Neuroendocrinology Flashcards
what do hormone signalling and neurotransmission have in common?
they both package peptides into vesicles, the peptides are released and interact with their receptors
where is the release point of the peptides in neurotransmission?
close to receptors
what do nerve cells synapse with?
mainly other neurones but some do synapse with effector cells
what is neuroendocrine transmission?
combination of neural and endocrine signalling
what is a neurohormone?
hormone released into blood as a result of nerve cell creating excitation and generating AP
what transduction occurs for release of a neurohormone?
electrical to chemical
what is paracrine transmission?
release something from cell that diffuses locally and affects neighbouring cells
what is autocrine transmission?
cells release things and what it has released affects its own growth
what is intracrine transmission?
something that happens entirely within the cell
what are neuroendocrine cells?
neurosecretory cells that release signal molecules from their synaptic terminal into the blood.
what are neuroendocrine cells controlled via?
synaptic tranmission rom pre-synaptic neurones (neuroendocrine integration)
what are two types of neurosecretory cells in the hypothalamus?
magnocellular (large cells)
parvocellular (small cells)
what is the structure of the pituitary gland?
bi-lobed with anterior and posterior lobe. Anterior is bigger
what is another word for posterior pituitary?
neurohypophysis
what are magnocellular cells?
hypothalamic cells that axons travel down into posterior pituitary and terminate there
what type of circulation is in the pituitary gland?
dual circulation
what exists in the posterior lobe?
inferior hypophyseal artery, capillary bed and inferior hypophyseal vein
what hormones are produced by magnocellular neurones?
hypothalamic hormones e.g. oxytocin and vasopressin. Stores in axon terminal in vesicles until electrically stimulated
how is the posterior pituitary part of the hypothalamus?
embryologically and functionally as neurones are hypothalamic and the released hormones are hypothalamic
what is the blood supply of the anterior pituitary?
superior hypophyseal artery which forms two capillary beds, first at base of hypothalamus (median eminence) and join to become portal veins. The portal veins form a second capillary bed in the anterior pituitary which drain through hypophyseal vein
how many different endocrine cells types are in the anterior lobe?
5
what happens when hormones are released into median eminence?
they drain into the portal vein and enter into the second capillary bed where they hormonally stimulate various cells of the anterior pituitary
what form the neural tube in the pituitary gland?
envagination of the floor of the 3rd ventricle
what then happens to the neural tube?
develops an envagination of the oral ectoderm (Rathke’s pouch) forming the anterior lobe
what happens to Rathke’s pouch?
pinches off and wraps around the neural stalk to form the anterior lobe
what do magnocellular neurones do?
project down into posterior pituitary and store hormones in axon terminals until stimulated for release into blood
What is ADH?
involved in osmoregulation
what is Oxytocin?
released by pituitary involved in uterine contraction during labour and milk release during lactation
how many hormones released from anterior pituitary?
5
what are the five hormones released by anterior pituitary?
TSH - stimulates thyroid ACTH - acts on adrenal cortex FSH/LH - testes/ovaries Growth Hormone - entire body Prolactin
posterior pituitary hormones
oxytocin and vasopressin
what is the structure of oxytocin and vasopressin?
peptide hormones (small)
when is vasopressin released?
when blood volume goes down and osmolality goes up (dehydration)
what does loss of water and high salt conc do?
stimulates osmoreceptors in hypothalamus to signal magnocellular neurones in hypothalamus to release vasopressin
what does vasopressin do?
leads to vasoconstriction increasing BP and increases water retention in kidney
what is function of oxytocin in labour?
stretches cervix leading to oxytocin release resulting in increased contractions of cervix/uterine leading to further release = positive feedback mechanism
what do sensory receptors in the nipples do?
stimulate release of oxytocin when mechanically stimulated so myoepithelial cells contract and lactation occurs
what are three categories of histological cells
chromophobes, acidophils, basophils
what are TSH secreting cells?
Thyrotrophs
what are ACTH secreting cells?
Corticotrophs
what are LH/FSH secreting cells?
Gonadotrophs
What are GH secreting cells?
Somatotrophs
what are prolactin secreting cells?
Lactotrophs
what stimulates release of ACTH from anterior pituitary?
CRH
what stimulates release of TSH from anterior pituitary?
TRH, inhibited by somatostatin
what stimulates release of LH/FSH from anterior pituitary?
GnRH (gonadotropin releasing hormone)
what stimulates release of prolactin from anterior pituitary?
inhibited by dopamine
what stimulates release of GH from anterior pituitary?
GHRH and inhibited by GHIH
what are primary problems?
issues with effector organ
what are secondary problems?
issues with pituitary itself
what are tertiary problems?
issues with hypothalamus
High TSH and low T3/T4
= primary hypothyroidism
Low TSH and high T3/T4
= primary hyperthyroidism
Low TSH and low T3/T4
= secondary hypothyroidism
what is the feedback loop by GH?
short. long feedback is indirectly by insulin like growth factor secreted by liver in response to GH
what is the somatotrope?
cell type in the pituitary that synthesises and releases growth hormone under influence of GHRH and somatostatin from the hypothalamus
explain short feedback loop of GH
GH released into portal veins circualtes around the body and when it re-circulates it acts on hypothalamus to decrease GHRH release and on pituitary to decrease GH release in order to reduce GH levels
what does growth hormone do to promote growth?
- increases gluconeogenesis in liver
- increases protein synthesis in muscle
- mobilises stored fats in adipose tissue for energy usage
what do insulin-like growth factors do? (IGFs)
synthesised by liver in response to GH. somatic cell growth, increasing chondrocyte function and bone modeling/remodelling
what feedback loop does IGF enter?
negative
factors stimulating GH secretion
GHRH, Ghrelin, Hypoglycaemia, Decreased Fatty Acids, Starvation, Exercise, Stress
factors inhibiting GH secretion
somatostatin,
GH,
Hyperglycaemia,
Increased fatty acids, IGFs
what is the action of growth hormone?
- stimulates production of IGF-1 in the liver
- increases lipolysis = more FFA
- increases gluconeogenesis = more blood sugar
- increases amino acid uptake into muscle
- stimulates chondrocytes = linear growth
- stimulates somatic growth = increased organ/tissue size
what type of control means GH peaks in early hours?
circadian
how does conc of GH change throughout life?
low at birth, increases and is stable in childhood, surges in puberty then decreases and stabilises
what is acromegaly?
excess growth hormone
why does acromegaly occur?
pituitary adenoma where there is increase in the GH-secreting somatotrophs
how does acromegaly affect feedback loop?
still negative and working but at much higher resting level so there is a rise in circulating GH
secondary cause of acromegaly?
tumour secreting GHRH
how are pituitary adenomas classified?
microadenoma <1 cm
macroadrenoma > 1cm
when are microadenomas present?
with symptoms of hormonal excess
when are macroadenomas present?
with the pituitary gland being so close to the optic chiasm, large growth can push things apart leading to visual loss, sellar enlargment, suprasellar damage and hypopituitarism
