The Endocrine System

1. The Endocrine System Co-ordination Homeostasis Hormones

2. Endocrine and Exocrine Glands • Exocrine glands release substances into ducts • e.g. salivary glands, sweat glands • Endocrine glands are ductless, and secrete hormones into tissue fluid from which they pass into the blood. • A hormone is a chemical messenger produced by an endocrine gland and carried by the bloodstream to another part of the body where it has a specific effect. • Most hormones are proteins, some are steroids (lipid-like)

3. Major Endocrine Glands

4. Nervous vs. Endocrine

5. Hypothalamus Pineal Gland

6. Pituitary Gland • Known as the master gland • Produces a range of hormones which control other endocrine glands • Growth Hormone (GH) induces cells to absorb amino acids and synthesise proteins • Overproduction of GH causes overelongation of bones • gigantism • Underproduction of GH • dwarfism

7. Hypothalamus • Links nervous and endocrine systems • Part of the brain that responds to both nervous signals and hormonal messages • Controls the pituitary by producing hormones • some will stimulate the production of hormones • some inhibit production.

8. Hormone Supplements • Insulin • diabetes results from the inability to produce or absorb insulin • this causes high blood glucose, excessive urine production, thirst, weight loss. • insulin is injected daily, sugar intake is restricted, regular exercise. • Anabolic Steroids • promote muscle growth • similar to testosterone • cause side-effects of liver damage, infertility and impotence

9. Thyroxine • Produced by the thyroid • Regulates metabolic rate (all the reactions in the body) • Iodine from the blood is absorbed into the thyroid • Iodine combines with tyrosine (an amino acid) to form thyroxine • Deficiency results in low metabolism and slow development in children (cretinism) • treatment: hormone replacement, iodine supplements • Over-production results in increases metabolism • hunger, weight loss, irritability, anxiety, excessive heat • treatment: thyroid-suppressing drugs, surgery.

10. Regulation of Thyroid Activity • Negative feedback loop between the pituitaryand the thyroid • Pituitary produces thyroid stimulating hormone (TSH) • High concentration of thyroxine • inhibits pituitary • less TSH • less thyroxine secreted • drop in level of throxine in the blood • Low concentration of thyroxine: • stimulates pituitary to produce TSH • TSH stimulates the thyroid • thyroxine is secreted, levels rise

11. Control of body temperature Hypothalamus Low temperature stimulates temperature receptors inhibition hormone stimulates pituitary Pituitary TSH secreted inhibition Thyroxine secreted Thyroid Thyroxin levels increase Metabolic rate increase Negative Feedback System of Thyroxin Temperature rises

12. Negative Feedback Loops • Maintain homeostasis • Examples: • Rising levels of thyroxine cause a reduction in the production of thyroxine • Rising levels of ADH cause a reduction in the production of ADH (see kidneys) • Rising levels of insulin cause a reduction in the production of insulin