Transcript The anterior pituitary (adenohypophysis)

The anterior pituitary
(adenohypophysis)
The posterior pituitary is part of the
brain; the anterior pituitary is not
• In embryonic development, anterior
pituitary arises from Rathke’s Pouch, an
outgrowth of the pharynx.
• Hypothalamic neurons communicate with
the anterior pituitary by chemical signals
called releasing factors and release
inhibiting factors. In almost all cases,
these are small peptides.
Magnocellular hypothalamic
neurons send their axons
through the pituitary stalk
and form neurohemal
synapses in the post.
pituitary, releasing small
peptide hormones ADH
(vasopressin) and oxytocin.
A
P
Parvocellular neurons in the
hypothalamus form
neurohemal synapses on
capillaries at the base or in
the pituitary stalk, releasing
factors that stimulate or
inhibit release of large
peptide or glycopeptide
hormones from nonneuronal pituitary cells.
Metabolism and Growth Hormones
Ant. Pituitary Releasing Targets
hormone(s) tissues/organs
Hormone
Effects/Final
Hormones
Adrenocorticotrophic H. ACTH
CRH (41 aa)
Adrenal cortex
secretion of Cort
(and Aldo, DHA)
Thyroid-stim. H.
TSH
TRH (3aa)
thyroid
T4 =thyroxine –
increased basal
metabolism
Growth H.
(somatotropin,
GH)
GHRH (44aa)
GIH =
Whole body, via
growth factors
Increase in stature
and body mass,
increased anabolism
somatostatin
(14aa)
Reproductive hormones
AP hormone Releasing
hormone(s)
Targets
Effects/Final
tissues/organs Hormones
GnRH (10aa)
Testes, Ovaries
Spermatogenesis
Follicular
maturation
Luteinizing H. LH GnRH
Testes, Ovaries
Testosterone
Progesterone,
Estrogens – 2ndary
sex characteristics
Prolactin PRL
Mammary
glands
Lactation
Follicle-stim. H.
FSH
PRLRH=TRH?
PIH = dopamine
Feedback control of hormone secretion in the
simple system
Sensor –
regulated
variable
gland
hormone
target
Simple negative
feedback
Here, hormone secretion
is self-regulated by
negative feedback from
the target to the gland,
and by a short loop in
which the gland is
sensitive to the hormone it
secretes.
The hierarchical structure of ant. pituitary axes
makes multiple feedback loops possible
Not all of these loops are operative in
any given system.
hypothalamus
Releasing factor
Ant. pituitary
Tropic hormone
Target gland
Final hormone(s)
Target - effects
The control of cortisol secretion is an example
hypothalamus
CRF
corticotrophs
ACTH
Adrenal cortex
cortisol
Hormone levels are diagnostic for
location of a lesion in the hierarchy
• Example 1: hypopituitary dwarfism vs
Laron dwarfism:
– Hypopituitary: hGH levels low, IGFs (insulinlike groth factors or somatomedins) low:
hypothalamus or pituitary is at fault
– Laron: hGH levels are high; IGFs low; liver
fails to respond to hGH: GH receptor is at fault
Example 2: Cushing’s Disease vs Cushing’s Syndrome
Cushing’s Disease: hyperpituitary hyperadrenalism: ACTH levels
elevated; excess cortisol secreted;
if brain is at fault, CRH levels high;
if pituitary at fault, CRH levels low.
Hypertension from excess aldosterone and masculinzation from excess
adrenal DEA are also consequences.
Cushing’s Syndrome (hyperadrenalism from any other cause):
-Ectopic ACTH secretion from tumor – cortisone levels very high
because no negative feedback; hypertension from excess
aldosterone - CRH levels would be very low
- Primary hyperadrenalism – CRH and ACTH levels low
-Iatrogenic – methyl prednisone or cortisone therapy for
inflammatory disease results in Cushingoid symptoms but with low
ACTH values – adrenal cortex shrinks; hypotension from
aldosterone deficit is one consequence.