Hypothalamic pituitary axis and growth hormone Flashcards
What is the hypothalamic pituitary axis?
a functional unit that links the endocrine and nervous system (hypothalamus and pituitary)
What is the sella turcica?
A socket of bone below the hypothalamus where the pituitary gland sits
What is the Infundibulum?
The pituitary stalk that physically connects the hypothalamus with the posterior pituitary
List a few processes that is regulated by the hypothalamic pituitary axis
- Body growth
- Reproduction
- Adrenal gland function
- Milk secretion
- Lactation
- Water homeostasis
What are the two parts of the pituitary gland and where to they originate from?
1) Anterior (adenohypophysis) = evagination of oral ectoderm (Rathke’s pouch)
2) Posterior (neurohypophysis) = neuroectoderm
Describe the function of the posterior pituitary gland
Stores and releases oxytocin and ADH (synthesised in supraoptic and paraventricular nuclei of the hypothalamus)
Describe the function of the anterior pituitary gland
Produces and secretes 6 hormones that is stimulated (or inhibited) by tropic hormones from the hypothalamus
Describe how the tropic hormones from the hypothalamus stimulate/inhibit the target endocrine cells of the anterior pituitary
- transported down to the median eminence
- released to the hypophyseal portal system (blood supply)
Oxytocin (effect and where its produced/secreted)
- Milk let down and uterus contraction in birth
- Produced in the hypothalamus; secreted from posterior pituitary
ADH/Vasopressin (effect and where its produced/secreted)
- Regulates body water volume
- Produced in the hypothalamus; secreted from posterior pituitary
TRH (effect and where its produced/secreted)
- Tropic
- Thyroid releasing hormone
- Produced and released from hypothalamus
PIH/Dopamine (effect and where its produced/secreted)
- Tropic
- Prolactin release-inhibiting hormone
- Produced and released from the hypothalamus
CRH (effect and where its produced/secreted)
- Tropic
- Corticotropin releasing hormone
- Produced and released from hypothalamus
GnRH (effect and where its produced/secreted)
- Tropic
- Gonadotropin releasing hormone
- Produced and released from hypothalamus
GHRH (effect and where its produced/secreted)
- Tropic
- Growth hormone releasing hormone
- Produced and released from hypothalamus
GHIH/Somatostatin (effect and where its produced/secreted)
- Tropic
- Growth hormone-inhibiting hormone
- Produced and released from hypothalamus
TSH (effect and where its produced/secreted)
- Thyroid stimulating hormone
- Produced and released from anterior pituitary
ACTH (effect and where its produced/secreted)
- Adrenocorticotropic hormone
- Secretion of hormones from adrenal cortex
- Produced and released from anterior pituitary
LH (effect and where its produced/secreted)
- Lutenising hormone
- Ovulation and secretion of sex hormones
- Produced and released from anterior pituitary
FSH (effect and where its produced/secreted)
- Follicle stimulating hormone
- Development of eggs and sperm
- Produced and released from anterior pituitary
PRL (effect and where its produced/secreted)
- Prolactin
- Mammary gland development and milk secretion
- Produced and released from anterior pituitary
GH (effect and where its produced/secreted)
- Growth hormone
- Growth and energy metabolism and stimulates IGFs
- Produced and released from anterior pituitary
What mechanism are the hormones of the hypothalamic pituitary axis regulated?
Negative feedback loop
What are the effects of GH in childhood and teenage years?
- Stimulates long bone growth
- IGFs stimulate both bone and cartilage growth
What are the effects of GH in adults?
- Maintain muscle and bone mass
- Promote healing and tissue repair
- Modulating metabolism and body composition
How is the production and release of GH regulated
- GHRH stimulates release
- GHIH/Somatostatin inhibits release
- Long loop negative feedback = mediated by IGFs
- Short loop = mediated by GH itself
List a few factors that INCREASES GH secretion
- After onset of deep sleep
- Exercise
- Decrease in glucose or fatty acids
- Fasting
- Stress
List a few factors that DECREASES GH secretion
- REM sleep
- Increase in glucose or fatty acids
- Obesity
Describe growth hormone deficiency
- Growth rated in childhood slower than expected for age
- No sexual development in teen years
- Leads to pituitary dwarfism
- Height is below 3rd percentile on standard growth charts
Describe growth hormone excess
- Leads to gigantism (from childhood)
- Rare, often caused by Pituitary adenoma
- Leads to acromegaly (large extremities -> hands, feet, lower jaw)
Describe the mechanism of how GH brings on its effect
1) Growth hormone binds to Growth hormone receptor
2) GH receptor activates Janus kinase (similar to tyrosine kinase)
3) Cross phosphorylation of JAK
4) Phosphorylation of GH receptor
5) Activates signalling pathway
6) Transcription factors activated and IGF produced
What is IGF?
- Insulin growth receptors
- Bind to IGF receptors and modulate: hypertrophy, hyperplasia, protein synthesis and lipolysis
What are the 2 IGFs in mammals and which period are they normally needed?
- IGF2 = mainly in fetal growth
- IGF1 = major growth factor in adults
What other hormones influence growth and what are their effects?
- Insulin = enhances somatic growth; interacts with IGF receptors
- Thyroid hormone = Promote CNS development and enhances GH secretion
- Androgens = Accelerate pubertal growth spurt; increase muscle mass
- Oestrogen = Decrease somatic growth; promote closure of epiphyseal plates
- Glucocorticoids = Inhibit somatic growth
