 1665 Robert Hooke looked at a slice of cork under a compound microscope and discovered the cork was made up of small “boxes” that he named cells  Cells are the Starting Point of life- › All living organisms on Earth are divided in pieces called cells. › Proteins and organelles › Tissues and systems. › Keep an organism alive and successful on Earth. › A main purpose of a cell is to organize. Cells hold a variety of pieces and each cell has a different set of functions. › Growth and development

 The British physiologists William Bayliss ( ) and Ernest Starling ( ) discovered secretin in They used the term "hormone" (from the Greek word horman, meaning "to set in motion") to describe the chemical substance they had discovered that stimulated an organ at a distance from the chemical's site of origin. Their famous experiment using anesthetized dogs demonstrated that dilute hydrochloric acid, mixed with partially digested food, activated a chemical substance in the duodenum (the upper part of the small intestine). This activated substance (secretin) was released into the bloodstream and came into contact with cells of the pancreas. In the pancreas it stimulated secretion of digestive juice into the intestine through the pancreatic duct.

 1914 Edward Kendall isolates thyroxine, the active hormone of the thyroid gland, and shares the 1950 Nobel Prize with Tadeus Reichstein and Philip Hench for discoveries relating to the structure and biological effects of adrenal cortical hormones.  1921 Frederick Banting, Charles Best and John Macleod discover the hormone insulin that leads to the first effective treatment for diabetes. Banting and Macleod win the 1923 Nobel Prize for their research and share their award with colleagues Best and James Collipp.

 Known living things are made up of one or more cells.  All cells arise from pre-existing cells by division.  The cell is the fundamental unit of structure and function in all living organisms.  The activity of an organism depends on the total activity of independent cells.  Energy flow (metabolism and biochemistry) occurs within cells.  Cells contain hereditary information (DNA) which is passed from cell to cell during cell division.  All cells are basically the same in chemical composition in organisms of similar species

 HORMONES! i.e secretin  What are hormones? Hormones are chemical messengers secreted into blood or extracellular fluid by one cell that affect the functioning of other cells. Most hormones circulate in blood, coming into contact with essentially all cells.

 The endocrine system is the interacting group of glands that secrete hormones, helping to control cells and organs throughout the body.  How do cells and organs at different locations in the body communicate with each other to maintain the physiology of healthy living organisms?

 Hormones are "signaling" molecules because they influence the activity of other cells that may be far from where the hormone was produced.  For a hormone to affect a target cell, it must attach to a receptor protein on the target cell membrane or inside the cell. Hormone binding to a receptor triggers an intricate set of biochemical interactions that can affect the target cell in myriad ways.  For example, hormones can influence cell metabolism, cell division, electrical activity, ribonucleic acid (RNA) and protein synthesis, or cell secretion

 The majority of hormones are peptides. These consist of short sequences of amino acids ; examples include insulin and growth hormone.  The class of hormones called steroids are synthesised from cholesterol—examples include male sex steroids such as testosterone and female sex steroids such as estrogen and progesterone.  Hormone production by an endocrine organ is regulated by complex interactions, called feedback loops, between the endocrine organ and its target organs..

 Cells manage to do everything so smoothly in our bodies. They do so by constantly sending and monitoring a stream of messages- a lot of different messages are communicated---- instructions, queries, corrections, requests for assistance, updates, notices of divide or expire. The main means of doing this is through hormones found in the endocrine system.  The discovery of secretin led to the further investigation of the function of hormones in our body which further allowed scientists to discover that they help our bodies function smoothly.