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Physiology 1021 Study Guide - Final Guide: Supraoptic Nucleus, Plasma Osmolality, Circumventricular Organs

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John Ciriello
Study Guide

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The Hypothalamus and the Limbic System
Functions of the Posterior Pituitary
-Involved in the release of two hormones: Oxytocin and Vasopressin (Anti-Diarrhetic
-Posterior Pituitary is actually part of the brain. Is made up of the axon terminals
neurons found in two parts of the Hypothalamus; the Paraventicular nucleus and
Supraoptic nucleus
-Paraventicular nucleus and Supraoptic nucleus contain neurons which produce
Vasopressin and Oxytocin
-These hormones are carried down the axon where it is released directly into the blood
stream at the posterior pertuitary
-Very important
in a lactating body (critical for milk let
-The pathway for Oxytocin is very
-This does not exist in
males and does not
always exist in
-When a
stimuli is applied to the nipple and
afferent neuron which through pathways through the spinal chord to the thalamus, which

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gets relayed to the Hypothalamus, then gets relayed to the Paraventicular and
Supraoptic nucleus.
-Once there that stimulus activates Oxytocin producing neurons
-As soon as those neurons are activated they produce more oxytocin
-And as it produces more Oxytocin it is carried down via the axons into the posterior
Pituitary where it is released into the blood stream and through the blood stream works
at the breast.
-This causes contraction of Myoepithelial cells which allows for milk let down
*This is and example of a Neural-Endocrine Reflex (see image above)
Unique Properties of Oxytocin
-Once suckling of the breast is induced the first time we see a rise in Oxytocin
production. The second time the level of Oxytocin rises even higher.
-Once Oxytocin is released into the blood stream, the Oxytocin comes back and works
on Oxytocin producing neurons. Therefore the next time the same stimulus is applied,
the number of action potentials rises. For the same stim more AP. More Oxytocin = more
milk let down OR if you are about to give birth Oxytocin neurons also respond to inter-
uterine pressure (contractions). More Oxytocin = Stronger Contractions
Oxytocin are Suckling of the Breast and Inter-Uterine Pressure
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