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Hormones General characteristics
Specific rates and rhythms of secretion Diurnal, pulsatile and cyclic, and patterns depending
on circulating substances
Operate within feedback systems Affect only cells with appropriate receptors The liver inactivates hormones, rendering the
hormones more water soluble for renal excretion
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Regulation of Hormone Release Hormones are released:
In response to an alteration in the cellular environment
To maintain a regulated level of certain substances or other hormones
Hormones are regulated by chemical, hormonal, or neural factors
Negative feedback Positive feedback
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Hormone Transport Hormones are released into the circulatory
system by endocrine glands Water-soluble hormones circulate in free,
unbound forms Lipid soluble hormones are primarily circulating
bound to a carrier
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Cellular Mechanism of Hormone Action Target cell Up-regulation Down-regulation Hormone effects
Direct effects Permissive effects
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Cellular Mechanism of Hormone Action Hormone receptors
Located in or on the plasma membrane or in the intracellular compartment of the target cell
Water-soluble hormones High molecular weight Cannot diffuse across the plasma membrane
Lipid-soluble hormones Easily diffuse across the plasma membrane and
bind to cytosolic or nuclear receptors
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Cellular Mechanism of Hormone Action Water-soluble hormones
First messenger Signal transduction Second-messenger molecules
Calcium Cyclic adenosine monophosphate (cAMP) Cyclic guanosine monophosphate (cGMP)
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Cellular Mechanism of Hormone Action Lipid-soluble hormones
Steroid hormones Androgens, estrogens, progestins, glucocorticoids,
mineralocorticoids, and thyroid hormones
Diffuse across the plasma membrane Bind to cytoplasmic or nuclear receptors
Activate RNA polymerase DNA transcription and translation
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Structure and Function of the Endocrine Glands Hypothalamic-pituitary axis
Hypothalamus Pituitary gland
Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis)
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Posterior Pituitary Hormones Synthesized with their binding proteins in the
supraoptic and paraventricular nuclei of the hypothalamus
Secreted by the posterior pituitary Antidiuretic hormone (ADH)
Controls plasma osmolality Oxytocin
Uterine contractions and milk ejection in lactating women
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Anterior Pituitary Hormones Adrenocorticotropic hormone Melanocyte-stimulating hormone Growth hormone Prolactin Thyroid-stimulating hormone Luteinizing hormone Follicle-stimulating hormone β-lipotropin β-endorphins
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Thyroid and Parathyroid Glands Thyroid gland
Two lobes lateral to the trachea Isthmus Follicles (follicle cells surrounding colloid) Parafollicular cells (C cells)
Secrete calcitonin Regulation of thyroid hormone secretion
Thyrotropin-releasing hormone and thyroid stimulating hormone
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Thyroid and Parathyroid Glands Thyroid hormones
90% T4 and 10% T3
Bound to thyroxine-binding globulin, thyroxine-binding prealbumin, or albumin
Affect growth and maturation of tissues, cell metabolism, heat production, and oxygen consumption
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Thyroid and Parathyroid Glands Parathyroid glands
Small glands located behind the upper and lower poles of the thyroid gland
Produce parathyroid hormone Regulator of serum calcium Antagonist of calcitonin
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Endocrine Pancreas The pancreas is both an endocrine and an
exocrine gland Houses the islets of Langerhans
Secretion of glucagon and insulin Cells
Alpha—glucagon Beta—insulin Delta—somatostatin and gastrin F cells—pancreatic polypeptide
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Endocrine Pancreas Insulin
Synthesized from proinsulin Secretion is promoted by increased blood glucose
levels Facilitates the rate of glucose uptake into the cells
of the body Anabolic hormone
Synthesis of proteins, lipids, and nucleic acids
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Endocrine Pancreas Glucagon
Secretion is promoted by decreased blood glucose levels
Stimulates glycogenolysis, gluconeogenesis, and lipolysis
Somatostatin Possible involvement in regulating alpha and beta
cell secretions
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Adrenal Glands Adrenal cortex
80% of an adrenal gland’s total weight Zona glomerulosa Zona fasciculata Zona reticularis
Adrenal medulla Innervated by the sympathetic and
parasympathetic nervous systems
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Adrenal Glands Adrenal cortex
Stimulated by adrenocorticotropic hormone (ACTH)
Glucocorticoid hormones Direct effects on carbohydrate metabolism Anti-inflammatory and growth-suppressing effects Influence awareness and sleep habits Most potent naturally occurring glucocorticoid is
cortisol
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Adrenal Glands Adrenal cortex
Mineralocorticoid hormones Affect ion transport by epithelial cells
Increase the activity of the sodium pump of the epithelial cells
Cause sodium retention and potassium and hydrogen loss
Most potent naturally occurring mineralocorticoid is aldosterone Regulated by the renin-angiotensin system
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Adrenal Glands Adrenal cortex
Adrenal estrogens and androgens Estrogen secretion by the adrenal cortex is minimal The adrenal cortex secretes weak androgens
Androgens are converted by peripheral tissues to stronger androgens such as testosterone
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Adrenal Glands Adrenal medulla
Chromaffin cells (pheochromocytes) Chromaffin cells secrete the catecholamines
epinephrine (majority) and norepinephrine
Release of catecholamines has been characterized as a “fight or flight” response
Catecholamines promote hyperglycemia
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Neuroendocrine Response to Stress The endocrine system reacts with the nervous
system to respond to stressors The stress response also involves the immune
system Influenced by corticotropin-releasing
hormone from the hypothalamus
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Tests of Endocrine Function Radioimmunoassay Enzyme-linked immunosorbent assay
(ELISA) Bioassay
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Aging and the Endocrine System Thyroid gland
Glandular atrophy, fibrosis, nodularity, and increased inflammatory infiltrates
Parathyroid glands Related to alterations in calcium balance
Inadequate intake, malabsorption, or renal changes
Adrenal glands Decreased clearance of cortisol