• 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.

A
P
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.
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.

Ant. Pituitary
Hormone
Releasing hormone(s)
Targets tissues/organs
Effects/Final
Hormones
Adrenocorticotrophic H. ACTH
CRH (41 aa)
Thyroid-stim. H.
TSH
TRH (3aa)
Adrenal cortex thyroid
Growth H.
(somatotropin,
GH)
GHRH (44aa)
GIH = somatostatin
(14aa)
Whole body, via growth factors secretion of Cort
(and Aldo, DHA)
T
4
=thyroxine – increased basal metabolism
Increase in stature and body mass, increased anabolism

AP hormone Releasing hormone(s)
Targets tissues/organs
Effects/Final
Hormones
Follicle-stim. H.
FSH
GnRH (10aa)
Luteinizing H. LH GnRH
Prolactin PRL PRLRH=TRH?
PIH = dopamine
Testes, Ovaries Spermatogenesis
Follicular maturation
Testes, Ovaries Testosterone
Progesterone,
Estrogens – 2ndary sex characteristics
Mammary glands
Lactation

Feedback control of hormone secretion in the simple system
Sensor – regulated variable gland hormone
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. target
Simple negative feedback

The hierarchical structure of ant. pituitary axes makes multiple feedback loops possible hypothalamus
Releasing factor
Ant. pituitary
Tropic hormone
Not all of these loops are operative in any given system.
Target gland
Final hormone(s)
Target - effects

The control of cortisol secretion is an example hypothalamus
CRF corticotrophs
ACTH
Adrenal cortex cortisol

• 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.