Neuroendocrinology Flashcards
What is the definition of a hormone?
→ a cell secretes a hormone
→ not targeted
→ has an effect on target cells depending on whether they have the receptor or not
How do neurotransmitters work?
→ nerve cell secretes NTs
→ across a spatially restricted area
→ acts on an effector cell
What is paracrine secretions?
→ secreted from cells
→ exerts effects at local interstitial fluid
What is autocrine signalling?
→ The cell has receptors for a hormone that it secretes
What are neuroendocrine cells?
→ neurosecretory cells that release signal molecules from their synaptic terminals into the blood
What are neuroendocrine cells controlled by?
→ synaptic transmission from presynaptic neurons
What are 3 examples of neuroendocrine cells?
→ chromaffin cells of adrenal medulla
→ hypothalamic magnocellular neurons
→ hypothalamic parvocellular neurons
How does neuroendocrine transmission work?
→ Nerve cell releases NT
→ NT acts on a neuroendocrine cell
→ Releases a signalling molecule from axonal end
→ it doesn’t synapse
→ terminals target capillaries
→ substance diffuses and acts as a hormone
What is the pituitary made from?
→ 2 independent structures
How does the pituitary form in the embryo?
→ Evagination of the floor of 3rd ventricle
→ Evagination of oral ectoderm
→ Rathkes pouch pinched off
What is the posterior lobe of the pituitary an extension of?
→ The hypothalamus
What are the two nuclei of the hypothalamus?
→ Parvocellular nuclei
→ Magnocellular nuclei
Where do the parvocellular nuclei project to?
→ small neurons with small axons → project to the median emininence → release hormones to the capillary network → carried by hypophyseal portal veins → to anterior pituitary
What is the posterior pituitary supplied and drained by?
→ Inferior hypophyseal artery
→ Inferior hypophyseal vein
What is the anterior pituitary supplied and drained by?
→ Superior hypophyseal artery
→ forms a network at the base of the hypothalamus
→ Portal veins - a second capillary network
Where do the magnocellular nuclei project ?
→ Project to the posterior pituitary
→ release capillaries supplied by inferior hypophyseal artery
What is the pathway of ADH?
→ Synthesized in the magnocellular nuclei
→ packaged into vesicles and transported along the axons
→ stored in axon terminals
→ released into the hypophyseal capillaries
What kind of hormones do the parvocellular nuclei release?
Trophic hormones
→ Hormone releasing hormones
What hormones does the posterior pituitary release?
→ Oxytocin
→ ADH
What hormones does the anterior pituitary release?
→ TSH → ACTH → FSH + LH → Growth hormone → Prolactin → Endorphins
How does ADH get regulated?
→ Sensory neurons in the hypothalamus detect changes in ECF osmolality
→ passed on to magnocellular neurons (supraoptic)
→ increase or decrease in firing of magnocellular neurons
→ + or - in the release of ADH into the posterior pituitary
Describe the cascade of TRH
→ Hypothalamic hormone TRH
→ changed into TSH in the anterior pituitary
→ stimulates thyroid
→ thyroid produces thyroid hormones
Where are the parvocellular and magnocellular nuclei found?
→ in the hypothalamus
What is the brain dependent on?
→ obligatory dependent on glucose
In the absence of circulating glucose where does glucose come from?
→ glycogen stores
When glycogen runs out where does glucose come from?
→ Gluconeogenesis
What does growth hormone stimulate?
→ Lipolysis
→ Promotes release of fatty acids
→ so tissues use fat
→ glucose can be used in the brain
What are the 7 factors that stimulate growth hormone?
→ GHRH → Ghrelin- secreted by endocrine cells of the stomach → Hypoglycaemia → Decreased fatty acids → Fasting → Exercise, sleep highest at night → stress
What is ghrelin and where is it released from?
→ Hunger hormone
→ Released by endocrine cells of the stomach
What are the 5 factors that inhibit growth hormone?
→ Somatostatin , from hypothalamic parvocellular neuroendocrine cells
→ GH
→ Hyperglycemia
→ Increased fatty acids
→ IGF-1- released by liver in response to GH
What are somatotropes?
→ endocrine cells in the anterior pituitary that secrete GH
How does IGF get produced?
→ GH released from somatotropes
→ GH acts on liver and increases gluconeogenesis
→ Increases IGF
What does IGF from the liver promote?
→ Increase somatic cell growth
→ Increase chondrocyte function (cartilage in bones)
→ Increase bone modelling
What does GH do in the muscle?
→ Increases protein synthesis
What does GH do in adipose tissue?
→ Promotes lipolysis so does fat can be used for energy and glucose can be stored and used for the brain
Muscle protein is not then needed for gluconeogenesis.
What are GH concentrations like during life?
→ birth is low
→ increases and stays constant at childhood
→ Increases dramatically during puberty
→ decline during adult life and old age
What does GH deficiency during childhood result in?
→ dwarfism
What is the condition with excess hormone called?
→ Acromegaly
What is acromegaly caused by?
→ pituitary adenoma
What are metabolic effects of acromegaly?
→ Insulin resistance
→ Impaired glucose tolerance and hyperinsulinemia
→dyslipidaemia
→hypertriglyceridemia due to inhibition of lipoprotein lipase
What doe supraoptic nucleus contain?
magnocellular neurones
Where does oxytocin and vasopressin release into?
hypophysial capillaries, inferior hypophysial vein
Where do the cell bodies of oxytocin cells lie?
mainly in the supraoptic and paraventricular in the hypothalamus
Where is the anterior part derived from?
up growth from the oral ectoderm of the primitive oral cavity called Rathke’s pouch
Where is the origin of the posterior part of the pituitary?
→origins in nervous tissue.
→It is formed from a downgrowth of the diencephalon that forms the floor of the third ventricle.
What is the difference between GH levels in older adults and younger adults?
Older adults have much smaller levels than young adults
