Flashcards in 4. The HPA Axis And Growth Hormone Deck (17):
Where is the pituitary in relation to the hypothalamus?
- the pituitary gland sits beneath the hypothalamus in a socket of bone called the sella turcica
What connects the hypothalamus and posterior pituitary?
Where do the anterior and posterior pituitary originate?
-anterior pituitary (adenohypophysis): Rathke's pouch , primitive gut tissue
-posterior pituitary (neurohypophysis) : originates from neuroectoderm, primitive brain tissue
Which 2 hormones are secreted by the posterior pituitary?
Oxytocin - milk let down, and uterus contractions after birth
Antidiuretic hormone - regulation of body water volume
They are produced by the supraoptic and paraventricular nuclei of the hypothalamus. Then transported down nerve cell axons to the posterior pituitary and release from there
Where are hormones destined for the anterior pituitary stored?
The hormones are synthesised in the hypothalamus and travel down the axons and are stored in the median eminence before release into the hypophyseal portal system.
What are the tropic hormones of the hypothalamus?
- tropic hormones affect the release of other hormones in the target tissue
-6 tropic hormones produced in the hypothalamus and these have direct effects on the release of anterior pituitary hormones.
1. TRH - thyrotropin releasing hormone
2. PRH - prolactin releasing hormone
3. PIH - prolactin release inhibiting hormone (dopamine)
4. CRH - corticotropin releasing hormone
5. GnRH - Gonadotrophin releasing hormone
6. GHRH - growth hormone releasing hormone
7. GHIH - growth hormone inhibiting hormone (somatostatin)
What are the hormones produced by the anterior pituitary?
Mnemonic GOAT FLAP (not the OA that's for posterior)
1. GH: Growth hormone
2. TSH: Thyroid stimulating hormone
3. FSH : follicle stimulating hormone
4. LH: lutenizing hormone
5. ACTH: Adrenocorticotropic hormone
6. PRL: prolactin
What are the roles of the anterior pituitary hormones?
GH: growth, energy metabolism and stimulates IGFs
TSH: secretion of thyroid hormone from the thyroid gland
FSH: development of eggs and sperm
LH: ovulation and secretion of sex hormones
ACTH: secretion of hormones from adrenal cortex
PRL: mammary gland development and milk secretion
What factors influence growth?
-hormones - growth hormone most important
What stimulates and what inhibits growth hormone?
- stimulated by hypothalamic GHRH
-inhibited by hypothalamic Somatostatin
The growth promoting effects are mainly exerted indirectly via insulin like growth factors (somatomedins). In response to GH, the cells of the liver and skeletal muscle produce and secrete IGFs
What is growth hormone essential for?
- normal growth - stimulates long bone growth
-IGFs stimulate bone and cartilage growth
-in adults GH and IGFs help maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and body composition
How is GH secretion controlled?
- principal control is via the hypothalamus
-GHRH - increase in GH secretion
-somatostatin - decrease in GH secretion
When do you get surges in GH?
-deep sleep (decrease in R.E.M. Sleep)
-stress - trauma, surgery, fever
-decrease in glucose or fatty acids (increase leads to reduced GH)
-fasting (obesity decreased GH secretion)
Explain long and short loop negative feedback with respect to GH?
- long loop is mediated by IGF (somatomedin) to the hypothalamus which inhibits GHRH and stimulates somatostatin which will inhibit GH from the anterior pituitary
-short loop is mediated by GH itself via stimulation of somatostatin release
Which receptor does GH use?
- GH receptors (tyrosine kinases) activate Janus Kinases (JAKs)
-activation of signalling pathways
-transcription factor activation and IGF production
Where are IGF1 and IGF2 found and what is their function?
- IGF2 mainly involved in fetal growth
-IGF1 major growth factor in adults
Act through IGF receptors to modulate hypertrophy, hyperplasia, protein synthesis and lipolysis