Download effect of training on endocrine system

 During exercise and exposure to extreme environments, the body is faced with tremendous
demands that require a multitude of physiological adjustments. Energy production must increase
and metabolic by-products must be cleared.
Cardiovascular and respiratory function must be
constantly adjusted to match the demands placed
upon these and other body systems, such as those
regulating temperature.
 While the body’s internal environment is in a
constant state of flux even at rest, during exercise
these well-orchestrated changes must occur
rapidly and frequently.
 The more rigorous the exercise, the more difficult
it is to maintain homeostasis. Much of the
regulation required during exercise is
accomplished by the nervous system. But another
physiological system affects virtually every cell,
tissue, and organ in the body. It constantly
monitors the body’s internal environment, noting
all changes that occur and responding quickly to
ensure that homeostasis is not dramatically
disrupted.
 It is the endocrine system that exerts this control
through the hormones it releases. Because we
cannot cover all aspects of endocrine control
during exercise, the focus will be on hormonal
control of metabolism and body fluids.
The Endocrine System
 As the body transitions from a resting to an active
state, the rate of metabolism must increase to provide
the necessary energy. This requires the coordinated
integration of many physiological and biochemical
systems. Such integration is possible only if all of the
involved tissues, organs, and systems can efficiently
communicate. Although the nervous system is
responsible for much of this communication, finetuning the physiological responses to any disturbance
in homeostasis is primarily the responsibility of the
endocrine system.
 The endocrine and nervous systems, often
collectively called the neuroendocrine system,
work in concert to initiate and control movement
and all of the physiological processes that support
exercise. The nervous system functions quickly,
having short-lived, localized effects, whereas the
endocrine system responds more slowly but has
longer-lasting effects.
 The endocrine system is defined as all tissues or
glands that secrete hormones. The major
endocrine glands are illustrated in figure.
Endocrine glands typically secrete their hormones
directly into the blood where they act as chemical
signals throughout the body. When secreted by the
specialized endocrine cells,
 Hormone are transported via the blood to specific
target cells—cells that possess specific hormone
receptors. On reaching their destinations,
hormones can control the activity of the target
tissue. Now hormones are more broadly defined as
any chemical that controls and regulates the
activity of certain cells or organs. Some hormones
affect many body tissues, whereas others target
very specific cells of the body.
Hormones
 Hormones are involved in most physiological
processes, so their actions are relevant to many
aspects of exercise and sport.
Chemical Classification of
Hormones
 Hormones can be categorized as two basic types:
steroid hormones and nonsteroid hormones.
Steroid hormones have a chemical structure
similar to cholesterol, since most are derived from
cholesterol. For this reason, they are soluble in
lipids so they diffuse rather easily through cell
membranes.
 This group includes the hormones secreted by: the adrenal cortex (such as cortisol and aldosterone),
 • The ovaries (estrogen and progesterone),
 • the testes (testosterone), and
 • the placenta (estrogen and progesterone).
 Nonsteroid hormones are not lipid soluble, so they
cannot easily cross cell membranes. The
nonsteroid hormone group can be subdivided into
two groups: protein or peptide hormones and
amino acid–derived hormones. The two hormones
produced by the thyroid gland (thyroxine and
triiodothyronine) and the two from the adrenal
medulla (epinephrine and norepi- nephrine) are
amino acid hormones. All other non- steroid
hormones are protein or peptide hormones.
 Most hormone secretion is regulated by a negative
feedback system. Secretion of a hormone causes
some change in the body, and this change in turn
inhibits further hormone secretion.
 Negative feedback is the primary mechanism
through which the endocrine system maintains
homeostasis. for example, when the plasma
glucose concentration is high, the pancreas
releases insulin. Insulin increases cellular uptake
of glucose, lowering plasma concentration of
glucose. When plasma glucose concentration
returns to normal, insulin release is inhibited until
the plasma glucose level increases again.
Endocrine glands and
Their Hormones
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Anterior pituitary
Growth hormone (GH)
Target Organ- All cells in the body
Function- Promotes development and enlargement
of all body tissues until maturation; increases rate
of protein synthesis; increases mobilization of fats
and use of fat as an energy source; decreases rate
of carbohydrate use
 Thyrotropin (TSH) hormone
 Target organ- Thyroid gland
 Functions- Controls the amount of thyroxin and
triiodothyronine produced and released by the
thyroid gland.
 Adrenocorticotropin (ACTH)
 Target organ- Adrenal cortex
 Functions- Controls the secretion of hormones
from the adrenal cortex
 Prolactin hormone
 Target organ- Breasts
 Function-Stimulates milk production by the
breasts
 Follicle-stimulating hormone (FSH)
 Target organ- Ovaries, testes
 Functions- Initiates growth of follicles in the
ovaries and promotes secretion of estrogen from
the ovaries; promotes development of the sperm in
the testes.
 Luteinizing hormone (LH)
 Target organ- ovaries and testis
 Functions- Promotes secretion of estro- gen and
progesterone and causes the follicle to rupture,
releasing the ovum; causes testes to secrete
testosterone
Posterior pituitary
 Antidiuretic hormone (ADH or vasopressin)
 Target organ- Kidneys
 Functions- Assist in controlling water excretion by
the kidneys; elevates blood pressure by
constricting blood vessels
Thyroid
 Thyroxine (T4) and triiodothyronine (T3)
 Target organ- all cell in the body
 Functions- Increase the rate of cellular
metabolism; increase rate and contractility of the
heart
Parathyroid
 Parathyroid hormone (PTH or parathor- mone)
 Target organ- Bones, intes- tines, and kidneys
 Functions- Controls calcium ion con- centration in
the extracellular fluid through its influence on
bones, intestines, and kid- neys
Adrenal medulla
 Epinephrine
 Target organ- Most cells in the body
 Functions- Stimulates breakdown of glycogen in
liver and muscle and lipolysis in adipose tissue
and muscle; increases skeletal muscle blood flow;
increases heart rate and contractility; increases
oxygen consumption
 Norepinephrine
 Target organ- most cells in the body
 Functions- Stimulates lipolysis in adi- pose tissue
and in muscle to a lesser extent; constricts
arterioles and venules, thereby elevating blood
pres- sure
Adrenal cortex
 Mineralocorticoids (aldosterone)
 Target organ- kidneys
 Functions- increase sodium retention and
potassium excretion through the kidneys
 Glucocorticoids (cortisol)
 Target organ- most cells of the body
 Functions - Control metabolism of carbohydrates, fats, and proteins; exert an antiinflammatory action
 Androgens and estrogens
 Target organ- Ovaries, breasts, and testes
 Functions- Assist in the development of female
and male sex charac- teristics
Pancreas
 Insulin
 Target organ- all cells in the body
 Functions-Controls blood glucose levels by
lowering glucose levels; increases use of glucose
and synthesis of fat
 Glucagon
 Target organ- all cells in the body
 Functions- Increases blood glucose; stimulates the
breakdown of protein and fat
Kidney
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Renin
Target organ- Adrenal cortex
Functions- Assists in blood pressure control
Erythropoietin (EPO)
Target organ- bone marrow
Functions- Stimulates erythrocyte production
Testes
 Testosterone
 Target organ- sex organs and muscles
 Functions- Promotes development of male sex
characteristics, including growth of testes,
scrotum, and penis, facial hair, and change in
voice; promotes muscle growth
Ovaries
 Estrogens and progesterone
 Target organs- Sex organs and adipose tissue
 Functions- Promote development of female sex
organs and char- acteristics; increase storage of
fat; assist in regulating the menstrual cycle
EFFECT OF EXERCISE ON
HORMONAL SECRETION
Metabolic Rate
 Exercise, particularly heavy weightlifting,
stimulates the release of luteinizing hormone from
your anterior pituitary gland, and luteinzing
hormone triggers testosterone production.
Exercise that involves intense bursts of energy
also stimulates the release of thyroxine from your
thyroid gland. Exercise can help you control or
reduce your weight because testosterone and
thyroxine speed up your metabolism.
Blood Sugar
 Insulin is a hormone that regulates your glucose, or blood
sugar, by transporting it to muscles and tissues that use
glucose for energy. Excessive insulin in your blood
reduces your sensitivity to insulin and can lead to
diabetes. More glucose stays in the blood when insulin
sensitivity goes down, and high blood glucose can cause
nausea, vomiting, shortness of breath, organ failure,
circulation problems and can lead to coma if left
untreated. Exercise might increase your insulin sensitivity
by reducing blood concentrations of insulin. Blood
insulin levels begin decreasing after 10 minutes of
aerobic exercise, and weight training might increase your
sensitivity to insulin at rest.
Blood Flow
 The adrenal medulla releases epinephrine during
exercise and increases epinephrine levels at higher
exercise intensities. Epinephrine increases the
amount of blood that your heart pumps.
Epinephrine also enhances your ability to use
muscles during exercise by widening blood
vessels, which lets your muscles get more oxygenrich blood. Thyroxine secretions during exercise
increase the amount of blood in your body by
about 30 percent, and these secretions might
remain elevated for around five hours.
Psychological Effects
 The effects of exercise on your endocrine system
might positively affect your mental state.
Exercise-induced testosterone might increase
confidence and libido. Conversely, low
testosterone levels might inhibit your motivation,
self-confidence, concentration and memory. Your
pituitary gland may produce a large increase in
blood endorphin levels shortly after exercise
begins. Endorphins block your sensitivity to pain,
and can reduce tension or anxiety by inducing a
sense of euphoria.
Pituitary Gland
 During exercise, the pituitary gland releases
human growth hormone, which tells the body to
increase bone, muscle and tissue production.
Thyroid Gland
 When you start exercising, the thyroid gland
(located at the base of the neck) sends out
hormones that regulate the body’s temperature,
heart rate and blood pressure. It also regulates the
alertness and focus that are needed to work at a
high intensity.
Adrenal Gland
 Located at the top of the kidneys, the adrenal
glands are responsible for the release of cortisol
into the bloodstream. Cortisol levels control blood
pressure, glucose and acts as an anti-inflammatory
agent. The adrenal glands also release aldosterone,
a hormone that regulates hydration levels, the
speed of the heart and the strength of contractions.
It also turns stored carbohydrates into energy.
Pancreas
 Insulin regulates glucose, or blood sugar, by
transporting it to the muscles and tissue that use
glucose for energy. Excessive insulin in the blood
reduces your sensitivity to insulin and can cause
diabetes, which is also linked to overweight and
obesity. Exercise improves insulin sensitivity and
reduces the reliance on insulin injections
EFFECT OF EXERCISE ON
HORMONAL SECRETION