15 Hypothalamic Pituitary Axis and Growth Hormone Flashcards
Where is the Pituitary Gland located?
Beneath Hypothalamus, in sella turcica (=socket of bone)
What are the hypothalamus and pituitary gland a link between?
Endocrine and nervous system
What processes do the hypothalamus and pituitary gland modulate?
1 Body growth 2 Lactation 3 Milk Secretion 4 Reproduction 5 Adrenal Gland function 6 Water homeostasis 7 Puberty 8 Thyroid gland function
What is the structure of the pituitary gland?
Anterior (adenohypophysis) Posterior (neurohypophysis) (Infundibulum= pituitary stalk)
How do the anterior and posterior pituitary glands differ?
1, Distinct embryological origins: Anterior- oral ectoderm Posterior- neuroectoderm= physically connected to hypothalamus 2, Distinct functions
How does the posterior pituitary gland function?
NEUROCRINE FUNCTION 1-Oxytocin and ADH - produced- neurosecretory cells in supraoptic+ paraventricular nuclei of hypothalamus 2- Transported down nerve cell axons 3- Stored and released in posterior pituitary- into general circulation via capillary bed
How does the anterior pituitary function?
1-Hormones-synthesised in hypothalamus- transported down axons- stored in median eminence 2- Hormones released into hypophyseal portal system- stimulate/inhibit endocrine cells in anterior pituitary 3- Endocrine cells secrete hormones into blood stream (hormones in anterior pituitary= also autocrine and paracrine)
What are the functions of the 2 hormones which are produced by the hypothalamus for release in the posterior pituitary?
1- Oxytocin- milk let down+ uterus contractions 2- Anti-Diuretic Hormone- regulation of body water volume
What is a tropic hormone?
A hormone that has a direct effect on the release of ANTERIOR pituitary hormones.
What are the 6 tropic hormones produced in the hypothalamus?
Releasing hormones: 1 TRH: Thyrotropin releasing hormone 2 CRH: Corticotropin releasing hormone 3 GnRH: Gonadotropin releasing hormone 4 GHRH: Growth hormone releasing hormone Inhibiting hormones: 5 GHIH: Growth hormone inhibiting hormone (SOMATOSTATIN) 6 PIH: Prolactin release inhibiting hormone (DOPAMINE)
What do trophic hormones do?
Affect growth
What are the 6 hormones produced by the anterior pituitary?
1- FSH- Follicle stimulating hormone (development- eggs and sperm) 2-LH- Lutenising Hormone (ovulation and secretion- sex hormones) 3- GH- Growth Hormone (stimulates IGFs- growth+energy metabolism) 4-Prolactin (mammary gland development and milk secretion) 5-TSH- Thyroid stimulating hormone 6- ACTH- Adrenocorticotropic hormone (secretion- hormones from adrenal cortex
Outline to negative feedback mechanism of the Hypothalamic-Pituitary- Adrenal Axis.
Stress- e.g. low BP- Hypothalamus- CRH–> anterior pituitary- ACTH–> adrenal cortex-cortisol. Cortisol then has negative feedback on Hypothalamus and Anterior pituitary
What is the main mechanism for growth promotion of Growth Hormones?
IGFs (insulin-like growth factors) (aka Somatomedins)- produced by Liver&Skeletal muscle- response to GH (Actions of IGFs can be endocrine, paracrine or autocrine) (Insulin and IGF1 can have Metabolic and Mitogenic effects)
Why is GH so important in childhood and teenage years?
Stimulates long bone growth (IGFs stimulate bone and cartilage growth)
What do GH and IGFs do in adults?
=Help maintain muscle and bone mass =Promote healing and tissue repair =Modulate metabolism and body composition
How is GH secretion controlled?
CNS-inputs to hypothalamus- affect GHRH and Somatostatin (GHIH)
What causes GH secretion to increase?
- Onset of deep sleep 2. Stress (trauma, surgery, fever) 3, Exercise 4, Decrease in glucose/fatty acids 5, Fasting
What causes GH secretion to decrease?
1, Obesity 2, REM sleep 3, Increase in glucose/fatty acids
What are the two negative feedback loops regulating GH secretion?
LONG LOOP: IGFs - inhibit GHRH release -stimulate GHIH (somatostatin release) therefore inhibits GH release SHORT LOOP: GH -stimulates GHIH (somatostatin) release
What happens if someone has Growth Hormone Deficiency (complete/partial)?
Pituitary dwarfism (proportionate) Growth rate slower than expected- below 3rd percentile Delayed/no sexual development in teenage years
How is GH deficiency treated?
GH therapy (response= good)
What happens if someone has Growth Hormone Excess?
Childhood: Gigantism (rare) Adulthood: Acromegaly (large extremities)
How does GH exert its effects on cells?
GH receptors activate Janus Kinases –> Activate transcription factor–> IGF production
What are the 2 IGFs found in mammals?
IGF1: Mainly involved- fatal growth IGF2: Major GF- in adults
How do IGFs act?
On IGF receptors, modulate: Hypertrophy Hyperplasia Increase protein synthesis rate Increase lipolysis in adipose tissue
Apart from GH, what other hormones influence growth and how? (5)
1, Insulin- interacts w./ IGF receptors 2, Thyroid Hormones- promote CNS development&GH secretion 3, Androgens- accelerate pubertal growth spurt, increase muscle mass, promote closure- epiphyseal plates 4, Estrogens- decrease somatic growth- promote closure- epiphyseal plates 5, Glucocorticoids- inhibit somatic growth
