L4- Posterior Pituitary and HPL Axis Flashcards
How large are AVP and OXY?
nonapeptides (9 amino acids) —> relatively short half-life
What is the co-peptide for AVP and OXY?
AVP: neurophysin II
OXY: neurophysin I
What is another name for AVP?
ADH
Cell bodies that produce AVP are located in which two hypothalamic nuclei?
Paraventricular (PVN) and supraoptic (SON)
PVN has two types of cells: magnocellular and parvocellular. Which cell types project to the posterior pituitary?
Only magnocellular neurons project to the posterior pituitary
Where do parvocellular neurons project to?
Parvocellular PVN neurons that contain AVP project to the median eminence and other brain regions. They are important for regulating mood (anxiety/stress)
AVP in magnocellular SON and PVN are important for maintaining what?
Fluid balance
What two factors stimulate the release of AVP from the PVN and SON of the hypothalamus into the posterior pituitary?
Increase in plasma osmolality and decrease in blood volume (blood loss greater than 10%)
Small changes in plasma osmolality triggers AVP release prior to thirst
Decrease in blood volume sensitizes the system
How does the sympathetic innervation affect AVP release?
AVP is mediated by an increase in sympathetic inputs, which releases magnocellular neuronal inhibition
How does AVP cause vasoconstriction?
AVP binds the V1 receptor in vascular smooth muscle cells producing contraction and increasing vascular resistance
V1 receptor is a G-protein coupled receptor and acts through IP3/DAG and phosphorylates myosin light chain kinase
How does AVP lead to reabsorption of water?
The principle function of AVP is to increase water reabsorption and conserve water.
AVP binds to V2 receptors in the principle cells of the distal tubule. PKA activation phosphorylates the water channel Aquaporin 2 which is then inserted in the membrane and allows increased water permeability.
What is the definition of diabetes?
Excessive urine production
What are the two etiologies of diabetes insipidus?
1) Decreased AVP release - most common defect
Hypothalamic or pituitary defect due to trauma, cancer, or infectious disease
2) Decreased renal responsiveness to AVP
Genetic: X-linked mutation in AVP type-2 receptor (90% males)
Acquired: lithium treatment, hypokalemia
Are AVP levels increased, decreased or normal in people with Diabetes Insipidus?
Normal
Oxytocin is released by magnocellular neurons whose cell bodies are located in what hypothalamic nucleus?
PVN
What is the main function of OXY?
Induce smooth muscle cell contraction in the breast and uterus.
Describe the feedback regulation of OXY
OXY release is regulated by positive feedback loops
Describe the chain of events from binding of OXY to its receptor to smooth muscle contraction
OXY binds to G protein-coupled receptors and activates PLC signaling pathways which increases intracellular calcium —> —-> phosphorylation of myosin light chain by MLCK
Remember; myosin is the “switch” in the initiation of smooth muscle contraction
How large is GHRH?
44 amino acids- large
GHRH (growth hormone releasing hormone) is produced in what hypothalamic nucleus?
Arcuate nucleus
What is the role of GHRH?
Stimulate growth hormone from the anterior pituitary
What is the role of growth hormone?
Growth hormone increases muscle mass and decreases fat –> promotes lean mass growth