Exam 5 Review:  Chapter 16:  Miscellaneous Endocrine Terms

pineal gland - A small organ, a part of the epithalamus, situated beneath the back part of the corpus callosum in the roof of the third ventricle of the brain which secretes the hormone melatonin; in the human it appears to play a role in sleep-wake cycles and may contribute to the regulation of the onset of puberty.

melatonin - The amine hormone, a derivative of the amino acid tryptophan, produced by the pineal gland; in humans rising levels induce sleep; it also inhibits the stimulation of gonadotropin (LH) activity before puberty.

thymus gland - A lobed endocrine organ located in the mediastinum, deep to the sternum, which is responsible for the maturation of T lymphocytes; it produces a number of local hormones including thymosin to contribute to T lymphocyte maturation; the thymus is at its largest at birth and shrinks over time, being replaced by fibrous connective tissue, and is usually absent by the end of the second decade of life.

thymosin - A peptide hormone secreted by the thymus that stimulates development of T cells/T lymphocytes.

enteroendocrine cell - Any of a group of diffuse neuroendocrine cells,.also referred to as APUD cells (amine precursor uptake and decarboxylation cells), scattered individually among the cells of the exocrine glands from the stomach to the colon; their amine hormones diffuse into the blood capillaries, and ultimately influence several digestive system target organs; these cells, along with the nervous system, control and coordinate the muscular and secretory activities of the gastrointestinal tract; enteroendocrine cells typically extend a cytoplasmic process into the digestive tract lumen forming an important communication site to monitor the luminal contents, of which dietary amino acids are the most important stimulants; there are more than a dozen different types of enteroendocrine cell and a given enteroendocrine cell will only secrete one type of hormone, or hormone-like substance; these include gastrin, histamine, endorphins, serotonin, cholecystokinin and somatostatin.

erythropoietin - A glycoprotein hormone which targets the bone marrow and stimulates the production of red blood cells; it is roduced by cells of the juxtaglomerular apparatus of the kidneys and it is released in response to decreased levels of oxygen detected in the blood.

stress response - A complex neuroendocrine reflex involving the hypothalamus, the adrenal cortex, and the adrenal medulla; (1) the short term response to stress is activity in the sympathetic division of the ANS and cooperative release of epinehrine and norepinephrine from the adrenal medulla -- short term responses which result include increased heart rate, increased blood pressure, increased blood glucose levels, increased bronchodilation, changes in blood flow leading to increased alertness, decreased digestive activity and reduced urine output, and an increased metabolic rate; (2) the long term response to stress is stimulation of the adrenal cortex to release more (a) aldosterone resulting in sodium and water retention by the kidneys leading to increased blood volume and blood pressure, and (b) glucocorticoids resulting in gluconeogenesis, increased blood glucose, metabolic shifts to fat and protein catabolism, and some suppression of the immune system.  See Figure 16.15 in the text.

growth factors - Growth factors are protein local hormones which bind to receptors on their target cells' surface, with the primary result of activating cellular proliferation and/or differentiation; many growth factors are quite versatile, stimulating cellular division in numerous different cell types; while others are specific to a particular cell-type; they are produced by cells in a wide variety of tissues and organs in the body.

general adaptation syndrome - When a stressor disrupts homeostasis, the body adjusts with an adaptive response, or an attempt to restore homeostasis; this adaptive response to stress varies in intensity and physical manifestation from person to person and from stressor to stressor; the three-stage response to stress is called the general adaptation syndrome; the phases of the general adaptation syndrome are alarm, resistance, and exhaustion.

alarm reaction - The first phase of the general adaptation syndrome: a stressor disturbs homeostasis and the CNS responds with (1) sympathetic division activity producing the "fight-or-fight" response and (2) release of epinephrine and norepinephrine from the adrenal medulla.  {For details, see short term stress definition above.]

resistance reaction - The second phase of the general adaptation syndrome: begins almost immediately after the alarm reaction and represents all the normal negative feedback responses attempting to reverse the physiological changes brought about by the stress and to return the body to a normal homeostasis.

exhaustion - The third phase of the general adaptation syndrome where the negative consequences of stress appear: only seen in chronic stress situations such as chronic disease, chronic emotional distress, in which the persons energy reserves, psychological and physical have been depleted, may include the long term stress responses of prolonged production of adrenal mineralocorticoids and glucocorticoids and may progress to any of a variety of serious illnesses.

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