The Endocrine System

http://www.brightstorm.com/science/biology/the-human-body/endocrine-system/

Introduction

• The endocrine system is the second part of the message-relaying system of the human body

• It is a system of glands that release chemical messengers into the bloodstream– These messengers are called hormones• These messengers act much more slowly that the

neurotransmitters of the nervous system– They must travel through the blood stream to where they are

needed – They do, however travel throughout the body

Glands of the Endocrine System

Glands of the Endocrine System

• Hypothalamus– A part of the brain that secretes hormones• Tell the pituitary gland to either secrete or stop

secreting• This provides a link between the nervous and

endocrine system

– Also produces hormones that regulate other body processes• These hormones travel to the pituitary for storage until

they are needed

Hormones of the Hypothalamus

• Antidiuretic Hormone– Stimulates the kidneys to conserve water by

producing more concentrated urine• Oxytocin– Stimulates the contractions of childbirth, among

other functions

Pituitary Gland (Master Gland)

• Pea-sized gland attached to the hypothalamus

• Posterior lobe stores hormones from the hypothalamus

• Front lobe secretes pituitary hormones– Most of these control

other glands

Hormone Target Effect

Adrenocorticotropic Hormone(ACTH)

Adrenal Glands Stimulates the cortex of each adrenal gland to secrete its

hormones

Thyroid-stimulating Hormone (TSH)

Thyroid Gland Stimulates the thyroid gland to secrete thyroid hormone

Growth Hormone (GH) Body Cells Stimulates body cells to synthesize proteins and grow

Follicle-Stimulating Hormone (FSH)

Ovaries, Testes Stimulates the ovaries to develop mature eggs; stimulates the testes

to produce sperm

Luteinizing Hormone (LH) Ovaries, Testes Stimulates the ovaries and testes to produce sex hormones

Prolactin (PRL) Mammary glands Stimulates the mammary glands to produce mile

Hormones Produces by the Pituitary Gland

Other Endocrine Glands

• Thyroid Gland – in the neck– Hormones increase the rate of metabolism in cells

throughout the body– Control how quickly cells use energy and make

proteins• Parathyroid gland – located behind the thyroid– Helps keep the level of calcium in the blood within a

narrow range– Stimulates bone cells to dissolve calcium in bone

matrix and release it into the blood

Other Endocrine Glands

• Pineal Gland – located at the base of the brain– Secretes the hormone melatonin which controls sleep-

wake cycles and several other processes• Pancreas – located near the stomach– Produces insulin and glucagon

• They work together to control blood sugar levels• Insulin causes excess blood glucose to be taken up the by

liver and store it as glycogen• Glucagon stimulates the liver to break down glycogen into

glucose and release it back into the blood stream• Also secretes digestive enzymes into the digestive tract

Other Endocrine Glands

• Adrenal Glands – located above the kidneys– Outer portion secretes cortisol which helps the

body deal with stress along with aldosterone which helps regulate mineral balance in the body

– Inner portion secretes the fight-or-flight hormones• Adrenalin – increases the among of oxygen and glucose

going to the muscles• http://www.abpischools.org.uk/page/modules/hormon

es/horm8.cfm?coSiteNavigation_allTopic=1

Other Endocrine Glands

• Gonads – secrete sex hormones– Testes secrete testosterone– Ovaries secrete estrogen• These two hormones are responsible for the changes of

puberty and the control of the production of gametes by the gonads

How do hormones work?

• They affect only certain cells called target cells– These target cells have specific receptors on their

surface that create a matching combination with its hormone• When the hormone binds to the receptor it causes a

change within in the cell• What happens depends upon if the hormone is a

steroid or non-steroid• http://www.wisc-online.com/objects/ViewObject.aspx

?ID=AP13704• http://www.youtube.com/watch?v=HrMi4GikWwQ&#

38;feature=related

Steroid Hormones

• Made of lipids like phospholipids and cholesterol– They are fat soluble so they can diffuse through

the plasma membrane of target cells and bind with the receptors in the cytoplasm

Non-Steroid Hormones

• Made of amino acids– They are not fat soluble so they can’t diffuse

across the plasma membrane– When they bind the trigger enzymes within the

cell membrane the active other molecules

Hormone Regulation

• Typically Controlled by feedback mechanisms– This is a loop in which a product (hormone) feeds

back to control its own production• Most involve negative feedback loops

– Keeps the concentration within a very narrow range

Negative Feedback

http://www.youtube.com/watch?v=CLv3SkF_Eag

Endocrine System Disorders

• Hypersecretion– Too much• Usually caused by a tumor• Too much growth hormone leads to gigantism

• Hyposecretion– Too little• Type I diabetes

Hormone Resistance

• Normal amounts of hormone but target cells do not respond to the hormones– Type II diabetes– Cells don’t take up glucose• Need to follow a specific diet along with medication• Insulin doesn’t work