Download 2-Anterior pituitary hormones

The endocrine system
is one of the body's two major communication system the
nervous system being the other.
The endocrine system consist s of all those glands termed
endocrine glands or gland of internal secretion . The
endocrine glands are glands without excretory ducts that
secrete hormones.
Hormones are chemical messengers that are carried by the
blood from endocrine glands to the cells upon which they
act . the cells influenced by a particular hormone are the
target cells for that hormone.
The endocrine system differs form most of the other organ
systems of the body in that the various glands are not
anatomically continuous however they do form a system in
the functional sense.
Classification of hormones
Hormones fall into three chemical classes :
1-amine hormones
amine hormones are derivatives of the amino
acid tyrosine they include the thyroid
hormones .epinephrine and nor epinephrine
(produced by the adrenal medulla) and
dopamine(produced by the hypothalamus ).
2-peptide hormones
The great majority of hormones are either peptides or
proteins . they range in size from small peptides
having only three amino acids to small proteins (some
of which are glycoproteins.) in many cases the initially
synthesized on the ribosomes of the endocrine cells .
many peptides serve as both neurotransmitters and as
hormones . for example most of the hormone secreted
by the endocrine glands in the gastrointestinal tract
(for example cholecystokinin) are also produced by
neurons in the brain where they function as
neurotransmitters
3- steroid hormones
steroid hormones are produced by the adrenal
cortex and the gonads (tests and ovaries ).as well
as by the placenta during pregnancy .in addition
1.25-dihydroxyvitamin D3.the active from of
vitamin D. is a steroid derivative .cholesterol is the
precursor of all steroid hormones.
Hormone transport in the blood
Peptide and catecholamine hormones are water –
soluble .therefore with the exception of a few
peptides these hormones are transported simply
dissolved in plasma .in contrast the steroid
hormones and the thyroid hormones circulate in
the blood largely bound to plasma proteins .
Effects of peptide hormones and
catecholamines
The receptors for peptide hormones and the catecholamine
hormones are located on the outer surface of the target cells
plasma membrane .when activated by hormones binding the
receptors trigger one or more of the signal transduction
pathways .that is the activated receptors directly influence :
1-ion channels that are part of the receptors .
2-Enzymne activity that is part of the receptors.
3-G proteins coupled in the plasma membrane to effector
proteins –ion channels and enzymes .
The changes in enzyme activity produce changes in the
conformation and hence the activity of various cellular
proteins .in some cases the signal transduction pathways also
lead to stimulation or inhibition of the synthesis of new
proteins by the cell .
The steroid hormones are lipid –soluble messengers .their
receptors are intracellular and are inactive when no
messenger is bound to them for certain lipid –soluble
messengers the inactive receptors are in the cytosol.
The messenger diffuses across the cells plasma membrane
and enters the cytosol .where the receptor is in the cytosol
the messenger combines with it there and hormones
\receptor complex then moves into the nucleus .with intra
nuclear receptors the hormones diffuses by itself into the
nucleus and binds to the receptor there .the receptor
activated by the the binding of hormone to it then
functions in the nucleus as any regulatory protein that
directly influences gene transcription .the result is an
increase in the cellular concentration of the protein or its
rate of secretion .
Inputs that control hormone secretion
Hormone secretion controlled mainly by three types
of inputs to endocrine cells :
1-changes in the plasma concentration of mineral ions or
organic nutrients .there are at least 5 hormones whose
secretion is directly controlled by the plasma
concentrations of specific mineral ions or organic
nutrients .in each case a major function of the
hormone is to regulate in a negative –feedback manner
the plasma concentration of the ion or nutrient
controlling its secretion .for example insulin secretion
is stimulated by an elevated plasma glucose
concentration and the additional insulin then causes
by several actions the plasma glucose concentration to
decrease .
2-neurotransmitters released from neurons
impinging on the endocrine cell .the
autonomic nervous system is the neural
input controlling many hormones (the
adrenal medulla is stimulated by
sympathetic preganglionic fibers the
secretion of insulin and gastrointestinal
hormones are stimulated and inhibited by
both sympathetic and parasympathetic
inputs ) the controlled by neurons in the
brain-
3-another hormone acting on the endocrine cell .In
many cases the secretion of a particular hormone
is directly controlled by the blood concentration of
another hormone .a hormone that stimulates the
secretion of another hormone is often referred to
as a topic hormone .the topic hormones usually
stimulate not only secretion but the growth of the
stimulated gland as well.
4-Chemical and physical factors in the lumen of the
gastrointestinal tract .this applies only to the
hormones secreted by the gastrointestinal tract
Control system involving the
hypothalamus and pituitary
pituitary gland comprising the anterior pituitary and
posterior pituitary is connected to the hypothalamus
by a stalk containing nerve axons and blood vessels
The axons whose cell bodies are in the hypothalamus
terminate in the posterior pituitary and release
oxytocin or vasopressin.
The anterior pituitary secretes growth hormone (GH) ,
thyroid-stimulating hormone (TSH) ,
adrenocorticotropic hormone (ACTH) , prolactin ,and
two gonado- tropic hormones- follicle- stimulating
hormone (LH).
Secretion of the anterior pituitary
hormones is controlled mainly by
hypophysiotropic hormones secreted
into capillaries in the median eminence
of the hypothalamus and reaching the
anterior pituitary via the portal vessels
connecting the hypothalamus and
anterior pituitary.
Each hypophysiotropic hormone is named for the
anterior pituitary hormone whose secretion it controls .
1-Corticotrophin releasing hormone (CRH) stimulates secretion
of ACTH(cortico- tropin) .
2-Growth hormone releasing hormone (GHRH) stimulates
secretion of growth hormone (GH).
3-Thyrotropin releasing hormone (TRH) stimulates secretion of
thyroid –stimulating hormone (thyrotropin) .
4-Gonadotropin releasing hormone (GnRH) stimulate secretion
of both luteinizing hormone and follicle – stimulating
hormone (the gonadotropins) .
5-Somatostatin (SS) inhibits secretion of growth hormone .
6-Prolactin- inhibiting hormone (PIH) inhibits secretion of
prolactin
7-Prolactin releasing hormone (PRH) stimulates secretion of
prolactin
Neural control of Hypophysiotropic
hormones
Neurons of the hypothalamus receive synaptic input,
both stimulatory and inhibitory , from virtually all
areas of the central nervous system , and specific
neural path ways influence secretion of the individual
hypophysiotropic hormones . A large number
ofneurotransmitters ,including the catecholam –ines
and acetylcholine , are found at the synapses on the
hormone – secreting hypothalamic neurons , and this
explain why the secretion of the hypophysiotropic
hormones can be altered by drugs that influence these
neurotransmitters.
For example , awide variety of stresses , both
physical and emotional , act via neural
pathways to the hypothalamus to increase
CRH secretion and , hence , ACTH and
cortisol secretion , markediy above basal
values . Thus , stress is the common
denominator of reflexes leading to
increased cortisol secretion . cortisol then
functions to facilitate an individuals
response to stress.
CRH- ACTH – cortisol sequence . The stress
input to the hypothalamus is via neural
pathways ,cortisol exerts a negative –
feedback control . over the system by
acting on (1) the hypothalamus to inhibit
CRH secretion and (2) the anterior
pituitary to reduce responsiveness to CRH
Hormonal feedback control of the
hypothalamus and anterior pituitary .
A prominent feature of each of the hormonal sequences
initiated by a hypophysiotropic hormone is negative
feedback exerted upon the hypothalamo-pituitary
system by one or more of the hormones in its
sequence . for example , in the CRH – ACTH – cortisol
sequence , the final hormone , cortisol , acts upon the
hypothalamus to reduce secretion of CRH by causing
a decrease in the frequency of action potentials in the
neurons secreting CRH . In addition , cortisol acts
directly on the anterior pituitary to reduce the
response of the ACTH- secreting cells to CRH . Thus ,
by a double barreled action , cortisol exerts a negative
– feedback control over its own secretion. Such a
system is effective in damping hormonal response,
that is , in limiting the extremes of hormone secretory
rates.
Another adaptive function of these negative –
feedback mechanisms is that they maintain the
plasma concentration of the final hormone in a
sequence relatively constant whenever a diseaseinduced primary change occurs in the secretion or
metabolism of that hormone.
Hormones not in a particular sequence can also
influence secretion of the hypothalamic and anterior
pituitary hormones in that sequence. For example,
estrogen markedly enhances the secretion of prolactin
by the anterior pituitary , even though estrogen
secretion is not controlled by prolactin.
1-Hypothalamus
1-Hypothalamus
The hypothalamus lies below the thalamus , it contains
different cell groups and pathways that form the
master command center for neural and endocrine
coordination . the pituitary gland is connected to the
hypothalamus by a stalk containing nerve axons and
blood vessels.
The axons, whose cell bodies are in the hypothalamus
terminate in the posterior pituitary and release
oxytocin or vasopressin. Between the hypothalamus
and anterior pituitary gland there is an unusual blood
flow directly from the hypothalamus to the anterior
pituitary.
Hypothalamus secretes hormones ,
which are collectively termed
hypophysiotropic hormones
(hypothalamic releasing
hormones). The major function of
these hormones is control of
secretion of hormones is control of
secretion of hormones by the
anterior pituitary.
The hypophysiotropic hormones
are :
.1 Corticotropic releasing hormone (CRH) , which
controls the secretion of ACTH (STIMULATION).
2. Thyrotropin releasing hormone (TRH) , Which
controls the secretion of TSH (STIMULATION) .
3. Growth hormone releasing hormone (GHRH) , Which
controls the secretion of GH (inhibition) .
4. Somatostatin (SS) , which controls the secretion of
GH (inhibition) .
5. Gonadotropin releasing hormone (GnRH) ,which
controls secretion of LH and Fsh (stimulation)
6. Dopamine (DA,also called prolactin – inhibiting
hormone , PIH), which controls secretion of prolactin
(inhibition).
II-PITUITARY GLAND (Hypophysis)
II-PITUITARY GLAND (Hypophysis)
The pituitary gland lies in a pocket (the sella turcica) of
the sphenoid bone at the base of the brain , just below
hypothalamus . The pituitary gland is composed of
two adjacent lobes:the anterior pituitary
(adenohypophysis) which has blood vessel connection
with hypothalamus , and the posterior pituitary
(neurohypophysis),which has neural connection with
hypothalamus.
1-Posterior pituitary hormones
The hormones are not synthesized in the posterior
pituitary itself but in the hypothalamus , and by the
axons , which terminate in posterior pituitary release
them . the hormones are :
a-Oxytocin , which controls of milk let –down , and
uterine motility .
b-vasopressin (antidiuretic hormone , ADH), Which
control of water excretion by the kidneys,and blood
pressure.
2-Anterior pituitary hormones
a-Growth hormone (GH, Somatotropin ) is the major
stimulus of postnatal growth : induces precursor cells
to differentiate and secrete insulin –like growth factor
I(IGF-I) , WHICH Stimulates cell division .GH
stimulates protein synthesis.
b-Thyroid-stimulating hormone (TSH.thyrotoropin)
.which stimulates secretion of T3; T4(thyroid gland) .
c-adrenocorticotropic hormone (ACTH. Corticotrophin)
which stimulates secretion of adrenal cortex.
d- Prolaction ,which stimulates breast growth and
milk production . Prolaction many be permissive
for certain reproductive functions in male .
e-Gonadotropic hormones :Folliclestimulating hormone(FSH),and
Luteinzing hormone(LH), which
controls of gonads (gamete
production and sex hormone
secretion)
f-Beta lipotropin ,which has unknown
function.
g-Beta endorphin,which has unknown
function.
III-The pineal gland
III-The pineal gland
The pineal gland is an outgrowth from the
roof of the diencephalons of the brain. It
is a rudimentary organ. Pineal gland
secretes the melatonin (candidate
hormone). The exact functions of
melatonin in hormons are unknown, but
this hormone probably plays an important
role in the setting of the bodys circadian
rhythms.
IV-The thyroid gland
IV-The thyroid gland
The thyroid gland is located in the lower pasrt of the neck
wrapped around the front of the trachea.It composed of
many spherical structures called follicles, each consisting of
a single layer of epithelial cell surrounding an extracellular
central space filled with a glycoprotein colloid called amine
hormones- thyroxine (T4) and triiododothyronine (T3),
parafollicular cells, which are located between follicles, secrete a
third hormone- a peptide called calcitonin, this hormone does
not contain iodine and not included in the term (thyroid
hormone). Iodine is an essential element that functions as a
component of T4 and T3. T4 is secreted in much larger
ammounts than is T3. However, a variety of tissues, particularly
the liver and kidneys, convert most of this T4 into T3. This is an
important point because T3 is a much more active hormone than
T4. Indeed, it is likely that T4 has little or no action unless it is
converted into T3.
Major function of thyroid
hormones:
Virtually every tissue in the body is afficted by the thyroid
hormone. This effect include :
1-Regulation of netabolic rate . The Thare the single most
important determinat of basal metabolic rate. TH
increase the oxygen consumption and heat production of
most body tissues ,anotable exception being the brain .
This ability to increase BMR is termed a calorigenic effect.
2-Control of growth .TH are essential for normal growth
because they are required for both the synthesis of growth
hormone and the growth-promoting effects of the
hormone. Accordingly , infants and children with
hypothyroidism (deficient thyroid function) manifest
retarded growth due to slowed bone growth .
3- Control of brain development and function .TH is
permissive for normal development of the central
nervous system during fetal life .Inadequate
production of maternal and fetal TH due to severe
iodine deficiency during pregnancy is one of the
world's most common preventable causes of mental
retardation termed endemic cretinism.
This effect on brain development must be
distinguished from other stimulatory
effects TH exerts on the nervous system
throughout life not just during infancy .
Ahypothyroid person exhibits
sluggishness and poor mental function
and these effects are completely reversible
at any time with administration of TH
.conversely a person with hyperthyroidism
(excessive secretion of TH) is jittery and
hyperactive.
Major functions of calcitonin:
1-Control of plasma calcium .It has
long been thought that calcitonin
helps to regulate plasma calcium
but present evidence indicates that
it plays a minor role in this regard.
V-Parathyroid glands
V-Parathyroid glands
The Parathyroid glands are located on the posterior
surface of the thyroid gland. There are four
Parathyroid glands .They secrete a hormone called
parathyroid hormone .Parathyroid hormone
production is controlled by the extracellular calcium
concentration acting directly on the secretory cells (
via a plasma –membrane calcium receptor ).
Decreased plasma calcium concentration stimulates
parathyroid hormone secretion and an increased
plasma calcium concentration does just the opposite.
Parathyroid hormone exerts multiple action that
increase extracellular calcium concentration:
1-It directly increases the resorption of bond by
osteoclasts which results in the movement of calcium (
and phosphate ) from bone into extracellular fluid.
2-It directly stimulates the activation of vitamin D and
this latter hormone then increases intestinal
absorption of calcium .Thus the effect of parathyroid
hormone on the intestinal tract is an indirect one.
3- It directly increases renal tubular calcium
reabsorption thus decreasing urinary calcium
excretion .
In addition parathyroid hormone
directly reduces the tubluar
reabsorption of phosphate thus raising
its uninary excretion .This keeps
plasma phosphate from increasing at a
time when parathyroid hormone is
stimultaneously causing increased
release of both calcium and phosphate
from bone .
VI-THE ADRENAL (SUPRARENAL
) GLANDS
VI-THE ADRENAL (SUPRARENAL )
GLANDS
There are two adrenal glands one on the top of of each kidney
.Each adrenal gland constitutes two distinct endocrine
glands an inner adrenal medulla which secretes amine
hormones and a surrounding adrenal cortex which
secretes steroid hormones .
A drenal medulla is really a modified sumpathetic ganglion
whose cell bodies do not have axons but instead release
their secretions into the blood thereby fulfilling a criterion
for an endocrine gland . The adrenal medulla secretes
mainly two amine hormones epinephrine (E) and
norepinephrine (NE) .In humans the adrenal medulla
secretes approximately four times more epinephrine than
norepinephrine .
epinephrine and norepinephrine exert actions similar to
those the sympathetic nerves .These effects are :
1-Increased hepatic and muscle glycogenolysis ( provides a
quick source of glucose).
2-Increased breakdown of adipose tissue triacylglycerol
(provides a supply of glycerol for gluconeogenesis and of
fatty acids for oxidation).
3-Decreased fatigue of skeletal muscle.
4-Increased cardiac output secondary to increased cardiac
contractility and heart rate.
5-Shunting of blood from viscera to skeletal muscles by
means of vasoconstriction in the former beds and
vasodilation in the latter.
6-Increased ventilation .
7-Increased coagulability of blood.
The adrenal medulla also secretes small amounts of
dopamine and several substances.
Hormones of the adrenal
cortex
The five hormones normally secreted in physiologically
significant amounts by the adrenal cortex are :
1-ALDOSTERONE (secreted by zona glomerulosa ) is
known as a mineralocoticoid because its effects are on
salt (mineral ) balance mainly on the kidneys handlind
of sodium potassium and hydrogen ions.
2-CRTISOL and CORTYCOSTERONE (secreted by zona
fasiculata and zona reticulais) are called
glucocorticoids because they have important effects on
the metabolism of glucose and other organic nutrients
.Cortisol is by far the more important of two
glucocorticoids in human
The main functions of the cortisol are :
1-Effect on organic metabolism :increased plasma
concentrations of amin acids glucose and free fattu acids.
2-Antigrowth effects : inhibits bond growth stimulates protein
catabolism responsible for the retarded growth that occuas
with illness .
3-Effects during stress:
a-Effect on organic metabolism :stimulation of protein
catabolism stimulation of liver uptake of amino acids and
their conversion to glucose (gluconeogenesis) inhibition of
glucose uptake and oxidation by many body cells (insulin
antagonism ) but not by the brain and stimulation of
triacylglycerol catabolism in adipose tissue with release of
glycerol and fatty acids into the blood .
b-Enhanced vascular reactivity that is increased ability to
maintain vasoconstriction in response to norepinephrine and
other stimuli .
c-Unidentified protective effects against the damaging
influences of stress .
d-Inhibitione of inflammation and specific
immune response.
4-Regulation of the immune system .
3- ANDROGENS ( secreted by zona fasiculata and zona
reticularis) consist of dehydroepiandrosterone and
androstenedione. Androgens also includes the male
sex hormone testosterone produced bu the testes . All
androgens have actions similar to those of testosterone
.
Because the adrenal androgens are much less potent
than testosterone they are of little physiological
significance in the male they do however play roles in
the female .
Effect of testosterone (androgens ) in the
male :
1-Required for initation and maintenance of spermatogenesis.
2-Decreases GNRH secretion via an action on the
hypothalamus.
3-Inhibits LH secretion via an action on the anterior pituitary.
4-Induces differentiation of male accessory reproductive organs
and maintains
their function .
5- Induces male secondary sex characteristic opposes action of
estrogen on breast growth .
6-Stimulates protein anabolism bone growth and cessation of
bone growth.
7-Required for sex drive and may enhance aggressive behavior.
Androgens in women:
Testosterone is found in low concentration in blood of
normal women. Other androgens are also found in
significant concentrations in the blood of women. All
these androgens play several important roles in the
female, including stimulation of the growth of pubic
hair , axillary hair , and possibly skeletal muscle. In
several diseases states, the female adrenals may secrete
abnormally large quantities of androgens , which
produce virilism.
VII-Thymus:
VII-Thymus:
This gland is situated in the anterior
mediastinum of the thorax. It is
relatively large at birth and continues
to increase in size until puberty, when
it gradually diminishes. Thymus is
primary lymphoid organ.
It secretes Thymopoietin hormone,
which control T-lymphocyte function.
VIII- The pancreas:
VIII- The pancreas:
The pancreas is an elongated gland located behind the
stomach , has both endocrine and exocrine functions.
Hormones are secreted by the islets of Langerhans ,
clusters of endocrine cells in the pancreas . There are
several distinct types of islet cells, each of which
secretesa different hormone. These hormones are:
1 – Insulin, which secreted by beta cells , Insulin's many
actions are often divided into two broad categories :
(A) – metabolic effects on carbohydrate, lipid, and
protein synthesis, and (B) – growth-promoting effects
on DNA synthesis, cell division , and cell
differentiation. The major controlling factor for insulin
secretion is the plasma glucose concentration , which
affects the beta cells directly.
2- Glucagon, is the peptide hormone
produced by the alpha cells of the
pancreatic islets . The major physiological
effects of glucagons are all in the liver and
are opposed to those of insulin : (a)
increased glycogen breakdown , (b)
increased gluconeogenesis , and ( c)
synthesis of ketones.
3- Somatostatin , secreted by delta cells has
unknown function.
4- Pancreatic polypeptide has unknown
function.
IX- Ovaries:
IX- Ovaries:
The ovaries are almond-sized organs in the upper pelvic
cavity , one on each side of the uterus .The ovary serves
a dual purpose: (1) oogenenesis , the production of the
gametes-the ova, and (2) secretion of the female
steroid hormones. The hormones secreted by ovaries
are:
1 – Estrogen is secreted during the follicular phase
mainly by the granulose cells ,
Following ovulation , it is secreted by the corpus luteum
. Effects of estrogen are:
a – Stimulates growth of ovary and follicles.
b- Stimulates growth of smooth muscle and proliferation of epithelial
linings of reproductive tact . In addition:
-Uterine tubes: increases contractions and ciliary activity.
-Uterus: increases myometrial contractions and responsiveness to
oxytocin.
-Vagina: increases layering of epithelial cells.
-Stimulates external genitalia growth .
- Stimulates breast growth , particularly ducts and fat deposition.
- Stimulates female body configuration development; narrow shoulders ,
broad hips , female fat distribution ( deposition on hips , abdomen,
and breast).
-Stimulates a more-fluid sebaceous gland secretion( this antiance effect
opposes the acne-producing effects of androgens)
-Stimulates development of femalepubic hair pattern ( growth , as
opposed to pattern, of pubic and axillary hair is androgen
-Stimulates bone growth and ultimate cessation of bone
growth ( closure of ebibhyseal osplates );protects
against osteoporosis; does not have an anabolic effects
on skeletal muscle .
-Vascular effects( deficiency products '' hot flashes'').
-Has feedback effects on hypothalamus and anterior
pituitary.
-Stimulates fluid retention.
-Stimulates prolactin secretion but inhibits prolactin's
milk-inducting action on the breast.
-Protects against atherosclerosis, at least in part by effect
on plasma cholesterol.
2- Progesterone is secreted in very small amounts by the
granulose and theca cells before ovulation, but its
major source is the corpus luteum . Effecte of
progesterone are:
a – Converts the estrogen-primed endometeium to an
actively secreting tissue suitable for implantation of an
embryo.
b- Induces thick, sticky cervical mucus.
c-Decreases contraction of uterine tubes and
myometrium.
d-Decreases proliferation of vaginal epithelial cells.
e- Stimulates breast growth , particularly glandular
tissue.
f-Inhibits milk-inducting effects on prolactin.
g-Has feedback effects on hypothalamus and anterior
pituritary.
h- Probably increases body temperature.
3- Inhibin, a peptide hormone , is
secreted by both the granuloses cells
and corpus luteum.
4- Relaxin and Activin , which have not
clear function.
X- Placenta:
X- Placenta:
Is a combination of interlocking fetal and
maternal tissues that serves as the organ of
exghange between mother and fetus for the
remainder of pregnancy.
Throughout pregnancy, plasma concentration
of estrogen and progesterone remain high
The placenta converts the androgens mainly
into estriol, the major estrogen of pregnancy
The trophoblast cells of the placenta produce
inhibin , and placental loctogen.
Gastrointestinal tract:
The hormones that control the gastrointestinal system
are secreted mainly by endocrine cells scattered
throughout the epithelium of the stomach and small
intestine .One surface of each endocrine cell is
exposed to the lumen of the GIT.
At this surface , various chemical substances in the
chime stimulates the cell to release its hormones from
the opposite, blood side of the cell .The
gastrointestinal hormones are: secretin
,cholecystokinin (CCK), gastrin, and glucosedependent insulinotropic peptide (GIP).
The major effects of each are:
1 – Secretin is released from the small intestine in
response to increased luminal acidity.
2- Chlecystokinin is released from the small intestine in
response to the products of fat and protein digestion,
and stimulates pancreatic enzyme secretion.
3- Gastrin is released from the antrum of stomach in
response to increased amount of amino acids and
peptides in stomach, and to parasympathetic nerves.
4- Glucose-dependent insulinotropic peptide is released
from small intestine in response to glucose and fat in
small intestine . GIP stimulates insulin secretion.
XII-Testes:
XII-Testes:
The testes are the primary reproductive organs in the
male.
The testes serve dual functions :
( 1) gametogenesis, and (2) secretion of steroid
hormones (sex male hormones). The Leydig cells (
interstitial cells), which lie in small connective tissue
spaces between the tubules , are the cells that secrete
testosterone .
The following hormones are released from test:
1 – Testosterone belongs to a group of steroid hormones
that have similar masculinizing actions and are
collectively called androgens. In the male, only the
testes secrete significant amounts of testosterone.
2- Inhibin is a protein hormone, released from sertoli
cells.
3- Mullerian –inhibiting hormone is released from
sertoli cells during embryonic life. It causes the
primordial female duct system to regress