Anterior Pituitary Hormones - PowerPoint Presentation

Slide1

Anterior Pituitary Hormones

L

ec

. 2

D

r.

S

haimaa

M

unther

Slide2

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

Slide3

Slide4

Slide5

Hormones 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.

Slide6

Thyroid-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

Slide7

The 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

Slide8

Hypothalamic

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

Slide9

Hypothalamus - 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

Slide10

Neuronal 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

Slide11

Hormonal

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.

Slide12

Endocrine ControlThere are three levels

Hypothalamic stimulation—from CNS

Pituitary stimulation—from hypothalamic trophic hormonesEndocrine gland stimulation—from pituitary trophic hormones

Slide13

Hypothalamic 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)

Slide14

Hypothalamic

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

Slide15

Negative 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.

Slide16

Regulation 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

Slide17

Feedback 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

Slide18

Negative Feedback Controls:

Long & Short Loop Reflexes

Long-loop feedback

Short-loop feedback

Slide19

Example for feedback Control Pathway for

Thyroid hormone

SecretionFigure 7-15

Slide20

Growth 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

Slide21

Slide22

Regulation 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

Slide23

GH

AXIS

Slide24

Intermediate 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

Slide25