Name the 3 systems of the Hypothalamus-Pituitary (Hypophysis) Axis (H-P Axis).
- Hypophysiotropic System: hormones made in the hypothalamus that act on the Anterior Pituitary (AP).
- Neurohypophysis System: hormones made in neuronal cell bodies the hypothalamus, sent down axons and released from the Posterior Pituitary (Peepee) into circulation
- Adenohypophysis System: hormones made in the AP and released into circulation
Which two hormones receive both positive and negative feedback from the hypothalamus?
Prolactin: Prolactin Releasing Hormone (PRL) and Dopamine (DA)
Growth Hormone: Growth Hormone releasing Hormone (GHRH) and Growth Hormone Inhibitory Hormone (GHIH)
What are neurophysins?
Considered pro-hormones for the neurohypophysis. Neurophysin-1 is a carrier protein for oxytocin and Neurophysin-2 is a carrier protein for ADH. Both of these carrier proteins are cleaved just before the hormones are released into the blood from the PP.
Describe the signaling pathway of ADH when it binds to collecting duct cells in the nephron along with its genomic and non-genomic functions
- ADH binds a Gs protein coupled receptor
- G protein is activated and signals Adenylyl cyclase
- Adenylyl cyclase converts ATP into cAMP
- cAMP activates protein kinase A (PKA)
Genomic: PKA phosphorylates the transcription factor CREB in the nucleus. Then transcription of the Aquaporin 2 (Aq2) receptor gene occurs and Aq2 protein channels are made
Non-genomic: PKA also activates microtubules that will carry the newly made Aq2 channels to the cell membrane
Describe the signaling pathway that oxytocin induces when it binds to smooth muscle cells.
- Oxytocin binds Gq protein coupled receptor
- G protein activates Phospholipase C (PLC)
- PLC converts PIP2 into DAG and IP3
- DAG and IP3 first inactivate PKA and then signal calcium release from the sarcoplasmic reticulum
- The calcium singlas more calcium to come into the cell from the extracellular space AND binds calmodulin.
- The calcium calmodulin complex activates myosin light chain kinase (MLCK)
- MLCK phosphorylates myosin allowing it to bind actin causing the cross bridge cycling and muscle contraction
General function of Growth Hormone (GH)
Raise blood glucose
-also inhibits release of GHRH from hypothalamus
Main functions of Insulin-like Growth Factor (IGF-1)
Responds to GH. IGF-1 causes the glucose that was released into the blood by GH to be taken up into cells for growth and proliferation. It also inhibits GH release AND GHRH release.
Describe the signaling pathway that Growth Hormone Induces when it binds any cell, both genomic and non-genomic effects.
- GH binds JAK-STAT receptor
- There are two JAK (Janis Kinase) proteins attached to the recepotr that phosphorylate each other, dimerize, and then phosphorylate the actual receptor where GH is bound.
- The JAK proteins then phosphorylate the STAT (Signal Transducer and Activator of Transcription) proteins.
Genomic: The STAT proteins (as the name implies) then travel to the nucleus and activate transcription factors to induce transcription
Non-genomic: STAT also signals PI-3-Kinase to block glucose channels preventing glucose uptake from cells
Signaling mode of Thyroid Stimulating Hormone
Gs
What is POMC?
Pro-opiomelanocortin: huge protein that is broken down to:
- Adrenocorticotropic Hormone (ACTH)
- melanocyte stimulating hormones (alpha and beta MSH)
- beta lipotropin
Main hormone secreted by the pineal gland.
Melatonin: created from Trp, main function is in the circadian rhythm and possibly antioxidant function.
