The Endocrine System

The Endocrine SystemCommunication throughout the body

What is the endocrine System? • It is one of the 2 regulatory systems

in the human body• It is made up of endocrine glands

that secrete chemical messengers called hormones

• Hormones travel through the blood allowing communication through all parts of the body

Jobs of the Endocrine System• Regulation of metabolism and tissue

maturation• Regulation of ion concentrations in

the blood• Maintaining water balance• Helps control production of immune

cells• Helps control heart rate and blood

pressure

. . . Still more!• Controls blood glucose and other

nutrients• Controls reproductive functions• Regulates uterine contractions and

milk production

What is an endocrine gland?• They are ductless organs that secrete their

hormones directly into the blood• Hormones cause a response in other cells, called

target cells, but only if the other cells have receptors.

Are there different types of hormones?• Yes!• There are two major categories:• Steroid hormones (lipid soluble)• Protein or peptide hormones (water soluble)

Steroid Hormones• Can pass through the cell membrane• Have receptor molecules inside the

cell• Usually take a longer period of time

to act• Can be reproductive hormones• Can be taken orally because they will

pass through the stomach walls

Protein Hormones• Cannot cross the cell membranes• Need receptor molecules on the

outside of target cells• Usually act very quickly• Cannot be taken orally because they

cannot pass through the stomach wall and will be digested

• A small amount can have a very big affect due to signal amplification

How do Steroid Hormones Work?• 1. They pass through the cell membrane• 2. They bind a receptor in the cytoplasm of a

target cell• 3. The receptor/Hormone complex enters the

nucleus• 4. Gene expression is started and new gene

products are formed

How do Protein hormones work?• 1. The water-soluble hormone binds a receptor

on the outside of the cell membrane• 2. A G protein activates an enzyme (adenylate

cyclase)• 3. This causes a series of intracellular changes

that can amplify the original signal• 4. Intracellular changes result in a change in

productivity, enzyme activation, gene expression, cell shape, or cell motion

How are Hormones controlled?• The Pituitary gland is the “master gland” that

controls the endocrine system• The pituitary gland is controlled by its close

neighbor, the hypothalamus (part of the nervous system)

Two types of feedback:Negative:• Used to maintain

values in a normal range

• Maintains homeostasis• Ex: Insulin and

glucagon keep blood glucose levels constant

Positive:• Used to break

homeostasis• Levels of hormones

cause more hormone to be produced.

• Ex: Oxytocin in child birth causes stronger and stronger contractions