Download Chapter 8: Chemical Signals Maintain Homeostasis

THE USE OF CHEMICAL
SIGNALS TO MAINTAIN
HOMEOSTASIS
Hormones
Endocrine System: a system of glands that secrete hormones
to regulate body function
Hormones: chemical messengers or regulators
• they are released by cells in one part of the body and affect
cells in other parts of the body to speed up or slow down
processes.
Endocrine Hormones – are produced in glands and secreted
directly into the blood and distributed by the circulatory
system.
Makes hormones
and regulates the
pituitary gland
Pineal gland (makes
melatonin which
regulates sleep
patterns)
Not a gland
How do Hormones Signal Cells?
• Note: Hormones do not affect ALL cells
• Depends on whether or not that cell has a receptor for the
particular hormone.
• There are 2 types of hormones:
1. Steroid Hormones
2. Protein Hormones
Steriod Hormones
• made from cholesterol (lipid);
• Complex ring of C, H, and O
• Soluble in fat but NOT water
• - ex: sex hormones
• - ex: cortisol (stimulates the conversion of amino acids to
glucose by the liver)
Steroid Hormones
HORMONE
RECEPTOR
Protein Hormones
• Made of chains of amino acids
• Soluble in water
• Ex: insulin, growth hormone
• The protein hormones attach to receptor sites on the cell
membrane
• The hormone-receptor complex leads to the production of
the enzyme adenylyl cyclase which causes the cell to convert
ATP into cyclic adenosine monophosphate (cyclic AMP)
• Cyclic AMP then activates enzymes in the cell.
Protein
Hormones
Control Systems
• The body relies on the nervous system and the endocrine
system for control of organs and tissues
• The nervous system allows the body to adjust quickly to
environmental changes
• The endocrine system is designed to maintain control over
longer durations
• The hypothalamus regulates the pituitary gland through
nerve stimulation
• However, endocrine glands – which are stimulated by the
pituitary gland – secrete chemicals that feedback to affect
nerve activity of the hypothalamus
Pituitary Gland (The Master Gland)
• “master gland” because it controls the other endocrine
glands
• Located at the base of the brain; connected to the
hypothalamus by a stalk
• The pituitary produces and stores
hormones
• The hypothalamus stimulates
release when necessary
their
2 Lobes of the Pituitary
Posterior Lobe
• Releases hormones that are actually made by the
hypothalamus
• The hormones travel from the hypothalamus to the pituitary
via special nerve cells
• They are stored in the pituitary and released into the blood
when necessary
• Ex: ADH (antidiuretic hormone), oxytocin
2 Lobes of the Pituitary
Anterior Lobe
• Produces its own hormones
• The release of these hormones is stimulated by other
hormones produced in the hypothalamus
• These anterior pituitary hormones will travel through the
blood to target cells
Epinephrine/
adrenaline
HORMONES THAT AFFECT
METABOLISM
3 Glands Affect Metabolism
• Thyroid gland
• Parathyroid gland
• Anterior pituitary
THYROID GLAND
Thyroid Gland
• Located at the base of the neck in front of the trachea
• Makes 2 important hormones: thyroxine (T4) and
triiodothyronine (T3)
• They regulate body metabolism, growth, and differentiation
of tissues.
• (Thyroid also makes hormone calcitonin – which acts on
bone cells to lower the amount of calcium in the blood)
Thyroxine and Metabolism
• People who secrete higher levels of thyroxine will
breakdown sugars and other nutrients at a faster rate.
• For these individuals, ~60% of glucose oxidized is released
as heat
• 40% is converted into ATP and is usually consumed during
daily activity.
• Thus, these individuals don’t gain weight
Hypothyroidism
• In contrast, individuals who produce lower levels of
thyroxine do not break down sugars as quickly.
• Excess blood sugar Is converted into glycogen, and the extra
sugar into fat.
• The slower blood sugar is used, the faster fat is stored.
Negative Feedback control
When metabolic rate decreases (b/c low thyroxine) the hypothalamus is activated.
The hypothalamus releases thyroid-releasing hormone to the anterior pituitary which
causes the release of thyroid-stimulating hormone by the pituitary.
TSH goes to the thyroid and signals the release of thyroxine.
Thyroxine inhibits the release of TRH.
Thyroid Disorders - Goiter
• Iodine, obtained from one’s diet, is an important component
of T3 and T4
• When not enough iodine is obtained from one’s diet, the
thyroid enlarges to produce a goiter
• Lack of iodine→ decrease in T3/4 → TRH → TSH →
thyroid stimulation – but with no hormones being produced,
no negative feedback to shut off the thyroid stimulation so
thyroid enlarges
Parathyroid Glands
Parathyroid Glands
• 4 small glands within the thyroid gland
• Usually nerves or other hormones regulate the endocrine
glands but the parathyroid glands respond directly to
chemical changes in their immediate surroundings.
• Produces parathyroid hormone (PTH) which regulates
blood calcium levels
Low calcium → PTH release → kidneys and intestines retain
absorb (retain) calcium
→ calcium is released by bones
When calcium levels reach normal levels again, the parathyroid
glands are inhibited.
Abnormally high levels of PTH would cause prolonged
breakdown of bones