L ec 2 D r S haimaa M unther T he Anterior Pituitary A denohypophysis The anterior pituitary adenohypophysis is derived embryonically from glandular tissue as an invagination of the pharynx called ID: 934217
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Slide1
Anterior Pituitary Hormones
L
ec
. 2
D
r.
S
haimaa
M
unther
The Anterior Pituitary
(A
denohypophysis)
The
anterior pituitary
( adenohypophysis) is derived embryonically from glandular tissue, as an invagination of the pharynx called (
rathke's
pouch).
It then migrates toward the embryonic nervous tissue destined to form the neurohypophysis.
When these two tissues come into contact, the pituitary gland is formed.
Unlike the neurohypophysis, which releases hormones originally synthesized in the hypothalamus, the adenohypophysis synthesizes its own hormones in specialized groups of cells.
Similar to the neurohypophysis, however, the release of these hormones into the blood is regulated by the hypothalamus
Slide3Slide4Slide5Hormones of T
he
Anterior Pituitary
T
he anterior pituitary secretes:
Thyroid-stimulating Hormone (TSH,
T
hyrotropin),
A
drenocorticotropic Hormone (ACTH,
or called
Adrenocorticotropin,or
Corticotropin
)
Gonadotropines
( Luteinizing Hormone (LH), & Follicle-Stimulating
H
ormone (FSH))
Prolactin (
Lacto tropes)
Growth hormone (
Somatotropin
)
Of the listed hormones, prolactin acts on the breast. the
remaining are tropic hormones ; that is, they stimulate secretion of hormonally active substances by other endocrine glands.
Slide6Thyroid-stimulating hormone (TSH or Thyrotropin) Regulates the growth and metabolism of the thyroid gland. S
timulates synthesis and release of the thyroid hormones, T3 and T4.
Adrenocorticotropic hormone (ACTH) Stimulates growth of the adrenal cortex
Stimulates steroid hormones
production in the adrenal cortex. specifically, it stimulates secretion of cortisol and other
corticosteroids.
Growth
hormone
(GH, Somatotropin
) Is one of the few hormones that exerts its effects on organs and tissues throughout the body. It is essential for normal growth and development of the skeleton as well as visceral, or soft, tissues from birth until young adulthood.Growth of the skeleton involves : An increase in bone thickness and an increase in bone length. through stimulation of osteoblast (bone-forming cell) activity and proliferation of the epiphyseal cartilage in the ends of the long bones. The growth of visceral tissues occurs by hyperplasia (increasing the number of cells) and hypertrophy (increasing the size of cells).
Hormones of
The Anterior Pituitary
Slide7The Gonadotropins , Follicle-stimulating hormone and Luteinizing hormone
E
xert their effects on the gonads (ovaries in the female and testes in the male). 1- produce gametes (ova and sperm) 2- secrete sex hormones (estrogen, progesterone, and testosterone)Follicle-stimulating Hormone (FSH)
Females
: stimulates growth & development of ovarian
follicles &
promotes secretion of estrogen by ovaries.
Males:
Act on sertoli cells for sperm productionLuteinizing Hormone (LH): Females: responsible for ovulation, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones. Males: stimulates leydig cell in the
testis
to secrete testosteroneProlactin: Females: stimulates breast development and milk production. Males: involved in testicular function
Hormones of
The Anterior Pituitary
Slide8Hypothalamic
hormones regulate
anterior pituitary trophic hormones that, in turn, determine target gland secretion.
There
is
a peripheral
hormones
feedback
which regulates
hypothalamic and pituitary hormones.
Hypothalamic and
Pituitary Hormones
Slide9Hypothalamus - Pituitary Axis
The hypothalamus and pituitary gland form a unit that exerts control over the function of several endocrine glands (thyroid, adrenals, and gonads), as well as a wide range of physiologic activities This unit constitutes an example of neuroendocrinology—brain-endocrine interactionsDue to their embryonic origins, the neurohypophysis and the adenohypophysis are regulated by the hypothalamus, using two very different mechanisms:Neuronal signalsH
ormonal signals
Slide10Neuronal Signals
A
ction potentials generated by the neurosecretory cells originating in the hypothalamus are transmitted down the neuronal axons to the nerve terminals in the neurohypophysis and stimulate the release of the hormones into the blood. Specific forms of sensory input that regulate the release of ADH and oxytocin
Slide11Hormonal
S
ignals
T
he
adenohypophysis does not have a direct anatomical connection
with the
hypothalamus; therefore, regulation of hormone secretion by way
of neuronal
signals is not possible, instead, these two structures are associated by a specialized circulatory system and the secretion of hormones from the adenohypophysis is regulated by hormonal signals from the hypothalamusThe neurosecretory cells synthesize two types of hormones:Releasing hormones Inhibiting hormones
Each
of these hormones helps to regulate the release of a particular hormone from the adenohypophysis. For example, thyrotropin-releasing hormone produced by the neurosecretory cells of the hypothalamus stimulates secretion of thyrotropin from the adenohypophysis.
Slide12Endocrine ControlThere are three levels
Hypothalamic stimulation—from CNS
Pituitary stimulation—from hypothalamic trophic hormonesEndocrine gland stimulation—from pituitary trophic hormones
Slide13Hypothalamic Releasing Hormones Seven releasing hormones are made in the hypothalamus
T
hyrotropin-releasing hormone (TRH)Corticotropin-releasing
h
ormone
(CRH)
G
onadotropin
-releasing hormone (GnRH)Growth hormone-releasing hormone (GHRH)Growth hormone-release
i
nhibiting hormone (GHIH)Prolactin-releasing factor (PRF)Prolactin-i
nhibiting
h
ormone
(
PIH)
Slide14Hypothalamic
hormones regulate
anterior pituitary trophic hormones that, in turn, determine target gland secretion.
There
is
a peripheral
hormones
feedback
which regulates
hypothalamic and pituitary hormones.
Hypothalamic and
Pituitary Hormones
Slide15Negative Feed Back
C
ontrol The trophic hormone from the adenohypophysis stimulates the release of a hormone from another endocrine gland.
This final endocrine gland hormone not only carries out its effects on its target tissues, it may also exert a negative feedback effect on the release of the hypothalamic and/or
adenohypophyseal
hormones.
Slide16Regulation of Anterior Pituitary Function
S
ecretion of the anterior pituitary hormones is regulated by:The central nervous system provides the primary drive for secretionHormones produced in peripheral target glands and peripheral input plays a secondary, though vital, role in modulating secretory
rates
S
ecretion of all the anterior pituitary hormones except PRL declines severely in the absence of stimulation from the hypothalamus ,
PRL secretion is normally under tonic inhibitory control by the hypothalamus
16
Slide17Feedback Control of
Anterior Pituitary Function
Environmental factors may increase or decrease pituitary activity by
increasing
or decreasing
hormone secretions from
hypothalamus
Pituitary secretions
increase the secretion of target gland hormones, which may
inhibit further secretion by acting at either the hypothalamus or the pituitaryPituitary hormones may also inhibit their own secretion by a short feedback loop17
Slide18Negative Feedback Controls:
Long & Short Loop Reflexes
Long-loop feedback
Short-loop feedback
Slide19Example for feedback Control Pathway for
Thyroid hormone
SecretionFigure 7-15
Slide20Growth Hormone
G
rowth hormone (GH), also called somatotropic hormone (STH
)
S
omatotropes
(GH producing cells) are by far the most abundant anterior pituitary cells, and account for at least half the cells
Target:
Most
tissuesMajor actions in humans :Promotes growth in stature and mass; Stimulates production of insulin-like growth factor (IGF-I); Stimulates protein synthesis; Usually inhibits glucose utilization and promotes fat utilization20
Slide21Slide22Regulation of GH Secretion
The hypothalamus secretes GHRH
GHRH acts on anterior pituitary to produce GH GH acts on liver to produce Somatomedins peptides (Insulin-like growth factor-1 (IGF-1) called Somatomedin C is the major factor produced)Ghrelin, from stomach also stimulates GH secretionHigh levels of IGF-1 and GH stimulate production of Somatostatin from the hypothalamusSomatostatin inhibits the secretion of GHHigh plasma levels of IGF-1 exert negative feedback on anterior pituitary to modify action of GHRH and to inhibit secretion of GH
Slide23GH
AXIS
Slide24Intermediate Lobe
of
The PituitaryIn some species there is a well-developed intermediate lobe of the pituitary, whereas in humans it is rudimentary, nevertheless, the intermediate lobe, contain hormonally active derivatives of the pro opiomelanocortin molecule that regulate skin pigmentation, among other functions
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