blood expelled from the heart every beat.
Since the SV is increased, the heart rate will decrease. For every beat of the
heart, more blood is able to be circulated through the body and thus the
heart will need to beat less times. Heart rate will be decreased at rest and
submaximal exercise compared to previous measurements as a person
participates in a consistent aerobic training program (Liberty University,
Cardiovascular and Peripheral Training Adaptations, 2021). There will also be an
increase in the person’s blood, RBCs and plasma volume as a result of
aerobic training. These changes will increase the oxygen carrying capacity
and performance. Lactate threshold will also increase which allows the
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person to perform exercise longer before fatigue is reached. The respiratory
exchange ratio (RER) is lowered during the start of exercise and submaximal
exercise through aerobic training. The RER is increased for end of a
maximum exercise bout through this type of training (Liberty University,
Cardiovascular and Peripheral Training Adaptations, 2021). With so many incredible
physiological adaptations to aerobic training, it is beneficial for everyone to
participate to some extent! Cardiovascular training and autoregulation allow
the body to efficiently move blood through the body to needed tissues to
maximize performance.
References
Dictionary.com. (n.d.). Autoregulation definition & meaning. Dictionary.com. Retrieved
November 11, 2022, from https://www.dictionary.com/browse/autoregulation
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Liberty University. (2021). Autoregulation. Retrieved from
https://canvas.liberty.edu/courses/315530/pages/watch-autoregulation?
module_item_id=41914160.
Liberty University. (2021). Cardiovascular and Peripheral Training Adaptations. Retrieved from
https://canvas.liberty.edu/courses/315530/pages/watch-cardiovascular-and-peripheral-
training-adaptations?module_item_id=41914234.
Powers, S. K., Howley, E. T., & Quindry, J. (2021). Exercise physiology: Theory and application
to fitness and performance. McGraw Hill LLC.
Name: Kennedy Mills
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