Anterior, Intermediate, and Posterior Pituitary Flashcards
What differentiates a tropic hormone from a trophic hormone?
Tropic: stimulates a specific target gland to secrete a different set of hormones
Trophic: Affects the growth, nutrition, or function of another endocrine gland/cell
What 3 components make up a pre-prohormone?
- Signal peptide
- Hormone
- Cryptic peptide
What components make up a prohormone? What was lost from the pre-prohormone?
Prohormones have hormone and cryptic peptide components, the signal peptide has been cleaved from the pre-prohormone.
Where is the cryptic peptide cleaved off a prohormone, producing the mature hormone?
At dibasic Lysine/Arginine sites.
What is the full name for POMC?
Pro-opiomelanocortin.
Which lobes of the pituitary express pro-opiomelanocortin (POMC)?
The anterior lobe and the intermediate lobe, but not the posterior lobe.
What POMC product is produced in the intermediate pituitary? What enzyme cleaves POMC to produce this?
Melanocyte stimulating hormone (MSH). Produced from the cleavage of POMC by prohormone convertase 2 (PC2).
What POMC product is produced in the anterior pituitary? What enzyme cleaves POMC to produce this?
Adrenocorticotropic hormone (ACTH). Produced from the cleavage of POMC by prohormone convertase 1 (PC1).
What product of POMC cleavage in the pituitary is also produced in the skin? What does this stimulate?
Melanocyte stimulating hormone (MSH) is also produced in the skin and stimulates the production of melanin for skin pigmentation.
What major endocrine function is controlled by the secretion of adrenocorticotropic hormone (ACTH) (Hint: tropic effect)?
Steroid secretion (glucocorticoids, mineralocorticoids, androgens) from the adrenal cortex.
What kind of receptors do POMC cleavage products bind to?
Melanocortin G-protein coupled receptors (GPCRs).
What trophic effect can ACTH have on the adrenal cortex?
Crucial for the development of the adrenal cortex.
When a melanocortin (POMC product) binds a GPCR, what kind of Galpha subtype is activated? What does this stimulate?
Galpha-s. Activates adenylyl cyclase (AC) to stimulate protein kinase A (PKA).
What is the function of the melanocytes in mammals? How are they stimulated?
Stimulated by melanocyte stimulating hormone (MSH), they release melanin which protects skin cells from UV radiation damage.
What is the function of the melanophores in amphibian or aquatic organisms? What stimulates this?
Stimulated by melanophore releasing hormone (MSH), they release pigment used for adaptive colour change/camouflage.
How do radiotrophic fungi use melanin?
As a photosynthetic pigment which allows them to absorb gamma rays just as plants absorb sunlight for energy.
How do microbes use melanin?
As protection from high temperature and chemical stresses.
Besides production of melanin or pigment in the skin, what other role does melanocyte stimulating hormone (MSH) have?
Contributes to appetite regulation/suppression in the hypothalamus.
How does the mechanism of stimulation by the hypothalamus differ for the anterior pituitary and the posterior pituitary?
Ant. Pit.: signalled by the arrival or hormones along the hypophyseal portal veins
Pos. Pit.: signalled by hormone-containing neurons which project from the hypothalamus
What other names are often used to refer to vasopressin (VP)?
Arginine vasopressin (AVP) or antidiuretic hormone (ADH).
How are vasopressin and oxytocin related?
They share structural homology except in 2 positions where the amino acids are different.
What are the 2 main functions of vasopressin?
- Osmoregulation (water balance)
2. Pressure regulation (vasoconstriction).
What are the 3 main functions of oxytocin in women?
- Uterine contraction
- Milk ejection
- Mother-offspring bonding
In what way is oxytocin released from the posterior pituitary?
Secreted in pulses.
