Neuroendocrinology Flashcards
What are neuroendocrine cells?
Neurosecretory cells that release hormones from synaptic terminals into the blood.
How are neuroendocrine cells controlled?
Synaptic transmission from presynaptic neurons.
Give three examples of neuroendocrine cells.
- Chromaffin cells of the adrenal medulla
- Hypothalamic magnocellular neurons
- Hypothalamic parvocellular neurons
Describe the embryology of the pituitary gland.
- Begins as two simultaneous invaginations, one downwards from the neural ectoderm and one upwards from the oral ectoderm.
- Upward invagination is called Rathke’s Pouch, and it is pinched off, while the downward growth is aligned with it.
Describe the separate blood and hormone supplies of the two lobes of the pituitary. PART 1
- Inferior hypophyseal artery supplies the posterior pituitary, divides into a capillary bed
- Capillary bed contacted by axons of magnocellular neurosecretory cells in the hypothalamus.
Describe the separate blood and hormone supplies of the two lobes of the pituitary. PART 2
- Cells can secrete hormones into capillary bed, and drain off by the inferior vein.
- Hormones secreted by hypothalamus through posterior pituitary can enter systemic circulation.
Describe the separate blood and hormone supplies of the two lobes of the pituitary. PART 3
- Anterior lobe is supplied by the superior hypophyseal artery indirectly.
- Artery vascularises the median eminence
- Artery divides into a capillary bed in the median eminence, and then this is drained off by the venules which become a portal system.
Describe the separate blood and hormone supplies of the two lobes of the pituitary. PART 4
- Portal veins supply to the anterior pituitary, where they revascularise into a capillary bed in the anterior pituitary.
- Secretions of anterior pituitary can be secreted into the bed, where it drains off via superior hypophyseal vein into systemic circulation.
Describe the separate blood and hormone supplies of the two lobes of the pituitary. PART 5
- Parvocellular neurosecretory cells, via axonal terminals, release hormones into the capillary bed of median eminence
- Signals are carried into capillary bed of the anterior lobe, where they act locally.
List the hormones that are released from the posterior lobe of the pituitary gland and where they act.
- oxytocin: uterine muscles
- ADH: kidney tubules
List the hormones that are released from the anterior lobe of the pituitary gland and where they act.
- TSH: thyroid
- ACTH: adrenal cortex
- FSH and LH: testes or ovaries
- Growth Hormone (GH): the entire body
- Endorphins: pain receptors in the brain
Describe ADH as an example of a neuroendocrine reflex.
- ADH’s main function is osmoregulation
- If body water is low, ADH is released from neuroendocrine cells and stimulates water retention in the kidney.
What are some growth hormone functions?
- role in growth and development
- allows growth to occur in relation to nutritional status
How is growth hormone secretion controlled hormonally?
- Ghrelin (endocrine cells of the stomach)
- GH-Releasing hormone (hypothalamic neurosecretory cells)
- Somatostatin/GHIH (hypothalamic neurosecretory cells)
How is growth hormone secretion controlled by negative feedback?
- By the GH in the circulation
- By IGF-1 (released by the liver in response to GH)
List some other factors that stimulate GH secretion.
- GHRH
- Ghrelin
- Hypoglycemia
- Fasting
- Exercise
- Stress
List some other factors that inhibit GH secretion.
- Somatostatin (GHIH)
- GH (negative feedback)
- Hyperglycemia
- Increased fatty acids
- IGF-1
Describe GH action in the body. PART 1
- Stimulates production of IGF-1
- Increases lipolysis in adipose tissue: raises free fatty acids (FFA)
- Increases gluconeogenesis
Describe GH action in the body. PART 2
- Increases amino acid uptake into muscle
- Stimulates chondrocytes
- Stimulates somatic growth: increased organ/tissue size
What is acromegaly and what is it caused by?
- Condition causing excess GH.
- Commonly due to pituitary adenoma: an increase in GH-secreting somatrophs.
- Or due to to GH-secreting tumors
What does acromegaly cause?
- Insulin resistance - impaired glucose tolerance and hyperinsulinemia.
- Rapid bone growth in face, hands and feet.
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 IGF from the liver promote?
→ Increase somatic cell growth
→ Increase chondrocyte function (cartilage in bones)
→ Increase bone modelling
How does IGF get produced?
→ GH released from somatotropes
→ GH acts on liver and increases gluconeogenesis
→ Increases IGF
What secretes GH?
Somatotropes
When blood glucose concentration is low, where does the body get its glucose from?
Glycogen stores/gluconeogenesis
What is the brain dependent on?
Glucose
Describe the cascade of TRH
→ Hypothalamic hormone TRH changed into TSH in the anterior pituitary
→ stimulates thyroid gland
→ thyroid produces thyroid hormones
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
→ higher/lower release of ADH into the posterior pituitary
What kind of hormones do the parvocellular nuclei release?
- Trophic hormones
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
