17 - Hypothalamus/Pituitary

what is the hypothalamus responsible for?

central control of:

visceral functions - visceromotor/endocrine

affective/emotional behavior - limbic

primary role in homeostasis

many other regulatory functions

what receptors does the hypothalamus have?

temp, osmolarity, hormone levels, metabolite levels

hypothalamus integrates sensory info from

visceral sensory, somatic sensory, limbic systems

where is the hypothalamus located?

rostral - laminal terminalis

superior - hypothalamic sulcus

lateral - rostrally by substantia innominata and caudally by posterior limb of internal capsule

medial - inferior portion of third ventricle (surrounds 3rd ventricle)

caudal - merges with midbrain tegmentum and periaqueductal gray

what is the ventral surface of the hypothalamus?

mammillary bodies

infundibulum - part of hypophyseal stalk

what is the blood supply to the hypothalamus?

perforating arteries from the circle of willis

ACA and A1 segment of ACA - preoptic, supraoptic regions, rostral portions of lateral hypothalamic region

PCA and P1 of PCA - tuberal and mammillary regions, middle/caudal parts of lateral hypothalamic area

where does the pituitary gland lie?

sella turcica

what is the blood supply to pituitary gland?

superior and inferior hypophyseal arteries from internal carotid artery

superior → anterior lobe

inferior → posterior lobe

all drain into cavernous sinus from there to general circulation

what are the divisions of the hypothalamus?

preoptic area, lateral zone, medial zone, periventricular zone

medial preoptic nucleus contains neurons that manufacture what?

gonadotropin-releasing hormone that travels down infundibular tract to anterior lobe of pituitary gland and causes the release of gonadotropins

lateral preoptic nucleus function?

does not have fully defined functions

what is the medial forebrain bundle

connects hypothalamus with rostral and caudal regions

lateral hypothalamic nucleus

feeding center - prompts more eating

lesion - less feeding behavior

supraoptic chiasmatic region parts

supraoptic nuclei - projections to neurohypophysis (post pituitary - oxytocin and anti diuretic hormone)

paraventricular nuclei - projections to neurohypophysis (posterior pituitary - oxytocin and ADH)

suprachiasmatic nuclei - input from the retina and may mediate circadian rhythm

anterior nuclei - maintenance of body temp

tuberal region parts

ventromedial nucleus - satiety center

dorsomedial nucleus - related to emotional behavior

arcuate nucleus - neurons that contain releasing hormones; related to anterior pituitary

mammillary region parts

four nuclei

LT memory formation

Korsakoff syndrome

function of periventricular zone

neurons that synthesize releasing hormones

send via tuberoinfundibular tract to the hypophyseal portal system of the pituitary gland

influence release of various hormones by anterior pituitary

function similar to neurons in arcuate nucleus

effect of stimulation or lesion of the principle hypothalamic nuclei

[chart]

what are hypothalamus afferents?

amygdala - emotions/memory

hippocampus - memory and context

thalamus - sensory/motor relay

retina - light cues for circadian rhythm

brainstem - visceral sensory input

spinal cord - autonomic related info

cerebral cx - emotion/decision making

cerebellum - coordination of motor and autonomic functions

bloodstream - detects hormones, glucose, temp

hypothalamus efferents

pituitary gland - hormone release

autonomic centers in brainstem and SC

thalamus

amygdala - emotional modulation

cortex via thalamus

septal area and basal forebrain - motivation and arousal

cerebellum

hypothalamic afferents

fornix

medial forebrain bundle

amygdalohypothalamic

hypothalamic efferents

mammillothalamic

mammillotegmental

hypothalamospinal

dorsal longitudinal fasciculus

what are the 4 main hypothalamic nuclei associated with ANS?

paraventricular nuc - primary

dorsomedial hypothalamic

lateral hypothalamus

posterior hypothalamus

the hypothalamus receives visceral and somatosensory information from

medial forebrain bundle

also solitary nuc, PAG, reticular formation

receptors within hypothalamus

blood temp, osmolarity, hormone levels

efferents from hypothalamic related to ANS

hypothalamus to brainstem and SC preganglionic ANS neurons

directly and indirectly via periaqueductal gray and reticular formation

major roles of hypothalamus in the limbic system

ANS responses commonly seen with strong emotions

homeostatic changes linked to emotional states - depression and stress linked to impaired immune function

general functions of hypothalamic system

integrating memory and emotion

memory storage

Korsakoff syndrome? sx?

progressive degeneration of the mammillary bodies, hippocampal complex, dorsomedial thalamic nucleus

thiamine deficiency - result of chronic alcoholism

sx - anterograde amnesia (inability to create new LT memories), difficulty holding conversations due to inability to remember what was recently said, confabulation

amygdala function in the limbic system?

associates behaviors and emotions to sensations

part of pathway for this involves the connections between the amygdala and hypothalamus

hypothalamus receives olfactory information

how does hypothalamus help with sleep?

GABAergic neurons in preoptic area inhibit histaminergic neurons and the midbrain reticular formation resulting in inhibition that reduces histamine release and decreases alertness and promotion of deep sleep

caudolateral hypothalamus

lateral zone, dorsomedial nuc, mammillary region

stimulation of caudolateral hypothalamus produces? lesion results in?

anxiety, anger, rage

increased symp activity, aggressive behavior hunger, increased body temp

opposite response (inhibited symp, decreased body temp)

where is rostromedial hypothalamus? stimulation and lesion results in?

supraoptic region

contentment, increased parasymp activity, passive behaviors, satiety, decreased body temp

lesion is opposite

degeneration of what part of hypothalamus is associated with Korsakoff’s Syndrome?

mammillary bodies

what are the tracts between the hypothalamus and pituitary?

supraopticohypophysial tract - oxytocin and ADH

tuberoinfundibular tract - GH, gonadotropins, corticotropin, thyrotropin, prolactin

the anterior pituitary are glandular cells that produce and secrete what? what are they controlled by?

hormones

hypothalamus

posterior pituitary are derived from?

neural derivative

axon terminals of neurons whose cell bodies are in the hypothalamus

the hypothalamus consists of? produces?

arcuate nucleus and periventricular zone

produce releasing factors and release inhibitor factors

examples of releasing and releasing inhibitor factors:

corticotropin releasing hormone

thyrotropin releasing hormone

gonadotropin releasing hormone

growth hormone releasing hormone

somatostatin

prolactin releasing inhibitor hormone

tuberoinfundibular tract

axons projecting to the median eminence and infundibulum

what does the tuberoinfundibular tract discharge?

releasing/inhibiting factors

releasing/inhibiting factors enter capillary plexus → hypophyseal portal system → adenohypophysis where they stimulate or inhibit the release of hormones from the adenohypophysis

examples of anterior pituitary hormones and their functions

ACTH (cortex of adrenal gland)

TSH - thyroxine to promote cellular metabolism

GH - promote growth in long bones and other tissues

prolactin - mammary glands for milk production

gonadotropins - ovarian hormones in females, testicular hormones in males

what do the supraoptic and paraventricular nuclei in the hypothalamus produce?

ADH/vasopressin, oxytocin

hypothalamus and posterior pituitary

axons to posterior pituitary

stored in axon terminals

released and enter vascular system

vasopressin function? what happens at high levels? what happens with a lesion?

increase water resorption by the kidney

vasoconstriction and increase BP

diabetes insipidus - polyuria, polydipsia

oxytocin function?

stimulates uterine contractions and milk ejection

suckling → sensory pathways → hypothalamus → oxytocin release → milk ejection

pituitary tumors types?

nonsecreting and secreting

secreting includes GH secreting, thyrotopin-secreting, adrenocorticotropic hormone-secreting (Cushing’s), prolactin-secreting, gonadotropin-secreting

prolactin-secreting adenomas sx

galactorrhea (milk production)

amenorrhea (absence of menstrual periods)

decreased libido, impotency or infertility

growth hormone-secreting adenomas can cause:

excess GH

gigantism if it occurs prior to completion of growth

acromegaly if after closure of growth plates, increased thickness of bones

Cushing disease causes and sx?

excess ACTH causing excess glucocorticoids

round face, truncal obesity, facial hirsutism, HTN, poor wound healing

what are the 3 hypothalamic reflexes

baroreceptor reflex

temperature regulation reflex

water balance reflex

baroreceptor reflex

baroreceptors in the aortic arch and carotid sinus detect changes in blood pressure, sensory input travels to the solitary nucleus in the medulla, solitary nucleus activates the dorsal vagal nucleus, influencing heart rate and cardiac output

high BP → reflex of decreased HR and contraction force to lower BP

low BP → reflex of high HR and force to increase BP

the hypothalamus modulates this reflex by sending projections to the dorsal vagal nucleus via the solitary nucleus

temperature regulation

intrinsic thermoreceptors in the hypothalamus monitor core body temp

increase blood temp → activates anterior hypothalamus and triggers sweating and cutaneous vasodilation

decrease blood temp → activates posterior hypothalamus and triggers shivering and cutaneous vasoconstriction

water balance reflex

blood osmolality is monitored by osmoreceptors in the anterior hypothalamus (preoptic and paraventricular nuclei)

efferent limb is hormonal → mediated by ADH and vasopressin

high blood osmolality → ADH release and more renal water reabsorption

low blood osmolality → less ADH release and less water reabsorption leading to more water excreted in urine