Hypothalamic factors and Anterior Pituitary Hormones

1. Hypothalamic factors and
Anterior Pituitary Hormones
By
Dr. Abdul Majid Siddiqui
MSc. Medical Physiology
Era University, Lucknow

2. Learning Objectives
To understand the structure and function of anterior pituitary
To understand the different hormones secreted by anterior
pituitary
To understand the control of hypothalamus over anterior
pituitary
Applied aspect of anterior pituitary

3. Hormone of Anterior Pituitary.
The pituitary gland also called
the hypophysis, is a small
gland—about 1 cm in diameter
and 0.5 to 1 gm in weight—that
lies in the sella turcica, a bony
cavity at the base of the brain,
and is connected to the
hypothalamus by the pituitary
stalk.
Physiologically, the pituitary
gland is divisible into two
distinct portions:
Anterior pituitary, also known
as the adenohypophysis,
Posterior pituitary, also known
as the neurohypophysis.

4. Anterior pituitary gland contains several different cell types
that synthesize and secrete hormones.

5. Six important peptide hormones plus several less important ones are
secreted by the anterior pituitary.
The hormones of the anterior pituitary play major roles in the control of
metabolic functions throughout the body,
1. Growth hormone promotes growth of the entire body by affecting
protein formation, cell multiplication, and cell differentiation.
2. Adrenocorticotropin (corticotropin) controls the secretion of some of
the adrenocortical hormones, which affect the metabolism of glucose,
proteins, and fats.
3. Thyroid-stimulating hormone (TSH) controls the rate of secretion of
thyroxine and triiodothyronine by the thyroid gland, and these hormones
control the rates of most intracellular chemical reactions in the body.
4. Prolactin promotes mammary gland development and milk
production.
Two separate gonadotropic hormones:-
5. Follicle-stimulating Hormone(FSH)
6. Luteinizing Hormone(LH),
They control growth of the ovaries and testes, as well as their
hormonal and reproductive activities.

6. Metabolic functions of the anterior
pituitary hormones.

7. Physiological Functions of Growth Hormone
All the major anterior pituitary hormones, except for growth hormone, exert
their principal effects by stimulating target glands, including thyroid gland,
adrenal cortex, ovaries, testicles, and mammary glands.
Effect on Growth
It causes growth of almost all tissues of
the body
Promotes increase in the size of cells.
Increase the rate of mitosis, resulting in
increase number of cells.
Causes differentiation of cells in bone
and muscle.

8. Effect on Bone and Cartilage
Growth hormone stimulate bone growth.
Increase the number of cells responsible for bone growth.
Increase deposition of protein by chondrocytic & osteogenic Causes
growth of epiphysial cartilage.
Delays fusion of epiphysial with the shaft.
Effects on Protein metabolism.
It increase the rate of protein synthesis in the cells by
Enhancing amino acid transport through the cell membrane.
Increases nuclear transcription of DNA to form mRNA.
Enhancing RNA translation to prone protein synthesis by ribosome.
Decreasing the catabolism of protein and amino acids.
Effects on Carbohydrate metabolism.
Decrease the use of glucose for energy;
Diminishes uptake of glucose by the cells and increase blood glucose conc.
Increase the secretion of insulin.

9. Effect on fat metabolism
Increase mobilization of fats from adipose tissue.
Increase free fatty acids in the blood.
Enhances use of fatty acids for energy.
Excess of growth hormone has a “Ketogenic effect.”
Effect On Electrolyte Metabolism
Causes rise in plasma phosphorous and fall in blood urea, N2 and
amino acid level.
Increases GI absorption of Ca++.
Reduces Na+ and K+ excretion.
Growth hormone is degraded in the Liver and Kidneys.

10. „OTHER HORMONES OF ANTERIOR PITUITARY
Thyroid-stimulating Hormone (TSH)
TSH is necessary for the growth and secretory activity of the thyroid
gland. It has many actions on the thyroid gland.
Adrenocorticotropic Hormone (ACTH)
ACTH is necessary for the structural integrity and the secretory activity of
adrenal cortex.
Follicle-stimulating Hormone (FSH)
Follicle-stimulating hormone is a glycoprotein made up of one α-subunit
and a β-subunit. The α-subunit has 92 amino acids and β-subunit has 118
amino acids. The half-life of FSH is about 3 to 4 hours.

11. Follicle Stimulating Hormones(FSH)
In males,
FSH acts along with testosterone and accelerates the process of
spermeogenesis
In females FSH:
1. Causes the development of graafian follicle from primordial follicle
2. Stimulates the theca cells of graafian follicle and causes secretion of
estrogen
3. Promotes the aromatase activity in granulosa cells, resulting in
conversion of androgens into estrogen
Luteinizing Hormone (LH)
LH is a glycoprotein made up of one α-subunit and one β-subunit. The α-
subunit has 92 amino acids and β-subunit has 141 amino acids. The half-
life of LH is about 60 minutes.
Actions of LH
In males, LH is known as interstitial cell-stimulating hormone (ICSH)
because it stimulates the interstitial cells of Leydig in testes. This
hormone is essential for the secretion of testosterone from Leydig cells

12. In females, LH:
Causes maturation of vesicular follicle into graafian follicle along with
follicle-stimulating hormone
Induces synthesis of androgens from theca cells of growing follicle
Is responsible for ovulation
Is necessary for the formation of corpus luteum
Activates the secretory functions of corpus luteum
Prolactin
Prolactin is a single chain polypeptide with 199 amino acids. Its half-
life is about 20 minutes. Prolactin is necessary for the final preparation of
mammary glands for the production and secretion of milk.
Prolactin acts directly on the epithelial cells of mammary glands and
causes localized alveolar hyperplasia.

13. Hypothalamus Controls
Pituitary Secretion:-
Almost all secretion by the
pituitary is controlled by either
hormonal or nervous signals from the
hypothalamus
Secretion by the anterior pituitary
is controlled by hormones called
hypothalamic releasing and
hypothalamic inhibitory hormones
(or factors) secreted within the
hypothalamus itself and then
conducted to the anterior pituitary
through minute blood vessels called
hypothalamic-hypophysial portal
vessels. In the anterior pituitary, these
releasing and inhibitory hormones act
on the glandular cells to control their
secretion.
Hypothalamic-hypophysial portal system

14. Hypothalamic Releasing and Inhibitory Hormones That Control
Secretion of the Anterior Pituitary Gland
Hormone Structure Primary Action on Anterior
Pituitary
Thyrotropin-releasing
hormone (TRH)
Peptide of 3 amino acids Stimulates secretion of TSH
by thyrotropes
Gonadotropin-releasing
hormone (GnRH)
Single chain of 10 amino Stimulates secretion of FSH
and LH by gonadotropes
Corticotropin-releasing
hormone (CRH)
Single chain of 41 amino
acids
Stimulates secretion of
ACTH by corticotropes
Growth hormone–releasing
hormone(GHRH)
Single chain of 44 amino
acids
Stimulates secretion of
growth hormone by
somatotropes
Growth hormone inhibitory
hormone(somatostatin)
Single chain of 14 amino
acids
Inhibits secretion of
growth hormone by
somatotropes
Prolactin-inhibiting
hormone (PIH)
Dopamine (a catecholamine) Inhibits secretion of
prolactin by lactotropes

15. APPLIED PHYSIOLOGY – DISORDERS OF ANTERIOR
PITUITARY GLAND
HYPERACTIVITY OF ANTERIOR PITUITARY
1. Gigantism
Gigantism is the pituitary disorder characterized by excess growth of the
body. The subjects look like the giants with average height of about 7 to 8
feet.
Causes
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 is because of tumor of acidophil cells in the
anterior pituitary.
2. Acromegaly
Acromegaly is the disorder characterized by the enlargement, thickening
and broadening of bones, particularly in the extremities of the body.
Causes
Acromegaly is due to hypersecretion of GH in adults after the fusion of
epiphysis with shaft of the bone.
Hypersecretion of GH is because of tumor of acidophil cells in the
anterior pituitary.

16. HYPOACTIVITY OF ANTERIOR PITUITARY
1. Dwarfism
Dwarfism is a pituitary disorder in children, characterized by the stunted
growth.
Causes
Reduction in GH secretion in infancy or early childhood causes dwarfism.
A. Normal hand;
B. B. Acromegalic hand

17. Dwarfism