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PowerPoint® Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham
C H A P T E R
Copyright © 2011 Pearson Education, Inc.
Part 1
17 The Endocrine System
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The Endocrine System: An Overview
• A system of ductless glands • Secrete messenger molecules called
hormones • Interacts closely with the nervous system • Endocrinology • Study of hormones and endocrine glands
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Endocrine Organs
• Scattered throughout the body • Pure endocrine organs are the …
• Pituitary, pineal, thyroid, parathyroid, and adrenal glands
• Organs containing endocrine cells include: • Pancreas, thymus, gonads, and the hypothalamus • Plus other organs secrete hormones (eg., kidney,
stomach, intestine) • Hypothalamus is a neuroendocrine organ
• Produces hormones and has nervous functions • Endocrine cells are of epithelial origin
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Location of the Major Endocrine Glands
Figure 17.1
Pineal gland Hypothalamus Pituitary gland
Parathyroid glands (on dorsal aspect of thyroid gland) Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Hormones • Classes of hormones • Amino acid–based hormones • Steroids—derived from cholesterol
• Basic hormone action • Circulate throughout the body in blood vessels • Influences only specific tissues— those with
target cells that have receptor molecules for that hormone • A hormone can have different effects on
different target cells (depends on the receptor)
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Control of Hormones Secretion
• Secretion triggered by three major types of stimuli: • Humoral—simplest of endocrine control
mechanisms • Secretion in direct response to changing
ion or nutrient levels in the blood • Example: Parathyroid monitors calcium • Responds to decline by secreting
hormone to reverse decline
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Control of Hormones Secretion
• Secretion triggered by three major types of stimuli (continued) • Neural
• Sympathetic nerve fibers stimulate cells in the adrenal medulla
• Induces release of epinephrine and norepinephrine • Hormonal
• Stimuli received from other glands • Certain hormones signal secretion of other
hormones • Example: Hypothalamus secretes hormones
stimulates pituitary stimulates other glands
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Types of Endocrine Gland Stimuli
Figure 17.2
(a) Humoral stimulus (b) Neural stimulus (c) Hormonal stimulus
Capillary (low Ca2+ in blood)
Parathyroid glands
Thyroid gland (posterior view)
PTH
Parathyroid glands
CNS (spinal cord)
Medulla of adrenal gland
Preganglionic sympathetic fibers
Capillary
Hypothalamus
Thyroid gland
Adrenal cortex Gonad
(Testis)
Pituitary gland
Capillary blood contains low concentration of Ca2+, which stimulates…
Preganglionic sympathetic fibers stimulate adrenal medulla cells… The hypothalamus secretes
hormones that…
…stimulate the anterior pituitary gland to secrete hormones that…
…secretion of parathyroid hormone (PTH) by parathyroid glands. PTH acts to increase blood Ca2+.
…to secrete catecholamines (epinephrine and norepinephrine) …stimulate other endocrine glands
to secrete hormones
1 1 1
2
3 2 2
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Control of Hormone Secretion
• Always controlled by feedback loops • Blood concentration declines below a
minimum --> More hormone is secreted • Blood concentration exceeds maximum
--> Hormone production is halted
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The Pituitary Gland
• Secretes nine major hormones • Attached to the hypothalamus by the infundibulum • 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
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The Pituitary Gland
Figure 17.3
Tuber cinereum
Mammillary body
Infundibulum Pars nervosa
Pars tuberalis Pars intermedia Pars distalis
Median eminence of hypothalamus
Optic chiasma
(c)
Anterior lobe Posterior lobe
(a)
(d)
Acidophil Basophil Chromophobe cell
Capillary with red blood cells
Spherical cluster of cells
(b)
Corpus callosum
Pituitary (hypophysis)
Brain stem
Mammillary body
Hypothalamus
Pineal
Thalamus
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The Anterior Lobe
• The pars distalis—largest division of the anterior lobe • Contains five different endocrine cell groups • Makes and secretes seven different hormones • Tropic hormones regulate hormone
secretion by other glands • Include: TSH, ACTH, FSH, LH
• GH, PRL, and MSH • Act directly on non-endocrine target tissues
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The Anterior Lobe
• Growth hormone, GH (somatotropic hormone) • Produced by somatotropic cells • Stimulates body growth by stimulating
increased protein production and growth of epiphyseal plates
• Stimulates growth directly and indirectly by the liver’s secretion of insulin-like growth factor-1.
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The Anterior Lobe
• Thyroid-stimulating hormone, TSH • Produced by thyrotropic cells • Signals thyroid gland to secrete thyroid
hormone • Adrenocorticotropic hormone, ACTH • Stimulates the adrenal cortex to secrete
hormones that help cope with stress
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The Anterior Lobe
• Melanocyte-stimulating hormone, MSH • In humans, MSH functions in appetite
supression • Gonadotropins— are produced by
gonadotropic cells and affect the gonads • Follicle-stimulating hormone, FSH, and
luteinizing hormone, LH
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The Anterior Lobe
• Prolactin—produced by prolactin cells • Targets milk-producing glands in the breast—
stimulates milk production • Endocrine cells of the pars distalis • Clustered in spheres and branching cords
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The Anterior Lobe
Table 17.1 Copyright © 2011 Pearson Education, Inc.
The Anterior Lobe
Table 17.1
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• The hypothalamus • Controls secretion of anterior lobe hormones • Exerts control by secreting: • Releasing hormones—prompt anterior
lobe to release hormones • Inhibiting hormones—turn off secretion of
anterior lobe hormones
Hypothalamic Control of Hormone Secretion from the Anterior Lobe
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• Releasing hormones • Are secreted like neurotransmitters • Enter a primary capillary plexus • Travel in hypophyseal portal veins to a
secondary capillary plexus (hypothalamohypophyseal portal system) • From the secondary capillary plexus,
hormones secreted by the anterior lobe enter general circulation and travel to target organs
Hypothalamic Control of Hormone Secretion from the Anterior Lobe
Copyright © 2011 Pearson Education, Inc. Figure 17.4a
The Anterior Lobe
When appropriately stimulated, hypothalamic neurons secrete releasing and inhibiting hormones into the primary capillary plexus.
Hypothalamic hormones travel through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from the anterior lobe.
Anterior pituitary hormones are secreted into the secondary capillary plexus.
Hypothalamus Hypothalamic neuron cell bodies
Hypophyseal portal system
Superior hypophyseal artery
(a) Relationship between the anterior pituitary and the hypothalamus
Anterior lobe of pituitary
TSH, FSH, LH, ACTH, GH, PRL
Primary capillary plexus Hypophyseal portal veins Secondary capillary plexus
1
2
3
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The Posterior Lobe
• Is structurally part of the brain • Its axons make up the hypothalamic–
hypophyseal tract • Arises from neuronal cell bodies in the
hypothalamus • Supraoptic nucleus • Paraventricular nucleus
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The Posterior Lobe
• Does not make hormones • Stores and releases hormones made in the
hypothalamus • Releases two peptide hormones • Antidiuretic hormone (ADH) [aka, vasopressin] • Oxytocin (OT)
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Relationship Between the Posterior Pituitary and Hypothalamus
Figure 17.4b
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.
Paraventricular nucleus
Supraoptic nucleus
Optic chiasma
Hypothalamus
Inferior hypophyseal artery
Oxytocin ADH
Infundibulum (connecting stalk) Hypothalamic- hypophyseal tract
Axon terminals Posterior lobe of pituitary
(b) Relationship between the posterior pituitary and the hypothalamus
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2
3
4
5
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The Posterior Lobe
• ADH (vasopressin) • Made in supraoptic nucleus • Targets kidneys to reabsorb water
• Oxytocin • Produced in the paraventricular nucleus • Induces smooth muscle contraction of
reproductive organs, ejects milk during breast feeding, and signals contraction of the uterus during childbirth
Copyright © 2011 Pearson Education, Inc. Table 17.1
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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) • Calcitonin
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The Thyroid Gland
Figure 17.5a
Hyoid bone Thyroid cartilage
Common carotid artery
Epiglottis
Superior thyroid artery
External carotid artery
Isthmus of thyroid gland
Left subclavian artery Left lateral lobe of thyroid gland
Inferior thyroid artery
Trachea
Right subclavian artery
Aorta
(a) Gross anatomy of the thyroid gland, anterior view
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The Thyroid Gland
Figure 17.5b
Colloid-filled follicles
Follicular cells (secrete thyroid hormone)
Parafollicular cell (secretes calcitonin)
(b) Photomicrograph of thyroid gland follicles (160×) Copyright © 2011 Pearson Education, Inc.
The Parathyroid Glands
• Lie on the posterior surface of the thyroid gland
• Contain two types of endocrine cells • Chief cells • Produce parathyroid hormone (PTH) • Increases blood concentration of Ca2+
• Oxyphil cells • Function unknown
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The Parathyroid Glands
Figure 17.6a, b
(b) Photomicrograph of parathyroid gland tissue (360×)
Capillary
Parathyroid cells (secrete parathyroid hormone) Oxyphil cells
Pharynx (posterior aspect)
Thyroid gland Parathyroid
glands
Trachea Esophagus
(a) Location of parathyroid glands, posterior view
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The Adrenal (Suprarenal) Glands
• Pyramid-shaped glands located on the superior surface of each kidney
• Supplied by about 60 suprarenal arteries • Nerve supply is almost exclusively
sympathetic fibers
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The Adrenal (Suprarenal) Glands
• Two endocrine glands in one • Adrenal medulla—a cluster of neurons • Derived from neural crest • Part of the sympathetic nervous system
• Adrenal cortex—forms the bulk of the gland • Derived from somatic mesoderm
• All adrenal hormones help one cope with danger, terror, or stress
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The Adrenal Medulla
• Chromaffin cells • Are modified ganglionic sympathetic neurons • Secrete amine hormones epinephrine and
norepinephrine • Enhance “fight-or-flight” response • Hormones are stored in secretory vesicles
• Are arranged in spherical clusters and some branching cords
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The Adrenal Cortex
• Secretes lipid-based steroid hormones • Cortex is composed of three layers (zones) • Zona glomerulosa—cells arranged in
spherical clusters • Zona fasciculata—cells arranged in parallel
cords; contains lipid droplets • Zona reticularis—cells arranged in a
branching network
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The Adrenal Cortex
• Hormones are corticosteroids • Adrenal corticosteroids are of two main
classes • Mineralocorticoids • Glucocorticoids
• Also secretes androgens
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Mineralocorticoids
• Aldosterone—secreted by the zona glomerulosa • Secreted in response to decline in blood
volume or blood pressure • Is the terminal hormone of the renin-
angiotensin mechanism
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Glucocorticoids
• Cortisol is the main type • Secreted by zona fasciculata and zona
reticularis • Helps the body deal with stressful situations
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The Adrenal Gland–Gross and Microscopic
Figure 17.7a, b
Cortex
Kidney
Medulla Adrenal gland
Capsule Aldosterone
Epinephrine and norepinephrine
Cortisol and androgens
Zona glomerulosa
Zona fasciculata
Zona reticularis
Adrenal medulla
(a)Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla
(b) Photomicrograph (140X)
Hormones secreted
Co
rtex
Me
du
lla
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Stress and the Adrenal Gland
Figure 17.8
Short-term stress More prolonged stress Stress
Hypothalamus
CRH (corticotropin- releasing hormone)
Corticotroph cells of anterior pituitary
To target in blood Adrenal cortex (secretes steroid hormones)
Glucocorticoids Mineralocorticoids
ACTH
Catecholamines (epinephrine and norepinephrine)
Short-term stress response 1.Increased heart rate 2.Increased blood pressure 3.Liver converts glycogen to glucose and releases glucose to blood 4.Dilation of bronchioles 5.Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output 6.Increased metabolic rate
Long-term stress response 1.Retention of sodium and water by kidneys 2.Increased blood volume and blood pressure
1.Proteins and fats converted to glucose or broken down for energy 2.Increased blood glucose 3.Suppression of immune system
Adrenal medulla (secretes amino acid– based hormones)
Preganglionic sympathetic fibers
Spinal cord
Nerve impulses
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The Pineal Gland
• Located on the roof of the diencephalon • Shaped like a pine cone • “Pineal sand” is radiopaque • Used as a landmark to identify other brain
structures in X rays • Pinealocytes secrete melatonin • A hormone that regulates circadian rhythms
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The Pancreas
• Located in the posterior abdominal wall • Contains endocrine and exocrine cells • Exocrine cells • Acinar cells —secrete digestive enzymes
• Endocrine cells • Pancreatic islet cells —islets of Langerhans • About one million islets—scattered
throughout the pancreas
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The Pancreas
• Main endocrine cell types • Alpha cells (α cells)—secrete glucagon • Signals liver to release glucose from glycogen • Raises blood sugar
• Beta cells (β cells)—secrete insulin • Signals most body cells to take up glucose
from the blood • Promotes storage of glucose as glycogen in
liver • Lowers blood sugar
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The Pancreas
• Pancreatic islets contain two rare cell types • Delta (∂) cells • Secrete somatostatin • Inhibits secretion of insulin and glucagon
• F (PP) cells • Secrete pancreatic polypeptide • May inhibit exocrine activity of the
pancreas
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The Thymus
• Located in the lower neck and anterior thorax • Important immune organ • Site at which T-lymphocytes arise from
precursor cells
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The Gonads
• Main sources of sex hormones • Testes and ovaries
• Male • Interstitial cells secrete androgens • Primarily testosterone • Promotes the formation of sperm • Maintains secondary sex characteristics
Male Hormones PLAY
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The Gonads
• Female • Ovaries
• Androgens secreted by the theca folliculi • Converted to estrogen by follicular granulosa
cells • Estrogen • Maintains secondary sex characteristics
• Progesterone • Prepares the uterus for pregnancy
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Other Endocrine Structures
• Endocrine cells occur within • The heart • Atria contain atrial natriuretic peptide
(ANP) • The GI tract • Enteroendocrine cells
• The placenta • Sustains the fetus and secretes several
steroid protein hormones
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Other Endocrine Structures
• The kidneys • Cells of the juxtaglomerular apparatus
(JGA) secrete renin • Endothelial cells and interstitial connective
tissue—secrete erythropoietin • The skin • Modified cholesterol molecules convert to a
precursor of vitamin D
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Pituitary Disorders
• Gigantism • Hypersecretion of GH in children
• Pituitary dwarfism • Hyposecretion of GH
• Diabetes insipidus • Pars nervosa does not make enough ADH
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Disorders of the Pancreas: Diabetes Mellitus
• Caused by • Insufficient secretion of insulin • Resistance of body cells to the effects of
insulin • Type 1 diabetes • Develops suddenly, usually before age 15 • T cell–mediated autoimmune response
destroys beta cells
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Diabetes Mellitus
• Type 2 diabetes • Adult onset • Usually occurs after age 40 • Cells have lowered sensitivity to insulin • Controlled by dietary changes and regular
exercise
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Disorders of the Thyroid Gland
• Grave’s disease • Most common type of hyperthyroidism • Immune system makes abnormal antibodies • Stimulates the oversecretion of TH by
follicle cells • Leads to nervousness, weight loss, sweating,
and rapid heart rate
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Disorders of the Thyroid Gland
• Myxedema • Adult hypothyroidism • Antibodies attack and destroy thyroid tissue • Low metabolic rate and weight gain are
common symptoms
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Disorders of the Thyroid Gland
• Endemic goiter • Due to lack of iodine in the diet
• Cretinism • Hypothyroidism in children • Short, disproportionate body, thick tongue,
and mental retardation
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Thyroid Disorders
Figure 17.10
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Disorders of the Adrenal Cortex
• Cushing’s syndrome • Caused by hypersecretion of glucocorticoid
hormones—usually a pituitary tumor • Addison’s disease • Hyposecretory disorder of the adrenal cortex • Deficiencies of both mineralocorticoids and
glucocorticoids
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Thyroid Disorders
Figure 17.11
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The Endocrine System Throughout Life
• Thyroid gland • Forms from a thickening of endoderm on the
floor of the pharynx • Parathyroids and the thymus gland • From endoderm lining the pharyngeal
pouches
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Embryological Origin of Selected Endocrine Organs
• Pineal gland • Originates from ependymal cells
• Pituitary gland—dual origin • Adenohypophysis originates from the roof
of the mouth • Neurohypophysis grows inferiorly from the
floor of the brain
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Embryological Origin of Selected Endocrine Organs
• Adrenal gland—dual origin gland • Adrenal medulla—from neural crest cells of
nearby sympathetic trunk ganglia • Adrenal cortex—from mesoderm lining the
coelom
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Embryological Origin of Selected Endocrine Organs
(b) Week 6. Inferior extension of the floor of the diencephalon forms the neurohypophyseal bud.
Neurohypophyseal bud
Hypophyseal pouch
Anterior Posterior
Hypothalamus
Brain
Neurohypophyseal bud
Pharyngeal pouches
Future parathyroid glands
Esophagus
(a) Week 5. Thyroid, thymus, and parathyroid glands form from pharyngeal endoderm. Hypophyseal pouch extends superiorly from ectoderm in the roof of the mouth.
Hypophyseal pouch
Future thyroid gland
Future thymus
Lung bud
Future mouth
Figure 17.12a, b
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Embryological Origin of Selected Endocrine Organs
Figure 17.12c, d
(c) Week 7. Hypophyseal pouch pinches off the surface ectoderm and is closely associated with the neurohypophyseal bud.
Neurohypophyseal bud
Hypophyseal pouch
(d) Week 8. Hypophyseal pouch forms the anterior lobe of pituitary; neurohypophyseal bud forms the posterior lobe. Distinct portions of each differentiate.
Anterior lobe
Pars tuberalis
Pars distalis
Pars intermedia
Third ventricle of brain
Posterior lobe
Infundibulum
Pars nervosa
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The Endocrine System Throughout Life
• Endocrine organs operate effectively until old age • Anterior pituitary
• Increase in connective tissue and lipofuscin • Decrease in vascularization and number of hormone-
secreting cells • Adrenal cortex
• Normal rates of glucocorticoid secretion continue • Adrenal medulla
• No age-related changes in catecholamines
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The Endocrine System Throughout Life
• Thyroid hormones • Decrease slightly with age
• Parathyroid glands • Little change with aging
• GH, DHEA, and the sex hormones • Marked drops in secretion with age