THE HUMAN BODY

1. THE HUMAN BODY The Digestive System

2. THE DIGESTIVE SYSTEM • In order to survive we require many things. Of the many things we need to do to survive, eating and drinking water are arguably the most fundamental and important. It is through food and water that the body gains the many nutrients it requires to function properly. The digestive system is responsible for breaking down the food we eat into tiny pieces that our cells and tissues can use.

3. The Process of Digestion • The first steps of digestion occur within our mouths. First off there is mastication, or chewing, of the food. Chewing allows our teeth to chop and grind our food into small, manageable pieces. Smaller pieces are easier to digest and swallow. • Another function of chewing is to mix our food with our saliva. Saliva contains enzymes which start to break down some of our food and also softens our food to make swallowing easier. • Now once our food has been sufficiently prepared it is sent to thestomach by swallowing.

4. The Esophagus • The esophagus is the tube that connects our mouths to our stomach. A flap of tissue called theepiglottis covers our wind pipe during swallowing to ensure that food does not enter our respiratory system. • The esophagus is a long tube surrounded by specialized muscles that are designed to push food down towards the stomach. • Peristalsis is the name of the muscular contractions that push food through the esophagus. At the end of this tube is a sphincter (muscular door/valve) that allows the food to enter the stomach.

5. The Stomach • The stomach is where the food meets our bodies’ collection of digestive enzymesand gastric juices. Over a few hours these gastric juices and enzymes break the food down into increasingly smaller pieces. • Eventually these pieces are finally ready to serve the body. This broken down food, known as chyme, leaves the stomach via the pylorus and enters the duodenum.

6. The Final Stages of Digestion • The duodenum is simply the first part of our small intestinal tract. • Our smallintestinesare like refineries in that they take the partially digested food and prepare it for use by our bodies. • It is the final stage of digestion where special chemicals from our liver and pancreasmix with partially digested food.

7. The Small Intestine • When the digestion is complete the nutrients required by the body are absorbed into our blood stream through the wall of the smallintestine. • This wall is not smooth but covered in millions of tiny finger like villi that contain blood vessels. It is here that the nutrients are absorbed. Our blood carries these nutrients throughout our body. • In total, it takes about 12 hours for food to pass through the small intestine. Like our esophagus, peristalsisis used to move food through the intestinal tract.

8. Parts of the Small Intestine

9. The Large Intestine and Out • Like our esophagus, peristalsis is used to move food through the intestinal tract. • Any undigested food that still remains enters our large intestines. • The large intestines serve as a “sponge” by removing water from the remaining food. • The dried remains are stored in the rectumuntil the body can expel them through the anus (another sphincter)as feces.

10. Five Stages of Human Nutrition • Ingestion: placing food into the the mouth. • Digestion: breakdown of complex food into their simple absorbable subunits. • Absorption: the passage of the products of digestion into the blood. • Assimilation: conversion of the absorbed nutrients into complex molecules for growth, repair and defence. • Egestion: expulsion of the undigested and unabsorbed material from the digestive system.