Hypothalamus Flashcards
where are the major control point of the ANS?
hypothalamus
medulla
pons
what does the hypothalamus integrate?
neural and hormonal responses
what is the role of the hypothalamic nuclei ?
involved in the body, behavior and autonomic nervous system to control tasks like hunger, temperature regulation, sexual behavior, circadian rhythms and hormone release
supraoptic and paraventricular nuclei in the hypothalamus are responsible for producing what two key hormones?
- Arginine Vasopressin (AVP), also known as antidiuretic hormone (ADH)
- Oxytocin
What is another name for the posterior pituitary gland? anterior?
Neurohypophysis
Adenohypophysis
Nuclei like the arcuate nucleus release hormones such as
Dopamine, which inhibits prolactin
How is the anterior pituitary different from the posterior pituitary in terms of communication with the hypothalamus?
The anterior pituitary requires a venous plexus (blood vessel system), while the posterior pituitary uses direct neural connections
Are the vascular connections between the hypothalamus and pituitary inside the blood-brain barrier?
No, they are outside the blood-brain barrier, allowing negative feedback from circulating hormones.
what are the releasing hormones and their targets for the anterior pituitary?
GHRH → Growth Hormone (GH)
GnRH → FSH and LH
CRH → ACTH
TRH → TSH
what are the hormones released from nerve endings that directly enter the blood stream from the posterior pituitary?
- Oxytocin for breast milk ejection, uterine contractions
- AVP/ADH for water retention in kidneys
what are the target sites for GH that is released from the anterior pituitary and what occurs?
- Liver: Stimulates production of IGF-1 (Insulin-like Growth Factor-1)
- Adipose tissue: lipolysis and reduces glucose uptake
- Muscles: Increases glucose and amino acid uptake, protein synthesis
- Bones: Stimulates growth, collagen production, and cell division
what are the two negative feedback pathways for GH release?
Both GH and IGF-1can inhibit the hypothalamus (reducing GHRH and increasing SST) and the anterior pituitary (reducing GH release)
how can cortical centers start hypothalamic activity?
You feel stressed → the prefrontal cortex activates the hypothalamus → triggers the Hypothalamic–Pituitary–Adrenal axis → releases cortisol
how is oxytocin regulated?
positive feedback loop, during labor uterine contractions cause oxytocin release → which causes more contractions → which releases more oxytocin
what does the hypothalamus release when it senses stress?
CRH (corticotropin-releasing hormone)
what does the release of CRH trigger?
the anterior pituitary to release ACTH (adrenocorticotropic hormone) and Beta-endorphins (natural painkillers)
What does ACTH signal the release of?
cortisol from the adrenal medulla
what is cortisol?
a glucocorticoid that causes a delayed increase (6 hours) in blood glucose to defend against hypoglycemia
what is the function of beta-endorphins?
reduce pain response and elevate mood
when are beta-endorphins and cortisol mainly released?
during catabolic states like stress, exercise, starvation, and hypoglycemia
what can happen if an insulin dose is too high for type I/II diabetics?
hypoglycemia will result and cause for the
increase in activity in the NTS and the hypothalamus
what portion of the brain is activated in heightened states of alertness?
locus ceruleus
** (key center for NE release)
what happens when stress activates the sympathetic nervous system?
- positive chronotropism (increased heart rate)
- positive inotropism (increased heart contractility)
- redirection of blood flow to skeletal muscles, heart and brain
- vasodilation in skeletal muscles through beta-2 adrenergic receptors
what can happen if stress causes the over activation of the vagus nerve (increased vagal activity)?
shut-down response (PNS)
- Lower heart rate
- Lower cardiac output
- Reduced blood flow to the brain → which can lead to fainting (syncope) or CNS ischemia
what can chronic opioid use be linked too?
impaired sexual dysfunction, hypogonadism, decreased libido, infertility and androgen deficiency
what does chronic opioid use inhibit the release of?
GnRH from the hypothalamus which will cause a ↓ GnRH → ↓ LH and FSH → ↓ testosterone and sperm production
what withdraw drug can be linked to endocrine dysfunction?
methadone
How does the hypothalamus regulate body temperature in response to cold and heat?
through reflexes:
- posterior hypothalamus responds to cold exposure by triggering reflexes like shivering
- anterior hypothalamus responds to heat by triggering sweating and vasodilation
What are the main ways the body produces and loses heat to maintain temperature balance?
- Heat Production through exercise, digestion and absorption of food and cellular metabolism
- Heat Loss through radiation, conduction, vaporization and excretion (very small amount)
Why is it important to regulate core body temperature?
it influences enzyme function
Where is the body’s temperature “set point” regulated, and how does the body maintain it?
hypothalamus
- it receives temperature signals from the peripheral nervous system, compares them to an internal “set point” and send autonomic signals to either increase heat loss or heat conservation/production
How does the body generate heat in response to cold exposure?
- Shivering and increased muscle activity via ANS and thyroid hormones
- Brown adipose tissue (BAT) produces heat directly
- White adipose tissue (WAT) can convert to BAT
- thyroid gland increases secretion of T3 and T4 which increases BMR
what is browning?
when WAT converts to BAT by activation of beta-3 adrenergic receptors
How does the body preserve heat during cold exposure?
Vasoconstriction of skin blood vessels mediated by alpha-1 adrenergic receptor activation by NE
Why is heat considered a stronger (pre-potent) stimulus than cold?
it can cause protein denaturation
how does the body cool down?
vasodilation, eccrine sweat gland activation (most effective), decreased TSH and increased respiration rate
how does the body prevent dehydration during exposure to high temperatures?
the body releases AVP through activation of warm receptors in the skin and warm venous blood returning to the hypothalamus
how is a fever produced during inflammatory responses?
exogenous pyrogens cause the immune system to release cytokines (IL-1B and IL-6) which trigger the brain to release PGE2 which activates the anterior hypothalamus ↑ cAMP and ↑ body temperature and ↑ in thermoregulatory set point
how do fever-reducing medications like NSAIDs work?
block PGE₂ production by inhibiting COX-2
what can happen if a fever persists for too long?
if the fever is too high or lasts too long, it can become dangerous and cause damage (like brain issues or dehydration)
how does cortisol effect appetite?
- Moderate stress = more hunger
- Chronic or severe stress = less or irregular hunger
what are the key players that increase appetite?
Ghrelin (hunger hormone)
- NPY (Neuropeptide Y)
- AgRP (Agouti-related peptide)
- MCH (Melanin-concentrating hormone)
- Orexin
- Endocannabinoids (same system marijuana activates)
what is leptin?
molecule released by fat cells after a meal to inhibit feeding behavior
*(many humans are resistant to leptin)
what happens when there is anorexigenic signals (appetite suppressant)?
leptin and insulin activate POMC neurons in the arcuate nucleus to produce POMC protein that splits into α-MSH and ACTH
what is the function of ⍺-MSH?
bind to MC4R (melanocortin-4 receptor) and inhibit food intake and increase energy use
what happens when there is orexigenic signals (appetite stimulant)?
ghrelin activates AgRP/NPY neurons to release AgRP and NPY which increase appetite
how does your body know when you are finished with a meal?
- high blood sugar, insulin, and CCK will signal via the vagus nerve to the brain and activate POMC neurons
- CRH increases cortisol (stress)
- gastric distension stimulates vagus
what does increased plasma leptin activate?
TORC1 genes which:
- activates CART gene → suppresses appetite
- activates KISS1 gene → signals reproductive readiness
what can low leptin in men and women cause?
- reduce rate of sperm production
- amenorrhea (loss of periods in women)
what can high levels of leptin lead to?
inhibition of LH
When your blood sugar drops (low plasma glucose), your body activates
orexigenic signals like ghrelin, galanin and orexins A and B
what area does ghrelin stimulate?
lateral hypothalamus area (LHA)
how does Neuropeptide Y (NPY) stimulate appetite?
released from the medial arcuate nucleus and inhibits the release of CRH through activation of GABA producing neurons
how does Orexin A and B stimulate appetite?
activates the LHA via GPCR pathways (Gs)
what occurs under chronic low level stress?
ghrelin stimulates the release of NPY and Agouti-related peptide
- NPY binds Y1 receptors to increase food intake and inhibit GABA release (more CRH)
- AgRP blocks MC4R pathway and inhibits POMC neurons
why do humans stress eat?
stress increases cortisol which increases hunger for comfort foods that activate the brain reward pathway
* over time the brain can become resistant to insulin and leptin, so it keeps thinking you’re hungry
why does ghrelin drop after gastric bypass surgery?
theory is food no longer touches certain parts of the stomach lining, which may be crucial for ghrelin production
how do the ENS & NTS (Nucleus Tractus Solitarius) connections influence appetite?
- chemoreceptors in the gut send signals like stomach distention to the NTS —> ARC of the hypothalamus
- high blood sugar causes astrocytes around POMC neurons to shrink which ↓ appetite
what are the appetite and drug therapies for Chemotherapy-Induced Nausea and Vomiting (CINV)?
- 5-HT₃ (Serotonin) Receptor Antagonists
- Anticholinergics
- Antihistamines
what are the two main drivers for sleep-wake cycles?
- Circadian Rhythm (Endogenous Clock)
- Sleep drive
what pattern do the two key hormones in the sleep-wake cycle follow and what do they do?
melatonin and cortisol follow a diurnal pattern
- melatonin is released by the pineal gland around 9 pm to help induce sleepiness
- cortisol rises in the early morning 4-6 am and help you to wake up
what is sleep hygiene?
set of behavioral and environmental recommendations to optimize sleep drive
when trying to diagnose a patient with insomnia and they present with restless leg syndrome what should you check?
ferritin levels
what are the non-pharmological approaches for treatment of insomnia?
- Cognitive behavioral therapy for insomnia (CBT-I, first line therapy)
- Sleep hygiene
- Sleep deprivation
- Meditation or relaxation techniques
what are the two ways thirst is triggered?
hypertonicity (increased plasma osmolality, mainly due to high sodium) or hypovolemia (low blood volume)
what happens after the body detects changes in osmolality or blood volume?
osmoreceptors (in the PVN and SON of the hypothalamus) and baroreceptors/angiotensin II (in blood vessels) send signals to the hypothalamus that activates the thirst response
AVP acts through what three types of GPCRs (G-protein coupled receptors)?
- V1A and V1B receptors use Gq → activate IP3 and DAG → increase calcium → cause vasoconstriction
- V2 receptors use Gs → increase cAMP → enhance water reabsorption in the kidney collecting ducts
where is the thirst response regulated?
lateral hypothalamus
what is diabetes insipidus and how is it treated?
a condition where AVP is deficient, causing excessive urination and thirst
- A synthetic form of AVP (like desmopressin) can be used to treat it
what pathway does oxytocin work through?
Oxytocin acts through a GPCR, specifically using the Gq pathway that increases intracellular calcium, which causes smooth muscle contraction
explain the Let-Down Reflex
neuroendocrine reflex triggered by suckling at the nipple
- Touch receptors in the nipple send signals via sensory nerves to the hypothalamus which activates oxytocin release and causes myoepithelial cells in the breast to contract
How does the limbic system influence the neuroendocrine system?
The amygdala activates the hypothalamus, increasing the release of hormones and neurotransmitters like serotonin, dopamine, and glutamate, which can affect appetite and stress responses
What are the effects of the limbic system on the autonomic and somatic motor systems?
It increases blood pressure, heart rate, and alertness (via ANS), and speeds up movement away from threats by reducing reaction time (via somatic motor control).
