hormone regulation & action

1. HORMONES: REGULATION
AND ACTION
This information is essential in order
to discuss the role of the
neuroendocrine system in the
mobilization of fuel for exercise

2. Hypothalamus and the Pituitary Gland
The pituitary gland is located at the base of the
brain, attached to the hypothalamus.
The gland has two lobes,
1. The anterior lobe (adenohypophysis), which is a
true endocrine gland, and
2 The posterior lobe (neurohypophysis),which is
neural tissue extending from the hypothalamus.

3. Both lobes are under the direct control of the
hypothalamus.
In the case of the anterior pituitary,hormone
release is controlled principally by chemicals
(releasing hormones or factors) that originate
in neurons located in the hypothalamus

4. These releasing hormones stimulate or inhibit the
release of specific hormones from the anterior pituitary
The posterior pituitary gland receives its hormones from
special neurons originating in the hypothalamus
The hormones move down the axon to blood vessels in
the posterior hypothalamus where they are discharged
into the general circulation

5. Anterior Pituitary Gland
The anterior pituitary hormones include :
Adrenocorticotrophic hormone (ACTH),
 Follicle stimulating hormone (FSH),
Luteinmng hormone (LH),
Melanocyte stimulating hormone (MSH),
 Thyroid~stimulating hormone (TSH),
Growth hormone (GH), and
Prolactin.

6. While prolactin directly stimulates the breast to
produce milk, the majority of the hormones
secreted from the anterior pituitary control the
release of other hormones.
TSH controls the rate of thyroid hormone
formation and secretion from the thyroid gland;

7. ACTH stimulates the production and
secretion of cortisol in the adrenal cortex;
LH stimulates the production of testosterone
in the testes and estrogen in the ovary;

8. Growth Hormone (GH) is secreted from the anterior
pituitary gland and exerts profound effects on the
growth of all tissues
GH stimulates the release of somatomedins, or as they
are commonly called today, insulin~like growth factors
(IGFs), from the liver and othertissues.
It causes muscle hypertrophy.
It exerts important effects on protein, fat. And
carbohydrate
metabolism .

9. Growth hormone secretion is controlled by
releaSing hormones secreted from the
hypothalamus Growth hormone-releasing
hormone (GHRH)
(GHRH) stimulates GH release from the anterior
pituitary, whereas another factor, hypothalamic
somatostatin, inhibits it.

10. IN SUMMARY
The hypothalamus controls the activity of both the
anterior pituitary and posterior pituitary glands
GH is released from the anterior pituitary gland
and is essential for normal growth .
GH increases duri,ng exercise to mobilize fatty
acids from adipose tissue and to aid in the
maintenance of blood glucose

11. Posterior Plituitary Gland
The posterior pituitary gland releases
two hormones:
1. oxytocin and
2.antidi uretic hormone (ADH), which is
also called vasopressin.

12. Oxytocin is a powerful stimulator of smooth
muscle, especially at the time of childbirth, and
is also involved in the milk "let down"
response needed for the release of milk from
the breast

13. Antidiuretic :Hormone Antidiuretic hormone
(ADH) does what its name implies: It reduces
water loss from the body.
 ADH favors the reabsorption of water from
the kidney tubules back into the capillaries to
maintain body fluid


14.  There are two major stimuli that result in an
increased secretion of ADH:
1) high plasma osmolality (a low water
concentration) that can be caused by excessive
sweating without water replacement. And
2) A low plasma volume, which can be due either to
the loss of blood or to inadequate fluid
replacement

15. Thyroid Gland
The thyroid gland is stimulated by TSH to
synthesize two iodine-containing hormones:
 tri iodothyronine (T3 ) and thyroxine (T4).
 T3 contains three iodine atoms and
 T4 contains four
TSH is also the primary stimulus for the release of
T3 and T4 into the circulation, where they are
bound to plasma proteins

16. Thyroid Hormones
Thyroid hormones are central in establishing the
overall metabolic rate (ie, a hypothyroid [low T3J
individual would be characterized as being
lethargic and hypokinetic).
It is this effect of the hormone that has been
linked to weight control problems, but only a
small percentage of obese individuals are
hypothyroid .

17. T'3 and T'4 act as permissive hormones in that
they permit other hormones to exert their full
effect.
During exercise the "free" hormone concentration
increases due to changes in the binding
characteristic of the transport protein, and the
hormones are taken up at a faster rate by tissues.

18. Calcitonin
The thyroid gland also secretes
calcitonin, which is in volved in a minor
way in the
regulation of plasma calcium (Ca +), a
crucial ion for normal muscle and nerve
function .

19. IN SUMMARY
Thyroid hormones T3 and T4 are
important for maintaining the
metabolic rate and allowing other
hormones to bring about their full
effect.

20. Parathyroid Gland
Parathyroid hormone is the primary hormone
involved in plasm a Ca++ regulation.
It releases parathyroid hormone in response to a
low plasma Ca++ concentration.
The hormone st imLllates bone to release Ca++
into the plasma and simultaneously increases the
renal absorption of Ca++; both raise the plasma
Ca++ leve

21. Parathyroid hormone also stimulates the kidney
to convert a form of vitamin D (vitamin D3) into a
hormone that increases the absorption of Ca++
from the gastrointestinal tract
Exercise increases the concentration of
parathyroid hormone in the plasma

22. Adrenal Gland
The adrenal gland is really two different glands, the
adrenal medulla, which secretes”
The catecholamines,
Epinephrine (E), and
Norepinephrine (NE), and the
Adrenal cortex, which secretes steroid
hormones.

23. Adrenal Medulla
The adrenal medulla is part of the sympathetic
nervous system
80 % of the gland's hormonal secretion is
epinephrine, which affects receptors in the:
1)cardiovascular and respiratory systems,
2)gastrointestinal tract,
3) Iiver, other endocrine glands, muscle, and
adipose tissue.

24. E and NE are involved in the
maintenance of blood pressure and
the plasma glucose concentration.

25. Adrenal Cortex
 The adrenal cortex secretes a variety of steroid
hormones having rather distinct physiological
functions
 The hormones can be grouped into 3 categories:
1. Mineralocorticoids (aldosterone), involved in the
maintenance of the Na + and K+ concentrations in
plasma,
2. Glucocorticoids (cortisol), invo lved in plasma glucose
regulation, and
3. Sex steroids (androgens and estrogens).

26. The adrenal cortex secretes aldosterone
(mineralocortico id), cortisol (glucocorticoid), and
estrogens and androgens (sex steroids).
 Aldosterone regulates Na+ and K+ balance
Aldosterone secretion increases with strenuous
exercise, driven by the renin-angiotens in system.
Cortisol responds to a variety of stressors.including
exercise, to ensure t hat fuel (glucose and free fatty
acids) is available, and to make amino acids available
for tissue repair.

27. Pancreas
The pancreas is both an exocrine and an endocrine
gland
The exocrine secretions include digestive enzymes and
bi carbonate which are secreted into ducts leading to
the small intestine.
 The hormones released from groups of cells in the
endocrine portion of the pancreas called the islets of
Langerhans , include:
insulin, glucagon, and somatostatin.

28. Insulin is secreted by the 13 cells of the islets of
Langerhans in the pancreas and promotes the
storage of glucose. amino acids. and fats.
Glucagon is secreted by the cells of the islets of
Langerhans in the pancreas and promotes the
mobilization of glucose and fatty acids.

29. Testes and Ovaries
Testosterone and estrogen are the primary sex
steroids secreted by the testis and ovary,
respectively
These hormones are not only important in
establishing and maintaining reproductive
function. they determine the secondary sex
characteristics associated with masculinity and
femininity

30. Testosterone
Testosterone is secreted by the interstitial
cells of the testes and is controlled by
interstitial cell stimulating hurmone (ICSH-
also known as LH), which is produced in the
anterior pituitary.
LH is in turn, controlled by a releasing hormone
secreted by the hypothalamus

31. Testosterone is both an anabolic (tissue building)
and androgenic (promoter of masculine
characteristics) steroid because it stimulates
protein synthesis.
 It is also responsible for the characteristic
changes in boys at adolescence that lead to the
high muscle-mass to fat-mass ratio.

32. The plasma testosterone concentration is
increased 10% to 37% during prolonged
submaximal work . during exercise taken to
maximum levels and during endurance or strength
training workouts
Chronic exercise (training) can decrease testosterone
levels in males and estrogen levels in females.

33. HORMONAL CONTROL OF
SUBSTRATE MOBILIZATION
DURING EXERCISE

34. The type of substrate and the rate at which it
is utilized during exercise depend to a large
extent on the intensity and duration of the
exercise.

35.  our discussion of the hormonal control of substrate
mobilization during exercise will be divided into two
parts.
1) The first part will deal with the control of muscle
glycogen utilization,and
2) the second part with the control of glucose
mobilization from the liver and free fatty acids
(FFA) from adipose tissue.

36. Muscle-Glycogen Utilization
At the onset of most types of exercise, and
for the entire duration of very strenuous
exercise, muscle glycogen is the primary
carbohydrate fuel for muscular work

37. The intensity of exercise, which is inversely
related to exercise duration, determines the
rate at which muscle glycogen is used as a
fuel.
The heavier the exercise, the faster
glycogen is broken down.

38. The plasma glucose concentration is maintained
through four processes that
1) mobilize glucose from liver glycogen stores
2) mobilize plasma FFA from adipose tissue to spare
plasma glucose,
3) synthesize new glucose in the liver
(gluconeogenesis) from amino acids, lactic acid ,
and glycerol. and
4) block glucose entry into cells to force the
substitution of FFA as a fuel.

39. Hormone-Substrate Interaction
if there were a sudden change in the plasma glucose
concentration during exercise, these hormones would
respond to that change For example:
If the ingestion of glucose before exercise caused an
elevation of plasma glucose, the plasma concentration of
insulin would increase.
This hormonal change would reduce FFA mobilization and
force the muscle to use additional muscle glycogen

40. During intense exercise, plasma glucagon , GH,
cortisol, E, and NE are elevated and insulin is
decreased.
These hormonal changes favor the mobilization of
FFA from adipose tissue that would spare
carbohydrate and help maintain the plasma
glucose concentration.

41. IN SUMMARY
The plasma FFA concentration
decreases during heavy exercise even
though the adipose cell is stimulated by
a variety of hormones to increase
triglyceride breakdown to FFA and
glycerol