Neuroendocrinology

Question 1

What are neuroendocrine cells?

Answer 1

Neurosecretory cells that release signal molecules (hormones) from their synaptic terminals into blood

Question 2

What are neuroendocrine cells controlled by?

Answer 2

Controlled via synaptic transmission from presynaptic neurons (neuroendocrine integration)

Question 3

Name some examples of neuroendocrine cells

Answer 3

• Chromaffin cells of adrenal medulla
• Hypothalamic magnocellular neurons
• Hypothalamic parvocellular neurons

Question 4

Outline th eembryology of the pituitary and it’s development

Answer 4

1. CNS develops from a vesicle which divides into 3
   
   • forebrain, hindbrain, midbrain (ventricles)
2. Evagination of floor of 3rd ventricle (neural ectoderm)
3. Evagination of oral ectoderm (Rathke’s pouch)
4. Rathke’s pouch pinched off
   
   • Illustrates how pituitary is two separate

Question 5

Describe the composition of the hypothalamus

Answer 5

composed of various nuclei (cell clusters)

Question 6

Descrieb the hypothalamic-pituitary axis mechanism for the anterior pituitary

Answer 6

Parvocellular nuclei (short axons): neurosecretory cells release hormones to capillaries of median eminence (supplied by superior hypophysial artery); conveyed by portal veins to anterior pituitary

Question 7

What is the median eminence?

Answer 7

floor of hypothalamus

Question 8

describe the signalling towards the posterior pituitary

Answer 8

Magnocellular nuclei: project to posterior pituitary and release to capillaries supplied by inferior hypophysial artery

Question 9

What are the 4 actions of posterior pituitary hormones?

Answer 9

uterus contraction
milk ejection
blood pressure raising
urine reduction

Question 10

What type of hormones are secreted by the anterior pituitary?

Answer 10

Tropic hormones (growth)

Question 11

What is teh relationship between the hypothalamus and the posterior pituitary?

Answer 11

The Posterior Pituitary is an extension of hypothalamus, with hormones stored in hypothalamic neuron terminals

Question 12

How are posterior pituitary hormones released into circulation?

Answer 12

Released under neural control into hypophysial capillaries and inferior hypophysial vein

Question 13

What role does the posterior pituitary play in osmoregulation?

Answer 13

ECFV osmolarity changes detected by sensory neurones in hypothalamus
Signalled via neural integration - passed onto magnocellular neurones → inc/dec. ADH release to cause effects

Question 14

What is TRH?

Answer 14

thyrotropin-releasing hormone

Question 15

What is TSH?

Answer 15

thyrotropin (thyroid-stimulating hormone)

Question 16

What occurs at the hypothalamic level of the hypothalamic-pituitary axis?

Answer 16

neurosecretion of releasing hormones from parvocellular

Question 17

What is GHIH?

Answer 17

growth hormone inhibiting hormone

Question 18

What is CRH?

Answer 18

Corticotropin-releasing hormone

Question 19

What is ACTH?

Answer 19

corticotropin (adrenocorticotropic hormone)

Question 20

What is GHRH?

Answer 20

growth hormone releasing hormone

Question 21

What is IGF-1?

Answer 21

insulin-like growth factor 1

Question 22

What are the functions of growth hormone?

Answer 22

Growth and development (anabolic) - decreased = dwarfism / increased = gigantism
Couples growth to nutritional status

Question 23

Where is GH (somatostatin) made?

Answer 23

GH (somatotropin) synthesised and secreted by somatotrophs of the anterior pituitary

Question 24

Where does the secretion of ghrelin (hunger hormone) occur?

Answer 24

endocrine cells of the stomach

Question 25

Where is GH-releasing hormone released?

Answer 25

hypothalamic neurosecretory cells

Question 26

Where is somatostatin secreted from?

Answer 26

hypothalamic neurosecretory cells

Question 27

What causes the negative feedback of GH?

Answer 27

GH in circulation

IGF-1 (released by liver in response to GH)

Question 28

What factors stimulate GH sceretion?

Answer 28

GHRH
Ghrelin
Hypoglycemia
Decreased fatty acids
Fasting 
Exercise, sleep
Stress

Question 29

Which factors inhibit the release of GH?

Answer 29

Somatostatin (GHIH)
GH
Hyperglycemia
Increased fatty acids
IGF-1

Question 30

How is GH used to test normal pituitary function?

Answer 30

Insulin tolerance test: monitor blood every 30 min for 2 hr after insulin injection. Insulin will lower blood sugar, GH (and cortisol) will rise in response if normal

Question 31

What are the actions of GH on the body?

Answer 31

• Stimulates production of IGF-1 by liver
• ↑ lipolysis: ↑ FFA
• ↑gluconeogenesis: ↑ BGL
• ↑ a.a uptake into muscle, protein synthesis and lean body mass
• Stimulates chondrocytes: linear growth
• Stimulates somatic growth: ↑organ/tissue size

Question 32

How does GH fluctuate during alifetime?

Answer 32

Low at birth, increases at childhood, peaks at puberty and declines through adult life

Question 33

When might GH replacement therapy be used?

Answer 33

GH deficiency can occur in adulthood so replacement therapy might be adequate to maintain metabolic effects

Question 34

What is acromegaly?

Answer 34

Excess growth hormone

Question 35

What are the causes of acromegaly?

Answer 35

Most commonly due to pituitary adenoma: increase in GH-secreting somatotrophs
Less commonly secondary: tumour elsewhere secretes GHRH

Question 36

How can we diagnose acromegaly?

Answer 36

Glucose tolerance test
1. Monitor blood GH every two hours following 75 g
glucose in oral solution
2. GH levels should be suppressed if normal
3. but doesn’t occur in acromegaly

Question 37

How does acromegaly affect metabolic functions of patients?

Answer 37

Excess GH leads to insulin resistance
Many patients will have impaired glucose tolerance and hyperinsulinemia
Also hypertriglyceridemia due to inhibition of lipoprotein lipase.