THE ENDOCRINE SYSTEM: HORMONES

The Endocrine System is basically a communicating system for the body. Multicellular organisms need to communicate from cell to cell to maintain homeostasis. Hormones are used in regulation. The other regualting and communicating system is the nervous system. Cells interect with each other through neurons. An electrical signal is released by ions flowing through a membrane. Neurons have fast, short-lasting responses. Hormones have slow, long-lasting responses. Hormones are chemical mesesengers that are released in one part of the body and affect another part of the body. Hormones have long term effects such as in

• metabolism
• growth
• development
• maturation
• reproduction

Hormones are released by ductless glands. Ductless glands are tissies that produce hormones and release the hormones directly into the bloodstream. Duct glands like the pancreas produce the enzyme and release them into another area through tubes like how the pancreas releases into the intestine. Hormones are specific to the target cell. Another theme is seen here, the lock and key mehtod. The hormone fits into the receotor proteins that the hormone attaches to specifically only to ones that have the shape that can fit with the hormone.

There are 2 major types of hormones:

1. Protein-based Hormones

These hormones are made of proteins including polypeptides suc as insulin and ADH (anti diuretic hormone). Glycoproteins are toher protein hormones that have proteins and carbohydrates. These include FSH (Follicle stimulating hormone) and LH( luteinizing hormone). Amines are another type which are modified by amino acids like epinephrine and melatonin. Protein based hormones are hydrophillic and are not lipid soluble. That means they can't diffuse across a membrane. The protein hormone has to bind to receptors on top of the plasma membrane that are embedded in the membrane. The homrone fits into the protein in the membrane and causes a conformational change. The protein that receives the hormone stimulus changes chape which causes another protein at the other end to carry the message along. This secondary messenger pathway is triggered. Enzyme action, uptake or secretion of molecules is activated.

2. Lipid-based Hormone

These hormone include steroids which are modifed cholesterol such as sex hormones and aldosterone. Lipid based hormones are hydrophobic which means they are lipid soluble. They can diffuse right through the cell membrane without being stopped at the cell membrane and having to go through a receptor on the membrane. These hormones bind to receptor proteins in the cytoplasm and some on the nucleus. Lipid hormones bind to DNA as transcription factors. The hormone causes a conformational change. The transcription factor is the protein on the DNa that coordinates which genes should be transcripted onto the mRNA to make a protein. Lipid hormones are carried on a protein carrier because they are not soluble in water since oil and water don't mix. The hormone can cause a major long term change in the body such as growth. The growth factors can affect hair, bone, muscle and gametes.

Oh Yeah Tuesday night's sherpa will be Shannah.