Maintaining Homeostasis The Endocrine System Maintaining Homeostasis

The Endocrine System Function: Maintains homeostasis using hormones. An endocrine (ductless) gland secretes its products (hormones) directly into the blood stream. Hormones are slow working but long lasting. Hormones can only affect specific target cells. What do we call glands that release their products through ducts to the outside of the body or into body cavities? Exocrine glands Examples: Sweat, tears, & digestive juices

Endocrine Gland Locations (Fig. 39-2) Hypothalamus Thyroid Pituitary gland Pancreas Parathyroid glands Ovary Thymus Testis Adrenal glands

II. Endocrine Gland Types & Functions A. Pituitary – Secretes 9 hormones that directly regulate many body functions, & controls the actions of several other endocrine glands. ** The pituitary gland is controlled by the hypothalamus

Hypothalamus – Produces hormones that control the pituitary gland, & makes hormones stored in the pituitary gland. Thyroid – Regulates the body’s metabolism using a hormone called thyroxine. Too much thyroxine = hyperthyroidism and too little = hypothyroidism What might the symptoms of each be? Parathyroid – Releases parathyroid hormone which acts to maintain homeostasis of the calcium levels in the blood and bones.

Adrenal – Release epinephrine & norepinephrine which help the body respond to stress (flight or fight response). Pancreas – produces insulin & glucagon which regulate the level of glucose in the blood. Ovary – produces estrogen and progesterone. These produce primary and secondary sex characteristics and regulate the menstrual cycle and pregnancy. Testis – produces testosterone for sperm production and primary and secondary sex characteristics.

III. How do hormones work? There are two types of hormones: Steroid hormones 1. Can cross the cell membrane directly into the cytoplasm and nucleus. 2. The hormone binds to a receptor protein inside the cell. 3. This hormone-receptor complex activates genes. 4. These genes code for proteins that carry out the actions associated with the hormone. 5. Estrogen, progesterone and testosterone are examples. Steroid Hormone Receptor Hormone-receptor complex Nucleus DNA Protein synthesis mRNA

C. Nonsteroid hormones – Cannot pass through the cell membrane. The hormone (first messenger) binds to a receptor on the cell membrane. This activates an enzyme on the inner surface of the cell membrane. The enzyme converts ATP into cyclic AMP (the second messenger). The second messenger activates or inhibits enzymes. These produce the hormones effects. Human growth hormone and insulin Hormone Receptor Cyclic AMP Enzyme activities Altered cellular function

Calcium and glucose levels Concept Map The Endocrine System regulates Growth Water balance Reproduction Metabolism Calcium and glucose levels Response to stress by means of the by means of the by means of the by means of the by means of the by means of the Pituitary Ovaries Testes Thyroid Pancreas Adrenals Parathyroids