Understanding the Endocrine System: Hormones and Their Functions in the Human Body

1. Chapter 9: The endocrine system Bio 24

2. 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

3. 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!

4. 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

5. 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

6. Steroid hormone action

7. Nonsteroid hormone action uses second messengers in the cell

8. 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

9. Control of hormone release • Some hormones are released in response to humoral stimuli: substances in the blood that are not hormones

10. 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

11. the major endocrine organs

12. Endocrine organs • Most hormones are released from epithelial cells that form endocrine glands • Major ones are shown here

13. The hypothalamus is the master controller through the pituitary glands

14. 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)

15. Hormones of the anterior pituitary: prolactin • Stimulates and maintains milk production • Men make it, too, but function is unknown!

16. 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

17. 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

18. 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

19. Structure of the thyroid

20. 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!

21. 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

22. 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

23. Goiter • A goiter is an enlarged thyroid • Can be caused by hyperthyroidism or hypothyroidism • Traditionally caused by dietary iodine deficiency