The Endocrine System

Endocrine System and hormones

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Homeostasis and the Endocrine System
Homeostasis-maintenance of a constant internal environment.
Mechanism of Homeostasis
Changes in the variable stimulate a receptor, the receptor communicates
with the control centre via an afferent pathway. The control centre
communicates with an effector via efferent pathway. The Effector causes a
response to stimulus. The response brings the variable back to normal and
the receptor provides feedback to the control centre.
1. Negative Feedback- any action caused by a stimulus which has the
effect of dimishing the stimulus.
2. Postitive Feedback- any action this is caused by a stimulus which had the effect of increasing the stimulus eg
car backfiring.
Endocrine system- endocrine glands secrete hormones into the blood, long term regulation of metabolism, growth
and development.
Hormones 2 types amino acid base or steroids (fat cells). Steroids enter the cell and are greeted by the receptor
chaperon complex. An amino acid hormone never enters the cell because of conflict of polarity.
Hormone Interaction
1. Permissiveness- one hormone requires another.
2. Synergism-effects amplified by other hormones.
3. Antagonism-hormones have opposite effects.
Control of Hormone Release
1. Humoral-blood concentration
2. Neural-direct nervous control
3. Hormonal-one hormone controls secretion of another.
Major Endocrine Organs
Pituitary Gland
Posterior Pituitary- made up of nervous tissue, storage tank for
hyperthelemic hormones, connected to the hypothalamus.
Hormones are: oxytocin, ADH
Anterior Pituitary
Endocrine tissue, controlled from the hypothalamus via hypophyseal portal system.
Hormones are: Growth hormone, Thyroid stimulating hormone, Adrenocortical trophic hormone, Follicle stimulating
hormone, Leuteinising hormone, Prolactin.
Thyroid Gland
Made up of large colloid cells.
Hormones are: Thyroxine (T4), Triiodothyronine (T3), Calcitonin.

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Parathyroid Glands
Consists of two functionally separate glands
Adrenal Medulla
At the centre of the adrenal gland made up of nervous tissue and under nervous control.
Hormones are: Secreted by the Chromaffin cells adrenaline and noradrenaline.
Adrenal Cortex
Outer layer of the adrenal gland.
Hormones are: The hormones are called corticosteroids ­as they are synthesised from cholesterol. Mineralocorticoid,
Glucocorticoids and Gondaocorticoids.
Has both exocrine and endocrine functions
Hormones are: Insulin, glycagon.…read more


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