endocrine system

• The zona glomerulosa of the adrenal cortex produces mineralocorticoids, such as aldosterone, which regulate blood volume and blood levels of sodium and potassium.
• The Endocrine System is composed of endocrine glands and specialized endocrine cells located throughout the body.
• Endocrine glands and cells secrete minute amounts of chemical messengers called hormones into the bloodstream, rather than into a duct.
• Hormones then travel through the general blood circulation to target tissues or effectors.
• Target tissues have receptors for a specific hormone.
• Hormones produce a particular response in the target tissues.
• Glands are organs that secrete hormones.
• The illustration shows pineal gland, hypothalamus, and pituitary located in the brain.
• Parathyroids (posterior part of thyroid) and thyroid are located near the throat.
• Thymus is located below the thyroid gland in the chest.
• The Adrenals are located above the kidney and pancreases (islet) is located between the kidneys.
• Ovaries (female) and Testes (male) are in the genital region.
• Autocrine hormones are released by cells and have a local effect on the same cell type.
• Paracrine hormones are released by cells that affect other cell types in close proximity.
• Eicosanoids are involved in vasodilation and vasoconstriction, promotion of sleep, pain, and fever.
• Eicosanoids play a role in up- or down-regulating inflammatory cytokines.
• Neurotransmitters and neuromodulators are secreted by nerve cells.
• Hormones and neurohormones are secreted into blood and bind to receptors on target tissues.
• Endocrine system functions include regulation of metabolism, control of food intake and digestion, modulation of tissue development, regulation of ion levels, control of water balance, regulation of cardiovascular function, control of blood glucose and other nutrients, and control of reproductive functions.
• Tropic hormone: Any of a class of hormones from the anterior pituitary gland that affect the secretion of other endocrine glands.
• The tropic hormones include thyroid-stimulating hormone, corticotropin, follicle-stimulating hormone, and luteinizing hormone.
• A hormone can stimulate only the cells that have the receptor for that hormone.
• The receptor site, where a hormone binds, is a specific location on the receptor molecule.
• Some hormones, such as epinephrine, can bind to a “family” of receptors that are structurally similar.
• Specificity in hormone binding is due to molecular shape and chemical characteristics.
• Lipid-soluble and water-soluble hormones bind to their own classes of receptors.
• Lipid-soluble hormones bind to nuclear receptors due to their lipid solubility and small molecular size, allowing to easily pass through the cell membrane.
• Water-soluble hormones bind to membrane-bound receptors, which are proteins that extend across the cell membrane, with their hormone-binding sites exposed on the cell membrane’s outer surface.
• When the hormone binds to the receptor, it turns on intracellular enzymes that ultimately cause the response dictated by the hormone-receptor interaction.
• Lipid-soluble hormones stimulate protein synthesis by diffusing across the cell membrane and binding to their receptors, with the complex now binding to hormone-response elements on DNA.
• Membrane-bound receptors act in two ways, either altering the activity of G proteins on the inner surface of the cell membrane or directly altering the activity of intracellular enzymes.
• Activation of G proteins, or intracellular enzymes, elicits specific responses in cells, including the production of molecules called, second messengers.
• Endocrine system functions also include stimulation of uterine contraction and milk release.
• The pancreas produces hormones such as insulin which target tissues like the liver, skeletal muscle, and adipose tissue.
• Insulin regulates blood glucose levels by causing them to drop after a meal and is secreted when glucose levels are high.
• Excess glucose is stored in the form of glycogen.
• Diabetes mellitus is caused by too little insulin or faulty insulin receptors.
• Symptoms of diabetes mellitus include hyperglycemia, exaggerated appetite, excess urine, dehydration, thirst, and fatigue.
• Type I diabetes is insulin dependent and requires daily injections.
• Type II diabetes is insulin independent and often found in obese people, can be treated with diet but can turn into type I.