Endocrine System Endocrine System maintains: Homeostasis, controls growth, development, reproduction, and metabolism by releasing different hormones.

What are hormones? Hormones-chemical messengers secreted by cells to regulate the activity of other cells Target organs contain receptor sites specific to a hormone

Steroid Hormone Actions: 1) diffuse through plasma membrane of target cell 2) enter the nucleus 3) bind to a specific receptor protein to form a complex 4) binds to DNA 5) activates certain genes which are translated to result in synthesis of new proteins

Non Steroid Hormone Action: does not enter target cells instead binds onto the target cell plasma membrane that results in a response by the cell to the hormone.

Negative Feedback Loops The net effects of the response to the stimulus is to shut off or reduce the original stimulus. Examples: blood glucose levels, acute stress levels

Positive Feedback Loops Response enhances the original stimulus so that the response is accelerated. Example: childbirth. The force of the baby’s head on the cervix causes the uterus to contract more and more

Endocrine gland stimuli types: Hormonal- endocrine glands release hormones because of the influence of other hormones Humoral- glands release hormones because of changing ions or minerals Neural- hormone release in response to nervous system stimulation (sympathetic)

Major Endocrine Organs: Pituitary- grape size, hangs from hypothalamus, surrounded by bone (sella turcica) Two parts: Anterior Posterior

Anterior Pituitary secretes: Growth hormone(GH)- effects growth of skeletal muscle and long bone Prolactin- targets breast to produce milk after childbirth Adrenocorticotropic(ACTH)- regulates the hormones in the adrenal cortex Thyroid Stimulations Hormone(TSH)- influences growth and activity of the thyroid Gonadotropic: regulates hormone activity of the gonads FSH- function- follicle stimulating hormone- egg and sperm production LH- triggers ovulation of an egg

Posterior Pituitary secretes: Oxytocin- released during childbirth to stimulate contractions of the uterine muscle Antidiuretic (ADH)- inhibits urine production by causing the kidneys to absorb water

Thyroid

Thyroid- located on the trachea (windpipe) Thyroid hormone (T4, T3)- controls the rate that glucose is burned or oxidized Calcitonin- decreases blood calcium levels by causing calcium to be deposited in bone

Parathyroid- tiny masses of tissue on the thyroid Parathyroid hormone (PTH)- regulator of calcium in the blood-breaks down bone to release Ca

Adrenal- on top of the kidney: Aldosterone- important in regulating concentrations of sodium and potassium-reabsorbs water, increases blood pressure Cortisol- helps the body to resist stress Androgens and Estrogens- are collectively called sex hormones (gonadocorticoids)

Medulla: Catecholamines- 2 examples are epinephrine (adrenaline) and norepinephrine

Pancreas- Behind the stomach in abdomen Insulin- acts on all body cells to increase the ability to transport glucose across plasma membranes-reduces blood glucose levels Glucagon- acts as an antagonist to insulin-raises blood glucose levels by breaking down glycogen in liver

Gonads Females: ovaries Males: Testes

Homeostatic Imbalances Goiter- enlargement of the thyroid gland that results when the diet is deficient in iodine Diabetes mellitus- glucose level rise in the absence of insulin Acromegaly- hypersecretion of GH (growth hormone) after long bones have finished growing. Leads to elongation of jaw, eyebrows, feet, and hands

Acromegaly

Gigantism

Goiter