Key Players of the Endocrine System

Major Endocrine Glands:

-Hypothalamus

-Pituitary

-Pineal

-Thyroid

-Parathyroids

-Adrenal glands

-Pancreas

-Ovaries/testes

Hypothalamus

The “Head Honcho of Homeostasis”
Receives and coordinates info about various vital activities, e.g. regulation of body T, intake of food/water, response to pain/emotional stress, reproductive behaviour, etc.
Acting as both neurons and secretory devices (glands), these unique cells provide the basis for neuroendocrine control.

Pituitary Gland

The “Master Gland” since it exerts control over other endocrine glands
Size of a lima bean, located at base of hypothalamus & attached to it by a thin stalk.
The Pituitary Gland is composed of two distinct lobes:

Anterior Pituitary

Specialized nerve cells in the hypothalamus manufacture and release specific chemical messenger molecules, neurohormones, to capillaries that travel to the anterior pituitary gland.
The neurohormones stimulate or inhibit the release of anterior pituitary hormones.
Anterior pituitary hormones enter bloodstream to stimulate target tissue, either another gland, or other tissue.

Anterior Pituitary Hormones

Posterior Pituitary

Stores and releases both ADH (antidiuretic hormone) and oxytocin produced by the hypothalamus.

1. ADH – when blood is hyperosmotic (salty meal, dehydration) or there is a loss of blood volume (injury) ADH is released and causes collecting ducts of kidney to reabsorb water thereby maintaining osmolarity and blood pressure.

Nicotine and stress stimulate ADH
Alcohol and caffeine block ADH

Diabetes insipidus is due to lack of ADH, produce up to 20 L of dilute urine every day! If caused by a tumour, treatment is to manage/remove the tumour; alternately, synthetic hormones can be taken.

2. Oxytocin

Stimulates contraction of uterine muscles for labour
Stimulates milk release from mammary glands during lactation

Pineal gland

Evolved on the top of the brain where light directly stimulated the pineal gland, still there on birds and reptiles and identified as the ‘third eye’ on lizards.

The pineal gland is embedded in the brain of mammals and so detects light indirectly:

Eye detects light (1) → signal sent from nerve in the eye to a region of the hypothalamus (2) → transfers signal to group of nerve cells (ganglia) at the top of the neck ® signal transferred to pineal gland (3) → INHIBITS melatonin release
Absence of light results in release of melatonin which maintains biological rhythms in mammals including the sleep-wake cycle and reproduction (melatonin interferes with LH and FSH).

Textbook Practice

p.473-482#1-3, 4-9

Page updated

Report abuse