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The Endocrine System
| Term | Definition | |
|---|---|---|
| endocrine cells | secretory cells that release hormones directly into the interstitial fluid, lymphatic system, or blood | |
| hormones | chemical messengers that stimulate specific cells or tissues into action | |
| amino acid derivatives | small molecules that are structurally similar to amino acids; class of hormones | e.g. derivatives of tyrosine such as thyroid hormones and catecholamines; derivatives of tryptophan such as melatonin |
| peptide hormones | chains of amino acids; class of hormones | e.g. hormones released by the pituitary gland |
| lipid derivatives | class of hormones that can be divided into eicosanoids and steroid hormones | |
| eicosanoids | small molecules with a five-carbon ring at one end; derived from arachidonic acid; group of lipid derivatives | coordinate cellular activities and affect enzymatic processes (such as blood clotting) |
| steroid hormones | group of lipid derivatives that are structurally similar to cholesterol | e.g. reproductive hormones; adrenal cortex hormones |
| target cells | specific cells that have receptors needed to bind hormones and respond to their presence | |
| humoral stimuli | changes in the composition of ECF; trigger endocrine activity | |
| hormonal stimuli | arrival or removal of specific hormone(s); trigger endocrine activity | |
| neural stimuli | arrival of neurotransmitters at neuroglandular junctions; trigger endocrine activity | |
| negative feedback system | self-amplifying cycle where a physiological change leads to even greater change in the same direction | |
| positive feedback system | process in which the body senses a change and activates mechanisms to reverse that change | |
| hypothalamus | contains centers involved with the unconscious regulation of visceral functions, emotions, drives, and the coordination of neural and endocrine functions; makes up the floor of the diencephalon | |
| pituitary gland (hypophysis) | major endocrine gland attached to the hypothalamus by the infundibulum | |
| infundibulum | a tapering, funnel-shaped structure that connects the pituitary gland to the hypothalamus | |
| diaphragm sellae | a dural sheet that encircles the infundibulum and holds the pituitary gland in position | |
| hypophyseal portal system | capillary network that branches among endocrine cells in the anterior lobe | |
| anterior lobe of the pituitary gland (adenohypophysis) | lobe of the pituitary gland made up of the pars distalis, pars tuberalis, and pars intermedia | |
| pars distalis | large, anterior portion of the adenohypophysis | |
| pars tuberalis | portion of the adenohypophysis that wraps around the infundibulum superior to the posterior lobe | |
| pars intermedia | portion of the adenohypophysis that is adjacent to the neurohypophysis | |
| thyroid-stimulating hormone (TSH) | anterior pituitary hormone secreted by thyrotropes in the pars distalis | targets the thyroid gland, triggering release of thyroid hormones T3, T4, CT |
| adrenocorticotropic hormone (ACTH) | anterior pituitary hormone secreted by corticotropes in the pars distalis | targets the adrenal cortex, stimulating secretion of glucocorticoids (GC) |
| follicle-stimulating hormone (FSH) | anterior pituitary hormone secreted by gonadotropes in the pars distalis | targets follicular cells in the ovaries or nurse cells in the testes, stimulating secretion of estrogens and promoting development of oocytes or sperm |
| luteinizing hormone (LH) | anterior pituitary hormone secreted by gonadotropes in the pars distalis | targets follicular cells in the ovaries or interstitial cells in the testes, stimulating ovulation and promoting secretion of progestins or androgens |
| prolactin (PRL) | anterior pituitary hormone secreted by lactotropes in the pars distalis | targets the mammary glands, stimulating the production of milk |
| growth hormone (GH) | anterior pituitary hormone secreted by somatotropes in the pars distalis | targets all cells, stimulating growth, protein synthesis, lipid mobilization, and catabolism; in the liver, causes the release of somatomedins, which stimulate protein synthesis in cartilage and muscle cells |
| melanocyte-stimulating hormone (MSH) | anterior pituitary hormone secreted by corticotropes in the pars intermedia | targets melanocytes, stimulating increased melanin production |
| thyrotropes | endocrine cells in the pars distalis of the adenohypophysis that secrete TSH | |
| corticotropes | endocrine cells in the pars distalis and pars intermedia of the adenohypophysis that secrete ACTH and MSH | |
| gonadotropes | endocrine cells in the pars distalis of the adenohypophysis that secrete FSH and LH | |
| lactotropes | endocrine cells in the pars distalis of the adenohypophysis that secrete PRL | |
| somatotropes | endocrine cells in the pars distalis of the adenohypophysis that secrete GH | |
| posterior lobe of the pituitary gland (neurohypophysis) | lobe of the pituitary gland that stores and releases ADH and OXT | hormones released are called neurosecretions |
| antidiuretic hormone (ADH) | aka vasopressin; neurosecretion released in response to a rise in electrolyte concentration or a fall in blood pressure | targets nephrons of the kidneys, causing kidneys to retain water (preventing dehydration) and peripheral blood vessels to constrict (elevating blood pressure) |
| oxytocin (OXT) | neurosecretion targeting the smooth muscle of the uterus or prostate gland and contractile cells of the mammary glands | causes uterine or prostate gland contractions, release of milk |
| thyroid gland | gland located on the anterior surface of the trachea slightly inferior to thyroid and cricoid cartilages | supplied by the superior thyroid artery (from the external carotid artery) and the inferior thyroid artery (from the thyrocervical trunk) |