Hypothalmic Axis Flashcards
the pituitary gland is also called the _____
hypophysis
what is the significance of the hypothalamo-pituitary axis?
connection from brain to body: allow brain to maintain homeostasis (control center for endocrine system)
What was believed to control/influence the body prior to discovery of hormones?
the 4 humours (choleric, phlegmatic, sanguine, melancholic)
Who first described the parts of the pituitary?
Rathke (19th century)
What did Aristotle identify the pituitary as?
connection between brain/body that 4 humours passes through
What are the 2 parts of the pituitary?
adenohypophysis (anterior pit.)
neurohypophysis (posterior pit.)
Who associated pituitary tumors with acromegaly? When?
Pierre Marie (1886)
Who pioneered a method to improve acromegaly patients? How?
Harvey Cushing (1909); removed part of pituitary
What experiment led to the discovery of growth hormone?
Evans & Long (1922) injected crude pituitary gland extract of animals -> increased growth
How were most hormone functions discovered?
animal experiments
What controls the pituitary?
Hypothalamus
The hypothalamo-pituitary axis is also known as: _____
adenohypophysial axis
What size is the pituitary? Where is it located?
0.5-1g (1cm diameter)
connected to hypothalamus stalk (under optic chiasm), within protective bone ‘saddle’ (sella turcica)
What physical changes happen in the pituitary during pregnancy and why?
increased size (>30%) need increased hormones for preg & lactation
What are the anatomical parts of the anterior pituitary?
pars tuberalis
pars intermedia
pars distalis
What are the anatomical parts of the posterior pituitary?
infundibular stalk
pars nervosa
How does the hypothalamo-hypophyseal tract develop? (2)
Rathke’s pouch (outgrowth of buccal cavity) -> detach and become anterior pituitary
Neuroectoderm outgrowh (from third ventricle) -> form infundibulum, pituitary stalk, median eminence, posterior pituitary
The anterior pituitary is formed from _____ cells, that develop from: ______.
ectodermal
Rathke’s pouch (outgrowth from buccal cavity/primitive mouth below)
What cells form the posterior pituitary? Where is their origin, and what else do they form?
neuralectoderm cells
from neurohypophyseal bud (downgrowth from forebrain floor)
forms infundibulum, median eminence, pituitary stalk
the pituitary is located below the ___ ____, encased in a cavity known as the ___ ___, within the ____ bone.
optic chiasma
turkish saddle
sphenoid
Describe the blood flow pathway through the pituitary and hypothalamus:
from body -> hypophysial artery -> median eminence capillary bed -> portal blood vessel -> anterior pituitary capillary bed -> vein -> back to body
Where are the major 2 capillary beds in the adenohypophysis located?
median eminence
anterior pituitary
What carries blood from the median eminence down to the anterior pituitary?
portal hypophysial vessel
There is some blood flow from the pituitary back to the hypothalamus, known as ___ flow. Why is this important?
retrograde flow
allow hormonal feedback from pit. to hypothalamus (short loop)
How does the hypothalamus control the anterior pit.?
through releasing or inhibiting hormones -> passed through hypothalamic-hypophyseal portal system
How does the hypothalamus control the posterior pituitary?
direct control (axons from hypothalamus extend down into posterior pit.)
True/False: the posterior pituitary does not make any hormones
True; hormones made by neuron cells from above, released through axons
True/False: posterior pituitary hormones cannot be stored
False; can be stored
The specialized neurons that make the posterior pit. hormones are known as ____ neurons
neurosecretory
What are the posterior pit. hormones?
vasopressin (ADH)
oxytocin
Describe the production and release of the posterior pituitary hormones:
produced in cell bodies of neurosecretory hormones (in hypothalamus) -> packaged in granules -> migrate to axons (in posterior pit.)
hypothalamus neurons stimulated -> trigger release from axon tips -> into capillaries/bloodstream
_____ hormones are released from the hypothalamus into the _______, and flow through the ____ down to the anterior pituitary.
hypophysiotrophic
median eminence
HHPS (portal vein)
True/False: a hypothalamic neurosecretory cell can produce a large variety of hormones
False: cells are highly specialized, can only produced 1 type of hormone
How are the hypothalmic cells organized?
in bundles according to function (each section makes different hormone)
what hypothalamic nuclei are responsible for the posterior pituitary? (2)
supraoptic nuclei
paraventricular nuclei
Which hypothalamic nuclei are responsible for the anterior pituitary?
hypothalamic-hypophysiotropic nuclei
What controls the hypothalamus?
signals from all other parts of brain -> neurotransmitters
What are the main neurotransmitters? (5)
norepinephrine epinephrine dopamine serotonin acetylcholine
What happens to hormone production if the hypothalamus is removed?
no posterior pit. hormones
most anterior pit. hormones stop
GH, FSH, LH fall to basal levels (very low)
PRL increases
What anterior pituitary hormones show some degree of autonomy in secretion?
GH, FSH, LH (will still have some low levels without hypothalamus)
How is PRL control different from the other pit. hormones?
hypothalamus does INHIBITORY control, not stimulatory
What are the subgroups of cells in the anterior pituitary gland? What do they produce?
- somatotrophs (GH)
- mammotrophs (PRL)
- thyrotrophs (TSH)
- gonadotrophs (LH, FSH)
- corticotrophs (ACTH, beta lipotropin)
What is the target(s) of ACTH?
adrenal gland
adipocytes
melanocytes
What anterior pit. hormone causes responses in almost all cells?
GH
What antierior pit. hormone targets the breasts and gonads?
PRL
Classify the anterior pit. cells based on their cell type (2 types)
- basophils: thyrotrophs, gonadotrophs, corticotrophs
2. acidophils: somatotrophs, mammotrophs
How are basophil hormones and acidophil hormones different?
basophil hormones more heavily glycosylated; protected from degradation (longer half life)
What hormone would have a longer half life: GH or FSH?
FSH
What is TRH and its role?
thyrotrophin releasing hormone (from hypothalamus)
stimulate release of TSH & PRL
minor stimulation of FSH release
What is GnRH and its role?
gonadotrophin releasing hormone (from hypothalamus)
stimulate release of LH, FSH
What hypthalmic hormone stimulates release of GH? What is its counterpart?
GHRH
somatostatin (SMS) will inhibit GH
What hormone works counterpart to TRH?
somatostatin (will inhibit TSH and PRL)
How is PRL controlled (primary control)
inhibited by dopamine from hypothalamus
___ and ____ promote FSH release
GnRH
TRH (minor)
Characteristics of hypothalmic hormones affecting anterior pituitary:
fast action
short half-life
bind to GPCR
What type of G proteins are used by trophic vs. inhibitory hypothalmic hormones?
trophic (stimulatory): Gas, Gaq
inhibitory: Gai
What are the different feedback loop types in the hypothalmic-pituitary axis?
- short feedback loop: AP hormones -> hypothalamus
- Fast feedback loop: from ultimate hormone -> hypothalamus & adenohypophysis
- Long feedback loop: ultimate hormone -> CNS, hypothalamus, adenohypophysis
What is the general release pattern of hypothalmic hormones, and why is this important? (2)
pulsatile release
- synchronized with target tissue
- must keep renewing stimulus (short half life of signals)
Role of the pineal gland:
take info from light signals -> help set biological rhythm
Major hormone of pineal gland:
melatonin (made from Trp)
How do melatonin levels change throughout the day, and throughout life stages?
production begin in evening -> peak at night -> fall low in day
highest in youth -> decline with age
Why does melatonin secretion decrease with age?
sleep is less crucial (no more development)
calcification of pineal gland
Describe the pathway controlling circadian rhythm from light stimulus
light -> retina -> SCN -> b-adrenergic receptor on pinealocyte -> activate cAMP pathway -> convert Trp to melatonin -> body (and also back to SCN for feedback)
What acts as the circadian pacemaker ‘clock?’
SCN (suprachiasmatic nucleus)
What is the effect of darkness on melatonin?
levels increase (up to 10-fold)
functions of melatonin:
core body temp
induce sleep
depress reproductive activity in animals
additional melatonin functions (possible)
antioxidant (anti-aging properties?)
enhance immunity (correlation, not necessarily causation)
help adjust jet-lag
sleeping aid in elderly
possible side effects of melatonin supplements:
daytime sleepiness
hypothermia
desensitized receptors
adverse effects in those with seizure disorders
adverse interaction with coumadin/warfarin
What is ‘chronotherapy?’
optimatl timing of medication, surgery, chemotherapy to align with hormone levels for maximum effectiveness
examples of chronotherapy:
asthma meds in morning (when attacks are the worst)
arthritis meds at night (when pain is worst)
breast cancer surgery after ovulation (when estrogen is low; to prevent tissue regrowth from estrogen acting as mitogen)
