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Flashcards in Endocrine System Control Deck (11):

Target cells

Target cells must have specific receptors to which hormones bind


Target cell activation depends on

-Blood levels of the hormone (how much hormone?)
- relative number of receptors on or in the target cell (how many receptors)
- affinity of binding between receptor and hormone (how easily do the two join together)


Hormone regulation

Hormones are continually secreted into the bloodstream
Circulation in the blood either freely (protein &AA based)or bound to plasma proteins (steroid & thyroid)
Blood levels vary within a very small range, and are controlled by negative feedback systems


Concentration of a circulating hormone reflects

- it's rate of release
- the speed of inactivation &a removal from the body
- mechanism of transport


The secretion of hormones is controlled by

- changes in plasma solute concentration of ions or organic nutrients - humoral stimuli
- regulation by the nervous system - neural stimuli
- regulation by other hormones - hormonal stimuli


Humoral stimuli

Hormones released in direct response to changing blood levels of certain ions & nutrients

Low CA2+ -> parathyroid hormone release
High blood glucose -> insulin release


Neural stimuli

Nerve fibres stimulate release of hormones
- periods of stress cause the sympThetic nervous system to stimulate the release of epinephrine & norepinephrine ( adrenaline & noradrenaline)


Hormonal stimuli

Many endocrine glands release hormones in response to hormones produced by other glands
- for example the hypothalamic-pituitary-target endocrine organ feedback loop


Positive feedback enhances

The response of the initial stimulus


Negative feedback reduces or reverses

The response of the initial stimulus

- hormone production usually regulated this way
- endocrine system tends to oversecrete, so the negative feedback system maintains homeostasis....


Nervous system modulation

The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanism...