endocrine 1.4 Flashcards
pituitary gland - components, connections
we have neural and vascular connections between the hypothalamus and pituitary gland
-via the infundibulum : connects hypothalamus to pituitary gland, contains axons from neurons of the hypothalamus as well as blood vessels
anterior : is a gland
posterior : extension of neural components
posterior pituitary connections
have the supraoptic and paraventricular nuclei that pass down the infundibulum
-(no connection between hypothalamus and ant pituitary)
median eminence
junction between hypothalamus and infundibulum
hypothalamo-hypophyseal portal vessels (or portal vein)
posterior pituitary hormones : synthesize where? what are hormones it releases
-synthesized in the hypothalamus, specifically the cell bodies of the supraoptic and paraventricular nuclei
-two hormones : oxytocin and vasopressin
neural extension of hypothalamus
oxytocin functions
1) contraction of smooth muscle cells in the breast which results in milk ejection during lactation
- positive feedback to increase more from suckling
2) contraction of uterine smooth muscle cells until the baby is born
vasopressin (or ADH)
released when high osmolality of water or low BP
-detected by hypothalamus and act on posterior pituitary to release vasopressin, goes towards nephron in kidneys and increases sodium retention and water retention
-water follows salt so if we retain salt we can retain water
-second mechanism is via carotid sinus receptors detecting low BP and release vasopressin
there is negative feedback to stop these from happening
anterior pituitary gland hormones and the hypothalamus
- hypothalamic neurons secrete hormones that control the secretion of all the anterior pituitary gland hormones
- hypophysiotropic hormones : hypothalamic hormones that regulate anterior pituitary gland function (can be excitatory or inhibitory)
hypophysiotropic hormone
hypothalamic hormones that regulate anterior pituitary gland function (can be excitatory or inhibitory)
- carried by the hypothalamo-hypophyseal portal vessels to the anterior pituitary gland capillaries, into the interstitial fluid surrounding the various anterior pituitary gland cells
- all hypophysiotropic hormones are the first in a 3 hormone sequence (except for DOPAMINE)
- good to have a sequence bc it permits a variety of important hormonal feedback and amplification of response
anterior pituitary hormones
secretes 6 peptide hormones
- FSH
- LH
- GH growth hormone
- TSH thyroid stimulating hormone
- prolactine
- ACTH Adrenocorticotropic hormone
FSH and LH
known as gonadotropins effect on the gonads
FSH LH and GH
stimulate target cells to synthesize and secrete other hormones and additional functions
prolactin
no control over secretion of other hormones
-breast development and milk production in women
GH
liver and other cells secrete IGF-1
- many organ and tissues do protein synthesis, carbohydrate and lipid metabolism
TSH and ACTH
stimulate target cells to synthesize and secrete other hormones
-ACTH stimulates adrenal cortex to secrete cortisol
TSH stimulates thyroid to release thyroxine and triodothyronine
similarities of anterior and posterior pituitary
- secrete hormones in the same manner
- are synthesized in cell bodies of the hypothalamic neurons
- passed down axons to the neuron terminal
- released in response to an AP
anterior pituitary hormone sequence
- hypophysiotropic hormones begin in the hypothalamus and end on the capillaries in the median eminence
- hypophysiotropic hormones enter the capillaries in the median eminence and empty into the hypothalami-hypophyseal portal vessels which carry them to the cells of the anterior pituitary gland
posterior pituitary hormone sequence
- hypothalamic neurons that secrete hormones that leave the hypothalamus and end in the posterior pituitary
- most capillaries into which the hormones are secreted are immediately drained into general circulation
effect of portal vessels on concentration
- portal vessels have a small amount of blood so we dont need to release a high amount of hormones to have a high concentration
- if we release hormones from the hypothalamus directly into the general circulation we have to have a higher concentration
hypothalamus releases hormones which have excitatory or inhibitory effects on Ant pit hormones*
GnRH, GHRH, SST, TRH, DA, CRH
GnRH
excitatory effect on release of gonadotropins (FSH and LH)
GHRH growth hormone releasing hormone and SST somatostatin effect on…
GHRH stimulates secretion of GH
SST inhibits GH
TRH thyrotropin releasing hormone
stimulates secretion of TSH
which hypophysiotropic hormones are peptides which are catecholamines?
dopamine is a catecholamine
all of the others are peptides
Dopamine
inhibits prolactin (-)
corticotropin releasing hormone (CRH)
stimulates secretion of ACTH adrenocropticotropin hormone
neural control of hypophysiotropic hormones
receives stimulatory and inhibitory input from all areas of the CNS
→ have specific neural pathways influence the secretion of individual hormones
NT ( catecholamine and seretonin) are released at synapses on the hypothalamic neurons
-Have circadian influence (24 hour cycle)
→ are linked to inputs from visual pathways that recognize the presence or absence of light eg. CRH
GH release, effects, role of leptin
GHRH in hypothalamus which releases GH from ant pit
GH acts on bones for growth and repair, and on the liver to increase IGF-1 which increases growth
When we have too much GH, IGF-1 has a negative feedback on ant pit and hypothalamus to stop the circuit
Leptin affects GH, when we have a lot of fat leptin increased and appetite lowers. if you have too much leptin it will impair your bone function
episodic endocrine secretion - diurnal rhythm (cortisol)
durnal : day and night
cortisol increases at 4am peaks at 6am. regulated with day and night patterns
naps do not increase cortisol
episodic endocrine secretion - ultradian (GnRH)
minutes or hours
GnRH increases by the hour
LH peaks every 1 or 2 hours as well
hormonal feedback control of the hypothalamus and anterior pituitary gland
negative feedback loops
long loop negative feedback : exerted onto the hypothalamus and/or anterior pituitary gland by the 3rd hormone in sequence
short loop negative feedback : exerted by the anterior pituitary gland hormone on the hypothalamus
nonsequence hormones on the hypothalamus and ant pit gland
have many stimulatory and inhibitory hormonal influences on the hypothalamus and/or anterior pituitary gland other than those from a feedback loop
example : estradiol and prolactin
