Endocrine System Flashcards
Endocrine System
the study of hormones and endocrine glands
a system of ductless endocrine glands secrete messenger molecules (hormones) into the blood
influences target cells on specific tissues
Endocrine Organs
scattered throughout the body contained within “pure” endocrine organs and partly within organs of other body systems
pure endocrine organs: pituitary, pineal, thyroid, parathyroid, and adrenal glands
organs containing endocrine cells: pancreas, thymus, gonads, and hypothalamus
endocrine cells are mainly of epithelial origin
Central Nervous System Effects on Regulation of Hormone Levels
pineal gland: in epithalamus of diencephalon
hypothalamus
pituitary gland (hypophysis): nerohypophysis (posterior pituitary gland) and adenohypophysis (anterior pituitary gland)
Pineal Gland
located on the roof of the diencephalon
shaped like a pine cone
synthesizes and secretes melatonin
Hypothalamus
the hypothalamus controls secretion of anterior pituitary lobe hormones by secreting: releasing hormones (prompts anterior pituitary lobe to release hormones) inhibiting hormones (turn off secretion of anterior pituitary lobe hormones)
Hypothalamic-Adenohypophysial Connection: Releasing Hormones
GnTH (gonadotropin releasing hormone) PRH (prolactin-releasing hormone) CRH (corticotropin-releasing hormone) TRH (thyrotropic releasing hormone) GHRH (growth hormone releasing hormone) MSHRH (melanophore-stimulating hormone releasing hormone)
Hypothalamic-Adenohypophysial Connection: Release-Inhibiting Hormones
GnIH (gonadotropin inhibiting hormone)
PRIH (prolactin release-inhibiting hormone)
MSHRIH (melanophore-stimulating hormone release-inhibiting hormone)
The Pituitary Gland
secretes many different hormones
attached to the hypothalamus
two basic divisions of the pituitary gland:
adenohypophysis (anterior lobe) has three major divisions (pars distalis, pars intermedia, and pars tuberalis)
neurohypophysis (posterior lobe) has two major divisions (pars nervosa and infundibular)
Hypophyseal Portal System of Anterior PItuitary
hypophyseal portal system is a specialized set of blood vessels, which deliver releasing hormones from the hypothalamus to the anterior pituitary
Hypophyseal Portal System of Anterior PItuitary (Pathway)
hypothalamic neurons release hormones into the primary capillary plexus -> hormones are carried by the hypophyseal portal veins to the secondary capillary plexus in the anterior pituitary -> hormones move out of capillaries and influence anterior pituitary cells to secrete hormones which move into the secondary capillary plexus and into the general blood circulation
Relationships of Hypothalamus and Posterior Pituitary (Pathway)
hypothalamic neurons synthesize oxytocin and ADH -> oxytocin and ADH are transported along the hypothalamic-hypophyseal tract to the posterior lobe -> oxytocin and ADH are stored in axon terminals in the posterior pituitary -> oxytocin and ADH are released into the blood when hypothalamic neurons fire
Pars Distalis
largest division of the anterior pituitary lobe
contains different types of endocrine cells
makes and secretes numerous different hormones
tropic hormones (e.g. ACTH, TSH, FSH, LH) regulate hormone secretion by other glands
hormones which act directly on non-endocrine target tissues e.g. GH, PRL, and MSH
Hormones Produced by Anterior Pituitary Gland
ACTH (adreno-coricotropin hormone) stimulates adrenal cortex
TSH (tyhrotropin/thyroid stimulating hormone)
FSH (follicular stimulating hormone)
LH (luteinizing hormone)
GH (growth hormone)
PRL (prolactin) stimulates milk production
LPH (liptropin)
MSH (melanophore stimulating hormone)
opioids (endorphins and enkephalins)
The Posterior Lobe of Pituitary
its axons make up the hypothalamic-hypophyseal axon tract
its axons arise from neuronal cell bodies in the hypothalamus
supraoptic nucleus makes ADH (antidiuretic hormone)
paraventricular nucleus makes oxytocin
The Thyroid Gland
located in the anterior neck
largest pure endocrine gland
composed of follicles and areolar connective tissue
produces two hormones:
thyroid hormone (TH) produced by follicular cells; dietary iodine is necessary for normal hormone production
calcitonin produced by parafollicular cells and decreases calcium in the blood
The Parathyroid Glands
lie on the posterior surface of the thyroid gland
contain two types of endocrine cells:
chief cells: produce parathyroid hormone (PTH) which increases calcium in the blood
oxyphil cells: function unknown
The Adrenal (Suprarenal) Glands
pyramid-shaped glands located on the superior surface of each kidney
nerve supply is almost exclusively sympathetic fibers to adrenal medulla
adrenal hormones help one cope with danger, terror, or stress
gland has cortex and medulla:
adrenal medulla (a cluster of neurons derived from neural crest and part of sympathetic nervous system)
adrenal cortex (forms the bulk of the gland, derived from somatic mesoderm)
Chromaffin Cells
of adrenal medulla
modified ganglionic sympathetic neurons
secrete hormones epinephrine and norepinephrine
enhance “fight-or-flight” response which increases heart rate and blood pressure and dilates bronchioles
Three Layers (Zones) of Adrenal Cortex
layers secrete steroid hormones
zona glomerulosa: secretes mineralocorticoids: aldosterone which maintains blood pressure
zona fasciculata: secretes glucocorticoid cortisol
zona reticularis: secretes glucocorticoid cortisol and androgen DHEA
Adrenal Gland Response to Short Term and Prolonged Stress
short term stress: preganglionic sympathetic fibers stimulate adrenal medulla to produce epinephrine and norepinephrine
prolonged stress: hypothalamusreleases corticotropin releasing hormone (CRH) which stimulates the adenohypophysis to release adrenocorticotropin hormone (ACTH) which signals the adrenal cortex to produce glucocorticoids and mineralcorticoids
The Pancreas
located in the posterior abdominal wall
contains endocrine and exocrine cells:
exocrine cells are acinar cells which secrete digestive enzymes
endocrine cells are contained within spherical bodies called pancreatic islets (islets of Langerhans)
Main Endocrine Cell Types in Pancreas
alpha cells: secrete glucagon which signals liver to release glucose from glycogen which raises blood sugar
beta cells: secrete insulin which signals most body cells to take up glucose from the blood which lowers blood glucose
delta cells secrete somatostatin which inhibits secretion of insulin and glucagon
F (PP) cells secrete pancreatic polypeptide and may inhibit exocrine activity of the pancreas
The Thymus
located in the lower neck and anterior thorax
important immune organ
site at which T-lymphocyte cells mature
Gonads
ovaries and testes produce steroid sex hormones
Male Testes
interstitial cells secrete androgens (primarily testosterone) that promotes the formation of sperm and maintains secondary sex characteristics
Female Ovaries
estrogen: maintains secondary sex characteristics
progesterone: prepares the uterus for pregnancy
Gonad Glycoprotein Hormones
gonads release glycoprotein hormones that influence gonadotropin secretion
inhibin: acts directly on the pituitary to selectively suppress the section of FSH
activin: opposes teh action of inhibin and stimulates the release of FSH
follistatin: binds to activin and blocks its action, which can indirectly contribute to the inhibition of FSH
Kidney Endocrine Cells
cells of the juxtaglomerular apparatus (JGA) secreterenin which signals adrenal cortex to produce aldosterone which increases retention of sodium in blood which increases blood pressure
endothelial cells of peritubular capillaries secrete erythropoietin which signals the bone marrow to produce more red blood cells
Hormones released by atria
the heart atria contain atrial natriuretic peptide (ANP) which stimulates kidney to secrete salt into urine which decreases both blood sodium concentration and blood pressure
Endocrine Cells in Organs
the GI tract: enteroendocrine cells
the placenta: sustains the fetus and secretes several steroid hormones
the skin: modified cholesterol molecules convert to a precursor of vitamin D
