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Neuro Week 2 > LM 2.1: Hypothalamus Structure & Function > Flashcards

LM 2.1: Hypothalamus Structure & Function Flashcards

1
Q

where is the hypothalamus located?

A

it’s part of the diencephalon and it’s located below the thalamus

it’s connected to the pituitary gland by the pituitary stalk!

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2
Q

what structure separates the thalamus from the hypothalamus?

A

hypothalamic sulcus

it also divides the left and right lateral walls of the 3rd ventricle

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3
Q

what is the function of the hypothalamus?

A

the nuclei synthesizes and secretes neurohormones

so it acts as a conduit between the nervous and endocrine systems via the pituitary gland regulating homeostatic functions such as hunger, thirst, body temperature, and circadian rhythms, appetite, body fat content etc.

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4
Q

what are nuclei of the hypothalamus?

A

discrete masses of grey matter in theCNS

the hypothalamus is composed of different nuclei

they each synthesize different hormones in response to physiological changes in the body, in order to maintain homeostasis

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5
Q

what are the 4 regions of nuclei of the hypothalamus?

A
  1. preoptic region
  2. supraoptic region
  3. tubular region
  4. mamillary region
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6
Q

which nuclei are in the preoptic region?

A

preoptic nucleus

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7
Q

which nuclei are in the supraoptic region?

A
  1. suprachiasmatic
  2. supraoptic
  3. paraventricular
  4. anterior nuclei
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8
Q

which nuclei are in the tubular region?

A
  1. dorsomedial
  2. ventromedial
  3. arcuate
  4. pre-mammillary
  5. lateral puberal nuclei
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9
Q

which nuclei are in the mamillary region?

A
  1. mamillary

2. posterior

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10
Q

what does the hypothalamus regulate?

A
  1. BP
  2. body temperature
  3. fluid and electrolyte balance
  4. body weight
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11
Q

how does the hypothalamus maintain homeostasis?

A

by regulating 3 interrelated functions

  1. endocrine secretion
  2. autonomic function
  3. emotions

by regulating these 3 function, it can regulate BP, temperature, fluid and electrolyte balance and body weight

hypothalamus controls the release of hormones by the pituitary gland (anterior and posterior pituitary)

the hypothalamus receives sensory and pathologic information, compares that information with physiological set points (or thresholds), and activates relevant visceral motor, neuroendocrine, and somatic motor effector systems that restore homeostasis and/or elicit appropriate behavior responses

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12
Q

what controls the secretion of hormones from the pituitary gland?

A

Secretion from the posterior pituitary gland can occur as a result of direct neuronal stimulation via the infundibulum (a stalk that connects the hypothalamus and posterior pituitary)

secretion from the anterior pituitary gland is dependent upon the portal plexus which is a vascular network that carries hypothalamic releasing hormones to the anterior pituitary gland (a.k.a hypothalamo-hypophyseal portal system)

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13
Q

what are the 4 stimulatory hypothalamic hormones?

A
  1. thyrotropin-releasing hormone (TRH)
  2. growth hormone-releasing hormone (GHRH) aka somatotropin
  3. gondadotropin-releasing hormone
  4. corticotropin-releasing hormone (CRH)
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14
Q

which nuclei is TRH released from and what is its effect?

A

released from the parvocellular neurosecretory neurons

it stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary

TSH then goes and acts on the thyroid gland which secretes T3 and T4

it also stimulates prolactin release from the anterior pituitary

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15
Q

which nuclei is GHRH released from and what is its effect?

A

released from the neuroendocrine neurons of the arcuate nucleus

GHRH stimulates release of Growth hormone (GH) in anterior pituitary

GH then acts on the liver which secretes insulin-like growth factors (IGFs)

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16
Q

which nuclei is GnRH released from and what is its effect?

A

released from the neuroendocrine cells of the Preoptic area

it stimulates follicle-stimulating hormone (FSH) release from anterior pituitary

it also stimulates Luteinizing hormone (LH) release from anterior pituitary

both FSH and LH are gonadotropins so they go and act on the endocrine cells of the gonads which secrete androgens in men and estrogen/progesterone in women

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17
Q

which nuclei is CRH released from and what is its effect?

A

it’s released from the parvocellular neurosecretory neurons

it stimulates adrenocorticotropic hormone (ACTH) release from anterior pituitary

ACTH then acts on the adrenal cortex which releases cortisol

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18
Q

what are the 2 inhibitory hypothalamic hormones?

A
  1. somatostatin

2. dopamine

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19
Q

from which hypothalamic nuclei is somatostatin released?

A

aka growth hormone inhibiting hormone

somatostatin is released by the cell bodies of neurons located in the periventricular, and ventromedial nuclei of the hypothalamus – it’s also produced in the pancreas

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20
Q

what is the function of somatostatin?

A
  1. inhibits secretion of Growth Hormone as well as TSH by somatotropes in the anterior pituitary
  2. inhibits insulin secretion by Beta cells of pancreatic islets
  3. inhibits Gastrin hormone in gastrointestinal tract
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21
Q

from which hypothalamic nuclei is dopamine released?

A

aka prolactin inhibiting factor (PIF)

it’s released from the cell bodies of neurons located in the arcuate and periventricular nuclei of hypothalamus

22
Q

what is the function of dopamine?

A

Inhibits secretion of Prolactin by lactotrophs in the anterior pituitary

23
Q

what is the difference between somatotropin and somatostatin?

A

somatotropin is also known as growth hormone releasing hormone and it stimulates the release of growth hormone in the anterior pituitary

somatostatin on the other hand inhibits the secretion of growth hormone!

24
Q

what is the other name for vasopressin?

A

anti-diuretic hormone = ADH

25
Q

where are oxytocin and vasopressin produced?

A

the hypothalamic nuclei

they’re just transported and stored in the posterior pituitary

26
Q

which hypothalamic nuclei produces vasopressin?

A

aka anti-diuretic hormone (ADH)

it’s produced by the supraoptic nucleus

27
Q

what is the function of vasopressin?

A

it indirectly regulates osmoreceptors in hypothalamus, baroreceptors in blood vessels, and chemoreceptors on kidney’s collecting ducts

so it increases water permeability in the distal convoluted tubules and collecting ducts of kidney nephron resulting in water reabsorption and increase in blood volume –> this way it regulates water balance and blood pressure

it also constricts the peripheral blood vessels which increases BP (hence the name vasopressin)

note: alcohol inhibits vasopressin and that’s why you have to pee all the time!

28
Q

which hypothalamic nuclei produces oxytocin?

A

the paraventricular nucleus

29
Q

what is the function of oxytocin?

A

controls maternal behavior, lactation and uterine contractions/ erection/ bonding and sexual arousal

causes contractions

so it effects the breast, uterine and other tissues

30
Q

which hypothalamic nuclei produces melanin-concentrating hormone?

A

MCH is produced by the tuberal lateral nucleus (lateral hypothalamic area)

31
Q

what is the function of melanin-concentrating hormone?

A

neuropeptide with appetite stimulant and sleep-promoting activities by projecting to a variety of brain areas

32
Q

how does the hypothalamus specific communicate with the anterior pituitary gland?

A

the hypophyseal portal system (the posterior pituitary gland receives direct signals through the infundibulum)

so when appropriately stimulated, the hypothalamic neurons secrete releasing and inhibiting hormones into the primary capillary plexus

the hypothalamic hormones then travel through the hypophyseal portal veins to the anterior pituitary gland where they stimulate or inhibit the release of hormones from the anterior pituitary gland

finally, anterior pituitary hormones are secretes into the secondary capillary plexus where they can leave and go perform their function

33
Q

what is the mechanism for how the hypothalamus maintains blood flow?

A

the hypothalamus promotes adjustments in cardiac output, vasomotor tone, blood osmolarity, adrenal clearance, and by motivating water and salt consumption

34
Q

what is the mechanism for how the hypothalamus regulates energy metabolism?

A

the hypothalamus monitors blood glucose levels, and regulates appetite, satiety, digestive functions, metabolic rate, and body temperature

35
Q

what is the mechanism for how the hypothalamus deals with crisis or life-threatening conditions?

A

the hypothalamus regulates the release of stress hormones, modulating the balance between sympathetic and parasympathetic tone, and influencing the regional distribution of blood flow

36
Q

how does the hypothalamus regulate reproductive activity or behavior?

A

the hypothalamus influences gender identity, sexual orientation, and courtship and mating behavior by regulating the menstrual cycle

37
Q

which 2 hormones are released by the posterior pituitary gland?

A
  1. vasopressin (ADH)

2. oxytocin

38
Q

what is the negative feedback loop of the hypothalamus?

A

for example, if the hypothalamus releases CRH, CRH will go and act on the anterior pituitary gland –> the AP will then release ACTH which will then go and act on the adrenal gland –> the adrenal gland will then release cortisol

cortisol will increase blood glucose levels but it will also go back and inhibit the hypothalamus from released CRH AND it will inhibit the anterior pituitary from releasing ACTH

on the other hand, if a patietnwas missing their adrenal gland and had low cortisol levels, then there would be a decrease in the degree of negative feedback inhibition on the hypothalamus and anterior pituitary so that more CRH from the hypothalamus na more ACTH from the anterior pituitary would be released as a compensatory mechanism so that cortisol levels will be normal

the clinical significance of negative feedback inhibition is that it works to keep hormone levels within a appropriate physiological range or ‘set point’

39
Q

what happens if anti-diuretic hormone levels are too high or too low?

A

too high = water retention, diluted blood, seizures

too low = dehydration, low BP

40
Q

what happens if corticotropin-releasing hormone levels are too high or too low?

A

too high = diabetes, high blood pressure, osteoporosis, abdominal obesity, acne, dysfunctional menstrual cycle, infertility, muscle loss and weakness (i.e. Cushing’s syndrome)

too low = weight loss, low blood pressure, gastrointestinal distress, anorexia nervosa, increased skin pigmentation in areas not exposed to sun (e.g. hand creases, genitals)

41
Q

what happens if gonadotropin-releasing hormone levels are too high or too low?

A

too high = Disrupted connection between the hypothalamus, pituitary gland, and gonads (i.e. menopause, removal of the testes or ovaries)

too low = Poor bone health, no puberty, infertility (i.e. Kallmann syndrome)

42
Q

what happens if growth hormone-releasing hormone levels are too high or too low?

A

too high = abnormal enlargement of hands, feet, and skull which alter facial features (i.e. acromegaly), diabetes, menstrual disorders

too low =
In children–delayed physical growth, delayed puberty

In adults—decreased muscle mass and increased body fat

43
Q

what happens if oxytocin levels are too high or low?

A

too high = beyond the brain, linked to enlarged prostate resulting in urination difficulty

too low = linked to breastfeeding difficulty in women and autism/poor social functioning in developing children

44
Q

what happens if somatostatin levels are too high or too low?

A

too high = beyond the brain diabetes, gallstones, intolerance to fat in the diet and diarrhea

too low = variety of physiological problems including uncontrolled growth hormone secretion

45
Q

what happens if thyrotropin-releasing hormone levels are too high or low?

A

too high = weigh loss, weak muscles, excessive sweating, excessive menstrual flow (i.e. hyperthyroidism)

too low = fatigue, depression, weight gain, feeling cold, constipation, dry skin, hair loss, heart problems, dyslipidemia, irregular menstrual cycles (i.e. hypothyroidism)

46
Q

lesion in the hypothalamus can cause which hormonal disorders?

A
  1. diencephalic syndrome
  2. precocious puberty
  3. hormonal deficiency
47
Q

what is Kallmann syndrome?

A

a genetically determined hypothalamic disorder marked by:

  1. failure to start or complete puberty. (hypogonadism)
  2. complete or partial lack of sense of smell (anosmia)

during embryonic development, GnRH neuron precursors and olfactory placode neurons are located at the SAME embryonic nasal region (meaning, they have the same embryonic origin) so these two sets of neurons migrate along same paths to their final destinations–> the olfactory axons go to Olfactory bulb and GnRH neurons go to hypothalamus

if there is a failure of development or failure of migration of these two sets of neurons, GnRH will not be synthesized and olfactory bulbs will not be formed either

this means that olfactory bulbs are either underdeveloped or completely missing (hyposmia vs anosmia) and GnRH neurons are also missing or in short supply

this lack of GnRh causes issues with egg/sperm formation which causes hypothalamic hypogonadism and lack of olfactory bulb neurons causes ansomia

therefore, clinically, a young adult patient reporting anosmia should be evaluated for hypogonadism and vice versa

48
Q

what is hypothalamic amenorrhea?

A

the absence or cessation of menses caused by a deficiency in the GnRH pulsatile secretion from hypothalamus, leading to reduced gonadotropin (FSH/ LH) secretion, resulting in hypogonadism

HA is an amenorrhea that results from stress, anxiety, excessive weight loss, low energy availability (low caloric intake, high energy expenditure due to excessive exercise, or both) –> it’s common in female athletes!

there is NO structural lesion present either in the hypothalamus or anterior pituitary; it is a functional amenorrhea– implying that it results from a functional disruption of pulsatile hypothalamic gonadotropin-releasing hormone (GnRH) due to low calorie intake or excessive expenditure of calories due to exercise!

49
Q

what happens when there’s no GnRH released from the hypothalamus?

A

there will be no downstream release of gonadotropins (FSH/LH) from the anterior pituitary

               -Therefore, there is no follicular development on the ovaries. And, since there are no follicles on the   		ovaries, there is no ovulation and there is no menses which  results in hypogonadism!

this is why hypothalamic amenorrhea is also called Hypothalamic-hypopituitary -hypogonadism

just remember that this is different than Kallmann syndrome!

50
Q

what part of the hypothalamus is affected by Huntington?

A

lateral hypothalamic nucleus

neuronal loss in the area may be a marker for disease progression

51
Q

which part of the hypothalamus is affected by Alzheimer’s and Parkinsons?

A

mammillary nucleus

histologic changes of the mammillary nucleus of the hypothalamus occur with Alzheimer’s and Parkinsons diseases

52
Q

what is Prader-Willi Syndrome?

A

a genetic disorder due to loss of function of specific genes and disrupted hypothalamic function/development

the often-abnormal position of the baby in the uterus at the onset of labor, the high incidence of fetal asphyxia / high incidence of premature or post-mature babies in PWS may all be related to abnormal fetal hypothalamic development

in newborns, symptoms include weak muscles, poor feeding, and slow development but beginning in childhood, the person becomes constantly hungry, which often leads to obesity and type 2 diabetes

in PWS, abnormal GnRH neurons in hypothalamus may responsible for the decreased levels of downstream sex hormones ( androgens) resulting in un-descended testes, small sex organs and insufficient growth during puberty in PWS

lack of GHRH hormone may contribute to the short stature of patients

faulty control of body temperature and daytime hypersomnolence may result from hypothalamic disturbances

the number of satiety neurons–in the hypothalamic paraventricular nucleus are markedly decreased in PWS—this is presumed to be the basis of the insatiable hunger (hyperphagia) and obesity of patients with the PWS

Neuro Week 2 (10 decks)

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