Download THE ENDOCRINE SYSTEM

Endocrine System

The endocrine glands secrete substances called hormones directly into the fluids of
the body.

A hormone are secretions from endocrine glands, endocrine cells and some neurons
that the bloodstream distributes to nonadjacent target cells.

Target cells are any cells that have receptors for a given type of signaling molecule
(hormone) and that may alter their behavior in response to it.
1. Oxytoxin (hypothalamus/pituitary gland)—its role is in childbirth and milk
production
2. Estrogen (ovaries)—its role is to maintain primary sex organs in females
3. Pheromones (exocrine glands, found in many vertebrate species, and insects)—
help member of the same species communicate with each other, mating, defense,
etc.

As a group, glands of the endocrine system help
1. Regulate metabolic processes, including rates of chemical reactions
2. Transport of substances across membranes
3. Water concentrations in the body
4. Body development and growth
ENDOCRINE GLANDS

Typically in vertebrates hormones are located in:
1. Hypothalamus
2. Pituitary Gland (pea-shape)
3. Pineal Gland
4. Thyroid Gland
5. Parathyroid Glands (4 in humans)
6. Thymus Gland
7. Heart
8. Digestive Organs
9. Pancreas
10. Adrenal glands (2)
11. Kidneys (2)
12. Testes (2)
13. Ovaries (2)
Hypothalamus:
 This brain region monitors internal organs and activities such as eating and sexual
behaviors.

This organ produces ADH (Antidiuretic Hormone) that induces water conservation
and oxytoxin that are important in childbirth and milk production.
Pituitary Gland:
 Suspended from the base of the hypothalamus by a slender stalk is a pea-size lobed
gland called the pituitary gland.
 The pituitary gland has anterior and posterior lobes.
 The posterior lobe of the pituitary gland also stores and secretes two of the hormones
that are synthesized in the hypothalamus.
 The anterior lobe produces ad secretes its own hormones, most of which govern the
release of hormones form other endocrine glands. Six hormones total are produced.
1. ACTH (corticotropin), TSH (thyrotropin), FSH (gonadotropin), and LH
(luteinizing hormone) are involved in stimulating other glands.
2. Prolactin and somatropin are involved in stimulating growth and development.
Pineal Gland:
 This gland is responsible for producing and releasing melatonin which affects our
biological clocks, overall level of activity, and reproductive cycles.
 Because this is a photosensitive organ, in the absence of light, this gland secretes that
hormone melatonin. Thus blood levels of melatonin vary from day to night, and they
vary with the changing seasons.
 The variations are known to influence the development of gonads, reproductive
cycles, and reproductive behavior in a variety of species.
Thyroid Gland:
 The human thyroid gland is located at the base of the neck in front of the trachea,
commonly known as the windpipe.
 The two main hormones that this gland produces are thyroxine and
triiodothyronine.
 These hormones are critical for the normal development of many tissues, and they
control the overall metabolic rate in humans.
 Adam’s Apple or Iodine deficiency—overproduction of TSH
Parathyroid Glands (4):
 This gland secretes PTH (parathyroid hormone) when the concentration of calcium
ions in their surroundings decreases.
 Their action affects how much calcium is available for enzyme activation, muscle
contraction, blood clotting, and etc.
Thymus Gland:
 The lobed thymus gland is located behind the breastbone, between the lungs.
 WBC (white blood cells) multiply, differentiate, and mature in this gland, which
secretes hormones collectively called thymosins. These roles in immunity.
Heart:
 The function of the heart in blood circulation is well known, but its endocrine
function is less appreciated.
 Fibers of cardiac muscle in the right atrium produce a hormone called the atrial
natriuretic peptide, which controls the release of a hormone form the posterior
pituitary gland (ADH) and is involved in the regulation of water levels in the body.
Digestive Organs:
 Many of the digestive processes are controlled by hormones, such as gastrin and
secretin that are involved in breaking down food materials.
Pancreas:
 This organ produces the hormones glucagon and insulin.
 Glucagon raises the glucose level in the blood by causing glycogen (a storage
polysaccharide) and amino acids to be converted to glucose in the liver.
 Insulin lowers the glucose level in the blood by stimulating the uptake of glucose by
the liver, muscle, and adipose cells.
Adrenal Gland:
 This gland is found above each kidney.
 This gland is composed of two parts the adrenal cortex (cover) and adrenal medulla
(inside).
 The adrenal cortex is responsible for production of the hormone cortisol that affects
glucose metabolism.
 The adrenal medulla produces the hormones epinephrine and norepinephrine that
interact with the nervous system to help adjust organ activities, especially during
times of excitement of stress (sympathetic).
Kidneys:
 Excretions of the kidneys have a urinary function as well as an endocrine function.
 The endocrine cells of the kidney produce the hormone erythropoietin, which are a
part of the angiotensin system that regulates water balance in the body and stimulates
red blood cell production in the bone marrow.
Ovaries:
 This organ produces the hormones estrogen and progesterone that develop and
maintain primary sex organs and influence secondary sexual traits.
Testes:
 This organ produces testosterone that develops and maintains primary sex organs
and influence secondary sexual traits.