A&P Chapter 15 The Endocrine System Notes......
Autocrines
Compared to hormones, Autocrines are much shorter distance signals used between cells. Autocrines are chemicals that exert effects on the same cells that secrete them.
Endocrine Vs. Exocrine Glands.
Exocrine glands produce nonhormonal substances, use ducts to secrete the substances onto a membrane surface. Examples of substances: sweat, saliva. Endocrine glands have no ducts and secrete hormones into surrounding tissue fluid and usually into the bloodstream or lymph system.
Hormones
Hormones are long-distance signals released by endocrine glands or cells. Hormones find their target cells, cells that have receptors unique and specific for the hormones. Some Impacts of Hormones: Can open or close ion channels, Can stimulate enzyme or other protein synthesis, Activate or deactivate enzymes, Induce secretion, Stimulate mitosis. Hormones can be amino acid based or steroid based. Hormones act on specific target cells that have receptors for them. Receptors can be intracellular (inside cells in nucleus) or extracellular (outside cells in plasma membrane).
Hormones are Classified Chemically: Amino Acid Based.
Most are amino acid based - water-soluble hormones. Cannot move through plasma membrane, bind extracellular receptors. Use second-messenger systems. Typically are faster-working and shorter-lasting effects.
Comparing the Nervous system to the endocrine system.
Nervous system works quickly, endocrine system works much more slowly. Nervous system uses short-distance chemical messengers (neurotransmitters) and endocrine system uses longer-distance chemical messengers (hormones) that travel in blood or lymph throughout the body.
Other organs with endocrine cells and function (but also have other functions).
Pancreas, gonads (ovaries and testes), placenta - important, major endocrine functions. Adipose cells, thymus, small intestine, stomach, kidneys, heart - some endocrine functions but not necessarily chief function.
Paracrines
Paracrines act locally, within same tissue but affect cell types other than those releasing paracrine chemicals
The Hypothalamus and Pituitary Gland
Pituitary lies below hypothalamus, connected by infundibulum. Pituitary gland secretes at least 8 hormones Has two major lobes: one is neural tissue and the other is endocrine (glandular). Posterior pituitary; Neural tissue. Releases neurohormones secreted by neurons received ready-made from hypothalamus. Hormone storage area for Oxytocin and ADH. Anterior pituitary; Glandular tissue. Makes and releases GH, TSH, ACTH, FSH, LH, PRL.
The Endocrine System Glands
Pituitary, Thyroid, Parathyroid, Adrenal, Pineal, Hypothalamus (considered neuroendocrine organ).
Hormones are Classified Chemically: Steroid Based.
Some are steroid based - lipid-soluble hormones. Can move through the plasma membrane, bind intracellular receptors. Have longer-lasting impacts but take longer to take effect.
Negative Feedback Mechanisms
Three types of stimuli that trigger endocrine glands to manufacture and release their hormones: Humoral - Hormone secretion in direct response to changing blood levels of certain ions and nutrients Neural- Nerve fibers stimulate hormone release Hormonal - Endocrine glands release hormones based on other endocrine gland hormone release
