MECH 430 Lecture Notes - Lecture 7: Posterior Pituitary, Paraventricular Nucleus Of Hypothalamus, Myoepithelial Cell
9 Jun 2018
School
Department
Course
Professor
Lecture 6
➢ Hormones of the posterior pituitary
• Cell bodies of the hypothalamic neurons
synthesize oxytocin or vasopressin. The
hormones are translocated down to the
axon terminus, located in the posterior
pituitary. When those neuron bodies are
stimulated, they release their contents
directly into the posterior pituitary to get
carried away by the bloodstream.
➢ Hormone secretion
o Hypothalamic nuclei
▪ hormone production
▪ extend axons to posterior pituitary gland
▪ specific nuclei produce specific hormone
• oxytocin (OT)
• vasopressin/ADH
▪ Specific localization of nuclei within the
specific region of hypothalamus
• Supraoptic (ADH)
• Paraventricular (OT)
o A certain amount is secreted via electrical stimulation,
but when you stimulate the neuron, it allows the
release to the posterior pituitary while also stimulating synthesis of these hormones to replace the
hormones.
➢ Posterior Pituitary Hormones
o Nonapeptide
▪ Composed of 9 amino acids
• formation of ring via disulfide bridge
• highly conserved amino acid sequences
o pigs have lysine-vasopressin instead arginine-
vasopressin
• structurally similar
o completely different function in terms of
physiological responses
o They are similar in structure, except for
position 3 and position 8.
➢ Hormones of the posterior pituitary
o oxytocin: contraction of smooth muscle cells:
▪ myoepithelial cells of the alveoli → alveoli of the breast
▪ smooth muscle cells of the uterus during labour assisting the birthing process
▪ in 3D, OT and ADH are very different and interact with different receptors
o vasopressin (antidiuretic hormone, arginine vasopressin) → 2 kinds of effects
find more resources at oneclass.com
find more resources at oneclass.com
▪ ➔ H20 retention by the kidney
▪ ➔ contraction of blood vessels (arterioles)
➢ Vasopressin (AVP/AVT) = antidiuretic hormone (ADH)
o various different names, which are related to the 2 physiological system
o Names derived from 2 physiologic systems regulated (osmotic and pressure/volume)
o Different inputs to regulate + different receptors used
o Synthesis & secretion
▪ Two systems
• Osmotic
• Pressure-volume
o Action
▪ different receptors are localized in different areas and have different functions
▪ stimulates the insertion of aquaporins, allowing for the conservation of water
o Function
▪ Water retaining hormone in mammals and along with thirst is the primary regulator of
osmolarity
▪ Regulation of osmolarity → involves osmostat
• Control/conservation of water → simple relationship
• By regulating water, you are also regulating sodium concentrations (complicated)
▪ Regulation of Na concentrations in plasma
• Pressure-volume changes – involves baroreceptors & invokes the RAS and
aldosterone
• Different system – renin-angiotensin system
and aldosterone
• Complicated
➢ Regulation of osmolarity
o Osmoreceptors located in the hypothalamus detect osmotic
changes in blood plasma
o Osmotat responds to a little as 1% change in osmolarity
o i.e. cell expands when blood too dilute or contract when
blood too concentrated
find more resources at oneclass.com
find more resources at oneclass.com
▪ contraction sends neural signal to supraoptic nuclei to release vasopressin
o a mechanism to detect the osmolarity of our blood is needed
o there are receptor cells located in the hypothalamus, which respond to changes in osmolarity of
the blood.
o The cell will expand or contract according to the osmolarity of the extracellular fluid (hypertonic
or hypotonic environment).
o When the blood is concentrated, contraction of cells —> sends neural signal to supraoptic nuclei,
which results in the release of vasopressin.
o changes in extracellular fluid (ECF) osmolarity modulate homeostatic responses that affect the
Na+ balance (left) & the water balance (right) to promote homeostasis according to the principle
of negative feedback
o hypertonic and hypotonic conditions lead to proportional changes in the intake or excretion of
water & sodium to maintain ECF osmolarity near a constant set-point
o hypertonicity → concentrated urine
o vasopressin acts on the kidneys to reduce urine volume to reabsorb water (concentrated urine)
➢ Vanilloid Receptor –Related Osmotically Activated Channel (VR-OAC), a candidate
osmoreceptor
o Isotonic: balanced with water in and water out
o Hypotonic: net flow of water is into the cell (cell expands)
o Hypertonic: net flow of water is out of the cell (cell shrinks)
o Receptor is membrane bound, but the intracellular domain is linked to the cytoskeleton. As the
cell expands or contracts, it pulls against the cytoskeleton itself. The conformation of the
receptor is thus changed, which results in the opening or closing of the channel (pore loop).
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Hormones of the posterior pituitary: cell bodies of the hypothalamic neurons synthesize oxytocin or vasopressin. The hormones are translocated down to the axon terminus, located in the posterior pituitary. When those neuron bodies are stimulated, they release their contents directly into the posterior pituitary to get carried away by the bloodstream. As the cell expands or contracts, it pulls against the cytoskeleton itself. The conformation of the receptor is thus changed, which results in the opening or closing of the channel (pore loop). G(alpha)s, dissociating from its complex, activating adenylyl cyclase, cleaving camp from atp. Pka: pka activates aquaporin pores to be inserted to the luminal side. Thirst: replacement of water in the body, urine production. Plasma and urine osmolarity and vasopressin: within a physiological range, thirst is not stimulated. So, as our osmolarity increases, thirst is not stimulated until we get above a certain set- point (blue area).
