Chemical Signals in Animals:
Endocrine System and Hormonal Control
Campbell Chapter 45
Nancy G. Morris
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

Hormones influence the metabolism of their
target cells by binding to receptor proteins
within the cell or on the surface of the cell.
(Figure 45.3)
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.
Figure 45.3
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
Interlukins – 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
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


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:
Table 45.1
Functions of vertebrate hormones:
Table 45.1
Hypothalamus




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 & posterior; numerous
functions
- Figure 45.6
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




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



Growth Hormone (GH)
Promotes growth directly
Stimulates production of
growth factors
Anterior Pituitary Gland


Thyroid-Stimulating Hormone (TSH)
Tropic hormone that stimulates the
thyroid gland to produce and secrete its
own hormone
Anterior Pituitary Gland



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:






blood pressure
heart rate
muscle tone
digestion
reproductive functions
rate of O2 consumption &
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
 Figure 45.9
 Hypothalamus secretes TRH 
 Anterior Pituitary stimulated to produce TSH 
 TSH binds to receptors & 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
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:

– epinepherine
– norepinepherine
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
Steroids
Androgens: male sex hormones
 Testosterone:

– Stimulate the development & 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 & maintainace of uterus for
reproduction

Gonadotropins from anterior pituitary (FSH and
LH) control the synthesis of both androgens &
estrogens