Chemical Signals in Animals:
Endocrine System and Hormonal Control
Endocrine vs. Nervous
The nervous system brings about
immediate responses, but the endocrine
system is slower acting and regulates
processes that occur over days or even
months.
Hormones
 Endocrine systems exert control through the
use of hormones.
 Hormones are chemical messengers produced
by ductless glands in one part of the body which
travel through the bloodstream and exert their
influence in another part of the body.
Hormones
 Hormones are secreted into the bloodstream
and regulate whole body processes like
growth, reproduction, complex behaviors
including courtship and migration.
 Hormones influence the metabolism of their
target cells by binding to receptor proteins
within the cell or on the surface of the cell.
Exocrine vs. Endocrine
Exocrine systems have ducts used for
transport of substances directly into the
body cavities: salivary glands
Endocrine systems are ductless and
secrete hormones directly into body
fluids: pituitary gland
Hormones
The endocrine and the nervous systems are
related
1) structurally
2) chemically
3) functionally
simultaneously maintaining homeostasis,
physiology and other body processes.
Hormones
• Neurosecretory cells: specialized nerve
cells that secrete hormones located
within endocrine organs and tissues.
Hormones
• Several chemicals serve as both
neurotransmitters and hormones.
• Epinephrine, produced by the adrenal
medulla, acts as the “fight or flight
hormone” and a neurotransmitter.
Control
• Positive and Negative Feedback regulate
mechanisms of both systems
• Positive feed back: output intensifies
and increases the likelihood of a
response
• Mammal milk production and release
Control:
- Antagonistic hormones work in
opposition to one other.
- Insulin and glucagon
Hormonal Control
• In Hydra, one hormone stimulates growth and
budding while inhibiting sexual reproduction.
• Invertebrates exhibit a diversity of hormones
which function in
1) homeostasis,
2)reproduction,
3)development, and
4)behavior.
Hormonal Control
• Chemical signals operate at virtually all levels of
organization:
• Local regulators
– Intracellular
– Cell to cell
• Tissue to tissue regulators
• Organ to organ regulators
• Organism to organism (pheromones)
Hormonal Control
Local regulators affect neighboring target cells
Histamine -- immune and regulatory responses
Interleukins – immune response
Growth factors – peptides and proteins that regulate
the behavior of cells in growing and developing
tissues
• Prostaglandins – modified fatty acids released into
interstitial fluid
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Hormonal Control
• Binding of a chemical signal to a specific
receptor protein triggers chemical events in the
target cell that result in a change in that cell.
• The response to a chemical signal depends on
the number and affinity of the receptor proteins.
Chemical Signals
•
Chemical signals often bind to a specific
protein receptor on the plasma membrane of
the target cell
•
Because of their chemical nature, most signal
molecules (peptides, proteins, glycoproteins)
are unable to diffuse through the plasma
membrane
Chemical Signals
•
The binding of the signal molecule
to a plasma membrane receptor
initiates a signal transduction
pathway, a series of events that
converts the signal into a specific
cellular response.
Chemical Signals
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A specific example is the binding on the
polypeptide hormone insulin to the
insulin receptor:
Insulin binding initiates a chain of events
that accounts for the blood sugar
lowering effects of insulin.
Vertebrate Endocrine System
Coordinates:
1)metabolism,
2)growth,
3)development, and
4)reproduction.
Major Endocrine Organs
Functions of Vertebrate Hormones
•
Some hormones have a single action
while other have multiple functions
•
Tropic hormones act on other
endocrine glands
Functions of Vertebrate Hormones:
Functions of Vertebrate Hormones:
Hypothalamus
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Region of the lower brain
Receives information from nerves
throughout the body and brain
Initiates endocrine signals appropriate to
the environmental conditions
Regulates the Pituitary Gland
Pituitary Gland
- Located at the base of the hypothalamus
-Two lobes: anterior and posterior;
numerous functions
Anterior Pituitary Gland
Anterior Pituitary Gland
 Produces many different hormones
 Regulated by factors of the hypothalamus
 Four are tropic hormones that stimulate
other endocrine glands to synthesize and
release their hormones: TSH, ACTH, FSH,
LH
Anterior Pituitary Gland
 Luteinizing Hormone (LH)
 Stimulates ovulation and corpus luteum
formation in females
 Stimulates spermatogenesis in males
Anterior Pituitary Gland
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Follicle-Stimulating Hormone (FSH)
Tropic hormone that affects the gonads
In males, necessary for spermatogenesis
In females, it stimulates ovarian follicle
growth
Anterior Pituitary Gland
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Growth Hormone (GH)
Promotes growth directly
Stimulates production of
growth factors
Anterior Pituitary Gland
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Thyroid-Stimulating Hormone (TSH)
Tropic hormone that stimulates the
thyroid gland to produce and secrete its
own hormone
Anterior Pituitary Gland
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Adrenocorticotropin (ACTH) stimulates
the adrenal cortex to produce and secrete its
steroid hormones
Melanocyte-Stimulating Hormone (MSH)
regulates the activity of pigment-containing
skin cells
Endorphins inhibit pain perception
Posterior Pituitary Gland
Posterior Pituitary Gland
 Synthesized in hypothalamus
 Secreted from posterior pituitary
 Oxytocin – induces uterine muscle
contraction; induces lactation
 Antidiuretic Hormone – acts on kidneys to
increase water retention thus reducing
urine volume
Pineal Gland
• Small mass near the center of the brain
• Produces melatonin
– modified amino acid that modulates skin
pigmentation
– secreted only at night; larger amounts secreted in
winter
– Involved in regulation of biorhythms
Thyroid hormones function in:
1) development
2) bioenergetics
3) homeostasis
Thyroid is on the ventral side of the
trachea.
 plays a major role in vertebrate
development: participates in embryonic
development
 control metamorphosis in amphibians
Thyroid gland maintains homeostasis in
mammals including:
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blood pressure
heart rate
muscle tone
digestion
reproductive functions
rate of O2 consumption and
metabolism (increases)
Serious metabolic disorders result from
deficiency or excess of thyroid hormones.
• Hyperthyroidism - high body temperature,
sweating, weight loss, irritability, high blood
pressure
• Hypothyroidism – can cause cretinism in
infants and weight gain, lethargy, and coldintolerance in adults
• Goiter - enlarged thyroid caused by a deficiency
in iodine
Thyroid hormone secretion is regulated by
hypothalamus and pituitary.
• Negative Feedback System.
• Hypothalamus secretes TRH 
• Anterior Pituitary stimulated to produce
TSH 
• TSH binds to receptors and T3 and T4
• High levels of T3, T4, and TSH inhibit TRH
Parathyroid hormone (PTH)
• balances blood calcium
• needs vitamin D to function
Pancreas Endocrine Tissues
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Islets of Langerhans:
Alpha cells secrete glucagon
Beta cells secrete insulin
antagonistic hormones that
regulate blood glucose
If glucose homeostasis is unbalanced:
• Type I diabetes mellitus (insulindependent diabetes)
• Type II diabetes (non-insulin-dependent
diabetes)
• Both types untreated will result in high
blood sugar:
– Kidneys excrete glucose
– More water is excreted
– Fat is the major source of fuel for cell
respiration.
Adrenal Glands:
• located on top of kidneys
• Adrenal medula synthesizes
catecholamines:
– epinephrine
– norepinephrine
• Glucose is mobilized
• Heart rate is increased
• Bronchioles dilate
Adrenal Glands:
• Adrenal cortex synthesizes and secretes
corticosteroids as directed by ACTH from the anterior
pituitary
– Mineralocorticoids affect salt and water balance
– Aldosterone stimulates kidney cells to reabsorb
sodium ions and water
– Glucocorticoids – promote glucose synthesis from
noncarbohydrate substances such as proteins
Stress and The Adrenal Glands
Steroids
• Androgens: male sex hormones
• Testosterone:
– Stimulate the development and maintenance
of male reproductive systems
– responsible for secondary male sex
characteristics
Steroids
• Estrogens: female sex hormones
– Maintain the female reproductive system
– responsible for secondary sex characteristics
• Progestins (Progesterone)
– Preparation and maintainace of uterus for
reproduction
• Gonadotropins from anterior pituitary (FSH and
LH) control the synthesis of both androgens and
estrogens