Hypothalamic pituitary axis Flashcards
FUNCTIONS OF THE HYPOTHALAMUS
5
Homeostatic control of metabolism
food intake, water intake, energy expenditure
Mediation of stress
Control of reproductive behavior and growth
Reproductive cycles, partuition, lactation and love
Control of body temperature
Integration of autonomic and endocrine functions (bringing together the secretory hypothalamus and neural outflows to autonomic endpoints – maintaining homeostasis)
True or false
Hypothalamus integrate the autonomic and endocrine function?
True function of hypothalamus Integration of autonomic and endocrine functions (bringing together the secretory hypothalamus and neural outflows to autonomic endpoints – maintaining homeostasis)
Hypothalamus role in maintaining homeostasis
A reminder about Homeostasis
The role of the secretory hypothalamus –
secretes chemicals (hormones) directly from
the brain into the blood stream and as such can influence
functions (body temp, growth, thirst, lactation etc)
throughout the body
Position of hypothalamus in the brain
Below the thalamus
thin sheet of tissue in the human, approx
3-4mm on either side of the third cerebral
ventricle
Important regions of the hypothalamus
paraventricular nucleus- collection of nerve cell bodies in the brain – composed of magnocellular and parvocellular
supraoptic nucleus
median eminence
paraventricular nucleus
The paraventricular nucleus (PVN, PVA, or PVH) is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary.
one of the most important autonomic control centers in the brain, with neurons playing essential roles in controlling stress, metabolism, growth, reproduction, immune, and other more traditional autonomic functions
The supraoptic nucleus
s a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm
the supraoptic nucleus (SON) contains neurosecretory cells that produce hormones (oxytocin and vasopressin/antidiuretic hormone).
medial hypothalamus
medial hypothalamus centrally governs diverse homeostatic processes, including energy and fluid balance, stress responses, growth, and reproductive behaviors.
- parvocellular
Lateral hypothalamus
The lateral hypothalamus (LH), also called the lateral hypothalamic area (LHA), contains the primary orexinergic nucleus within the hypothalamus that widely projects throughout the nervous system; this system of neurons mediates an array of cognitive and physical processes, such as promoting feeding behavior
From which part of the hypothalamus are the hormones’ released?
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
which areas of the brain is not protected by blood-brain barrier?
Four areas of the brain are not protected by the blood-brain barrier. These areas include the posterior pituitary gland, pineal gland, the median eminence of the hypothalamus and the area postrema.
portal vessel fenestration
Is hypothalamus connected to the pituitary gland ?
Yes
Important structural and functional relationship with the pituitary gland
Hypothalamus is connected to the pituitary gland by a stalk comprised of
nerve fibers and specialized portal vessels – the infundibulum
pituitary gland is divided into the anterior (front) and posterior (back) parts
Anterior pituitary gland secrets hormones to the
called Master gland
THYROID GLAND
ADRENAL GLAND
MAMMARY GLAND
How does the hypothalamus coordinate the release of hormone from the anterior pituitary gland?
Parvocellular neurosecretory cells in the hypothalamus (paraventricular nucleus) produce neuro-hormones (releasing factors) that are released into the vicinity of portal vessels in the median eminence cells, transported to the anterior pituitary where they cause the release of hormones from specialized secretory cells
the hormones released by the parvocellular cells in the hypothalamus are transported via the ….. .
The hypophysiotropic hormones released are transported via …. to the anterior pituitary gland.
Axon
Blood
what is the release factor of Follicle stimulating hormone
Gonadotropin releasing hormone (GnRH) —> Gonadotroph—-> Follicle stimulating hormone
Luteinising hormone —–> function Gonads / Reproduction
what is the release factor of Thyroid stimulating hormone
Thyrotropin releasing hormone (TRH) –> Thyrotrophs –> Thyroid stimulating hormone and Luteinising hormone
—> Thyroid / Development and energy expenditure
what is the release factor of Adrenocorticotropic hormone
Corticotropin releasing hormone (CRH)–> Corticotrophs –>Adrenocorticotropic hormone –> Adrenal / Stress
Growth Hormone Releasing Growth hormone
Growth Hormone Releasing Hormone (GHRH) –> Somatotrophs –> Growth hormone —> Widespread anabolic actions
Pathways of stress hormones - an example of anterior pituitary function (in addition to “fight or flight”)
stress whether it be phsychological, emotional or physiological is detected in the brain and leads to the release of corticotropin releasing hormone (CRH) from nerve fibres originating from neurons in the paraventricular nucleus of the hypothalamus
transported via the portal system to the anterior pituitary where it acts on corticotrophs causing release of adrenocorticotropic hormone (ACTH) which acts on the
cortex of the adrenal gland causing the release of cortisol
cortisol when released into the blood stream acts throughout the body to mobilise energy stores and suppress the immune system
Control of sex hormones by the hypothalamus and pituitary
Gonadotropin releasing hormone (GnRH) is produced in neurons of the preoptic area of the hypothalamus
GnRH activity is pulsatile and under the feedback control of a number of hormones as well as light stimuli signifying day length
GnRH is released into the portal system to act on “gonadotrophs” in the anterior pituitary causing the release of follicle stimulating hormone(FSH) and luteinising hormone (LH) which act on both the ovaries and testes
in males to produce testosterone and sperm; in females to cause estrogen release – cyclic release of LH and FSH menstrual cycle
Which neurons produce Gonadotropin releasing hormone ?
Neurons in Preoptic area of hypothalamus
follicle stimulating and luteinizing hormone
in males to produce testosterone and sperm; in females to cause estrogen release – cyclic release of LH and FSH menstrual cycle
Posterior pituitary function
- the control of vasopressin and oxytocin release (produced in magnocellular neurons in the hypothalamus)
Vasopressin
Vasopressin known as antidiuretic hormone. It’s ahormonemade by the hypothalamus in the brain and stored in the posterior pituitary gland. It tells your kidneys how much water to conserve.ADHconstantly regulates and balances the amount of water in your blood. Released in response to dehydration (change of tonicity, increase in concentration of the blood, increase in osmolarity and changes in plasmodium) and hemorrhage (reduction in blood volume) which is recorded by the receptors in kidney and release of angiotonin ll. These changes is recorded by the osmoreceptors neurons in the OVLT and that information in then transferred to magnocelluar in the hypothalamus down their axons to the posterior pituitary
Release of Vasopressin
released in response to
1-dehydration (Changes in tonicity) detected by the osmoreceptor in the OVLT
2- Hemorrhage (Reduction in blood volume) detected by the Cardiac volume receptors and release of angiotensin Il
1. Vasopressin to kidneys to change urine output)
Oxytocin release
- Suckling of newborn babies, crying from mothers own or even unrelated babies
Oxytocin to breasts to release milk – uterus to cause contractions at term
Where are these hormones and releasing factors produced in the hypothalamus?
Individual nuclei within the hypothalamus are responsible for specific functions
Vasopressin /oxytocin
(magnocellular neurons)
Corticotropin releasing hormone (CRH) Thyrotropin releasing hormone (TRH) Oxytocin / vasopressin (parvocellular neurons) Oxytocin / vasopressin is also produced by the parvocellular neurons however they only act as a neurotransmitter in the brain and it’s not released form postpitutatry
The role of oxytocin…..new insights
What’s love got to do with it?
When prairie voles mate, two posterior pituitary hormones, oxytocin and vasopressin, are released. If the release of these hormones is blocked, prairie-voles’ sex becomes a fleeting affair, similar to that normally enjoyed by their montane cousins
Oxytocin and love
Oxytocin released into the brain (from parvocellular oxytocin-containing neurons) of the female during sexual activity is important for forming a monogamous pair bond with her sexual partner. Vasopressin appears to have a similar effect in males
Other studies have shown that differences within individual prairie voles can be correlated with their level of parenting and monogomous behavior – implications for human behavior
Oxytocin can activate reward pathways in the brain, which then release dopamine. Such neurotransmitters are so heavily concentrated in these reward pathways in the ventral pallidum after mating that are likely to lead to the conditioning of partner preference formation.
Role of oxytocin released from the magnocellular cell
Magnocellular release (into the bloodstream) Oxytocin, been best known for its roles in female reproduction. It is released in large amounts during labor, and after suckling. It is a facilitator for childbirth and breastfeeding. It is a stimulant widely employed to induce or augment labor, especially at term, when adequate oxytocin receptors are present
Integration of autonomic and endocrine functions
Integration of endocrine and autonomic functions is centred in the paraventricular nucleus of the hypothalamus (PVN)
