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Endocrine System
Modified from:http://www2.kumc.edu/instruction/nursing/nrsg812/endocrine/
Images from:
http://www.endocrineweb.com/
gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookENDOCR.html
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Mechanisms of Hormone Action
• Certain secretory cells release chemical agents (hormones) for the purpose of mediating biologic responses in distant Target Cells.
• Hormones sources
– Single amino acid (catecholamines)
– Chains amino acids (peptide hormones of hypothalamus)
– Cholesterol (steroids)
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Mechanisms of Hormone Action• Hormones control and integrate many body functions
with this system.
• In general, hormonal control regulates the metabolic functions of the body, the types of effects that occur inside the cell and determined the character of the cell itself.
• The endocrine system works with the nervous system to regulate: metabolism, water and salt balance, blood pressure, response to stress, and sexual reproduction.
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3 Forms of Hormonal Communication1. Endocrine = hormones are secreted into blood to
regulate the function of distant target cell
2. Paracrine = endocrine cells secrete into surrounding extracellular space. Target cells are neighbors
3. Neuroendocrine = Directly into blood (norepin), & into brain interstitial space (Vasopressin)
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Endocrine System
• Endocrine System Hormones/Glands whose functions are solely endocrine include:
• pituitary (hypophysis)
• pineal
• thyroid
• parathyroids
• adrenals
• pancreas
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Hypothalamus and Pituitary• Pituitary has direct
neural and blood connection to the hypothalamus
• Hypothalamus sends releasing factors to anterior pituitary
• Hypothalamus stimulates posterior pituitary via neural pathway
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Hypothalamus• Hypothalamus can synthesize and release hormones from its
axon terminals into the blood circulation. • controls pituitary function and thus has an important,
indirect influence on the other glands of the endocrine system.
• exerts direct control over both the anterior and posterior portions of the pituitary gland.
• regulates pituitary activity through two pathways: a neural pathway and a portal venous pathway.
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Hypothalamus
• Neural pathways extend from the hypothalamus to the posterior pituitary lobe, where the hormones are stored and secreted.
• Portal venous pathways connect the hypothalamus to the anterior pituitary lobe, carry releasing and inhibiting hormones
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Pituitary Gland• Pituitary Gland is located at the base of the
skull in an indentation of the sphenoid bone.
• Is joined to the hypothalamus by the pituitary stalk (neurohypophyseal tract) and consists of the anterior pituitary and the posterior pituitary
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Anterior pituitary gland (adenohypophysis)• Called the master gland, because its anterior lobe
has direct control over the secretion of:
• ADH - antidiuretic hormone (vasopressin)
• ACTH - adrenocorticotrophic hormone
• TTH - thyrotrophic hormone
• GH - growth hormone
• FSH - follicle stimulating hormone
• LH - leutinizing hormone
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Posterior pituitary• Stores and secretes hormones made in the
hypothalamus and contains many nerve fibers.
• ADH (Antidiuretic Hormone/Vasopressin), which controls the rate of water excretion into the urine
• Regulates Na+ & K+ reabsorption in the kidneys this influences blood volume & blood pressure
• Oxytocin, which, among other functions, helps deliver milk from the glands of the breast.
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Adrenal Glands• Adrenal Glands
have an outer cortex and an inner medulla.
• The adrenal cortex and medulla are major factors in the body's response to stress.
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Kidneys—Renal Hormones• Renin is an hormone/enzyme
(released from juxtaglomerular cells)
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Thyroid Gland• Thyroid function is regulated by the
hypothalamus and pituitary, feedback controls an intrinsic regulator mechanism
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Thyroid Problems• Thyroid gland enlargement may or may not be
associated with abnormal hormone secretion.
• An enlarged thyroid gland can be the result of:
• iodine deficiency (Goiter)
• inflammation, or
• benign or malignant tumors
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Parathyroid Glands• There are 4 parathyroid glands
located behind the thyroid.
• Parathyroid Glands are important in calcium metabolism phosphorus metabolism
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Pancreas
• endocrine gland, secreting the hormones insulin and glucagon, exocrine gland, producing digestive enzymes.
• Secretes insulin, glucagon (regulate blood sugar)
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Cellular Mechanisms of Hormone Action• Hormonal interaction with target cells begin with
reversible binding to specific receptors
1. Interactions with membrane receptor (protein)2. Interactions with nuclear receptors (steroid)
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Amino Acid Based Hormones• Bind to receptor sites on cell membranes
• Amino acid hormone binding causes changes to occur receptor can activate carrier molecules which transport substances across the membrane
• receptor can activate second messengers
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Second Messengers• Second Messengers set a series of reactions in
motion
• Activate adenylate cyclase, generates cAMP from ATP
• cAMP activates other proteins within the cell increases glycogenolysis & lipolysis
• Open Ca2+ ion channels, activates calmodulin
• Hydrolyzes phospholipase C into inositol triphosphate & diacylglycerol
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Steroid Hormones• Steroid hormones are produced
by chemical modification of cholesterol
•Major classes steroid hormones•glucocorticoids (cortisol)•mineralocorticoids (aldosterone)•androgens (testosterone)•estrogens (estradiol)•Vitamin D metabolites
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Steroid Hormones
• Diffuse into cell and influence DNA
• Bind to a protein associated with DNA
• Cause DNA to increase synthesis of specific amino acids
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Feedback Loops• The release of a hormone is often triggered by a
change in the concentration of some substance in the body fluids.
• Each hormone has a corrective effect, eliminating the stimulus, which then leads to a reduction in hormone secretion.
• This process is called a negative feedback homeostatic control system to keep hormones at normal levels. (if levels increased it would be called positive feedback)
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Blood Sugar Control• Insulin and glucagon are produced by small groups
of cells in the pancreas (islets of Langerhans).
• Beta cell make insulin (beta cells) and Alpha cells that make glucagon
• Insulin is released when the blood sugar rises too high. Insulin tells the cells to use sugar.
• Glucagon is produced when the blood sugar is falling too low. Glucagon tells the liver to release sugar that was stored there when the blood sugar was higher.