© 2009 The McGraw-Hill Companies, Inc. All rights reserved The Endocrine System.

© 2009 The McGraw-Hill Companies, Inc. All rights reserved

The Endocrine SystemThe Endocrine System

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How are the endocrine and nervous systems similar? The Endocrine System and the Nervous

System are two communication systems for sending information to and from the brain

They operate differently of course

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Introduction The endocrine system includes the organs of the body that

secrete hormones directly into body fluids such as blood Regulates chemical reaction in cells and therefore control

functions of the organs, tissues, and other cells

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target tissues

Glandssecrete

hormones

into

bloodstream

to

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What are hormones? Chemicals secreted by a cell that affect the functions of other cells How do they affect behavior? Hormones affect the growth of bodily structures (muscles and

bones), affecting what you can do physically They affect metabolic processes, influencing the amount of

energy you have Certain hormones cause the differences between boys and girls Other hormones prepare the body for action during stress Hormones also act in the brain to directly influence moods and

drives

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Hormones work like neurotransmitters in that they have a special molecular structure that match the structure of a receptor

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Hypothalamus Controls the pituitary gland It monitors the amount of hormones in the

blood Sends out messages to correct hormonal

imbalances

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Controlled by the hypothalamus Located at the base of the brain How does the pituitary gland act as the “Master

Gland?” It secretes a large number of hormones, many of

which control the output of hormones by other endocrine glands – it’s the boss of other glands

Secretes the growth hormone - GH

Pituitary Gland

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Thyroid Gland Located below the larynx (voice box) Controls how fast your body uses energy with

controls your weight…metabolism Secretes the hormone thyroxine which

controls the rate at which your body burns and uses energy

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Thyroid Gland What happens if there’s too much or too

little thyroxine? Hypothyroidism – too little; become tired Hyperthyroidism – too much; overactive,

lose weight and sleep

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ExtraParathyroid Glands

Four located on the posterior surface of the thyroid gland

Secrete parathyroid hormone (PTH) It’s responsible for bone growth and for

regulating the calcium level in body

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Adrenal Glands Located on top of each kidney Becomes active when angry or scared Secretes the hormones… Epinephrine (adrenaline) Norepinephrine (noradrenaline) Same effects as sympathetic nervous system

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Adrenal Glands

epinephrine (adrenaline) increases blood pressure, breathing rate and energy level

norepinephrine (nonadrenaline) causes the heartbeat and breathing to increase; raises blood pressure

Both generate the extra energy needed to handle a difficult situation Both can heighten emotions such as fear and anxiety Norepinephrine sends out a chemical that will clot blood faster just

in case we get cut Glands also secrete cortical steroids – help muscles develop and

cause the liver to release stored sugar when the body requires extra energy for emergencies

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ExtraOther Hormone-Producing Organs Pineal gland

Small gland Located between

cerebral hemispheres Melatonin

Regulates circadian rhythms

May play a role in onset of puberty

Thymus gland Located between

lungs Thymosin

Helps with immunity

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Pancreas Located behind the stomach Both exocrine gland and endocrine

gland Exocrine – secretes digestive

enzymes into a duct leading to the small intestine

Endocrine – secretes hormones into bloodstream

Regulates the metabolism of sugar Secretes insulin which lowers

blood sugar (used to treat Type 1 Diabetes

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The Gonads The Ovaries Reproduction in females Secrete estrogen and progesterone Their levels vary…PMS Responsible for female sex characteristics

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The Gonads Testes Testosterone important in physical development of male In prenatal period, it helps decide the sex of a fetus In adolescence, it’s important for growth of muscle and

bone along with the growth of male sex characteristics

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Hormone versus a Neurotransmitter When a chemical is used as a

neurotransmitter, it is released right beside the cell that it is to excite or inhibit

When a chemical is used as a hormone, it is released into the blood, which diffuses it throughout the body

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