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Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 31
Endocrine Control
© Learning
Cengage
© Cengage
2015 Learning
2015
31.1 What Are Animal Hormones?
• Animal hormones: intercellular
communication molecules that are
secreted by endocrine cells
– Distributed by the blood; typically act at a
distant site from their source
• Only cells with the appropriate receptors
(target cells) can respond to a specific
hormone
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Categories of Hormones
• Two major categories of hormones:
– Cholesterol-derived hormones
– Amino acid-derived hormones
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Categories of Hormones (cont’d.)
• Amino acid-derived hormones: bind to
receptors at the plasma membrane of a
target cell
– Initiates second messenger signaling cascade
that brings about the target cell’s response
– Often results in the activation of an enzyme
– Example: glucagon binds to receptor; causes
activation of glycogen-degrading enzyme
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Categories of
Hormones (cont’d.)
1
hormone receptor
in plasma membrane
second
messenger
2
3
4
Altered
transcription
pattern
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Categories of Hormones (cont’d.)
• Steroid hormones: synthesized from
cholesterol
– Directly affects gene expression
– Diffuses into a target cell and forms a
hormone–receptor complex
• Hormone–receptor complex: transcription factor
that binds to a promoter in the target cell’s DNA
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Categories of
Hormones (cont’d.)
1
2
3
receptor
5
4
hormone–
receptor
complex
gene
product
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Hormone Receptor Function
• Many hormones target more than one type
of cell
– Elicit a different response in each cell type
– Example: antidiuretic hormone (ADH)
• Affects urine formation in the kidneys
• Triggers smooth muscle contraction in blood
vessels
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31.2 What Are the Components of the
Human Endocrine System?
• Endocrine glands: aggregations of
epithelial cells that produce and secrete
hormones into the blood
– Collectively make up the endocrine system
• Portions of the endocrine system and
nervous system are closely linked
– Most organs respond to hormones and
signals from the nervous system
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3D ANIMATION: Endocrine System
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What Are the
Components of the
Human Endocrine
System? (cont’d.)
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31.3 How Does the Hypothalamus Interact
With the Pituitary Gland?
• Hypothalamus: main center that controls
the internal environment
– Lies deep inside the forebrain and connects
with the pituitary gland
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How Does the Hypothalamus Interact With
the Pituitary Gland? (cont’d.)
hypothalamus
anterior
lobe of
pituitary
posterior
lobe of
pituitary
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Posterior Pituitary Function
• Neurosecretory cells in the hypothalamus
synthesize peptide hormones
– These hormones are transported along axons
in the posterior pituitary
– An action potential triggers the release of
hormone into the blood
– Posterior pituitary releases two hormones:
• Antidiuretic hormone (ADH)
• Oxytocin
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ANIMATION: Anterior pituitary function
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Anterior Pituitary Function
• The anterior pituitary makes peptide
hormones and secretes them in response
to hormones from the hypothalamus
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Anterior Pituitary Function (cont’d.)
• Anterior pituitary hormones:
– Adrenocorticotropic hormone (ACTH)
– Thyroid-stimulating hormone (TSH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
– Prolactin
– Growth hormone (GH)
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Hormonal Growth Disorders
• Growth hormone production surges during
teenage years, causing a growth spurt,
then declines with age
• Oversecretion of growth hormone during
childhood leads to pituitary gigantism
• Too little growth hormone during childhood
can cause pituitary dwarfism
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Hormonal Growth Disorders (cont’d.)
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31.4 What Is the Role of the Pineal Gland?
• Pineal gland: lies deep inside the brain;
secretes the hormone melatonin under
low-light or dark conditions
– Melatonin: helps regulate human sleep–wake
cycles
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31.5 What Are the Thyroid and Parathyroid
Glands?
• Thyroid gland: endocrine gland located in
the base of the neck
– Thyroid hormone (triiodothyronine and
thyroxine): increases metabolic activity
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What Are the Thyroid and Parathyroid
Glands? (cont’d.)
• The anterior pituitary gland and
hypothalamus regulate thyroid hormone
secretion
– Decline in thyroid hormone causes
hypothalamus to secrete thyroid-releasing
hormone (TRH)
– TRH causes the anterior pituitary to secrete
thyroid-stimulating hormone (TSH)
– TSH stimulates secretion of thyroid hormone
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What Are the Thyroid and Parathyroid Glands? (cont’d.)
STIMULUS
TH declines
below a set
point
RESPONSE
Hypothalamus
1
TRH
4
Anterior Pituitary
2
TSH
Thyroid Gland
3
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TH secretion increases
and metabolic rate rises.
Hormonal Regulation of Blood Calcium
Level
• There are four parathyroid glands on the
thyroid’s posterior surface
– Parathyroid hormone (PTH): regulates the
concentration of calcium ions in the blood
– Calcitonin: thyroid hormone that encourages
bones to take up and incorporate calcium;
opposes the actions of PTH
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31.6 What Are the Roles of the Adrenal
Glands?
• Adrenal gland: endocrine gland that is
located atop the kidney
– Adrenal cortex: releases steroid hormones
– Examples:
• Aldosterone: acts in kidneys and makes urine
more concentrated
• Cortisol: affects metabolism and immune
responses
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What Are the Roles of the Adrenal Glands? (cont’d.)
STIMULUS
Blood level
of cortisol
declines.
adrenal
cortex
adrenal
medulla
RESPONSE
Hypothalamus
1
CRH
4
Anterior Pituitary
2 ACTH
Rise of cortisol level
in the blood inhibits
the secretion of CRH
and ACTH.
Adrenal Cortex
3
Cortisol secretion
increases and has the
following effects:
Cellular uptake of glucose from blood slows in many tissues,
especially muscles (but not in the brain). Protein breakdown
accelerates, especially in muscles.
Some of the amino acids freed by this process get converted
to glucose.
© Cengage Learning 2015
kidney
Fats in adipose tissue are degraded to fatty acids and enter
blood as an alternative energy source, indirectly adrenal
cortex adrenal medulla kidney conserving glucose for the brain.
What Are the Roles of the Adrenal Glands?
(cont’d.)
• Adrenal medulla: responds to stimulation
by releasing norepinephrine and
epinephrine into the blood
– Brings on a fight–flight response
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Hormones, Stress, and Health
• Long-term elevation of cortisol is
unhealthy (example: Cushing’s syndrome):
– Interferes with immunity, memory, and sexual
function
– Raises the risk of cardiovascular problems
• Abnormally low levels of cortisol (example:
Addison’s disease)
– Fatigue, depression, weight loss, and
darkening of the skin
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31.7 What Are Sex Hormones?
• Sex hormones: steroid hormones
produced by the gonads
– Essential to reproductive function
– Influence secondary sexual characteristics
• Traits that differ between the sexes, but do not
function directly in reproduction
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What Are Sex Hormones? (cont’d.)
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What Are Sex Hormones? (cont’d.)
• Testosterone: responsible for development
of male sex organs and secondary sexual
characteristics
• Estrogens: function in reproduction and
cause development of female secondary
sexual characteristics
• Progesterone: prepares a female body for
pregnancy and helps maintain a
pregnancy
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What Are Sex Hormones? (cont’d.)
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31.8 How Does the Pancreas Regulate
Blood Sugar?
• Pancreas: lies in the abdominal cavity,
behind the stomach
– Exocrine cells: secrete digestive enzymes into
the small intestine
– Endocrine cells: grouped in clusters called
pancreatic islets (e.g., beta cells and alpha
cells)
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How Does the Pancreas Regulate Blood
Sugar? (cont’d.)
• Beta cells secrete insulin when blood
glucose levels rise
– Insulin causes its target cells to take up and
store glucose
– Encourages synthesis of fats and proteins
and inhibits their breakdown
– Lowers blood glucose levels
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How Does the Pancreas Regulate Blood
Sugar? (cont’d.)
• Alpha cells secrete glucagon when blood
glucose levels fall
– Glucagon binds to receptors on liver cells:
activates enzymes that break glycogen into
glucose subunits
– Raises the level of glucose in blood
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ANIMATION: Hormones and glucose
metabolism
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How Does the Pancreas Regulate Blood
Sugar? (cont’d.)
• The regulation of blood glucose is
disrupted in diabetes mellitus
• Type 1 diabetes: autoimmune response
destroys insulin-secreting beta cells
– Symptoms usually appear in childhood and
adolescence
• Type 2 diabetes: target cells do not
respond to insulin
– Symptoms typically start in middle age
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How Does the Pancreas Regulate Blood
Sugar? (cont’d.)
© Cengage Learning 2015
31.9 Do Invertebrates Have Hormones?
• Some components of the endocrine
system occur in invertebrates
– Example: roundworms, annelids, and
mollusks make steroid hormones
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Do Invertebrates Have Hormones?
(cont’d.)
• Invertebrates do not have the same glands
as vertebrates do, but they produce the
homologous hormones in other glands
– Example: octopuses produce estrogens,
progesterone, and cortisol in a gland near
their eye
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Do Invertebrates Have Hormones?
(cont’d.)
• Hormone-signaling systems unique to
invertebrates have also evolved
– Example: a hormone unique to arthropods
called ecdysone controls molting (periodic
shedding of the exoskeleton)
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Do Invertebrates Have Hormones?
(cont’d.)
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31.10 Application: Endocrine Disrupters
• Endocrine disrupters:
– DDT (a pesticide)
– PCBs (used to make electronic products,
caulking, and solvents)
– Phthalates (found in plastics and scented
products) – these chemicals are still in wide
use
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Application: Endocrine Disrupters (cont’d.)
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