The Hypothalamus Flashcards
What is the hypothalamus?
a bilateral paired structure that occupies the side walls and floor of the third ventricle
What separates the thalamus and hypothalamus?
hypothalamic sulcus
What does the hypothalamus have control over?
- reproduction
- growth and metabolism
- food and fluid intake
- attack and defence
- temperature control
- sleep-wake cycle
- memory
How are most of the hypothalamic functions expressed?
through its control of the pituitary gland and the ANS
Where are parvocellular neuroendocrine cells found?
the preoptic and tuberal regions of the hypothalamus
What are parvocellular neuroendocrine cells sensitive to?
the blood concentration of hormones that are secreted by the anterior pituitary
What is the stalk of the pituitary gland called?
the infundibulum
What is the tuberoinfundibular tract?
the pathway of axons from the tuberal region of the hypothalamus to the infundibulum
What do action potentials travelling down the tuberoinfundibular tract cause?
calcium-dependent exocytosis of releasing or inhibitory hormones (mostly releasing) from the neuroendocrine cells
What happens to releasing hormones of the hypothalamus?
they are picked up and secreted into the capillaries to the anterior pituitary, where they release their hormones via the pituitary portal system
What does each hormone of the anterior pituitary have?
a separate releasing factor of hypothalamic origin responsible for its secretion except for FSH
Where does the arterial supply of the pituitary gland come from?
branches of the internal carotid artery
What happens to the capillaries that supply the pituitary gland?
they drain into portal vessels which pass into the anterior pituitary then break up to form a second capillary bed which bathes the endocrine cells and eventually drains into the cavernous sinus
What are the 6 hormones secreted by the anterior pituitary and what do they do?
- prolactin - for the development of mammary glands and lactation
- TSH - stimulates thyroid gland to synthesise and release T3 and T4
- ACTH - stimulates the release of certain adrenal cortical steroids
- GH - for growth of long bones and some tissues
- FSH - for growth of ovaries and development of sperm ducts
- LH - induces ovulation with FSH
Where are magnocellular neurons found?
in the supraoptic and paraventricular nuclei
What do magnocellular neurons give rise to?
the hypothalamo-hypophyseal tract
Where does the hypothalamo-hypophyseal tract terminate?
in the posterior pituitary
What are the 2 hormones secreted by the posterior pituitary?
ADH and oxytocin
What are Herring bodies?
axonal swellings that contain ADH and oxytocin and provide a local depot for release by smaller, terminal swellings into the capillary bed
What happens to hormones released from both the anterior and posterior pituitary?
they drain into capillaries which drain into the cavernous sinus and then into general circulation
What does ADH act on?
the distal convoluted tubules and collecting ducts of the kidneys
What happens if ADH is not produced?
it can result in diabetes insipidus
What is the principal function of oxytocin?
to participate in a neurohormonal reflex to cause the release of milk when an infant is breastfeeding
What are the 4 steps of breastfeeding?
- stimulation of the mother’s nipple by the infants suckling produces brain activity
- hypothalamic cells are stimulated to release oxytocin from the posterior pituitary
- oxytocin causes cells of the mammary glands to contract which releases milk
- the baby receives milk and continues suckling until sated
How does oxytocin cause expression of milk?
it enters general circulation and stimulates myoepithelial cells surrounding the lactiferous ducts of the breast
What are other functions of oxytocin?
stimulating action on uterine muscle contractions during labour
What are the mechanisms that facilitate heat loss?
- dilation of peripheral blood vessels beneath the skin to increase heat radiation
- increased sweating
- increased respiratory rate
What is heat conservation controlled by?
the posterior hypothalamic area
What does regulation of food intake involve?
satiety centres in the hypothalamus which are very sensitive to blood glucose levels
What are the mechanisms that help with heat conservation?
- peripheral vasoconstriction with a subsequent decrease in the heat lost by radiation
- increased body metabolism
- shivering of voluntary muscles
- decreased respiratory rate
How does the hypothalamus provide a baseline for caloric and nutrient intake?
by interaction between the lateral and ventromedial nuclei, which make up the appestat
What does stimulation and destruction of the lateral hypothalamic satiety centre cause respectively?
- stimulation - excessive eating
- destruction - refusal to eat
What does stimulation and destruction of the ventral hypothalamic satiety centre cause respectively?
- stimulation - inhibits the urge to eat
- destruction - overeating and gross obesity
What does stimulation of the anterior and posterior hypothalamic areas produce respectively?
- anterior - parasympathetic effects
- posterior - sympathetic effects
