• hormone
- ex: caterpillar butterfly
• specificity
• communication systems
1. endocrine system
2. nervous system
- coordination between the
aaatwo systems
• See table on next page!
• pheromones
- Ex: ant
- Ex: giant silk moth
• found in other organ systems
• endocrine glands
Chapter 45 Hormones & the Endocrine System
The Body’s Long-Distance Regulators
 Hormone- secreted chemicals that are formed in specialized cells, travel in body
fluids, & act on specific target cells in other parts of the body, changing the target
cells’ functioning; in animals, hormones are secreted into the extracellular fluid,
circulate in the hemolymph (blood), and communicate regulatory messages
throughout the body
 Ex: The ecdysteroid hormone stimulates the growth of adult cells, the programmed
death of larval cells, & behavior that bring about the pupal stage. Communication
of hormones regulates the timing of metamorphosis & ensure unison of the
development of different body parts
 Each hormone has specific receptors in the body. A hormone can reach all the cells
in a body, but only specific target cells can respond because they have matching
receptors for that hormone
 The body has 2 basic communication & regulation systems:
1. Endocrine system- functions in chemical signaling; hormones secreted by
endocrine cells regulate reproduction, development, energy metabolism, growth, &
behavior
2. Nervous system- network of specialized cells, neurons, that transmit signals along
specific pathways. These signals regulate neurons, muscle cells, & endocrine cells
 Because signaling by neurons can regulate the release of hormones, the nervous &
endocrine systems often overlap in function
45.1 Hormones & Other Signaling Molecules Bind to Target Receptors, Triggering
Specific Response Pathways
Intracellular Communication
 The ways in which signals are transmitted between animal cells are classified by:
the type of secreting cell & the route taken by the signal in reaching its target (see
table on next page)
Signaling by Pheromones
 Pheromones- chemicals that are released into the external environment that don’t
act within the body; define territory, warn predators, & attract mates
 Ex: a foraging ant marks its path back to the nest with a pheromone when it
discovers a new food source & guide colony when migrating to new location
 Ex: giant silk moth releases sex pheromone into the air by a female enables her to
attract males
Endocrine Tissues & Organs
 Some endocrine system cells are found in organs that are parts of other organ
systems
o Ex: in human digestive system, stomach contains isolated endocrine cells
 Other endocrine cells are grouped into endocrine glands, ductless organs (i.e.
thyroid & parathyroid glands of neck)
1
Type of
intracellular
communication
Endocrine
signaling
Route Taken
by secreted
molecules
Function
Example/
applications
Secreted
hormones reach
target cells via
hemolymph
(bloodstream)
Maintains
homeostasis
Mediates
responses to
environmental
stimuli
Regulates
growth &
development
Paracrine
Signaling
Local
regulators act
over short
distance &
locally
Secreted
molecules
trigger a
response in
neighboring
cells, target
cells near the
secreting cell
Hormones
coordinate
body’s
responses to
stress,
dehydration
Trigger
behavioral &
physical
changes of
sexual maturity
& reproduction
Cytokines are
local regulators
that enable
communication
between
immune cells
Autocrine
Signaling
Diffuse locally
Secreted
molecules
trigger a
response in
the cells that
secrete them.
Target cell is
secreting cell
Synaptic
Signaling
neurotransmitte
rs (molecules
secreted by
neurons, the
target cells)
diffuse a very
short distance
across synapses
(specialized
junctions) to
bind to
receptors on
the target cell
Neurosecretory
cells secrete
molecules that
diffuse from
nerve cell
endings into
the
bloodstream
Trigger
responses in
cells of target
tissues
(neurons,
muscles,
glands)
Neuroendocrine
signaling
Neurohormones
trigger
responses in
target cells
anywhere in
the body
Picture
Antidiuretic
hormone (ADH)
kidney function
& water balance
2
• endocrine vs exocrine
glands
- prefix & suffix


Endocrine glands secrete hormones directly into surrounding fluid
Exogrine glands have ducts that carry secreted substances onto body surfaces or
into cavities
 Endo/exo- secretion into/out of body fluids; crine- movement away from
secreting cell
Chemical Classes of Hormones
Chemical
Composition
Example
Solubility in aqueous &
Class
lipid-rich environments
Polypeptides Formed by cleavage
Insulin’s made Water soluble
(proteins &
of 1 long polypeptide up of 2
Insoluble in liquids; can’t
peptides)
chain
polypeptide
pass through plasma
chains
membranes, so bind to
amines
Synthesized from a
Epinephrine & cell-surface receptors that
relay info into the nucleus
single amino acid,
thyroxine
through intracellular
either tyrosine or
pathways
tryptophan
Steroids
Four fused carbon
Cortisol &
Lipid-soluble
rings
ecdysteroid
Can pass through
All derived from the
membranes readily
steroid cholesterol
Receptors reside in
cytoplasm or nucleus
Cellular Response Pathways
Lipid-Soluble hormones
Water Soluble Hormones
• diffuse out across membranes of endocrine
• secreted by exocytosis, travel freely in
bloodstream & bind to cell-surface signal cells where they bind to transport proteins that
keep them soluble in the aqueous environment of
receptors, inducing changes in
the bloodstream; when they leave bloodstream,
cytoplasmic molecules & may alter gene
they diffuse into target cells, bind to intracellular
transcription (synthesis of mRNA)
signal receptors, & trigger changes in gene
• its binding to a signal receptor protein
transcription
triggers events at the plasma membrane
• Perform entire task of transducing a signal
that result in cellular response (i.e.
within target cell
• Hormone activates receptor, which directly
activation of enzyme, change in uptake/
triggers cell’s response, resulting in change in
secretion of specific molecules,
gene expression
rearrangement of cytoskeleton, make
proteins in cytoplasm move into nucleus • Steroid hormone receptors are located in
cytosol prior to binding to hormone. When it
& alter transcription of some genes).
binds to cytosolic receptor, a hormone-receptor
Signal transduction- series of changes in complex forms, which moves into the nucleus.
cellular proteins that converts the
There, the receptor portion of the complex alters
extracellular chemical signal to a specific transcription of specific genes by interacting
intracellular response
with specific DNA-binding protein.
• Ex: Response to short-term stress:
• Ex: estradiol (form of estrogen in female birds
adrenal glands secrete epinephrine. When & frogs), has a specific receptor in liver cells.
Binding of it to this receptor activates
it reaches liver, it binds to a G protein
coupled receptor in the plasma membrane transcription of the gene for protein vitellogenin,
which is secreted & transported in the blood to
of target cells, triggering a cascade of
the reproductive system after mRNA is
events involving the synthesis of cAMP
translated.
as a short-lived second messenger, which • Nonsteroid lipid-soluble hormones (i.e.
activates protein Kinase A, which leads to thyroxine & vitamin D) have receptors located in
activation of an enzyme required for
the nucleus that bind hormone molecules that
glycogen breakdown & inactivation of an diffuse from the bloodstream across the plasma
enzyme necessary for glycogen synthesis. membrane & nuclear envelope. Once bound by a
This results in the liver releasing glucose hormone, the receptor binds to specific sites in
the cell’s DNA & stimulates transcription of
into the bloodstream, providing fuel
specific gene
3
• one hormone, multiple
effects
- ex: epinephrine
• lipid soluble hormones
- ex: estrogen
Multiple Effects of Hormones
 Many hormones elicit more than 1 type of response. The effects can vary if
target cells differ in the molecules that receive or produce the response to that
hormone
 Ex: epinephrine in mediating body’s response to short-term stress (column 2)
 Tissue vary in response to epinephrine because they vary in their receptors or in
their signal transduction pathways. Target cell recognition of epinephrine
involves G protein-coupled receptors (column 3)
Target
What epinephrine
Signal transduction / recognition
cell type
triggers
Liver
Glycogen breakdown
Liver cells have ϐ-type epinephrine
receptor that activates enzyme protein
kinase A, which regulates glycogen
metabolism
Skeletal
Increased blood flow
In blood vessels supplying skeletal muscle,
muscles
that same kinase A activated by the same
epinephrine receptor (as liver) inactivates
muscle-specific enzyme, resulting in
smooth muscle relaxation & increased
blood flow
Digestive Decreased blood flow
Intestinal blood vessels have an α-type
tract
epinephrine receptor, which triggers a
distinct signaling pathway involving a
different G protein & different enzymes,
resulting in smooth muscle contraction &
restricted blood flow to intestines

Lipid-soluble hormones exert different effects on different target cells too
o Ex: estrogen that stimulates a bird’s liver to synthesize yolk protein
also stimulates its reproductive system to synthesize proteins that form
the white egg
Signaling by Local Regulators
 Local regulators are secreted molecules that link neighboring cells (paracrine
signaling) or directly regulate the secreting cell (autocrine signaling)
 Once secreted, local regulators act on their target cells within seconds
4
• local regulating chemicals
1. polypeptide regulators
2. Nitric Oxide
↓ O2 levels in blood 
endothelial cells release NO 
enzyme released that
vasodilates surrounding
smooth muscle
- penis erection / Viagra
3. prostaglandins has many
functions
- help sperm reach egg
- help induce labor
- promote fever &
aaainflammation
- how aspirin works
- help form blood clots
- how aspirin helps
- negative effects on
aaaaaaaaastomach
• endocrine & nervous
system act together
- ex: butterfly life cycle
- periodic molting of
larva signaled by
neurosecretory cells
- juvenile hormone
determines when
metamorphosis takes
place
- applications of
knowledge of endocrine
signaling in insects
 Many chemical compounds function as local regulators:
1. Polypeptide regulators include cytokines & most growth factors, which
stimulate cell proliferation & differentiation
2. Nitric oxide (NO) gas functions in body as both neurotransmitter & local
regulator
o When level of O2 in blood falls, endothelial cells in blood vessel walls
synthesize & release NO, which activates an enzyme that relaxes
surrounding smooth muscles, resulting in vasodilation, which improves
blood flow to tissues
o Viagra sustains erection by prolonging activity of NO response
pathway, since NO promotes vasodilation, which enables sexual
function by increasing blood flow to penis  erection
3. Prostaglandins- group of local regulators that are modified fatty acids; first
discovered in prostate gland secretions that contribute to semen; produced by
many cell types & have various functions
o In semen that reaches female’s reproductive tract, they stimulate the
smooth muscles of the female’s uterine walls to contract, helping sperm
reach the egg
o During childbirth, the placenta’s prostaglandin-secreting cells cause
nearby muscles of the uterus to become more excitable, helping to
induce labor
o In immune system, they promote fever & inflammation & intensify
sensation of pain
 Aspirin & ibuprofen have anti-inflammatory & pain-relieving
effects because they inhibit prostaglandin synthesis
o Help regulate aggregation of platelets in formation of blood clots
 Because blood clots can cause heart attack by blocking blood
flow in vessels that supply the heart, people at risk for heart
attack take aspirin on regular basis
 because prostaglandins help maintain a protective
lining in the stomach, long-term aspirin therapy can
cause stomach irritation
Coordination of Neuroendocrine & Endocrine Signaling
 in all animals (except simplest invertebrates), endocrine & nervous system act
together to control reproduction & development
 ex: butterfly life cycle
o larva must periodically molt, shedding old exoskeleton & secreting
new one. Signals that direct molting are in brain
 neurosecretory cells produce prothoracicotrophic hormone
(PTTH), which stimulates a pair of endocrine glands behind
the brain to release ecdysteroid, which triggers each successive
molt as well as metamorphosis of larva into butterfly during
final molt
 juvenile hormone, secreted by another pair of endocrine glands
behind brain, determines when metamorphosis takes place. It
maintains larval characteristics & modulates activity of
ecdysteroid
 high levels of juvenile hormone  ecdysteroid
stimulates larval molting
 low levels of juvenile hormone, ecdysteroid-induced
molting produces pupal form
o knowledge of endocrine signaling in insects has important applications
for agricultural pest control
 ex: synthetic chemicals that can bind to the ecdysteroid
receptor cause insect larvae to molt prematurely & die
5
45.2 Feedback Regulation & Antagonistic Hormone Pairs are Common in
Endocrine Systems
Simple Hormone Pathways
Simple Endocrine Pathway
Simple neuroendocrine pathway
Reaction to Endocrine cells respond directly to
Stimulus is received by sensory
stimulus /
internal or environmental stimulus
neuron, which stimulates a
what is
by secreting a particular hormone
neurosecretory cell
secreted
Function
travels in the bloodstream to target
secretes a neurohormone
of secreted cells, where it interacts with its
cell
specific receptors
Target
Signal transduction within target
Neurohormone diffuses into the
cells
cells elicit physiological response
bloodstream & travels to target
cells
Example
stimulus= release of acidic contents
regulates milk release during
of stomach into duodenum.
nursing. Suckling by infant
Low pH in duodenum stimulates
stimulates sensory neurons in
certain endocrine cells, S cells, to
nipples, generating signals in
secrete hormone secretin, which
nervous system that reaches
enters the bloodstream & travels to
hypothalamus. Nerve impulses
the pancreas. Target cells in
from hypothalamus trigger release
pancreas release bicarbonate into
of neurohormone oxytocin from
ducts leading to duodenum, raising
posterior pituitary gland that
pH
elicits mammary glands to secrete
milk
Type of
Negative; response to secretin
Positive; response increases
feedback
(bicarbonate release) reduces
stimulus & amplifies signaling
loop
stimulus (low pH)
Mammary glands secrete milk in
Release of bicarbonate increases pH response to circulating oxytocin
in intestine, eliminating stimulus &
Milk released in response to
shutting off pathway
oxytocin leads to more suckling
Prevents excessive pathway activity & more stimulation
6
• positive feedback amplifies
stimulus & response
• negative feedback dampens
stimulus; restoration
- homeostatic control
systems are mostly negative
• negative feedback loop
pairs
Feedback Regulation
 Positive feedback reinforces stimulus, leading to even greater response
 Negative feedback- response reduces initial stimulus; by decreasing or
abolishing hormone signaling, it prevents excessive pathway activity
o Hormone pathways involved in homeostasis involves more negative
feedback loops, since they help restore a preexisting state
 Some homeostatic control systems rely on pairs of negatively regulated
hormone pathways, each counterbalancing each other
Insulin & Glucagon: Control of Blood Glucose
 Metabolic balance depends on a blood glucose concentration of 70 – 110
mg/100 mL. It’s important to maintain this concentration because glucose is a
major fuel for cellular respiration & key source of carbon skeletons for
biosynthesis
 2 antagonistic (opposing) hormones, insulin & glucagon, regulate the
concentration of glucose in the blood. Both operate in simple endocrine
pathways regulated by negative feedback
a. When blood glucose rises above normal range, release of insulin triggers
uptake of glucose from blood into body cells, decreasing blood glucose
concentration
b. When blood glucose drops below normal range, release of glucagon promotes
release of glucose into blood from energy stores (i.e. liver glycogen) increasing
blood glucose concentration
 The combined activity of these 2 hormones controls the concentration of
glucose in the blood because these 2 hormones have opposing effects
 Both are produced in the pancreas, where there are clusters of endocrine cells
called pancreatic islets. Each has alpha cells, which make glucagon, & beta
cells, which make insulin.
 Hormone-secreting cells make up 1 – 2% of mass of pancreas. Other cells in
there produce & secrete bicarbonate ions & digestive enzymes, both of which
are exocrine secretions that are released into small ducts that empty into the
pancreatic duct, which leads to small intestine.
7
• how the antagonistic
hormones affect glucose
levels
• diabetes mellitus & origin
of name
• types of diabetes
- resistance to insulin
signaling in type 2
Target Tissues for Insulin & Glucagon
Insulin
Both
Glucagon
lowers blood glucose
Liver is critical target
influences blood glucose levels
levels by stimulating
(nutrients absorbed by
through its effects on target
nearly all body cells
blood vessels of small
cells in liver. Liver & muscles
outside brain to take
intestine are transported
store sugar as glycogen. When
up glucose from blood directly to liver by
blood glucose level decreases
(brain cells can take up hepatic portal vein)
to level at or below normal
glucose without
within liver, glucagon & range, glucagon signals liver
insulin) insulin
insulin regulate nutrient
cells to increase glycogen
decreases blood
processing in ways that
hydrolysis, convert amino acids
glucose by slowing
support glucose
& glycerol to glucose, &
glycogen breakdown
homeostasis.
release glucose into
in liver & inhibiting
bloodstream. Net result is
conversion of glycerol
return of blood glucose levels
& amino acids to
to normal range
glucose
 Some disorders can disrupt glucose homeostasis with serious consequences, most
prevalently, diabetes mellitus
 Diabetes mellitus- disease caused by deficiency of insulin or decreased response to
insulin in target tissues; diabetes means copious urination, mellitus means presence
of sugar in urine
o Blood glucose levels rise, but cells aren’t able to take up enough glucose to
meet metabolic needs, so instead, fat becomes the main substrate for
cellular respiration.
o In severe cases, acidic metabolites formed during fat breakdown
accumulate in blood, threatening life by lowering blood pH & depleting
sodium & potassium ions from body
 People with diabetes mellitus may have blood glucose levels that exceed capacity
of kidneys to reabsorb glucose.
o Glucose that remains in kidney filtrate is excreted, resulting in presence of
sugar in urine (indicative of this disease)
 As glucose is concentrated in urine, more water’s excreted with it,
resulting in excessive volumes of urine
Type 1 diabetes (insulin
Type 2 diabetes (non-insulin
dependent)
dependent)
Characteristics Autoimmune disorder in
Failure of target cells to respond
which immune system
normally to insulin (resistance to
destroys beta cells of pancreas insulin signaling)
Relationship
Destroys person’s ability to
Insulin’s produced, but target cells
with insulin
produce insulin
fail to take up glucose from blood,
& glucose levels remain elevated
When it usually during childhood
Excess body weight & lack of
appears
exercise; mainly appears after 40.
Over 90% of people with diabetes
have type 2
Treatment
Insulin is injected several
Regular exercise & healthy diet
times a day. Insulin used to be help control blood glucose levels
extracted from animal
pancreases, but is now
obtained from genetically
modified bacteria
 Resistance to insulin signaling in type 2 is sometimes due to a genetic defect in
insulin receptor or insulin response pathway. In many cases, events in target cells
suppress activity of response pathway that's supposed to function
o Can be due to inflammatory signals in innate immunity
8
• hypothalamus
- ex: seasonal changes
• hypothalamus’s signals travel
to pituitary gland
• posterior pituitary
• anterior pituitary
1. oxytocin
2. ADH
• anterior hormone is either
releasing or inhibiting
- ex: prolactin-releasing
aahormone
• capillaries & portal vessels
45.3 The Hypothalamus & Pituitary are Central to Endocrine Regulation
Coordination of Endocrine & Nervous Systems in Vertebrates
 Hypothalamus- endocrine gland located in brain that plays central role in integrating
endocrine & nervous system in vertebrates; receives info from nerves throughout body;
in response, it initiates endocrine signaling appropriate to environmental conditions
o Ex: nerve signals from brain pass sensory info to hypothalamus about seasonal
changes. Hypothalamus then regulates release of reproductive hormones
required during breeding season
 Signals from hypothalamus travel to pituitary gland, located at hypothalamus’s base
that has discrete posterior and anterior lobes that secrete different sets of hormones
 Posterior pituitary is an extension of hypothalamus. Hypothalamic axons that reach
into the posterior pituitary secrete neurohormones synthesized in the hypothalamus
 Anterior pituitary is an endocrine gland that synthesizes & secretes hormones in
response to signals from hypothalamus. Many act as tropic hormones, which regulate
the function of other endocrine cells or glands
Posterior Pituitary Hormones
 Neurosecretory cells of hypothalamus synthesize the 2 posterior pituitary hormones:
1. Oxytocin- regulates milk secretion by mammary glands & contractions of uterus
during birthing; targets in the brain, where it influences behaviors related to maternal
care, pair bonding, & sexual activity
2. antidiuretic hormone (vasopressin)- regulates kidney function by increasing water
retention in kidneys, decreasing urine volume, helping maintain blood osmolarity
 After traveling the posterior pituitary within the long axons of the neurosecretory cells,
the hormones are stored in pituitary cells, to be released in response to nerve impulses
transmitted by the hypothalamus
Anterior Pituitary Hormones
 Endocrine signals generated by hypothalamus regulate hormone secretion by the
anterior pituitary
 Each hormone is either a releasing hormone or an inhibiting hormone. Every anterior
pituitary hormone is controlled by at least one releasing hormone
 Ex: Prolactin-releasing hormone is a hypothalamic hormone that stimulates the anterior
pituitary to secrete prolactin, which has activities that include stimulating milk
production
 The hypothalamic releasing & inhibiting hormones are secreted near capillaries at the
base of the hypothalamus. The capillaries drain into short blood vessels, portal vessels,
which subdivide into a second capillary bed within the anterior pituitary. Releasing &
inhibiting hormones have direct access to the gland they control
 Hormones secreted by the anterior pituitary regulate diverse set of processes in human
body (i.e. metabolism, osmoregulation, & reproduction)
9
Gland
Hormone
Hypothalamus
Hormones released from
posterior pituitary &
hormones that regulate
anterior pituitary
Posterior
pituitary gland
Oxytocin
Antidiuretic hormone
(ADH)
Anterior
pituitary gland
Growth hormone (GH)
Prolactin
Follicle-stimulating
hormone (FSH)
Lutenizing hormone (LH)
Thyroid-stimulating
hormone (TSH)
Adrenocorticotropic
hormone (ACTH)
Thyroid gland
Parathyroid
glands
Triiodotyhronine
(T3)&thyroxine (T4)
Calcitonin
Chemical
Class
Peptide
Representative Actions
Stimulates contraction of uterus & mammary
gland cells
Promotes retention of water by kidneys
peptide
Protein
Protein
glycoprotein
Glycoprotein
Glycoprotein
peptide
Amines
Peptide
Parathyroid hormone
(PTH)
Adrenal glands
Epinephrine &
norepinephrine
Stimulates production of ova & sperm
Stimulates ovaries & testes
Gonads: Testes
Androgens
Gonads: Ovaries
Estrogens
Pineal gland
Hypothalamic hormones
Stimulates thyroid gland
Stimulates adrenal cortex to secrete
glucocorticoids
Stimulate & maintain metabolic processes
lowers blood calcium level
TSH
Calcium in
blood
Calcium in
blood
Lowers blood glucose level
Protein
Amines
Glucocoticoids
mineralocorticoids
Water/ salt
balance
Raises blood calcium level
Insulin
glucagon
Nervous
system
Stimulates growth (especially bones) & metabolic
functions
Stimulates milk production & secretion
Peptide
Pancreas
Regulated by
Raises blood glucose level
Raise blood glucose level; increase metabolic
activities; constrict certain blood vessels
Raise blood glucose level
steroids
Promote reabsorption of Na & secretion of K in
kidneys
Support sperm formation; promote development
& maintenance of male secondary sex
characteristics
progestins
Stimulate uterine lining growth; promote
development & maintenance of secondary sex
characteristics
Promote uterine lining growth
Melatonin
Involved in biological rhythms
steroids
Amine
Glucose in
blood
Nervous
system
ACTH
K in blood;
angiotensin II
FSH & LH
Light/dark
cycles
10
Thyroid Regulation: A Hormone Cascade Pathway
(note: “” means stimulates)
• hormone cascade pathway

- ex: activation of thyroid
gland when infant exposed to
cold

- negative feedback pathway
brings self-limiting response
to original stimulus in target
cells

- application of thyroid
hormone regulation in
mammals

• hypothyroidism
Disorders of Thyroid Function & Regulation
 Hypothyroidism- too little thyroid function; effects: weight gain, lethargy,
intolerance to cold in adults
 Hyperthyroidism- excessive secretion of thyroid hormone; effects: high body
temperature, profuse sweating, weight loss, irritability, high blood pressure
 Graves’ disease- autoimmune disorder that’s most common form of
hyperthyroidism; common symptom is protruding eyes, which are caused by
fluid accumulation behind the eyes; body produces antibodies that bind to &
activate receptor for TSH, resulting in sustained thyroid hormone production
 Specific link between diet & thyroid hormone synthesis reflects chemical
nature of thyroid hormone
 Term “Thyroid hormone” refers to a pair of similar hormones derived from
amino acid tyrosine
1. Triiodothyronine (T3) contains 3 iodine atoms; target cells convert most of
T4 to T3 by removing 1 iodine atom
2. Tetraiodothyronine or thyroxine (T4) has 4 iodine atoms; thyroid gland
mostly secretes T4
 In mammals, same receptor binds both hormones.
 Without enough iodine, the thyroid gland can’t synthesize adequate amounts of
T3 & T4,
• hyperthyroidism
- Graves’ disease
• nutrition affects thyroid
hormone production
• thyroid hormone = T3 & T4
1. T3
2. T4
- insufficient iodine
Signals to the brain  hypothalamus
secretes hormone  stimulation or
inhibition of release of tropic anterior
pituitary hormone  secretion of
another hormone by target endocrine
tissue that exerts systematic metabolic
or development effects
Ex: young child’s body temperature
drops  hypothalamus secretes
thyrotropin-releasing hormone (TRH)
 anterior pituitary secretes thyroidstimulating hormone (TSH) aka
thyrotropin  release of hormone by
thyroid gland (organ consisting of 2
lobes on ventral side of trachea).
Thyroid hormone accumulates, it
increases metabolic rate  thermal
energy released  body temperature
raises
Usually negative feedback. In thyroid
hormone pathway, thyroid hormone
carries out negative feedback. Because
thyroid hormone blocks TSH release
from anterior pituitary & TRH release
from hypothalamus, the negativefeedback loop prevents overproduction
of thyroid
Regulates bioenergetics; helps maintain
normal blood pressure, heart rate, &
muscle tone; regulates digestive &
reproductive functions
11
- low blood levels of T3 &
T4  no negative feedback
 pituitary continues
secreting TSH  goiter
• bone-forming & branching
of nerve cells
- congenital
hypothyroidism
- radioactive iodine thyroid
scan
• ex: thyroid hormone
• ex: prolactin
• ex: MSH
- cachexia
• FSH & LH are
gonadotropins
• ACTH stimulates steroid
hormone by adrenal cortex
• growth hormone
- liver releases IGFs
- hypersecretion of GH
- hyposecretion of GH

The resulting low blood levels of T3 & T4 can’t exert usual negative feedback
on hypothalamus & anterior pituitary, resulting in pituitary continuing to
secrete TSH. Elevated TSH levels cause enlargement of thyroid gland resulting
in goiter
 Thyroid hormones function in the normal functioning of bone-forming cells &
branching of nerve cells during embryonic development of brain
 Congenital hypothyroidism- inherited condition of thyroid deficiency; retarded
skeletal growth & poor mental development can be avoidied if treatment with
thyroid hormones begins early in life
 Iodine in the body helps production of thyroid hormone, enabling radioactive
forms of iodine to produce images of thyroid gland to diagnose for thyroid
disorders
Evolution of Hormone Function
 Functions of given hormone diverge between species over evolution
 Ex: thyroid hormone regulates metabolism across many evolutionary lineages,
but in frogs, it stimulates resorption of tadpole’s tail during metamorphosis
 Ex: anterior pituitary hormone prolactin stimulates mammary gland growth &
milk synthesis in mammals, regulates fat metabolism & reproduction in birds,
delays metamorphosis in amphibians, & regulates salt & water balance in
freshwater fishes
 Ex: anterior pituitary hormone melanocyte-stimulating hormone (MSH) in
amphibians, fishes and reptiles, it regulates skin color by controlling pigment
distribution in skin cells; in mammals, MSH functions in hunger & metabolism
& coloration
o Specialized action of MSH that's evolved in mammalian brain has
medical applications. Many patients with cancer, AIDS, tuberculosis
suffer from wasting condition cachexia, characterized by weight loss,
muscle atrophy, & loss of appetite; because activation of one brain
receptor for MSH stimulates metabolism of fat & decreases appetite,
scientists hypothesize that activation of this MSh receptor causes
cachexia
Tropic & Nontropic Hormones
 TSH regulates thyroid gland, making it a tropic hormone.
 Follicle-stimulating hormone (FSH) & Lutenizing hormone (LH) stimulate
activities in male & female gonads (testes & ovaries); called gonadotropins,
which are regulated by hypothalamic gonadotropin-releasing hormone (GnRH)
 Adrenocorticotropic hormone (ACTH)- stimulates production & secretion of
steroid hormones by adrenal cortex
 Growth hormone- stimulates growth through tropic & nontropic effects;
secreted by anterior pituitary; exerts diverse metabolic effects that raise blood
glucose levels, opposing effects of insulin
 Liver, a major target, responds to GH by releasing insulin-like growth factors
(IGFs) which circulate in blood & directly stimulate bone growth
 Hypersecretion of GH during childhood can lead to gigantism. Hypersecretion
in adulthood stimulates bony growth in the few tissues that are responsive to
the hormone, resulting in acromegaly (overgrowth of extremities)
 Hyposecretion of GH in childhood retards long-bone growth & leads to
pituitary dwarfism. If diagnosed before puberty, can be treated with human GH
45.4 Endocrine Glands Respond to Diverse Stimuli in Regulating Homeostasis,
Development, & Behavior
Parathyroid Hormone & Vitamin D: Control of Blood Calcium
 Homeostatic control of blood calcium important because calcium ions are
essential to normal function of all cells
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• blood Ca2+ levels fall 
tetany
• blood Ca2+ levels rise 
organ damage
• parathyroid gland & PTH
• PTH’s effects on blood Ca2+
- bone
- kidneys
- vitamin D activation
• thyroid gland’s role in
calcium homeostasis
- calcitonin
- in different organisms
• adrenal glands
1. adrenal cortex
2. adrenal medulla
• hormones of adrenal
medulla:norepinephrine&
epinephrine
• function of the hormones:
1.increase availability of
energy sources
2. affect cardiovascular &
respiratory systems

If blood Ca2+ level falls too much, tetany (skeletal muscles contract
convulsively)
 If blood Ca2+ level rises too much, precipitates of calcium phosphate can form
in body tissues, leading to widespread organ damage
 Parathyroid gland- set of 4 small structures embedded in posterior surface of
thyroid, play a major role in blood Ca2+ regulation; When blood Ca2+ falls
below set point of 10 mg/ 100 mL, they release parathyroid hormone (PTH)
 PTH raises level of blood Ca2+ by direct & indirect effects
 In bone, PTH causes mineralized matrix to decompose & release Ca2+ into
blood
 In kidneys, PTH stimulates reabsorption of Ca2+ through renal tubules
 Inactive form of vitamin D, steroid-derived molecule, obtained from food or
synthesized by skin when exposed to sunlight.
 Vitamin D activation begins in liver & completed in kidneys, stimulated by
PTH. Active form of vitamin D acts directly on intestines, stimulating uptake of
Ca2+ from food & augmenting effect of PTH. As blood Ca2+ rises, a negative
feedback loop inhibits further release of PTH from parathyroid glands
 If blood Ca2+ rises
above set point,
thyroid gland releases
calcitonin, hormone
that inhibits bone
reabsorption &
enhances Ca2+ release
by kidney
 In fishes, rodents, and
some other animals,
calcitonin is required
for Ca2+ homeostasis,
while humans only
need it during
extensive bone growth
of childhood
Adrenal Hormones: Response to Stress
 Vertebrates’ adrenal glands are associated with kidneys.
 In mammals, each adrenal gland’s made up of 2 glands with different cell types,
functions, & embryonic origins:
1. Adrenal cortex- outer portion; consists of true endocrine cells
2. Adrenal medulla- central portion; secretory cells derive from neural tissue during
embryonic development
 Each adrenal gland’s a fuse endocrine & neuroendocrine gland
Catecholamines from the Adrenal Medulla
 Adrenal medulla secretes hormones epinephrine & noreprinephrine in response to
stress, both of which are catechomlamines- class of amine hormones synthesized
from amino acid tyrosine
1. They increase the amount of chemical energy available for immediate use. They
increase rate of glycogen breakdown in liver & skeletal muscles, promote glucose
release by liver cells, & stimulate release of fatty acids from fat cells. The released
glucose & fatty acids circulate in blood & can be used by body cells as fuel
2. Increase heart rate & stroke volume & dilate bronchioles in lungs, raising rate of
oxygen delivery to body cells
o This is why Doctors prescribe epinephrine as heart stimulant or to open
pathways during asthma attack
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3. alter blood flow
• primary functions of
epinephrine& norepinephrine
• nerve signals regulate secretion
by adrenal medulla
• adrenal cortex responds to
endocrine signals
• stress  hypothalamus release
ACTH  endocrine cells secrete
corticosteroids
1. glucocorticoids- glucose
metabolism; makes more glucose
available as fuel
- glucose synthesis from
breakdown of muscle proteins
- anti-inflammatory effect
- chronic inflammatory
conditions don’t use
glucocorticoids because of
its powerful effect on
metabolism
2. mineralocorticoids affect
mineral metabolism
- ex: Aldosterone in ion & water
homeostasis of blood
- ex: Aldosterone also functions
in response to stress
• corticosteroids in sex hormones
3.
alter blood flow, causing constriction of some blood vessels & dilation of others. This pushes
blood away from skin, digestive organs, & kidney, while increasing blood supply to heart,
brain, & skeletal muscles
 Epinephrine has stronger effect on heart & metabolic rates, norepinephrine modulates blood
pressure
 Nerve signals carried from brain via involuntary (autonomic) neurons regulate secretion by
adrenal medulla. Function in simple neurohormone pathway
o Stress  nerve impulses travel to adrenal medulla  release of catecholamines from
neursecretory cells
Steroid Hormones from the Adrenal Cortex
 Whereas adrenal medulla reacts to nervous input, adrenal cortex responds to endocrine signals
 Stress  hypothalamus secretes a releasing hormone that stimulates the anterior pituitary to
release tropic hormone ACTH. ACTH reaches adrenal cortex via bloodstream  endocrine
cells to synthesize & secrete corticosteroids, a family of steroids
1. Glucocorticoids- have primary effect on glucose metabolism; by augmenting fuel-mobilizing
effects of glucagon from pancreas, they promote glucose synthesis from noncarbohydrate
sources, making more glucose available as fuel.
o Glucocorticoids (i.e. cortisol) act on skeletal muscle, causing breakdown of muscle
proteins. Resulting amino acids are transported to liver & kidneys, where they’re
converted to glucose & released into blood. Synthesis of glucose from muscle
proteins provides circulating fuel when body requires more glucose than liver can
mobilize from glycogen stores
o When they’re introduced into body at levels above those normally present, they
suppress certain components of body’s immune system.
 This anti-inflammatory effect is why they’re used to treat inflammatory
diseases (i.e. arthritis)
 Long-term use can have serious side effects, so nonsteroidal antiinflammatory drugs (NSAIDs) (i.e. aspirin or ibuprofen) are
preferred for treating chronic inflammatory conditions
2. Mineralocorticoids- affect mineral metabolism, especially maintenance of salt & water balance
 Ex: Aldosterone functions in ion & water homeostasis of blood.
o Low blood volume or pressure  production of Angiotensin II  secretion of
Aldosterone  cells in kidneys reabsorb sodium ions & water from filtrate  blood
pressure & volume raised
 Aldosterone also functions in body’s response to severe stress
o Rise in blood ACTH increases rate at which adrenal cortex secretes Aldosterone &
glucocorticoids
 Corticosteroid products include small amounts of steroid hormones that function as sex
hormones
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• sex hormones
1. androgens
- testosterone
- gender
- male puberty
Gonadal Sex Hormones
 Sex hormones affect growth, development, reproductive cycles, & sexual
behavior
 Gonads produce & secrete 3 major categories of steroid hormones:
1. Androgens- testes primarily synthesize these
 Main one is testosterone. It functions before birth.
o Alfred Jost was interested
in how hormones
determine whether an
individual develops as
male or female. Working
with rabbits, he carried
out a surgical study that
established that for
mammals, female
development is the default
process in embryos. Male
development requires a
signal from male gonad.
 Androgens play major role at
puberty when they’re responsible
for development of human male
secondary sex characteristics.
High concentrations of androgen  low voice, male patterns of hair growth,
increases in muscle & bone mass
 Muscle-building/ anabolic action of testosterone & steroids does increasing muscle mass,
but also cause severe acne outbreaks & liver damage & decreases sperm count &
testicular size
2. Estrogens- responsible for maintenance of female reproductive system & for
development of female secondary sex characteristics
 Main one is estradiol.
 Estrogens & other gonadal sex hormones are components of hormone cascade pathways.
Synthesis of these hormones is controlled by gonadotrophins (FSH & LH) from anterior
pituitary gland. FSH & LH secretion is controlled by GnRH released from hypothalamus
3. Progestins
 In mammals, progestins, including progesterone, are involved in preparing &
maintaining tissues of uterus required to support growth & development of embryo
Endocrine Disruptors
 Pregnant women as risk for complications were prescribed disethylstilbestrol (DES), a
synthetic estrogen, which altered reproductive system development in the fetus.
Daughters of women who took DES are more frequently afflicted with certain
reproductive abnormalities (i.e. vaginal & cervical cancer), structural changes in the
reproductive organs, & increased risk of miscarriage.
 DES is an endocrine disruptor, a foreign molecule that interrupts normal function of
hormone pathway
Melatonin & Biorhythms
 Pineal gland- small mass tissue near center of mammalian brain; primary source of
hormone melatonin, modified amino acid
 Melatonin regulates functions related to light & to seasons marked by changes in day
length; primary function relate to biological rhythms associated with reproduction &
daily activity levels affects skin pigmentation in many vertebrates
 Melatonin’s secreted at night & amount released depends on length of night
o Ex: in winter, when days are short & nights are long, more melatonin’s secreted
 Release of melatonin’s by pineal gland’s controlled by suprachiasmatic nucleus (SCN)
group of neurons in hypothalamus. This functions as a biological clock & receives input
from specialized neurons in retina of eye
o
- steroids on muscles
2. estrogen
- estradiol
- hormone cascade
pathways
3. progestins
• DES endocrine disruptor
• pineal gland
• melatonin
- biological rhythms
- secreted at night
- release controlled by SCN
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