Where Does The Food Go? I’m Hungry!

1. Where Does The Food Go? I’m Hungry! "Baby Nick" by Michael Kobre is licensed under CC BY 4.0 “Lecture 2: Digestion, Absorption, Transport PowerPoint" by Dr. Michael Kobre, Achieving the Dream OER Degree Initiative, Tompkins Cortland Community College is licensed under CC BY 4.0

2. Digestion, Absorption, Transport Gastrointestinal (GI) tract: or the digestive tract are the principal organs including the stomach and the intestines. The inner space within the GI tract is called the lumen. This is the space where food consumed travels as it’s processed.

3. GI tract • Consists of a flexible muscular tube that conducts food ingested starting with the mouth, and running through the esophagus, stomach, small intestine, large intestine, and rectum to the anus.

4. Digestion, Absorption, Transport • Digestion: is the body’s way of breaking down foods into nutrients and the preparation for absorption into the intestinal cells ad blood stream. • Absorption: the passage of nutrients from the Gastrointestinal tract into the intestinal cells and either the blood or lymph.

5. GI Tract Anatomy "Digestive system diagram en.svg" is licensed under CC BY 4.0 "Gastrointestinal System" is licensed under CC BY 4.0

6. Digestion in the Mouth • The process of digestion begins in the mouth. • Mastication: Is the chewing action by teeth that crushes food into smaller pieces that mix with fluids in the mouth to ease in the swallowing process.

7. "MouthAnatomy" by Blausen is licensed under CC BY 4.0

8. Chemical Digestion in the Mouth Saliva: the salivary glands secrete saliva into the mouth and begin the chemical digestive process. Because of the short time the food is in the mouth the salivary enzymes contribute little to chemical breakdown of food in the mouth. Some carbohydrate digestion starts in the mouth but most digestion occurs in the small intestine.

9. Digestion • Once the food has been thoroughly chewed and mixed with saliva in the mouth, the food is then swallowed and it passes through the Pharynx, a short conducting tube that is a shared entrance to both the trachea (for breathing) and the Esophagus The Epiglottis closes off the entrance to the trachea, so that food won’t pass into the lungs.

10. Mouth and Pharynx Anatomy "Anatomy of Nose-Pharynx-Mouth-Larynx.jpg" by OpenStax College is licensed under CC BY-NC-ND 4.0

11. Digestion • The food then travels down to the Upper esophageal sphincter (a muscular doorway), consisting of a band of circular muscle which relaxes (opens). The chewed food then passes into the esophagus slides down the esophagus to the lower esophageal sphincter (2nd door), which opens into the stomach.

12. Digestion- Movement of food "PeristalsisN.jpg" by OpenStax College is licensed under CC BY 4.0

13. Digestion • After the mixture of food and saliva enters the stomach, the lower esophageal sphincter closes behind the Food bolus (mixture of food and saliva) to prevent the contents of the stomach which is highly acidic, from refluxing (acid reflux) back into the esophagus.

14. Digestion • Once the food has entered the stomach, the three layers of muscle that surround the stomach begin a contraction and mixing process called peristalsis. this mixes the food bolus with the stomach’s acid and digestive enzymes. This mixing action turns the bolus into a semi-liquid food mass called chyme.

15. Digestion • Once the food chyme is fully mixed. It is slowly moved downward through the stomach where small amounts of the food chyme gets released into the small intestine through the pyloric sphincter. As the food moves through the stomach, it is slowly mixed up and further kneaded causing to mixture to become less solid and more liquid.

16. Digestion • Between the stomach and the top of the small intestine, the semi-liquid food chyme passes by ducts from two accessory organs outside of the GI tract; the Pancreas and the Gallbladder. Both of these ducts conduct juices that mix with the food chyme and are necessary for continued chemical digestion in the small intestine.

17. Digestion- Liver, Gall Bladder, Pancreas accessory organs "Diagram showing the position of the liver and the gallbladder CRUK 351.svg" by Cancer Research UK is licensed under CC BY 4.0

18. Digestion • The food chymecontinues down through the small intestine entering its three segments, the duodenum, the jejunum, and the ileum, almost ten feet of small intestine coiled within the abdomen.

19. Digestion • After finishing its travel through the small intestine, any food chyme that has not yet been absorbed arrives at the ileocecal valve, a muscular doorway leading into the large intestine (colon). Once in the large intestine, water is reabsorbed from the unabsorbed food chyme back into the large intestine’s cell and into the body.

20. Digestion Small intestine – Large intestine conection "Cecum and ileocecal valve.JPG" by Anatomist90 is licensed under CC BY 4.0

21. Digestion • As water is reabsorbed into the cells of the large intestine, the food chyme is transformed into a semisolid waste product. This fecal waste is held back by strong muscular contractions of the rectal and anus sphincters. Once the rectum fills with feces, the muscles relax and feces with pass out of the rectum (defecation).

22. Muscular movement of food during digestion • Peristalsis: is a wavelike series of muscular contractions in the GI tract that push its contents (food bolus/chyme) along it’s length. This action is caused by the contractions of both circular and longitudinal muscles surrounding the GI tract.

23. Muscular Action of Digestion • Stomach Peristalsis: The stomach has the strongest muscles of the GI tract. In addition to circular and longitudinal muscles, the stomach also has an extra layer of diagonal muscle fibers. The stomach’s contractions are the only movements we can actually sense as food moves through the GI tract during processing. (stomach churning)

24. Muscular Action of Digestion • Segmentation: Is the action of periodic squeezing or partitioning of the intestine along it’s length by its circular muscles. The action is very similar to kneading bread by hand and it helps breakup large food particles. • Sphincter muscles: the muscular doorways between the different organs along the GI tract.

25. "Anatomy and physiology of animals Peristalis.jpg" by Sunshineconnelly is licensed under CC BY 4.0 "FG20_04b.jpg" by yundongshenglixue is licensed under CC BY 4.0 "Digestive Process.jpg" by OpenStax College is licensed under CC BY 4.0

26. The Secretions of Digestion • To chemically digest food into small molecules that the body can absorb, five different GI organs produce secretions: • Salivary Glands • Stomach • Pancreas • Liver/Gallbladder • Small intestine

27. The Secretions of Digestion • These secretions enter the GI tract at different locations and bring water and a variety of specific enzymes into the digestive process to chemically digest (break apart bonds in) carbohydrates, Lipids and Protein. This important process prepares nutrients for absorption.

28. Digestive Enzymes • Are proteins molecules (catalysts) produced by the body and found in the digestive juices that act on food substances, causing them to break down (hydrolysis) into simpler, smaller, absorbable compounds. Digestive enzymes are the “chemical knives” of digestion. They break molecules apart by cutting bonds between the atoms of nutrients.

29. Digestive Enzymes Classes • Carbohydrase: a class of enzymes that hydrolyzes (breaks/cuts apart) carbohydrates. • Lipase: a class of enzymes that hydrolyzes lipids. • Protease: a class of enzymes that hydrolyzes proteins.

30. Digestive Glands and their Secretions • Mouth: the Salivary glands secrete saliva into the mouth. the principal enzyme, Salivary Amylase begins carbohydrate digestion in the mouth. This enzyme breaks starch down into simple sugars.

31. Digestive Glands and their Secretions • Stomach: Cells in the stomach wall called gastric cells secrete hydrochloric acid (HCL) at a PH level of around 1.5-2. This highly acidic level prevents bacterial growth and kills most all bacteria that enter the body with food. This low PH would also damage the stomach lining if the stomach didn’t protect itself by secreting a protective mucus layer.

32. Digestive Glands and their Secretions • Goblet cells of the stomach walls synthesize and secrete mucus, a slippery substance that again, protects the cells of the GI tract from exposure to digestive enzymes, juices and acids. The mucus secreted formed a coating in the stomach and GI tract that is called a mucus membrane.

33. Digestive Glands and their Secretions - Stomach Histology of the stomach lining • The cells of the stomach produce acid, mucus, and enzymes that function to: denature protein, chemically digest proteins, and protect the stomach’s lining respectively. "Normal gastric mucosa intermed mag.jpg" by Nephron is licensed under CC BY 4.0

34. Digestive Glands and their Secretions • Liver (gallbladder): The liver synthesizes a substance called bile. Bile is an emulsifier that prepares lipids for digestion and absorption. Bile is stored in the gallbladder and released into the first part of the small intestine when lipids are processed. • Emulsifier: a compound with polar chemical properties that assists in mixing of oils and fats with enzymes in watery solutions. Lipids don’t normally mix with water . without bile, lipids cannot be processed or digested in the GI tract.

35. Digestive Glands and their Secretions • Pancreas: an accessory organ that produces pancreatic juice which contains enzymes for the digestion of carbohydrate, fats, and protein, as well as bicarbonate. The Pancreas sends it’s secretions to the first part of small intestine. • Bicarbonate: is an alkaline secretion that neutralizes the PH of the acidic contents arriving in the small intestine from the stomach.

36. Protective Factors of the GI tract. • Both the small and large intestine, maintain a neutral PH level and allow the growth of bacteria known as intestinal flora. In a healthy person, this bacteria does no harm and actually helps protect the GI tract from infectious harmful invaders. Bacteria in the GI tract also produce small amounts of vitamin K and fatty acids the body uses.

37. Protective Factors of the GI tract. • In addition to the bacteria, the secretions of saliva, mucus, gastric juice, and digestive enzymes also help to protect against disease causing invaders. The GI tract also has many different kinds of immune system cells that help protect against intestinal diseases.

38. Absorption • Most absorption (moving nutrients into the body proper) mainly takes place in the small intestine. Averaging 12 feet in length, the loosely coiled small intestine has an immensely large surface area which allows it to absorb digested nutrients at high volumes within a short period of time.

39. "SmallIntestine Anatomy.png" by BruceBlaus is licensed under CC BY 4.0

40. Absorption • If you could look at the inner surface of the small intestine looks smooth and moist. The lining is contoured with hundreds of folds and thousands of tiny projections. These projections are called villi. If we magnifiy a villi you will see it contains hundreds of cells that have even small projections called Microvilli

41. Absorption • The microvilli are made up of cells that secrete the intestinal juices into the small intestine. The villi constantly sway and catch nutrient molecules that are small enough to be absorbed. The nutrients are then transported into the intestinal cells and then blood and lymph. Nutrient particles that are too big to be transported into the body are further digested at the surface of the villi and microvilli until they are small enough to be absorbed.

42. Small Intestinal Lining "Histology Small IntestinesN.jpg" by OpenStax College is licensed under CC BY 4.0

43. Digestive Transport systems • The intestinal cells and their microvillisynthsize many different types of enzymes and pathways which process and transport the different classes of nutrient molecules.

44. Nutrient Transport systems • The process of absorbing nutrients by the intestinal cells usually occurs by three methods: • Simple diffusion: where water and small lipids cross passively into cells. • Facilitated Diffusion: where large water soluble vitamins use a membrane carrier protein for transport into the cell. • Active transport: where glucose, and amino acids are pumped into the cell using the cell’s energy to transport them against their concentration gradients.

45. Nutrient Transport systems "Scheme facilitated diffusion in cell membrane-en.svg" by Mariana Ruiz Villarreal is licensed under CC BY 4.0

46. Nutrient Transport systems • Interesting Nutrition Myth: People should not eat many nutrient combinations at the same time because our digestive system cannot process more than one type of nutrient at a time is not true! • Ex: Drinking milk or water while eating or fruit and meat together. Research shows some nutrients actually enhance the absorption of others when eaten together.

47. Our Circulatory systems transport nutrients around the body • Our circulatory systems are a closed system of vessels that delivers blood constantly to all cells of the body. As our blood circulates, it picks up and delivers nutrients and waste products to cells so they can maintain their normal functions. All cells in the body have a connection with this system of vessels.

48. Our Circulatory system transports nutrients around the body Major blood vessels Intestinal blood supply "Circulatory System en.svg" by Mariana Ruiz Villarreal is licensed under CC BY 4.0 "Colonic blood supply.svg" by Filip em is licensed under CC BY 4.0

49. The Lymphatic vessel system • Provides passageway for fluid in tissue spaces of the body to return back to blood vessels.. The lymph has no pump to move it’s fluid it relies on the body's muscles to contract and create pressure in the lymphatic vessels for fluid movement back into the blood stream. Large lipids and Fat soluble vitamins use The Lymphatic system for transport out of the digestive system.

50. The Health and Regulation of the GI Tract • Like all of the different organ systems of the body, the principle of homeostasis plays a major role in the functioning of the digestive tract. • The body’s endocrine (hormones) and nervous systems control digestive and absorptive functions in the GI tract.