Neuroendocrinology Flashcards
What is neural, hormonal, and local signalling?
Endocrine (left)- a hormone is secreted from a hormone secreting cells and that enters the blood, getting distributed to arrive at the target cell
Specificity depends on the hormone and the target cell receptor
Neurocrine (middle)- Nerve cell sends neurotransmitter to neuron or effector cell via a nerve impulse
Highly localised as sent over an intrasynaptic cleft
Neuroendocrine (right)- a nerve cell which generates a nerve impulse to release a neurohormone, so synapses terminate near a capillary bed, so neurohormone gets released into the circulation to affect target cells anywhere in the body with its corresponding receptor
What are neurosecretory cells and what is neuroendocrine integration?
Neuroendocrine cells are neurosecretory cells that release signal molecules (hormones) from their synaptic terminals into the blood
Controlled via synaptic transmission from presynaptic neurons (neuroendocrine integration)
Examples:
Chromaffin cells of adrenal medulla which will secrete adrenaline
Hypothalamic magnocellular neurons make posterior pituitary secrete ADH/vasopressin
Hypothalamic parvocellular neurons
What is the embryology of the pituitary gland like?
Evagination of floor of 3rd ventricle (neural ectoderm)
Evagination of oral ectoderm (Rathke’s pouch)
Rathke’s pouch pinched off
How is the hypothalamus-pituitary axis structured?
Hypothalamus; composed of various nuclei (cell clusters)
Parvocellular nuclei; neurosecretory cells release hormones to capillaries of median eminence (supplied by superior hypophysial artery); conveyed by portal veins which travel to anterior pituitary where they regulate endocrine secretion
Magnocellular nuclei; project to posterior pituitary and release to capillaries supplied by inferior hypophysial artery
They extend their axons all the way down to the posterior pituitary where they terminate in a capillary network
The posterior pituitary has a different blood supply from the inferior hypophysial artery
The secretions from the posterior pituitary are form those magnocellular axons so technically they are hypothalamic hormones not posterior pituitary ones
What are the posterior pituitary hormones?
Posterior pituitary hormones; oxytocin and vasopressin (ADH)
PP is basically an extension of hypothalamus, with hormones stored in hypothalamic neuron terminals.
Released under neural control into hypophysial capillaries, inferior hypophysial vein
How is osmoregulation a neuroendocrine reflex?
Within the hypothalamus we have neurons that detect the osmolarity of the ECF.
These neurons integrate signals concerning osmolarity and their activity regulates the output of the neuroendocrine cells
An example is the supraoptic neurons, project down to the posterior pituitary to secrete ADH increasing water conservation
The osmoreceptors do not project directly to the magnocellular neurons but its too complicated
How is growth hormone secretion controlled?
GH (somatotropin) synthesised and secreted by somatotrophs of the anterior pituitary
Increased by:
GH-releasing hormone (hypothalamic neurosecretory cells)
Ghrelin (‘hunger hormone’ secreted by endocrine cells of the stomach)
Decreased by:
GH-inhibiting hormone (also known as somatostatin, from hypothalamic parvocellular neuroendocrine cells)
Negative feedback control by:
-GH in circulation
-IGF-1 (insulin-like growth factor 1)- released by liver in response to GH
Hypoglycaemia, a fall in the blood glucose concentration, stimulates the hypothalamus to increase the stimulation of GHRH to increase GH in order to increase gluconeogenesis
Diurnal rhythm also acts on the hypothalamus to release somatostatin which inhibits GH
What are the effects of growth hormone?
Increases lipolysis in adipose tissue
Increases gluconeogenesis in the liver so increases glucose production
Increases protein synthesis in the muscle
Increases somatic cell growth
Increased bone growth in children and bone remodelling in adults
Increases the production of insulin-like growth factors and some of the effects are indirect so promoted by IGFs not the GH
It also inhibits the pituitary gland and hypothalamus via a negative feedback loop
What are the factors that control GH secretion?
Stimulatory: GHRH Ghrelin Hypoglycaemia Decreased fatty acids Fasting Exercise, sleep Stress Inhibitory: Somatostatin (GHIH) GH Hyperglycaemia Increased fatty acids IGF-1
How does GH affect the human physiology?
Stimulates production of IGF-1 by liver
Increases lipolysis: raises free fatty acids (FFA)
Increases gluconeogenesis: raises blood sugar
Increases amino acid uptake into muscle, protein synthesis and lean body mass
Stimulates chondrocytes: linear growth
Stimulates somatic growth: increased organ/tissue size
What happens when there is an excess growth hormone?
Excess growth hormone; acromegaly
Most commonly due to pituitary adenoma: increase in GH-secreting somatotrophs
Less commonly secondary: tumour elsewhere secretes GHRH
Metabolic consequences:
Excess GH leads to insulin resistance
Many patients will have impaired glucose tolerance and hyperinsulinemia
May also have dyslipidaemia
