Hypothalamus and Pituitary Gland Flashcards
describe generally the HPA axis
Generally a stimulus will cause the Hypothalamus
to secrete a hormone
This will cause the pituitary to secrete a hormone
This will act on a target organ which may or may
not secrete another hormone
The final hormone produced will cause an effect
what is the pituitary gland composed of
anterior
posterior
what is the anterior lobe of the pituitary derived from
Anterior derived from the upward migration from the roof of the mouth called the Rathke’s pouch
what is the posterior lobe of the pituitary derived from
Posterior derived from the downward migration of the neuroectoderm from the diencephalon.
what lobe of the pituitary is directly connected to the hypothalamus
posterior via the infindubulum
what hormones does the anterior pituitary release
Thyroid Stimulating Hormone (TSH)
Prolactin (PRL)
Growth Hormone (GH)
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)
Adrenocorticotropic hormone (ACTH)
what hormones from the hypothalamus stimulate the hormones in the anterior pituitary
Thyroid Releasing Hormone (TRH) → TSH - this causes the adrenals to produce T4 and T3 ( I inhibited by SS)
Nipple suckling → PRL - this causes milk glands immunosystem (inhibited by dopamine)
Growth Hormone Releasing Hormone (GHRH) → GH (inhibited by SS)
Gonadotrophin Releasing Hormone (GnRH) and kisspeptin → FSH - this causes sex steroids, inhibin, ovulation, spermatogenesis
Gonadotrophin Releasing Hormone (GnRH) and kisspeptin → LH - this causes sex steroids, inhibin, ovulation, spermatogenesis
Corticotrophin Releasing Hormone (CRH) → ACTH - this produces cortisol in the adrenals
what does the posterior pituitary hormone release
ADH
oxytocin
where are the posterior pituitary hormones produced
- they are produced in the hypothalamus
- ADH in the supraoptic nuclei
- oxytocin in the paraventricular nuclei
describe the blood supply to the pituitary
- supplied by the superior hypophyseal artery
anterior pituitary
- superior hypophyseal artery goes and forms a primary plexus
- this goes down via hypophyseal portal veins
- this goes into a secondary plexus where the hormones are secreted into the blood
posterior pituitary
- this is attached to the anterior pituitary via short blood vessels, therefore posterior pituitary can influence the anterior pituitary
what is negative feedback
Thyroid Releasing Hormone (TRH) → TSH
Nipple suckling → PRL
Growth Hormone Releasing Hormone (GHRH) → GH
Gonadotrophin Releasing Hormone (GnRH) → FSH
Gonadotrophin Releasing Hormone (GnRH) → LH
Corticotrophin Releasing Hormone (CRH) → ACTH
what happens if too much hormone is produced
If too much hormone is produce by the target
organ, this causes inhibition of pituitary and
hypothalamus hormone
what happens if too little hormone is produced
If too little hormone is produced by the target
organ, this stimulates the hypothalamus to
produce its hormone which in turn will stimulate
the pituitary and so on.
Describe how G protein works
- on a G protein alpha subunit is attached to a gamma and beta subunit
- when the ligament binds to the G protein this causes it to become phosphorylated so GDP is converted to GTP
- this causes the alpha subunit to detach
- alpha subunit then binds to adenyl cycle
- this causes ATP to convert to cAMP
- this increases the activity of PKA
- this causes the cell response
- after the ligand leaves GTP is converted back to GDP this causes alpha subunit to bind to the gamma and beta subunit again
what does ADH do
- increase the number of aquaporins in the collecting duct s
- this increases the amount of water reabsorption
- works via a G protein
which artery do the hypophyseal arteries branch from
internal carotid artery
what inhibits prolactin
Dopamine
What does prolactin inhibit
GnRH
what two hormones does somatostatin inhibit
GH
TSH
why is there an increase in TSH in hypothyrosdim
- due to negative feedback
- there is low T3/T4 this stimulates the production of TSH
the stimulus of nipple sucking causes the production of which two hormones
oxytocin and prolactin
Which hormone stimulates the production of GnRH
Kisspeptin
what is the final hormone that is produced to stimulate growth
IGF-1
how do the posterior pituitary organs cause their effect on their target organs
Neurones
what does the hypothalamus regulate
- Pituitary function
- Feeding (appetite and satiety)
- Stress response
- Water balance
- Sleep-wake cycle
- Thermoregulation
- Emotions
Name some nuclei of the hypothalamus
- paraventricular
- anterior
- Supraoptic
- Dorsomedial
- Ventromedial
- Arcuate
- Posterior
- Mamillary body
what does the pituitary gland sit in
Sella turicia
what happens when the pituitary has a tumour to the eyesight
can get a bitemporal hemianopia
what is a bitemproal hemianopia
Bitemporal hemianopia = loss of vision in the outer halves of both eyes.
what is the drug used to replace ADH
Desmopressin
describe how the thyroid axis works
- hypothalamus produces TRH
- TRH activates the anterior pituitary gland to produce TSH
- TSH causes the production of thyroxine in the adrenal gland
- thyroxine(T4) casques liothyroonine(T3) to be produced
- when thyroxine increases beyond a certain level this inhibits TRH and TSH
what is primary under activity
this is when the target hormone doesn’t get produces so causes an increase in the hypothalamus stimulatory hormone and an increase in the pituitary hormone that is being produced
what is secondary under activity
this is when the pituitary hormone does release its releasing hormone
- this results in a decrease in the hormone being released by the target hormone
- therefore resulting in a increase in hypothalamus stimulatory hormone
what is primary overactivity
- this is when there is a tumour at the target organ, this causes an increase in the target hormone
- this would cause a decrease in the pituitary hormone and hypothalamus stimulating hormone
what is secondary overactivity
- this is when there is an tumour on the pituitary gland
- causes increase in pituitary hormone which causes an increase in the target hormone
- this causes a decrease in the hypothalamus stimulatory hormone
describe how the GH axis works
GH is stimulated by GHRH, and ghrelin.
Ghrelin also stimulates GHRH.
- GH activates SS production
- when SS is too high it inhibits GH production
GH stimulates IGF production in the liver.
IGF inhibits GH and GHRH via negative feedback.
IGF also stimulates SS to reduce GH levels by activating SS
what is the role of GnRH
- promote GH cell clusters for coordinated responses
- increases GH cell number
- increases GH synthesis
- stimulates GH release
what causes McCunae-Albright syndrome
Caused by spontaneous mutation. ( R201 mutation)
– not inherited
= mosaic mutation - this means that not all the cells have the mutation
Prevents downregulation of cAMP via GPCRs.
what are the symptoms of McCunae-albright syndrome
hyper-functioning endocrine organs (goitre),
- precocious puberty
- hyperthyroid gotire
- adrenal hyperplasia
- somatotroph hyperplasia
bone deformities
Café-
au-lait skin pigmentation.
describe how the adrenal axis works
CRH and ADH stimulate ACTH.
ACTH stimulates cortisol release from the adrenal glands.
Cortisol inhibits CRH, ADH and ACTH all via negative feedback.
describe how the HPA axis works
- hypothalamus relates CRH and arginine vasopressin
- CRH stimulates ACTH production
- A little part of arginine-vasopressin causes ACTH production
- ACTH is in the pituitary gland
- ACTH causes production of cortisol in the adrenal gland
- when cortisol rises too much it causes the inhibition of CRH, ACTH, Arginine vasopressin
if there is
- too much cortisol
- too little cortisol
what is caused
- Too much = Cushings
- too little = Addisons
describe how the circadian rhythm is linked to cortisol
Cortisol levels start to rise at about 3 am.
Cortisol levels peak in the morning between 6-9 am.
After this the levels start to decline throughout the whole day.
what are the two types of Cushing syndrome
- ACTH independent
- ACTH dependent
describe ACTH independent cushings syndrome
- ACTH levels are not being primarily impacted.
- Issue with the axis lies downstream of the pituitary gland.
- Adrenal tumour may be the cause or steroid use
- Cortisol levels are raised.
describe ACTH dependent Cushing syndrome
- ACTH levels are being raised primarily.
- Issue due to a pituitary defect, such as an adenoma.
- Both ACTH and cortisol levels are increased.
what are the symptoms of Cushing syndrome
- Weight gain.
- Muscle weakness.
- Skin changes.
describe how Addisons disease is caused
Decreased levels of cortisol,
lack of adrenal gland steroid production.
describe the gonadal axis
Kisspeptin stimulates GnRH in the hypothalamus.
GnRH stimulates LH and FSH in the pituitary glands.
Oestrogen and testosterone are then produced in the gonads.
Oestrogen and testosterone inhibit kisspeptin and LH/FSH via negative feedback.
- they inhibit LH and FSH by inhibin
what happens if there is continuous GnRH drive
Receptor desnsitisation – used therapeutically when gonadal axis needs to be inhibited
• Prostate cancer
• Breast cancer
what is the function of oxytocin
• Social recognition
– “love hormone” • Pro-sociality
– For and maintain attachment bonds with others • Perceptual selectivity/social salience
– intranasal oxytocin increases gaze to the eye region
what does absence of ADH cause
- diabetes insipidus symtpoms - massive thirst - polyuria - nocutira - greater than 12 litres a day
How does the prolactin axis works
Prolactin is stimulated by nipple sucking and also TRH. Dopamine inhibits PRL release. Prolactin inhibits GnRH to reduce LH/FSH secretion. Prolactin matures mammary glands and helps produce milk.
What is the transcription factor PUOF1 responsive for
- development of TSH, GH, PRL
what does a mutation in PUOF1 cause
Severe dwarfism
