Hypothalamus anatomy

Question 1

What does the diecephalon consist of?

Answer 1

Epithalamus, thalamus and hypothalamus

Question 2

What are the nuclei of the hypothalamus and what is their function?

Answer 2

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

Question 3

What are the three types of input into the hypothalamus?

Answer 3

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

Question 4

What direct receptors does the hypothalamus have?

Answer 4

Osmoreceptors that Respond to increase in blood osmolarity

Question 5

What is the hypothalamic response to high blood osmolarity?

Answer 5

ADH release from supraoptic nucleus
Secreted via posterior pituitary
Kidneys concentrate urine (retain water)
Stimulate neurons within the thirst centre in the lateral hypothalamus

Question 6

What is an example of indirect hypothalamic sensing?

Answer 6

Energy level sensing via Neurons in arcuate nucleus sense blood glucose and hormones

Question 7

How does the hypothalamus respond to energy levels?

Answer 7

Satiety centre
Responds to high glucose levels
Inhibits eating

Appetite centre
Responds to low glucose levels
Stimulates eating

Question 8

What effect does the hormone leptin have?

Answer 8

Leptin causes satiety “fullness” (anorexigenic)

Question 9

What effect does ghrelin have?

Answer 9

Ghrelin stimulates appetite “hunger” (orexigenic)

Question 10

How does the hypothalamus act as a biological clock?

Answer 10

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

Question 11

Define Circadian rhythm

Answer 11

A biological process with 24-hour endogenous rhythmicity matching the rotation of the earth

Question 12

Define Ultradian rhythm

Answer 12

Occurring more frequently than every 24 hours

Question 13

Define Infradian rhythm

Answer 13

At intervals longer than 24 hours (estrus cycle)

Question 14

Where do the hypothalmic neurones terminate?

Answer 14

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

Question 15

Hypothalamic hormones from the anterior pituitary can fit into one of two catagories:

Answer 15

Releasing hormones

Inhibitory hormones

Question 16

What is CRH?

Answer 16

Corticotropin releasing hormone (corticotropin = ACTH)

Question 17

What is TRH?

Answer 17

Thyrotropin releasing hormone which causes the release of Thyroid stimulating hormone

Question 18

What is GHRH?

Answer 18

Growth hormone/somatotropin releasing hormone

Question 19

What is GnRH?

Answer 19

Gonadotropin releasing hormone

Question 20

What is PRL-RH

Answer 20

Prolactin releasing hormone

Question 21

What is somatostatin?

Answer 21

Growth hormone inhibitory hormone

Question 22

What is GnIH?

Answer 22

Gonadotropin inhibitory hormone

Question 23

What doe dopamine do?

Answer 23

Inhibits prolactin

Question 24

What is the difference between tonic and episodic stimulation?

Answer 24

Neurohormones can have constant (tonic) secretion, with increases and decreases
Or can also be secreted as pulse or surge (episodic)

Question 25

How is tonic inhibition of prolactin maintained?

Answer 25

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