hypothalamus and anterior pituitary 2014 (1)

8/17/2019 Hypothalamus and Anterior Pituitary 2014 (1)

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Hypothalamus and

Anterior Pituitary



Learning Outcomes

• Outline the endocrine functions of the hypothalamus.

• List the hypothalamic hormones and state their function.• Describe the functional relationship between the hypothalamus and the

pituitary gland.(Hypothalamic pituitary axis)

• elate the cell types of the anterior pituitary to the hormones secreted.

• List the tropic hormones secreted by the anterior pituitary and statetheir target endocrine organs and actions.

• Describe the actions and regulation of growth hormone.

• Outline the actions and regulation of prolactin.

• List the hormones of the posterior pituitary.

• !xplain how "asopressin (A#P) acts on water reabsorption in the$idneys

• Describe the "asopressin secretory response to changes in bloodosmolality.

• !xplain the smooth muscle response to oxytocin in the breast and

uterus.



Pituitary gland

%onsists of two parts

Anterior pituitary (adenohypophysis & as it consistsof glandular tissue and deri"ed from the roof of the

mouth)Posterior pituitary (neurohypophysis & as it containsneural tissue and deri"ed from the brain)



Hypothalamus

!ndocrine function is one of many functions of thehypothalamus

Hypothalamic hormones

'.egulate anterior pituitary function – o signicant direct action on other parts of the body

– egulate the anterior pituitary

– Ha"e indirect control through anterior pituitaryhormones

*.Are transported to posterior pituitary to be secreted – Act on other parts of the body when secreted by the

posterior pituitary



Hypothalamo+Hypophysealelationship

• #ascular connections

– Hypothalamus and adenohypophysis(anterior pituitary)

• eural connections

– Hypothalamus and neurohypophysis(posterior pituitary)



Hypothalamic

nuclei

Superior

hypophyseal

artery

Paraventicular

nucleus

Supraoptic

nucleus

1ry capillary

Portal vein

2ry capillary

Hypothalamo-

hypophysealportal

system

Anterior PituitaryPosterior Pituitary

Hypothalamo-

hypophyseal

tract



Hypothalamic hormones in,uencinganterior pituitary

• -hyrotropin releasing hormone

• %orticotropin releasing hormone

• onadotropin releasing hormone

• rowth hormone releasing hormone

• /omatostatin

• Prolactin inhibiting hormone (dopamine)




• -hese hormones are transported to theanterior pituitary "ia the hypothalamo+hypophyseal portal system

• eleasing hormones ha"e specicity.0ut there is some degree of crossin,uence




• -hyrotropin releasing hormone & stimulates -/H1stimulates prolactin

• %orticotropin releasing hormone & stimulatesA%-H

• onadotropin releasing hormone & stimulates 2/Hand LH

• rowth hormone releasing hormone & stimulatesH

• /omatostatin & inhibits H1 inhibits TSH

• Prolactin inhibiting hormone (dopamine) & inhibitsprolactin




• 3ost are stimulatory hormones

• /omatostatin and prolactin inhibitingnhormone are inhibitory hormones.

• Of the anterior pituitary hormones1 all areregulated mainly by releasing

(stimulatory) hormones except forprolactin



Anterior pituitary hormones

2O4 hormones act on other endocrine glands &tropic hormones

• Acting on thyroid –

-hyroid stimulating hormone (-/H1 thyrotropin)

• Acting on adrenal cortex –

Adrenocorticotropic hormone (A%-H1corticotropin)

• Acting on gonads (ovary/testis) –2ollicle stimulating hormone (2/H)

Luteini5ing hormone (LH)




-H!! hormones ha"e direct endocrinee6ects.

• rowth hormone (somatotropin)

• Prolactin• 3elanocyte stimulating hormone (3/H)

All anterior pituitary hormones are peptidehormones




Di6erent hormones are secreted by di6erent cells inthe anterior pituitary

-hyrotrophs & secrete -/H

%orticotrophs + secrete A%-Honadotrophs & secrete 2/H and LH

/omatotrophs & secrete H

Lactotrophs + secrete prolactin

-here are non secreting cells distributed amongthese secretory cells

basophils

acidophils




-he se"en hormones are di6erent from eachother but some among them ha"esimilarities

-/H1 2/H and LH ha"e common structuralfeatures

• -hey are glycoproteins• !ach consists of two polypeptide chains1 α

and β7 and α is common to all




A%-H and 3/H ha"e similarities

• -hey are formed from one common

precursor molecule

• Part of A%-H has similar amino acidse8uence as 3/H

• A%-H has acti"ity similar to 3/H but to alesser extent




rowth hormone and prolactin arestructurally similar



rowth Hormone

-he most important hormone that in,uencesgrowth.

!ssential for normal growth of the body. -hus "ery important until growth to adulthood is

achie"ed.

9n the adult its importance is less

Howe"er1 growth hormone secretion continuesthroughout life



rowth hormone

/ecreted by somatotrophs

rowth promotion in almost all tissues

9n,uence carbohydrate1 protein and lipid metabolism

Actions of H

'. Direct

*. 9ndirect & H acts on the li"er to stimulate the

production of insulin li$e growth factor 9 (92 91somatomedins). 3ost growth associated actions ofH occur through 92 9



Actions of H

Protein metabolism:

H tends to increase free fatty acid le"el inplasma

'.9ncreases cellular amino acid upta$e

*.Promotes protein synthesis and inhibitsproteolysis

;.%auses positi"e nitrogen balance

9ncreases lean body mass



Actions of H

Lipid metabolism:

H tends to increase free fatty acid le"el in plasma

'.9ncreases lipolysis in adipose tissue & increases

hormone sensiti"e lipase acti"ity*.9ncreased upta$e of 22A by muscle and li"er

;.H tends to be $etotogenic

Decreases percentage of fat in the body



Actions of H

%arbohydrate metabolism:

H tends to increase blood glucose le"el

'.9nhibits upta$e of glucose by s$eletal

muscle and adipose tissue (may besecondary to an increase in 22A in blood)

*.9ncrease in gluconeogenesis

;.Decreases insulin sensiti"ity &diabetogenic hormone. <hen present inexcess causes diabetes mellitus



Actions of H

!lectrolyte metabolism:

'.%auses a= retention

*.%alcium absorption increased



Actions of H

-hrough 92 9:

• 9ncreases growth of s$eteton1 epiphyseal plate1muscle and "iscera

• 9ncreases – %ell proliferation

– %ell di6erentiation

– %ell metabolism

9ncreases height due to action on the epiphysealplates & only before epiphyses fuse



egulation of H secretion

0asal le"els > & ; ng?mL

0ut secretion is not constant

-ime of day & highest le"els in the early partof night

Age & adolescents ha"e higher le"els




Hypothalamus

Anterior pituitary

Liver

IGF I

GH

GHRHSomatostatin

- ve- ve

- ve

Ghrelin




Hypothalamus

Anterior pituitary

Liver

IGF I

GH

GHRHSomatostatin

- ve- ve

- ve

Non REM Sleep

Hypoglycaemia

ExerciseArginine

Stress

opamine

REM Sleep

Hyperglycaemia

FFA

cortisol

- ve!ve



Prolactin

/ecreted by lactotrophs

3ain hormone responsible for mil$ production

-hus it is suppressed in males and nonpregnant1 non lactating females. -hus thereason for ma@or regulator being aninhibiting factor

Other stimuli during pregnancy increaseprolactin secretion



Actions of Prolactin

'. 3il$ production (lactogenesis)increases transcription of genes for en5ymes thatcatalyse the formation of constituents of mil$.

*. Promotes breast de"elopmentplays a secondary role to oestrogen andprogesterone which are the more importanthormones that in,uence breast de"elopment

;. 9nhibit the secretion of gonadotropin releasinghormone



egulation of Prolactin /ecretion

3a@or in,uence

• Prolactin inhibiting hormone (dopamine)

• -here may also be a prolactin releasing

factor secreted by the hypothalamus

• Le"els are the same in males and non

pregnant1 non lactating females



egulation of Prolactin /ecretion

Other stimuli

• -H & stimulates release of prolactin

• lucagon1 secretin1 #9P1 9P can be stimulatory

• Physical or mental stress increases secretion• /ecretion has a diurnal rhythm7 increasing

during sleep

• During pregnancy high le"els of oestrogensincrease prolactin secretion



/ummary

• -he hypothalamus regulates anterior pituitary function

"ia the hypothalamo+hypophyseal portal system

• 3ost hypothalamic hormones are stimulatory to

anterior pituitary

• Anterior pituitary secretes tropic hormones that

regulate other endocrine glands• rowth hormone and prolactin are the two non+tropic

hormones of the anterior pituitary

• H has a wide range of e6ects on metabolism and

growth7 e6ects on growth are mainly through 92 9• Prolactin1 the mil$ producing hormone1 has little

function in the male and in non pregnant1 non lactatingfemales

hypothalamus and anterior pituitary 2014 (1)

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