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Pineal Gland
· Located near the center of the brain in humans, and is stimulated by nerves from the eyes.
o In some other animals, the pineal gland is closer to the skin and directly stimulated by light.
· Secretes melatonin, which is derived from the amino acid tryptophan.
· Secretes at night when it’s dark, thus secretes more in winter when the nights are longer.
· Melatonin
o Promotes sleep
o Affects reproductive functions by depressing the activity of the gonads
o Affects thyroid and adrenal cortex functions.
o Is tied to circadian rhythm (having an activity cycle of about 24 hours), annual cycles, and biological clock functions.
Thyroid Gland
· Located in the front of the neck, below the larynx (voice box).
· The small, two-inch gland consists of two lobes, one on each side of the windpipe, connected by tissue called the isthmus.
Thyroxin
· Hormone produced by the thyroid glands
· Regulates metabolism by controlling the rate of oxidation in cells.
o It acts to increase the rates of chemical reactions in almost all cells of the body, thus increasing the general level of body metabolism.
Pancreas
· An elongated, tapered organ located across the back of the abdomen, behind the stomach.
· The pancreas is made up of two types of tissue:
o Exocrine tissue: secretes digestive enzymes into pancreatic duct, which empties into the bile duct and then the duodenum
o Endocrine tissue: consists of the islets of Langerhans, secretes hormones into the bloodstream.
§ Hormones are insulin and glucagon (which regulate the level of glucose in the blood) and somatostatin (which prevents the release of the other two hormones).
§ Insulin - secreted by the beta cells in response to high blood sugar.
· Causes cells (muscle, red blood cells, and fat cells) to take glucose in from the blood, which ultimately lowers the high blood glucose levels back to the normal
§ Glucagon - secreted by the alpha cells when blood glucose is low.
· Acts mainly on the liver to release stored glucose from its cells into the blood and to produce glucose out of building blocks obtained from other nutrients found in the body, for example, protein
Adrenal
· The adrenal glands lie at the tops of the kidneys.
· Produces Adrenaline (aka Epinephrine)
o Small amount helps to maintain normal blood pressure.
o In situations of stress, "fight or flight”, a large amount is produced very quickly
§ Raises blood sugar levels by stimulating the liver to change glycogen into glucose
§ Causes fatty tissue to release fat into the blood
§ Increases the heart rate
§ Increases blood flow to the muscles
§ Reduces blood flow to the skin and the intestines
§ Widens the bronchioles
§ Dilates the pupils
Pituitary gland
o The “master" gland of the endocrine system, because it controls the functions of the other endocrine glands.
o The pituitary gland is no larger than a pea, and is located at the base of the brain attached to the hypothalamus (a part of the brain that affects the pituitary gland) by nerve fibers. The pituitary gland itself consists of three sections:
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o The anterior lobe
o The intermediate lobe
o The posterior lobe Pituitary
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o Somatotropin (aka human growth hormone - HGH) is excreted into the blood by the somatotrope cells of the anterior pituitary gland
o It is a single-chain protein that is composed of 191 amino acids.
o It influences many functions:
§ Stimulates division and multiplication of the chondrocytes of cartilage
§ Increases both calcium retention and the mineralization of bones
§ Stimulates cell growth in every organ of a human body
§ Increases metabolism
§ Repairs damaged cells
§ Induces protein synthesis
§ Decreases protein degradation
§ Stimulates the immune system