Chapter 9: The endocrine system

Bio 24

The endocrine system

• One of two communication systems in the body

• Consists of hormones: chemicals secreted into the blood that travel throughout the body to act on specific target cells

• Only cells with the appropriate receptors will respond to the hormonal signal

Functions of the endocrine system

• Hormones are essential for:– reproduction– regulation of the immune system– utilization of energy– maintenance of bone and muscle mass– growth– regulation of salt and water balance and blood pressure– regulation of our moods & emotions– many other things!

The endocrine vs. the nervous system

Endocrine system• uses chemical signals

• chemical signals secreted into the blood

• effects take minutes or hours and may be long-lasting

Nervous system• uses chemical and

electrical signals• chemical signals travel

only across a synapse• effects take a fraction of

a second and usually mediates rapid responses

2 main categories of hormones

• Amino acid-based hormones (most common) include proteins, peptides, and amino acid derivatives– Include insulin, growth hormone, thyroid hormones

• Steroid hormones are small lipid molecules made from cholesterol that can cross cell membranes– Include testosterone, estrogen, progesterone, and

cortisol

Steroid hormone action

Nonsteroid hormone action uses second messengers in the cell

Control of hormone release

• Release of most hormones is controlled by other hormones

• Hormones that control the release of other hormones are called tropic hormones

Control of hormone release

• Some hormones are released in response to humoral stimuli: substances in the blood that are not hormones

Control of hormone release

• Release of some hormones is controlled by the nervous system

• The nervous and endocrine systems often work together in a coordinated fashion

THE MAJOR ENDOCRINE ORGANS

Endocrine organs

• Most hormones are released from epithelial cells that form endocrine glands

• Major ones are shown here

The hypothalamus is the master controller through the pituitary glands

Hormones of the anterior pituitary: growth hormone

• Growth hormone promotes growth of bones and muscles in children, and maintenance of muscle mass in adults

• Growth hormone excess can result in gigantism (if in childhood) or acromegaly (if in adulthood)

Hormones of the anterior pituitary: prolactin

• Stimulates and maintains milk production

• Men make it, too, but function is unknown!

Hormones of the anterior pituitary: adrenocorticotropic hormone (ACTH)

• ACTH is a tropic hormone that regulates the activity of part of the adrenal glands called the adrenal cortex

• Glucocorticoids released from the adrenal cortex increase blood glucose and are involved in our stress response; mineralocorticoids regulate salt and water balance by controlling urine composition

Hormones of the anterior pituitary: follicle-stimulating hormone (FSH) and luteinizing

hormone (LH)

• Both these hormones control the hormonal activity of the gonads: testes and ovaries

• Both are essential for the development of both sperm and eggs

Hormones of the anterior pituitary: Thyroid-stimulating hormone (TSH)

• TSH influences the growth of and hormone release from the thyroid gland

• The thyroid gland releases thyroid hormones, which contain amino acid-like molecules bound to iodine atoms and also calcitonin, which regulates calcium deposition in bones

Structure of the thyroid

Thyroid hormone targets

• Thyroid hormones act on essentially every cell in the body

• Control metabolic rate and energy utilization• Also important for normal growth and

development and reproductive function• Thyroid disease is quite common!

Thyroid deficiency• Hypothyroidism (underactive thyroid) is most

often caused by autoimmune disease that attacks the thyroid

• Symptoms include fatigue, persistent feeling of cold, bloating and weight gain, dry skin, and mental slowness

• Can be very well treated by taking thyroid hormone pills

• Thyroid deficiency in children can cause mental retardation and dwarfism, known as cretinism

Thyroid excess• Hyperthyroidism (overactive

thyroid) can also result from autoimmune disease or a benign tumor of the thyroid

• Graves’ disease is one form of hyperthyroidism that also causes exophthalmos (bulging eyes)

• Symptoms include rapid heart rate, heat intolerance, and nervous behavior

• Hyperthyroidism is harder to treat

Goiter

• A goiter is an enlarged thyroid

• Can be caused by hyperthyroidism or hypothyroidism

• Traditionally caused by dietary iodine deficiency