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Chapter 20 Outline
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Endocrine Glands and Hormones
Hypothalamic Control of the Endocrine System
Pituitary Gland
Thyroid Gland
Parathyroid Glands
Adrenal Glands
Pancreas
Pineal Gland and Thymus
Endocrine Functions of the Kidneys, Heart, Gastrointestinal
Tract, and Gonads
• Aging and the Endocrine System
• Development of the Endocrine System
Introduction
• Endocrine glands are ductless organs.
• They secrete their molecular products
(hormones) into the bloodstream.
• All endocrine organs have an extensive
distribution of many blood vessels.
• The endocrine system and the nervous system
both function to communicate signals throughout
the body to bring about homeostasis.
– Table 20.1 lists similarities and differences between
the two organ systems.
Comparison of the Endocrine
and Nervous Systems
Organs of the Endocrine System
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Hypothalamus
Antidiuretic hormone (ADH)
Oxytocin (OT)
Regulatory hormones
Pituitary gland
Anterior pituitary secretes:
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Growth hormone (GH)
Luteinizing hormone (LH)
Melanocyte-stimulating hormone (MSH)
Prolactin (PRL)
Thyroid-stimulating hormone (TSH)
Posterior pituitary releases:
Antidiuretic hormone (ADH)
Oxytocin (OT)
Pineal gland
Melatonin
Parathyroid glands
(located on posterior surface
of thyroid)
Parathyroid hormone (PTH)
Thyroid gland
Calcitonin (CT)
Thyroid hormone (TH)
Thymus
Thymopoietin
Thymosins
Heart
Atriopeptin
Adrenal glands
Cortex:
Corticosteroids
Medulla:
Epinephrine (E)
Norepinephrine (NE)
Gastrointestinal (GI) tract
Cholecystokinin (CCK)
Gastric inhibitory peptide (GIP)
Gastrin
Secretin
Vasoactive intestinal peptide (VIP)
Kidney
Calcitriol
Erythropoietin (EPO)
Pancreatic islets
Glucagon
Insulin
Somatostatin
Pancreatic polypeptide
Testes (male)
Androgens
Inhibin
Ovaries (female)
Estrogen
Inhibin
Progesterone
Figure 20.1
Overview of Hormones
• Endocrine glands produce informational
molecules called hormones.
• Hormones can only affect cells (target
cells) or organs (target organs) that have
receptors for a specific hormone.
• Cells or organs that do not possess
receptors for a specific hormone do not
respond to that hormone.
Classes of Hormones
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•
The study of the structural components of the
endocrine system, the hormones they produce,
and the effects of these hormones on target
organs is termed endocrinology.
There are three major classes of hormones
based on their chemical structure:
1. Peptide hormones—growth hormone
2. Steroid hormones—estrogen
3. Biogenic amines—thyroid hormone
Control of Hormone Secretion
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Hormone secretion is regulated by a selfadjusting mechanism called a feedback
loop.
There are two types of feedback loops:
1. Negative feedback loop
2. Positive feedback loop
Negative Feedback Loop
• In this type of loop, the stimulus starts the
process like an elevation in blood glucose
(eating a meal).
• The hormone secreted in response to
elevated glucose is insulin.
• Insulin brings about a decrease in blood
glucose.
Negative Feedback Loop
Figure 20.2
Positive Feedback Loop
• Only a few examples in the human body
• In this type of loop, the stimulus doesn’t
produce an opposite and counteracting
effect like a negative feedback loop
• The stimulus accelerates the process
Positive Feedback Loop
Figure 20.2
Hypothalamic Control of the
Endocrine System
• The hypothalamus is the interface
between the nervous system and the
endocrine system and is the master gland
of the endocrine system.
• It controls and oversees most endocrine
functions.
• It is located in the inferior region of the
diencephalon just superior to the pituitary
gland.
Mechanisms of Hypothalamic
Control
The hypothalamus controls most endocrine activity
in three ways:
1. Controls release of regulatory hormones from
the anterior pituitary gland
2. Secretes oxytocin (OT) and antidiuretic
hormone (ADH) from the posterior pituitary
gland
3. Controls the stimulation and secretion activities
of the adrenal medulla
Mechanisms of Hypothalamic
Control
Figure 20.3
Pituitary Gland
• Also called the hypophysis
• Located just inferior to the hypothalamus
• Housed within the sella turcica of the
sphenoid bone
• Connected to the hypothalamus by a thin
stalk called the infundibulum
• Divided into anterior and posterior lobes
Pituitary Gland
Figure 20.4
Anterior Pituitary
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•
Also known as the adenohypophysis
Divided into three distinct areas:
1. Pars distalis
2. Pars intermedia
3. Pars tuberalis
Control of Anterior Pituitary
Hormone Secretions
• Hormones secreted from anterior pituitary
gland are regulated by regulatory
hormones secreted from the
hypothalamus.
• These regulatory hormones from the
hypothalamus to the anterior pituitary
travel through a blood vessel network
called the hypothalamo-hypophyseal
portal system.
Regulatory Hormones Secreted
by the Hypothalamus
Hypothalamo-Hypophyseal
Portal System
Figure 20.6
Hormones of the Anterior
Pituitary
There are seven major hormones secreted from
the anterior pituitary:
1. Thyroid stimulating hormone (TSH)
2. Prolactin (PRL)
3. Adrenocorticotropin hormone (ACTH)
4. Growth hormone (GH)—also called
somatotropin
5. Follicle stimulating hormone (FSH)
6. Lutenizing hormone (LH)
7. Melanocyte-stimulating hormone (MSH)
Anterior Pituitary Hormones,
Target Organs, and Effects
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Hypothalamus
Median eminence
Infundibulum
Anterior pituitary
Posterior pituitary
Muscle
Thyrotropic cells secrete
thyroid-stimulating hormone
(TSH), which acts on the
thyroid gland.
Somatotropic cells secrete
growth hormone (GH), which acts
on all body tissues, especially bone,
muscle, and adipose connective tissue.
Thyroid
Adipose
connective tissue
Bone
Mammary gland
Mammotropic cells secrete
prolactin (PRL), which acts on
mammary glands and testes.
Gonadotropic cells secrete
follicle-stimulating hormone (FSH)
and luteinizing hormone (LH)
which acts on the gonads (testes
and ovaries).
Testis
Corticotropic cells secrete
adrenocorticotropic
hormone (ACTH), which acts
on the adrenal cortex.
Ovary
Pars intermedia cells secrete
melanocyte-stimulating hormone
(MSH), which acts on melanocytes
in the epidermis.
Adrenal
cortex
Adrenal gland
Figure 20.7
Testis
Melanocytes
Posterior Pituitary
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Derived from the embryonic
diencephalon
Comprised of the following regions:
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pars nervosa
infundibular stalk
Neural connection between the
hypothalamus and the posterior pituitary
is the hypothalamo-hypophyseal tract
Hypothalamo-Hypophyseal Tract
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Hypothalamus
Paraventricular nucleus
Supraoptic nucleus
Hypothalamo-hypophyseal tract
Optic chiasm
Infundibulum
Posterior pituitary
Anterior pituitary
Telodendria
Figure 20.8
Pituitary Gland Hormones
Thyroid Gland
• The largest gland entirely devoted to
endocrine activities
• Located just inferior to the thyroid cartilage
and anterior to the trachea
• Butterfly shape with right and left lobes
connected by a midline isthmus
Thyroid Gland
Figure 20.9
Thyroid Follicle
• Functional unit of the thyroid gland
• Comprised of simple cuboidal cells that
produce an iodinated glycoprotein called
thyroglobulin (TGB) that is stored
internally as a colloid
• The follicle cells and the internal storage
area for TGB is collectively called the
thyroid follicle
Thyroid Follicle
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Thyrohyoid muscle
Thyroid cartilage
Common carotid artery
Superior thyroid vessels
Cricoid cartilage
Left lobe of thyroid gland
Isthmus of thyroid gland
Inferior
thyroid artery
Inferior
thyroid veins
Right lobe of thyroid gland
Trachea
(a)
Follicular cells
Capillary
Parafollicular cell
Thyroid follicle
Connective
tissue
capsule
Follicle lumen (contains colloid)
LM 400x
(b)
a(right): © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b(right): © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Figure 20.9
Parafollicular Cells
• Large endocrine cells located between
thyroid follicles called parafollicular cells
• Secrete calcitonin, which helps to
regulate serum calcium
Thyroid Gland–Pituitary Gland
Negative Feedback Loop
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Hypothalamus
stimulatory
1 A stimulus (e.g., low body temperature)
inhibitory
causes the hypothalamus to secrete
thyrotropin-releasing hormone (TRH),
which acts on the anterior pituitary.
Negative feedback
inhibition
TRH
5
2 Thyrotropic cells in the
anterior pituitary release
thyroid-stimulating
hormone (TSH).
Increased body temperature is detected by the
hypothalamus, and secretion of TRH by the
hypothalamus is inhibited. TH also blocks the
interactions of TRH from the hypothalamus
and anterior pituitary to prevent the formation
of TSH.
Anterior
pituitary
Target organs in body
TSH
4 TH stimulates target cells to increase metabolic
TH
activities, resulting in an increase in basal body
temperature.
3 TSH stimulates follicular cells of the thyroid
gland to release thyroid hormone (TH).
Figure 20.10
Parathyroid Glands
Small glands
(usually four)
embedded on
the posterior
surface of the
thyroid gland
Figure 20.11
Parathyroid Glands
There are two types of cells that are seen in
the parathyroid gland:
1. Chief cells (principal cells)—secrete
parathyroid hormone (PTH) that helps
regulate serum calcium
2. Oxyphil cells—function unknown
Cells of the Parathyroid Gland
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Connective tissue capsule
of parathyroid gland
Oxyphil cell
Muscles on posterior
side of pharynx
Chief cells
Capillary
Thyroid gland
(posterior aspect)
Parathyroid glands
Chief cells
Esophagus
Trachea
Oxyphil cells
LM 135x
(a) Posterior view
Figure 20.11
(b) Histologic views
b: © Victor Eroschenko
Parathyroid Hormone
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1 Low blood calcium (Ca2+) levels are
Ca2+ ions
detected by the parathyroid gland.
PTH molecules
2 Parathyroid hormone (PTH)
is secreted into bloodstream.
4 Rising Ca2+
in blood inhibits
PTH release.
Bloodstream
3 Target organs respond to
PTH, or its effects, to increase
blood calcium levels:
Bone
Kidney
Intestine
Figure 20.12
• Osteoclasts resorb bone
connective tissue, releasing
Ca2+ into the bloodstream.
• Kidney retains Ca2+ and
promotes activation of an
inactive form of vitamin D to
calcitriol, an active form of
vitamin D.
• Small intestine increases
absorption of more Ca2+
under the influence of calcitriol.
Thyroid and Parathyroid Hormones
Adrenal Glands
• Paired glands anchored on the superior border
of the two kidneys; also called suprarenal glands
Figure 20.13
Adrenal Glands
• Divided functionally into an outer adrenal
cortex and an inner adrenal medulla
Figure 20.13
Adrenal Cortex
Three distinct layers of cells (from superficial to
deep):
1. Zona glomerulosa—produce
mineralocorticoids, the main one being
aldosterone
2. Zona fasciculata—produce glucocorticoids,
the main one being corticosterone
3. Zona reticularis—produce the sex hormones,
estrogen- and testosterone-related hormones
Adrenal Cortex Hormones
Adrenal Medulla
• Forms the inner core of the adrenal gland
• Consists of chromaffin cells, which are
modified cells of the sympathetic division of the
autonomic nervous system
• These cells secrete norepinephrine and
epinephrine
Figure 20.13
Adrenal Cortex and Medulla
Pancreas
• Located between the duodenum and
spleen and posterior to the stomach
Pancreas
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Inferior
vena cava
Pancreatic islet cells
Abdominal
aorta
Spleen
Alpha cell
Body of
pancreas
Beta cell
Blood
capillary
Bile
duct
Delta cell
F cell
Pancreatic
ducts
Tail of
pancreas
Pancreatic
acinus
Alpha cell
Beta cell
Duodenal
papilla
Delta cell
F cell
Duodenum
of small
intestine
Head of
pancreas
Pancreatic islet
Diaphragm
Celiac trunk
Inferior
vena cava
Spleen
Liver (cut)
Pancreatic
acini
Body of
pancreas
Gallbladder
Head of
pancreas
LM 150x
Duodenum
Figure 20.14
(a)
Abdominal
aorta
Left
kidney
Tail of
pancreas
(b)
a: © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Pancreas
• Both an exocrine (ducted gland) and endocrine
(ductless) gland
• About 98–99% of pancreatic cells are
pancreatic acini that produce alkaline
pancreatic secretions into ducts
• The remaining 1–2% of cells are small clusters
of endocrine cells called pancreatic islets
(islets of Langerhans)
• The hormones of the islet cells closely regulate
the level of blood glucose
Pancreatic Islets
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Inferior
vena cava
Pancreatic islet cells
Abdominal
aorta
Spleen
Alpha cell
Body of
pancreas
Beta cell
Blood
capillary
Bile
duct
Delta cell
F cell
Pancreatic
ducts
Tail of
pancreas
Pancreatic
acinus
Alpha cell
Beta cell
Duodenal
papilla
Delta cell
F cell
Duodenum
of small
intestine
Head of
pancreas
Pancreatic islet
Diaphragm
Celiac trunk
Inferior
vena cava
Spleen
Liver (cut)
Pancreatic
acini
Body of
pancreas
Gallbladder
Head of
pancreas
LM 150x
Duodenum
Figure 20.14
(a)
Abdominal
aorta
Left
kidney
Tail of
pancreas
(b)
a: © The McGraw-Hill Companies, Inc./Photo and Dissection by Christine Eckel; b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Pancreatic Islets
Comprised of four different types of
endocrine cells, each secreting a different
hormone:
1. Alpha cells—secrete glucagon
2. Beta cells—secrete insulin
3. Delta cells—secrete somatostatin
4. F cells—secrete pancreatic polypeptide
Pancreatic Hormones
Pineal Gland
• Secretes melatonin, which is involved in
maintaining the 24-hour circadian cycle
and sexual maturation
• It is located in the posterior region of the
epithalamus
Pineal Gland and Thymus
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Hypothalamus
Antidiuretic hormone (ADH)
Oxytocin (OT)
Regulatory hormones
Pituitary gland
Anterior pituitary secretes:
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Growth hormone (GH)
Luteinizing hormone (LH)
Melanocyte-stimulating hormone (MSH)
Prolactin (PRL)
Thyroid-stimulating hormone (TSH)
Posterior pituitary releases:
Antidiuretic hormone (ADH)
Oxytocin (OT)
Pineal gland
Melatonin
Parathyroid glands
(located on posterior surface
of thyroid)
Parathyroid hormone (PTH)
Thyroid gland
Calcitonin (CT)
Thyroid hormone (TH)
Thymus
Thymopoietin
Thymosins
Heart
Atriopeptin
Adrenal glands
Cortex:
Corticosteroids
Medulla:
Epinephrine (E)
Norepinephrine (NE)
Gastrointestinal (GI) tract
Cholecystokinin (CCK)
Gastric inhibitory peptide (GIP)
Gastrin
Secretin
Vasoactive intestinal peptide (VIP)
Kidney
Calcitriol
Erythropoietin (EPO)
Pancreatic islets
Glucagon
Insulin
Somatostatin
Pancreatic polypeptide
Testes (male)
Androgens
Inhibin
Ovaries (female)
Estrogen
Inhibin
Progesterone
Figure 20.1
Thymus
• Located just superior to the heart and just
deep to the sternum
• Larger in infants and children than in
adults
• Functions in association with the lymphatic
system to regulate and maintain body
immunity
Other Organs with Endocrine
Functions
Pituitary Gland Development
Figure 20.15
Thyroid Gland Development
Figure 20.16