The Endocrine System Communication 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