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Endocrine System Study Guide
Regulation- The process by which living things are able to respond to their environment
Nervous System vs. Endocrine System
The Nervous System is fast acting, has short lived effects, send electrochemical messages
through impulses, in which the message travels along neurons and neurotransmitters, in which
messages travel across the synapse
The Endocrine system is slow-acting, has longer lasting effects, messages are chemical,
in the form of hormones, and travel in the blood
The Endocrine System
Is made of a series of glands that secrete hormones into the bloodstream
How are endocrine glands different from exocrine?
o Exocrine secretions are secreted into an organ or cavity
o Endocrine secretions go into the bloodstream
What are two examples of exocrine glands discussed in the Fall?
o Pituitary Gland
o Pancreas
Hormones are the chemical messengers of the endocrine system
Hormones affect the rate of metabolic activity in a specific (target) body tissue
Hormones attach to receptors on/in target cells and either activate or repress protein
synthesis and activate enzymes already present in the cytoplasm
Hormone secretion works through feedback mechanisms, positive and negative feedback,
negative feedback stops producing a certain hormone because it would be harmful to
have it in your system for too long, an example is when you are dehydrated, and ADH is
produced to cause some water reabsorption if you then decide to drink a quart of water,
the ADH production will stop because you have already replenished your water supply
and if it is produced more disastrous effects could occur, it will cause, positive feedback
is much rarer, and is when the hormone continues to get produced until the desired result
is achieved, an example is childbirth, hormones cause the uterus to contract, until the end
result, which is the birth of the baby to occur
Four Classes of Hormones
Peptide Hormones- usually short chains of amino acids but can include polypeptides and
protein hormones, though their amino acid chains are generally short as well examples are
insulin and thyroxin
Amino Acid Derivatives- Hormones derived from a single amino acid chain, an example
is epinephrine, which is formed on another amino acid derivative, tyrosine
Steroids- complex rings of carbon carbon and hydrogen atoms, steroids are lipid based, as
they are synthesized from cholesterol, and have a structure similar to cholesterol, they are
secreted from the ovaries, placenta, testes, and adrenal cortex
Prostaglandins- Made of two fatty acid carbon chains attached to a five carbon ring, and
are considered a special type of hormone because they are made by every cell in the body,
instead of specialized glands, act locally, prostaglandins are not really “hormones” as they exert
their effects on nearby cells instead of being carried by the bloodstream but are considered
because they have effects similar to hormones and act in conjugation with those of the endocrine
If hormones affect the Rate of Metabolic activities, what must they Effect in the Target Cells?
 Hormones can cause the activation or inhibit the activity of an enzyme already present in
the cell
 Hormones can cause enzymes to be produced or not produced, in this instance, the
hormones must interact with the DNA of the cell
 Hormones can cause an enzyme to continue performing its task until the end result is
achieved (Positive Feedback) and hormones can stop the enzyme while it is performing
its task because an overabundance would be produced (Negative Feedback)
Two Modes of Enzyme Action
One messenger model
o Lipid hormones are able to diffuse through the cell membrane and bind to
receptors located in the cytoplasm of the cell
o Lipid soluble hormones target the cytoplasmic receptors which readily diffuse
into the nucleus and act on DNA, inhibiting or stimulating the production of
certain proteins
Two messenger model
o Peptide based hormones are unable to diffuse through the plasma membrane
o The first message is the binding of the hormone to the membrane receptor
o The second messenger within the cell translates the outer message and carries out
its function within the cell
o Peptide hormones must bind with cell-surface receptors which activates a
chemical pathway that involves a second messenger, which is often the chemical
cAMP (cyclic adenosine monophosphate)
(AMP, ADP and ATP are nucleotides, made of a phosphate, sugar and nitrogenous base)
1. The binding of the hormone on the receptor site of the cell membrane activates a second
membrane protein (referred to as G-protein/GTP)
2. The activated G-protein in turn, activates the membrane enzyme, adenylate cyclase, suing
the energy from a GTP molecule
3. Adenylate cyclase then catalyzes the production of cAMP from ATP
o The cAMP then activates specific enzymes within the cell and thus initiates the
hormone’s specific action
A hormone’s effect depends on the type of receptor and the secondary messenger present
o Same receptors but different intracellular proteins
The Hypothalamus
The hypothalamus is a region of the brain that can receive nerve impulses from the brain
and scan the chemical composition of the blood
The hypothalamus is the connection between the nervous and endocrine systems
The hypothalamus sends chemical signals to the pituitary gland
One region of the hypothalamus secretes hormones called releasing hormones called
releasing factors that controls the secretions of the anterior pituitary gland
One region of the hypothalamus secretes and stores peptide hormones via the secretions
of the posterior pituitary gland
The Pituitary Gland
Called the master gland
Controls the other glands of the endocrine system
Hormones of the Pituitary Gland
1. Thyroid Stimulating Hormone-TSH, stimulates cells of the thyroid to release thyroxin
2. Growth Hormone-GH, controls growth by causing bones to increase in size, also causes
cells to reproduce at a quicker rate
3. Follicle-Stimulating Hormone- FSH - Stimulates the production of eggs in the ovaries of
females and sperm in males
4. Luteinizing Hormone- LH - Controls the production of sex hormone in males and
females, and controls the release of eggs in females
5. Prolactin- Stimulates milk production and breast development in females
6. Adrenocorticotropic Hormone- ACTH - Stimulates production and release of steroid
hormones from adrenal cortex; used in treatments of arthritis, asthma, and allergies
7. Epinorphins- block pain senses by binding to receptors on the brain
8. Oxytocin Hormone- produced by the hypothalamus and secreted by the posterior
pituitary, causes attraction, stimulates of smooth muscles of uterus during childbirth,
maternal behaviors, and sperm ejaculation in males
9. Antidiuretic hormone- (ADH/vasopressin) produced by hypothalamus secreted by
posterior pituitary, causes the nephrons of the kidney to excrete less water in the urine as
they are more permeable to water reabsorption
Thyroid Gland
Located in the pharynx just below the larynx and in front of the trachea
o The thyroid gland releases thyroxin
 Thyroxin controls metabolism in the cells of the body
 Thyroxin contains iron
 Thyroxin regulates the rate of fat, protein and carbohydrate metabolism as
well as cellular respiration
o The thyroid gland also produces calcitonin
 Calcitonin prevents excessive rise in blood calcium
Dynamic Equilibrium
Ability of the body to keep the chemical composition of the blood within a limited range
o Example: Blood Sugar levels
Negative Feedback- process by which blood chemistry remains in equilibrium
In negative feedback, a substance causes a response to occur in the body
This response then shuts off the original signal
Once this signal is shut off, the response decreases, causing the signal to be released
Parathyroid Glands
Produce parathormone and are located in the thyroid
Parathormone controls the metabolism of calcium which is necessary for growth, health
of bones and teeth
Blood Clotting- nerve functions + muscle contraction
Adrenal Glands
Found over the kidneys
o 2 glands in one, adrenal medulla and adrenal cortex
Adrenal Medulla
Center of gland and are controlled by the nervous system
Adrenaline (epinephrine)- stimulates the elevation of blood-glucose concentration, and
stimulates “fight or flight” reactions
Noradrenaline (norepinephrine)- Stimulates reactions similar to those produced by
adrenaline, but causes more vasoconstriction and is less effective in the conversion of
glycogen to glucose
Adrenal Cortex
Glucocorticoids (corticosterone, cortisol, cortisone etc.)- Stimulate formation of
carbohydrate from protein, thus elevating glycogen stores and helps maintain normal
blood sugar levels
o Stimulated to be released by ACTH from anterior pituitary gland
Mineralocorticoids (aldosterone, deoxycorticosterone, etc- Stimulate kidney tubules to
reabsorb more water and less sodium
Cortical sex hormones- (testosterone)- stimulates the development of secondary sexual
characteristics especially those of the male
Other Glands
Thymus- secretes thymosin, which stimulates the production of T lymphocytes
 Located on center of chest
Pineal Gland- secretes melatonin “biological clock”
 Located in the brain
Kidney- secretes erythropoietin which increases RBC production
 Renin- renin leads to the production of angiotensin which raises blood pressure by
constricting arterioles
Fat cells- Secrete leptin
Gonads- Reproductive glands
Testes- Male Gonads
o Testosterone- male hormone
 Stimulates the development of secondary sex characteristics in males
(deeper voice, body hair, sperm production, muscle development and
growth spurts)
 Also helps to regulate the development of sperm
Ovaries- Female gonads
o Produces two hormones
 Estrogen- responsible for the secondary sex characteristics in females
(breast development, menstruation, broadening of hips, body hair)
 Progesterone- helps to regulate the menstrual cycle
The Pancreas
Endocrine cell clusters are referred to islet cells or islets or langerhans
Each islet has a good blood supply and within a cluster of these cells, there are two cell
types, alpha and beta cells
Alpha cells secrete glucagon; beta cells secrete insulin
Both are involved in the regulation of metabolism but have opposing effects
Hormones of the pancreas control blood sugar levels
o Insulin is released by the pancreas and attaches to the cells of the muscles and
 Insulin causes these cells to take sugar out of the blood
o Glucagon- target cells are in the liver
 Causes the liver to release glucose in the blood
~Tasdid Khandaker