Oxytocin and ADH Flashcards
What is the difference between OT and AVP?
Two different AA side chains
Where are both AVP and OT synthesized?
Supraoptic nucleus (mainly AVP) Paraventricular nucleus (mainly OT)
How is OT transported?
Created in the paraventricular nucleus and sent in vesicles down the magnocellular axon to the posterior pituitary
When does OT have a burst in males?
At ejaculation to produce contractions for sperm release
Mechanism which OT binds and causes smooth muscle contraction?
OT bind OTR-> GPCR-> IP3 (Ca channels open) and DAG-> Prostaglandin (PGF2a)-> uterine and smooth muscle contraction
What is the Ferguson reflex?
- ) Head of baby pushes against cervix
- ) Nerve impulses from cervix transmitter to brain
- ) Brain stimulates release of oxytocin (hypothalamus)
- ) Oxytocin carried in bloodstream to uterus
- ) Oxytocin simulates uterine contractions and pushes baby towards cervix
What is the secretory unit of the breast?
The alveolus
What surrounds the alveolus of the breast?
Myoepithelial cells
What does OT cause contraction of to cause the let down reflex?
Myoepithelial cells
Characteristics of the four stages of labor:
0: Uterine tranquility and refractoriness
1: Uterine awakening, extending to complete cervical dilation
2: Active labor, from complete cervical dilation to delivery of newborn
3: From delivery of fetus to expulsion of placenta
What physiologically is occurring during each of the four stages of labor?
0: Progesterone and relaxin promote inactivity
1: Estrogens increase OT receptors by 80x at 36 weeks
2: Oxytocin, prostaglandins, estrogen increases OT receptors 200X during early labor
3: Oxytocin increases especially in last stage of labor
What effect does estrogen have in the OT cycle?
It up regulates OT
What affect does progestogens have in the OT cycle?
Decreases response of smooth muscle from OT
How does suckling cause OT release?
Suckling stimulates PRL release by removing the inhibition of DA
How does suckling affect the menstrual cycle?
GnRH is inhibited by suckling reducing LH and FSH release inhibiting the ovarian menstrual cycle
When is relaxin released and what are its affects?
It is released during pregnancy to keep the uterus in a quiet state also during labor in the cervix to dilate it
What is the half-life of OT?
3-6 minutes
Where is ADH mainly produced?
Supraoptic nucleus
What is ADH produced as?
A preprohormone
What does the preprohormone of ADH consist of?
Signal peptide
ADH
Neurophysin II
What causes the most cases of hereditary hypothalamic diabetes insipidus?
A point mutation in neurophysin II
What is neurophysin II?
A carrier of ADH
What is the primary signal for secretion of ADH?
An increase in ECF osmolality
What inhibits ADH release?
High fluid volume or blood pressure
What transports AVP from hypothalamus to neurohypophysis?
Magnocellular neurons
What are the receptors for AVP?
V2R in the renal collecting duct
Sequence of events for AVP action in renal tubules?
- ) ADH binds V2R
- ) Activates PKA
- ) Phosphorylation of CREB stimulates transcription of mRNA to produce more AQP2
What is the threshold at which ADH can be released?
When osmolality increases as little as 1% from 280 mEq/L
ADH is also released when blood volume is decreased by what percent and what senses this?
Reduced by 10% by baroreceptors in the atria
ADH half-life:
18 minutes
What breaks down ADH and what can occur in this organ failure?
Kidneys and Liver
Failure in these organs can lead to high ADH levels
In pregnancy, what hormone causes the changes in osmolarity and volume?
Relaxin
What occurs to ADH in aging adults?
The kidneys become less sensitive to nocturnal plasma levels of ADH
Two types of diabetes insipidus:
Central
Nephrogenic
What causes central DI?
Failure of AVP secretion
What causes nephrogenic DI?
Kidneys not adequately responding to ADH levels
What is the differential diagnosis following water deprivation in DI?
Central: decreased plasma ADH low urine osmolality
Nephrogenic: increased plasma ADH extremely low urine osmolality
What does SIADH stand for?
Syndrome of inappropriate ADH secretion
What is SIADh essentially?
The opposite of DI
What occurs in SIADH?
Secretion of inappropriately high levels of ADH
What is the sign of SIADH?
Any urine with greater than 100 Osm with hyponatremia is SIADH
Why is urine Na osmolality so high in SIADH?
Because the volume expansion causes a release of ANP increasing natriuresis
Treatment of SIADH?
Fluid restriction
Drug treatment of SIADH?
V2 receptor antagonists: Conivaptan and Tolvaptan
