A&P 16: The Endocrine System Flashcards
Endocrine system
2nd great control system of the body; interacts with the nervous system to coordinate and integrate the activity of body cells
Endocrinology
the scientific study of hormones and the endocrine organs
Endocrine glands
ductless glands; produce hormones, which are released into the surrounding tissue fluid; typically have a rich vascular and lymphatic drainage that receives their hormones
Neuroendocrine organ
the hypothalamus is considered this type of organ because, along with its neural functions, it produces and releases hormones
Autocrines
chemicals that exert their effects on the same cells that secrete them; short-distance signal
Paracrines
chemicals that act locally (within the same tissue) but affect cell types other than those releasing the chemicals
Amino-acid based hormones
most hormones are classified chemically on this basis
Steroids
hormones synthesized from cholesterol; of the hormones produced by the major endocrine organs, only gonadal and adrenocortical hormones fall into this category
Eicosanoids
some researchers add a third class of hormones, which includes leukotrienes and prostaglandins; nearly all cell membranes release these biologically active lipids (made from arachidonic acid)
Target cells
a hormone influences the activity of only those tissue cells that have receptors for it (a hormone alters the cellular activity of these)
Second messengers
with the exception of the thyroid hormone, amino acid-based hormones exert their signaling effects through these intracellular ___ ____ generated when a hormone binds to a receptor in the plasma membrane
Cyclic AMP (cAMP)
second messenger used by neurotransmitters and olfactory receptors
First messenger
the hormone, acting as this, binds to its receptor in the plasma membrane
G protein
hormone binding causes the receptor to change shape, allowing it to bind to a nearby inactive one of these proteins; acts like a light switch - off when GDP is bound to it and on when GTP is bound
Adenylate cyclase
the activated G protein (moving along the membrane) binds to this effector enzyme; some G proteins stimulate this, some inhibit it
Protein kinases
enzymes that phosphorylate (add a phosphate group to) various proteins, many of which are other enzymes
Phosphodiesterase
the action of cAMP persists only briefly because the molecule is rapidly degraded by this intracellular enzyme; the quick work of this means no extracellular controls are necessary to stop the activity
Phospholipase C
the PIP2-calcium signaling mechanism involves a G protein (Gq) and this membrane-bound effector; splits a plasma membrane phospholipid (PIP2)
Phophatidyl Inositol Bisphosphate (PIP2)
Phopholipase C splits this plasma membrane phospholipid into 2 second messengers (diacylglycerol DAG) & inositol triphosphate (IP3))
Diacylglycerol (DAG)
like cAMP, activates a protein kinase enzyme, which triggers responses within the target cell
Inositol triphosphate (IP3)
releases Ca2+ from intracellular storage sites
Calmodulin
the liberated Ca2+ takes on a 2nd messenger role, either by directly altering the activity of specific enzymes and channels or by binding to this intracellular regulatory protein; once Ca2+ binds to this, it activates enzymes that amplify the cellular response
Up-regulation
persistently low levels of a hormone can cause its target cells to form additional receptors for that hormone
Down-regulation
prolonged exposure to high hormone concentrations can decrease the number of receptors for that hormone; desensitizes target cells, so they respond less vigorously to hormonal stimulation, preventing them from overreacting to persistently high hormone levels
Negative feedback mechanism
the synthesis and release of most hormones are regulated by some type of this mechanism, in which some internal or external stimulus triggers hormonal secretion; as levels of a hormone rise, it causes target organ effects, when then feed back to inhibit further hormone release; as a result, blood levels of many hormones vary only within a narrow range
Humoral stimuli
some endocrine glands secrete their hormones in direct response to changing blood levels of certain critical ions and nutrients; simplest endocrine controls; PTH, insulin, and aldosterone are released in response to this type of stimuli
Neural stimuli
in a few cases, nerve fibers stimulate hormone release; classic example = response to stress, in which the sympathetic nervous system stimulates the adrenal medulla to release norepi and epi
Hormonal stimuli
many endocrine glands release their hormones in response to hormones produced by other endocrine organs
Half-life
the length of time for a hormone’s blood level to decrease by half; varies from a fraction of a minute to a week; water-soluble hormones have the shortest ones
Permissiveness
situation in which one hormone cannot exert its full effects without another hormone being present
Synergism
occurs when more than 1 hormone produces the same effects as the target cell and their combined effects are amplified; ex. glucagon and epi cause the liver to release glucose to the blood; when acting together, the amount of glucose released is 150% of what is released when each hormone acts alone
Antagonism
occurs when 1 hormone opposes the action of another hormone; ex. insulin (lowers blood glucose levels) is antagonized by glucagon (raises blood glucose levels)
Pituitary gland (hypophysis)
tiny; seated in the sella turcica of the sphenoid bone; secretes at least 8 hormones; “pea on a stalk”
Infundibulum
the funnel-shaped stalk of the pituitary; connects the pituitary to the hypothalamus superiorly
Posterior pituitary (lobe)
composed largely of neural tissue such as pituicytes (glia-like supporting cells) and nerve fibers
Neurohormones
posterior pituitary releases these hormones secreted by neurons received ready-made from the hypothalamus; = hormone storage area; not a true endocrine gland that manufacturers hormones
Neurohypophysis
posterior lobe plus the infundibulum
Anterior pituitary (lobe)
adenohypophysis; composed of glandular tissue; manufactures and releases a number of hormones
Hypothalmic-hypophyseal tract
nerve bundle running through the infundibulum that maintains the neural connection with the hypothalamus and the posterior lobe of the pituitary, which is actually part of the brain
Paraventricular & supraoptic nuclei
the hypothalamic-hypophyseal tract arises from neurons in these nuclei of the hypothalamus; neurosecretory cells that synthesize 1 of 2 neurohormones and transport them along their axons to the posterior pituitary; ___ neurons primarily make oxytocin; the ___ neurons mainly produce antidiuretic hormone
Primary capillary plexus
in the infundibulum; communicates inferiorly with the small hypophyseal portal veins with a secondary capillary plexus in the anterior lobe
Hypophyseal portal veins
with the primary and secondary capillary plexuses, make up the hypophyseal portal system
Portal system
unusual arrangement of blood vessels in which a capillary bed feeds into veins, which in turn feeds into a 2nd capillary bed
Releasing and inhibiting hormones
via the hypophyseal portal system, these hormones, secreted by neurons in the ventral hypothalamus circulate to the anterior pituitary, regulate secretion of its hormones
Oxytocin
a strong stimulant of uterine contractions; released in significantly higher amounts during childbirth and in nursing women
Antidiuretic hormone (ADH)
prevents wide swings in water balance, helping the body avoid dehydration and water overload
Vasopressin
under certain conditions, such as severe blood loss, exceptionally large amounts of ADH are released; at such high blood concentrations, ADH causes vasoconstriction, primarily of visceral blood vessels, raising blood pressure; this response targets different ADH receptors found on vascular smooth muscle; for this reason, ADH is also called this
Diabetes insipidus
one result of ADH deficiency; syndrome marked by intense thirst and huge urine output; “tasteless overflow”; distinguished from diabetes mellitus (“honey”) in which insulin deficiency cause large amounts of blood glucose to be lost in the urine
Tropic hormones (tropins)
4 of the 6 anterior pituitary hormones - TSH, ADH, FSH, LH; regulate the secretory action of other endocrine glands
Somatotropic cells
these cells of the anterior lobe of the pituitary produce growth hormone (GH), AKA somatotropin
Growth hormone (GH)
anabolic (tissue building) hormone that has both metabolic and growth-promoting actions
Insulin-like growth factors (IGFs)
GH mediates most of its growth enhancing effects indirectly via a family of these growth-promoting proteins; the liver, skeletal muscle, bone, and other tissues produce these in response to GH; if produced by the liver, act as hormones; if made in other tissues, act locally as paracrines
Growth hormone-releasing hormone (GHRH)
stimulates GH release
Growth hormone-inhibiting hormone (GHIH)
AKA somatostatin; inhibits GH release
Gigantism
hypersecretion of GH in children results in this because GH targets the still-active epiphyseal (growth) plates
Acromegaly
if excessive GH is secreted after the epiphyseal plates have closed, this condition results; “enlarged extremities”; characterized by overgrowth of bony areas still responsive to GH (bones of the hands, feet, and face)