The Digestive System continued

The Stomach Located beneath the diaphragm on the left side of your body is the muscle J-shaped organ. Three processes occur in the stomach: Chemical digestion - Glands that line the inner wall of the stomach secrete gastric juices that include; mucus, hydrochloric acid and protein digesting enzymes. Mechanical digestion - The stomach is made up of three muscle layers: longitudinal, circular and angular. The contraction and relaxation of these muscles mixes the food together with the digestive juices. The ingested food is now called chyme. Storage - Undigested materials will stay in the stomach until it is time to pass through the pyloric sphincter and enter the small intestine.

The Small Intestine The name is misleading, because the small intestine is the longest part of the digestive tract. It averages 7 m in length (can be 4.5 to 10.5m), but its diameter is small in comparison to the large intestine. Most of the digestion and absorption occurs in this area. Through rhythmic muscle relaxation and contraction, the undigested chyme mixes with digestive enzymes and further chemical breakdown occurs. The nutrients are now in their simplest form and absorption can take place. The small intestine is divided up into three regions: duodenum, jejunum, and ileum.

The Small Intestine Duodenum - The smallest and widest region of the small intestine. The surface area in this region is increased by the presence of folds. This allows for maximum chemical breakdown and absorption. Jejunum - This region contains more folds and glands than the duodenum. The chemical breakdown of carbohydrates and proteins occurs in this region. Ileum - The longest region of the small intestine contains fewer and smaller villi. Undigested materials are pushed into the large intestine.

Villi Villi are small folds that line the small intestine wall. Each villi is covered with even smaller folds called microvilli. Each villi and microvilli are highly concentrated with blood vessels. Nutrients such as amino acids, glucose, and fatty acids diffuse by active or passive transport into the capillaries.

Villi The blood vessels transport these nutrients to all areas and cells of the body. The illustration on the right shows the finger-like projections of the villi and the network or capillaries within. If you look closely, you can see the tiny cells surrounding each projection. Those tiny cells are the microvilli.

The image above illustrates the relationship between the small intestine, villi, and microvilli.

The Large Intestine The large intestine receives the undigested and unabsorbed materials from the small intestine through the ileocecal sphincter valve. Generally, all the chemical and mechanical breakdown of food has been completed prior to it entering the large intestine. However absorption of water and minerals occurs in this area of the digestive tract. The presence of intestinal bacteria helps to decompose the waste material and they also release vitamin B12, vitamin K, and some amino acids for absorption.

The Large Intestine The large intestine is divided into different sections: ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anus.

Undigested material first collects in a small chamber called the cecum. It then passes through all the sections of the colon as the waste products prepare for elimination. The solid waste is now called feces or stool and is eliminated through the anus. The anal sphincter controls the timing for elimination.

Organs of Digestion 5/student_view0/chapter26/animation__organs_of_ digestion.html 5/student_view0/chapter26/animation__organs_of_ digestion.html

Homework Create a data table that explains the function of each of the following accessory organs: Salivary gland, liver, gall bladder, pancreas and appendix Read P214 – 218 & P222 – 226 Review for tomorrow’s quiz!