4 Flashcards
When does the size of the pituitary increase?
during pregnancy
what is the turkish saddle?
“Turkish saddle”, defines a superior depression of the. sphenoid bone where the pituitary gland sits. The sella turcica originally
how is the location of the optic chiasm and pituitary connected?
pituitary is located behind the optic chiasm
What are the components of the Hypothalamo-hypophyseal tract?
Hypothalamo-hypophyseal tract is derived from two different ectodermal components:
1) Oral part- Rathke’s pouch: outgrowth of the buccal cavity detaches itself and becomes the ANTERIOR pituitary
2) Neural part- The infundibulum develops from an outgrowth of the neuroectoderm from the floor of the third ventricle. It gives rise to the pituitary stalk, the median eminence and the POSTERIOR pituitary.
hypothalamus organized into discrete __
hypothalamus organized into discrete nuclei
What are the nuclei of the hypothalamus?
a group of similarly functioning neurones
Does anterior pituitary contain many blood vessels?
anterior pituitary is highly vascularized: capillary bed in anterior pituitary is connected to capillary bed in median eminence through portal veins
What is the median eminence
The median eminence is a part of the hypothalamus from which regulatory hormones are released. It is integral to the hypophyseal portal system, which connects the hypothalamus with the pituitary gland
The median eminence is the structure where secretions of the hypothalamus (releasing and inhibiting regulatory hormones, known as “hypophysiotropic hormones”) collect before entering the portal system emptying into the general circulation.
Where are releasing factors released to by the hypothalamus?
Releasing factors are secreted into median eminence that go to pituitary
What is the purpose of the retrograde flow?
Retrograde flow of blood allows for –ve feedback from pit. to hypothalamus
some black gets pushed back to hypothalamus so hypothalamic releasing factors can have an impact on the hypothalamus
What is a nerve plexus
A nerve plexus is a plexus (branching network) of intersecting nerves
The peptides released at the median eminence enter __
The peptides released at the median eminence enter the primary plexus capillaries
anterior vs posterior pituitary in terms of scretions
The anterior pituitary receives signalling molecules from the hypothalamus, and in response, synthesizes and secretes seven hormones. The posterior pituitary does not produce any hormones of its own; instead, it stores and secretes two hormones made in the hypothalamus.
Describe the blood supply of median eminence
Blood coming from the capillary plexus of the median eminence is carried into a capillary bed in the anterior pituitary by long portal veins.
__ are secreted into median eminence that go to __
Releasing factors are secreted into median eminence that go to pituitary
What and where is released by axon terminals of hypothalamic neurones
Axon terminals of hypothalamic neurons release hypophysiotropic hormones in the area of the median eminence
What is the blood vessel that carriers hypothalamic hormones to the anterior pituitary?
portal vein
What is the blood vessels that transport anterior pituitary hormones to the central blood flow?
The pituitary hormones enter the blood stream via the venous capillaries
Where can the receptors for hypothalamic releasing factors be found?
Primarily in pituitary, but can also be found through out the body
their role is unknown
what is posterior pituitary made up of?
Posterior pituitary is composed of the nerve ending (axons) of neurons whose cell bodies are located in the hypothalamus
How are hormones of posterior pituitary made/released?
the nerve ending of hypothalamic hormones that make up the posterior pituitary release hormones into circulation that go out directly to the general circulation
aka from posterior pituitary to circulation
- Hormones (oxytocin and vasopressin) are produced in the cell bodies, packaged into granules which migrate to the ends of the axons located in the posterior pituitary
- Stimulation of neurons in the hypothalamus triggers the release of the hormones from the axon tips located in the posterior pituitary
- The hormones are taken up by capillaries and enter the blood stream
neurotransmitters vs hormones
neurotransmitters go from one neurone to other, hormones go from neurones into circulation
What are the roles of SON and PVH
supra optic nucleus and paraventricular nucleus release oxytocin and vasopressin directly into the circulation in posterior pituitary
What are projection neurones?
projection neurones are neurones that connect one neurone to the other
hypothalamus has both projection and neurosecretory neruoens
What are the 3 main classes of hypothalamic neurones? and their locations
Magnicellular Neuron-Location: SON, PVH
Parvicellular Hyposeotropic Neurone. Location: PeVH, PVH, Arc
Hyptohalamic Projection Neuron: PVH, LHA, Arc
describe Magnicellular Neuron
Magnocellular neurons (MCN) are neuroendocrine cells located in the hypothalamus; they are among the largest cells in the brain,
major nuclei- supra optic (SON) nucleus and paraventricular nucleus (PVH)
release oxytocin and vasopressin directly into the circulation
these are peptide hormones-> stored in vessicles
receive their names due to anatomical position
these neurones are large compared to other neurones to in NS
Kidney, uterus, Mammary gland
describe Parvicellular Hyposeotropic Neurone
Parvicellular neurones- produce releasing/trophic hormones; spread amongst various nuclei- located around the 3rd ventricle
PVH, PeVH, arcuate nucleus (Arc)
Smaller in size
their granules are only observed in axonal endings
Nerve endings go to the anterior pituitary-> trophic hormones are released by the associated nuclei using this neuron
describe Hyptohalamic Projection Neuron
hypothalamic projection neurones are neurones that connect one neurone to the other
hypothalamus has both projection and neurosecretory neurones
Location: PVH, LHA, Arc
Which cell’s morphology does pituitary’s morphology resemble? What does that mean?
morphology of pituitary cells resembles any of those, who produce a lot of proteins- a lot of ER
thus pituitary cells are peptide producing cells
What are functions/structures of posterior vs anterior pituitary?
posterior pituitary- collection of axons-> releases hormones made in the hypothalamus
anterior pituitary-> receiving inhibiting or stimulating factors from median eminence-> produces hormones itself
What are the 2 divisions found in paraventricular nucleus? WHat are the major hormones released by each?
Magnicellular- Oxytocin, vasopressin
Parvicellular- corticotropin releasing hormone (CRH), TRH, vasopressin
WHat are the major hormones released by arcuate nucleus (Arc)?
GnRH, GHRH, Melanocortins, prolactin, somatostatin
Where does hypothalamus receive signals from?
hypothalamus receives sensory inputs from:
- the external environment (e.g., light, nociception, temperature, odorants) and
- internal environment (e.g., blood pressure, blood osmolality, blood glucose and hormone levels)
Where does hypothalamus send signals to?
anterior pituitary gland, posterior pituitary gland, cerebral cortex, premotor and motor neurons in the brainstem and spinal cord, and parasympathetic and sympathetic preganglionic neurons
Define what are Circumventricular organs (CVOs)?
Circumventricular organs (CVOs) are structures in the brain characterized by their extensive and highly permeable capillaries, unlike those in the rest of the brain where there exists a blood–brain barrier (BBB) at the capillary level - Exposed to hormones, metabolites and toxins
Name Circumventricular organs (CVOs)
- organum vasculosum of the lamina terminalis (OVLT)
- Subfornical organ (SFO)
- Median eminence (ME)
- Subcommissural organ (SCO)
- Area postrema (AP)
Describe Supraoptic and paraventricular nuclei:
- Named after the location of the cell bodies of the neurons
- Large neurons (120-200 nm diameter)
- Neuron are specific, producing mainly oxytocin or vasopressin
- The hormone granules are visible and can be observed traveling down the axons (8 mm/h)
- axons end in the pituitary
describe Hypothalamic-hypophysiotropic nuclei
Hypothalamic-hypophysiotropic nuclei (PeVH, PVH, Arc)
- Located near the wall of the third ventricle
vSmaller neurons, hormone granules can only be observed in the axon terminal
vNerves terminate in the external layer of the median eminence near the primary plexus
__ pituitary receives blood from media eminence
anterior
__ pituitary is the collection of hypothalamic nerve endings
posterior
What are the 5 types of cells in the anterior pituitary
- corticotroph
- thyrotroph
- gonadotroph
- somatotroph
- lactotroph
what are the products and targets of corticotroph
ACTH
b-lipotropin
Target: adrenal gland, adipocytes, melanocytes
what are the products and targets of thyrotroph
TSH
Target: thyroid gland
what are the products and targets of gonadotroph
LH, FSH
Target: gonads
what are the products and targets of somatotroph
GH
Target: all tissues. liver
what are the products and targets of lactotroph
PRL
Target: breast gonads
Name basophils and acidophils of the anterior pituitary + their products
Basophils:
Thyrotropes →TSH
Gonadotropes → LH or FSH
Corticotropes→ACTH
Acidophils:
Somatotropes →GH
Lactotropes→ PRL
Major functions of TRH
Stimulates the release fo TSH and PRL;
minor stimulation of FSH release
Major functions of GnRH
stimulates the release of LH and FSH
Major functions of GHRH
stimulates the release of GH
Major functions of SMS
inhibits the release of GH; also gastrin, VIP, glucagon, insulin, TSH and PRL
Major functions of CRH
stimulates the release of ACTH
Major functions of dopamine
inhibits the release of PRL
What is the half-life of hypothalamic hormones affecting the anterior pituitary. How is it related to the time of action?
releasing factors have Short half-life in circulation and fast action as they need to act before they decompose
What kind of hormones are the hormones of the anterior pituitary
peptide
How does feedback control happens in terms of hypothalamic hormones affecting the anterior pituitary
Some feedback control through modulation of receptor numbers
increased amount of releasing factor-> less receptors
What is the signalling method for the hypothalamic hormones affecting the anterior pituitary
Post-receptor intracellular signaling by G-proteins
- Trophic hormones: Gs⍺ and Gq⍺ proteins.
- Inhibitory hormones: Somatostatin and dopamine act via Gi⍺ and other mechanisms.
Gq⍺ leads to __
Gq leads to Ca+ release
Gs⍺ leads to __
GS leads to cyclic AMP and adenylyl cyclase
action of trophic hormones is dependent on the __
action of trophic hormones is dependent on the renewal of the stimulus
Why is the renewal of stimulus important in trophic hormone signalling?
when there’s high number of releasing factors, the number of receptors goes down and the signalling goes down
in order to get more signalling, more stimulus should also occur- this is achieved by the short life and the fact that releasing factors are released in pulses
What is SCN?
The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms- circadian pacemaker (“clock”) that controls many physiological functions including pineal
the proteins of SCN are expressed at certain times- have their own clock- this clock can be regulated by light and melatonin (external hormone to SCN)
What kind of receptors can be found in SCN? WHat are the consequences?
SCN has melatonin Receptors – light and melatonin can reset the clock (other minor factors such as temperature)
Apart from having melatonin receptors, how else is SCN and melatonin connected?
SCN can also regulate the production of melatonin
How fast does SCN affect the pineal gland, why?
this action of SCN on the pineal gland takes a lot of time- due to long neurones chains of projection neurones (one neurone leading to other and to the other)
How is adrenergic receptors connected with the pineal gland?
The adrenergic receptors are the mainstay receptors of pineal gland function. They form the bridge between the circadian controlled release of melatonin production of the pineal gland. which is in part controlled by SCN
what kind of receptor is adrenergic receptor?
g-protein
Which gland secretes melatonin/ When
pineal
melatonin secretion is the highest during darkness, peaking at 12pm, when we are asleep
goes down with the light, when we wake up
What is the precursor for melatonin
melatonin is made of tryptophan
How do humans sense the level of light
humans have no photoreceptors, but a direct nervous connection form SCN to the pineal gland
photoreceptors within the retina can lead to SCN which than sends signals to the pineal gland
how do melatonin levels change with age?
decrease with age
Where are melatonin receptors found. What would that suggest?
not only in SCN, but also throughout the body
thus melatonin affect more than just the circadian rhythm in SCN
what are some of the melatonin’s functions?
May entrain body’s biological rhythms to the dark-light cycle eg. Core body temperature
- Induction of sleep
- Depression of reproductive activity, inhibition of ovulation and semen production in some animals –questionable role in humans
- Seasonal fluctuations may affect the timing of breeding, migration and hibernation in mammals
Adverse side effects of melatonin
- Daytime sleepiness and Hypothermia
- Desensitization of melatonin receptors if doses too high
- Possible adverse events in those with seizure disorders
- Possible interaction with those taking coumadin/warfarin
Describe the structure of anterior pituitary hormones
anterior pituitary hormones are peptide hormones; can be made from one chain or 2 separate protein chains coming from 2 different genes
Name single peptide chain anterior pituitary hormones
single chain hormones are GH, prolactin and ACTH
Name 2 peptide chain anterior pituitary hormones and describe their structure
gonadotropins , LH and FSH are made of 2 protein chains of which alpha chain is common for all 3
each of these 3 have a specific beta chain
alpha and beta chains are made from different genes
PVH’s neurons
magnicellular neuron
parvicellular hypophysiotropic neuron
hypothalamic projection neuron
Arc’s neurons
parvicellular hypophysiotropic neuron
hypothalamic projection neuron
