Get BIOLOGY help

Discussions and homework support for your

Biology Class

Digestive System

Digestive System Slide 1 Purpose of the Digestive System Now that we know the types of compounds we need to obtain from our food, let’s look at how we get those compounds out of the food and into our bodies. We will now take a look at the digestive system. The purpose of the digestive system is to breakdown organic compounds like fats, proteins, and carbohydrates into their smallest parts, so that they can be absorbed. We also need to absorb vitamins and minerals. Slide 2 Digestion begins in the Mouth Digestion begins in the mouth. Recall that we said if you chew on a piece of bread or a cracker and letting the bolus of food sit on your tongue for a few minutes you will start to notice a sweet sensation on your tongue. An enzyme in your salvia called salivary amylase begins to breakdown the starch in the bread or cracker. Enzymes are involved in chemical digestion. Salvia also contains substances that kill bacteria and is important in dissolving your food. Mechanical digestion also begins in the mouth. In mechanical digestion large pieces are broken into small pieces. The teeth and tongue are responsible for mechanical digestion. When food items are made smaller there is a greater surface area for the enzymes of the digestive tract to work. Slide 3 Peristalsis Food is swallowed in small clumps called a bolus. The bolus will pass from the mouth to the stomach through a long tube called the esophagus. Food moves through the esophagus by wave like contractions called peristalsis. Peristalsis is similar to the movement of an earthworm. Muscles will pinch the food from behind and push it forward. Slide 4 Cardiac Sphincter Contrary to what you may have been told, very little digestion occurs in the stomach. The stomach acts as a storage organ and allows food to pass slowly into the small intestine. Food enters the stomach from the esophagus through the cardiac or gastroesophogeal sphincter. A sphincter is a circular closure similar to a drawstring on a garbage bag. In some people this sphincter does not close properly. This can lead to heartburn or the more severe acid reflux disease. Acid from the stomach enters the sphincter and burns the esophagus. Slide 5 Protective mechanisms of the stomach The stomach is very acidic. The stomach secretes gastric juice, which contains hydrochloric acid and an inactive form of the enzyme pepsin. The pepsin begins to breakdown proteins into smaller peptides. Little other digestion occurs in the stomach. Since the stomach is very acidic, the cells of the stomach must have mechanisms to protect themselves from damage. Cells in the stomach are constantly being replaced and some cells lining the stomach secrete mucous which acts as a protective barrier against acid. In addition the cells of the stomach contain protein; this is why pepsin is secreted in an inactive form, so that the cells are not damaged. Pepsin does not become acid until it is exposed to the acid of the stomach.
Digestive System Slide 6 What is an Ulcer? Many of you may have heard that ulcers are caused by stomach acid; this is not technically true. We now know that ulcers are caused by bacteria called H.Pylori. These bacteria damages the cells of the stomach that secrete mucous, which leaves areas of the stomach susceptible to the stomach acid. Today ulcers are treated with a regime of antibiotics, which helps the body rid itself of the H. pylori infection. Slide 7 Alcohol absorption The stomach also contracts and aids in mechanical digestion. In addition, a few substances such as alcohol are absorbed directly from the stomach. This is why you become intoxicated more rapidly on an empty stomach compared to a stomach full of food. The presence of food in the stomach slows the absorption of alcohol. Slide 8 Pyloric sphincter At the bottom of the stomach is another sphincter, the pyloric sphincter. This sphincter is much stronger than the cardiac sphincter. The pyloric sphincter regulates the passage of food into the small intestine. Only a small amount of food enters the small intestine at a time. It takes several hours after a meal for the stomach to empty its contents into the small intestine. Food entering the small intestine must be in small amounts, so that the enzymes can effective breakdown the organic compounds into their smaller units, so that they can eventually be absorbed. Slide 9 Accessory organs It is in the small intestine that most of the digestion occurs. The small intestine can be broken into three parts: the duodenum, the ileum, and the jejunum. It is the duodenum that several other accessory organs secrete their enzymes and other substances for the chemical digestion of food. The liver produces a substance called bile, which is stored in the gallbladder. Bile is necessary for the digestion of fat. Recall that fats do not dissolve in water and food is mostly water. Bile is needed to keep fats from sticking together in large clumps that would not be able to be digested. The pancreas secretes several enzymes into the small intestine; these enzymes breakdown proteins, fats, and carbohydrates. The pancreas also secretes bicarbonate, which neutralizes the acid in the food that just came from the stomach. The small intestine itself also produces several enzymes to breakdown food.
Digestive System Slide 10 Villi and microvilli After your food has been broken down into its smallest parts or monomers, these small particles are absorbed in the small intestine. The small intestine is very long and is covered on the inside by small finger like projections called villi. These villi are covered by smaller finger like projection called microvilli. The villi and microvilli increase the surface area of the small intestine. The greater surface area increases the amount of nutrients that are absorbed by the body. Inside of the villi are small lymph vessels called lacteals and small blood vessels called capillaries. Food components, such as amino acids, that are able to dissolve in water are absorbed directly into the blood. Fat soluble substances, such as fatty acids, are absorbed into the lacteals. The villi are specially designed and are only one cell in thickness. They also contain absorptive cells that aid in the absorption of nutrients. It is through the blood or lymph systems that foods you eat enter your body. Eventually the lymph system connects to the blood, and it is through the blood that the nutrients in your food reach your cells. Slide 11 End products of digestion At the time your food is absorbed, you have broken down carbohydrates into monosaccharides, proteins into amino acids, fats into glycerol and fatty acids, and nucleic acids into nucleotides. Recall that the breakdown of the polymers into monomers occurs through the process of hydrolysis. Slide 12 Large intestine What about substance like cellulose that are not broken down and absorbed by the body? These substances continue through the digestive system to the large intestine. The large intestine absorbs water and salt. At the end of the large intestine, substances that can not be digested are excreted out of the body through the anus. The image on this slide presents a review of the digestive system. Slide 13 Digestive System Review YouTube Video Digestive System Slide 14 Check Your Understanding Now that we have learned about the digestive system, let’s check your knowledge of the subject. The following slides will have a series of questions on the topic. Be sure to click “Submit” after answering each question. Slides 15 through 30 Interactive Digestive System Quiz A nongraded assessment of your knowledge of the digestive system. Slide 31 Summary This slide is a summary of all of the “Check Your Understanding” questions from this lecture. Be sure to review the questions you answered incorrectly.
Digestive System Slide 32 Review of unit 2 We have now reached the end of unit 2. In this unit we have covered the basics of chemistry, studied organic molecules, as well as explored the digestive system.

Psychology Homework

Stuck with a homework question?  Find quick answer to Accounting homeworks

Ask Psychology Tutors

Need help understanding a concept? Ask our Accounting tutors

Psychology Exams

Get access to our databanks of Discussion questions and Exam questions

How We Safeguard Your Tutor Quality

All tutors are required to have relevant training and expertise in their specific fields before they are hired.  Only qualified and experienced tutors can join our team 

All tutors must pass our lengthy tests and complete intensive interview and selection process before they are accepted in our team


Prior to assisting our clients, tutors must complete comprehensive trainings and seminars to ensure they can adequately perform their functions

Interested in becoming a tutor with Online Class Ready?

Share your knowledge and make money doing it

1. Be your own boss

2. Work from home

3. Set your own schedule