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Human Anatomy and Physiology
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Terms to Know for the Endocrine System
1.
Endocrine system: cells, tissues and organs that secrete hormones directly into body fluids (thyroid and parathyroid
glands secrete hormones into the blood and are therefore endocrine glands)
2.
Exocrine secretions: reach some internal or external body surfaces through ducts
3.
Hormone: substance that an endocrine gland secretes and that blood or body fluids transport
4.
Target cells: specific cells on which hormones exert their effect; they have specific receptors for the hormones
5.
Amines: made of amino acids; include norepinephrine and epinephrine
6.
Peptides: made of amino acids; include antidiuretic hormone, oxytocin, thyrotropin-releasing hormone
7.
Proteins: made of amino acids; include parathyroid hormone, growth hormone, prolactin
8.
Glycoproteins: made of protein and carbohydrate; include follicle-stimulating hormone, luteinizing hormone and
thyroid-stimulating hormone
9.
Steroids: made of cholesterol; include estrogen, testosterone, aldosterone, cortisol
10. Steroid hormones: hormones that are soluble in lipids and which can diffuse into cells relatively easily; combine
with specific protein molecules (receptors) and activate specific genes of the target cell
11. Nonsteroid hormones: include amines, peptides and proteins; combine with receptors in cell membrane of target
cell; deliver message by uniting with binding site of receptor molecule
12. Hormone-receptor complex: Combination of hormone molecule and the receptor molecule to
which it binds
13. Binding site: component of receptor molecule where hormone binds
14. Activity site: part of the receptor cell that interacts with other membrane proteins
15. First messenger: initial hormone that binds to receptor cell and which triggers a cascade of biochemical activity
16. Second messenger: the biochemicals in the cell that induce changes in response to the hormone’s binding
17. Cyclic adenosine monophosphate (cAMP): the second messenger associated with one group of hormones;
activates a set of enzymes called protein kinases
18. G protein: protein activated by a hormone-receptor complex; activates the enzyme adenylate cyclase
19. Adenylate cyclase: enzyme bound to inside of cell membrane; causes ATP molecules in the cytoplasm to form a
circle and make cAMP
20. Protein kinases: enzymes which transfer phosphate groups from ATP molecules to various protein substrate
molecules (called phosphorylation); this alters the shapes of the substrate molecules and activates some of them so
that they can alter various cellular processes, including:
a. Altering membrane permeabilities
b. Activating enzymes
c.
d.
e.
f.
Promoting synthesis of certain proteins
Stimulating or inhibiting specific metabolic pathways
Moving the cell
Initiating the secretion of hormones or other substances
21. Phosphodiesterase: enzyme that inactivates cAMP, so that its action is short-lived
22. Diacylglycerol (DAG): type of second messenger
23. Inositol triphosphate (IP3): type of second messenger
24. Prostaglandins: group of compounds with powerful, hormone-like effects; act more locally than hormones, usually
affecting only the organ where they are produced; potent and present in very small quantities; they are lipids
synthesized from arachidonic acid (a fatty acid) in cell membranes; they are made by cells in the following places:
a. Liver
b. Kidneys
c. Heart
d. Lungs
e. Thymus gland
f. Pancreas
g. Brain
h. Reproductive organs
Examples of effects: relax smooth muscles in the airways of the lungs and in blood vessels; contract smooth muscles in
the walls of the uterus and intestines; stimulate hormone secretion from the adrenal cortex and inhibit secretion of
hydrochloric acid from the stomach wall; influence movements of water molecules and sodium ions in the kidneys; help
regulate blood pressure; powerful effects on male and female reproductive physiology
25. Arachidonic acid: fatty acids from which prostaglandins are synthesized
26. Negative feedback systems: control many hormone secretions; an endocrine gland or the system controlling it is
sensitive to the concentration of a substance the gland secretes or to the product of a process it controls; whenever
this concentration reaches a certain level, the endocrine gland is inhibited (a negative effect), and its secretory
activity decreases; as concentration of the gland’s hormone decreases, the concentration of the regulated product
decreases too; inhibition of the gland ceases; when gland is no longer inhibited, it begins to secrete its hormone
again; these negative feeback systems stabilize the concentrations of some hormones
27. Hypothalamus: portion of brain below thalamus and forming floor of third ventricle; controls the anterior pituitary
gland’s release of hormones that stimulate other endocrine glands to release hormones; constantly receives
information about the internal environment from neural connections and cerebrospinal fluid
28. Anterior pituitary: enclosed in a capsule of dense collagenous connective tissue and consists largely of epithelial
tissue organized in blocks around many thin-walled blood vessels; contains five types of secretory cells (a – d are
each produced by one type of cell)
a. Growth hormone (GH)
b. Prolactin (PRL)
c. Thyroid-stimulating hormone (TSH)
d. Adrenocorticotropic hormone (ACTH)
e. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (secreted by same type of cell)
f. In males, luteinizing hormone is interstitial cell stimulating hormone (ISCH)
29. Posterior pituitary (hypophysis): lobe of pituitary gland that secretes oxytocin and antidiuretic hormone
(vasopressin)
30. Pituitary stalk (infundibulum): attaches pituitary gland to the hypothalamus
31. Hypophyseal portal veins: capillaries from hypothalamus which merge and pass downward along the pituitary
stalk and give rise to a capillary net in the anterior pituitary
32. Growth hormone (GH): stimulates cells to increase in size and to divide more rapidly; enhances movement of
amino acids across cell membranes and speeds the rate that cells utilize carbohydrates and fats; two secretions from
the hypothalamus (GH releasing hormone and GH release-inhibiting hormone) control the secretion of GH; also
influenced by nutritional state; during low blood glucose concentration or protein deficiency, GH is released;
increase in blood protein and glucose concentrations leads to decrease in GH secretion
33. Prolactin (PRL): stimulates and sustains a woman’s milk production following the birth of an infant; excess PRL in
males may cause a deficiency of male sex hormones
34. Thyroid-stimulating hormone (TSH): controls thyroid gland secretions; hypothalamus partially regulates TSH
secretion by producing thyrotropin-releasing hormone (TRH); circulating thyroid hormones inhibit release of TRH
and TSH; as blood concentration of thyroid hormones increases, secretions of TRH and TSH decrease
35. Adrenocorticotropic hormone (ACTH): controls the manufacture and secretion of certain hormones from the
outer layer (cortex) of the adrenal gland (above the kidneys); ACTH is regulated in part by corticotropin releasing
hormone (CRH), which the hypothalamus releases in response to decreased concentrations of adrenal cortical
hormones; also, stress may increase ACTH secretion by stimulating the release of CRH
36. Follicle-stimulating hormone (FSH): a gonadotropin; hormone secreted by the anterior pituitary gland to stimulate
follicular development in a female, or sperm cell production in a male
37. Luteinizing hormone (interstitial cell stimulating hormone) (ICSH) or (LH): a gonadotropin; hormone secreted
by the anterior pituitary gland to control formation of corpus luteum (structure that forms from tissues of ruptured
ovarian follicle and secretes female hormones) in females and testosterone secretion in males
38. Thyrotropin-releasing hormone (TRH): hormone secreted by the hypothalamus to regulate the secretion of TSH
(Thyroid stimulating hormone)
39. Gonadotropins: hormones that exert their actions on the gonads or reproductive organs
40. Antidiuretic hormone (ADH): specialized neurons in the hypothalamus signal the posterior pituitary to secrete;
travels down axons through the pituitary stalk to the posterior lobe and vesicles near the ends of the axons store
ADH; nerve impulses release ADH into blood; produces a diuretic effect by reducing the amount of water the
kidneys secrete; in this way, ADH regulates the water concentration of body fluids; secretion of ADH is regulated
by the hypothalamus; osmoreceptors in the brain sense changes in the osmotic pressure of body fluids; when
dehydration increases concentration of blood solutes, osmoreceptors sense the increase in osmotic pressure and
signal the posterior pituitary to release ADH; travels through the bloodstream to the kidneys; as a result, the kidneys
produce less urine and water is conserved; drinking too much water dilutes body fluids and inhibits the release of
ADH
41. Oxytocin (OT): specialized neurons in the hypothalamus signal the posterior pituitary to secrete; travels down
axons through the pituitary stalk to the posterior lobe and vesicles near the ends of the axons store OT; nerve
impulses release OT into blood; contracts smooth muscles in the uterine wall and stimulates uterine contractions in
the later stages of childbirth (triggered by stretching of uterine and vaginal tissues late in pregnancy); in the breast,
OT contracts certain cells associated with milk producing glands and their ducts; this action forces liquid from milk
glands to milk ducts and ejects milk from the breasts for breat-feeding; OT is also a diuretic, but much weaker than
ADH
42. Diuretic: a chemical that increases urine production
43. Antidiuretic: a chemical that decreases urine formation
44. Osmoreceptor: receptor sensitive to changes in osmotic pressure of body fluids
45. Thyroid gland: a very vascular structure that consists of two large lobes connected by a broad isthmus; just below
the larynx on either side and in front of the trachea; covered by a capsule of connective tissue; made up of many
secretory parts called follicles; filled with colloid; follicular cells synthesize thyroxine (T 4) and T3
46. Follicles: secretory parts of the thyroid gland
47. Colloid: clear, viscous fluid that fills the cavities of follicles in the thyroid gland
48. Thyroxine (tetraiodothyronine): T4 (contains four atoms of iodine)
49. Triiodothyronine (T3): contains three atoms of iodine); five times more potent than T 4
a. Both T3 and T4 regulate the metabolism of carbohydrates; increase the rate at which cells release energy
from carbohydrates; increase the rate of protein synthesis; stimulate breakdown and mobilization of lipids;
required for normal growth and development; essential to nervous system maturation
50. Calcitonin: hormone that is produced by the thyroid glands extrafollicular cells (not the follicles themselves); work
with PTH to regulate concentrations of blood calcium and phosphate ions; release of calcitonin is regulated by the
blood concentration of calcium ions; calcitonin inhibits the bone-reabsorbing activity of the osteoclasts and
increases the kidneys’ excretion of calcium and phosphate ions; this lowers the blood calcium and phosphate ion
concentrations
51. Parathyroid glands: secrete parathyroid hormone (PTH)
52. Parathyroid hormone (PTH): increases blood calcium concentration and decreases blood phosphate ion
concentration; affects bones, kidneys and intestine; inhibits the activity of osteoblasts (build bone) and stimulates
osteocytes and osteoclasts to reabsorb bone and release calcium and phosphate ions into the blood; causes kidneys to
conserve blood calcium and to excrete more phophate ions in the urine; stimulate calcium absorption from food in
the intestine to further increase blood calcium concentration
53. Adrenal glands: closely associated with the kidneys; sit atop each kidney like a cap; embedded in masses of
adipose tissue that enclose the kidneys; composed of central and outer portions
54. Adrenal medulla: central portion of the adrenal gland; consists of irregularly shaped cells organized in groups
around blood vessels; closely connected with sympathetic division of the autonomic nervous system; adrenal
medullary cells are modified postganglionic neurons; preganglionic nerve fibers lead to them from the central
nervous system; stimulated to release its hormones by impulses arriving on sympathetic nerve fibers at the same
time impulses are stimulating other effectors; sympathetic impulses originate in hypothalamus in response to stress;
adrenal medullary secretions function with the sympathetic nervous system in preparing the body for energyexpending action – “fight or flight.”
55. Adrenal cortex: outer part of the adrenal gland; makes up the bulk of the adrenal gland; composed of closely
packed epithelial cells, organized in layers (outer, middle and inner zones of the cortex); cells are well-supplied with
blood vessels, just as the cells of the medulla are; produces more than 30 different steroids, including several
hormones: most important adrenal cortical hormones are aldosterone, cortisol, and certain sex hormones
56. Epinephrine (adrenaline): makes up 80% of the adrenal medullary secretion; synthesized from norepinephrine;
causes increased heart rate; increased force of cardiac muscle contraction; increased breathing rate; elevated blood
pressure; decreased digestive activity
57. Norepinephrine (noradrenaline): causes increased heart rate; increased force of cardiac muscle contraction;
increased breathing rate; elevated blood pressure; decreased digestive activity
58. Aldosterone: a steroid synthesized by cells in the outer zone of the adrenal cortex; a mineralocorticoid; causes
kidney to conserve sodium ions and excrete potassium ions; aldosterone stimulates water retention indirectly by
osmosis; decrease in blood concentration of sodium ions or an increase in the blood concentration of potassium ions
stimulates the cells that secrete aldosterone; kidneys indirectly stimulate aldosterone secretion if blood pressure falls
59. Mineralocorticoid: helps regulate the concentration of mineral electrolytes
60. Cortisol (hydrocortisone): a glucocorticoid; produced in middle zone of adrenal cortex and is a steroid; keeps
blood glucose concentration within the normal range between meals because a few hours between meals can exhaust
the supply of liver glycogen, a major source of glucose; release of cortisol is controlled by negative feedback
a. Inhibits protein synthesis in tissues, increasing blood concentration of amino acids
b. Promotes fatty acid release from adipose tissue, increasing utilization of fatty acids as an energy source and
decreasing use of glucose
c. Stimulates liver cells to synthesize glucose from noncarbohydrates, such as circulating amino acids and
glycerol, increasing blood glucose concentration
61. Glucocorticoid: affects glucose metabolism
62. Corticotropin-releasing hormone (CRH): secreted by hypothalamus into hypophyseal portal veins, which carry
CRH to anterior pituitary, which stimulates it to secrete ACTH; ACTH stimulates the adrenal cortex to release
cortisol; cortisol inhibits release of CRH and ACTH; as these concentrations fall, cortisol production drops; high
stress (injury, disease, extreme temperature, emotional upset) sends nerve impulses to the brain, which signals the
hypothalamus to release more CRH, leading to higher cortisol concentration until the stress subsides
63. Adrenal androgens: male types of sex hormones (some of which are converted to female hormones, estrogens, in
the skin, liver and adipose tissue); supplement the supply of sex hormones from the gonads; stimulate early
development of reproductive organs
64. Pancreas: elongated, flattened organ posterior to stomach; behind parietal peritoneum; joined to duodenum by duct;
consists of two major types of secretory tissues; dual function as exocrine gland that secretes digestive juice and as
endocrine gland that releases hormones; endocrine portion consists of islets of Langerhans
65. Islets of Langerhans: made of two types of cells
a. Alpha cells – secrete hormone glucagons
b. Beta cells – secrete hormone insulin
66. Glucagon: stimulates the liver to break down glycogen and certain noncarbohydrates, such as amino acids, into
glucose; raises blood glucose concentration; elevates blood sugar more effectively than epinephrine; low blood
sugar stimulate alpha cells to release glucagons; when blood sugar concentration rises, glucagons secretion falls; this
prevents hypoglycemia when glucose concentration is relatively low (between meals or during exercise)
67. Insulin: opposite of glucagon; stimulates liver to form glycogen from glucose; inhibits conversion of
noncarbohydrates into glucose; promotes facilitated diffusion of glucose cells across cell membranes with insulin
receptors
a. Cardiac muscle
b. Adipose tissue
c. Resting skeletal muscle (glucose uptake by exercising muscle does not depend on insulin)
Actions of insulin decrease blood glucose concentration; insulin secretion promotes transport of amino acids into
cells, increases protein synthesis, and stimulates adipose cells to synthesize and store fat
68. Pineal gland: small structure located deep between the cerebral hemispheres, where it attaches to the upper portion
of the thalamus near the roof of the third ventricle; consists of specialized pineal cells and supportive neuroglial
cells; secretes melatonin in response to light conditions outside the body; nerve impulses originating in the retinas of
the eyes send light information to the pineal gland; in the dark, nerve impulses from the eyes decrease, and
melatonin secretion increases
69. Melatonin: secreted by the pineal gland; helps regulate circadian rhythms
70. Circadian rhythms: patterns of repeated activity associated with environmental cycles of day and night (sleep wake
rhythms, seasonal fertility in many mammals)
71. Chronobiology: study of circadian and other rhythms
72. Thymus gland: lies in the mediastinum posterior to the sternum and between the lungs; large in young children but
shrinks with age; secretes a group of hormones called thymosins; plays an important role in immunity
73. Thymosins: hormones that affect the production and differentiation of certain white blood cells (lymphocytes)
74. Ovaries: produce estrogen and progesterone
75. Placenta: produces estrogen, progesterone and gonadotropin
76. Testes: produce testosterone
77. Atrial natriuretic peptide: hormone produced by the heart; stimulates urinary sodium secretion
78. Erythropoietin: red blood cell growth hormone secreted by the kidneys
79. Stressor: a factor that can stimulate a stress response
80. Stress: condition that a stressor produces in the body
81. General stress syndrome (general adaptation syndrome): reactions that are physiological responses to stress (under
hypothalamic control); fight or flight:
a. Raising blood concentrations of glucose, glycerol and fatty acids
b. Increasing heart rate, blood pressure and breathing rate
c. Dilating air passages
d. Shunting blood from skin and digestive organs to the skeletal muscles
e. Increasing epinephrine secretion from the adrenal medulla
Summary of responses to stress: Hypothalamus releases CRH, which, in turn, stimulates the anterior pituitary to secrete
ACTH; ACTH causes the adrenal cortex to increase cortisol secretion; cortisol increases blood amino acid concentration,
fatty acid release, and glucose formation from noncarbohydrates; actions of cortisol supply cells with biochemicals
required during stress
82. Diabetes mellitus: a condition due to insulin deficiency or the inability to respond to insulin; disturbs carbohydrate,
protein and lipid metabolism
83. Goiter: a bulge in the neck resulting from an enlarged thyroid gland
84. Hirsutism: excess hair growth, especially in women
85. Hyperglycemia: excess blood glucose
86. Hypoglycemia: deficiency of blood glucose
87. Polyphagia: excessive eating
88. Virilism: masculinization of a female