Download Amino acid-derived hormones

All hormones in the human body can be
divided into lipid-derived, amino acidderived, and peptide hormones.
Learning Objective

Recognize characteristics associated with lipid-derived, amino acid-derived, and peptide
hormones
Key Points
o
Most lipid hormones are steroid hormones, which are usually ketones or alcohols and are
insoluble in water.
o
Steroid hormones (ending in '-ol' or '-one') include estradiol, testosterone, aldosterone,
and cortisol.
o
The amino acid-derived hormones (ending in '-ine') are derived from tyrosine and
tryptophan and include epinephrine and norepinephrine (produced by the adrenal
medulla).
o
Amino acid-derived hormones also include thyroxine (produced by the thryoid gland) and
melatonin (produced by the pineal gland).
o
Peptide hormones consist of a polypeptide chain; they include molecules such as
oxytocin (short polypeptide chain) or growth hormones (proteins).
o
Amino acid-derived hormones and protein hormones are water-soluble and insoluble in
lipids.
Terms

estrogen -any of a group of steroids (lipid-hormones) that are secreted by the ovaries and
function as female sex hormones

epinephrine -(adrenaline) an amino acid-derived hormone secreted by the adrenal gland in
response to stress

oxytocin -a hormone that stimulates contractions during labor, and then the production of milk
Types of Hormones:
Although there are many different hormones in the human body, they can be divided into three classes
based on their chemical structure: lipid-derived, amino acid-derived, and peptide hormones (which
includes peptides and proteins). One of the key, distinguishing features of lipid-derived hormones is that
they can diffuse across plasma membranes whereas the amino acid-derived and peptide hormones
cannot.
1. Lipid-Derived Hormones (or Lipid-soluble
Hormones)
Most lipid hormones are derived from cholesterol, so they are structurally similar to it . The primary class
of lipid hormones in humans is the steroid hormones. Chemically, these hormones are usually ketones or
alcohols; their chemical names will end in "-ol" for alcohols or "-one" for ketones. Examples of steroid
hormones include estradiol, which is an estrogen, or female sex hormone, and testosterone, which is an
androgen, or male sex hormone. These two hormones are released by the female and male reproductive
organs, respectively. Other steroid hormones include aldosterone and cortisol, which are released by the
adrenal glands along with some other types of androgens. Steroid hormones are insoluble in water; they
are carried by transport proteins in blood. As a result, they remain in circulation longer than peptide
hormones. For example, cortisol has a half-life of 60 to 90 minutes, whereas epinephrine, an amino acid
derived-hormone, has a half-life of approximately one minute.
Lipid-derived hormones
The structures shown here represent (a) cholesterol, plus the steroid hormones (b) testosterone and (c) estradiol.
2. Amino Acid-Derived Hormones
The amino acid-derived hormones are relatively small molecules derived from the amino acids tyrosine
and tryptophan . If a hormone is amino acid-derived, its chemical name will end in "-ine". Examples of
amino acid-derived hormones include epinephrine and norepinephrine, which are synthesized in the
medulla of the adrenal glands, and thyroxine, which is produced by the thyroid gland. The pineal gland in
the brain makes and secretes melatonin, which regulates sleep cycles.
Amino acid-derived hormones
(a) The hormone epinephrine, which triggers the fight-or-flight response, is derived from the amino acid tyrosine. (b)
The hormone melatonin, which regulates circadian rhythms, is derived from the amino acid tryptophan.
3. Peptide Hormones
The structure of peptide hormones is that of a polypeptide chain (chain of amino acids). The peptide
hormones include molecules that are short polypeptide chains, such as antidiuretic hormone and oxytocin
produced in the brain and released into the blood in the posterior pituitary gland. This class also includes
small proteins, such as growth hormones produced by the pituitary, and large glycoproteins, such as
follicle-stimulating hormone produced by the pituitary .
Peptide hormones
The structures of peptide hormones (a) oxytocin, (b) growth hormone, and (c) follicle-stimulating hormone are shown.
These peptide hormones are much larger than those derived from cholesterol or amino acids.
Secreted peptides, such as insulin, are stored within vesicles in the cells which synthesize them. They are
then released in response to stimuli (e.g., as high blood glucose levels in the case of insulin). Amino acidderived and polypeptide hormones are water-soluble and insoluble in lipids. These hormones cannot
pass through plasma membranes of cells; therefore, their receptors are found on the surface of the target
cells.
The endocrine system plays a role in
growth, metabolism, and other
processes by releasing hormones into
the blood.
Learning Objective

Evaluate hormones and their purpose in the body
Key Points
o
Hormones serve as chemical messengers in the body and help maintain homeostasis.
o
Hormones are released into bodily fluids, like blood, which carry them to target cells.
o
Target cells respond to a hormone when they express a specific receptor for that hormone.
o
Hormones also play a role in the regulation of cell death, the immune system, reproductive
development, mood swings, and hunger cravings.
o
In the adrenal gland, epinephrine and norepinephrine regulate responses to stress; in the thyroid
gland, thyroid hormones regulates metabolic rates.
Terms

target cell
any cell having a specific receptor for a hormone

hormone
any substance produced by one tissue and conveyed by the bloodstream to another to affect physiological
activity

endocrine system
a control system of ductless glands that secrete hormones which circulate via the bloodstream to affect cells
within specific organs
The Endocrine System: Hormones
An animal's endocrine system controls body processes through the production, secretion, and regulation of
hormones. Hormones serve as chemical "messengers" that function in cellular and organ activity to maintain the
body's homeostasis. Maintaining homeostasis within the body requires the coordination of many different systems
and organs. Communication between neighboring cells and between cells and tissues in distant parts of the body
occurs through the release of hormones into body fluids (usually blood), which carry them to their target cells.
Target cells, those having a receptor for a signal, respond to a hormone when they express a specific receptor for
that hormone. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a
number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological
effects. Different tissue types may also respond differently to the same hormonal signal.
By releasing hormones, the endocrine system plays a role in growth, metabolism, and sexual development.
Hormones also play a role in induction or suppression of cell death, activation or inhibition of the immune system,
mood swings, and hunger cravings. In humans, common endocrine system diseases include thyroid disease and
diabetes mellitus.
Examples of endocrine glands include the adrenal glands, which produce hormones, such as epinephrine and
norepinephrine that regulate responses to stress, and the thyroid gland, which produces thyroid hormones that
regulate metabolic rates. In organisms that undergo metamorphosis, the process is controlled by the endocrine
system. The transformation from tadpole to frog, for example, is complex and nuanced to adapt to specific
environments and ecological circumstances .