Download The endocrine system

Human Endocrine System
CH Chen
What is endocrinology?
Endocrinology =
Intercellular Chemical Communication
Endocrinology is about communication
systems & information transfer.
What are endocrine systems for?
Endocrine Functions
• Maintain Internal Homeostasis
•
•
•
•
Support Cell Growth
Coordinate Development
Coordinate Reproduction
Facilitate Responses to External Stimuli
• Homeostasis
• Growth and Development
• Reproduction
• Energy Metabolism
• Behavior
Nervous system
•The nervous system exerts
point-to-point control through
nerves, similar to sending
messages by conventional
telephone. Nervous control is
electrical in nature and fast.
Hormones travel via the
bloodstream to target cells
•The endocrine system broadcasts its
hormonal messages to essentially all
cells by secretion into blood and
extracellular fluid. Like a radio
broadcast, it requires a receiver to get
the message - in the case of endocrine
messages, cells must bear a receptor
for the hormone being broadcast in
order to respond.
Types of cell-to-cell signaling
Classic endocrine hormones travel via
bloodstream to target cells;
neurohormones are released via
synapses and travel via the bloostream;
paracrine hormones act on adjacent
cells and autocrine hormones are
released and act on the cell that
secreted them. Also, intracrine
hormones act within the cell that
produces them.
Response vs. distance traveled
Endocrine action: the hormone is distributed in blood and binds to distant target cells.
Paracrine action: the hormone acts locally by diffusing from its source to target cells in
the neighborhood.
Autocrine action: the hormone acts on the same cell that produced it.
Blood
vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Response
(c) Autocrine signaling
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine signaling
Response
What kinds of hormone are there?
Known Hormonal Classes
• Proteins & peptides
chemcases.com/olestra/
images/insulin.jpg
• Lipids (steroids, eicosanoids)
• Amino acid derived
(thyronines, neurotransmitters)
chem.pdx.edu/~wamserc/
ChemWorkshops/ gifs/W25_1.gif
• Gases (NO, CO)
website.lineone.net/~dave.cushman/
epinephrine.gif
Water-soluble (hydrophilic)
Lipid-soluble (hydrophobic)
Polypeptides
Insulin
Steroids
0.8 nm
Cortisol
Amines
Epinephrine
Thyroxine
Signaling by Pheromones
• Members of the same animal species sometimes
communicate with pheromones, chemicals that are
released into the environment
• Pheromones serve many functions, including marking
trails leading to food, a wide range of functions that
include defining territories, warning of predators, and
attracting potential mates
© 2011 Pearson Education, Inc.
Figure 45.3
We now know
What is the classical
that nearly
endocrine system?
every tissue
secretes
chemical
signals that act
as hormones,
heart, immune
cells, stomach,
intestines, bone
cells, liver, skin,
glial cells, etc.
www.cushings-help.com/ images/endocrine.jpg
Other Organs with
Endocrine Activity
Placenta
 Releases hCG throughout gestation
Digestive Tract
 Gastrin and secretin
Heart
 ANH
Kidneys
 Renin
Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Organs containing
endocrine cells:
Thymus
Heart
Adrenal
glands
Testes
Liver
Stomach
Pancreas
Kidney
Kidney
Small
intestine
Ovaries
Regulation of hormone secretion
 Sensing and signaling: a biological need is sensed,
the endocrine system sends out a signal to a target
cell whose action addresses the biological need. Key
features of this stimulus response system are:





receipt of stimulus
synthesis and secretion of hormone
delivery of hormone to target cell
evoking target cell response
degradation of hormone
Control of Endocrine Activity
•The physiologic effects of hormones depend
largely on their concentration in blood and
extracellular fluid.
•Almost inevitably, disease results when hormone
concentrations are either too high or too low, and
precise control over circulating concentrations of
hormones is therefore crucial.
Control of Endocrine Activity
The concentration of hormone as seen by target
cells is determined by three factors:
•Rate of production
•Rate of delivery
•Rate of degradation and elimination
Hormone transport
• Hormones circulate both free and bound to
plasma proteins.
eg. FT4 Vs TT4
TT4 = FT4 + FT4 combine to TG
free hormone
• Is the fraction available for binding to
receptors and therefore represents the
active hormone.
• Dictates the magnitude of feedback
inhibition that controls hormone release.
• Is the fraction that is cleared from the
circulation .
• Correlates best with clinical states of
hormone excess and deficiency.
HORMONE
-combined to plasma protein
• The binding of hormones to plasma
proteins is through noncovalent
interactions and tends to increase the half
life of the hormone in the circulation.
Feedback Control of Hormone
Production
Feedback loops are used
extensively to regulate
secretion of hormones in the
hypothalamic-pituitary axis.
An important example of a
negative feedback loop is seen
in control of thyroid hormone
secretion
Cellular Response Pathways
• Water and lipid soluble hormones differ in their paths
through a body
• Water-soluble hormones are secreted by exocytosis,
travel freely in the bloodstream, and bind to cellsurface receptors
• Lipid-soluble hormones diffuse across cell membranes,
travel in the bloodstream bound to transport proteins,
and diffuse through the membrane of target cells
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SECRETORY
CELL
Lipidsoluble
hormone
Watersoluble
hormone
VIA
BLOOD
Transport
protein
Signal receptor
TARGET
CELL
Signal
receptor
NUCLEUS
(a)
(b)
SECRETORY
CELL
Lipidsoluble
hormone
Watersoluble
hormone
VIA
BLOOD
Transport
protein
Signal receptor
TARGET
CELL
Cytoplasmic
response
OR
Gene
regulation
Signal
receptor
Cytoplasmic
response
NUCLEUS
(a)
(b)
Gene
regulation
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Second
messenger
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
EXTRACELLULAR
FLUID
Plasma
membrane
Hormone-receptor
complex
EXTRACELLULAR
FLUID
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
NUCLEUS
CYTOPLASM
DNA
Vitellogenin
mRNA
for vitellogenin
Multiple Effects of Hormones
• The same hormone may have different effects on
target cells that have
– Different receptors for the hormone
– Different signal transduction pathways
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Same receptors but different
intracellular proteins (not shown)
Different receptors
Different cellular
responses
Different cellular
responses
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
Glycogen
deposits
Glycogen
breaks down
and glucose
is released
from cell.
(a) Liver cell
Vessel
dilates.
(b) Skeletal muscle
blood vessel
Vessel
constricts.
(c) Intestinal blood
vessel
Endocrine is subject to regulation by
nervous system, including brain
pineal gland
hypothalamus
pituitary gland
Coordination of Endocrine and Nervous
Systems in Vertebrates
• The hypothalamus receives information from the
nervous system and initiates responses through the
endocrine system
• Attached to the hypothalamus is the pituitary gland
composed of the posterior pituitary and anterior
pituitary
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Cerebrum
Pineal
gland
Thalamus
Hypothalamus
Cerebellum
Pituitary
gland
Spinal cord
Hypothalamus
Posterior
pituitary
Anterior
pituitary
• The posterior pituitary stores and secretes
hormones that are made in the hypothalamus
• The anterior pituitary makes and releases hormones
under regulation of the hypothalamus
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Hypothalamus
Neurosecretory
cells of the
hypothalamus
Neurohormone
Axons
Posterior
pituitary
Anterior
pituitary
HORMONE
ADH
TARGET
Kidney
tubules
Oxytocin
Mammary glands,
uterine muscles
Tropic effects only:
FSH
LH
TSH
ACTH
Neurosecretory
cells of the
hypothalamus
Nontropic effects only:
Prolactin
MSH
Nontropic and tropic effects:
GH
Hypothalamic
releasing and
inhibiting
hormones
Portal vessels
Endocrine cells
of the anterior
pituitary
Pituitary
hormones
Posterior
pituitary
HORMONE
TARGET
FSH and LH
Testes or
ovaries
TSH
ACTH
Prolactin
MSH
GH
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Liver, bones,
other tissues
Hypothalmus
Located deep within the cerebrum.
 Some cells relay messages from the autonomic nervous system to the central
nervous system.
 Other cells respond as gland cells to release hormones.
Circadian Clock
Produces melatonin (synthesized
from seratonin, a derivative of
tryptophan)
• Secreted directly in CSF to blood
• High levels at night make us sleepy; low level during day
• Pineal gland is stimulated by darkness and inhibited by
light
• Function in regulating circadian rhythms (sleep, body
temp, appetite)  biological clock
GH
Levels
awake
strenuous
exercise
sleep
• Acts on the liver, stimulating it to
release several polypeptide hormones.
• Stimulates amino acid uptake and
protein synthesis in target cells.
• Ultimately stimulates cell growth (cell
size and number), especially in muscle
and bone.
• Also stimulates fat breakdown.
Dwarfism
hyposecretion of GH
Kenadie - worlds
smallest girl due to
primordial dwarfism
Little People Big World
Gigantism
hypersecretion of GH
Bao Xishun, a 7ft 8.95in herdsman
from Inner Mongolia
Acromegaly
hypersecretion of GH
7 ft 1 ¼ inches
How is growth hormone
controlled?
© Kenneth L. Campbell, 1997. All rights reserved.
Posterior Pituitary
Diabetes Insipidus
Oxytocin and Pregnancy
Posterior Pituitary Gland
• Production of
– Vasopressin (antidiuretic hormone; ADH; AVP)
– Oxytocin
• Vasopressin (antidiuretic hormone; ADH; AVP)
– Acts on the renal tubules to reduce water loss by
concentrating the urine
– Deficiency causes diabetes insipidus (DI), characterized by
the production of large amounts of dilute urine
– Excessive or inappropriate production predisposes to
hyponatremia if water intake is not reduced in parallel with
urine output
• Oxytocin
– Stimulates postpartum milk letdown in response to suckling
larynx
thyroid
trachea
Thyroid gland selectively uptakes iodine
to produce T3 & T4
• Thyroxine (T4)
• Triiodothyronine (T3)
Both control metabolic rate and cellular
oxidation
• Calcitonin (from parafolicular cells)- lowers
blood CA ++ levels and causes CA++
reabsorption in bone
Example
Pathway
Stimulus
Cold
Sensory neuron

Hypothalamus
Neurosecretory cell
Hypothalamus secretes
thyrotropin-releasing
hormone (TRH ).
Releasing hormone
Blood vessel

Negative feedback
Anterior pituitary
Tropic hormone
Endocrine cell
Anterior pituitary secretes
thyroid-stimulating
hormone (TSH, also known
as thyrotropin ).
Thyroid gland secretes
thyroid hormone
(T3 and T4 ).
Hormone
Target
cells
Response
Body tissues
Increased cellular
metabolism
How is the thyroid controlled?
© Kenneth L. Campbell, 1997.
All rights reserved.
Disorders of Thyroid Function and
Regulation
• Hypothyroidism, too little thyroid function, can
produce symptoms such as
– Weight gain, lethargy, cold intolerance
• Hyperthyroidism, excessive production of thyroid
hormone, can lead to
– High temperature, sweating, weight loss,
irritability and high blood pressure
• Malnutrition can alter thyroid function
© 2011 Pearson Education, Inc.
• Graves disease, a form of hyperthyroidism caused
by autoimmunity, is typified by protruding eyes
• Thyroid hormone refers to a pair of hormones
– Triiodothyronin (T3), with three iodine atoms
– Thyroxine (T4) with four iodine atoms
• Insufficient dietary iodine leads to an enlarged
thyroid gland, called a goiter
© 2011 Pearson Education, Inc.
Goiter
Lack of iodine in diet
hyposecretion of T3 & T4
Cretinism
hyposecretion of
T3 & T4
Myxedema
hyposecretion of T3 & T4
myxedema
After thyroid
treatment
Exophthalmoshyperthyroidism
PTH release:
1) stimulates osteoclasts
2) enhances reabsorption of Ca++ by kidneys
3) increases absorption of Ca++ by intestinal mucosal
cells
Hyperparathyroidism- too much Ca++ drawn out of bone;
could be due to tumor
Hypoparathyroidism- most often follow parathyroid
gland trauma or after removal of thyroid--- tetany,
muscle twitches, convulsions; if
untreatedrespiratory paralysis and death
Thyroid Hormone Regulation
Calcium Homeostasis
Pancreas
Combination
Organ
 Exocrine tissues called
acini secrete digestive
enzymes into the small
intestine.
 Endocrine tissues
secrete hormones.
 Glycogenolysis.
 Gluconeogenesis.
• Produced by the  cells of the Islets of
Langerhan
• Catalyze oxidation of glucose for ATP
production
• Lowers blood glucose levels by promoting
transport of glucose into cells.
• Stimulates glucose uptake by the liver and
muscle cells.
• Stimulates glycogen synthesis in the liver and
muscle cells.
• Also stimulates amino acid uptake and protein
synthesis of muscle tissue
• Produced by the  cells of the Islets of
Langerhans
• Stimulates change of glycogen to glucose in
the liver.
• Synthesis of glucose from lactic acid and non
carbohydrate molecules such as fatty acids
and amino acids
• Causes  in blood glucose concentration
hypoglycemic- low blood sugar; deficient in glucagon
Insulin
Body cells
take up more
glucose.
Blood glucose
level declines.
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level rises
(for instance, after eating a
carbohydrate-rich meal).
Homeostasis:
Blood glucose level
(70–110 mg/m100mL)
STIMULUS:
Blood glucose level
falls (for instance, after
skipping a meal).
Blood glucose
level rises.
Liver breaks
down glycogen
and releases
glucose into
the blood.
Alpha cells of pancreas
release glucagon into
the blood.
Glucagon
Type I Diabetes
hyposecretion of insulin
insulin dependant
juvenile onset
Type II Diabetes
late onset (adult)
insensitivity of cells to insulin
manage by exercise & diet
International Diabetes Federation Definition:
Abdominal obesity plus two other components:
elevated BP, low HDL, elevated TG, or impaired
fasting glucose
Diabetes Prevention Program:
Reduction in Diabetes Incidence
Adrenal Glands
adrenal cortex
adrenal medulla
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
© 2011 Pearson Education, Inc.
Hormones of the Adrenal
Medulla
• Adrenalin (epinephrine): converts glycogen to
glucose in liver
• Noradrenalin (norepinephrine): increases
blood pressure
(sympathetic nervous system)
• Corticosteroids: glucose levels)
• Epinephrine and norepinephrine
– Trigger the release of glucose and fatty acids into the
blood
– Increase oxygen delivery to body cells
– Direct blood toward heart, brain, and skeletal
muscles, and away from skin, digestive system, and
kidneys
• The release of epinephrine and norepinephrine occurs
in response to involuntary nerve signals
Steroid Hormones from the Adrenal
Cortex
• The adrenal cortex releases a family of steroids called
corticosteroids in response to stress
• These hormones are triggered by a hormone cascade
pathway via the hypothalamus and anterior pituitary
(ACTH)
• Humans produce two types of corticosteroids:
glucocorticoids and mineralocorticoids
© 2011 Pearson Education, Inc.
Hormones of the Adrenal
Cortex
Glucocorticoids- cortisol
1. Decrease protein synthesis
2. Increase release and use of fatty acids
3. Stimulates the liver to produce glucose from non carb’s
Mineralcorticoids- aldosterone
1. Stimulates cells in kidney to reabsorb Na+ from filtrate
2. Increases water reabsorption in kidneys
3. Increases blood pressure
Sex Steroids- small amts (androgens)
1. Onset of puberty
2. Sex drive
(b) Long-term stress response
and the adrenal cortex
(a) Short-term stress response
and the adrenal medulla
Stress
Spinal cord
(cross section)
Hypothalamus
Nerve
signals
Releasing
hormone
Nerve
cell
Anterior pituitary
Blood vessel
Adrenal medulla
secretes epinephrine
and norepinephrine.
Nerve cell
ACTH
Adrenal cortex
secretes mineralocorticoids and
glucocorticoids.
Adrenal
gland
Kidney
Effects of epinephrine and norepinephrine:
• Glycogen broken down to glucose;
increased blood glucose
• Increased blood pressure
• Increased breathing rate
• Increased metabolic rate
• Change in blood flow patterns, leading to
increased alertness and decreased digestive,
excretory, and reproductive system activity
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
• Retention of sodium
ions and water by
kidneys
• Proteins and fats broken
down and converted to
glucose, leading to
increased blood glucose
• Increased blood
volume and blood
pressure
• Partial suppression of
immune system
Cushing’s
Syndrome
Hypersecretion of cortisone;
may be caused by an ACTH
releasing tumor in pituitary
Symptoms: trunkal obesity
and moon face, emotional
instability
Treatment: removal of adrenal
gland and hormone
replacement
Addison’s
Disease
Hyposecretion of glucocorticoids and mineral
corticoids;
Symptoms- wt loss, fatigue, dizziness, changes
in mood and personality, low levels of plasma
glucose and Na+ levels, high levels of K+
Treatment- corticosteroid replacement therapy
Thymus
Located anterior to the heart
Produces- thymopoetin and thymosin
helps direct maturation and specialization of
T-lymphocytes (immunity)
Gonads
Ovaries- produce estrogen and
progesteroneresponsible for maturation of the
reproductive organs and 2ndary sex characteristics in
girls at puberty
Female
Reproductive
System
Gonads
Testes- produce sperm and testosterone (initiates
maturation of male repro organs and 2ndary sex
characteristics in boys at puberty)
Male Reproductive System
Figure 46.14

Hypothalamus
GnRH


FSH
LH
Leydig cells
Sertoli cells
Inhibin
Spermatogenesis
Testis
Testosterone
Negative feedback
Negative feedback
Anterior pituitary
Primary
oocyte
within
follicle
Ovary
Growing
follicle
In embryo
Primordial germ cell
Mitotic divisions
2n
Oogonium
Mitotic divisions
2n
First
polar
body
Primary oocyte
(present at birth), arrested
in prophase of meiosis I
Completion of meiosis I
and onset of meiosis II
n
n
Secondary oocyte,
arrested at metaphase of
meiosis II
Ovulation, sperm entry
Mature follicle
Ruptured
follicle
Ovulated
secondary
oocyte
Completion of meiosis II
Second
polar
body
Corpus luteum
n
n
Fertilized egg
Degenerating
corpus luteum
(a)
Control by hypothalamus
GnRH
1
Anterior pituitary
2
(b)
Inhibited by combination of
estradiol and progesterone

Hypothalamus
FSH

Stimulated by high levels
of estradiol

Inhibited by low levels of
estradiol
LH
Pituitary gonadotropins
in blood
6
LH
FSH
3
(c)
Ovarian cycle
7
Growing follicle
Maturing
follicle
8
Follicular phase
Corpus
luteum
Ovulation
Ovarian hormones
in blood
5
Degenerating
corpus luteum
Luteal phase
Estradiol secreted
by growing follicle in
increasing amounts
4
(d)
LH surge triggers
ovulation
FSH and LH stimulate
follicle to grow
Progesterone and
estradiol secreted
by corpus luteum
Peak causes
LH surge
(see 6)
10
9
Estradiol
Progesterone
Progesterone and estradiol promote thickening
of endometrium
Estradiol level
very low
Uterine (menstrual) cycle
(e)
Endometrium
Days
Menstrual flow phase
0
5
Secretory phase
Proliferative phase
10
14 15
20
25
28
Menstrual Versus Estrous Cycles
• Menstrual cycles are characteristic only of humans and
some other primates
– The endometrium is shed from the uterus in a bleeding
called menstruation
– Sexual receptivity is not limited to a timeframe
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• Estrous cycles are characteristic of most mammals
– The endometrium is reabsorbed by the uterus
– Sexual receptivity is limited to a “heat” period
– The length and frequency of estrus cycles vary from
species to species
© 2011 Pearson Education, Inc.
Menopause
• After about 500 cycles, human females undergo
menopause, the cessation of ovulation and
menstruation
• Menopause is very unusual among animals
• Menopause might have evolved to allow a mother to
provide better care for her children and grandchildren
© 2011 Pearson Education, Inc.
Epididymis
Seminiferous tubule
Testis
Primordial germ cell in embryo
Cross section of
seminiferous tubule
Mitotic divisions
Spermatogonial
stem cell
2n
Mitotic divisions
Sertoli cell
nucleus
Spermatogonium
2n
Mitotic divisions
Primary spermatocyte
2n
Meiosis I
Secondary spermatocyte
Meiosis II
Lumen of
seminiferous tubule
Neck
Tail
Plasma
membrane
Midpiece
n
n
Spermatids
(two stages)
Early
spermatid
n
n
n
n
Differentiation
(Sertoli cells
provide nutrients)
Head
Acrosome
Nucleus
Mitochondria
Sperm cell
n
n
n
n
Nature 2012 Aug 23;488(7412):471-.5
Sexual Reproduction: An Evolutionary
Enigma
• Sexual females have half as many daughters as asexual
females; this is the “twofold cost” of sexual
reproduction
• Despite this, almost all eukaryotic species reproduce
sexually
© 2011 Pearson Education, Inc.
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
Generation 4
Sex is costly and dangerous
• Energetic costs: mate finding, courtship, male male competition
• Increased predation risk
• Disease: STDs
• Genetic cost: sexual reproduction means that a
parent passes on only 1/2 of its genes to offspring
• Demographic cost: all other things being equal, an
asexual clone will replace sexual individuals in a
“mixed” population, because asexual females will
produce twice as many daughters as sexual
females (John Maynard Smith)
The Adaptive Significance of of
Sex
Why is sexual reproduction so
common in multicellular organisms?
• Sexual reproduction results in genetic recombination,
which provides potential advantages
– An increase in variation in offspring, providing an
increase in the reproductive success of parents in
changing environments
– An increase in the rate of adaptation
– A shuffling of genes and the elimination of harmful
genes from a population
© 2011 Pearson Education, Inc.
Sexual Dimorphism
Consequences of Sexual Selection
 The typical result is sexual dimorphism, a difference
in the outward appearances of males and females of
the same species.
Charles Darwin first proposed in 1871 that sexual
dimorphism could be explained by sexual
selection
 Traits which distinguish sex above primary sexual
organs are called secondary sexual characteristics.
121
Sexual Selection
123
Runaway Sexual Selection
When a secondary sexual
trait confers greater
fitness, the stage is set for
runaway sexual selection:
regardless of the original
reason for female
preference, female choice
exaggerates fitness
differences among males:
• leads to evolution of
spectacular plumage (e.g.,
peacock) and other
seemingly outlandish
plumage and/or displays
124
Female Choice
Evolution of secondary
sexual
characteristics in
males may be under
selection by female
choice:
in the sparrow-sized male
widowbird, the tail is a
half-meter long: males
with artificially elongated
tails experienced more
breeding success than males
with normal or shortened
tails
126
The Handicap Principle
Can elaborate male secondary sexual
characteristics actually signal male quality to
females?
Zahavi’s handicap principle suggests that
secondary characteristics act as handicaps -- only
superior males could survive with such burdens
Hamilton and Zuk have also proposed that showy
plumage (in good condition) signals genetic
factors conferring resistance to parasites or
diseases
127