1. What does endo- mean?2. What is a hormone?3. What does the word negative mean?4. What does the word diffusion mean?5. What is mitosis?6. What is an enzyme?7. What does a mRNA molecule do?

Bell Work

The Endocrine System

The ductless gland system

A variety of organs that help coordinate and direct cellular activity by using hormones.

A hormone is chemical substance that are secreted by cells into the extracellular fluids and regulate the metabolic activity of other cells in the body.

Because hormones are being used and they have to diffuse, the results of the endocrine system are much slower than the nervous system.

What is the endocrine system?

Steroids – hormones that are made from cholesterol that includes the sex hormones and adrenal cortex hormones

Amino acid-based molecules – nonsteroidal hormones that are derived from amino acids, which have a amino group (-NH2)and a carboxyl group (-COOH). They include proteins, peptides, and amines

Prostaglandins – made from highly active lipids found in the cells’ plasma membranes

Hormone Classifications

Reproduction Growth and development Mobilizing body defenses against stressors Maintaining electrolyte, water, and nutrient

balance of the blood Regulating cellular metabolism and energy

balance.

The major processes of hormones

Hormones only affect certain cells or organs that are called target cells or target organs.

They affect the target by altering its cellular activity

Facts of hormones

Change the permeability or electrical state of the cell membrane

Cause the synthesis of proteins or certain regulatory molecules

Activate or inactivate enzymes Stimulate mitosis

Typically, it will…

How do hormones work?

Mechanisms of Hormone Action

The hormone1. Diffuses through the membrane of the

target cell2. Then it enters the nucleus3. It binds to a specific receptor protein there4. Hormone-receptor complex then binds to

specific sites on the cell’s DNA5. This activates certain genes to transcribe

mRNA molecules6. mRNA is translated in the cytoplasm, which

results in the synthesis of a new protein

Lipid-soluble Mechanism Steps (used by steroids and thyroid hormones)

These are unable to enter the cell so, they must bind to receptors on the target cell’s plasma membrane and utilize a second-messenger system

Nonsteroidal hormones

The hormone binds to the membrane receptor

This sets off a series of reactions that activates an enzyme

The enzyme catalyzes a reaction that produces a second messenger molecule (Examples: cyclic adenine monophosphate or cAMP, G proteins, calcium ions)

These molecules start making the changes inside the cell that produce the desired effect.

Steps in this mechanism

Negative feedback – a stimulus triggers the release of hormones, but the presence of the hormone inhibits further release of more hormones

Types of stimulus◦ Hormonal – endocrine organs are stimulated by

other hormones◦ Humoral – endocrine organs are stimulated by

changing blood levels of certain ions and nutrients

◦ Neural - endocrine organs are stimulated by nerve fibers

So, what prompts the endocrine glands to release hormones?

Figure 9.2 from page 302