CHAPTER 46
LECTURE
SLIDES
To run the animations you must be in
Slideshow View. Use the buttons on the
animation to play, pause, and turn audio/text
on or off. Please note: once you have used
any of the animation functions (such as Play or
Pause), you must first click in the white
background before you advance the next slide.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Endocrine System
Chapter 46
Types of Chemical Messengers
• Hormone
– Regulatory chemical that is secreted into
extracellular fluid and carried by the blood
– Can act at a distance from source
• Endocrine system
– Organs and tissues that produce hormones
• Only targets with receptor can respond
3
Types of Chemical Messengers
• Paracrine regulators do not travel in blood
– Allow cells of organ to regulate each other
• Pheromones are chemicals released into
the environment to communicate among
individuals of a single species
– Not involved in normal metabolic regulation
within an animal
4
Types of Chemical Messengers
• Some neurotransmitters are distributed by
the blood and act as a hormone
– Norepinephrine coordinates the activity of
heart, liver, and blood vessels during stress
• Neurons can also secrete a class of
hormones called neurohormones that are
carried by blood
– Antidiuretic hormone is secreted by neurons
of the brain
5
6
Endocrine System
• The endocrine system includes all the
organs that secrete hormones
– Endocrine – product secreted into
extracellular fluid and carried in blood
– Exocrine – secrete product into a duct
• 2 basic hormone characteristics
1. Must be sufficiently complex to convey
regulatory information to their target cells
2. Must be adequately stable to resist
destruction before reaching their target cells 7
8
3 Classes of Hormones
1. Peptides and proteins
– Glycoproteins
2. Amino acid derivatives
– Catecholamines
– Thyroid hormones
– Melatonin
3. Steroids
– Sex steroids
– Corticosteroids
9
Classes of Hormones
• Hormones may be categorized as:
• Lipophilic (nonpolar) – fat-soluble
–
–
–
–
Steroid hormones and thyroid hormones
Travel on transport proteins in blood
Bind to intracellular receptors
Tend to act over brief time period
• Hydrophilic (polar) – water-soluble
–
–
–
–
All other hormones
Freely soluble in blood
Bind to extracellular receptors
Tend to have much longer active period
10
11
Paracrine Regulators
• Paracrine regulation occurs in most organs
• Growth factors
– Proteins that promote growth and cell division in specific organs
• Epidermal growth factor
– Activates mitosis in skin
• Nerve growth factor
– Stimulates growth and survival of neurons
• Insulin-like growth factor
– Stimulates cell division in developing bone
• Cytokines
– Specialize in control of cell division and differentiation in immune
system
12
Paracrine Regulators
• Paracrine regulation of blood vessels
• Nitric oxide (NO)
– Function as neurotransmitter
– Produced by endothelium of blood vessels
• Dilates arteries to control blood pressure
• Endothelin stimulates vasoconstriction
• Bradykinin promotes vasodilation
• Paracrine regulation supplements
autonomic nervous system
13
Paracrine Regulators
• Prostaglandins
– Diverse group of fatty acids that are produced
in almost every organ
– Regulate a variety of functions
• Smooth muscle contraction, lung function, labor,
and inflammation
– Synthesis is inhibited by nonsteroidal antiinflammatory drugs (NSAIDs) such as aspirin
and ibuprofen
14
Lipophilic Hormones
• Lipophilic hormones include the steroid
hormones and the thyroid hormones
• Also retinoids, or vitamin A
• Can enter cells through plasma membrane
15
Lipophilic Hormones
• Circulate in the blood bound to transport
proteins
• Dissociate from carrier at target cells
• Pass through the cell membrane
• Bind to an intracellular receptor, either in
the cytoplasm or the nucleus
• Hormone-receptor complex binds to
hormone response elements in DNA
• Regulate gene expression
16
17
Hydrophilic Hormones
• Peptide, protein, glycoprotein, and
catecholamine hormones
• Too large or polar to cross cell membrane
• Bind to receptors on plasma membrane
• Initiate signal transduction pathways
• Activation of protein kinases
– Activate or deactivate intracellular proteins by
phosphorylation
• Production of second messengers
18
19
Hydrophilic Hormones
• Receptor kinases
– For some peptide hormones (like insulin) the
receptor itself is a kinase
• Can directly phosphorylate intracellular proteins
that alter cellular activity
– For other peptide hormones (like growth
hormone) the receptor itself is not a kinase
• Rather, it activates intracellular kinases
20
Hydrophilic Hormones
• Second-messenger systems
– Many hydrophilic hormones work through
second messenger systems
– Two have been described
• One involving cyclic adenosine monophosphate
(cAMP)
• One that generates 2 lipid messengers: inositol
triphosphate (IP3) and diacyl glycerol (DAG)
21
Hydrophilic Hormones
• Second-messenger systems
– Receptors are linked to a second-messengergenerating enzyme via membrane proteins called G
proteins
• G protein–coupled receptors (GPCR)
– When the G protein activates the enzyme, the
second-messenger molecules increase
• Cellular response depends on the type of G
protein activated
– Some activate while others inhibit their secondmessenger-generating system
– Single hormone can have distinct actions in 2
different cells
22
The Pituitary Gland
• Also known as the hypophysis
• Hangs by a stalk from the hypothalamus
• Consists of two parts
– Anterior pituitary (adenohypophysis)
• Appears glandular
– Posterior pituitary (neurohypophysis)
• Appears fibrous
– Different embryonic origins
– Different hormones
23
The Posterior Pituitary
• Appears fibrous because it contains axons
that originate in cell bodies within the
hypothalamus and that extend along the
stalk of the pituitary as a tract of fibers
– Develops from outgrowth of the brain
• Stores and releases two hormones
– Both are actually produced by neuron cell
bodies in the hypothalamus
– Neuroendocrine reflex
24
The Posterior Pituitary
• Antidiuretic hormone (ADH)
– Peptide hormone that stimulates water
reabsorption by the kidney, and thus inhibits
diuresis (urine production)
• Oxytocin
– Like ADH, composed of 9 amino acids
– In mammals, it stimulates the milk ejection
reflex and uterine contractions during labor,
and it regulates reproductive behavior
25
26
The Anterior Pituitary
• Develops from a pouch of epithelial tissue
of the embryo’s mouth
– Not part of the nervous system
• Produces at least 7 essential hormones
• Tropic hormones or tropins
– Act on other endocrine glands
• Can be categorized into three families
– Peptide hormones, protein hormones, and
glycoprotein hormones
27
The Anterior Pituitary
• Peptide hormones
– Cleaved from a single precursor protein
• Fewer than 40 amino acids in size
– Adrenocorticotropic hormone (ACTH)
– Melanocyte-stimulating hormone (MSH)
• Protein hormones
– A single chain of about 200 amino acids
– Growth hormone (GH)
– Prolactin (PRL)
28
The Anterior Pituitary
• Glycoprotein hormones
– Dimers, containing alpha (a) and beta (b)
subunits, each around 100 amino acids
– Thyroid-stimulating hormone (TSH)
– Luteinizing hormone (LH)
– Follicle-stimulating hormone (FSH)
– FSH and LH
• Function in both men and women
• Referred to as gonadotropins
29
The Anterior Pituitary
• Anterior pituitary is controlled by hormones from
hypothalamus
• Neurons secrete releasing hormones and
inhibiting hormones, which diffuse into blood
capillaries at the hypothalamus’ base
• Each hormone delivered by the
hypothalamohypophyseal portal system
regulates a specific anterior pituitary hormone
– Portal system has 2 capillary beds (not 1)
30
31
The Anterior Pituitary
• The hypothalamus and the anterior
pituitary are partially controlled by the very
hormones whose secretion they stimulate
• Negative feedback or feedback inhibition
– Acts to maintain relatively constant levels of
the target cell hormone
• Positive feedback not as common
– Causes deviations from homeostasis
– Control of ovulation
32
Goiters are
caused by a
lack of iodine
in the diet
33
The Anterior Pituitary
• Pituitary gland was referred to as the
“master gland”
– Hypophysectomy caused a number of deficits
• Effects may be direct or indirect
– Direct: activation of nonendocrine targets
• Growth hormone, prolactin, and MSH
– Indirect: activation of other endocrine glands
• Tropic hormones ACTH, TSH, LH, and FSH
34
Anterior Pituitary Disorders
• Growth Hormone
– Stimulates protein synthesis and growth of
muscles and connective tissues
– Stimulates production of insulin-like growth
factors that stimulate cell division in
epiphyseal growth plates – elongation of bone
• Gigantism vs pituitary dwarfism
– Also functions in adults to regulate protein,
lipid, and carbohydrate metabolism
• Acromegaly
35
Other anterior pituitary hormones
• Prolactin
– Acts on glands that are not endocrine glands
– Actions appear diverse
• Milk production in mammals, “crop milk” and brood patch in
birds, electrolyte balance in kidneys
•
•
•
•
TSH stimulates thyroid
ACTH stimulates only adrenal cortex
FSH and LH act only on the gonads
MSH regulates melanophores or melanocytes
that contain melanin
36
The Thyroid Gland
• In humans, the thyroid gland is shaped like
a bow tie, and lies just below the Adam’s
apple in the front of the neck
• Secretes
– Thyroid hormones
• Thyroxine
• Triiodothyronine
– Calcitonin
37
The Thyroid Gland
• Thyroid hormones bind to nuclear
receptors
• Regulates enzymes controlling
carbohydrate and lipid metabolism
– Hypothyroidism vs hyperthyroidism in adults
• Often functions synergistically with other
hormones
• Trigger metamorphosis in tadpoles
38
39
The Thyroid Gland
• Calcitonin
– Peptide hormone
– Stimulates the uptake of calcium (Ca2+) into
bones – lowering blood Ca2+ levels
– Appears less important in the day-to-day
regulation of Ca2+ levels in adult humans
40
The Parathyroid Glands
•
•
•
•
4 small glands attached to the thyroid
Produce parathyroid hormone (PTH)
Raises blood Ca2+ levels
Stimulates osteoclasts to dissolve calcium
phosphate crystals in the bone matrix and
release Ca2+ into blood
• Stimulates the kidneys to reabsorb Ca2+ from the
urine
• Vitamin D activated by a PTH controlled enzyme
– Stimulates the intestinal absorption of Ca2+
41
42
The Adrenal Glands
• Medulla (inner portion)
– Stimulated by the sympathetic division of the
autonomic nervous system
– Secretes the catecholamines epinephrine and
norepinephrine
• Cortex (outer portion)
– Stimulated by anterior pituitary hormone ACTH
– Corticosteroids
• Glucocorticoids (like cortisol) act on various cells to maintain
glucose homeostasis
• Aldosterone (mineralocorticoid) helps regulate mineral
balance
43
44
The Pancreas
• Exocrine and endocrine gland
• Connected to the duodenum of the small
intestine by the pancreatic duct
• Islets of Langerhans are scattered clusters
of cells throughout the pancreas
• These govern blood glucose levels
through two hormones with antagonistic
functions
45
The Pancreas
• Insulin
– Secreted by beta (b) cells of the islets
– Stimulates cellular uptake of blood glucose
and its storage as glycogen in the liver and
muscle cells, or as fat in fat cells
• Glucagon
– Secreted by alpha (a) cells of the islets
– Promotes the hydrolysis of glycogen in the
liver and fat in adipose tissue
46
47
Diabetes Mellitus
• Diabetics cannot take up glucose from
blood
• Type I (insulin-dependent diabetes)
– Individuals lack insulin-secreting b cells
– Treated by daily injections of insulin
• Type II (noninsulin-dependent diabetes)
– Most patients have this form
– Very low number of insulin receptors
– Treated by diet and exercise
48
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
49
The Gonads
• Ovaries and testes in vertebrates
• Produce sex steroids that regulate
reproductive development
• Estrogen and progesterone
– “Female” hormones
• Androgens
– “Male” hormones
– Testosterone and its derivatives
50
The Pineal Gland
• Located in the roof of the third ventricle of
the brain
• Secretes hormone melatonin
• Functions of melatonin
– Reduces dispersal of melanin granules
– Synchronizes various body processes to a
circadian rhythm
• Secretion of melatonin activated in the dark
51
Other Hormones
• Some hormones are secreted by organs
that are not exclusively endocrine glands
• Atrial natriuretic hormone is secreted by
the right atrium of the heart
– Promotes salt and water excretion
• Erythropoietin is secreted by the kidney
– Stimulates the bone marrow to produce red
blood cells
52
Insect Hormones
• Insects undergo two types of
transformations during postembryonic development
• Molting
– Shedding of old exoskeleton and
secretion of a new larger one
• Metamorphosis
– Radical transformation from the
larval to the adult form
53
Insect Hormones
• Hormonal secretions influence both
molting and metamorphosis
• Brain hormone stimulates prothoracic
gland to produce ecdysone, or molting
hormone
– High levels cause molting
• Corpora allata produces juvenile hormone
– Low levels result in metamorphosis
54
55