Hypothalamic & Pituitary Hormones and their interesting facts and usage

1. Hypothalamus and
Pituitary Glands and
their Hormones

3. The hypothalamus and pituitary gland
• The hypothalamus and pituitary gland function
cooperatively as master regulators of the endocrine
system.
• Together, hormones secreted by the hypothalamus
and pituitary gland control important homeostatic
and metabolic functions, from reproduction to
control of thyroid physiology.

6. Size: About 1 centimeter and weight is 0.5 to 1 gram.
• Location: Lies in the sella turcica, a bony cavity at the base of the
brain, and is connected to the hypothalamus by the pituitary stalk.
• Parts: The pituitary gland is divided into:
➢ the anterior pituitary
➢ the posterior pituitary
• Between these is a small, relatively avascular zone called the pars
intermedia.
•Hypothalamus is located just above the pituitary gland.
Pituitary Gland (Hypophysis)

7. Pituitary Gland

8. Hormones of Pituitary
1. Anterior Pituitary
1. Growth Hormone (GH) or somatotropin
2. Adrenocorticotropic hormone (ACTH) or corticotropin
3. Thyroid-stimulating hormone (TSH) or thyrotropin
4. Follicle-stimulating Hormone (FSH)
5. Luteinizing Hormone (LH)
6. Prolactin (PL)
2. Posterior Pituitary
1. Antidiuretic hormone (ADH) or vasopressin
2. Oxytocin
3. Middle Pituitary
• Melanocyte stimulating hormone (MSH)

9. Hormones of anterior pituitary gland
Hormones Functions
Growth hormone
(GH) or
somatotropin
This hormone promotes growth in childhood. For adults, it
helps to maintain healthy muscle and bone mass.
Adrenocorticotropic
(ACTH) or
corticotropin
Stimulates adrenal gland to secrete some of the adrenocortical
hormones, e.g. cortisol, which helps to reduce stress, maintain
healthy blood pressure.
Thyroid-stimulating
hormone (TSH) or
thyrotropin
Stimulates thyroid gland to produce thyroxine & tri-iodothyronine,
which is crucial in maintaining a healthy metabolism.
Follicle-stimulating
hormone (FSH)
It stimulates the releasing of eggs in women and helps ensure the
normal function of sperm production in men.
Luteinizing hormone
(LH)
In women, this hormone regulates estrogen. In men, it regulates
testosterone.
Prolactin Development of mammary glands during pregnancy
It stimulates milk production.

10. Tropic Hormones: First five hormones of anterior pituitary
stimulate the other endocrine glands. i.e. Growth Hormone,
Adrenocorticotropic hormone, Thyroid-stimulating hormone,
Follicle-stimulating Hormone, Luteinizing Hormone.
Growth hormone also stimulates the secretory activity of liver and
other tissues.
Therefore, these five hormones are called tropic hormones.
Prolactin is concerned with milk secretion.
Gonadotropic Hormones
Follicle-stimulating hormone and the luteinizing hormone are
together called gonadotropic hormones or gonadotropins
because of their action on gonads.
Terminology

11. Hormones of posterior pituitary gland
Hormones Functions
Antidiuretic hormone
(ADH) or vasopressin
This hormone controls the rate of water excretion into the
urine, thus helping to regulate water balance in the body.
Oxytocin This hormone causes pregnant women to start contractions
which is necessary for child birth at the appropriate time
Promotes milk flow in nursing mothers
For men, oxytocin function is less important, but it does have
a role to play in moving sperm.

12. ANTERIOR PITUITARY
• Anterior pituitary is also known as the master gland,
as it regulates many other endocrine glands through
its hormones.
• The Anterior Pituitary gland contains several different
cell types that synthesize and secrete hormones.
Usually, there is one cell type for each major hormone
formed in the anterior pituitary gland.

13. i. Somatotropes secrete growth hormone (GH)
ii. Corticotropes secrete adrenocorticotropic hormone (ACTH)
iii. Thyrotropes secrete thyroid-stimulating hormone (TSH)
iv. Gonadotropes secrete gonadotropic hormones: follicle-
stimulating hormone (FSH) and luteinizing hormone (LH)
v. Lactotropes secrete prolactin (PRL)
• Somatotropes stain strongly with acid dyes and are therefore
called acidophils.
• Thus, pituitary tumors that secrete large quantities of hGH are
called acidophilic tumors.
Cell types in anterior pituitary:

14. REGULATION OF SECRETION
• Almost all pituitary secretion is controlled by hormonal or nervous
signals from the hypothalamus.
• The relationship between hypothalamus and pituitary gland is
called hypothalamo-hypophyseal relationship.
• Secretion by the anterior pituitary is controlled by hormones called
hypothalamic releasing and hypothalamic inhibitory hormones (or
factors) secreted within the hypothalamus and then conducted to
the anterior pituitary through minute blood vessels called
hypothalamic-hypophysial portal blood vessels.
• However, secretion from the posterior pituitary is controlled by
nerve signals that originate in the hypothalamus and terminate in
the posterior pituitary and these nerve signals are transported by
nerve fibers of hypothalamic-hypophyseal tract.
Hypothalamo-hypophyseal Relationship

15. Hypothalamo-hypophyseal Relationship

16. REGULATION OF ANTERIOR PITUITARY SECRETION
by Hypothalamus
• Special neurons in the
hypothalamus synthesize
and secrete the
hypothalamic releasing and
inhibitory hormones that
control secretion of the
anterior pituitary hormones.
• These hormones are
transported to anterior
pituitary through
hypothalamo-hypophyseal
portal vessels.

17. Hypothalamic hormones that act on anterior pituitary are :
1. Growth hormone-releasing hormone (GHRH): Stimulates the
release of growth hormone and Growth hormone-inhibitory
hormone (GHIH) or somatostatin: Inhibits the growth hormone
release
2. Thyrotropic-releasing hormone (TRH): Stimulates the release of
thyroid stimulating hormone
3. Corticotropin-releasing hormone (CRH): Stimulates the release
of adrenocorticotropin
4. Gonadotropin-releasing hormone (GnRH): Stimulates the
release of gonadotropins, FSH and LH
5. Prolactin-inhibitory hormone (PIH): Inhibits prolactin secretion.
It is believed that PIH is dopamine.
REGULATION OF ANTERIOR PITUITARY
SECRETION by Hypothalamus

18. Growth Hormone (GH)
• Growth hormone, also called somatotropic hormone or
somatotropin, is a small protein molecule that contains
191 amino acids in a single chain.
• It causes growth of almost all tissues of the body that
are capable of growing.
• It promotes increased sizes of the cells and increased
numbers of cells by mitosis.
• It promotes specific differentiation of certain types of
cells such as bone growth cells and early muscle cells.

19. • Specific effects: Aside from its general effect in causing
growth, GH has multiple specific metabolic effects
Growth Hormone (GH)
1. On metabolism:
GH increases the synthesis of proteins, mobilization of lipids and
conservation of carbohydrates. Thus, in effect, GH enhances body
protein, decreases fat stores, and conserves carbohydrates.
a. Synthesis of proteins by:
i. Increasing amino acid transport through cell membrane
ii. Increasing RNA translation
iii. Increasing transcription of DNA to RNA
iv. Decreasing catabolism of protein

20. b. Mobilization of lipids by:
• It causes increased mobilization of fatty acids from adipose
tissue, thereby increased free fatty acids in the blood, and
increased use of fatty acids for energy. Therefore, under the
influence of GH, fat is used for energy in preference to use of
carbohydrates and proteins.
• The ability of GH to promote fat utilization, together with its
protein anabolic effect, causes an increase in lean body mass.
• During the utilization of fatty acids for energy production, lot of
acetoacetic acid is produced by liver and is released into the
body fluids, leading to ketosis.
• Sometimes, excess mobilization of fat from the adipose tissue
causes accumulation of fat in liver, resulting in fatty liver.

21. c. Conservation of carbohydrates by:
1. Decrease in the peripheral utilization of glucose for the
production of energy.
2. Increase in the deposition of glycogen in the cells.
3. Decrease in the uptake of glucose by the cells: The cells become
saturated with glycogen. Thus, no more glucose can enter the
cells from blood. So, the blood glucose level increases.
4. Diabetogenic effect of GH: Hypersecretion of GH increases blood
glucose level enormously. It causes continuous stimulation of the
β-cells in the pancreas and increase in secretion of insulin. In
addition, GH also stimulates β-cells directly and causes insulin
secretion. As a result, β-cells are burnt out at one stage. This
causes deficiency of insulin, leading to diabetes mellitus. This
effect of GH is called the diabetogenic effect.

22. 2. On bones
• In embryonic stage, GH is responsible for the differentiation and
development of bone cells.
• In later stages, GH increases the growth of the skeleton. It
increases the length and the thickness of the bones.
• GH increases the length of the bones, until epiphysis fuses with
shaft, which occurs at the time of puberty.
• After the epiphyseal fusion, length of the bones cannot be
increased. However, it stimulates the osteoblasts strongly. So,
the bone continues to grow in thickness throughout the life.
• Particularly, the membranous bones such as the jaw bone and
the skull bones become thicker under the influence of GH.

23. 2. On bones

24. Mode of Action of GH – Somatomedin
• GH causes the liver to form several small proteins called insulin-
like growth factors (IGFs, also called somatomedins) that mediate
some of the growth and metabolic effects of GH.
• Somatomedin is defined as a substance through which growth
hormone acts. At least four somatomedins have been isolated.
The most important of these is somatomedin C (also called IGF-I).
• GH receptor is called growth hormone secretagogue (GHS)
receptor.
• GH binds with the receptor situated mainly in liver cells and forms
the hormone-receptor complex which ultimately results in
somatomedin secretion.
• Somatomedin in turn, executes the actions of growth hormone.

25. The pygmies of Africa
• The pygmies of Africa have a
congenital inability to
synthesize significant
amounts of somatomedin C.
• Their plasma concentration
of growth hormone is either
normal or high.
• They have diminished
amounts of somatomedin C
in the plasma; this
apparently accounts for the
small stature of these
people.

28. 1. Excess GH before Adolescence: Gigantism
• Gigantism is the pituitary disorder
characterized by excess growth of the
body.
• Gigantism is due to hypersecretion of
GH in childhood or in pre-adult life
before the fusion of epiphysis of bone
with shaft.
• Hypersecretion of GH may occur due
to over activity of the GH-secreting
cells or their tumors.
HYPERACTIVITY OF ANTERIOR PITUITARY

29. Gigantism
Signs and symptoms:
1. Huge stature, with a height of more than 7 or 8 feet. The limbs
are disproportionately long.
2. Giants are hyperglycemic and they develop diabetes mellitus due
to exhaustion of the pancreatic beta cells.
3. Tumor of the pituitary gland causes constant headache.
4. Pituitary tumor also causes visual disturbances as it compresses
the some of the optic nerves in the brain.

30. Figure 1 A 22-year-old man with gigantism due to excess growth hormone is shown to the left of
his identical twin. The increased height (Panel A) and enlarged hand (Panel B) and foot (Panel C)
of the affected twin are apparent. Their height and features began to diverge at the age of
approximately 13 years.

31. • Acromegaly is the disorder characterized by the enlargement,
thickening and broadening of bones, particularly in the extremities of
the body.
• If a tumor of cells that produce GH occurs after adolescence, i.e. after
the epiphyses of the long bones have fused with the shafts—the person
cannot grow taller, but the bones can become thicker and the soft
tissues can continue to grow.
2. Excess Growth Hormone After Adolescence: Acromegaly

32. Signs and symptoms:
i. Acromegalic or gorilla face
ii. Enlargement of hands and feet
iii. Kyphosis (extreme curvature of upper back – thoracic spine)
iv. Thickening of scalp. Scalp is also thrown into folds or wrinkles like
bulldog scalp
v. Overgrowth of body hair
vi. Enlargement of visceral organs such as lungs, thymus, heart, liver
and spleen
vii. Hyperactivity of thyroid, parathyroid and adrenal glands
viii. Hyperglycemia and glucosuria, resulting in diabetes mellitus
ix. Headache
x. Visual disturbance.
2. Excess Growth Hormone After Adolescence: Acromegaly

34. HYPOACTIVITY OF ANTERIOR PITUITARY
Panhypopituitarism
• This term means decreased secretion of all the anterior pituitary
hormones.
• The decrease in secretion may be congenital (present from
birth), or it may occur suddenly or slowly at any time during life,
most often resulting from a pituitary tumor that destroys the
pituitary gland.

35. Panhypopituitarism in the Adult: Panhypopituitarism occurring in
adulthood can results from tumours that compress that pituitary
gland or due to thrombosis of the pituitary blood vessels.
The general effects of adult panhypopituitarism are:
(1) hypothyroidism
(2) depressed production of glucocorticoids by the adrenal glands
(3) suppressed secretion of the gonadotropic hormones so that
sexual functions are lost
Thus, the picture is that of a lethargic person (from lack of thyroid
hormones) who is gaining weight (because of lack of fat
mobilization by growth, adrenocorticotropic, adrenocortical, and
thyroid hormones) and has lost all sexual functions.

36. HYPOACTIVITY OF ANTERIOR PITUITARY
Dwarfism is a pituitary disorder in children, characterized by
stunted growth.
Causes
1. Tumor of pituitary compresses and destroys the normal cells
secreting GH.
2. Deficiency of GH-releasing hormone secreted by hypothalamus
3. Deficiency of somatomedin C
4. Panhypopituitarism: In this condition, there is reduction in the
secretion of all the hormones of anterior pituitary gland.
Dwarfism

37. Signs and symptoms
1. In children, the skeletal growth is stunted. The maximum
height of anterior pituitary dwarf at the adult age is only
about 3 feet.
2. The proportions of different parts of the body are almost
normal, only the head becomes slightly larger in relation to
the body
3. Pituitary dwarfs do not show any deformity and their mental
activity is normal.
4. Reproductive function is not affected, if there is only GH
deficiency. However, during panhypopituitarism, the dwarfs
do not obtain puberty due to the deficiency of gonadotropic
hormones.
***Dwarfs who have pure GH deficiency can be completely cured if treated early
in life.

38. POSTERIOR PITUITARY or NEUROHYPOPHYSIS
• Posterior pituitary is made
up of glial-like cells called
pituicytes and
unmyelinated nerve fibers.
• Pituicytes are supporting
cells and do not secrete
any hormone.
• Unmyelinated nerve fibers
come from supraoptic and
paraventricular nuclei of
the hypothalamus.

39. HORMONES OF POSTERIOR PITUITARY
Posterior pituitary hormones are:
1. Antidiuretic hormone (ADH) or vasopressin
2. Oxytocin
Source of Secretion of Posterior Pituitary Hormones
• The posterior pituitary does not secrete any hormone of its own.
ADH and oxytocin are synthesized in the hypothalamus.
• From hypothalamus, these two hormones are transported to the
posterior pituitary through the nerve fibers of hypothalamo-
hypophyseal tract.
• In the posterior pituitary, the hormones are stored at the nerve
endings.
• Whenever impulses from hypothalamus reach the posterior
pituitary, these hormones are released from the nerve endings
into the circulation. Hence, these two hormones are called
neurohormones.

40. ANTIDIURETIC HORMONE (ADH)
Antidiuretic hormone is a polypeptide containing 9 amino acids.
Antidiuretic hormone has two actions:
1. Retention of water
2. Vasopressor action
1. Retention of water
• Major function of ADH is retention of water by acting on kidneys.
• It increases the reabsorption of water from collecting tubules and
duct in the kidneys.
• In the absence of ADH, the tubules and ducts are totally
impermeable to water so dilute urine is excreted.
• This leads to loss of large amount of water through urine. The
excretion of large amount of water is called diuresis.
• So when ADH is present it increases water reabsorption, causing
excretion of less dilute urine.

41. 2. Vasopressor action
• In large amount, ADH shows vasoconstrictor action.
• It causes constriction of the arteries in all parts of the body.
• Due to vasoconstriction, the blood pressure increases.
• However, the amount of ADH required to cause the vasopressor
effect is greater than the amount required to cause the
antidiuretic effect. This occurs strongly when the blood volume
decreases 15% to 25% or more; the secretory rate then
sometimes rises to as high as 50 times normal.

42. OXYTOCIN
• Oxytocin is a polypeptide having 9 amino acids.
• Oxytocin is secreted in both males and females.
• In females, oxytocin acts on mammary glands and uterus.
1. Action of oxytocin on mammary glands
2. Oxytocin Causes Contraction of the Pregnant Uterus

43. Ducts of the mammary glands are lined by
myoepithelial cells.
• Due to the suckling stimulus of baby, the
receptors are stimulated. The impulses
travel to paraventricular and supraoptic
nuclei of hypothalamus.
• The hypothalamus then sends impulses
to the posterior pituitary through
hypothalamo-hypophyseal tract.
• These impulses cause release of oxytocin
into the blood.
• Oxytocin reaches the mammary gland to
cause contraction of myoepithelial cells,
resulting in ejection of milk from
mammary glands. This is called milk
ejection reflex or milk letdown reflex.
1. Action of oxytocin on mammary glands

44. 2. Oxytocin Causes Contraction of the Pregnant Uterus
• Throughout the period of pregnancy, oxytocin secretion is
inhibited by estrogen and progesterone. At the end of pregnancy,
the secretion of these two hormones decreases suddenly and
the secretion of oxytocin increases.
• During the later stages of pregnancy, the number of receptors for
oxytocin increases in the wall of the uterus, thus the uterus
becomes more sensitive to oxytocin.
• Oxytocin secretion increases during labor. At the onset of labor,
the cervix dilates and the fetus descends through the birth canal.
During the movement of fetus through cervix, the receptors on
the cervix are stimulated and send many impulses to the
paraventricular and supraoptic nuclei of hypothalamus.
• These two hypothalamic nuclei secrete large quantity of
oxytocin, which enhances labor by causing contraction of uterus.