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The Pituitary
Endocrinology 3
How is the pituitary organised?
Pituitary
Which hormones are produced?
How are the hormones released?
BM Endocrinology 2011
Helen Christian
Where do the hormones act?
Consequences of too much/too little
hormone
Pituitary location
and
MRI appearance
Structure of the pituitary gland
Anterior
A
t i
=adenohypophysis
Ant
Posterior
= neurohypophysis
Post
1
Development of the pituitary
Organisation of the pituitary
5 weeks
20 weeks
pituitary fossa
Organisation
of the
pituitary
‘transphenoidal surgery’
The discovery of hypothalmic control of the pituitary
hypothalamus
Median eminence
Optic chiasm
‘neurosecretion’
internal carotid
branch
Anterior pituitary
Posterior pituitary
jugular vein
Geoffrey Harris 1913 – 1971
1977 Schally and
Guillemin Nobel prize
for identifying releasing
factors
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Ultrastructure of anterior pituitary
Anterior pituitary
PRL
ACTH
five endocrine cell
types each secrete
different hormone(s)
cell types can be
differentiated by
antibody labelling and
cell structure
capillary
non-secretory
supporting cell type
‘folliculo-stellates’
Fenestrated capillaries
Feedforward and feedback control
- ve
inhibitory
feedback
fenestrations
Hypothalamus
R l
Releasing
i hormone
h
- ve
feedforward control
Anterior pituitary
Trophic hormone
capillary
Endocrine gland
Target
e.g. cortisol release
from the adrenal
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The hypothalamic-pituitary-thyroid
axis
cold
hypothalamus
TRH
Inhibitory
feedback
Ch i l type:
Chemical
t
polypeptide
l
tid hormone
h
from
f
POMC
precursor, secreted by corticotroph cells
Thyrotrophin
Releasing
Hormone
thyrotrophs
anterior pituitary
TSH
Receptor: G protein coupled receptor to cAMP
Thyroid
Stimulating
Hormone
thyroid
T3 and T4
GPCRGPCR
cAMP
Pathology of
TSH secretion is
v rare
The hypothalamo-pituitary-adrenal
axis
hypothalamus
Adrenocorticotrophic hormone
(ACTH)
Stress
hypoglycaemia
Actions:
stimulates secretion of cortisol (glucocorticoid
hormone) from adrenal cortex in stress
stimulates growth of adrenal cortex
Diurnal rhythm of plasma ACTH
and cortisol
Inhibitory
feedback
anterior pituitary
corticotrophs
ACTH
adrenal cortex
Corticotrophin
Releasing
Hormone
co
ortisol
CRH
glucocorticoids,
cortisol
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Gonadotrophins: LH and FSH
ACTH pathology
Actions: reproduction
excess ACTH
ACTH, and in turn excess
glucocorticoid, - Cushing's disease
deficiency of ACTH, in turn
glucocorticoid deficient- Addison's
disease
….see adrenal lecture week 5
Female:
FSH follicle development and ovulation, LH
synthesis of sex steroids by the ovary
Male:
LH controls testosterone production
p
production
p
FSH stimulates sperm
Deficit: infertility in adult life
lack of sexual maturation
Excess: precocious puberty
See Trinity term Reproduction lectures
Hypothalamo-pituitary-gonadal axis
hypothalamus
GnRH
anterior pituitary
gonadotrophs
-ve
LH + FSH
ovary
estrogen
LH = luteinising
hormone
FSH = follicle
stimulating
hormone
Cyclical release
in menstrual
c cle
cycle
Control of prolactin release
hypothalamus
dopamine INHIBITORY
anterior pituitary
lactotrophs
PRL
tyrosine kinase enzyme
-linked receptors
testes
testosterone
suckling +ve
Breast growth and milk production
Inhibits reproduction
lactational amenorrhaea
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Control of prolactin release
Growth hormone axis
Hypothalamus
Only
yp
pituitary
y hormone whose
principal control is inhibitory
GHRH
Anterior pituitary
somatotrophs
PRL production is stimulated
by estrogen during pregnancy
Dopamine agonists e.g.
bromocryptine, suppress
lactation
Pathology: prolactinomas
hypersecrete PRL – cause
infertility and milk production
Growth hormone release is pulsatile
Li
Liver
IGFs
GH -ve
GH
GH Enzymelinked receptors
Long bone and muscle growth
GH pathology
Gigantism due to excess
GH secretion
Short stature if lack GH
nb if prior to epiphyseal
plate fusion at puberty
March 2010
Sultan Kosen 8ft 1 is the
tallest man in the world
and China’s He Pingping
the smallest at 2ft 5in.
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Acromegaly
Mutations in Aryl hydrocarbon-interacting protein
predisposes to pituitary adenoma in childhood
Due to excess GH
secretion after
epiphyseal plates
have fused
Enlargement of
hands and feet
Coarsening of
facial features –
largening of nose
DNA extracted from the skeleton of a 7ft 7in patient b1761 kept in
Hunterian museum, London. The same mutation was identified in
4 living N Ireland families who presented with gigantism.
Weight gain
Pituitary tumours
hormonal effects: hormone-secreting tumours effects
depend on cell type
mechanical effects: affects vision as presses on optic
chiasm
Posterior pituitary
Formed by axons and
terminals of
hypothalamic
neurosecretory neurons
Ant
Post
Secretes peptide
hormones anti-diuretic
hormone ((ADH,, also
known as vasopressin)
and oxytocin
Adenoma
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Stimulation of posterior pituitary
hormone release
hypothalamus: oxytocin and ADH
produced in cell bodies
Antidiuretic hormone - ADH
( = vasopressin)
Chemical type: Peptide 9 amino acids
Receptors
G protein coupled to cAMP
Stimulus
depolarises
neuron
axon
Ca2+
posterior
pituitary
Actions
increases
c eases water
ate reabsorption
eabso pt o in
collecting ducts of kidney
action potential
exocytosis
See Trinity term Kidney lectures
Stimuli of ADH release
Plasma osmolality
Blood volume
Diabetes insipidus
Too little ADH function
Two types:
hypothalamic: lack of
ADH production renal:
lack of ADH action
‘Brattleboro rat’ lacks
ADH, drinks 70% of
body weight per day,
urinates constantly
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Oxytocin
Chemical nature: peptide
Receptors: PLC-coupled
Control of oxytocin release
stretch of cervix/vagina at parturition
suckling – nipple stimulation causes
milk-ejection reflex
Actions:
Pathology
contraction of uterine
muscle
l in
i childbirth
hildbi th
deficit may cause prolonged labour
milk ejection by contraction
of breast myoepithelium
knockout mice labour normal but no
milk-ejection
See Trinity term Reproduction lectures
Pituitary : the master gland
Endocrinology
Week 1 General principles
Week 1 Hormone action
Week 2 Endocrine pancreas
Week 3 Pituitary
Week 4 Thyroid
Week 5 Adrenal
Week 6 Endocrinology Cells and Tissues
Any questions email: [email protected]
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