Download Introduction to Endocrinology Body communicating system 1

Introduction to Endocrinology
Body communicating system
1-Nural: act locally to central cell function, in which chemical "neurotransmitters" are released at
the synaptic junction.
2-Endocrine: in which glands or specialized cells release into blood circulating chemicals
"hormones" that influence the function of cells at other location in the body.
3-Neuroendocrine: in which neurons secrete substances "neurohormones" that reach the
circulating blood and influence the function of cells at other location in the body.
4-Paracrine: in which cells secrete substances that diffuse into the extracellular fluid and affect
neighboring cells.
5-Autocrine: in which a cell secretes substances that affect the function of the same cells, by
binding to the cell surface receptors.
The Endocrine System
Endocrine means internal secretion "secretion into capillaries".
Hormones are molecules carried out by the blood to another organ, where they control certain
aspects of metabolism.
There are 3 general classes of hormones:
1-Proteins and Polypeptides: including hormones that are secreted by the anterior and posterior
pituitary gland, pancreatic hormones and parathyroid hormones. These hormones are the most in
the body. They range in size from 3 amino acids as in Thyrotropin-releasing hormone (TRH) to 200
a.a. as in growth hormone. In general polypeptides with 100 or more amino acids are called
protein and less are peptides. They are synthesized on the rough endoplasmic reticulum of the
different endocrine cells, first as non active large protein "prehormone", cleaved to prohormone,
then transferred to Golgi complex for packaging into secretory vesicles. Enzymes in the vesicles
cleave it to produce active hormone, vesicle are stored
then secretion by exocytosis
2-Steroid: including adrenocortical hormones "cortisol and aldesterone", the ovaries "estrogen and
progesterone", the testes "testosterone" and the placenta "estrogen and progesterone". They are
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
lipid soluble and are synthesized from cholesterol. They are not stored, once are synthesized they
diffuse through the cell membrane to the blood.
3-Derivative of the amino acid Tyrosine: including thyroid gland "thyroxin and triiodothyronine", and
the adrenal medullae "epinephrine and nor epinephrine". Epinephrine is secreted about four
times more than nor epinephrine, they are stored and released by exocytosis.
There are no known polysaccharides or nucleic acid hormones
Feedback Control
1-Negative feedback: prevents over activity after hormone release, conditions or products resulting
from the action of a hormone tend to suppress its further release.
2-Positive feedback: as in the release of estrogen by the ovary.
There are cyclic variations in hormone release due to seasonal changes, various stage of
development and aging and diurnal cycle or sleep "for example, the secretion of growth hormone
increases during the early period of sleep, but reduces during late stages.
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
The Pituitary Gland "Hypophysis"
It is a small gland with two distinct parts, anterior and posterior originated from different sources.
The anterior part secretes six important hormones, while the posterior part secretes two
important hormones.
Hormones of the anterior lobe:
1-Growth hormone "Somatotropine". About 30-40% of the anterior pituitary cells are Somatotropes
that secrete Somatotropine. Somatotropine contains 191 amino acids in a single chain. It causes
growth almost all capable growing tissue of the body by promotes increased size of the cells and
increased mitosis. It has some other metabolic effects such as increase the rate of protein
synthesis, increase mobilization of fatty acids from adipose tissue and decrease the rate of glucose
utilization.
Abnormalities: Dwarfism vs. Gigantism
2-Adrinocortticotropin hormone (ACTH). About 20% of the anterior pituitary cells secrete ACTH. It
controls the secretion of some adrenocortical hormones, which in turn affect the metabolism of
glucose and proteins.
3-Prolactine. Prolactine promotes mammary gland development and milk secretion
4-Thyroid Stimulating Hormone (TSH). It is about 3-5% of the anterior lobe, controls the secretion of
Thyroxin (T4) and Triiodothyronine (T3)by Thyroid gland, in which they control the rate of most
intracellular chemical reactions of the entire body. Also stimulates iodine absorption by thyroid
gland
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
5-Follical Stimulating Hormone (FSH). In females it stimulates maturation of ovarian follicles in ovary.
In males it stimulates maturation of seminiferous tubules, stimulates spermatogenesis, and also
stimulates production of androgen-binding protein from Sertoli cells of the testes
6-Luteinizing Hormone (LH). LH controls the growth of ovary and testes as well as their hormonal
and reproductive activities. In females: Stimulates ovulation and stimulates formation of corpus
luteum. In males: Stimulates testosterone synthesis from Leydig cells (interstitial cells)
Hormones of the posterior lobe:
1-Antidiuretic Hormone "Vasopressin". Help control water concentration by controlling the rate of
water excretion into Urine, by increasing water permeability in the distal convoluted tubule and
collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume
2-Oxytocin. Helps express milk from the mammary gland to the nipples during sucking, and
possibly help in delivery of the baby.
Intermediate pituitary lobe (pars intermedia)
Melanocyte-stimulating hormone MSH, Stimulates melanin synthesis and release from skin/hair
melanocytes.
The Thyroid Gland
The Thyroids gland is located immediately below the larynx on each side of and anterior of the
trachea. It is one of the largest of the endocrine glands. The Thyroid secretes two significant
glands hormones "thyroxin T3 93%, tiiodothyrosine T4 7%, 4 times potent". Bothe have the
profound effect of increasing the metabolic rate of the body. Their secretion is controlled by the
(TSH) …….(feedback). The thyroid gland also secretes Calcitonin, an important hormone for
calcium metabolism.
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
Functions:
1-Increase the number and activity of mitochondria.
2-Increase active transport.
3-Effect on growth.
4-Increase heart rate.
5-Increase respiration.
6-Effect on other endocrine glands.
Parathyroid Gland
Normally there are four parathyroid glands in humans, located immediately behind the thyroid.
Two hormones are secreted by the thyroid gland.
1-Parathyroid Hormone (PTH): first synthesized in the ribosomes as polypeptide chain of 110 amino
acids, then cleaved to prohormone with 90 amino acids, then to hormone of 84 amino acids by
Golgi complex. It functions in increasing calcium absorption in the intestine.
2-A peptide hormone Cacitonin: tends to decrease calcium concentration. In general its affect is
opposite to PTH.
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
Adrenocortical Hormones
There are two adrenal glands in humans, each of which weights 4 grams. They lie at the superior
poles of the two kidneys. Each gland is composed of two distinct parts. The adrenal medulla is in
the central about 20% of the gland and secretes epinephrine and norepinephrine.
The adrenal cortex, which secretes entirely different groups of hormones derived from cholesterol
and are called Corticosteroids, such as "Aldesteron 90%, corticosterone, deoxycortisol and
cortisone".
Aldesteron functions:
1- Increase renal tubular re-absorption of sodium and secretion of potassium.
2- Stimulates sodium and potassium transport in sweat gland, salivary gland and intestinal epithelial
cells.
Epinephrine and norepinephrine are secreted due to stimulation of the sympathetic nerves with a
percentage of 80% epinephrine and 20% norepinephrine. Their circulation causes constriction of all
blood vessels of the body. They increase the heart activity, inhabitation of the gastrointestinal tract
and dilation of the pupils of the eye.
Epinephrine effect is stronger on heart and weaker on blood vessel constriction.
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
Insulin, Glucagon and Diabetes Mellitus
In addition to the digestive functions of the pancreas, its secrets two important hormones "Insulin
and Glucagon". The pancreas is composed of two major types of cells: The Acini, which secretes
digestive juices into Duodenum and the Islets of Langerhans, which secretes insulin and glucagon.
The human pancreas has one to two millions islets of Langerhans. The islets contain three different
types of cells "alpha, beta and delta". The beta cells constituting about 60% of all the cells, lie mainly
in the middle and secrete Insulin and amylin. The alpha cells constituting about 25% of all cells and
secrete Glucagon. The Delta cells about 10% and secretes Somatostatin.
1-Insuline
Was first isolated in 1922, it is a small protein composed of two amino acid chains connected with
each other with disulfide linkage. The high carbohydrate concentration in the blood causes rapid
secretion of insulin. The insulin in turn causes rapid uptake, storage and use of glucose by almost
all cells of the body, but specially muscles, adipose tissue and liver. Insulin also promotes fat
synthesis and storage in the adipose tissue, and promotes protein synthesis and storage.
2-Glocagon
Glucagon is a polypeptide hormone composed of 29 amino acids and secreted by alpha cells. It
breaks down of liver glycogen "Glycogenlysis".
Testes
The testicle (testis, meaning "witness" plural testes) is the male generative gland in animals. Testes are
components of both the reproductive system (being gonads) and the endocrine system (being endocrine
glands). The respective functions of the testes are: producing sperm (spermatozoa) and producing male
sex hormones of which testosterone is the best-known Both functions of the testicle, sperm-forming and
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬
endocrine, are under control of gonadotropic hormones produced by the anterior pituitary: luteinizing
hormone (LH) and follicle-stimulating hormone (FSH)
Secreted hormone
From cells
Effect
Anabolic: growth of muscle mass and strength,
increased bone density, growth and strength,
Androgens (chiefly
testosterone)
Leydig cells
Estradiol
Sertoli cells
Prevent apoptosis of germ cells
Inhibin
Sertoli cells
Inhibit production of FSH
Virilizing: maturation of sex organs, formation
of scrotum, deepening of voice, growth of
beard and axillary hair.
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as a part of the female
reproductive system. Ovaries in females are homologous to testes in males, in that they are both
gonads and endocrine glands. Ovaries secrete both estrogen and progesterone. Estrogen is
responsible for the appearance of secondary sex characteristics of females at puberty and for the
maturation and maintenance of the reproductive organs in their mature functional state.
Progesterone functions with estrogen by promoting cyclic changes in the endometrium (it
prepares the endometrium for pregnancy), as well as by helping maintain the endometrium in a
healthy state during pregnancy.
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‫ سيتم مساءلة و مقاضاة كل من يقوم بالنسخ من اجل المتاجرة‬.‫ جامعة طرابلس‬/ ‫كلية العلوم‬/ ‫حقوق الطبع و النسخ خاصة لقسم علم الحيوان‬