Chapter 45
HORMONES AND
THE
ENDOCRINE SYSTEM
How do hormones work and
how are they controlled?
ENDOCRINE PART 1
Overview: The Body’s Long-Distance Regulators
 Animal hormones are chemical signals that are
secreted into the circulatory system and
communicate regulatory messages within the body
 Hormones reach all parts of the body, but only
target cells are equipped to respond
Concept 45.1: The endocrine system and the nervous system act
individually and together in regulating an animal’s physiology
 Animals have two systems of internal
communication and regulation: the nervous
system and the endocrine system
 The nervous system conveys high-speed electrical
signals along specialized cells called neurons
 The endocrine system secretes hormones that
coordinate slower but longer-acting responses
Overlap Between Endocrine and Nervous Regulation
 The endocrine and nervous systems function
together in maintaining homeostasis,
development, and reproduction.
 Specialized nerve cells known as neurosecretory
cells release neurohormones into the blood
 Both endocrine hormones and neurohormones
function as long-distance regulators of many
physiological processes
Control Pathways and Feedback Loops
 There are three types of hormonal control
pathways: simple endocrine, simple
neurohormone, and simple neuroendocrine
 A common feature is a feedback loop connecting the
response to the initial stimulus
 Negative feedback regulates many hormonal
pathways involved in homeostasis
LE 45-2a
Example
Pathway
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell
Blood
vessel
Target
effectors
Response
Liver
Glycogen
breakdown,
glucose release
into blood
Simple endocrine pathway
LE 45-2b
Pathway
Example
Stimulus
Suckling
Sensory
neuron
Hypothalamus/
posterior pituitary
Neurosecretory
cell
Posterior pituitary
secretes oxytocin
Blood ( )
vessel
Target
effectors
Response
Smooth muscle
in breast
Milk release
Simple neurohormone pathway
LE 45-2c
Example
Pathway
Hypothalamic
neurohormone
released in
Sensory response to
neural and
neuron
hormonal
signals
Hypothalamus
Stimulus
Neurosecretory
cell
Hypothalamus
secretes prolactinBlood releasing
vessel hormone ( )
Endocrine
cell
Blood
vessel
Anterior
pituitary
secretes
prolactin ( )
Target
effectors
Mammary glands
Response
Milk production
Simple neuroendocrine pathway
Concept 45.2: Hormones and other chemical signals bind to target cell
receptors, initiating pathways that culminate in specific cell responses
 Hormones convey information via the
bloodstream to target cells throughout the
body
 Three major classes of molecules function as
hormones in vertebrates:



Proteins and peptides
Amines derived from amino acids
Steroids
 Signaling by any of these hormones involves
three key events:



Reception
Signal transduction
Response
How do hormones act on target cells
 Lipid-based hormones (lipid-soluble)
 hydrophobic & lipid-soluble
diffuse across cell membrane & enter cells
 bind to receptor proteins in cytoplasm & nucleus
 bind to DNA as transcription factors
 turn on genes

 Protein-based hormones (water-soluble)
 hydrophilic & not lipid soluble
can’t diffuse across cell membrane
 bind to receptor proteins in cell membrane
 trigger secondary messenger pathway
 activate internal cellular response
 enzyme action, uptake or secretion of molecules…

Cell-Surface Receptors for Water-Soluble Hormones
 The receptors for most
water-soluble
hormones are
embedded in the
plasma membrane,
projecting outward
from the cell surface
 Binding of hormone
causes signal
transduction inside
the cell. (2nd
messengers)
SECRETORY
CELL
SECRETORY
CELL
Hormone
molecule
VIA
BLOOD
Signal receptor
Hormone
molecule
VIA
BLOOD
TARGET
CELL
Signal
transduction
pathway
OR
Cytoplasmic
response
TARGET
CELL
Signal
receptor
DNA
DNA
Nuclear
response
NUCLEUS
Signal
transduction mRNA
and response
NUCLEUS
Synthesis of
specific proteins
Receptor in plasma membrane Receptor in cell nucleus
Intracellular Receptors for Lipid-Soluble Hormones
 Steroids, thyroid hormones, and the
hormonal form of vitamin D enter target cells
and bind to protein receptors in the cytoplasm or
nucleus
 Protein-receptor complexes then act as
transcription factors in the nucleus, regulating
transcription of specific genes.
 The hormone epinephrine has multiple effects in
mediating the body’s response to short-term stress
different cell responses
Different receptors
Epinephrine
Epinephrine
Epinephrine
a receptor
 receptor
 receptor
Glycogen
deposits
Vessel
constricts
Intestinal blood
vessel
Vessel
dilates
Skeletal muscle
blood vessel
Different intracellular proteins
Glycogen
breaks down
and glucose
is released
from cell
Liver cell
different cell responses
Concept 45.3: The hypothalamus and pituitary integrate
many functions of the vertebrate endocrine system
 The hypothalamus and the pituitary gland
control much of the endocrine system
LE 45-6
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Ovary
(female)
Testis
(male)
Ovaries (female)
Relation Between the Hypothalamus and Pituitary Gland
• The hypothalamus, a region of the lower brain,
contains neurosecretory cells
• The posterior pituitary, or neurohypophysis, is
an extension of the hypothalamus
• Hormonal secretions from neurosecretory cells are
stored in or regulate the pituitary gland
LE 45-7
Hypothalamus
Neurosecretory
cells of the
hypothalamus
Axon
Posterior
pituitary
Anterior
pituitary
HORMONE
TARGET
ADH
Kidney tubules
Oxytocin
Mammary glands,
uterine muscles
 Other hypothalamic cells produce tropic
hormones, hormones that regulate endocrine
organs
 Tropic hormones are secreted into the blood and
transported to the anterior pituitary
 The tropic hormones of the hypothalamus
control release of hormones from the
anterior pituitary.
LE 45-8
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Neurosecretory cells
of the hypothalamus
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Portal vessels
Nontropic and Tropic Effects
Growth hormone
Hypothalamic
releasing
hormones
(red dots)
Endocrine cells of the
anterior pituitary
Pituitary hormones
(blue dots)
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH
Endorphin
TARGET
Testes or
ovaries
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Pain receptors
in the brain
Growth hormone
Liver
Bones
Posterior Pituitary Hormones
 The two hormones released from the posterior
pituitary act directly on nonendocrine tissues
(nontropic hormones)
 Oxytocin induces uterine contractions and milk
ejection
 Antidiuretic hormone (ADH) enhances water
reabsorption in the kidneys
Anterior Pituitary Hormones
 The anterior pituitary produces both tropic and
nontropic hormones
Tropic Hormones
 The four strictly tropic hormones are
 Follicle-stimulating hormone (FSH)  stimulates sex organs
 Luteinizing hormone (LH)  stimulates sex organs
 Thyroid-stimulating hormone (TSH)  stimulates thyroid
 Adrenocorticotropic hormone (ACTH)  stimulates adrenal
gland
• Each tropic hormone acts on its target endocrine
tissue to stimulate release of another hormone(s)
with direct metabolic or developmental effects.
Nontropic Hormones
 Nontropic hormones produced by the
anterior pituitary:



Prolactin
Melanocyte-stimulating hormone (MSH)
-endorphin
Growth Hormone
 Growth hormone (GH) has tropic and nontropic
actions
 It promotes growth directly and has diverse
metabolic effects
 It stimulates production of growth factors
How do specific hormones
work?
ENDOCRINE SYSTEM PART 2
Parathyroid Hormone and Calcitonin: Control of Blood
Calcium
 Two antagonistic hormones, parathyroid
hormone (PTH) and calcitonin, play the major
role in calcium (Ca2+) homeostasis in mammals
LE 45-11
Thyroid gland
releases
calcitonin.
Calcitonin
Reduces
Ca2+ uptake
in kidneys
Stimulates
Ca2+ deposition
in bones
STIMULUS:
Rising blood
Ca2+ level
Blood Ca2+
level declines
to set point
Homoeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
STIMULUS:
Falling blood
Ca2+ level
Blood Ca2+
level rises
to set point
Parathyroid
Stimulates
2+
Ca release gland
from bones
PTH
Increases
Ca2+ uptake
in intestines
Active
vitamin D
Stimulates Ca2+
uptake in kidneys
Insulin and Glucagon: Control of Blood Glucose
 The pancreas secretes insulin and glucagon,
antagonistic hormones that help maintain glucose
homeostasis
 Glucagon is produced by alpha cells
 Insulin is produced by beta cells
LE 45-12
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydraterich meal)
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
Liver breaks
down glycogen
and releases
glucose into the
blood.
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Alpha cells of pancreas
release glucagon into
the blood.
Glucagon
Target Tissues for Insulin and Glucagon
 Insulin reduces blood glucose levels by
 Promoting the cellular uptake of glucose
 Slowing glycogen breakdown in the liver
 Promoting fat storage
 Glucagon increases blood glucose levels by
 Stimulating conversion of glycogen to glucose in the liver
 Stimulating breakdown of fat and protein into glucose
Diabetes Mellitus
 Diabetes mellitus is perhaps the best-known
endocrine disorder
 It is caused by a deficiency of insulin or a decreased
response to insulin in target tissues
 It is marked by elevated blood glucose levels
 Type I diabetes mellitus (insulin-dependent) is
an autoimmune disorder in which the immune
system destroys pancreatic beta cells
 Type II diabetes mellitus (non-insulindependent) involves insulin deficiency or reduced
response of target cells due to change in insulin
receptors (hence why it is age-onset!)
Adrenal Hormones: Response to Stress
 The adrenal glands are adjacent to the kidneys
 Each adrenal gland actually consists of two glands:
the adrenal medulla and adrenal cortex
Catecholamines from the Adrenal Medulla
 The adrenal medulla secretes epinephrine
(adrenaline) and norepinephrine (noradrenaline)
 These hormones are members of a class of
compounds called catecholamines
 They are secreted in response to stress-activated
impulses from the nervous system
 They mediate various fight-or-flight
responses
Stress Hormones from the Adrenal Cortex
 Hormones from the adrenal cortex also
function in response to stress
 They fall into three classes of steroid hormones:
 Glucocorticoids, such as cortisol, influence glucose
metabolism and the immune system


Mineralocorticoids, such as aldosterone, affect salt and
water balance
Sex hormones are produced in small amounts
LE 45-13
Stress
Nerve
Spinal cord signals
(cross
section)
Hypothalamus
Releasing
hormone
Nerve
cell
Anterior pituitary
Blood vessel
Nerve cell
ACTH
ACTH
Adrenal
gland
Kidney
Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose;
increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to
increased alertness and decreased
digestive and kidney activity
Long-term stress response
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium 1. Proteins and fats
broken down and
ions and water by
converted to glucose,
kidneys
leading to increased
2. Increased blood
blood glucose
volume and blood
pressure
2. Immune system may
be suppressed
Gonadal Sex Hormones
 The gonads, testes and ovaries, produce most of the
sex hormones: androgens, estrogens, and
progestins.
 The testes primarily synthesize androgens, mainly
testosterone, which stimulate development and
maintenance of the male reproductive system
 Testosterone causes increase in muscle and bone
mass and is often taken as a supplement to cause
muscle growth, which carries health risks.
 Estrogens, most importantly estradiol, are
responsible for maintenance of the female
reproductive system and the development of female
secondary sex characteristics
 In mammals, progestins, which include
progesterone, are primarily involved in preparing
and maintaining the uterus
Melatonin and Biorhythms
 The pineal gland, located in the brain, secretes
melatonin