Hypothalamic Pituitary Axis Flashcards
What are names for the anterior and posterior pituitary?
Anterior: pars distalis, adenohypophysis
Posterior: pars nervosa, neurohypophysis
What are trophic hormones?
Hormones that stimulate the production of hormones from the anterior pituitary
What is the relationship between the hypothalamus and posterior pituitary?
NEUROENDOCRINE: Cell bodies are based in the hypothalamus which is where hormones are synthesized, and axons extend down infundibulum and terminate in the posterior pituitary.
What is the difference between the paraventricular nucleus and the supraoptic nucleus?
Both produced in the hypothalamus, but…
paraventricular: secretes oxytocin (OT)
supraoptic: secretes vasopressin (AVP/ADH)
What are neurophysins? What is the Neurohypophysis?
Neurophysin: Precursor peptides of OT and ADH produced in the hypothalamus
Neurohypophysis: nerve terminals for the secretion vesicles containing neurophysins and proteolytic enzymes
How is AVP/ADH released?
- Reduced extracellular fluid volume results in increased plasma osmolality, which triggers vasopressin release
- Reduced extracellular fluid volume results in decrease in left atrial volume, which results in low arterial blood pressure, which triggers vasopressin release
What does AVP/ADH do?
Increases H2O reabsorption in renal tubules and vasoconstriction of vascular smooth muscle to maintain blood pressure.
When is oxytocin released?
Birth canal distension and infant suckling induces positive feedback, triggering oxytocin release
What does oxytocin do?
Increase uterine muscle contraction during birth and milk ejection from mammary gland
How does oxytocin influence behaviour?
- Increases maternal behaviour in presence of estrogen
- Released during sexual arousal in both sexes
- Acts as neuromodulators to influence social recognition, memory, and affiliative behaviours
How does AVP influence behaviour?
- Stimulates release of ACTH (regulates cortisol and androgen production)
- Plays a greater role in males in social recognition and memory
- Aggression, courtship, scent marking, and learning
How does anterior pituitary hormone make it to the blood?
Neurosecretory neurons in hypothalamus secrete into the hypothalamic-hypophysial portal system into the anterior pituitary and either captures them in vesicles for storage or releases them into veins.
What are examples of anterior pituitary cells and the hormones they make?
Corticotroph: ACTH
Thyrotroph: TSH
Gonadotroph: FSH, LH
Lactotroph: PRL (acidophile)
Somatotroph: GH (acidophile)
What are hypophysiotrophic hormones?
Hormones that can regulate hypophyseal hormones (secreted by anterior pituitary) via stimulation or inhibition.
Includes TRH (regulates TSH), CRH (regulates ACTH), GnRH (regulates FSH, LH), GRHR (regulates GH).
What is the pathway for TSH?
TRH stimulates release of TSH from anterior pituitary which travels to thyroid gland and promotes release T3 and T4 which alters metabolic rate
What is the pathway for ACTH?
CRH stimulates release of ACTH from anterior pituitary which travels to adrenal cortex and promotes release of cortisol which alters metabolic actions
What is the pathway for growth hormone?
GRHR stimulates release of growth hormone from anterior pituitary which travels to…
- Liver, influence release of somatomedins that affect bone and soft tissue’
- many other tissues and promotes or inhibits metabolic actions
What is the pathway for LH and FSH?
GnHr stimulates release of LH and FSH from anterior pituitary. LH and FSH go to gonads (ovaries/testes) and induces production of sex hormones (estrogen, progesterone, testosterone) and gamete production.