S8: the hypothalamic pituitary axis, growth hormone & pituitary disorders

Question 1

Describe the relationship between the hypothalamus and the anterior pituitary gland

Answer 1

Hypothalamic pituitary axis = hypothalamus and pituitary constitute the major link between the nervous and endocrine system
Anterior pituitary arises from evagination of oral ectoderm (primitive gut tissue)
Hormone synthesis in the hypothalamus are stored in the median eminence & then release into hypophyseal portal system -> stimulate endocrine cells in the AP gland

Question 2

Describe the relationship between the hypothalamus and the posterior pituitary

Answer 2

Posterior pituitary (originates from neuroectoderm – primitive brain tissue) is physically connected to the hypothalamus through the infundibulum 
Oxytocin & ADH produced by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus -> transported down axons to the posterior pituitary 
Stored and released from posterior pituitary into the general circulation to act on distant targets

Question 3

Name the hormones produced by the hypothalamus (6+2) and briefly describe their biological roles

Answer 3

Oxytocin = milk let down & uterus contractions during birth
ADH = regulation of body water volume
TRH = thyrotropin releasing hormone
PIH = prolactin release-inhibiting hormone (dopamine)
CRH = corticotropin releasing hormone
GnRH = gonadotropin releasing hormone 
GHRH = growth hormone releasing hormone 
GHIH = growth hormone-inhibiting hormone (somatostatin)

Question 4

Name the hormones produced by the anterior pituitary gland (6) and briefly describe their biological roles

Answer 4

Thyroid stimulating hormone (TSH) = secretion of thyroid hormone from thyroid gland
Adrenocorticotropic hormone (ACTH) = secretion of hormones from adrenal cortex
Luteinising hormone (LH) = ovulation & secretion of sex hormones
Follicle stimulating hormone (FSH) = development of eggs & sperm
Prolactin (PRL) = mammary gland development & milk secretion
Growth hormone (GH) = growth & energy metabolism; stimulates IGFs

Question 5

Describe the factors controlling GH secretion (long and short loop negative feedback)

Answer 5

Long loop: mediated by IGFs
-inhibit release of GHRH from hypothalamus
-stimulates the release of somatostatin from hypothalamus
-inhibit release of GH from anterior pituitary
Short loop: mediated by GH itself via stimulation of somatostatin release

Question 6

Describe how GH exerts its effects on cells both directly and indirectly through Insulin like growth factors

Answer 6

GH receptors activate JAKs -> activation of signalling pathways -> transcription factor activation and IGF production
IGFs acts through IGF receptors to modulate cell growth, cell number, increase in the rate of protein synthesis, increase in the rate of lipolysis in adipose tissue

Question 7

Describe the clinical feature of disease states resulting from malfunction of the hypothalamic pituitary axis

Answer 7

Pituitary tumours
Hypopituitarism = GH, gonadotropin, TSH, ACTH & ADH deficiency
-GH deficiency = DWARFISM in childhood, delayed/no sexual development during teen years
Hyperpituitarism = prolactin, GH & ACTH excess
-GH excess = results in GIGANTISM in childhood, ACROMEGALY (large extremities) in adulthood

Question 8

Outline the endocrine tests use to assess pituitary function

Answer 8

Thyroid axis: fT4, TSH
Gonadal axis: LH, FSH, testosterone in men, oestradiol in women
Prolactin: serum prolactin
HPA: 0900 cortisol
GH: GH/IGF-1
For the first 3 basal blood test sufficient, last 2 dynamic blood test may be needed

Question 9

Outline management and treatment options for pituitary disorders

Answer 9

Prolactinoma: dopamine agonists
Acromegaly: surgical removal of tumour, radiation therapy & drug therapy