Feb 13th Flashcards
General Mechanism of Hormonal Action
- Hypothalamic Neuroendocrine Cells release Hormone 1 into the blood vessels leading to the anterior pituitary.
- Anterior Pituitary Cells respond by secreting Hormone 2 into general circulation.
- Hormone 2 acts on:
Endocrine target tissues → Stimulates the release of Hormone 3.
Non-endocrine target tissues → Directly triggers physiological effects. - Hormone 3 (if released) enters general circulation and further regulates tissue responses.
- Tissue Response → Leads to the desired biological effect (e.g., metabolism, growth, stress response).
How is the pituitary gland connected to the hypothalamus?
Through the infundibulum (stalk).
What protects the pituitary gland?
Bone (sella turcica of the sphenoid bone).
What are the two parts of the pituitary gland?
- Anterior pituitary (adenohypophysis) – endocrine gland.
- Posterior pituitary (neurohypophysis) – extension of neural tissue.
What is the difference between the anterior and posterior pituitary?
- Anterior pituitary produces & releases hormones.
- Posterior pituitary stores & releases hormones made by the hypothalamus.
Dopamine (PIH – Prolactin Inhibiting Hormone)
Inhibits secretion of prolactin (PRL).
Prolactin Releasing Hormone (PRH)
Stimulates release of prolactin (PRL).
Thyrotropin-Releasing Hormone (TRH)
Stimulates secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary.
Corticotropin-Releasing Hormone (CRH)
Regulates secretion of adrenocorticotropic hormone (ACTH), which influences cortisol production.
Somatostatin (GHIH – Growth Hormone Inhibiting Hormone)
Inhibits secretion of growth hormone (GH).
Growth Hormone-Releasing Hormone (GHRH)
Stimulates secretion of growth hormone (GH).
Gonadotropin-Releasing Hormone (GnRH)
Regulates secretion of luteinizing hormone (LH) & follicle-stimulating hormone (FSH), which control reproductive functions.
CRH
- in the Hypothalamic-anterior pituitary-adrenal
cortex axis - corticotropin releasing hormone (from the hypothalamus)
ACTH
-in the Hypothalamic-anterior pituitary-adrenal
cortex axis
-adrenocorticotropic hormone (from the anterior pituitary)
cortisol
- in the Hypothalamic-anterior pituitary-adrenal
cortex axis - glucocorticoid, chronic stress hormone
Where is CRH synthesized?
In the paraventricular nucleus (PVN) of the hypothalamus.
What stimulates CRH production?
Noradrenergic signaling, which increases pre-proCRH gene & protein expression.
How is CRH synthesized?
- Pre-proCRH gene → 196 AA precursor
- Processed to active CRH (41 AA)
- Released pulsatilely into circulation
What inhibits CRH release?
Cortisol (negative feedback loop) inhibits both CRH release & gene expression.
Where is CRH produced?
In the parvocellular neuroendocrine cells of the paraventricular nucleus (PVN) of the hypothalamus.
Where is CRH released?
At the median eminence into blood vessels of the hypothalamic-pituitary portal system.
What does CRH stimulate in the anterior pituitary?
Corticotropes, which secrete ACTH.
What is the main function of ACTH?
ACTH stimulates the adrenal cortex to produce cortisol, which regulates metabolism and the stress response.
What is ACTH derived from?
Pro-opiomelanocortin (POMC).