IB Biology Topic 6
Human Health and Physiology

Introduction – The human body is composed of cells organize into tissues, tissues organized into organs and organs organized into an organ system. This chapter will cover some of the major organ systems of the boy and how those organ systems interact with each other = physiology.

6.1 Digestion
Why do we digest food? – Here is the series of the events in order: ~Ingestion: You eat the food. ~Digestion: A series of chemical reactions, whereby you convert the ingested foot to smaller and smaller molecular forms. ~Absorption: Small molecular forms are absorbed through cells of your digestive system and pass into nearby blood or lymphatic vessels ~Transport: Your circulatory system delivers the small molecular nutrients to your body cells.

Digestion solves a problem of molecular size. – Many of the foods we ingest have very large molecules –to large to pass across any cell membrane. – In order to get into our bloodstream, molecules must pass through the cell membranes of our intestines and then through the cell membrane of the capillary. Therefore any food we eat must be chemically digested to a suitable size. (Page 165)

Digestion allows you to turn molecules into ‘your own’ – Plant cells characteristically store excess carbohydrates in the form of starch whereas animals store excess carbohydrates as glycogen. – Each type of living organism has its own unique set of proteins. – When we digest food molecules we break them down (hydrolyze them) into their smallest components (as in the right-hand column of the table above.) The components then can be reassembled into larger molecules (macromolecules) that are useful to you.

The role of enzymes during digestion – Digestive enzymes are added along the way of our alimentary canal.