Transcript Posterior Pituitary & Pineal Glands

Posterior Pituitary Gland
The Pineal Gland
Description of Glands: The pituitary
 The pituitary gland has dimensions of about 12mm by
8mm in an average adult.
 There are three major divisions in the gland and they
are the anterior lobe, the posterior lobe, and the
neurophysis. (we will focus on the posterior lobe)
 Despite its name, the pituitary gland is not actually a
gland, but is a large collection of axonal projections
from the hypothalamus that end behind the anterior
pituitary gland.
Description of Glands: The pineal
 The pineal actually isn’t a gland, but it is a
neuroendocrine transducer which means that it
converts incoming nerve impulses into outgoing
hormones
 The pineal gland is small weighing slightly more than
one gram
 It is microscopically made of pinealocytes which are
supporting cells
 It releases hormones in response to biotechnical
messages from outside the body the information is
received through the eyes.
Where are the glands Located?
 The pituitary Gland is in the hyposophyseal fossa of
the sphenoid and is connected to the hypothalamus by
the infundibulum.
 The Pineal gland is located deep within the brain
between the two cerebral hemispheres, above the third
ventricle of the spinal cord
Hormones produced
 The posterior pituitary gland produces two hormones:
antidiuretic hormone also known as vasopressin, and
Oxytocin
 The pineal Gland produces only one hormone called
Melatonin.
Hormones cont’d
 The pineal gland also contains numerous polypeptides
such as vasotocin, GnRH, and TRH and
neurotransmitters like somatostatin, noerpinephrine,
seretonin and histamine
 Melatonin is a protein hormone
 Both Oxytocin and Vasopressing (ADH) are protein
hormones consisting of 9 amino acids
Target Cells for each hormone
 Antidiuretic hormone affects the kidneys, and the
vascular system. It binds to the cells in the collecting
duct of the kidney
 Oxytocin targets the smooth muscle (myoepithelial)
cells in the mammary aveoli, and also the smooth
muscles in the uterus when a woman is giving birth.
 Oxytocin also affects the brain – it is found in the
cerebrospinal fluid in high concentrations after a
woman has had her baby.
 Melatonin can penetrate any cell in the body
Effects of ADH on Target cells
 The antidiuretic hormone affects the kidneys by
binding to the receptors on cells in the collecting
ducts of the kidney and promotes reabsorbtion of
water back into the circulation.
 It stimulates water reabsorbtion by stimulating
insertion of aquaporins into the membranes of the
kidney tubules
 The aquaporins transport solute-free water through
tubular cells and then back into the blood which
causes a decrease in plasma osmolarity and an increase
in osmolarity of urine.
Effects of Oxytocin on target cells
 Oxytocin stimulates the milk letdown in the
mammary glands because it stimulates the contraction
of the myoepithelial cells causing milk o be ejected
into the ducts.
 It also stimulates contractions in a woman when giving
birth.
 Lastly, oxytocin stimulates the establishment of
maternal behaviour after the baby is born.
Effects of Melatonin on the target
cells
 Melatonin secretion is enhanced when the
sympathetic nervous system is stimulated.
 In children, it acts to keep a child’s body from
becoming sexually mature.
 It appears to play a role in regulating sleeping cycles
(higher levels of melatonin are found in young
children which accounts for their increased need for
sleep)
Triggers/Controls for the hormone
production
 The main variable in the controls/triggers of ADH is the plasma
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osmolarity (concentration of solutes in blood) which is detected
by the osmoreceptors (neurons connected to blood vessels)
which relay into the hypothalamus
If there is a high concentration of solutes, ADH is produced and
secreted out of neurons in the bloodstream
If the concentration is low, ADH is suppressed because the
osmoreceptors are no longer active
This allows the body to regulate the amount of water in the body
Other variables which affect the triggers or controls of ADH are
blood pressure, volume of blood (censored by stretch receptors
in the heart, which are not as sensitive of a control as the
osmolarity )
Triggers/Controls cont’d
 Oxytocin is triggered by nervous stimulation of the
hypothalamus, or mechanoreceptors in the uterus and
vagina during parturition
 When a baby suckles on its mothers nipple the release of
oxytocin is triggered and when there is distension in the
cervix.
 The pineal gland releases melatonin when there is little
light entering the eyes, it is secreted from serotonin which
is obtained from the amino acid tryptophan
 There are two melatonin receptors called Me|1a and Me|1b
which are found in high densities in the retina, anterior
pituitary and hypothalamus
Complications due to
damage/malfunction of the gland
 A cause of overproduction of ADH in the posterior pituitary
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gland is a brain tumour.
If there is an overproduction of ADH in the posterior pituitary
gland it can lead to water retention serum hypo-osmolarity,
hypoatramic, and high urine osmolarity.
A cause of ADH underproduction can be cause by head trauma,
pituitary tumours, or surgery that damaged the hypothalamus or
pituitary
If there is an underproduction it may lead to excretions of large
volumes of urine (causing dehydration and thirst) and an
increased plasma osmolarity.
There have been no known issues involving an overproduction of
oxytocin however, it has been found that children that do not
produce any oxytocin due to a tumour in the pineal gland, reach
sexual maturity at a younger age than normal children.
Complications continued
 In mammals, if there is a lesion or non existent pineal
gland, it means that the animals cannot detect the
proportions of day and night, and therefore they
cannot tell what season it is and therefore do not know
when to hibernate or when to breed
 In humans a non functioning pineal gland would
cause a person to have less trouble when switching
time zones changing job shifts but it may increase
their risk of insomnia, and their biological rhythms
and patterns may be off.