Anatomy and Function of the Digestive System Partnership for Environmental Education and Rural Health Texas A&M University peer.tamu.edu

Nutrition versus Digestion Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed. Recall the definition of nutrition. Using these definitions, describe the relationship between nutrition and digestion and then share your answer with a neighbor. Nutrition is the process by which an animal takes in and utilizes food substances through various chemical reactions and physiological processes. Therefore digestion is the method or process through which animals obtain nutrition.

The Digestive System How many structures of the digestive system can you name? Images - http://www.bcvet.net/diagnostics.php, http://www.dog-nutrition-naturally.com/nutrition-facts.html Mouth, teeth, tongue, esophagus, stomach, small intestine, pancreas, liver, large intestine, cecum, colon, rectum

Functions Digestion - breaking down food by mechanical and enzymatic action in the stomach and intestines into substances that can be used by the body. Absorption Protection from microorganisms & noxious substances Remove undigested material & waste Immunological function Metabolism Endocrine functions

Types of Digestion Mechanical Digestion- the physical break down of food into smaller pieces without changing its chemical structure. Increases the surface area of food particles Chemical Digestion- food is chemically broken down; its chemical structure is changed. Enzymes and acids Can you think of places where this might happen? Answer: mechanical - teeth grinding, tongue turning, muscles in esophagus, stomach, and intestines squeezing. chemical – stomach, small intestine, pancreas, liver - acid and enzymes

Break It Down What types of digestion are occurring in the following images? Puppy – mechanical by chewing and chemical with saliva Stomach – mechanical by churning and chemical with acid and enzymes

Digestion Begins Prehensile organs (lips, tongue) Mouth Move food to the mouth Mouth Taste – accept or reject food Mechanical digestion – mastication (chewing) Mix digesta (food) with saliva

Saliva Lubricates food with mucoproteins Initiates enzymatic digestion Salivary amylase – breaks down carbohydrates Salivary lipase – breaks down lipids Buffers stomach – prevents pH from rapidly changing Salivary glands

Esophagus Muscular tube from pharynx to stomach Peristalic (wave-like) contractions propel food down to stomach Made of striated and smooth muscle Ruminants have striated muscle throughout in order to regurgitate food.

Simple Stomach Muscular bag that mixes food by peristalic contractions & holds for gradual release to small intestine Digests proteins Denatures (breaks apart) with hydrochloric acid Enzymatic digestion with pepsin Produces mucus to protect from acids pH of stomach is about 2 With out mucus develop ulcers Absorption of alcohol and volatile fatty acids

Photo from: http://www.rivm.nl/interspeciesinfo/intra/human/stomach/ Cardia region – produces mucus Body region – produces mucus enzymes and hydrochloric acid

Ruminants What makes the ruminant stomach unique? Identify the ruminant animals from the following images. The ruminant stomach has 4 compartments: the reticulum, rumen, omasum, and abomasum Ram and cow are ruminants

Ruminant Stomach Occupies nearly ¾ of the abdominal cavity 4 chambers Reticulum – formation of bolus (cud) and regurgitation Rumen - microbial digestion of feed and production of volatile fatty acids Omasum – water and inorganic mineral absorption Abomasum – “true stomach”, secretes acids and enzymes The function of the omasum is poorly understood and this is currently the most popular theory on its function The abomasum must process large quantities of bacteria and so secretes lysozyme which breaks down bacterial cell walls.

Pictures from: http://www. wisconsincentral http://www.mhhe.com/cgi-bin/netgrader.pl

Review Break #1: What are the functions of the digestive system? Give an example of the two types of digestion that occur in the digestive system. What is the function of saliva? How does food move down the esophagus? Which part of the ruminant stomach is most like a simple stomach? Why?

Folds Upon Folds What organ do you think is shown here? What might be the purpose of the villi? Pictures from: http://imageshack.us/photo/my-images/42/picture7v.jpg/ Small intestine villi Villi contain extensive circulatory and lymphatic system components to transport nutrients following absorption Microvilli are the microscopic projections from the cells of the villi

Small Intestine Primary site for enzymatic digestion and nutrient absorption Divided into 3 regions: Duodenum – most digestive enzymes enter here Jejunum Ileum Folded and lined with villi and microvilli – increases the surface area (therefore absorption efficiency) 600 fold

Pancreas, Liver and Gallbladder Pancreas – adds enzymes and buffers to the duodenum Enzymes digest starches, fats, and proteins Produces insulin and glucagon Liver – produces bile Emulsifies large fat globules into a suspension of fine droplets for enhanced digestion Gallbladder – stores bile Horses have no gallbladder, bile is secreted directly into the stomach Buffers keep the pH of the small intestine around 5 – 7; if the pH is too low digestability decreases Insulin regulates glucose metabolism and glucagon opposes insulin Fine droplets of fat are soluble in aqueous solutions

click here for more information on the liver and pancreas

Why is the term “large” used to describe the large intestine? Image from http://www.edenwellness.org/articles/colonsewer.html Although the large intestine is much shorter than the small intestine its diameter is much greater.

Cecum The start of the large intestine Large in herbivores Contains bacteria that aid in the enzymatic digestion of cellulose cecum

Large Intestine Composed of the cecum, colon, and rectum Bulks up and stores material Absorbs water, volatile fatty acids, and some minerals Site of microbial digestion Digestion of cellulose producing volatile fatty acids – particularly important in non-ruminants Synthesis of vitamin K and certain B vitamins Animals cells do not produce the enzyme cellulase and so are unable to digest cellulose (a major component of plants) on their own. Bacteria in the large intestine produce cellulase allowing herbivores to gain energy from plant material. The horse has a significant bacterial population in its large intestine (hindgut) providing as much as 60-75% of its nutrient requirements from hindgut fermentation (if fed high amounts of fiber).

Review Break #2: Where does the majority of digestion and absorption of nutrients occur? What are the functions of the liver, pancreas, and gallbladder? What are villi and what is their purpose? Why is the large intestine so important to non-ruminants?

Fun Digestive Facts: The domesticated dog’s digestive system is similar to a human's; except, the dog's intestinal tract is shorter, due to the amount of protein dogs consume. Cows produce about 100 liters of saliva a day, humans produce about 1.5 Sheep and goats produce gas at the rate of 5 liters per hour

Summarize it! Take time to summarize the structure and function of the digestive system. With a partner, go through each organ of the digestive system and tell its location and function. Be sure to say whether mechanical, chemical, or both types of digestion occur there. Use the diagram in your notes or your flow chart to help!

References Digestive Physiology of Herbivores Applied Animal Nutrition Feeding the Endurance Horse