Neuroendocrine regulation and pituitary Flashcards
Overview of neuroendocrine regulation
Hypothalamus secretes stimulating factors (on) or inhibiting factors (off) which act on the anterior and posterior pituitary gland
Pituitary gland secretes trophic factors/hormones which act on gonads, thyroid and adrenal. These release primary hormones into circulation that target tissues
How does hypothalamus act on the pituitary gland
Synapses with the posterior pituitary gland and releases adh and oxytocin
Causes the anterior pituitary gland (by release of regulatory hormones) to release primary hormones including GH and prolactin (during pregnancy makes mammary glands develop milk ducts)
The anterior pituitary gland targets endocrine glands
Where is the hypothalamus located
at the base brain
What does the hypothalamus use the pituitary gland as
output organ
Hypo to posterior
Hypothalamus has modified neurosecretory cells, modified nerve endings which release ADH directly into circulation and act on the posterior pituitary gland
Hypo to anterior and
Hypo releases trophic hormone into median eminence and the Hypothalamo-pituitary portal vessel to anterior pituitary
Blood flow 1 direction, only hypo signals to anterior pituitary
Means small amounts of hormone needed to bring about response in anterior
Anterior v vascularised- easily secrete hormones into blood
Hypothalamic nuclei
have diverse functions Areas for neuroendocrine control: paraventricular nucleus (oxytocin release- lactation) Supraoptic (vasopressin/release) Arcuate nucleus and periventricular zone (neuroendocrine control)
Cells in the periventricular zone
They are suprachiasmatic neurones- receive retinal innervation and synchronize circadian rhythms (based on daylight). Light/dark cycle drives neuroendocrine signals
Send output to sympathetic and parasympathetic output neurones in spinal cord to control activity of ANS
Neurosecretory cells
responsible for release of regulatory hormones to control pituitary gland
Hypo regulatory hormones: releasing/stimulating factors
CRF- corticotropin releasing factors TRH- thyrotropin releasing hormone GHRH- growth hormone releasing hormone GnRH- gonadotropin releasing hormone PRF- prolactin releasing factor
Hypo regulatory hormones: Inhibiting factors
GHIH- growth hormone inhibiting hormone
PIH- prolactin inhibiting hormone
MSH-IH- melanocyte stimulating hormone inhibiting hormone
Anatomy of pituitary gland
Different sorts of tissues
Pars nervosa- posterior, nerve like
Pars distalis- anterior, has secretory vesicles with hormones
Pars intermedia in the middle, has neither anterior nor posterior, releases MSH
Anterior pituitary hormones, four trophic hormones
Thyroid Stimulating hormone
AdrenoCorticoTrophic Hormone
Follicle Stimulating Hormone
Lutenizing hormone
Anterior pituitary hormones: two primary hormones
Growth Hormone
PRoLactin
caps intentional
GnRH from hypo triggers release of
LH, FSH from pituitary
Which acts on testes, ovary
TRH
TSH
Thyroid
CRF
ACTH
adrenal
GHRH
GH (somatotropin)
multiple tissues
SRIF
GH
multiple tissues
PRF and PIH
Prolactin
Breast
Negative feedback control
In loops
Hormone released from endocrine gland switches off its own production and feeds back onto anterior pituitary- inhibits release of pituitary hormones
Pituitary hormones feed back onto anterior pituitary and hypothalamus to switch off production of hormones
hypo- releasing hormone- AP-Pituitary hormone- endocrine gland- hormone
Effects of growth hormone (somatotropin,/somatotrophin)
Incr cell size, number and differentiation
Stimulate proteinsynthesis
incr bone growth
Stimulate fat utilization (breakdown)
Alter carbohydrate metabolism (growth requires energy, release of glucose)
GH main role
Regulator of post natal growth
GH acts at … and how?
receptor tyrosine kinase
Binds, triggers phosphorylation of TK residues inside the cell, activates kinase cascade (activation of MAP kinases etc)
Effects of GH on proteinsynthesis
First GH acts on liver to bring about production of somatomedins (insulin-like growth factors)
GH and somatmedins act on the nucleus to incr transcription, and acts on ribosomes to incr translation. They also incr uptake of amino acids via transporters into the cell- building blocks
Overall incr PS
Somatomedins
small proteins produced by the liver in response to GH
At least 4 produced- somatomedin C most important
Long half life vs GH (20h vs <20 mins)
GH released in response to
GHRH
Release of GH decr by
GHIH or somatostatin
GH secretion control
GHIH and GHRH released from ventromedial hypothalamus
GH regulated by short feedback loop
What factors is GH controlled by
sleep, exercise, stress
somatomedins feed back onto
GHIH production positively
GHRH production negatively
Deficit of GH
dwarfism, may be:
- anterior pituitary dysfunction
- GH deficit
- normal GH by hereditary somatomedin deficit
Accelerated ageing- loss of GH after adolescence
- decr PS
Excess GH
Gigantism- early life pituitary tumour
Acromegaly- pituitary tumour after adolescence
Acromegaly
excess production GH Most affects middle aged Premature death Slow onset so freq incorrectly diagnosed Most common symptoms are abnormal growth of hands and feet
Acromegaly: treatment
Aim to reduce GH production:
- surgical removal of tumour
drug therapy: octrotide and lanreotide (somatostatin analogues), bromocriptine
-Radiation therapy
Daily Pattern of GH release
Surge overnight
Shows circadian rhythm
GH secretion is episodic
in bursts
surge at birth, puberty
Stable at adulthood
Decline in old age
insulin induced hypoglycaemia
stimulated GH secretion
decr glucose, FAs, AAs
Incr GH
