1. University of Duhok
College of Veterinary Medicine
Department of Theriogenology, Anatomy, and Physiology
Physiology of the Endocrine System(L2)
Prepared by
Dr.Tareek Abdulqadir Abdal
Lecturer
2. 2. Intermediate lobe of pituitary gland : Lies between the anterior pituitary and the posterior
pituitary glands.
It produces melanocyte stimulatory hormone (MSH) in all vertebrates, that contributes to the
adaptation of body color to the color of the environment in fish, amphibians, and reptiles.
The target cells for MSH are pigment cells in the skin called melanocytes which contain melanin
granules, the melanin produced from phenylalanine(amino acid) which gives skin, eyes, and hair
their normal coloration ,when the enzyme that converts this amino acid to the amino acid
tyrosine and then into the melanin is defective many congenital conditions are results such as:
1. Albinism
2. Piepaldism
3. Vitiligo
3. 1. Albinism:
A group of genetic disorders in human and animals in which there is partial or total lack of the
pigment melanin in the eyes, skin, and hair.
Types of albinism
There are two principal types of albinism:
1. Oculocutaneous, the most common one, affecting the eyes, skin and hair.
2. Ocular affecting only the eyes.
4. • the iris of the eye contains a pigmented epithelium that gives the eye its color. The color of
the iris is determined by the amount of pigment—blue eyes have the least pigment, brown
eyes have more, and black eyes have the greatest amount of pigment, In albinism the eyes
appear pink because the absence of pigment allows blood vessels to be seen.
• also melanin lets the correct development of the eye, its deficiency is associated with
uncontrolled pendular eye movements (nystagmus).
• The skin also protects itself against the dangers of ultraviolet (UV) light by increasing its
production of melanin pigment, which absorbs UV light while producing a tan ,in albinism
the susceptibility to skin cancer(melanoma) is increased.
5. • In some animals, an intermediate “lobe” of the pituitary gland is highly developed and
secreted a large amount of MSH. Furthermore, this secretion is independently controlled
by the hypothalamus in response to the amount of light to which the animal is exposed .
For instance, some arctic animals develop darkened fur in the summer and yet have
entirely white fur in the winter, so it will be harder for predators to spot.
6. 2. Piebaldism
It’s a genetic condition, typically present at birth in
both human & animals, in which there is a develops
of unpigmented or white patch of skin or hair.
3. Vitiligo
It’s a disease in which the pigment cells of the skin (melanocytes) are destroyed in certain
areas of the body and it is occur after birth in both animal and human.
7. 3. Anterior pituitary glands
•The anterior pituitary gland is the true glandular part of the pituitary gland (master gland),
Communication between the hypothalamus and the anterior pituitary occurs through
chemicals (releasing hormones and inhibiting hormones) that are produced by
neurosecretory cells in the hypothalamus and delivered to the anterior pituitary through
blood vessels in the infundibulum.
•Then they released into a capillary network
that supplies the endocrine cells of the anterior
pituitary where they initiate the production of
specific hormones by the anterior pituitary.
8. The releasing and inhibiting hormones secreted by the hypothalamus are the following:
1. Corticotropin-releasing hormone (CRH), which stimulates the secretion of adrenocorticotropic
hormone (ACTH).
2. Thyrotropin-releasing hormone (TRH), which stimulates the secretion of thyroid-stimulating
hormone (TSH).
3. Gonadotropin-releasing hormone (GnRH), which stimulates the secretion of follicle-stimulating
hormone (FSH) and luteinizing hormone (LH).
4. Growth hormone-releasing hormone (GH-RH), which stimulates secretion of growth hormone(GH),
and growth hormone-inhibiting hormone (GH-IH), also called Somatostatin, which inhibits secretion
of growth hormone (GH).
5. Prolactin-releasing hormone (PRL-RH), which stimulates secretion of prolactin, and prolactin-
inhibiting hormone (PRL-IH), also called Dopamine, which inhibits secretion of prolactin (PRL).
9.
10.
11. Growth hormone (GH, or somatotropin): Are produced and secreted by somatotroph cells of the
anterior pituitary gland.
Physiologic Effects of Growth Hormone:
1. Effects on Growth:
a. GH stimulates the transcription of DNA in the nucleus, causing the formation of increased quantities
of RNA. This promotes the movement of amino acids into cells and the incorporation of these amino
acids into proteins by the ribosomes in the cytoplasm, thus promoting overall tissue and organ
growth.
b. GH also stimulates growth of the skeletal frame by causes the liver to form several small proteins
called somatomedins( insulin-like growth factors “IGFs”) that have the potent effect of increasing all
aspects of bone growth.
12. -The pygmies of Africa have a congenital inability to synthesize significant amounts of somatomedin in
the liver, even though their plasma concentration of growth hormone is either normal or high.
There are two principal mechanisms of bone growth:
First, in response to GH stimulation, the long bones grow in length at the epiphyseal cartilages, where
the epiphyses at the ends of the bone are separated from the shaft(diaphysis).
-This growth first causes increased deposition of protein by the chondrocytic (cartilage cells)and
increased rate of reproduction of cartilage cells thus causes deposition of new cartilage.
-then followed by its conversion into new bone (converting cartilage cells into osteogenic cells, thus
causing deposition of new bone), thus elongating the shaft and pushing the epiphyses farther and
farther apart.
13.
14. •At the same time, the epiphyseal cartilage itself is progressively used up, so that by late
adolescence, no additional epiphyseal cartilage remains to provide for further long bone
growth.
•At this time, bony fusion occurs between the shaft and the epiphysis at each end, so that
no further lengthening of the long bone can occur.
•Second, osteoblasts in the bone periosteum and in some bone cavities deposit new bone
on the surfaces of older bone. Simultaneously, osteoclasts in the bone remove old bone.
•When the rate of deposition is greater than that of resorption, the thickness of the bone
increases.
•Growth hormone strongly stimulates osteoblasts. Therefore, the bones can continue to
become thicker throughout life under the influence of growth hormone.
15. 2. Effects on metabolism Growth hormone has important effects on protein, lipid and carbohydrate
metabolism it has both anabolic and catabolic effects.
a) Protein metabolism: GH stimulates the cellular uptake of amino acids and protein synthesis in many
organs of the body (anabolism). These actions are useful when eating a protein-rich meal; amino
acids are removed from the blood and used to form proteins.
b) Fat metabolism: GH stimulates the catabolism of fat and the release of fatty acids from adipose
tissue during periods of fasting to provide alternate energy sources.
c) Carbohydrate metabolism: raising blood levels of fatty acids above normal rapidly impair insulin’s
actions on tissue glucose utilization this mean that the growth hormone causes insulin resistance
and decreased glucose utilization by the cells and increased glucose production by the liver.
•The increase plasma concentration of glucose and fatty acids is useful to provide alternate energy
sources.
16. Factors affecting GH secretion
A. Increase in:
1. Starvation
2. fasting
3. hypoglycemia
4. exercise
5. excitement
6. trauma
7. during the first 2 hours of deep sleep.
B. Decrease in :
1. High free fatty acids in blood.
2. Increase plasma growth hormone
3. Hyperglycemia
4. High plasma Cortisol
17.
18. 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.
19. Abnormalities of Growth Hormone Secretion
1. Hypopituitarism deficiency in GH or defects in its binding to their receptor during the
growing years results in dwarfism (below the age20 years).
2. Hyperpituitarism an excessive secretion of GH in children can produce gigantism (below
the age 20 years), these children may grow up to 8 feet tall, at the same time maintaining
normal body proportions.
3. Hyperpituitarism above 20 years result in Acromegaly, an excessive GH secretion that
occurs after the epiphyseal discs have sealed, however, cannot produce increases in height.
In adults, the over secretion of GH results in deformities in the bones of the face, hands,
and feet with prognathism (elongation of the lower jaw) it is accompanied by the growth of
soft tissues and coarsening of the skin.
22. Prolactin (PRL): is produced in special cells, lactotropes in the anterior pituitary gland, Its function:
1. Is the stimulation of milk production by the mammary glands of women after the birth of a
baby(after parturition).
2. promote growth and differentiation of mammary epithelial tissue during pregnancy to prepare the
mammary gland to store and release of milk.
3. Inhibit the action of Gonadotropins(FSH & LH ) inhibition of ovulation & amenorrhea.
•Hyperprolactinemia in women cause amenorrhea by inhibiting gonadotropins, when prolactin secretion
is reduced by drugs, normal menstrual cycles and fertility return.
•Hyperprolactinemia in men is associated with impotence and hypogonadism that disappear when
prolactin secretion is reduced.
23. Regulation of Prolactin secretion
•Prolactin secretion is controlled by prolactin released hormone (PRH) and prolactin-inhibiting
hormone (PIH) from the hypothalamus, during pregnancy when estradiol (estrogen) levels
remain high the secretion of prolactin from the anterior pituitary is tonically inhibited by
stimulating secretion of PIH, after parturition, when the placenta is expelled after birth,
declining levels of estrogen causes an increase in the secretion of prolactin. Milk production is
therefore stimulated.
•The act of nursing helps to maintain high levels of prolactin secretion via a neuroendocrine
reflex . Sensory endings in the breast, activated by the stimulus of suckling(The stimulus of
suckling also results in the reflex secretion of oxytocin from the posterior pituitary),relay
impulses to the hypothalamus and inhibit the secretion of PIH and promote PRH.
