Module 2
1. Module 2
1.47. Module Glossary
Module 2—The Endocrine System
Module Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
acromegaly: a condition brought about by excessive secretion of human growth hormone in an adult; hands, feet, and nose widen and become enlarged; jaw protrudes; voice becomes husky; barrel chest may develop; sweat glands enlarge; heart enlarges; high blood pressure may develop; enlarged tissues press on nerves, especially the optic nerves, causing loss of vision, particularly in the outer fields; and pressure on the brain causes severe headaches
There is an increased likelihood of developing diabetes mellitus.
adrenal cortex: the outer portion of the adrenal gland composed of three distinct layers of cells that respond to hormonal signals from the anterior pituitary by producing three groups of hormones, including the glucocorticoids, mineral corticoids, and gonadocorticoids; reacts to stress stimuli and affects salt and water balance
adrenal medulla: the central or middle part of the adrenal gland composed of modified nervous tissue that responds to sympathetic nerve signals by secreting the fight-or-flight hormones, epinephrine and norepinephrine, in reaction to stress
aldosterone: a hormone produced by the adrenal cortex in response to an increase in certain enzymes and high levels of ACTH; acts to increase sodium ion reabsorption
alpha cells: cells in the islets that secrete glucagon
antagonistic hormones: two hormones that produce opposite effects
anterior pituitary: an endocrine gland consisting of secretory cells that synthesize and secrete several hormones directly into the bloodstream
beta cells: cells in the islets that secrete insulin
calcitonin: a hormone produced by the C cells (parafollicular cells) in the thyroid gland that decreases blood calcium levels by increasing uptake of calcium into the skeleton and inhibiting decomposition of bone when the blood levels of calcium are too high
C cells (parafollicular cells): cells located between the follicles of the thyroid gland that are responsible for synthesizing calcitonin
cellular respiration: a process occurring in the mitochondria of cells of all living organisms in which energy-rich compounds, such as carbohydrates (glucose), proteins, and fats, are burned with oxygen to release energy in the form of ATP and waste products, such as water and carbon dioxide
cortisol: also called hydrocortisone or cortisone; involved in enhancing short-term stress responses and in stimulating conversion of protein and fat into glucose
Cortisol is produced by the adrenal cortex in response to stimulation by ACTH.
diabetes insipidus: a condition caused by lack of ADH, which results in excessive production of very dilute urine
ADH may be produced in insufficient quantities by the hypothalamus or the posterior pituitary may fail to release it into the bloodstream when a tumour develops.
diabetes mellitus: a serious chronic disorder that results when the pancreas does not produce enough insulin, insulin receptors, or body cells do not respond to insulin
Levels of blood glucose tend to rise sharply (spike) after meals (hyperglycemia) and remain at significantly elevated levels.
endocrine gland: a cell, tissue, or organ that produces secretions that are released directly into the bloodstream; a ductless gland; for example, the thyroid gland
epinephrine: a hormone produced by the adrenal medulla in response to stress; also called adrenaline
The adrenal gland produces about 80% epinephrine and 20% norepinephrine.
exocrine gland: a cell, tissue, or organ that produces secretions that are released through ducts or channels; for example, a sweat gland
fight-or-flight response: a short-term stress response that ensures increased amounts of glucose and oxygen are available to muscle cells for cellular respiration, which results in increased available energy for use by muscles
follicle: as it relates to the thyroid gland, a microscopic structure consisting of a circle of cells called follicle cells surrounding a central cavity
The thyroid gland consists of many follicles.
gigantism: a condition where a person produces excess hGH during childhood, resulting in a height of 8 feet or more
glucagon: a hormone secreted by the alpha cells in the islets of the pancreas that raises blood glucose levels by stimulating liver cells to convert glycogen to glucose; also stimulates fat cells (adipose cells) to convert fat to glucose
glucocorticoids: a group of hormones produced by the adrenal cortex, of which cortisol is of prime importance; influence glucose metabolism from protein and fat and immune function by suppressing inflammation
gonadotropic hormones: hormones that affect the reproductive organs; also called the gonads
hormone: a circulating chemical messenger that is produced by specialized cells, circulated in the bloodstream, and co-ordinates the various parts of the body by interacting with target cells
hyperglycemia: a condition resulting from high levels of blood glucose; occurs in individuals with diabetes mellitus
hypoglycemia: a condition resulting from low levels of blood glucose; occurs in individuals who secrete excessive amounts of insulin when a tumour develops in the beta cells or in diabetics who have injected too much insulin
hypothalamus: the region of the brain located below the cerebral hemispheres and thalamus and just above the pituitary gland; functions in maintaining homeostasis, and is especially important in co-ordinating the endocrine and nervous systems; secretes hormones of the posterior pituitary as well as releases hormones that regulate the anterior pituitary
insulin: a hormone secreted by the beta cells in the islets of the pancreas that lowers blood glucose levels by promoting the uptake of glucose by most cells of the body, and the synthesis and storage of glycogen in the liver; also stimulates protein and fat synthesis
islets of Langerhans (islets): clusters of alpha and beta cells that secrete glucagon and insulin, respectively, into the blood
lipid-soluble hormone: a hormone that is chemically identified as a lipid or steroid, such as testosterone, estrogen, progesterone, or cortisol
long-term stress responses: responses, mainly stimulated by cortisol, which are of long duration
metabolism: all of the chemical reactions that occur in living organisms to support and sustain life processes
One type involves the buildup or synthesis of complex compounds from simple ones. A second type consists of the breakdown or decomposition of complex compounds into simple ones. Cellular respiration is one of the major metabolic processes.
mineralocorticoid: a hormone produced by the adrenal cortex that regulates salt and water homeostasis by influencing the reabsorption of sodium ions
negative feedback: a mechanism where deviation from the optimum state causes a return to the optimum state; acts to eliminate any deviation from optimal conditions and leads to stability
neurosecretory cells: specialized nerve cells in the hypothalamus that extend into the posterior pituitary and secrete ADH and oxytocin into the posterior pituitary and, subsequently, into the bloodstream
norepinephrine: a second hormone produced by the adrenal medulla in response to stress, but in much smaller quantities than epinephrine
About 20% of adrenal medulla secretions are norepinephrine.
pancreas: a gland with dual functions
The non-endocrine part secretes digestive enzymes into the intestine through the pancreatic duct, while the endocrine portion, called the islets of Langerhans, secretes insulin and glucagon into the bloodstream.
pituitary dwarfism: a condition where a person does not produce enough hGH during childhood, resulting in short stature
positive feedback: a mechanism where movement away from the optimum state causes further deviation from the optimum state; usually leads to instability and is tolerated by the body only for a short time
posterior pituitary: an extension of the hypothalamus composed of nervous tissue that secretes hormones produced in the hypothalamus into the bloodstream; consists of a temporary storage site for hormones produced in the hypothalamus
precursor: an inactive form of a molecule that can easily be changed into the active form
releasing hormones: hormones produced by neurosecretory cells in the hypothalamus that stimulate or inhibit the secretion of hormones by the anterior pituitary; sometimes called releasing factors
set point (set value): ideal or optimum conditions
target cells: cells with specialized receptor structures
When stimulated, these receptor structures cause a response in the target cells.
thyroxine: a hormone produced by the follicle cells of the thyroid gland; mainly controls the rate at which the body metabolizes carbohydrates, fats, and proteins for energy and stimulates the proper development of the nervous system
The precursor thyroglobin can easily be changed into the active thyroxine by the addition of iodine atoms.
tropic hormone: a hormone that has another endocrine gland as its target cell
Type 1 diabetes (juvenile diabetes or insulin-dependent diabetes): an autoimmune disorder in which the immune system produces antibodies that attack and destroy the beta cells of the pancreas so that they are unable to produce insulin; usually diagnosed at an early age and the individuals require daily injections of insulin
Type 2 diabetes (adult-onset diabetes or insulin-independent diabetes): a disorder that develops slowly over time because the insulin receptors on the body’s cells stop responding to insulin or because the beta cells of the pancreas produce less and less insulin over time; appears to be related to being overweight or obese
vasopressin: also called antidiuretic hormone (ADH)
water-soluble hormone: a hormone that is chemically identified as being either an amino acid or a protein, such as epinephrine, human growth hormone, thyroxine, insulin, and glucagon