Hypothalamus and Anterior Pituitary 2014 (1)
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Transcript of Hypothalamus and Anterior Pituitary 2014 (1)
8/17/2019 Hypothalamus and Anterior Pituitary 2014 (1)
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Hypothalamus and
Anterior Pituitary
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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.
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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)
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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
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Hypothalamo+Hypophysealelationship
• #ascular connections
– Hypothalamus and adenohypophysis(anterior pituitary)
• eural connections
– Hypothalamus and neurohypophysis(posterior pituitary)
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Hypothalamic
nuclei
Superior
hypophyseal
artery
Paraventicular
nucleus
Supraoptic
nucleus
1ry capillary
Portal vein
2ry capillary
Hypothalamo-
hypophysealportal
system
Anterior PituitaryPosterior Pituitary
Hypothalamo-
hypophyseal
tract
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Hypothalamic hormones in,uencinganterior pituitary
• -hyrotropin releasing hormone
• %orticotropin releasing hormone
• onadotropin releasing hormone
• rowth hormone releasing hormone
• /omatostatin
• Prolactin inhibiting hormone (dopamine)
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Hypothalamic hormones in,uencinganterior pituitary
• -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
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Hypothalamic hormones in,uencinganterior pituitary
• -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
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Hypothalamic hormones in,uencinganterior pituitary
• 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
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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)
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Anterior pituitary hormones
-H!! hormones ha"e direct endocrinee6ects.
• rowth hormone (somatotropin)
• Prolactin• 3elanocyte stimulating hormone (3/H)
All anterior pituitary hormones are peptidehormones
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Anterior pituitary hormones
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
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Anterior pituitary hormones
-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
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Anterior pituitary hormones
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
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Anterior pituitary hormones
rowth hormone and prolactin arestructurally similar
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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
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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
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Actions of H
Protein metabolism:
H tends to increase free fatty acid le"el inplasma
'.9ncreases cellular amino acid upta$e
*.Promotes protein synthesis and inhibitsproteolysis
;.%auses positi"e nitrogen balance
9ncreases lean body mass
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Actions of H
Lipid metabolism:
H tends to increase free fatty acid le"el in plasma
'.9ncreases lipolysis in adipose tissue & increases
hormone sensiti"e lipase acti"ity*.9ncreased upta$e of 22A by muscle and li"er
;.H tends to be $etotogenic
Decreases percentage of fat in the body
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Actions of H
%arbohydrate metabolism:
H tends to increase blood glucose le"el
'.9nhibits upta$e of glucose by s$eletal
muscle and adipose tissue (may besecondary to an increase in 22A in blood)
*.9ncrease in gluconeogenesis
;.Decreases insulin sensiti"ity &diabetogenic hormone. <hen present inexcess causes diabetes mellitus
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Actions of H
!lectrolyte metabolism:
'.%auses a= retention
*.%alcium absorption increased
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Actions of H
-hrough 92 9:
• 9ncreases growth of s$eteton1 epiphyseal plate1muscle and "iscera
• 9ncreases – %ell proliferation
– %ell di6erentiation
– %ell metabolism
9ncreases height due to action on the epiphysealplates & only before epiphyses fuse
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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
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egulation of H secretion
Hypothalamus
Anterior pituitary
Liver
IGF I
GH
GHRHSomatostatin
- ve- ve
- ve
Ghrelin
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egulation of H secretion
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
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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
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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
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Actions of Prolactin
'. 3il$ production (lactogenesis)increases transcription of genes for en5ymes thatcatalyse the formation of constituents of mil$.
*. Promotes breast de"elopmentplays a secondary role to oestrogen andprogesterone which are the more importanthormones that in,uence breast de"elopment
;. 9nhibit the secretion of gonadotropin releasinghormone
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egulation of Prolactin /ecretion
3a@or in,uence
• Prolactin inhibiting hormone (dopamine)
• -here may also be a prolactin releasing
factor secreted by the hypothalamus
• Le"els are the same in males and non
pregnant1 non lactating females
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egulation of Prolactin /ecretion
Other stimuli
• -H & stimulates release of prolactin
• lucagon1 secretin1 #9P1 9P can be stimulatory
• Physical or mental stress increases secretion• /ecretion has a diurnal rhythm7 increasing
during sleep
• During pregnancy high le"els of oestrogensincrease prolactin secretion
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/ummary
• -he hypothalamus regulates anterior pituitary function
"ia the hypothalamo+hypophyseal portal system
• 3ost hypothalamic hormones are stimulatory to
anterior pituitary
• Anterior pituitary secretes tropic hormones that
regulate other endocrine glands• rowth hormone and prolactin are the two non+tropic
hormones of the anterior pituitary
• H has a wide range of e6ects on metabolism and
growth7 e6ects on growth are mainly through 92 9• Prolactin1 the mil$ producing hormone1 has little
function in the male and in non pregnant1 non lactatingfemales