Hypothalamus Flashcards
What are the components of the diencephalon?
epithalmus
thalmus
hypothalamus
How does the hypothalamus receive information?
Direct sensing by receptors
indirect humoral sensing (via blood)
Indirect neural sensing (via nerves)
What are the nuclei of the hypothalamus and what are their functions?
Paraventricular (PVN) - oxytocin, ADH, TRH, CRH
Supraoptic (SON) - oxytocin, ADH
Suprachiasmatic (SCN) - circadian rhythm
Lateral (LN) - arousal, hunger
Arcuate (AN) - energy, GnRH
Mammillary - wakefulness
Describe the hypothalamus’ response to thermoreceptors
Neurons in anterior hypothalamus:
- respond to heat (thermoregulation cooling centre)
- => peripheral vasodilation + sweating
Neurons in posterior hypothalamus:
- respond to cold (thermoregulation heating centre)
- => peripheral vasoconstriction, piloerection, shivering
What is the response of the hypothalamus to osmoreceptors?
Respond to increase in blood osmolarity (haemoconcentration/dehydration):
- ADH from supraoptic nucleus
- excreted via posterior pituitary
- kidneys concentrate urine/retain water
- stimulate neurons in thirst centre in lateral hypothalamus
Describe how the hypothalamus control energy balance
Neurons in arcuate nucleus
Sense blood glucose:
- satiety centre responds to high glucose levels => inhibits eating
- appetite centre responds to low glucose level => stimulates eating
sense hormones:
- leptin => satiety
- Ghrelin => stimulates appetite
Satiety
how does the hypothalamus act as a biological clock?
light sensed by retina, nerve signal arrives at hypothalamus (suprachiasmatic nucleus)
Stimulates pineal gland (melatonin)
What is circadian rhythm?
a biological process with 24-hour endogenous rhythmicity matching the rotation of the earth
what is ultradian rhythm?
occurring more frequently than every 24 hours
What is infradian rhythm?
at intervals longer than 24 hours (estrus cycle)
How does cortisol act in a biological rhythm and how is this clinically relevant?
High every morning - circadian
Peaks and troughs throughout day - ultradian
Circadian cortisol rhythm is basis for a diagnostic test:
- morning and evening sample
- <30% decrease = healthy
Describe the secretory neurons of the posterior pituitary gland
Cell bodies in hypothalamus (supraoptic and paraventricular nuclei)
Axons descend into posterior pituitary
Nerves terminate on BVs and release hormones from storage (ADH and oxytocin) directly into circulation
What connects the hypothalamus and the anterior pituitary?
hypophyseal portal veins
What releasing hormones are secreted by the hypothalamus?
CRH - corticotropin/ACTH releasing hormone
TRH - thyrotropin/thyroid stimulating hormone/TSH releasing hormone
GHRH - growth hormone/somatotropin releasing hormone
GnRH - gonadotropin releasing hormone
PRL-RH - prolactin releasing hormone
What inhibitory hormones are secreted by the hypothalamus?
GHIH/somatostatin - growth hormone inhibitory hormone
GnIH - gonadotropin inhibitory hormone
Dopamine (neurotransmitter) - inhibits prolactin and other homrones
