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David Sadava, David M. Hillis,
H. Craig Heller, May R. Berenbaum
La nuova
biologia.blu
Anatomia e fisiologia dei viventi S
Animal Hormones
What Are Hormones And How Do They Work?
Endocrine cells produce and release chemical
signals directly into the extracellular fluid (ECF).
Hormones are endocrine signals that enter the blood
and activate target cells far from the site of release.
What Are Hormones And How Do They Work?
Paracrines affect target cells near the release site.
Example: histamine, a mediator of inflammation.
Autocrines bind to receptors on the same cells that
secrete them.
What Are Hormones And How Do They Work?
Three types of hormones:
• Peptides or proteins (water-soluble)
• Steroid hormones (e.g., estrogen,
testosterone) are synthesized from the
steroid cholesterol
• Amine hormones
What Are Hormones And How Do They Work?
Water-soluble hormone receptors are
transmembrane glycoprotein complexes with three
domains:
• binding domain (outside the plasma membrane),
• transmembrane domain,
• cytoplasmic domain that extends into the cytoplasm.
How Do the Nervous and Endocrine Systems Interact?
One hormone can trigger different responses in
different types of cells.
Example: epinephrine (amine hormone) and the
fight-or-flight response.
The nervous system stimulates
endocrine cells in the adrenal
glands to secrete epinephrine.
What Are the Major Endocrine Glands and Hormones?
Some endocrine cells exist as single cells (e.g., in the
digestive tract).
Endocrine glands: aggregations of endocrine cells
that secrete hormones into the ECF.
Exocrine glands have ducts that carry their signals to
the outside of the body or a body cavity.
The Endocrine System of Humans
What Are the Major Endocrine Glands and Hormones?
The pituitary gland is attached to the hypothalamus
of the brain.
The anterior pituitary
originates from gut
epithelial tissue; contains
endocrine cells controlled
by neurohormones from
the hypothalamus.
The posterior pituitary
originates from neural
tissue; contains axons
from hypothalamic
neurons.
What Are the Major Endocrine Glands and Hormones?
Hypothalamic neurons secrete two neurohormones
into the posterior pituitary:
1. Antidiuretic hormone (ADH) increases the water
retained by the kidneys when necessary.
2. Oxytocin stimulates uterine contractions in
childbirth and milk flow.
What Are the Major Endocrine Glands and Hormones?
The anterior pituitary secretes four tropic hormones
that control other endocrine glands:
• Thyrotropin (thyroid-stimulating hormone)— TSH
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
• Corticotropin (ACTH)
What Are the Major Endocrine Glands and Hormones?
The anterior pituitary also secretes growth hormone,
prolactin, enkephalins, and endorphins.
Growth hormone (GH) promotes growth by
stimulating cells to take up amino acids.
Endorphins and
enkephalins are the body’s
natural painkillers, acting as
neurotransmitters in the
brain.
What Are the Major Endocrine Glands and Hormones?
Hypothalamic hormones include:
• Thyrotropin-releasing hormone (TRH)
• Gonadotropin-releasing hormone (GnRH)
• Prolactin-releasing and release-inhibiting hormones
• Growth hormone-releasing hormone and growth
hormone release-inhibiting hormone (somatostatin)
• Corticotropin-releasing hormone
How Do the Nervous and Endocrine Systems Interact?
Multiple negative feedback loops also control
hormone secretion from the anterior pituitary.
What Are the Major Endocrine Glands and Hormones?
The thyroid gland secretes two hormones.
Thyroxine, which regulates metabolism, is produced
by follicle epithelial cells.
Thyroglobulin is produced and secreted into the lumen
of the follicle, where it is iodinated and stored until
processed by the epithelial cells to generate T3 and
T4.
Triiodothyronine, or T3:
Tetraiodothyronine, or T4:
The Thyroid Gland Consists of Many Follicles
Thyrotropin releasing hormone (TRH), produced in the
hypothalamus activates the TSH-producing pituitary
cells.
Anterior pituitary secretes thyrotropin or thyroidstimulating hormone (TSH), which activates the
follicles to produce thyroxine.
What Are the Major Endocrine Glands and Hormones?
Regulation of calcium levels in the blood is critical to
body function.
There are several mechanisms for controlling blood
calcium levels:
• Deposition or absorption of bone
• Excretion or retention of Ca by kidneys
• Absorption of Ca from digestive tract.
What Are the Major Endocrine Glands and Hormones?
These mechanisms are controlled by three hormones:
1. Calcitonin is released by the thyroid gland and
lowers blood Ca by regulating bone turnover.
2. Parathyroid hormone (PTH) is secreted by the
parathyroid glands.
When Ca levels are low, PTH is released, which
stimulates bone turnover and increases blood Ca
levels.
3. Calcitriol (synthesized from vitamin D)
Calcitriol promotes absorption of Ca from the gut.
Hormonal Regulation of Calcium
What Are the Major Endocrine Glands and Hormones?
Islets of Langerhans— endocrine cells in the
pancreas that produce three hormones:
•Beta ( cells produce insulin
•Alpha (  cells produce glucagon—stimulates liver
to convert glycogen to glucose when blood glucose
levels fall below normal
•Delta ( cells produce somatostatin—inhibits
release of both insulin and glucagon
What Are the Major Endocrine Glands and Hormones?
The adrenal gland is a
gland within a gland.
The adrenal medulla
produces epinephrine
(adrenaline) and
norepinephrine in
response to stressful
situations.
What Are the Major Endocrine Glands and Hormones?
Epinephrine and norepinephrine bind to adrenergic
receptors on target cells.
 -adrenergic receptors respond
more to norepinephrine.
-adrenergic receptors
respond to both.
What Are the Major Endocrine Glands and Hormones?
The outer adrenal cortex produces corticosteroids
from cholesterol:
•Glucocorticoids influence blood glucose
concentration
•Mineralocorticoids influence salt and water balance
•Sex steroids are important in sexual development,
behavior and anabolism.
Aldosterone, the main mineralocorticoid, stimulates
kidneys to conserve sodium and excrete potassium.
What Are the Major Endocrine Glands and Hormones?
Cortisol (a glucocorticoid) mediates metabolic stress
responses.
Cortisol and similar drugs are used to reduce
inflammation and allergic responses.
The anterior pituitary controls cortisol release by
corticotropin (adrenocorticotropic hormone, or
ACTH).
ACTH release is controlled in turn by corticotropinreleasing hormone from the hypothalamus.
What Are the Major Endocrine Glands and Hormones?
Gonads produce sex steroids.
• Androgens—male, testosterone
• Estrogens and progesterone—female, estradiol
In development, sex hormones determine whether a
fetus will become male or female.
Sex hormones exert their effects by the seventh week
of human development.
What Are the Major Endocrine Glands and Hormones?
Androgens, produced in the presence
of a Y chromosome, are required for
male reproductive structures to
develop.
Without androgen, female
reproductive structures develop.
What Are the Major Endocrine Glands and Hormones?
At puberty, production of sex hormones increases.
Gonad activity is controlled by tropic hormones called
gonadotropins from the anterior pituitary:
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
Gonadotropins are controlled by hypothalamic
gonadotropin-releasing hormone (GnRH)—its release
increases at puberty.
What Are the Major Endocrine Glands and Hormones?
The pineal gland produces the amine hormone
melatonin from tryptophan.
Melatonin is released in the dark and indicates length
of the night—light inhibits its release.
Involved in photoperiodicity—seasonal changes in
day length trigger physiological changes.
How Have Hormones Evolved?
Chemical signaling was critical for the evolution of
multicellular organisms.
Signaling molecules are highly conserved, but their
functions differ.
As organisms diversified, the same hormone–receptor
systems diversified to serve different functions.
Example: the
hormone prolactin.
Prolactin’s Structure Is Conserved, but Its Functions Have Evolved
How Have Hormones Evolved?
In arthropods, hormones control molting and
metamorphosis.
Three hormones regulate molting and maturation:
PTTH (prothoracicotropic hormone) from cells in the
brain stimulates the prothoracic gland to secrete
ecdysone.
Ecdysone diffuses to target tissues and stimulates
molting.
How Have Hormones Evolved?
Juvenile hormone is also
released from the brain, which
prevents maturation to adult
form.
Control of development by
juvenile hormone is important
in insects with complete
metamorphosis.
What Are the Major Diseases?
Diabetes mellitus is caused by lack of the protein
hormone insulin (type I) or by a lack of insulin
responsiveness in target cells (type II).
Glucose transporters in cell membranes are controlled
by insulin. When insulin is absent, transporters are
returned to the cytoplasm, and glucose uptake is
inhibited.
Today, insulin replacement therapy using
manufactured insulin allows people with type I
diabetes to lead almost normal lives.
What Are the Major Diseases?
A goiter is an enlarged thyroid gland, associated with
either hyperthyroidism (excess thyroxine) or
hypothyroidism (thyroxine deficiency).
The most common cause of
hypothyroid goiter is iodine
deficiency—follicle cells can’t
produce thyroxine.
Without thyroxine in the blood,
TSH levels remain high, and the
thyroid continues to produce
thyroglobulin.
Adapted from
Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014
Inc. All rights reserved