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ENDOCRINOLOGY
The scientific study of the endocrine
glands and their hormones
THINGS NEED TO KNOW
• General Features of the Endocrine System
and Important definitions
• Evolution of the Endocrine System
• Classes of Hormones
• Actions of Hormones
General Features of the
Endocrine System
1. Endocrine glands are ductless
2. Endocrine glands have a rich supply of blood.
3. Hormones, produced by the endocrine glands
are secreted into the bloodstream.
4. Hormones travel in the blood to target cells
close by or far away from point of secretion.
5. Hormones receptors are specific binding sites
on the target cell.
Important Definitions
• What are hormones?
Hormones are organic chemical messengers produced and
secreted by endocrine cells into the bloodstream.
Hormones regulate, integrate and control a wide range
of physiologic functions.
Important Definitions Cont.
• What are endocrine glands?
Endocrine glands are ductless glands comprised
of endocrine cells. This means that these glands
do not have ducts that lead to the outside of the
body. For example, sweat glands are NOT
endocrine glands (they are instead exocrine
glands) because sweat glands have ducts that
lead to the outside surface of your skin (that’s
how the sweat gets out). The fact that endocrine
glands are ductless means that these glands
secrete hormones directly into the blood stream
(instead of to the outside of your body).
Important Definitions Cont.
• What are target cells?
Target cells refer to cells that contain specific receptors
(binding sites) for a particular hormone. Once a hormone
binds to receptors on a target cell, a series of cellular
events unfold that eventually impact gene expression
and protein synthesis.
Important Definitions Cont.
• What are hormone receptors?
Hormone receptors are binding sites on the target cell
(either on the surface or in the cytoplasm or nucleus of
the target cell) that are activated only when specific
hormones bind to them. If a hormone does not/cannot
bind to it’s receptor, then no physiologic effect results.
See next slide for a picture of a hormone bound to its receptor
Growth hormone regulates cell growth by binding
to growth hormone receptors on target cells.
THINGS NEED TO KNOW
• General Features of the Endocrine System
and Important definitions
• Evolution of the Endocrine System
• Classes of Hormones
• Actions of Hormones
Evolution of the
Endocrine System
• It is likely that the vertebrate endocrine
system evolved from bacterial signaling
systems that allowed bacteria to both
perceive extra- and intracellular signals.
• Primitive endocrine signaling likely arose
from cells releasing chemical signals to
communicate with neighboring cells
(paracrine signaling).
Classes of Hormones
• Steroids vs. Peptide Hormones
Hormones fall into 2 general classes based
on their molecular structure and synthesis.
• All steroid hormones are made initially
from the precursor (precursor = first step in
biosynthetic pathway) cholesterol.
See next slide for a diagram of the biosynthetic pathway of steroid hormones
from cholesterol.
Steroid Hormones
• Steroid hormones are produced by the
gonads and adrenal cortex.
• Thyroid hormones are not steroids, but will
be categorized with steroids for simplicity.
• Steroid hormones are made from
cholesterol in the smooth endoplasmic
reticulum and mitochondria of endocrine
cells.
Steroid Hormones
• Steroid hormones cannot be stored in
vesicles in the endocrine cells that
produce them. As soon as steroid
hormones are produced, they diffuse out
of the endocrine cell and enter the
bloodstream.
• Steroid hormones are lipid soluble and
their receptors are located inside their
target cell.
Steroid hormones:
Penetrate the cell and bind to a receptor protein inside the target cell. This
also will trigger signal transduction pathway (for triggering mRNA
transcription for synthesizing a specific protein).
• Estrogen, progesterone, vitamin D and NO.
– Usually, the intracellular receptor activated by a hormone is a
transcription factor.
17
Peptide Hormones
• Peptide hormones are comprised of
chains on amino acids.
• Like most proteins, peptide hormones are
synthesized on ribosomes of the (rough)
endoplasmic reticulum of endocrine cells.
• Peptide hormones can be stored in
vesicles in endocrine cells until they are
needed at some later point.
Peptide Hormones
• Peptide hormones do not readily pass
through cell membranes (lipid bilayers)
and they are referred to as water soluble.
• Receptors for peptide hormones are found
on the cell surface of their target cells.
Most chemical signals bind to plasma-membrane proteins,
initiating signal-transduction pathways.
Mechanism of chemical signaling:
The chemical signals secreted by a cell either:
Protein hormones:
Bind to a receptor protein on the surface of the target cell which
will trigger signal transduction pathway.
21
Actions of Hormones
•
•
•
•
•
•
•
•
•
Fetal development and differentiation
Cell growth and cancer
Metabolism
Cardiovascular function
Renal function
Skeletal function
Reproductive function
Immune function
Central nervous system function
• Nervous and endocrine systems are the main internal
communication and regulation systems.
• The animal hormone-secreting cells constitute the endocrine
system.
• Hormone secreting organs are called Endocrine Glands (ductless
glands ‫) الغدد الصماء‬.
• Hormone is a chemical signal secreted into blood stream and
regulates communicating messages within the body.
• Target cell is the site that reached by the hormone to which it
responds.
• Complete changes in the body is regulated by hormones (e.g.
metamorphosis in insects).
• Types of hormones are [Polypeptide H., Amino acid derivatives H
or Steroid H.].
23
• Tropic hormones: )‫ الهرمونات المحفزة (المنبهة‬target other endocrine glands
and are important to understanding chemical coordination.
• Many endocrine organs contain specialized nerve cells called
neurosecretory cells that secret hormones.
• The hormone epinephrine has two functions:
– As a hormone of the endocrine system.
– As a signal in the nervous system.
• Feedback is common in regulation the activity of both endocrine
and nervous systems (homeostasis) (Fig. 45.1, page 956):
– Calcitonin and parathyroid hormones play an important role in
maintaining the concentration of the blood calcium constant.
– They are secreted from thyroid and parathyroid glands respictively.
• Hormones regulate the development of
invertebrates (e.g. insects)
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The Vertebrate Endocrine System
 Tropic hormones
(‫)الهرمون المنبه للغدد‬

other endocrine
glands and are
important to
understanding
chemical coordination.
‫الصنوبرية‬
‫النخامية‬
‫الدرقية‬
Target
‫الكظرية‬
• Human has 9
endocrine glands.
25
Fig. 45.5, Page 960
The hypothalamus and pituitary integrate many
functions of the vertebrate endocrine system
•
The hypothalamus integrates endocrine and
nervous function.
–
Neurosecretory cells of the hypothalamus produce
hormones.
a) Releasing hormones stimulate the anterior pituitary
(adenohypophysis) to secrete hormones.
b) Inhibiting hormones prevent the anterior pituitary from
secreting hormones.
1)- Pituitary gland: secrets 9 hormones ( 7 hormones by the
anterior part and 2 hormones by the posterior part).
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A)- Anterior pituitary hormones.
1)
Growth hormone (GH): a protein.
•
•
•
•
•
•
Stimulates growth and metabolism.
Secretion regulated by hypothalamic hormones.
Acts directly on tissues or acts via growth factors.
Gigantism: ‫ العملقة‬excessive GH during development.
Acromegaly: excessive GH production during adulthood.
Hypopituitary dwarfism ‫القزمية‬: childhood GH deficiency.
2) Prolactin (PRL): a protein.
•
Stimulates milk production and secretion from mammary
gland ‫الغدد اللبنية‬. This secretion regulated by hypothalamic
hormones.
3) Gonadotropins (Gonotropic ‫)محفز للمناسل‬: glyocoproteins.
•
Follicle-stimulating hormone (FSH).
–
–
•
Stimulates production of sperms and ova.
Secretion regulated by hypothalamic hormones.
Luteinizing hormone (LH) ‫ال ُمحفز لتكوين الجسم األصفر‬.
– Stimulates ovaries and testes.
– Secretion regulated by hypothalamic hormones.
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4)
Thyroid-stimulating hormone (TSH): a glycoprotein.
•
•
•
5)
Stimulates thyroid gland.
Secretion regulated by thyroxine in blood.
Secretion regulated by hypothalamic hormones.
Adrenocorticotropic hormone (ACTH): a peptide
•
•
6)
Stimulates adrenal cortex secretion of glucocorticoids
Secretion regulated by glucocorticoids and hypothalamic
hormones.
Melanocyte-stimulating hormone (MSH): a peptide.
•
7)
May play a role in fat metabolism.
Endorphins: peptides.
•
•
Inhibit pain perception.
Effects mimicked by heroin and other opiate drugs.
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The anterior pituitary gland hormones
Melanocytestimulating H.
Adrenocorticotropic
Fig. 45.6b, Page 963
Also called gonadotropine
hormones ‫هرمونات المناسل‬
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B)- Posterior pituitary hormones.
– Oxytocin: a peptide.
• Stimulates contraction of the uterus and mammary glands.
• Secretion regulated by the nervous system.
– Antidiuretic hormone (ADH): ‫ ُمضاد إلدرار البول‬a peptide.
• Promotes retention of water by the kidneys (in Kidney tubules).
• High level decreases urination and vice versa.
• Secretion regulated by water/salt balance.
2- Pineal gland: ‫الغدة الصنوبرية‬
is a small mass of tissue near the center of the mammalian brain
and involved in biorhythms.
– The pineal gland secretes the hormone, melatonin, an amine.
• Involved in biological rhythms associated with reproduction.
• Secretion regulated by light/dark cycles.
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 Posterior pituitary
(neurohypophysis)
stores and secretes
hormones produced
by the hypothalamus.
Antidiuretic H
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3. Thyroid gland: secrets hormones function in development,
bioenergetics, and homeostasis ‫ثبات البيئة الفسيولوﭽـية الداخلية‬
•
The thyroid gland of mammals consists
of two lobes located on the ventral
surface of the trachea. It contains 4
small Parathyroid glands. It plays role in
maintaining normal blood pressure,
heart rate digestion ..etc.
•
Thyroid
releasing H.
Thyroid glands secretes 3
hormones:
I.
Tri-iodothyronine [(T3), 3 I
atoms]: amino acid derivative.
II. Thyroxine [(T4), 4 I atoms]:
Thyroid
stimulating H.
amino acid derivative.
–
Stimulates and maintain metabolic
processes.
–
Secretion regulated by TSH
hormones.
See Fig. 45.7, Page 965
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Fig. 45.8, Page 965
III.
Calcitonin: a peptide.


a)
Lowers blood Ca2+ levels.
Its secretion regulated by calcium in blood.
Hyperthyroidism: the excessive secretion of thyroid
hormones causes:
•
•
•
•
•
b)
high body temperature
sweating
weight loss
Irritability
high blood pressure.
Hypothyroidism: an insufficient ‫ قليل‬amount of thyroid
hormones because deficiency of I in human diet (causes Goiter).



Infants: cretinism.
Adults: weight gain, lethargy, cold intolerance.
Goiter ‫تضخم الغدة‬: often associated with iodine deficiency ‫نقص‬.
33
Parathyroid gland: Parathyroid hormone (PTH): a peptide
• PTH is secreted by The four parathyroid glands which embedded
in the surface of the thyroid gland. It functions as:
– Raises blood Ca2+ levels.
– Secretion regulated by calcium in the blood.
– Causes osteoclasts ‫ فقد الكالسيوم‬to break down bone, releasing Ca2+ into
the blood.
– Stimulates the kidneys to reabsorb ‫ تعيد إمتصاص‬Ca2+.
– Stimulates kidneys to convert vitamin D to its active form, which
stimulate intestine to absorb Ca2+.
– PTH and calcitonin are antagonistic ‫ متضادين‬hormones. Thus PTH and
calcitonin regulate blood calcium level (important role in homeostasis).
• Hypoparathyoidism (tetany): it is a lack of PTH which causes:
– Ca2+ levels in the blood drop.
– Convulsive contractions of the skeletal muscles.
34
Hormonal control of Ca2+ homeostasis in mammals blood
Read
carefully
the caption
of Figure
45.9, Page
967
35
5. Pancreas: Endocrine tissues of the pancreas secrete insulin and
glucagon, antagonistic hormones that regulate blood glucose
•
The pancreas has both endocrine and exocrine functions.
–
Exocrine function: secretion of bicarbonate ions and digestive
enzymes.
–
Endocrine function: insulin and glucagon secreted by beta and alpha
cells of islets of Langerhans ‫جيوب النجرانز‬.
1. Insulin: a protein secreted by beta cells.
•
Lowers blood glucose levels.
–
–
–
•
–
Stimulates all body cells (except brain cells) to take up glucose.
Slows glycogenolysis ‫( يبطىء تحلل الجليكوجين‬a source of glucose).
Inhibits gluconeogenesis ‫يوقف تكوين الجلوكوز‬.
Secretion regulated by glucose in blood (negative feedback).
Hypoinsulinism: diabetes mellitus ‫نقص اإلنسولين‬.
•
•
•
Hereditary factors ‫ عامل وراثى‬and play a role in its development.
High blood sugar levels – sugar excreted in the urine.
Symptoms: excessive urination ‫ كثرة التبول‬and excessive thirst ‫العطش‬.
36
a)
Type I diabetes mellitus (insulin-dependent diabetes).
•
•
•
b)
Autoimmune disorder.
Usually appears in childhood ‫الطفولة‬.
Treatment: insulin injections.
Type II diabetes mellitus (non-insulin-dependent diabetes).
•
•
•
Usually due to target cells having a decreased responsiveness to
insulin ‫قلة اإلستجابة لإلنسولين‬.
Usually occurs after age 40 – risk increases with age.
Accounts for over 90% of diabetes cases.
2. Glucagon: a protein secreted by alpha cells.
•
Raises blood glucose levels.
–
–
Stimulates glycogenolysis ‫ تحلل الجليكوجين‬in the liver and skeletal
muscle to produce glucose.
Secretion regulated by glucose in blood (negative feedback).
37
Fig. 45.10
38
6. The adrenal gland: adrenal medulla and adrenal cortex help
the body manage stress
•
The adrenal glands are located adjacent to the kidneys.
–
–
The adrenal cortex ‫ القشرة‬is the outer portion.
The adrenal medulla is the inner portion.
I- Adrenal medulla ‫المركز‬.
–
–
a)
b)
Developmentally and functionally related to the nervous system.
It produces the following hormones (in response to stress):
Epinephrine (adrenaline ‫)هرمون القلب‬.
Norepinephrine (noradrenaline).
They are amino acid derivatives (synthesized from tyrosine)
and function as:
•
•
•
Raises blood glucose level and blood fatty acid level.
Increases heart rate and stroke volume and dilates bronchioles.
Shunts blood away from skin, digestive organs, and kidneys,
and increases blood flow to heart, brain, and skeletal muscle.39
II- Adrenal cortex: reacts to stress.
•
Secretion of corticosteroids (a family of steroid hormones) is
regulated by the nervous system in response to stress for example:
a)
Glucocorticoids.
• Raises blood glucose level.
• Secretion regulated by ACTH (Adrenocorticotropic hormone).
• Abnormally high doses are administered as medication to
suppress the inflammation response.
b)
Mineralocorticoids (example: aldosterone, which affects salt and
water balance).
•
•
Promotes re-absorption of Na+ and excretion of K+ in kidneys.
Their secretion regulated by K+ in blood.
– A third group of corticosteriods are Sex hormones.
• Androgens secreted by the adrenal cortex may account for the female
sex drive.
• The adrenal cortex also secretes small amounts of estrogens and
progesterone.
40
41
Fig. 45.14
7. Tests
and ovaries: Gonadal steroids regulate growth,
development, reproductive cycles, and sexual behavior
a)
Testes hormones:
–
Testosterone): steroids.
•
•
•
b)
Supports sperm formation.
Promote development and maintenance of male sex characteristics.
Secretion regulated by FSH and LH.
Ovaries hormones:
1) Estrogens: steroids.
•
•
•
2)
Stimulate uterine lining growth.
Promote development and maintenance of female sex
characteristics.
Secretion regulated by FSH and LH.
Progesterone: steroids.
•
•
Promotes uterine lining growth.
Secretion regulated by FSH and LH.
42
8- Thymus gland:
Secretes Thymosin: a peptide.
It stimulates T lymphocytes.
Protein hormones affect target cells via
receptors on the membrane protein
Steroid hormones inter the target cells
and trigger protein synthesis via
receptors in the nucleus.
43
44
Page 961
45
Table 45.1 (continued)
PLZ OPEN THE VIDEO
www.youtube4VVYPIk=v?hctaw/moc.aTh
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• Many of the body's most basic functions
are regulated by the endocrine system —
eight different glands located
• PLZ OPEN THE VIDEO
www.youtube8KiY=v?hctaw/moc.gHPYe6
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Growth hormone (HG(
.
Q1: Write whether each of the following •
statements is True (T) or False (F):
•
1-The adrenal gland is epinephrine source. •
• 2-Epinephrine and norepinephrine hormones are responsible for the "fight or flight"
response to danger
• 3-Luteinizing hormone (LH) stimulates hormone production by the ovaries and testes
• 4-Posterior pituitary is endocrine organ that does not actually manufacture hormones
but, rather, stores hormones produced elsewhere.
• 5-The hypothalamus produces a releasing hormone that stimulates the pituitary to
secrete GH.
• 6-FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are trophic
hormones that are also known as gonadotropins
.
• The mammary glands of a pregnant female will begin to
produce milk in response to changes in the level of
prolactin
• High levels of T3 and T4 inhibit the secretion of TRH and
TSH.
• Pituitary dwarfism disorder is caused by hyposecretion of
growth hormone.
• When Ca2+ levels fall, PTH stimulates bone cells to
decompose the matrix of bone and stimulates
reabsorption of Ca2+ in the renal tubules.
• Every time you eat a cookie or candy bar, your blood
sugar increases. This triggers an increase in the
hormone insulin
• Insulin and glucagon hormones have antagonistic effects
• At low blood sugar, pancreatic alpha cells stimulated, glucagon
released, breakdown of glycogen in target cells.
•
.The adrenal gland is epinephrine source •
14-Type 1 diabetes mellitus is an autoimmune disease in which the •
immune system attacks beta cells in the pancreas.
• 15-The adrenal medulla is stimulated by nerve signals carried from
the brain.
•
Q2: Choose the correct answer (one answer only):
•
•
1- oxytocin regulated by;
•
a) nervous system
•
b) hypothalamic hormones
•
c) ACTH
•
d)Glucocorticoids
•
•
2-estrogens is;
•
a) steroid hormone
•
b)protein hormone
•
c)glycoprotein
•
d) amine
•
•
•
3- Aldosterone act to:
•
a) rise blood glucose level
•
b) lowers blood glucose level
•
c) Increases heart rate and stroke volume
•
d)promote reabsorption of Na and excretion of K in kidneys
•
4-The hormone which stimulates contraction of uterus and mammary gland cells is called;
a-LH
b-Oxytocin
•
c-FSH
d-Estrogen
•
•
•
5-The hormone which lowers the blood glucose level is;
•
a-Glucagon
b-Glucocorticoid
•
c-Insulin
d-Adrenaline
•
•
6-Melatonin is a hormone produced by the;
•
a-Anterior pituitary
b-Posterior pituitary
•
c-Pineal gland
d-Adrenal gland.
•
•
7-FSH(Follicle Stimulating Hormone)and LH(Luteinizing Hormone)are tropic hormone that are known as---------a-Androgen
b-Prostaglandins
•
c-Gonadotropins
d-Adrenaline.
•
•
8-The anterior lobe of the pituitary produces and secretes ------hormones;
•
a-Seven
b-Six
•
c-Two
d-None of the above.
•
9-Which of the following pairs of hormones do not have antagonistic (opposite) effects:
•
a)- insulin & glucagon
b)- PTH & calcitonin
•
c)- epinephrine & glucagon
d)- all of the above
•
•
10-Which of the following glands shows endocrine and exocrine function:
•
a)- thyroid
b)- pineal
•
c)- pancreas
d)- all of the above
•
•