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HYPOPHYSIS (PITUITARY GLAND)
DEFINITION:-
The pituitary gland is reddish-grey,small ovalshaped structure, situated at the base of brain in the
sella turcica of sphinoid bone.
WORD MEANING :The pituitary(L.pituita=phlegm ) which collected
wastes from the brain and these lubricated the nasal
and pharyngeal passages.
When the true function of the gland was established
the term hypophysis( hypo+Gr. Phyein=to grow) was
substituted
ANATOMY
It situated in the sella turcica of the sphenoid bone.
It is attached to the floor of third ventricle by the
stalk. average Weight in adults- 0.5 to 0.6 g. the
weight varries with age ,sex and physiologic state.It
is somewhat larger in females, weighing from 0.6 to
0.7g. It increases in size through the fourth decade
of life,and during pregnancy.Anatomically it consist
of two parts but microscopically it consist of 6 parts
DIVISION:-
(1) Adenohypophysis(ant. pituitary)
(a) pars distalis or anterior
(b) pars tuberalis
(c) pars intermedia
(2) Neurohypophysis (post. pituitary)
(a) pars nervosa
(b) median eminence
(c) infundibulum(neural stalk)
DEVELOPMENT
Pituitary gland is originate from the ectoderm.it develops
from two out growths.A glandular diverticuluam-rathkes
pouch-grows upwards from the primitive buccal cavity and
meets with a similar neural out growth from the floor of
third ventricle.The stalk of rathke’s pouch disapperas but
that nural out growth persists and forms infundibulum.
Ant. Wall of rathke’s pouch develops the pars distails from
the top arises the pars tuberalis, from the post.wall develops
the pars intermedia.The pars intermedia invest the pars
nervosa to some extent. The original cavity of rathke’s
pouch forms the interglandular cleft .
BLOOD SUPPLY
The pituitary gland gets blood supply from the hypophysial
arteries which originating from the internal carotid artery
and circle of willis.the superior hypophyseal arteries supply
the anterior lobe and the infirior hypophyseal arteries supply
the posterior lobe .
NERVE SUPPLY
Ant. Lobe-there is definite evidence of a nervous control of
ant. Lobe but only a few fibres either from the hypothalamohypophyseal tract of nerve fibers or from carotid plexus of
cervical sympathatic have been traced to it. They are
probably vasomotor nerves.
Post. Lobe – two tracts of non-medullated nerve fibers arises
from the hypothalamus and supply the pars nervosa.
ADENOHYPOPHYSIS
Histology- it includes pars destalis 75% , pars tuberalis , and
intermedia 25%.
The present idea is that the different pituitary harmones are
liberated by seprate cell types.so possibly six kinds of cells
secrete six seprate harmones.studies employing histochemical,
electronmicroscopic techniques have made such classifications
possible
CHROMOPHOBES (chief cells-50%)
These cells are not stained with either basic dyes or acid dyes
and lack typical secretory granules.chromophobe cells in general
have got less cytoplasm than chromophils. the earlier hypothesis
is that the chromophobes are non-functional and have recently
been doubted.
CHROMOPHIL
Cells are so named as they have got affinity toward dyes . Early
staining methods show only twotypes of chromophils :
Acidophil (eosinphil or oxyphil, 35%) – recent studies claim
that acidophil cell secretes both growth hormone.
(a) Somatotropic cells:- these cells are oval and the
cytoplasm is packed with dense,round granules- 350400nm in size, stained with orange G of an azan stain.
tumors of an acidophil cells are associated with acromegaly
& gigantism.
(b) Lactotropic cells:- these types of cells stained with
erythropsin or acid fuschin. No. of these cells varies in
relation to the reproductive cycle– increasing significantly
during pregnency &lactation.these cells are belived to
secrete prolactin.
Basophils(mucoid cell-15%):There are different kind of cell secreting different types of
trophic hormones like –
(a) Thyrotropic cells:- secrete TSH.
(b) Gonadotropic cells:- secrete GTH which are 2 types1. FSH.
2. LH or ICSH.
(c) Somatotropic cells:- secrete GH.
(d) Corticotropic cells:- secrete ACTH and LH.
FUNCTIONS OF PARS DISTALIS OF
PITUITARY
Anterior pituitary is the master gland of the endocrine system
because it produces protien tropic hormone which affect
the other ductless gland .
Following hormones are believed to be secreted :a. Growth hormone or somatotropic hormone(GH or STH).
b. Adrenocorticotropic hormone(ACTH).
c. Thyrotropic hormone(TSH).
d. Gonadotropic hormone:1. FSH
2. LH or ICSH
3. MH or LTH.
1.GROWTH HORMONE or SOMATOTROPIC
HORMONE(GHorSTH)
:-Secreted by acidophil cells.
CHEMISTRY:-mol. Weight is about 21000-48000. it is not effective by oral administration as it is inactivated by pepsin &trypsin.
ACTION OF GROWTH HORMONE:Skeletal Growth:-stimulates the multiplication of the epiphyseal
cortilage and thus increases the length of cartilage bone.in
hypophysectomised animals a membrane appears at the
epiphyseal line which inhibit the growth of the cortilage cells.
Regulates general body growth:- It increases the body growth due
to the direct effect in the tissue.
1. Muscles – stimulates the growth of muscles. In
gigantism & acromegaly there is an increased growth of muscles.
2.Visceras- in hypophysectomised animal the liver cells
and reduced in size with impared functions.
3. It stimulates the growth of thymus.
4. Increases secretion of milk during lactation.
5. Nervous system is not affected by STH.
Metabolism – a. on protein metabolism:- it increases the neuclic
acid and protien synthesis, decreases nitrogen excrition in the
urine and the nitrogen thus retained helps in the synthesis of
tissue protein. STH is a protein anabolic hormone and prevents
the catabolism of amino acids.
b. on fat metabolism:- it increases the oxidation of
fat and decreases the catabolism of amino acid causing
utilisation of amino acid in the protein synthesis.
c. on carbohydrates metabolism:- it stimulates
carbohydrates storage. Administration of GH produces hyper glycemia and glycosurea, GH is diabetogenic especially in man
Administration of ACTH produces similar effect as induced by
GH.
STH and ACTH exert antagonistic action to those of insulin.
d. Ion or mineral metabolism:- it increases intestinal
absorption of calcium as well as its excretion. In addition to Ca,
Na, K,Mg,phosphate and chloride are retained.
e. the growth hormone also has lactogenic effects.
REGULATION OF GH SECRETION:1.Hypothalamus:- secretion of growth hormone by pituitary
acidophil cells are regulated by the hypothalamic hormone,the
GHRF.
2.Other factors :- Certain factors may affect the GH secretion,
these are –stimuli which increase GH secretion areHypoglycemia,Fasting
Exercise
Sleep:-Deep sleep stimulate growth. The
young allowed to sleep always stimulate growth.
STRESS :Different stressful stimuli affect the secretion of GH. Surgical
stress emotional stress etc. darkness inhibits
growth,crowding stimulates growthes slowly,noise
sometimes inhibits growth.
HARMONS :(a) Thyroid hormone stimulates growth through the secretion
of GH.
(b) Androgen stimulate growth ,but on prolongad treatment
stops growth by closing the epiphysis.
(c) ACTH infusion can stimulate HGH release during
starvation
FEEDBACK CONTROL:Growth hormone secretion also controlled by the feedback
inhibition process which is controlled by the GHIH
releasing of the hypothalamus.
INHIBITORY FACTORS OF GROWTH
(a) Hormonal factors. Oestrogen and other ovarion
hormones have got influence on growth as because
females are shorter than the males. It is suggested that
ovarion hormones retard growth through inhibition of
GH secretion.
(b) Adrenal corticoids . Corticoids interfere with the growth
process. Administration of corticoids causes dwarfism.
The corticoids inhibit the stimulating effect of GH on
epiphysis .
(2) THYROID STIMULATING
HORMONES (TSH)
CHEMISTRY :- it is a glycoprotein with molecular weight of
about 25000. It is not effective by oral administration as it
is inactivated by proteolytic enzymes.
CONTROL OF TSH SECRETION:- thyrotrophin secretion is
under the control of (1) hypothalamus
(2) thyroxin level in the blood.
(1) Hypothalamus:- stimulation of hypothalamus by fine
electrodes causes release of a tripeptide humoral factor
known as thyrotrophin releasing factor (TRF) which
circulates through the blood stream (hypophyseal portal
system) and helps in the liberation of thyrotrophin from
the anterior pituitary .
(2) Thyroxin level in the blood:- the rate of secretion of
thyrotrophin is controlled by the thyroxin content of the blood .
High thyroxin content in the blood inhibits a low thyroxin
content in the blood stimulates secretions . If the low thyroxin
content persists for a prolonged period there will be continuous
secretion of a large amount of thyrotrophin which causes thyroid
hyperplasia.
FUNCTIONS OF TSH:The main role of TSH is to regulate the synthesis and
production of thyroid hormone from the thyroid gland.
These peripheral hormones play a basic job in our
metabolism. In fact, they are important in catabolism, the
mechanism by which our body burns calories and
produces heat.
Thyroid hormones are also very important in regulating
other physiological actions:
o
brain development during fetal period,
o
heart function,
o
emotional reactions such as anxiety, nervousness or
happiness
Finally, they can interfere in the reproductive system by
altering menstrual regularity and libido, or in the skeletal
system by regulating bone mass.
(3) ADRENOCORTICOTROPHIC
HORMONE (ACTH)
Secreted by basophil cells.
CHEMISTRY :- polypeptide in nature consisting of 39 amino
acides residues. Molecular weight about 4500. It has been
isolated in a α and β forms. Both these forms contain a large
number of aminoacid and have got straight chain linkage.
Unlike other pituitary hormones.
ACTION:The hypophysis can regulate some aspects of the stress.
Generally, stress can be defined as an emotional and
physiological response to a disagreeable situation.
The pituitary is important in some severe and acute stress situations,
during which it produces a hormone called ACTH. ACTH
stimulates the adrenal cortex, where it regulates the synthesis and
production of cortisol. During severe trauma, burns, illness, fever,
hypotension, physical exercises, surgery
and hypoglycemia, cortisol production increases. Cortisol supports
the body's adaptation to the stress condition, by increasing glucose
use, the heart activity or electrolyte exchanges. Finally, ACTH also
exerts a less important function in the adrenal cortex: steroid
production. In 1975 scientists identified another peptide: endorphin,
which acts in experimental animals as a natural pain reliever in
times of stress.
Endorphin and ACTH are made as parts of a single large protein,
which subsequently splits. This may be the body's mechanism for
coordinating the physiological activities of two stress-induced
hormones. The same large pro-hormone that contains ACTH and
endorphin also contains short peptides called melanocytestimulating hormones. These substances are analogous to the
hormone that regulates pigmentation in fish and amphibians, but
in humans they have no known function.
CONTROL OF ACTH SECRETION:ACTH secretion is under the of (1) hypothalamus
(2) steroid feedback mechanism.
(3) short feedback mechanism.
(4) stress control mechanism.
4.GONADOTROPHIC HORMONES(GTH)
The basophil cells secrete gonadotrophins which control the growth
and activity of the gonad and indirectly all other process
connected with it.the anterior pituitry controls the gonads is
proved by the following facts.
1. Hypophysectomy, in young, retards growth and activity of the
gonads.
2. Hypopituitarism in children (dwarfism) retards sexual
devlopment and in adults leads the sexual degeneration
(impotency,amenorrhoea etc.).
There are two gonadotrophins (1) FSH
(2) LH or LTH or ICSH.
(3) LTH(prolactin)
CHEMISTRY:The GTH are glycoprotein in nature and the molecular weight of
about 30000.
-:FUNCTIONS OF GTH:Function of FSH:1. In females:-a. increases the no. & size of Graffian follicals and
prepares them for ovulation. After the menopause production rate
of FSHis increased approximately 15-fold.
2. In males:- stimulates spermatoogenesis. In old age in the male
(as testicular function wanes) the production of FSH increases.
Function of LH:1. In females:The adenohypophysis produces two hormones, called luteinizing
hormone (LH) and follicle stimulating hormone (FSH) which are
required for development and maintenance of the sexual
characteristics .
LH and FSH begin to be secreted
at puberty in a pulsatile fashion.
In women, FSH favors the
development of one ovarian
follicle at each menstrual cycle,
and the production of estradiol
by the granulosa cells. LH
mediates ovulation (departure of
the oocyte from the ovarian
follicle) and the production of
progesterone by the corpus
luteum.
2. In males:- In men, LH stimulates production of testosterone by
the Leydig cells of the testis. Testosterone is the main androgen
hormone and it is responsible for male sexual development (male
hairs, muscles, voice changes at puberty). In this general scenario,
it is easy to understand how big is the role of pituitary in sexual
life: by gonadotropins, this gland regulates the entire fertile period
of woman and the fertility of men. LH stimulates the production
of androgen-binding protein (ABP) by the Sertoli cells of the
testis. This protein allows high local, near the sperm,
concentrations of testosterone, on which the full maturation of the
spermatozoa depends.
CONTROL OF GONADOTROPHIN SECRETION
Gonadotrophin secretion is under the control of
(1) Hypothalamus , and (2) sex hormones.
1 Hypothalamus :- hypotalamus nuclei are known to secrete
specific releasing factors for the release of specific
gonadotrophic hormones.
luteinising hormone-releaseing,factor(LRF) for LH
(ICSH) and Follicle-stimulateing hormone-releasinfg
factor (FSH-RF) for FSH are secretecd from
hypothalamus when they are necessry
2 Sex hormone :- injection of oestrogen or androgen for
long periods,cause degeneration of anterior pituitary.
secretion of gonadotrophin is inhibited causing
atrophy of gonads
This shows that conc. Of sex hormons in blood regulates
secretions of gonadotrophins . A high conc. Inhibits ,where as a
low concentration stimulates secretion.
(c) LUTEOTROPHIC HORMONES (LTH) or
MAMMOTROPHIC HORMONE (MH) :it is secreted during pregnancy and lactation in women by
acidophil cells. It is peptied hormones, molecular weight is about
25000 and 180 to 190 amino acids are found .
ACTION OF PROLACTIN :The pituitary gland regulates lactation by producing the
hormone prolactin. This hormone is responsible for the
maintenance of lactation, after the mammary gland has
been prepared for milk production by estrogens. During
the entire post-partum period prolactin is increased
because breast suckling stimulates prolactin
production. The high prolactin value is also the reason
why women are infertile during this period. In fact, this
hormone can inhibit the production of gonadotropins
and block follicle maturation in the ovary.
EVIDENCES :1. Hypophysectomy in lectating animals prevents the onset of
lactations (e.g. simmonds disease)
2. Injection of prolactin stimulate milk secretion in the fully
develops mammary glands
3. Synthetic ergot alkaloids,which diminish prolactin
secretion probably inhibit the release of performed hormone
granules from the lactotrophs
this shows that the ant. Pituitary produces a hormone(LTH)
which controls the activity of mammary glands. The
physiological role of LTH in the male is not known.’
CONTROL OF PROLACTIN SECRETION:1.
HORMONES:- The sex hormones and the placental gonado
trophins inhibit prolactin secretion.
although breast are fully devloped, yet lactation
does not occur during pregnency. It starts after parturition and
expulsion of placenta.
2. NERVOUS SYSTEM:- Suckling of the baby generates afferent
impulses which reflexly stimulate prolactin secretion through
htpothalamus. It is believed that suckling inhibits the median
eminence factor (PIF) and thus prolactin secretion from the
anterior pituitary is increased.
1. DYSFUNCTION OF ACIDOPHIL CELLS:a. Hyperactivity1.) in the young:-Gigantism
2.) in the adult :-Acromegaly
b. Hypoactivity
–
a. in the young-dwarfism,three types :
1.) lorain-levy type
2.) brissaud type
3.) mixed type.
b. in the adult- acromicria (very rare)
GIGANTISM
Caused by hyperactivity of the acidophil cells, in the young.
1. Skeleton- avery tall (7-8 feet) minimum 6.8 feet
2. Muscles and visceras-proportionally large
3. Metabolism- a. hyperglycaemia,reduced sugar tolerance and
may be ,glycosurea(due to over secretion of STH and ACTH)
b. BMR- raised
c. SWEATING-increased(to help hit lost)
4. Changes in other glands
a. thyroid- enlarged and hyperactive,hence may cause
additional graves disease.
b. adrienal cortex-hyper active and enlarged
c. thymus- enlarged
d. gonads-at first hyper active than may a trophy(over work
and exhaustion)
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ACROMEGALY
Caused by hyperactivity of the acidophil cells, in adults
1. Skeletona. overgrowth of two jaws.
b. hand and feet- enlarged.
c. Bowing of the spine (kyphosis)
due to above mentioned skeletal causes a,b,c,the
subject assumes gorilla like appearance.
2. Subcutaneous tissues- of the hand ,feet,nose,scalp and skin
increase in amount producing deep furrows.
3. Metabolism-a. hyperglycaemia,reduced sugar tolerance and may
be ,glycosurea(due to over secretion of STH and ACTH)
b. BMR- raised
c. SWEATING-increased(to help hit lost)
4. Viscera- are all enlarged such as heart,lungs,lever,spleen etc.
5. Other endocrines:a. thyroid- enlarged and hyperactive,hence may cause additional
graves disease.
b. adrienal cortex-hyper active and enlarged
c. thymus- enlarged
d. gonads-at first hyper active than may a trophy(over work
and exhaustion)
Other manifestation:In males- diminished libido and sometimes impotence.
In females- devlopement of sterility, menstrual disturbences,failure
of breast devlopment.
DWRFISM
Caused by hypoactivity of the acidophil cells, in the young.
Three types –
1.lorain-levy type(infantism):a. stunded growth.
b. sex organ & secondary sex character do not grow
c. intelligence- normal and proportionally to age.
d. metabolism- normal.
2. Brissaud type- (fat boy of dikens) same as lorain-levy type, plus
excess deposition of fat in the body.
3. Mixed type:-
DYSFUNCTION OFBASOPHIL CELLS
CUSHING’S DISEASE
Definition:- Cushing syndrome is a disease that occurs
when your body produces too much of the hormone
cortisol. It may also occur if you use take too much cortisol
or other steroid hormones
Causes :- Cushing syndrome is a condition that results from
an excess of cortisol, a hormone produced by the adrenal
glands. The most common cause of Cushing syndrome is
Cushing's disease, caused by excessive production of the
hormone ACTH by the pituitary gland. ACTH stimulates
the adrenal glands to produce cortisol.
Cushing syndrome can be caused
by a tumor of the pituitary gland,
a tumor of the adrenal gland, a
tumor somewhere other than the
pituitary or adrenal glands
(ectopic Cushing syndrome), or
by long-term use of
corticosteroids (drugs commonly
used to treat conditions such as
rheumatoid arthritis and asthma).
Risk factors for Cushing
syndrome are adrenal or pituitary
tumors, long-term therapy with
corticosteroids, and being female.
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DYSFUNCTION OF THE
CHROMOPHOBE CELLS
Usually caused by atumour of
the inactive chromophobe
cells.
1. In children;
A; frochich’s syndroe
(adiposogential dystrophy).
(a) stunted
growth(dwarfism). (b)
idiotic.
(c)sexual
infantilism . (d) generalised
obesity
LAURENCE-MOON-BIEDL SYNDROME (often familial).
This is same as frohich’s syndrome(children type) plus (a)
polydactylism,and (b) retinitis pigmentosa.
2 . In adults- frochich’s
syndrome-(adult type).
A. in males (a) mental disposition and apperance resemble
females (b) degeneration of sex (c) hand and feet are small and
tapering (d)skin of face and body is smooth and hairless.
B. in female- (a) extreme adiposity (b) degeneration of sex .
TOTAL DISFUNCTION OF PARS DISTALIS
Hyperactivity (degenrative changes)
(1) In children .progeria
apperance of early senility-often seen in pituitary dwarfs .
(2) In adults . Simmonds disease
Due to degeneration of anteriar lobe of pituitary
1. Cachexia-Loss of weight
2. Sexual degeneration –amenorrhoea ,sterility,impotency
3. Asthenia –extreme weakness
4. Anorexia- loss of appetite
5. Low BMR
6. Mental deterioration
7. Hypoglycaemia ( 8) anaemia
NEUROHYPOPHYSIS
SYNTHESIS,TRANSPORT AND STORAGE OF
NEUROHYPO- PHYSEAL HORMONES
1.VASOPRESSIN(PITRESSIN)
Chemistry:-it is octapeptide. Vasopressin has molecular weight of
about 1100.
Vasopressin(ADH) is released in response to stress, and also in
response to dehydration. Vasopressin has got antidiuretic
propertyand increases facultative reabsorption of H2O and thus
reduces the volume of urine formed.
EVIDENCES:-disease of the post pituitary, hypothalamus or injury
to the nerve tracts of gland produces a condition in which large
amount of very dilute urine is produced. This condition is called
diabetes insipidus.
CONTROL OF THE SECRETION OF
VASOPRESSIN (ADH)
1.
2.
3.
4.
5.
Water deprivation
Negative pressure breathing
Positive pressure breathing
Haemorrhage and other changes in the blood volumue
Hypoxia
OXYTOCIN(PITOCIN)
CHEMISTRY- it is octapeptide molecular weight of oxytosin is
about 1000 oxytocin shares some of the activities of ADH or
vice versa and thus oxytocin is minimally antidiuretic .
ACTION OF OXYTOCIN;1. Uterus – the action of oxytocin on uterus depends upon the
species and pretreatment of the animal with oestrogen.
2. Milk ejection –it causes contraction of the myoepithilial
cells around the mammery alveoli.
3. Metabolism –it produces hyperglycemia.
4. Sperm transport –oxytocin facilitates the transport of
sperm in the female genital tract.
5. Water metabolism –oxytocin given alarge doses and in
abundant fluid volume may cause water intoxication due to
antidiuretic effect of oxytocin on the nephron.
DISORDERS OF THE FUNCTION OF THE
POSTERIOR PITUITARY
Destruction of the neurohypophysis causes dibetes insipidus
(insipid =taste less).this is a condition in which large quantities
of urine of very low sp. Gr. – 1.002 to 1.006 and low cloride
content are excreted. but further development of lesion may
destroy the pars distalis with amelioration of the diabetes.
SOME IMPORTANT QUESTIONS:1. Which endocrine Glands are regulated by anterior pituitary
hormones?
2. Describe Hypophysis with its hormone.
3. Anterior pituitary is called the master gland of endocrine system.
Why?
4. Write short notes on:- 1.Cushing’s syndrome.
2.Gigantism.
3.Acromagaly.
4.Dwarfism.
5. Describe hormones of post. pituitary.
6. Functions of ACTH.
7. Describe trophic hormones.
8. Describe regulation of Growth hormone secretion.
REFERED BOOKS:1.Dr. C. C. Chatterjee
2.Gerard J Tortora
3. A K Jain.
4. Dr. Choudhary