hypothalamus and pituitary gland Flashcards
what is the third ventricle?
narrow vertical slit in the forebrain full of CSF
where is the 3rd ventricle found
Runs antero-posteriorly along the midline above the midbrain between right and left thalamus
what is the hypothalamus?
A group of nuclei on the sides of the anterior-most part of 3rd ventricle
what structures are immediately below the hypothalamus?
optic nerves and optic chiasm
what is the pituitary gland>
a pea-sized structure that lies along the midline in a bony recess below the hypothalamus
what does the pituitary stalk connect?
connects the hypothalamus and the pituitary gland
which nervous system is the pituitary closely linked to?
autonomic nervous system
what do axons of the hypothalamus project into to activate the ANS?
cells in the lateral medulla of the brainstem
what info does the cerebral cortex detect and where does it send this info?
detects visual/auditory info about a threat –> sends to hypothalamus
explain the chain of events that occur to activate the fight or flight mechanism?
cerebral cortex detects visual/auditory info about a threat –> hypothalamus –> medulla –> spinal cord to activate sympathetic NS
where is the arcuate nucleus found?
under the 3rd ventricle
what does the grey matter of the hypothalamus contain?
many small nuclei with separate functions
where is the pituitary gland found?
in the pituitary fossa in the sphenoid bone below the hypothalamus
what surrounds the pituitary gland?
cavernous sinuses - complex venous structures
what are the main parts of the pituitary gland?
anterior lobe - adenohypophysis
posterior lobe - neurohypophysisare
how does the anterior lobe of the pituitary develop?
Develops from ectoderm in the roof of the mouth. This pouch of tissue eventually migrates upwards and separates from the oral cavity
how does the posterior lobe of the pituitary develop?
Develops from a downward pouch of brain tissue in the 3rd ventricle floor. Upper part of the pouch remains connected to the hypothalamus (forms the pituitary stalk) .
what is the median eminence?
region where the stalk joins the hypothalamus
what is the anterior pituitary?
endocrine gland
what is the posterior pituitary?
part of the brain
what is the infundibulum?
another name for the pituitary stalk
what are the 2 outputs of the hypothalamus to the pituitary?
magnocellular neurons
parvocellular neurons
what are magnocellular neurons and how do they project to the pituitary?
hypothalamic cell bodies which have axons that project down pituitary stalk to the posterior lobe of the pituitary.
Neurons release peptides into the capillaries in the posterior pituitary which then circulate in the blood to other organs
what are parvocellular neurons and how do they project to the pituitary?
hypothalamic cell bodies which have shorter axons that release peptides onto a capillary plexus in the pituitary stalk neck
what are cavernous sinuses?
• Cavities in the sphenoid bone containing a complex venous meshwork
what nerves run through/near the cavernous sinuses?
- Oculomotor nerves V1 and V2 of the trigeminal and the final part of the internal carotid artery pass through the sinus
- Cranial nerves 3&4 run along upper lateral border of the sinus
- V1 & V2 run along lower lateral corner
- CN 6 runs through middle of the mesh below the carotid
how do cranial nerves 3 and 4 enter the bony orbit?
via the superior orbital fissure
what does the hypothalamus control?
homeostasis - maintains temperature, body water, body weight, sleep-waking cycles and reproduction
what is the relay pathway of visceral sensory info from the vagus and what does it control?
nucleus of the solitary tract
feeds into the hypothalamus and controls digestion
what is the relay pathway of info from the spinal cord and what does it control?
brain stem reticular formation
feeds into the hypothalamus
controls body temperature control
what is the relay pathway of visual information and what does it control?
retina –> hypothalamus
controls circadian rhythm
what is the relay pathway of complex sensory information (smell, emotion) and what does it control?
limbic and olfactory system –> hypothalamus
feeding and reproduction
what are the main sensors of body temp?
- Thermoreceptors in the anterior nucleus of hypothalamus detect blood temp
- Cutaneous thermoreceptors (normally C fibre endings) detect skin temp
how does info from the cutaneous thermoreceptors get to the hypothalamus?
lateral spinothalamic tract – medulla –> hypothalamus
what heat loss effectors are activated when body temperature is too high?
- Sweat glands under the skin secrete sweat –> heat loss via evaporation
- Cutaneous vasodilation –> redirects blood into superficial capillaries in the skin –> heat loss via conduction + convection
- Person becomes inactive –> muscle activity generates heat which increases core temp
what heat gain effectors are activated when the body temperature is too low?
- sweat production stops
- piloerection - erector pilli muscles contract and lift hair follicles to trap heat
- vasoconstriction - blood rerouted to body core so heat isnt lost
- shivering - increases heat production
what fuel does shivering use?
glucose
what happens when a person is shivering but the glucose runs out?
person becomes hypothermic
how can we adapt to hot climates over time?
no. + activity of sweat glands + no of cutaneous capillaries is increased
how can we adapt to cold climates over time?
increased secretion of thyroid stimulating hormone + deposition of body fat
which hypothalamic nuclei are involved in water balance regulation?
paraventricular and supraoptic nucleus
explain the pathway for ADH to be released?
cells in the paraventricular and supraoptic nuclei send axons down to the posterior pituitary
end as secretory terminals in PP capillaries
terminals secrete ADH
what does ADH do?
increases water reabsorption in the kidney collecting ducts and reduces water loss in urine
what is oxytocin released into?
PP capillaries
what does oxytocin do?
Activates the milk let-down reflex in a lactating mother
what does prolactin do?
stimulates milk production
describe the milk let down reflex?
sucking action on breast transmits signal to hypothalamus via spinothalamic tract
hypothalamus secretes oxytocin –> makes smooth muscle contract in the milk ducts to expel milk
what type of reflex is the milk let down reflex?
neuro-hormonal reflex
how is oxytocin beneficial to a mother?
oxytocin is released into mother’s brain via collateral branches of oxytocin axons which project into regions of the brain associated with reward
Oxytocin is believed to promote maternal bonding with baby + reduce post-natal depression –> breast-feeding is good for mother+baby
what is another role of oxytocin other than milk release?
also responsible for contractions of the pregnant uterus during childbirth
why are ADH and OXY in the posterior pituitary?
needed for a fast response
why are ADH and OXY needed for a fast response?
- ADH needed quickly during injury when you’re losing large volumes of blood+water –> Acute blood loss triggers release of ADH
- Milk-let down action has to be fast so the baby doesn’t wait
describe the blood supply in the pituitary?
• 2 sets of capillaries
o First set are in the infundibulum
o Second set are in the anterior pituitary body
o Portal vein connects the 2
explain the dual hormone secreting system in the pituitary
hypothalamic nuclei axons end on capillaries in first part of the portal system
release hormones into capillaries
hormones are then released onto cell of the anterior pituitary which are stimulated to secrete a second set of hormones which pass back into the venous blood
name the 6 hypothalamic releasing hormones
CRH - corticotrophin releasing hormone GnRH -gonadotrophin releasing hormone TRH - thyrotropin releasing hormone GHRH - growth hormone releasing hormone GHIH - growth hormone inhibiting hormone PIF - prolactin inhibiting factor
what does CRH do?
releases Adrenocorticotrophic hormone (ACTH)
what does GnRH do?
acts on cells in the anterior pituitary to release both Luteinising Hormone (LH) & Follicle stimulating hormone (FSH) act on the ovaries to stimulate ovulation and maturation of the egg
what does TRH do?
acts on the anterior pituitary to release Thyroid Stimulating Hormone (TSH)
what does GHRH do?
releases growth hormone (GH)
what does GHIH do?
somatostatin) inhibits release of Growth Hormone (GH)
what does PIF do?
inhibits prolactin release
how can hormones from the anterior pituitary act directly?
act on target tissues directly
how can hormones from the anterior pituitary act indirectly?
by stimulating the release of further hormones/cytokines
explain the HPA axis
Cortisol Releasing Hormone (CRH) acts on the anterior pituitary to make ACTH. ACTH acts on adrenal cortex to stimulate the release of cortisol
why are anterior hormones released in a rhythmic fashion?
partly bc of all the complex feedback regulation
