The Endocrine System

• The endocrine system is a collection of glands that secrete chemical messages we call hormones.

• The vertebrate endocrine system consists of glands (pituitary, thyroid, adrenal), and diffuse cell groups scattered in epithelial tissues.

• ductless, which means that their secretions (hormones) are released directly into the bloodstream and travel to elsewhere in the body to target organs, upon which they act.

The roles of hormones in selecting target cells and delivering the hormonal message. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.

Classification

• Hormones are grouped into three classes based on their structure:

• steroids • peptides • amines

Steroids

• Steroids are lipids derived from cholesterol

• Steroid hormones are secreted by the gonads, adrenal cortex, and placenta.

Sex Steroids• Natural sex steroids are made by the (ovaries or testes)[3], by

adrenal glands, or by conversion from other sex steroids in other tissue such as liver or fat.

• Sex steroids include:androgens: Mainly male hormones

– testosterone – androstenedione – dihydrotestosterone – dehydroepiandrosterone – anabolic steroids

estrogens: mainly female hormones– estradiol – estrone – estriol

progestagens: mainly female hormones– progesterone – progestins

Corticosteroid

• Glucocorticoids such as cortisol control carbohydrate, fat and protein metabolism and are anti-inflammatory.

• Mineralocorticoids such as aldosterone control electrolyte and water levels, mainly by promoting sodium retention in the kidney.

Anabolic steroid

• Anabolic steroids, or anabolic-androgenic steroids (AAS), are a class of steroid hormones related to the hormone testosterone.

• They increase protein synthesis within cells, which results in the buildup of cellular tissue (anabolism), especially in muscles.

Anabolic steroids can cause many adverse effects

• the most common being elevated blood pressure, especially in those with pre-existing hypertension, and harmful changes in cholesterol levels,

• have been shown to alter fasting blood sugar and glucose tolerance tests

• increase the risk of cardiovascular disease or coronary artery disease

Anabolic steroids can cause many adverse effects

• Acne is fairly common due to stimulation of the sebaceous glands by increased testosterone levels.

• can accelerate the rate of premature baldness for males who are genetically predisposed, but testosterone itself can produce baldness in females.

• High doses of oral anabolic steroid compounds can cause liver damage

Peptides

• Peptides are short chains of amino acids; most hormones are peptides. They are secreted by the pituitary, parathyroid, heart, stomach, liver, and kidneys.

Amines

• Amines are derived from the amino acid tyrosine and are secreted from the thyroid and the adrenal medulla.

The major human endocrine glands include

• the hypothalamus and pituitary gland• the thyroid gland• the pancreas• the adrenal glands• the gonads or sex organs • the pineal gland

Hypothalamus and Pituitary gland• The pituitary gland is called the “master

gland” but it is under the control of the hypothalamus.

• important to the female menstural cycle, pregnancy, birth, and lactation (follicle-stimulating hormone (FSH) & leutinizing hormone (LH) )

• antidiuretic hormone or ADH - helps prevent excess water excretion by the kidneys

• endorphins, which belong to the category of chemicals known as opiates and serve to deaden our pain receptors.– The natural response to rub an injured area, such

as a pinched finger, helps to release endorphins in that area.

Thyroid Gland

• regulate metabolism, therefore body temperature and weight

• contain iodine, which the thyroid needs in order to manufacture these hormones– person lacks iodine in his/her diet, the thyroid

cannot make the hormones, causing a deficiency

the pancreas

• Ducted gland - secreting digestive enzymes into the small intestine

• Ductless gland - the islets of Langerhans secrete insulin and glucagon to regulate the blood sugar level

the adrenal glands• sit on top of the kidneys• consist of two parts, the outer cortex and the inner

medulla• medulla secretes epinephrine (= adrenaline) and

other similar hormones in response to stressors such as fright, anger, caffeine, or low blood sugar

• The cortex secretes corticosteroids such as cortisone, well-known as being anti-inflammatory, thus are prescribed for a number of conditions

the gonads or sex organs• the female ovaries and male testes (singular =

testis) secrete hormones• is controlled by pituitary gland hormones• both sexes make some of each of the

hormones– male testes secrete primarily androgens including

testosterone – Female ovaries make estrogen and progesterone

• baby’s placenta also secretes hormones to maintain the pregnancy

pineal gland

• located near the center of the brain in humans• stimulated by nerves from the eyes• secreted melatonin at night when it’s dark– secretes more in winter when the nights are

longer– Melatonin promotes sleep (makes you feel

sleepy). It also affects reproductive functions by depressing the activity of the gonads

pineal gland

• it affects thyroid and adrenal cortex functions.• SAD or seasonal affective disorder

(syndrome) is a disorder in which too much melatonin is produced, especially during the long nights of winter, causing profound depression, oversleeping, weight gain, tiredness, and sadness.