Endocrine Day 1- HPA relationship Flashcards
What is an endocrine hormone?
- Substance released from ductless gland into circulation so it can be carried to site of action
- endocrine system is slow to act and longer lasting compared to neurotransmitters.
- also endocrine hormones released in larger quantity
- Endocrine hormones help maintain homeostasis
- nervous system can perpetuate and magnify response of endocrine system
What is a neuroendocrine hormone?
- Neuron releasing neurohormone into a blood vessel
- Example is HPA system (hypthalamus-pituitary)
- rapid response by hypothalamic releasing hormone, longer lived response by activation of pituitary hormone release
- pituitary hormones then target other glands and they in turn make their own hormone.
- This is called the multiplier effect
- pituitary hormones then target other glands and they in turn make their own hormone.
- rapid response by hypothalamic releasing hormone, longer lived response by activation of pituitary hormone release
What is a paracrine hormone?
- Hormone released from one cell to act on cell nearby either directly (going directly to cell) OR via blood stream
- Can be autocrine as well.
- hormone released can influence cell which released the hormone
How do lipophilic hormones function?
- Lipophilic hormones are able to easily diffuse into cell membrane by concentration gradient
- Once inside cell either:
- 1) attach to cytoplasmic receptor (intracellular receptor)
- hormone-receptor complex diffuses through nucleus and binds to DNA
- 2) Diffuse through cytoplasm through nuclear membrane on its own
- 1) attach to cytoplasmic receptor (intracellular receptor)
How do hydophilic hormones function at celluar level?
- Bind to membrane receptors
- can’t readily pass through lipid bilary of membrane
- linked to second messaenger systems inside target cells
- see elevation in cAMP, Ca, or other second messenger systems.
- influence cellular activity on nuclear level
- specific proteins produced (enzymes, protein hormone, structural proteins, etc)
- this causes effect on cell to make a biological response
- see elevation in cAMP, Ca, or other second messenger systems.
How do thyroid hormones work?
- Lipophilic in nature
- composed of aromatic amina acid
- easily pass through cell membrane and nuclear membrane to have effect on cell.
How does the second messenger systems work?
- Water soluble (hyrophilic) hormone binds to external plasma membrane receptor, alter G protein in membrane of target cell
- Activate PIP–> IP3, DAG
- Results in intracellular stores of Ca
- activates kinase enzymes, causing phosphorylation of proteins, enzymes and activates them
- Drives some physiologicla response
- Also, can directly affect Ca channel to allow Ca to come into cell
- this is how hormones have physiological function
What is home to the neuroendocrine system?
Hypothalamus
What things does the hypothalmaus monitor?
- Body temp
- immune cell products (cytokines)
- hormone levels secreted by endocrine galnds
- monitoring elecytrolytes
- stress hormones
- reproductive hormones
What is released by the medial preoptic nucleus?
- Master sex hormone of body
- way to remember: you check someone out before (pre) with your eyes (optic). Checking someone out makes the master sex hormone (LHRH AKA GnRH)*
What does the anterior hypothalamic nucleus make?
- Thyrotropin-releasing hormone (TRH)
- master metabolic hormone- regulates thyroid
way to remember: thyroid sits on the anterior portion of your trachea, TRH is released from anterior hypothalamic region
What is released from paraventricular nucleus?
- Corticotropin releasing hormone (CRH)- master stress hormone
- Oxytocin
- Vasopressin
sister nucleus is supraoptic nucleus.
way to remember: The paraventricular nucleus has a sister named supraoptic nucleus. Both sisters have twins named ADH and oxytocin. Paraventricular also has a son named CRH and it’s stressful having a son.
What does the supraoptic nucleus release?
- Oxytocin
- Vasopressin
What does the periventricular nucleus make?
- Somatostatin- primary inhibitory hormone
- inhibits GH secretion from anterior pituitary
way to remember: Peri S.S. officer has a baricade that inhibits growth hormone
What does the ventromedial nucleus secrete?
- GHRH- growth hormone-regulating hormone
way to remember: On ventromedial location on a guy are pecs. Guy trying to make pecs grow from GHRH
What is secreted from arcuate nucleus?
- GHRH
- Dopamine (not a neuropeptide but a catecholamine)
- LHRH
way to remember: (warning, crude) Arucate is “arching” under ventromedial like a banana hammock. Guy wearing banana hammock is secreting:
- GHRH (to grow…)
- LHRH (master sex hormone)
- Dopamine (happy hormone)
What is the median eminence?
- Basal most portion of hypothalamus
- Extension of pituitary stalk and pituitary gland
- Where all neurons coming out of nuclei of hypothalamus (containing inhibitory and releasing hormone) terminte.
- median emminence contains nerve terminals and blood vessels, joining together
What are some other names for the posterior pituiatry?
What does it contain?
- AKA Neural lobe, neurohypophysis
- contain neurons with oxytocin and vasopressin
What are some other names for the anterior pituitary?
What is it made of?
- Adenohypophysis or pars distalis
- Epithelial cells developed from top of palate (rathke’s pouch)
Way to remember: think top of palate is your adenoids, the anterior pituitary forms from tissue on top of palates, therefor also called adenohypophysis
What is the sella turcica?
- “turkish saddle”
- where pituitary sits in sphenoid bone
What can happen if a tumor is so large, it pushes the pituitary upwards?
Loss of vision d/t the compression of the optic chiasm/optic nerve directly above pituitary
What is a macroadnemoa, microadenoma and how are they each treated?
-
Macroadenoma >10 mm
- Causes mechanical damage to other anterior pituitary cells in gland, causing hormonal deficits
- typically a pituitary tumor oversecretes one hormone (or maybe more)
- typically need to be surgically removed
-
Microadenoma <10 mm
- typically only causes overproduction of a hormone (prolactin, GH production most common)
- typically medically/pharmacologiclaly managed with somatostatin
Why is somatostatin used to treat pituitary tumors?
- Anytime somatostatin is active, it’s inhibitory
- has receptors all over the body
- somatostatin and analogs developed into drugs ot control tumor growth. Can treat microadenomas. helpful if it’s overproducing growth hormone
What is the blood supply for the anterior pituitary?
- Internal carotid artery–> superior hypophyseal artery-> primary capillary plexus–> long portal veins–> secondary capillary plexus–> sinusoids–> anterior pituitary cells
- The blood around anterior pituitary is venous blood
- more susceptible to loss of perfusion with drops in BP
What is the blood supply to the posterior pituitary?
- Internal carotid artery–> inferior hypophyseal artery–> posterior pituitary
- supplied by arterial blood (unlike anterior pituitary)
- since it is provided by arterial supply, smooth muscle can vasoconstrict and autoregulate the flow (upto a point) with decreasing BP
- Posterior pituitary mainly contains neurons and is much less vascularized compared to the anterior pituitary
What kind of junction is in median eminence?
Neuron-capillary junction
- Has dnse material- nerve terminals which contain releasing factors hormones, in direct contact with capillary lumens
- capillary lumens have endothelial cells
- form gap junctions
- allow solutes to pass from blood to neural tissue and defeat BBB
- Allows hypothalamus to monitor concentraiton of solutes in blood stream
- capillary lumens have endothelial cells
What do the fenestrated capillaries in the median eminence allow?
Allows particle to pass form blood to neural tissue- no BBB here
What are circumventricular organs?
- Organs where the BBB does not exist
- One’s we’re concerned about are:
- Neurohypophysis (posterior pituitary)
- OVLT- Organum vasculosum of lamina terminalis
- Median eminence
way to remember: nom nom nom passes the BBB. “eats” up the blood
What is the pathway of a most typical type of hypothalmaic neuron?
- Produces hypothalamic releasing hormone. Cell body in one of the hypothalmic nuclei with axonal projections onto the primary capillary plexus of the median eminence
- releases neuronal contents into blood vessels
- Lumpkin called these “hypophysiotropic neurons” in class
What is another type of hypothalamic functional unit besides the hypophysiotropic neurons?
- Neurons that carry oxytocin/vasopressin from paraventricular or supraoptic nuclei, down into neural lob (posterior pituitary)
What are some characteristics of oxytocin/vasopressin?
- Both composed of 9 aa, differing by only 2 aa
- also called nonapeptides
Where does oxytocin act?
Smooth muscle- uterus, breast (let down for milk production)
What causes stimulation fo ADH secretion?
- Extracellular fluid osmolality increase
- volume decrease
- pressure ecrease
- CSF increase
- pain
- stress
- temperature increase
- b-adrenergic agonist
- Drugs
- nicotine
- opiates
- barbitutartes
- sulfonylureas
- antineoplastic agents
What causes ADH inhibition?
- Temperature decrease
- alpha adrenergic agonist
- ethanol
- cortisol
- thyroid hormone
What does GHRH stimulate from anteior pituitary? What are the cells stimulated called?
- GHRH releases GH
- somatotrophs- cells that release GH
- elevates cAMP, causes proliferation of somatotrophs
- somatotrophs- cells that release GH
What does SS cause in the anterior pituitary?
- Inhibits GH and TSH
- inhibits cAMP
- Inhibits cell production
- inhibits cAMP, inhibits cellular activity
What does TRH stimulate in anterior pituitary? What are the cells activated called?
- TRH (thyrotropin releasing hormone) releases TSH (thyroid stimulating hormone) from anterior pituitary
- thyrotrophs- cells that secrete TSH
- TRH also stimualtes prolactin secretion but NOT major physiological hormone
What effect does dopamine have on anteior pituitary?
- Dopamine is inhibitory towards prolactin
- What would happen in neurons producing dopamine were blocked/destoryed?
- Increase in prolactin levels
- What would happen in neurons producing dopamine were blocked/destoryed?
What s GnRh (aka LHRH)’s effect on anterior pituitary?
- LHRH stimulates LH/FSH prodcution
- gonadotrophs- cells that produce LH/FSH
What is corticotropin-releasing hormone’s role in anterior pituitary?
- CRH stimulates cells making ACTH
- Corticotrophs- cells release ACTH
The only significant physiological significant stimulator and inhibitory is ___ ___
growth hormone
What is long-loop negative feedback?
- When hormone released from target cells goes back to pituitary and hypothalamus to inhibit further secretion
- blood-borne mediated
What is short loop negative feedback?
- When hormone released from pituitary feeds back on hypothalamus and stops further increase
- blood borne mediated.
What is ultra short loop negative feedback?
- When axonal collaterals off releasing hormone neuron goes back and inhibits further activity of neuron
- nueronally mediated (basis for pulastile anterior pituitary hormone secretion)
Every pituitary hormon is ____ in nature. Why?
Pulsatile
- This prevents overstimulation and desensitization
- allows episodic release of hormone
- hormones never are released, with hormonal levels continuously high, unless something is wrong
