1. The Endocrine System Mr.G.Burgess 2010.

2. How does the Endocrine System work?  Endocrine cells release their hormones from endocrine glands into the bloodstream.  these hormones travel through the circulatory system to distinct targets cells.

3. Endocrine Glands http://training.seer.cancer.gov/module_a natomy/unit6_3_endo_glnds.htmlhttp://training.seer.cancer.gov/module_a natomy/unit6_3_endo_glnds.html, 2004 Pituitary Gland : controls the functioning of other glands in the body Thyroid Gland : produces thyroxin to control the basal metabolic rate. Adrenal Gland : secretes hormones that help the body deal with stress. Testis :form spermatozoa and secrete androgens Pineal Gland : secretes melatonin, a hormone that affects moods and reproductive processes Thymus : matures blood stem cells to become activated T-helper cells. Pancreas : produces insulin to reduce the amount of sugar in the blood and enzymes that aid in digestion. Ovary : matures oocytes into ova and secretes estrogen and progesterone

4. What is a hormone?  A chemical messenger which is effective in very small quantities  created in endocrine glands  secreted into the circulatory system and transported throughout the body with the blood

5. Hormone definition contd.…  Act on receptors of specific target cells (proteins found on the cell membranes)  either stimulate a target tissue and increase activity or  inhibit a target tissue and decrease activity.

6. Glands and target cells  GLANDS - are organs that are specialized for secreting substances needed by an organism  TARGET CELLS - specific cells with protein sites that bind with hormones

7. Protein hormones  polypeptides synthesized from amino acids (smallest units of proteins)  i.e insulin and human growth hormones (HGH)  these hormones locate their specific target tissues by matching with receptor proteins in the plasma membrane of their target tissue

8. Protein hormones contd....  Each hormone can link with only a certain receptor  the protein hormone never enters the cell  they activate an enzyme in the cell membrane which then converts one substance to another substance called a second messenger.

9. Protein hormones contd....  The second messenger causes a series of reactions.  The actual protein hormone is the first messenger and never enters the target cell, it is the second messenger that causes the response

10. Steroid Hormones  Synthesized from cholesterol in the adrenal cortex and gonads  these hormones pass through the membrane of target cells and combine with receptors in the cell’s cytoplasm  no second messenger involved

11. Steroid hormones contd.…  Steroid-receptor complex moves into the nucleus and activates a gene  the activated gene is transcribed and translated  a protein is formed which changes the cells chemistry  this action leads to the response

12. Feedback  Feedback is defined as a situation in which hormones released by the cell of a given system act to regulate the secretion of the hormone which stimulates their release  i.e. Hormone A stimulates the release of hormone B which then regulates the release of hormone A

13. Feedback  NEGATIVE FEEDBACK  Hormone B feeds back to reduce secretion of hormone A  POSITIVE FEEDBACK  hormone B feeds back to stimulate the release of hormone A

14. Feedback Example  Thyroxine --- metabolism  the hypothalamus detects when the level of thyroxine in blood is low--hypothalamus secretes (TSH releasing factor) into the blood stream--anterior pituitary increases the secretion of TSH into the bloodstream-- reaches the thyroid---the thyroid stimulates an increase in thyroxine

15. Feedback example contd....  When thyroxine reaches “set level” in blood, the hypothalamus stops secreting TSH releasing factor

16. Gland/hormone/action

17. Gland/Hormone/Action

18. Glands/Hormones/Action

19. Pituitary Gland  Called the “master gland” because its secretions stimulate other endocrine glands to synthesize and secrete their hormones.  BUT the hypothalamus controls the pituitary gland  pituitary gland has 3 parts: anterior lobe, intermediate lobe and posterior lobe

20. Pituitary Gland

21. References 1.Endocrine Glands & Their Hormones, SEER's Training website, J.Young, et al., http://training.seer.cancer.gov/stws_about.html, April 5, 2004 http://training.seer.cancer.gov/stws_about.html 2.Online Biology Dictionary, http://www.biology-online.org/, R.Lee, April 5, 2004.http://www.biology-online.org/