Transcript The Endocrine System

The Endocrine System
• The endocrine system is a collection of glands
that secrete chemical messages we call
hormones.
• The vertebrate endocrine system consists of
glands (pituitary, thyroid, adrenal), and diffuse
cell groups scattered in epithelial tissues.
• ductless, which means that their secretions
(hormones) are released directly into the
bloodstream and travel to elsewhere in the
body to target organs, upon which they act.
The roles of hormones in selecting target cells and delivering the hormonal message. Images
from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Classification
• Hormones are grouped into three
classes based on their structure:
• steroids
• peptides
• amines
Steroids
• Steroids are lipids derived from
cholesterol
• Steroid hormones are secreted by the
gonads, adrenal cortex, and
placenta.
Sex Steroids
• Natural sex steroids are made by the (ovaries or testes)[3], by
adrenal glands, or by conversion from other sex steroids in other
tissue such as liver or fat.
• Sex steroids include:
androgens: Mainly male hormones
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testosterone
androstenedione
dihydrotestosterone
dehydroepiandrosterone
anabolic steroids
estrogens: mainly female hormones
– estradiol
– estrone
– estriol
progestagens: mainly female hormones
– progesterone
– progestins
Corticosteroid
• Glucocorticoids such as cortisol control
carbohydrate, fat and protein
metabolism and are anti-inflammatory.
• Mineralocorticoids such as
aldosterone control electrolyte and
water levels, mainly by promoting
sodium retention in the kidney.
Anabolic steroid
• Anabolic steroids, or anabolicandrogenic steroids (AAS), are a class
of steroid hormones related to the
hormone testosterone.
• They increase protein synthesis within
cells, which results in the buildup of
cellular tissue (anabolism), especially in
muscles.
Anabolic steroids can cause
many adverse effects
• the most common being elevated blood
pressure, especially in those with preexisting hypertension, and harmful
changes in cholesterol levels,
• have been shown to alter fasting blood
sugar and glucose tolerance tests
• increase the risk of cardiovascular disease
or coronary artery disease
Anabolic steroids can cause
many adverse effects
• Acne is fairly common due to
stimulation of the sebaceous glands by
increased testosterone levels.
• can accelerate the rate of premature
baldness for males who are genetically
predisposed, but testosterone itself
can produce baldness in females.
• High doses of oral anabolic steroid
compounds can cause liver damage
Peptides
• Peptides are short chains of amino acids; most
hormones are peptides. They are secreted by
the pituitary, parathyroid, heart, stomach,
liver, and kidneys.
Amines
• Amines are derived from the amino acid
tyrosine and are secreted from the thyroid
and the adrenal medulla.
The major human endocrine glands
include
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the hypothalamus and pituitary gland
the thyroid gland
the pancreas
the adrenal glands
the gonads or sex organs
the pineal gland
Hypothalamus and Pituitary gland
• The pituitary gland is called the “master
gland” but it is under the control of the
hypothalamus.
• important to the female menstural cycle,
pregnancy, birth, and lactation (folliclestimulating hormone (FSH) & leutinizing
hormone (LH) )
• antidiuretic hormone or ADH - helps prevent
excess water excretion by the kidneys
• endorphins, which belong to the category of
chemicals known as opiates and serve to
deaden our pain receptors.
– The natural response to rub an injured area, such
as a pinched finger, helps to release endorphins in
that area.
Thyroid Gland
• regulate metabolism, therefore body
temperature and weight
• contain iodine, which the thyroid needs in
order to manufacture these hormones
– person lacks iodine in his/her diet, the thyroid
cannot make the hormones, causing a deficiency
the pancreas
• Ducted gland - secreting digestive enzymes
into the small intestine
• Ductless gland - the islets of Langerhans
secrete insulin and glucagon to regulate the
blood sugar level
the adrenal glands
• sit on top of the kidneys
• consist of two parts, the outer cortex and the inner
medulla
• medulla secretes epinephrine (= adrenaline) and
other similar hormones in response to stressors
such as fright, anger, caffeine, or low blood sugar
• The cortex secretes corticosteroids such as
cortisone, well-known as being anti-inflammatory,
thus are prescribed for a number of conditions
the gonads or sex organs
• the female ovaries and male testes (singular =
testis) secrete hormones
• is controlled by pituitary gland hormones
• both sexes make some of each of the
hormones
– male testes secrete primarily androgens including
testosterone
– Female ovaries make estrogen and progesterone
• baby’s placenta also secretes hormones to
maintain the pregnancy
pineal gland
• located near the center of the brain in humans
• stimulated by nerves from the eyes
• secreted melatonin at night when it’s dark
– secretes more in winter when the nights are
longer
– Melatonin promotes sleep (makes you feel
sleepy). It also affects reproductive functions by
depressing the activity of the gonads
pineal gland
• it affects thyroid and adrenal cortex functions.
• SAD or seasonal affective disorder
(syndrome) is a disorder in which too much
melatonin is produced, especially during the
long nights of winter, causing profound
depression, oversleeping, weight gain,
tiredness, and sadness.