Hypothalamic Pituitary Axis And Growth Hormone Flashcards
What factors influence growth (4)
Genetics, environment, hormones and nutrition
What is the most important endocrine regulator of growth
Growth hormone
What stimulates the release of growth hormone from the pituitary gland
GHRH - growth hormone releasing hormone
What socket of bone does the hypothalamus sit in
Sella turcica
From where does the anterior pituitary arise from
Oral ectoderm (primitive gut tissue)
Where does the posterior pituitary originate from
Neuroectoderm (primitive brain tissue)
What is the connection between the hypothalamus and posterior pituitary called
Infundibulum
What hormones are released from the posterior pituitary gland
Oxytocin and antidiuretic hormone
What hormones are produced in the posterior pituitary
None - hormones are only stored here
Where in the hypothalamus are oxytocin and antidiuretic hormones produced
Supraoptic and paraventricular nuclei
Where are hormones stored before they are released to the anterior pituitary gland
Median eminence
What does oxytocin do
Releases milk as part of the suckling reflex and caused uterus contractions during birth
What does ADH do
Regulate body water volume
What are the 6 hormones produced by the hypothalamus which travel to the anterior pituitary
TRH PIH CRH GnRH GHRH GHIH
What are tropic hormones
Hormone that affect the release of other hormones
What hormones are produced by the anterior pituitary gland and what are their functions
TSH - secretion of thyroid hormone from the thyroid gland
ACTH - secretion of cortisol from adrenal cortex
LH - ovulation and secretion of sex hormones
FSH - development of eggs and sperm
PRL - mammary gland development and milk secretion
GH - growth and energy metabolism and stimulates IGFs
What hormone causes the anterior pituitary gland to produce and release TSH
Thyrotropin releasing hormone
What hormone causes the anterior pituitary gland to produce and release ACTH (adrenocorticotropic hormone)
CRH (corticotropin releasing factor)
What hormone causes the anterior pituitary gland to produce and release prolactin (PRL)
Negative control of the prolactin release-inhibiting hormone (PIH)
What hormone causes the anterior pituitary gland to produce and release growth hormone
Growth hormone releasing hormone
Growth hormone inhibiting hormone inhibits
What hormone causes the anterior pituitary gland to produce and release luteinising hormone and follicle stimulating hormone
Gonadotrophin releasing hormone
How are the hypothalamic and anterior pituitary hormones regulated
Negative feedback
What is another name for growth hormone inhibiting hormone
Somatostatin
Why is growth hormone not orally active like thyroid hormone
It is a protein and so it is degraded in the stomach
How does growth hormone give its affect
Either directly or indirectly (through insulin-like growth factors)
Which cells release IGFs
Liver and skeletal muscle cells
What does growth hormone during childhood
stimulates long bone growth by
- stimulating length and width growth before epiphyseal closure
- and width after epiphyseal closure
- IGF stimulates bone and cartilage growth
What do GHs and IGFs do in adults
Help maintain muscle and bone mass
Promote healing and tissue repair
Modulate metabolism
What causes an increase in the production of growth hormone
- deep sleep
- stress (trauma/surgery)
- exercise
- less glucose and fatty acids
- fasting
What causes a decrease in growth hormone secretion
- somatostatin
- rapid eye movement sleep
- glucose and fatty acids
- obesity
How are IGFs involved in the negative feedback loops
mediates long loop
- inhibit GHRH from hypothalamus
- stimulates somatostatin release from anterior pituitary gland
- inhibit GH from anterior pituitary
What mediates the short loops of the growth hormone negative feedback
GH via stimulation of somatostatin release
What does growth hormone deficiency result in
Pituitary dwarfism (proportionate dwarfism)
What is the treatment for pituitary dwarfism
GH therapy - injection of GH produced through recombinant DNA technology
What does growth hormone excess in childhood result in
Gigantism
What does pituitary dwarfism result in
- slow growth rate (below 3rd percentile)
- delayed/no sexual development
What usually causes gigantism
Pituitary adenoma
What des growth hormone excess in adults result in
Acromegaly - large extremities
How does GH have its direct effect on cells
Binds to tyrosine kinase receptors activating Janus kinases (linked to the receptors) which then phosphorylates the receptors and itself to activate the signalling pathways including IGF production
What are the 2 main growth factors and what do they do
IGF2 - involved in fetal growth
IGF1 - major growth hormone in adults
What modulates the activity of IGFs
Binding proteins
What do IGFs modulate
- hypertrophy
- hyperplasia
- increase in protein synthesis
- increase rate of lipolysis in adipose tissue
What other others influence growth
- insulin
- thyroid hormones
- androgens
- estrogens
- glucocorticoids
How is the release/production of prolactin controlled
Prolactin is produced when there is a lack of prolactin inhibiting hormone (e.g. Dopamine). The production is under inhibitory control
