Download the endocrine system

THE ENDOCRINE SYSTEM
This is a communication system that uses chemicals called hormones to send messages to specific
areas of the body.
It is important to understand the difference between a secretion and a hormone. A secretion is
something that a gland releases into the blood stream and a hormone is a secretion! It is a
chemical messenger that travels to and reacts only with a targeted area of the body.
With that in mind, the organs that are affected by their particular hormones are the targets and
they contain cells called target cells that react with the hormone.
Hormones have the ability to increase or decrease metabolic processes of the target cells, thereby
altering an activity in the body.
They are classified as either :
-steroids/ enter the nucleus of the target cells and affect the way they function
-proteins/ attach themselves to the surface of the target cells and affect the way they function
HORMONE RELEASE
this is determined by a bodily process called negative feedback.
This means that when levels are unbalanced the body recognizes this and hormones are released
to balance this back again. Remember homeostasis.
Think of this process like a thermostat. It is set to maintain a balance in temperature. When it
goes over or under the set temperature, it cuts in or out to get the temperature back to the
correct setting. This is what the Endocrine system does.
An example in the body would be after eating a meal high in sugar, the islets of langerhans (cells
in the pancreas) secrete insulin into the blood to bring glucose levels back to normal.
In a diabetic, either the pancreas is not producing insulin, or is not recognising the insulin once it
is produced.
The brain controls the balance of hormones.
EXOCRINE GLANDS
They are glands that secrete their products into ducts, which either open on to a surface, like
sweat glands, or empty into an organ or space, like saliva.
ENDOCRINE GLANDS
They are glands that secrete their products straight into the blood stream. They do not have ducts.
GLANDS OF THE ENDOCRINE SYSTEM
1.Hypothalamus
-also part of the nervous system
-regulates the pituitary gland
-situated in the centre of the brain
2.Pituitary gland
-also called the Master Gland
-located at the base of the brain
-has 2 lobes
-stimulates other endocrine glands to release their hormones
3.Pineal gland
-located in the centre of the brain
secretes the hormone melatonin
4.Thyroid gland
-located just below the larynx
-has 2 lobes one on either side of the trachea
-looks like a butterfly
-secretes thyroxine and calcitonin
5. Parathyroid glands
-four tiny glands embedded in the posterior wall of the thyroid gland
-secretes parathyroid hormone(PTH)
6.Thymus gland
-located in the upper thorax behind the sternum
-role is to mature the immune system
-secretes thymosin which develops T cells
7.Pancreas
-also part of the digestive tract
-secretes hormones from tiny cells called islets of langerhans
-secretes insulin and glucagon
8. Adrenal gland
-two small glands situated on top of the kidneys
9. Gonads
-sex glands
-in the female they are the ovaries and in the male they are the testes
-their hormones are needed to develop sexual characteristics and egg and sperm production
-the hormones are oestrogen, progesterone and testosterone
In your role as a Phlebotomist, you will perform many tests that are requested by the Doctor
relating to the Endocrine system.
Here are a few, with an explanation of what they do. Try and think about WHY THESE MIGHT BE
ORDERED.
1.Growth hormone(GH)
-stimulates the growth of bone and soft tissue, stimulates the synthesis of glucose during times of
fasting
2.Prolactin
-stimulates the breast to develop and produce milk
3.thyroid stimulating hormone(TSH)
-stimulates the thyroid gland to produce thyroid hormones,T3 and T4
4.Adrenocoticotropic hormone(ACTH)
-stimulates the adrenal gland to secrete hormones, especially cortisol
5.Gonadotropic hormones
-follicle stimulating hormone(FSH),stimulates the ova and sperm
-luteinising hormone(LH),causes ovulation in females and stimulates the secretion of progesterone
in females and testosterone in males
6.Antidiuretic hormone(ADH)
-stimulates water reabsorption by the kidney, also constricts blood vessels
7.Oxytocin
-contracts uterine muscle during labour and releases milk from the mammary glands
8.Thyroid hormones (T3 and T4)
-T3=Triiodothyronine and thyroxine
-T4=tetraiodothyronine
-they control the metabolic rate and regulate growth and development
9.calcitonin
-decrease plasma levels of calcium by increasing excretion of calcium by the kidneys
10.Parathyroid hormone(PTH)
-increases plasma calcium which increases reabsorption from the kidneys and increasing calcium
absorption from the diet
11.Epinephrine(adrenaline) and norepinephrine
-stimulates the fight or flight response, increases blood glucose
12.cortisol
-helps regulate glucose, fat and protein metabolism, raises blood glucose and is part of the stress
response
13.Aldosterone
-causes the kidneys to reabsorb sodium and water and to excrete potassium, helps regulate fluid
and electrolyte balance
14.Testosterone
-helps develop secondary sex characteristics
-aids in production of sperm
15.Insulin
-secreted by the islets of langerhans in the pancreas
-helps regulate metabolism of carbohydrates, proteins and fats, lowers blood glucose
16.Glucogon
-secreted by islets of langerhans in the pancreas
-raises blood glucose
17.Oestrogen and progesterone
-secreted by the ovaries
-stimulates the development of ova and development of secondary sex characteristics in the
female
18.Thymosins
-stimulates the maturation of T lymphocytes
19.Melatonin
-secreted by pineal gland and helps set biorhythms
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