“HYPOTHALAMUS AND HORMONES OF ANTERIOR
At the end of lecture students should be able to know,
Anatomy,embryology and histology of pituitary gland.
Lobes of pituitary.
Secretions of ant pituitary gland.
“ANATOMY OF PITUITARY GLAND(HYPOPHYSIS)”
#The pituitary gland also known as the
#Is located directly below the
hypothalamus and rests in the sella
turcica,a derpression in the shenoid
from and prevent cerebrospinal fluid
from entering the sella turnica.
#This important gland is protected on three sides by
bone,and on top by a tough membrane.
#It is about 1.0 cm long,1.0 to 1.5cm wide,and 0.5cm
thick,about the size and shape of a plump lima bean.
#Because of the closeness of the pituitary to the optic
chiasma,an enlarge pituitary generally affects visison by the
impinging upon the optic pathways,optic chiasma is 5 to
10mm abaove this diaphragm.
“EMRYOLOGY OF PITUITARY GLAND”
THE ANTERIOR LOBE,
#Epithelial in structure.
#Derived from rathkeys pouch,an upgrowth
THE POSTERIOR LOBE,
#Is derived from the floor of the third ventricle
and remains attached to the hypothalamic
the brain by a stalk or infundibulum,in which a
very narrow channel of communication with
ventricle remain open.
“HISTOLOGY OF PITUITARY GLAND”
#consists of columns or masses of epitheloid cells.
#they secrete “somatotropes(growth hormone)
and mamotropes(PRL) hormone”.
#beta cells, #they produce
#inactive cell,they don’t secrete any hormone .
#they are called chief or reserve cells,#non
“LOBES AND PARTS OF ANTERIOR PITUITARY GLAND”
#adenohypophysis is the lardest lobe accounting for about
75% of the total weight of the gland.
#has 2 parts,
#Posterior lobe has 4 parts.
2,pars nervosa.(non medullary nerve
fibres,varying amount of nerve cells and neroglia)
“DIFFERENCE BETWEEN TWO LOBES”
A significant difference between the two lobes,
The abundance of functional secretory cells in the
o and the presence of only suporting pituicytes in the
o neurohypophysis.the neurohypophysis as its name
o has a greater supply of large nerve endings.Secretry
o and secrete hormones directly from the
o the neurohypophysis obtains its hormones from
o in the hypothalamus.These modified nerve cells project
o axons down a stalk of nerve cells and blood vessels
o the infundibular stalk or infundibulum,into the pituitary
o In this way a direct link exists between the nervous
o the endocrine system.
“RELATIONSHIP BETWEEN THE PITUITRAY AND
#The pituitary gland called the master gland because of its
control over most of the other endocrine glands in the body
organs.In truth,the hypothalamus might better deserve the
title “master gland” since substance released from the
hypothalamus control the secretions of the adenophysis and
hormones secreted from the neurohypophysis are
synthesized and regulated by nerve crnters in the
#The hypothalamus secretes at least nine releasing or
these substances are either releasing factors or inhibiting
factors,while others are actually hormones.the hypothalamus
and the adenohypophysis are connected by an axtensive
system of blood vessels called the HYPOTHALAMIC
HYPOPHYSEAL PORTAL SYSTEM.Hormones produced in
the hypothalamus are transported through the portal vessels
to the adenohypophysis where they either stimultae or inhibit
the release of the appropriate pituitary hormones.
#The link between the hypothalamus and the
neurohypophysis relies one nerve impulses,hence the name
neurohpophysis for the posterior pituitary.the
neurohypophysis is composed of unmylinated axons of
nerves whose cell bodies are in the hypothalamus and
pituicytes,which have a supporting rather than a secretory
#The hypothalamus and pituitry gland have intimate
anatomical and functional relationship in turn these
structures regulate the function of number of endocrine
glands including the thyroid,adrenal,and gonades and play
an imp role in regulation of growth,metabolism,lactation and
Hypothalamic anterior pituitary system
#The hormones in this system are all water soluble.
#The hypothalamic hormones are synthesized in the neuron
cell body.packaged in vesicle,and transported down the
axon to be stored and released from the nerve terminals.
#In the hypothalamic ant piy system,hormonal release is
mainly pulsatie.A possible exception is the thyroid system.
#The hypothalamic hormones thyrotropin realeasing
hormones(CRH),growth hormone releasing
hormone(GHRH),somatostatin,and prolaction inhibiting
factor(PIF) are synthesized in neyuronal cell bodies in the
arcuate and the para ventriclar nuclei.gonadotropin releasing
hormone is synthesized in the preoptic nucleus.
#The nerve endings all come together in the median
eminanace region of the hypothalamus.The hormones are
then secreted into the hypophysal portal system and
transported to the nat pituitary.
#Hypothalamic hormones bind to receptor on cells of the ant
pituitary and modify the secretion of thyroid stimulating
hormone(LH),follicle stimulating hormone(FSH)growth
hormone and prolactin.
Pituitary gland secretion.
Anterior pituitary gland secretion.
2.Thyroid stimulating hormone,
6.Follicle stimulating hormone.
Posterior pituitary gland secretion
Relationship between the pituitary and hypothalamus.
#Is the most imp hormone for normal growth of adult size,
#Is a single chain polypeptide that is homologous with
prolactin and human placental lactogen.
#REGULATION OF GROWTH HORMONE SECRETION.
Growth hormone is released in pulsati;le fashion.
Secretion is increased by sleep,stress,hormones related to
puberty,starvation,exercise and hypoglycemia.
Secretion is decreased by
#HYPOTALAMIC CONTROL_GHRH AND
GHRH stimulates the synthesis and secretion of growth
hormone.SOMATOSTATIN inhibits secretion of growth
hormone by blocking the response of the ant pituitary to
#NEGATIVE FEEDBACK CONTROL BY SOMATOMEDINS.
Somatomedins are produced when growth hormone acts on
Somatomedians inhibit the secretion of growth hormone by
acting directly on the ant pit and by stimulating the secretion
of somatostatin from the hypothalamus.
#NEGATIVE FEEDBACK CONTROL BY GHRH AND
GHRH inhibits its own secretion from the
hypothalamus.Growth hormone also inhibits its own
secretion by stimulating the secretio of somatostatin from the
Growth hormone actions
“GROWTH HORMONE ACTIONS”
#In the liver ,growth hormone genertaes the production of
somatomedins(insulin like growth factor) which serve as the
intermediaries of several physiological actions.
#IGF receptor has tyrosine kinase activity similar to the
#DIRECT ACTION OF GROWTH HORMONE.
Dec glucose uptake into the cells(diabetogenic)
Inc protein synthesis in muscle ant inc lean body mass,
Inc production of IGF.
#ACTIONS OF GROWTH HORMONE VIA IGF.
Inc protein synthesis in chondrocytes and inc linear
growth(pubertal growth spurt)
Inc protein synthesis in muscle and lean body mass
Inc protein synthesis in most organ and inc organ size
PHASES OF GROWTH(AFTER BIRTH)
1#,rapid growth in 1st year(net wt gain from 8 to 20lbs aprox)
2#,slow but progressive growth(from 3 to 12 yrs)
3#,slow phase may be terminal(after30years)
MAIN TYPES OF GROWTH
o #Neural.immediate growth of brain,spinal
their optimum size.
o #Lymphoid.tonils thymus,adenoid reach thir peak on
“PATHOPHYSIOLOGY OF GROWTH HORMONE”
#GROWTH HORMONE DEFICIENCY
In children causes failur to grow,short stature,mild obesity
and delayed puberty.
Can be caused by,
a)lack of ant pituitary growth hormone,
b)hypothalamic dysfunction(dec GHRH)
c)failure to generate IGF in the livert,
d)growth hormone receptor deficiency.
#GROWTH HORMONE EXCESS,
Can be realated with somatostatin analogs(eg
octreotide),which inhibit growth hormone secretion.
Hypersecretion of growth hormone cause acromegaly.
a)before puberty excess growth hormone causes inc linear
b)after pubery excess growth hormone causes inc peiosteal
bone growth inc organ size and glucose intolerance.
#Belongs to the same glycoprotein family
#each has an alpha subunit and a beta subunit.
#the alpha subunit are identical.
#the beta subunits are different and are responsible for the
unique biological activity of each hormone.
“TSH(THYROID STIMULATING HORMONE)
#Is also known as thyrotropin.
#it stumulate the synthesis and secretion of thyroid
hormones in several ways.the main effect of TSH is to
stimulate the secretion of thyroxine,the main thyroid
#An excessiove amount of TSH inc the blood flow into the
thyroid gland.As a result the cells grow excessively
producing an enlagred thyroid gland called goiter.
#The secretion of TSH is controlled by hypothalamus.
#the secretion of TRH depends on the amount of thyroxine
circulating in the blood.
#Low blood levels stimulate an inc in TRH.When a normal
level of thyroxine is reached,the production of TRH slows to
a rate that merely maintains a stable condition.
#It has been found that cold temperature also stimulate the
production of TRH and the susequent secretion of TSH.
#Receives its name from the corpus luteum,
#a temporary endocrine tissue in the ovaries that secretes
the female sex hormones progesterone and estrogen.
#LH a gonadotropin hormonestimulates ovulation,the
monthly release of a mature egg from an ovary.
#In the male the same hormone used to b called interstial
cell stimulation hormone(ICSH)but now is called luteinizing
hormone in both sexes.
#Its target cells are interstial cells(between spaces)cells in
the testes that secrete the male hormone testosterone.
#the mechanism for the control of LH depends on a specific
gonadotropin releasing hormone(GnRH) from the
hypothalamus,which is regulated by a typical negative
system involving levels of progesterone,estrogen and
“FOLLICLE STIMULATING HORMONE”.
#FSH or follitropin is also gonadotropin hormone of the
#In females,FSH stimulatesthe growth of follicle cells in the
ovaries that eventually developeinto mature egg
cells(oogenesis) during each menstrual cycle.
#it also stiulate the follicle cells to secrete estrogen.In the
male FSH stimulate the cells testesthat produce
#the regulatory mechanism for FSH is similar to the negative
feedback systems of other hormone of the
#the specific regulating factor from the hypothalamus is
called follicle stimulatimg hormone releasing
factor(FSHRF),which is released according to the blood
levels of male and female sex hormones
Follicle stimulating hormone
“ACTH,MSH,B_LIPOTROPIN AND B_ENDORPHIN.”
#Are derived from a single precursor PRO
#Alpha MSH and beta MSH are produced in the
intermediatry lobe which is rudimentry in human adults.
#Is also called corticotropin or adrenocorticotropin.
3It stimulates the adrenal cortex to produce and secrete
steroid hormones called glucocorticoids.
#Secretions of ACTH are regulated by the liberation of
corticotropin releasing hormones(CRHS)from the
hypothalamus.which are in turn regulated by a feedback
system influenced by such factors as stress,insulin,and ADH
and other hormones
“MELANOCYTE STIMULATING HORMONE”
#The exact hormonal function of melanocyte stimulating
hormone is uncertain.in fact MSH may be calssified more
correctly as a precurser to an active hormone.
#The fetus produces MSH in the intermediate lobe(pars
intermedia) of the pituitary gland,located between the ant
and pos lobes.the intermediate lobe degenerate shortly
before birth and remains in the fully developed body only as
a non functional remnanat.MSH is also present in small
amounts in the ant lobe.
#The presence of MSH indirectly inc the activity of
melanocytes(pigmentd cells that affect skin,eye,and hair
#One form of MSH called alpha MSH is produced by the
stimulation of ACTH ,when ACTH is released from the ant
pit.alpha melanocytes is also released.Normally the amount
of MSH released is not enough to stimulate melanocytes.
#When ACTH is also produced ,however the combination of
alpha msh and ACTH causes a change in pigmentation.The
reason why alpha melanocytes is not effective by itself is
that it is secreted in small amounts,while the quantity of
ACTH is large.Thus it is likely that ACTH is considerably
more imp than alpha MSH in determining the amount of
melanin in the skin,and in turn skin colour.
#MSH is ecreted by basophilic cells,
#Its secretion is stimulated by a hypothalamic regulating
factor called melanocyte stimulating hormone releasing
facctor(MRF),and inhibited by melanocyte stimulating
hormone inhibiting factor(MIF).
#A def of MSH causes pale skin,and an axcess causes the
skin to darken.
Melanocyte stimulating hormone
#Single chain polypeptide
#Is the major hormone responsible for lactogenesis,
#Participate with estrogen in breast developmnt.
#Is structurally homologous to growth hormone.
REGULATION OF PROLACTIN SECRETION.
#Hypothalamic control by dopaomine and thyrotropin
#Prolactin secretion is tonically inhibited by
dopamine(prolactin inhibiting factor) secreted by
hypothalamus.thus interruption of the hypothalamus piy tract
causes inc secretion of prolactin and sustained lactation.
#TRH inc prolactin secretion.
NEGATIVE FEED BACK CONTROL.
#Prolactin inhibits its own secretion by stimulating the
hypothalamic realease of dopamine.
“ACTIONS OF PROLACTIN”
#.stimulate milk production in the breast(casein,lactalbumin).
#.stimulate breast development(in a supportive role with
#.inhibits ovulation by dec synthesis and release of
gonadotropin releasing hormone(GnRH)
#.inhibits spermatogenesis(by dec GnRH)
“PATHOPHYSIOLOGY OF PROLACTIN”
#prolactin deficiency(destruction of the ant pit results in the
failure to lactate.
#prolactin excess.results from hypothalamic destruction (due
to loss of the tonic inhibitory control by dopamine) or from
prolactin sec tumours(prolactinoma)
#Causes failure to ovulate and amenorrhea because it
#Can be treated with bromocriptine,which reduces prolactin
secretion by acting as dopamine agonist.