Endocrine System HORMONES

Target Cells or Target Organs Specific tissue cells or organs affected by a given hormone. Classification of Hormones Steroids Nonsteroids

Mechanism of Steroid Hormone Action 1) diffuse through the plasma membranes 2) enters the nucleus 3) binds to a specific receptor protein 4) Hormone-receptor complex binds to DNA 5) mRNA is produced 6) mRNA is translated in the cytoplasm resulting in the synthesis of new protein

Steroidal Hormones Glucocorticoids – increase blood glucose Mineralocorticoids – regulates the mineral content of the blood (such as K + and Na + ) Androgens – testosterone is most important; causes the development of the adult male characteristics.

Steroidal Hormones Estrogens – causes the development of the adult female characteristics. Progesterone – acts with estrogen to bring about the menstrual cycle.

Mechanism of Nonsteroidal Hormone Action 1) Binds to the plasma membrane receptor 2) sets off a series or reactions that activates an enzyme 3) Enzyme catalyzes a reaction that produces a second messenger molecule 4) Additional intracellular changes that promote the typical response of the target cell to the hormone

Nonsteroid Hormones Peptides Proteins Amines

Peptides Oxytocin – stimulates contraction of uterus and the milk “let-down” reflex Antidiuretic Hormone (ADH) – promotes retention of water by kidneys Calcitonin – reduces blood calcium level Parathyroid Hormone (PTH) – raises blood calcium levels Thymosin – “programs T cells” (A type of white blood cell that is of key importance to the immune system)

Proteins Growth Hormone(GH) – stimulates growth of skeletal muscles and long bones; causes fats to be broken down and used for energy Prolactin (PRL) – stimulates and maintains milk production by the mother’s breasts Follicle-stimulating hormone (FSH) – stimulates follicle (developing eggs) development in the ovaries

Proteins Luteininzing hormone (LH) – triggers ovulation of an egg from the female ovary Thyroid-stimulating hormone (TSH) – influences growth and activity of the thyroid gland

Proteins Adrenocorticotropic hormone (ACTH) – stimulates adrenal cortex to secrete glucocorticoids Insulin – reduces blood sugar Glucagon – raises blood sugar

Amines Melatonin – involved in rythmic activities (daily or seasonal) Thyroxine (T 4 ) and triiodothyronine (T 3 ) – stimulates metabolism Epinepherine and Norepinepherine – increase blood glucose and rate of metabolism; constrict certain blood vessels