- Works with nervous system to maintian body homeostasis

- regulates long term processes like growth and the reproductive system

- Is comprised of specific glands that secrete hormones into the blood that ultimately alter the activities of specific "target" organs

ductless organs that secrete their molecules directly into the bloodstream

- hormone passes through blood

- All endocrine cells are located within highly vascularized areas to ensure that their products enter the bloodstream immediately

- Hormones are molecules that have a specific effect on specific organs

- Only target cells in target organs with specific receptors for the hormone respond to that hormone

- Most hormones in body are peptide hormones

- Chains of amino acids

Longer chains are called protein hormones

- E.g. human growth hormone

- Type of lipid (fatty substance/energy supply) derived from cholesterol

- E.g. testosterone

- Small molecules produced by altering the structure of a specific amino acid

- E.g. thyroid hormone

- Return to homeostasis

- A stimulus starts a process

- Eventually either the hormone that is secreted or a product of its effects causes the process to slow down or turn off

- Many hormonal systems work by negative feedback mechanisms

- A stimulus starts a process which accelerates

- Either to ensure that the process continues to run, or to speed up the activities of the process

- Few hormonal systems work by positive feedback mechanisms

- E.g. Lactation from the mammary glands

- Anterior and posterior lobes

- Located in sella turcica of sphenoid bone

- Attached to inferior surface of hypothalamus via the infidibulum (pathway between hypothalamus and pituitary)

- Carries axons from the nuclei located in the hypothalamus

- Axons from hypothalamic nuclei travel through the infundibulum to innervate posterior lobe of the pituitary gland (action potential- nerve impulse)

-Homones are then released in response to action potentials from the hypothalamus

- Antidiuretic hormone (ADH)- stimulates water reabsorption in the kidney

- Oxytocin- stimulates uterine contraction and milk letdown

- Capillaries in hypothalamus pick up releasing factors (RF) from the hypothalamus

- Capillaries unite to form a portal vein; carries RFs to anterior lobe

- Each RF is secific to a hormone of adenohypophysis and controls release of that hormone 

- TSH

- ACTH

- FSH

- LH

- Prolactin

- GH

- MSH

- 2 lobes lying either side of the trachea just inferior to the thyroid cartilage of the larynx

- Joined across the midline by the isthmus (bridge)

- Secrets thyroxine and triiodothyronine

- Iodine that triggers body cells to increase metabolism

- Calcitonin- hypocalcemic agent that decreases osteoclast activity (decrease blood calcium)

- Idodine deficiency that restricts synthesis of thyroid hormones

- Iodized salt marketed during the 1920's in response to deficiencies endemic to parts of the U.S. (soils with inadequate iodine=less iodine in foods)

- Two glands located on the posterior surface of each thyroid lobe (4 total)

- Secretes parathormone (extra calcium in blood/kidney)

- Hypercalcemic agent that acts on bone and the kidney

- Gland located at the superior pole of each kidney

- Cortex is composed of:

- Zona glomerulosa (secretes aldosterone; hypernatremic and hypokalemic agent that targets the kidney- salt)

- Fasciculata (secretes cortisol; aids in coping with stress and targes various body cells- sugar)

- Reticularis (secretes sex steroids - androgens, estrogens- sex)

- Adrenal medulla (secrete epinephrine, norepinephrine, and dopaine that have varying effects and target organs)

- Gland closely associated with the upper GI

- Secretory units: Islets of Langerhans scattered throughout the pancreas secretions

- Insulin- beta cells; hypoglycemic agent; targets adipose tissue, liver and skeletal muscle- elevate sugar levels

- Glucagon- alpha cells; hyperglycemic agent; targets liver and adipose- lowers sugar levels

- Testes (testicles) are suspended within the scrotum

- Interstitial cells of Leydig located within semiferous tubules

- Located between sternum and pericardial sac

- Largest at puberty and regresses thereafter

- Part of epitalamus of brain

- Secretes melatonin which regulates circadian rhythms

- Day/night-wake/sleep cycles

- Secretes renin

- Released to regulate the body's salt and water balance, and blood volume

- Secretes erythropoietin

- Critical for the formation of red blood cells by the bone marrow

- Secrete gastrin, secretin, and cholecystokinin

- Aid in gastric motality

- E.g., regulating gastric acid levels, secretion of pancreatic digestive enzymes, release of bile

- Human chorionic gonadotropin

- Maintains progesterone levels to maintain pregnancy