Hypothalamus anatomy Flashcards
What does the diecephalon consist of?
Epithalamus, thalamus and hypothalamus
What are the nuclei of the hypothalamus and what is their function?
Paraventriclar (PVN) - oxytocin, ADH, TRH, CRH
Suproptic (SON) - Oxytocin and ADH
Suprachiasmatic (SCN) - Circadian rhythm
Lateral (LN) - arousal and hunger
Arcuate (AN) - energy, GnRH
Mammillary- Wakefulness
What are the three types of input into the hypothalamus?
Direct sensing by receptors
Indirect humoral sensing (via blood)
Receptors for circulating hormones
Indirect neural sensing (via nerves)
Visceral and somatic sensory nerves
Limbic system (emotions)
Reticular activating system
What direct receptors does the hypothalamus have?
Osmoreceptors that Respond to increase in blood osmolarity
What is the hypothalamic response to high blood osmolarity?
ADH release from supraoptic nucleus
Secreted via posterior pituitary
Kidneys concentrate urine (retain water)
Stimulate neurons within the thirst centre in the lateral hypothalamus
What is an example of indirect hypothalamic sensing?
Energy level sensing via Neurons in arcuate nucleus sense blood glucose and hormones
How does the hypothalamus respond to energy levels?
Satiety centre
Responds to high glucose levels
Inhibits eating
Appetite centre
Responds to low glucose levels
Stimulates eating
What effect does the hormone leptin have?
Leptin causes satiety “fullness” (anorexigenic)
What effect does ghrelin have?
Ghrelin stimulates appetite “hunger” (orexigenic)
How does the hypothalamus act as a biological clock?
Light sensed by retina is transmitted via nerve pathways
Arrives at hypothalamus: Specifically, the suprachiasmatic nucleus (SCN) (biological clock)
Stimulates the pineal gland (to make melatonin) and other pathways
Define Circadian rhythm
A biological process with 24-hour endogenous rhythmicity matching the rotation of the earth
Define Ultradian rhythm
Occurring more frequently than every 24 hours
Define Infradian rhythm
At intervals longer than 24 hours (estrus cycle)
Where do the hypothalmic neurones terminate?
On the primary plexus capillaries of the hypothalamus that then travel down via the hypophyseal portal veins to the secondary plexus of the anterior pituitary
Hypothalamic hormones from the anterior pituitary can fit into one of two catagories:
Releasing hormones
Inhibitory hormones
What is CRH?
Corticotropin releasing hormone (corticotropin = ACTH)
What is TRH?
Thyrotropin releasing hormone which causes the release of Thyroid stimulating hormone
What is GHRH?
Growth hormone/somatotropin releasing hormone
What is GnRH?
Gonadotropin releasing hormone
What is PRL-RH
Prolactin releasing hormone
What is somatostatin?
Growth hormone inhibitory hormone
What is GnIH?
Gonadotropin inhibitory hormone
What doe dopamine do?
Inhibits prolactin
What is the difference between tonic and episodic stimulation?
Neurohormones can have constant (tonic) secretion, with increases and decreases
Or can also be secreted as pulse or surge (episodic)
How is tonic inhibition of prolactin maintained?
Prolactin held in an inhibited state until released
Inhibition maintained by dopamine which is an inhibitory neurotransmitter and hormone
via the paraventricular nucleus of hypothalamus (tuberoinfundibular dopamine (TIDA) neurons).
Remains inhibited until stimulated by TRH, GnRH, Prolactin-releasing peptide or nervous stimulation from nursing/suckling
