Endocrine System


Endocrine System

what is it?

a collection of glands which secrete their product directly into circulation to be carried to a distant target

AUTOCRINE= act on the cells which synthesised them

PARACRINE= synthesised close to site of action

ENDOCRINE= synthesised by endocrine flands an travel in circulation


water soluble hydrophilic hormones

bind to receptors on the cell surface as they can pass through the cell wall as its made of lipids

- normally made up of short chains of amino acids

- they are soluble in aqueous medium so cant cross cell membranes

- bind to receptors on cell membrane initiating reactions within the cells which lead to alteration in cell function

their alteration in signal transduction results in:

-> a change in gene transcription

->a change in cytoplasmic function

lipid soluble lipophilic hormones

however can cross the cell membrane and bind to receptors in te cytoplasm or nucleus of the target cell

- not soluble in an aqueous medium so they can cross cell membranes

- enter the target cell and bind to receprots in the cell leading to an alteration in cell function

their alteration in signal transduction resutls in:

->a change in gene transcription 

The Pituitary Gland

Lies below the hypothalamus consisiting of two fused glands


neurohormones from the hypothalamus control relase of hormones form anterior pitutitary

they reach the anteriro pituitary through a specialised circulatory stystem called the HYPOTHALAMOHYPOPHYSEAL PORTAL SYSTEM

a protal system: a way of transporting substances direclty from one tissue to another without having to go through the whole circulatory system first

there are two sets of capillary beds, blood passes through them in series, the blood from metarterole (links arteries and capillaries) in first capillary bed thorugh a protal vein into a second capillary bed 

releasing and inhibiting hormones from hypothalamus -> first capillary plexus -> portal veing -> secondary capullary plexus -> diffuse into adenohypophysis (anterior pituitary)

Tropic Hormones regualte activity of…


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