THE ENDOCRINE SYSTEM

Mr. Wright 2011

Chapter 11:

IntroductionSection 11.1

The Endocrine System

The body has two systems designed for communication:The Nervous SystemThe Endocrine System

Allows the body to change to different situations.

The Endocrine System

Made up of glands. Glands secrete hormones. Hormones enter the bloodstream and

are carried to specific target cells.

Local Hormones

Some hormones never enter the bloodstream… they stay in the same area and are called local hormones.Paracrine – affect neighboring cellsAutocrine – affect the secreting cells

themselves.

Exocrine Glands

Exocrine glands secrete things outside the body.Example: Sweat

General Characteristics

Section 11.2

Comparing Nervous & Endocrine

Nervous System Endocrine System

Involved in communication.

Releases neurotransmitters into synapses.

Very precise. Very brief.

Involved in communication.

Releases hormones into bloodstream

Very precise. Can be brief or very long.

Things the Endocrine System Controls… The endocrine system regulates many

metabolic processes.Rates of chemical reactions.Transport across membranes.Regulate water and electrolyte balances.ReproductionDevelopmentGrowth

Glands of the Endocrine System

Hormone ActionSection 11.3

Hormones

There are 3 main types of hormones:SteroidsNonsteroidsProstalandins

Steroid Hormones

Steroid hormones are made or rings of carbon and hydrogen atoms.

They are insoluble in water, but are soluble in lipids (fats) like cell membranes. Thus, they can enter and exit cells easily.

Nonsteroid Hormones

Nonsteroid hormones cannot enter cells. Instead, they combine with receptors in

the cell membrane.

Prostaglandins

Prostaglandins are special lipids synthesized from fatty acids in the cell membrane.

Produced in the liver, kidneys, heart, lungs, brain, and several endocrine glands.

Prostaglandins

Produce many diverse effects.Relax/Contract smooth (involuntary)

muscles.Stop production of stomach acid.Influence movements of salt and water in

the kidney.Regulates blood pressure.Stimulates other hormones.

Control of Hormonal Secretions

Section 11.4

Hormonal Secretions

As hormone levels increase in the blood, hormone secretion decreases.The more there is, the less we need.The opposite of this statement is true as

well.

Hormonal Secretions

Hormonal secretion is controlled by negative feedback.Negative feedback – the mechanism is

controlled by an imbalance that corrects it.

Examples of Negative Feedback

The hypothalamus stimulates the pituitary gland to secrete hormones.

The pituitary gland secrets hormones which stimulate the ovaries to secrete hormones needed for puberty.

If the ovary hormone levels in the blood are too high, the hypothalamus stops stimulation.

Examples of Negative Feedback

When blood sugar levels are high, the pancreas secretes insulin.

Blood sugar levels decrease.

Once blood sugar levels are low enough, pancreas stops secreting insulin.

Conclusion

As a result of negative feedback, hormone levels in the blood remain relatively stable, with only slight changes.

The Pituitary GlandSection 11.5

Structure The pituitary gland is

found hanging beneath the brain.

Very small. Attached to the brain

by a small stalk called the infundibulum.

2 halves:AnteriorPosterior

Function

Controlled mostly by the brain. Releasing hormones – hormones the

brain (hypothalamus) secretes to signal the pituitary to release its hormones.

Each releasing hormone acts on a specific part of the pituitary.

Hormones - Anterior

Human Growth Hormone (HGH)Stimulates cells to increase in size and

divide more frequently.HGH is released when there are low protein

or sugar levels in the blood.Disorders:

Hormones - Anterior

Prolactin (PRL)Pro- = with, for-lactin = milkStimulates milk production

in females.PRL is found in males.

○ Excess PRL in males decreases the amount of male sex hormones.

Hormones - Anterior

Thyroid-Stimulating Hormone (TSH)Controls the secretion of hormones by the

thyroid.

Adrenocorticotropic Hormone (ACTH)Controls the secretion of hormones by the

adrenal gland.

Hormones - Anterior

Follicle-Stimulating Hormone (FSH)Stimulates the gonads.Gonads – reproductive organs

○ Testes in males○ Ovaries in females

Remember what follicles are?

Hormones - Posterior

Antidiuretic Hormone (ADH)Decreases urine formation.Does this by lowering the amount of water

secreted by the kidneys.Stimulated by fluid levels in the body.

Hormones - Posterior Oxytocin (OT)

Stimulates uterine contractions during childbirth.

Contracts smooth muscles in the uterus.

Stimulated by stretching of uterine and vaginal tissues.

Thyroid GlandSection 11.6

Structure

Consists of two lobes connected by the isthmus.

Just below the larynx and in front of the trachea.

Thyroid Hormones

Thyroxine (T4)Regulates the metabolism of sugars, lipids,

and proteins.Determines how many calories you need to

consume to live.

Thyroid Hormones

Triiodothyronine (T3)Same function as Thyroxine, though this is 5

times more potent.Both are stimulated by iodine levels in the

body.This iodine comes from food.

Thyroid Hormones

CalcitoninIncreases calcium and phosphate

concentrations in the blood.Does this by regulating

osteoclast/osteoblast activity and the kidneys.

Thyroid Problems

CretinismCaused by not having enough thyroid

activity (hypothyroidism).Symptoms:

○ Stunted Growth○ Abnormal Bones○ Mental Retardation○ Sluggishness

Thyroid Problems

GoitersToo much thyroid activity (hyperthyroidism)

leads to a swelling of the tissues behind it.This causes a large bulge in the neck called

a goiter.

Parathyroid GlandsSection 11.7

Structure

You have four. They are very small. Found on the posterior thyroid. Covered in CT.

Parathyroid Hormone

Parathyroid Hormone (PTH)Increases blood calcium levels

and decreases blood phosphate levels.

Similar to calcitonin.

Adrenal GlandsSection 11.8

Structure

Located superior to the kidneys… sits on top of them like a cap.

Made up primarily of epithelial cells and blood vessels.

2 parts:Adrenal medulla – centerAdrenal cortex - outsides

Hormones – Adrenal Medulla Epinephrine and Norepinephrine

Similar in structure and function.Epinephrine is actually made from

norepinephrine.Several effects:

○ Increases heart rate.○ Elevates blood pressure.○ Increases blood sugar.○ Addictive

ADRENALINE!!!

Disorders - Adrenaline

People who have too much adrenaline produced will suffer from high blood pressure, high blood sugar levels, increased heart rate, etc… hypertension.

Disorders - Adrenaline

Those who do not have enough adrenaline produced may be lackadaisacal and/or unexcitable – hypotension.

Hormones – Adrenal Cortex Aldosterone

Helps regulate the concentration of minerals. (Na and K)

Does this by increasing water retention.

Hormones – Adrenal Cortex Cortisol

Increases glucose levels in the blood.

Very similar to T3 and T4.

Hormones – Adrenal Cortex The adrenal cortex also produces some

sex hormones. This is not the primary source of these

hormones, however, so we will talk about them more once we get to the gonads next week.

The PancreasSection 11.9

Structure

Long, flattened organ behind the stomach.

Connected to the small intestine by a small duct.

Structure

Has two functions:Digestive (Will discuss later)Endocrine

The endocrine cells are arranged into special groups called islets of Langerhans.Alpha cellsBeta cells

Hormones - Pancreas

GlucagonRaises blood sugar concentration.

○ More effective than epinephrin/norepinephrinReleased by alpha cells.

Hormones - Pancreas

InsulinLowers blood sugar concentration.Direct opposite to glucagon.Released by beta cells.Often released after eating.

Disorder - Diabetes

Caused by an insulin deficiency. Blood sugar levels rise. The kidneys will excrete excess sugars

into urine, which also causes more water to be added.Leads to dehydration and extreme thirst.

Disorder - Diabetes

Insulin also helps glucose move into cells, which means this isn’t happening anymore.

Cells will break down proteins instead, causing tissues to disappear and leading to weight loss.

Type 1 Diabetes

Autoimmune disease – the body’s immune system destroys its own beta cells.

Also called juvenile diabetes. Treated via insulin injections.

Type 2 Diabetes Develops in people over age 40. Milder symptoms. Generally seen in overweight people. Beta cells work, but body cells lose sensitivity

to insulin so injections don’t work. Treated via diet changes, exercise, etc.

Other Endocrine Glands

Section 11.10

The Pineal Gland

Small structure located deep between the cerebral hemispheres.

Hormones – Pineal Gland

MelatoninReleased in response of light amounts

outside of the body.○ More is released in the dark.

Responsible for your “biological clock”○ Circadian rhythm○ Determines daily sleep cycle, but also puberty

and menstrual cycle.

Thymus Gland

Found posterior to the sternum, in between the lungs.

Large in children but shrinks with age.

Hormones - Thymus

ThymosinsProduce white blood cells.Also determines the type of each white

blood cell.Will discuss more when we get to immune

system.

Reproductive Glands

Include the ovaries, placenta, and testes.

Will be discussed in much more detail when we get to that chapter.

Hormones - Gonads

FemalesEstrogenProgesterone

MalesTestosterone

Will discuss in more detail later.

Stress and HealthSection 11.11

Stress

When the body senses danger, it triggers physiological responses designed to take care of it.Includes an increase in certain hormones.

This condition is called stress. Anything that causes it is called a

stressor.

Types of Stress

Physical – temperature, oxygen levels, infection, injury, etc.

Psychological – thoughts, feelings, sense of loss, unpleasant social interactions

Doesn’t have to be a negative thing, either. Can be friendly contact, feelings of joy, sexual arousal, etc.

Responses to Stress

Controlled by the hypothalamus of the brain.“Fight or Flight”

Things your body does:Raise blood sugar levelsIncrease heart rate, blood pressure,

breathing rateExcess blood to musclesIncreases epinephrine levels

Stress Drawbacks

These reactions can cause:High blood pressureUlcer formationLower WBC count/increased risk of

infection.