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Ch35: Chemical Signaling w/i
Animals w/ Hormones
• A hormone is a chemical signal produced
to send messages around the body
 it typically acts a distant site, carried by blood
• hormones are produced in called the
endocrine glands
Figure 35.1 Majors glands of the
human endocrine system
35.1 Hormones
• The glands that produce hormones are
generally controlled by the nervous system
• the two are so closely linked that they are often
considered a single system—neuroendocrine
system
 the hypothalamus (part of the brain) is the
main switchboard of the neuroendocrine
system for controlling the body.
35.1 Hormones
• The CNS regulates the body’s hormones
through a chain of command
 for example, the hypothalamus controls the
pituitary gland with a hormone (thyrotropicreleasing hormone/TRH)
• this causes the pituitary to release a hormone
which controls an endocrine gland. (thyroidstimulating hormone/TSH)
 the hypothalamus also secretes inhibiting
hormones that keep the pituitary from
secreting specific hormones
35.1 Hormones
• Hormones are effective messengers
because they travel in the blood to a
specific target cell
 cells that respond to a particular hormone
have receptor proteins shaped to fit that
hormone and no others
35.1 Hormones
• Hormones secreted by endocrine glands
belong to four different chemical
categories




polypeptides
glycoproteins
amines
steroids
35.1 Hormones
•
Homones signal their communication by a series of
simple steps
1.
issue the command
•
2.
transport the signal
•
3.
most hormones are transported by the bloodstream
hit the target cell(s)
•
4.
the hypothalamus controls the release of many hormones
the hormone binds to a receptor
have an effect
•
the hormone bound receptor triggers a change in cell activity
How hormonal communication works
1. The young teenager sees an attractive
teen, so the hypothalamus secretes a
releasing hormone GnRH
2. GnRH stimulates the anterior pituitary
to release its hormones FSH & LH
3. FSH & LH stimulates the gonads to
secrete testosterone in boys and
estrogen in girls
4. Testosterone or estrogen bind to cell
receptors, changing the cell, in brain
cells it results in a crazy teen behavior!
35.2 How Hormones Target Cells
• Steroid hormones bind to protein
receptors located in the cytoplasm or
nucleus of the target cell
 Testosterone, estrogen, and progesterone are
steroid hormones
 steroids are lipid-soluble so they can pass
across cell or nuclear membrane
35.2 How Hormones Target Cells
• The steroid hormone-receptor complex
move in the nucleus and bind to DNA
 this activates transcription of a gene
subsequently making a protein and changing
the behavior of a cell
Figure 35.3 How steroid hormones
work
35.2 How Hormones Target Cells
• peptide hormones binds to receptors
within the plasma membrane
 the hormone binding to the receptor triggers
changes in the receptor protein causes
changes in the cell
• second messengers usually amplifying this change
by activating enzymes
• cyclic AMP (cAMP) & Ca+2 are second messengers
Figure 35.4 How peptide hormones work
Figure 35.5 How second
messengers work
Marie, I showed this slide but did not go over it. John
35.3 The Hypothalamus and the
Pituitary
• The pituitary gland is located beneath the
hypothalamus and is the location where
nine hormones are produced
 the pituitary is actually two glands
• posterior lobe regulates water conservation and,
in women, milk letdown and uterine contraction
• anterior lobe regulates other endocrine glands
35.3 The Hypothalamus and the
Pituitary
• The posterior pituitary is under the control
of the hypothalamus and they are
connected by a tract of neurons
 Two hormones are produced by the
hypothalamus and transported/stored in the
posterior pituitary
• vasopressin or antidiuretic hormone (ADH)
regulates the kidney’s conservation of water
• oxytocin initiates uterine contractions during
childbirth and milk release in mothers
Figure 35.6 The posterior pituitary contains
hormones that originate in the hypothalamus
35.3 The Hypothalamus and the
Pituitary
•
•
The Hypothalamus controls the anterior
pituitary by secreting “releasing hormones” that
cause the anterior pituitary to release its
hormones
The anterior pituitary is a complete gland that
produces and secretes seven hormones
1. thyroid-stimulating hormone (TSH) stimulates the
thyroid gland to produce thyroxine
2. adrenocorticotropic hormone (ACTH) stimulates
the adrenal gland to produce hormones
35.3 The Hypothalamus and the
Pituitary
3. growth hormone (GH) simulates the growth of
muscle and bone throughout the body
4. Follicle-stimulating hormone (FSH)
1. in females, triggers the maturation of egg cells and
stimulates the release of estrogen
2. in males, it regulates sperm development
5. Luteinizing hormone (LH)


in females, it triggers ovulation of an egg
in males, it stimulates the gonads to produce
testosterone
35.3 The Hypothalamus and the
Pituitary
6. Prolactin (PRL) hormone stimulates the
breasts to produce milk
7. Melanocyte-stimulating hormone
(MSH)


its function in humans is poorly understood
in reptiles and amphibians it stimulates skin
color changes
Figure 35.7 The role of the pituitary
35.3 The Hypothalamus and the
Pituitary
• The hypothalamus controls the production
and secretion of the anterior pituitary
hormones by secreting both:
 releasing hormones (stimulate the production
& release of an anterior pituitary hormone)
 and inhibiting hormones (inhibit production &
release an anterior pituitary hormone)
35.3 The Hypothalamus and the
Pituitary
• Negative feedback (feedback inhibition)
also controls how many hormones in the
anterior pituitary are produced
 when enough of the target hormone has been
produced, the hormone itself feeds back to
the hypothalamus and inhibits the release of
the releasing hormones from the
hypothalamus and also directly inhibits the
anterior pituitary
Figure 35.9 Negative feedback
35.4 The Pancreas
• The pancreas has both exocrine and endocrine
functions, secreting digestive enzymes and
hormones
• the hormones, produced in the islets of Langerhans, are
insulin and glucagon
– insulin promotes the uptake of blood glucose (glycogen in the
liver and triglycerides in fat cells)
– glucagon causes liver cells to release stored glucose and fat
cells to break down triglycerides
Figure 35.10 Insulin and glucagon secreted by the
pancreas regulate blood glucose levels
35.4 The Pancreas
• Diabetes mellitus is a serious disorder in
which affected individuals’ are unable to
take up glucose from the blood
 there are two kind of diabetes mellitus
• Type I is a hereditary autoimmune disease that
attacks the islets of Langerhans, resulting in
abnormally low insulin secretion (treat w/ shots)
• Type II is an abnormally low number of insulin
receptors in the target tissue (treat w/ diet)
35.5 The Thyroid, Parathyroid, and
Adrenal Glands
• The thyroid gland makes several hormones
 calcitonin stimulates the bones to absorb calcium
from the blood
 thyroxine increases the bodies metabolic rate and
promotes growth
• thyroxine contains iodine and if a diet is low in iodine, the
thyroid cannot make enough thyroxine to inhibit the
hypothalamus
– as a result, the hypothalamus stimulates the thyroid to grow
producing a goiter
Figure 35.11 The thyroid gland
secretes thyroxine
35.5 The Thyroid, Parathyroid, and
Adrenal Glands
• The parathyroid glands are four small
glands attached to the thyroid
 these glands produce parathyroid hormone
(PTH), a hormone that is essential for survival
because it releases calcium out of the bones
(calcitonin causes bones to absorb calcium)
 this regulates calcium blood levels, which is
necessary for muscle & heart contractions
Figure 35.12 Maintenance of
proper calcium levels in the blood
35.5 The Thyroid, Parathyroid, and
Adrenal Glands
• The adrenal glands are just above the
kidneys and has two parts
 medulla is the inner core and produces
epinephrine and norepinephrine
 cortex is the outer region and produces the
steroid hormones cortisol and aldosterone
35.5 The Thyroid, Parathyroid, and
Adrenal Glands
• The medulla releases epinephrine (adrenaline)
and norepinephrine in times of stress
 act as emergency signals stimulating rapid
deployment of body fuel
• The cortex secretes cortisol, which acts to
maintain nutritional well-being
• The cortex secretes also secretes aldosterone
which is essential for survival
 it affects water and sodium reabsorption in the
kidneys