Endocrine System

Overview: Purpose, Basic Structures

Endocrine System

What is the function of the endocrine system?

• To coordinate body functions by facilitating communication between cells in response to environmental and cellular signals.

Purpose?• Control development and growth (childhood and

adolescence)• Regulates blood pressure, heart rate• Responds to danger, stress• Regulates metabolism• Helps fight infection• Control human reproduction

What’s a “gland”?• Group of cells that manufacture secretions• 2 types of glandular secretions

• Exocrine – deposited into body cavities, surface of skin through ducts

• Endocrine – sent directly into bloodstream

• Coordinate body functions

How do they do this?• Intracellular communication• Endocrine glands: respond to signals from the

environment, other cells• Signals vary…

• Environmental (gases, gravity, nutrients, sunlight, temp)

• Cellular (hormones) originate inside the body

Important to note…• Almost any organ can produce endocrine

secretions• Endocrine system composed of 10 endocrine

glands

Endocrine glands

Endocrine glands a.k.a. “ductless glands”

• Secretions enter blood directly through capillaries• Don’t direct secretions to any particular part of the body… • Yet not every cell of the body responds to these

secretions…

How does a cell know if it is supposed to respond?

• Receptors!• Special surface molecules (often proteins) that permit cell

to detect various types of stimuli

• Cells with receptors sensitive to endocrine secretions are called target cells

Target cells• Genetically programmed to modify their

metabolism when they detect a specific endocrine secretion.

• So…Only target cells will respond to the particular secretion

Review: Answer these questions1. What glands comprise the endocrine system?

What do they produce?2. Once endocrine secretions are released, where

are they deposited? How does this differ from exocrine secretions?

3. Endocrine secretions are what type of signals?

Hormone Function

Guiding Questions1. What is the function of a ligand? 2. How do hormones work?3. What is an effector?4. What is the function of carrier proteins?

What is the function of a ligand?• Ligand: general name for a group of chemicals

that attach to receptors.• Hormones are a type of ligand

• For a ligand to propagate a chemical change, it must have the proper shape to fit into the receptor• When bound to the receptor it causes many chemical

reactions within the cell.

How do hormones work?• Hormones are released from a gland.

They bind to a receptor either on the inside or the outside of the target cell depending on the location of the receptor.• Activates one of several chemical reactions

in the cell.

• Receptors that are on the surface of the cell = surface receptor

• Receptors that are located within the cell = internal receptors

What is an effector?• The target cell—the cell a hormone attaches to

initiate a biological change

What is the function of carrier proteins?To bring hormones that use internal receptors to the

target cellOR

Once inside the cell, to bring hormones to the receptor

Endocrine secretions

Guiding Questions1. How are endocrine glands different from exocrine glands?2. How do endocrine secretions “know” where to go once

they’re secreted?3. How are autocrine secretions different from paracrine

secretions?4. Do endocrine secretions usually target cells that are close

to the point of origin of the secretion or far from it?5. What type of feedback loop does the endocrine system

“use” to control the body? Give an example of one.

How are endocrine glands different from exocrine glands?

• Exocrine: secretions are deposited into body cavities or onto the surface of the skin via ducts

• Endocrine: secretions are sent directly to the bloodstream

How do endocrine secretions “know” where to go once they’re secreted?

• Secretions travel to every part of the body, but only target cells (cells with the correct receptor for the secretion) react.

How are autocrine secretions different from paracrine secretions?

• Autocrine: interact with the cells that created it. Cells control their own activity. They do not travel in the blood

• Paracrine: secretions travel short distances to target cells.• Most important function: coordinate cells within an organ.

• Pheromones: leave the body and signal the cells of other organisms.

Do endocrine secretions usually target cells that are close to the point of origin of the secretion or far from it?

• Both—it depends on the function of the secretion.

What type of feedback loop does the endocrine system “use” to control the body? Give an example of one.

• Negative feedback loop• A signal that inhibits an endocrine gland by preventing

further secretion of a particular hormone.• Similar to temperature control in a building

Negative feedback continued• Animation• Thyroxine

Types of hormones

What do hormones do, again?• Signals a cell to alter its metabolism… but must

be programmed to do so• Hormones can be many things…

• Agonists – chemicals that act as hormones (phytoestrogens from food that act like certain hormones)

• Antagonists – chemicals that block the actions of hormones• A.k.a. mimics/hormone disruptors

Guiding Questions1. What is the function of a hormone?2. What is an agonist? What is its function?3. What is an antagonist? What is its function?4. What are the two types of hormones? What are

their functions?

2 types of hormones: • Peptide – biological molecule made of amino acid

chains• Lipid – made from existing lipids in body, taken in

through diet• Body converts cholesterol to a particular hormone• Can be interconverted, too

Peptide hormones• 1 many amino acids (polypeptide)• Effects usually rapid• Often involved in immediate changes in

metabolism, but some permanent• Ex. Growth hormone

• Bind to surface receptors• Broken down by enzymes to prevent accumulation in

blood

• Some taken in, where they bind to internal receptors

Lipid hormones• Fluid regulation, sexual reproduction• 2 types:

• Hormone-like lipids• Single chain of fatty acids (ex. prostaglandins, a signaling hormone)

• Steroids• More complex• Specific signaling

• Not water soluble; carried via carrier molecules• Can move across cell membrane easily, interacting w/ DNA• Broken down by enzymes to prevent accumulation• Can cause metabolic problems, cancer if levels too high

Two kinds of lipid hormones:Hormone-like Lipids: single chain of fatty acid

• Prostaglandins• Produced by any cell• Immune system control and blood pressure regulation

Steroids: made from cholesterol molecules

The endocrine glands

Guiding Questions Part 11. How many distinct endocrine glands are there?2. Which gland is the “master gland?”3. Describe the anatomy, and the location, of the

pituitary gland.4. What are releasers and how do they function?5. How is the posterior pituitary controlled?6. Where is the pineal gland located, and what

hormones does it produce?

Guiding Questions, Part 27. Describe the anatomy of the adrenal gland and name its parts.8. Describe the location and the function of the adrenal gland. 9. Where is the thyroid located? How does it control metabolic

rate?10. Is the pancreas an endocrine gland and/or an exocrine gland? 11. Describe the cellular organization of the pancreas. What cells

are responsible for the endocrine role of the pancreas? What endocrine secretions do these cells produce, and what is the purpose of those secretions?

12. Where is the pancreas located?

Guiding Questions, Part 3!13.Where is the thymus gland? What does it secrete?

What does the thymus gland control?14.What are gonads? What do they do?15. Identify the female gonads, their location, and

what they produce.16. Identify the male gonads, their location, and what

they produce.17.Describe the function of testosterone, estrogen,

and progesterone.

The Endocrine Glands – Pituitary and Pineal

The pituitary gland is known as the master endocrine gland because its numerous hormones control most of the other endocrine glands and is intimately linked to the overall coordination of the body’s organ systems.

The pineal gland is responsible for producing melatonin and serotonin.

The Endocrine Glands - Adrenal

The adrenal glands are made up of an outer cortex and an inner medulla.

The adrenal cortex produces corticosteroids and androgens. The adrenal medulla produces adrenaline and noradrenaline.

The Endocrine Glands – Thyroid and Parathyroid

The thyroid gland helps control the metabolic rate.

The parathyroid gland increases calcium levels in the blood.

The Endocrine Glands – Pancreas and Thymus

pancreas

The pancreas produces hormones and digestive enzymes.

The thymus gland produces secretions that stimulate the immune system.

The Endocrine Glands - Gonads

Gonad: An organ of the reproductive system

Testis: The male gonad; produces sperm and testosterone

Ovary: The female gonad; produces eggs, estrogen, and progesterone

Wellness and illness over the life span

Guiding QuestionsEndocrine: Pathology of the Endocrine System1. How would one know if the endocrine system is affected by disease?Endocrine: Aging of the Endocrine System1. What happens to hormones as a person ages?2. What can people do to counteract the effects of an aging endocrine system?

How would one know if the endocrine system is affected by disease?

• Disorders result from the overproduction or underproduction of one or more hormones.

• Not always a simple answer• A decrease in hormone production might be due to an

inability to detect signals, lack of signals, diminished blood flow to the gland, or diseased endocrine cells, or tumors.

Diabetes insipidus & diabetes mellitus

Description Effects

Diabetes insipidus

Inadequate production of antidiuretic hormone, caused by a malfunction of the posterior pituitary gland

Produces extreme water loss resulting in frequent urination. The person has to drink a lot of water to prevent dehydration and to fight the constant feeling of thirst.

Diabetes mellitus

Type I: Caused by decreased insulin productionType II: Body’s inability to detect insulin signalsCan be caused by viral infections, high carbohydrate diets, and obesity

Results in high blood sugar and other disorders due to abnormal glucose levels. Glycosylation –extra sugars stick to tissues and the immune system destroys them. Can lead to blindness, blood vessel destruction, and kidney failure

Graves Disease• Inflammation of thyroid gland due to elevated

thyroid hormone production (hyperthyroidism)• Caused by an autoimmune disease.• Results:

• Elevated metabolic rate• Feelings of nervousness or tension• Feeling tired throughout the day

Hypothyroidism• Thyroid gland doesn’t produce enough thyroxine

• Children: genetic defect• Adults: thyroid or pituitary gland malfunction

• Results • Children: mental retardation and short stature• Adults: lethargy, weight gain, dry hair and skin, sensitivity

to cold

What happens to hormones as a person ages?

• 13 weeks of development• Sex hormones assist in the formation of sex

characteristics

• Puberty• Sex hormones at highest levels

• Adults• Taper off after age 30 in men and age 40 in women

What happens to hormones as a person ages?

• Children• Growth hormone, insulin, and thyroxine are important in growth.• Thymus starts out very small and grows until a person reaches

puberty, then it becomes smaller & less active as a person ages.• Highly sensitive to small amts of chemicals that act like sex

hormones• Causes defects in genitalia (males) and causes females to

enter puberty sooner, may be more susceptible to breast cancer.

• If blood vessels are defective and prevent blood flow to a certain body part then that part may not reach normal size and function

When a person ages…• Decrease in size of endocrine glands and decrease

in hormone production• can be accelerated in people with cardiovascular

problems and diabetes

• Diminished blood flow through capillaries• Reduce atmospheric gases, hormones and nutrients

needed for hormone production

• Uptake of nutrients• Each gland ages individually

What can people do to counteract the effects of an aging endocrine system?

• HRT-hormone replacement therapy• Estrogen=most common• Natural (phytoestrogens) or prescrriptions• Many physicians believe its difficult to regulate hormone

levels using oral supplements.