Importance of the
Endocrine System
Chemical Controls
• The endocrine system consists of a number of
glands and their respective hormones.
• The endocrine hormones are chemicals secreted
by endocrine glands directly into the blood which
affect cells in other areas of the body.
• Hormones may affect a specific target within the
body or have a broad-spectrum effect on body
function where several organs are affected at the
same time by the hormone’s release.
Endocrine Glands
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Pituitary
Pineal
Thyroid
Parathyroid
Thymus
Adrenal
Pancreas
Ovary/Testes
Steroid vs. Protein Hormones
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Steroid Hormones
Lipids – made from
cholesterol.
They diffuse from blood
into the cell and attach to a
receptor molecule.
Taken into nucleus and
attaches to chromatin at
specific gene location.
Hormone activates gene
and required protein is
made.
Protein Hormones
• Proteins – made of amino
acid chains.
• They attach to receptor
proteins in cell membrane.
• The hormone-receptor
complex produces a
molecule that acts as a
messenger and activates
enzymes within the cell.
See also Section 8.1, Figures 4 & 5
The All-Powerful Pituitary Gland
• Referred to as the “master gland” because it exercises
control over the other glands.
• Connected to the hypothalamus.
• The pituitary makes and stores hormones and the
hypothalamus tells it when to release them using nerve
impulses.
• The pituitary has two lobes – anterior and posterior.
• The posterior lobe stores and releases hormones made by
the hypothalamus.
• The anterior lobe produces and releases its own
hormones.
• See figure 6 on page 376 for examples of the hormones
stored and/or produced by each lobe of the pituitary gland.
FIN
Hormones That Affect
Blood Sugar
Blood Sugar Hormones
 The pancreas has cells that produce digestive
enzymes and those that produce hormones – we
will discuss the hormones.
 Cells in the Islets of Langerhans (special
pancreatic cells) produce insulin and glucagon.
 Insulin is a hormone that allows for the uptake of
glucose by body cells.
 Glucagon is a hormone that promotes the
conversion of glycogen to glucose. (A la Unit 1)
Blood Sugar Too High?
 Pancreas secretes insulin – cells take in
excess glucose from blood.
 Liver also converts excess glucose into
glycogen.
 Glucose levels in the blood drop back to
normal because excess glucose has gone
from blood into cells or has been stored in
the liver as glycogen.
Blood Sugar Too Low?
 Pancreas releases glucagon into the blood
which goes to the liver.
 The liver starts to convert (breakdown) the
glycogen it stores into glucose molecules
which are then released into the blood.
 Insulin and glucagon have opposing actions
in terms of blood sugar management.
Diabetes
 Diabetes is a chronic disease that occurs when the body
cannot produce any insulin, or enough of it, or is unable to
use the insulin in makes properly.
 Three main types:
– Type 1 → occurs when the pancreas is unable to produce insulin
because of degeneration of the cells that make it (onset is usually
in childhood).
– Type 2 → is associated with decreased insulin production or
ineffective use of insulin (onset is usually in adulthood).
– Gestational diabetes occurs in 2-4% of all preganancies and is
associated with a increased risk of diabetes in both mother and
child.
Diabetes
 What could happen???
– After meals, blood sugar spikes (hyperglycemia),
excess glucose exits body in urine and the threat of
dehydration exists.
– After time goes by, cells become starved for glucose
and have to rely on other fuels. This can result in
problems as harmful byproducts of the alternate fuel
pathways.
– If energy levels get too low, organs will be shut down
and failure occurs.
FIN
Hormones That Affect
Metabolism
Glands & Metabolism
• Metabolism is the sum of the chemical reactions
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required to live.
Metabolism (metabolic rate) is affected by the
thyroid gland, parathyroid glands, and anterior
pituitary gland.
The thyroid gland is situated just below the
larynx.
The parathyroid glands sit on the thyroid.
The pituitary gland is situated just below the
hypothalamus.
The Thyroid Gland
• The thyroid is located just below the larynx and it
secretes the hormone thyroxine.
• Thyroxine aids in the oxidation (breakdown) of
sugar and nutrients in the body.
T3 (tri-iodothyronine)
thyroxine
The Thyroid Gland
• People that produce ample amounts of thyroxine
usually can eat a lot of food without gaining any
weight because it is broken down very quickly.
• People that have hypothyroidism are the
opposite…they have low levels of thyroxine and
because of this they do not oxidize nutrients fast
enough and they gain weight quickly.
Controlling the Thyroid
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The thyroid is brought into action by a negative feedback system
which involves the hypothalamus and pituitary gland.
• Low Metabolic Rate…
• Detected by the hypothalamus – it releases thyroidreleasing hormone (TRH) which goes to the
pituitary.
• Pituitary receives TRH and produces thyroidstimulating hormone (TSH) which goes into blood to
get to thyroid gland.
• Upon receiving TSH, the thyroid gland secretes
thyroxine which raises metabolic rate.
The Parathyroid Glands
• The parathyroids are four smaller glands found
within the thyroid gland.
• Their control/action is not under the influence of
the nervous or endocrine systems – the
parathyroids respond directly to changes in their
immediate surroundings.
• The parathyroids produce parathyroid
hormone (PTH) which raises the levels of
calcium in the blood.
Growth Hormone
• Growth hormone (somatotropin) is made and released
by the anterior pituitary.
• Growth hormone:
– causes tissues to increase in number and/or size. In muscles,
the cells increase in size by promoting protein synthesis and
inhibiting protein breakdown. In bones, the cells elongate and
the skeleton lengthens.
– promotes the breakdown of fats into fatty acids which can
actually replace glucose as the primary fuel. Glucose builds up in
the blood – good for the brain – while the fatty acids provide a
ton of energy for growth. (This is why you often see a loss of fat
accompanying a growth spurt.)
• Too much or too little during childhood can result in
dwarfism or gigantism.
FIN