Endocrine system
By
Dr. Sadat A. Aziz
The pituitary gland:
It consists of two major portions,
1. The posterior pituitary gland
2. The anterior pituitary gland
The hormones of the anterior pituitary gland:
• They are in turn regulated by releasing
hormones which are secreted from the
hypothalamus and get to the anterior pituitary
gland through blood.
 Growth hormone (GH)
It is released by the anterior pituitary
gland, it promotes growth through:
a. Increases the rate of protein
synthesis.
b. Stimulates cell division and mitosis.
c. It stimulates growth and wound
healing.
Disorders of the growth hormones:
1. Pituitary dwarfism:
Hyposecretion of GH during childhood results in an abnormal growth
rate (a final height of only 3 to 4 feet) with a symmetric and normal body
proportions.
This condition is treatable if it is diagnosed properly at the early stages
of life.
2. Giantism (or gigantism): Hypersecretion of GH during childhood
leads to this condition which is characterised by excessive growth of the
long bones and the person may attain a height of 8 feet
3. Acromegaly:
• it is a clinical condition resulted from hypersecretion of GH in an adult,
• it is mainly caused by a pituitary gland lesion such as tumour.
• This condition is characterised by disproportionately growth of the facial bones, the
hands and feet.
• Also the skin becomes thicker, and the tongue may protrude
Prolactin:
• It is secreted by anterior pituitary gland.
• The secretion of prolactin can be regulated
by breast-feeding.
• Functions:
• It initiates and maintains milk production
by the mammary glands.
•
Other hormones of the anterior pituitary gland:
• Follicle-Stimulating Hormone
• Luteinizing Hormone
The pancreas:
It extends from the curve of
the
duodenum
to
the
spleen. The pancreas is
considered an exocrine and
endocrine gland.
The pancreatic endocrine function
The hormone-producing cells of the pancreas are called
islets of Langerhans
Glucagon:
•
it is secreted by alpha cell of pancreas in response to
hypoglycemia, a low blood glucose level.
• It stimulates the process of gluconeogenesis,
enhances liver to change glycogen to glucose and
increases fats and excess amino acids turn over to
energy.
• So it raises the blood glucose level.
Insulin:
• it secreted by beta cells of pancreas in response to hypergycemia, high blood glucose level.
•
It increases the glucose up take by the cells.
• In addition, it stimulates the liver and skeletal muscles to change glucose to glycogen
(glycogenesis).
• A deficiency of insulin hormone or its dysfunction is led to a condition called diabetes
mellitus.
Types of diabetes mellitus:
1. Diabetes mellitus type I: due to insulin hormone deficiency
2. Diabetes mellitus type II: resulted from defects in insulin receptors
Somatostatin: It is released by delta cells and decreases secretion of both insulin and glucagon
Adrenal glands:
• The two adrenal glands are each located on top of
a kidney.
• Each adrenal gland consists of two parts: an inner
adrenal medulla and an outer adrenal cortex.
Adrenal medulla:
The cells of the adrenal medulla secrete catecholamines
(epinephrine and norepinephrine) in response to stress
situation and prepare body for “fighting or flight”.
Adrenal cortex: The adrenal cortex secretes three
types
of
steroid
hormones:
mineralocorticoids
(aldosterone), glucocorticoids (cortisol), and sex
hormones (estrogens and androgens).
 Aldosterone: Aldosterone stimulate
reabsorption of sodium and water,
and the excretion of potassium by
the kidney tubules.
 Cortisol: It is secreted in response to several
physiological stress situations such as disease,
physical injury, fear, anger, exercise, and hunger.
Functions of cortisol:
1. Cortisol increases the use of fats and excess
amino acids (gluconeogenesis) for energy and
decreases the use of glucose.
2. Cortisol also has an anti-inflammatory effect.
THYROID GLAND
The thyroid gland is located on the front and sides of the trachea just below the larynx and is shaped somewhat
like a butterfly.
It produces thyroxine (T4) and triiodothyronine (T3).
These hormones regulate the metabolic rate and the activity of the brain, muscles, heart, and virtually all
other organs.
Disorders associated with thyroid hormones:
1.
Goiters: resulted from iodine defficiency, characterised by thyroid gland enlargement.
2.
Cretinism: hyposecretion of thyroid hormone in new-born leads to development of this condition
characterised by a sever physical and mental disabilities.
3.
Grave`s disease: resulted from hypersecretion of thyroid hormone, characterised by an increase in the
metabolic rate, weight loss, excessive sweating, fatigue and exophthalmos.
Parathyroid gland:
It secrets parathyroid hormone in response to
hypocalcaemia.
• Function:
Parathyroid
homeostasis
hormone
by
regulates
enhancing
calcium
intestinal
reabsorption, reducing renal excretion, and
increasing bone resorption of calcium.
Para-follicular cells of the thyroid gland:
• They are involved in the synthesis and secretion of
calcitonin in response to hypercalcemia.
•
in general, has effects opposite to those of
parathyroid hormone tends to decrease plasma
calcium concentration by enhancing calcium
deposition in the bone, increasing calcium
secretion.