Hypothalamus and pituitary

Question 1

Overview of hypothalamus and pituitary

Answer 1

• Hypothalamus is part of the diencephalon
• Hypothalamus allows the brain and endocrine system to communicate
• Neuroendocrine neurons stimulate the release of or directly releases hormones from the hypothalamus/pituitary complex
• Hypothalamus has receptors for many hormones allowing for feedback
• Hypothalamus regulates feeding, fighting, fleeing and fucking (4 Fs)

Question 2

Neuroendocrine neurons

Answer 2

• Often multipolar cells with branching dendrites
• Also releases chemical messengers from boutons, but instead of synapses it releases chemicals (hormones) near capillaries
• These hormones (released from the hypothalamus) have short T1/2s are released into capillaries at the median eminence (base of the hypothalamus)
• The hormones (releasing hormones) are delivered by the hypothalamic-hypophyseal portal system (thru the adenohypophysis) to the anterior pituitary, where they cause the ant pituitary to release (stimulating) hormones to other glands around the body via circulation

Question 3

Hormones of the anterior pituitary

Answer 3

• Releases trophic hormones: these hormones stimulate the activity of other glands (i.e. adrenals, gonads, thyroid)
• Thus hormones from the hypothalamus are “releasing” hormones b/c they trigger the release of ant pituitary hormones
• Ant pituitary hormones are “stimulating” b/c they trigger stimulation of other glands
• Therefore the pituitary is an amplifier of the hypothalamus’ master control
• There is negative feedback at the level of the hypothalamus (senses levels of stimulating hormone and the final hormone) and the anterior pituitary (senses levels of the final hormone only)

Question 4

Anterior vs posterior pituitary

Answer 4

• Both are covered by the sella tursica
• Anterior pituitary is epithelial in origin (derived from mouth)
• The posterior pituitary is neural in origin (derived from brain)
• Anterior pituitary releases hormones in response to hormones from hypothalamus
• Posterior pituitary contains neuroendrocrine axons form cells in the hypothalamus, which directly release hormones (vasopressin and oxytocin) into capillaries in the posterior pituitary (no intermediate step)

Question 5

General anatomy of hypothalamus

Answer 5

• 4 regions (from anterior->posterior): pre optic, anterior, tuberal, and mammillary
• There are some processes that are controlled by turning them on and off: feeding (hunger), body temp
• Other processes are controlled only by turning on: social, stress, thirst

Question 6

Preoptic region

Answer 6

• One of the subdivisions of the pre optic region is the medial pre optic area (MPOA)
• MPOA coordinates, among other things, male sexual behavior and maternal behavior
• MPOA responds to testosterone, estrogen, and progesterone (gonadal hormones)
• Projects to the amygdala
• Also involved in heat loss center, along w/ AHA (see AHA card)
• MePO (another pre-optic region) regulates third w/ PVN and SON (anterior regions)

Question 7

Anterior region 1

Answer 7

• One of the subdivisions is the anterior hypothalamic area (AHA), which is involved in aggressive behavior (responds to testosterone)
• Has similar neural (amygdala) and hormonal (testosterone) inputs
• Along w/ the MPOA the AHA is involved in heat loss
• Temp sensitive neurons in the MPOA and AHA sense an increase in body temp and initiate heat-loss mechanisms: sweating and peripheral vasodilation
• Lesions in AHA and MPOA can cause hyperthermia (predictable)

Question 8

Anterior region 2

Answer 8

• Another subdivision of the anterior region is the paraventricular and supraoptic nuclei (PVN and SON)
• The PVN is involved in the initiation of thirst, due to decrease in ECF volume (stimulates osmoreceptors in PVN) and increase in osmolality of ECF
• These two regions work w/ MePO in pre-optic region to regulate thirst
• PVN and SON send axons to posterior pituitary and release vasopressin to promote water retention, and oxytosin release
• PVN also plays a role in response to chronic stress via CRH neurons which control secretion of cortisol from adrenals
• PVN also stimulates thyroid

Question 9

Anterior region 3

Answer 9

• Another subdivision of the anterior region is the suprachiasmatic nucleus (SCN)
• Regulates circadian rhythms, receives light info from specialized ganglion cells in the retina
• Controls rhythms in body thru secretion of melatonin from the pineal gland (melatonin only released in the dark)

Question 10

Tuberal region

Answer 10

• A subdivision of the tuberal region is the ventromedial nucleus (VMH)
• VMH is the satiety center, which turns off hunger
• Lesions in the VMH cause an increase in food intake
• Initiating hunger controlled by lateral hypothalamus
• VMH is also important for female sexual behavior, and it responds to estrogen

Question 11

Mammillary region

Answer 11

• A subdivision of the mammillar region is the posterior nucleus (PN)
• PN is the center of heat gain, activated by lower than normal body temp
• PN activates shivering, piloerection, and peripheral vasoconstriction
• Lesions in PN lead to hypothermia (can be predictable)

Question 12

Lateral hypothalamus

Answer 12

• Involved in initiating hunger and heat regulation

- May be part of the tuberal region

Question 13

Arcuate nucleus

Answer 13

• Part of tuberal region

- Deals with hunger, satiety, let pin, fat, insulin, glucose