Digestion From food to poo Crash Course VIDEO: Pieces of food Chemical digestion (enzymatic hydrolysis) Food Nutrient molecules enter body cells Small molecules Undigested material ELIMINATION ABSORPTION DIGESTION INGESTION Mechanical digestion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB Learning Objective Explain why digestion of large food molecules is essential

The Need for Digestion Two reasons for the digestion of food: 1.Change food into useable forms: – Food that humans eat contain substances made by other organisms. Manu of which are not suitable for human tissue. – Thus the must be broken down and changed into useful forms – Example: Proteıns  amıno acıds  dıfferent proteıns

The Need for Digestion Two reasons for the digestion of food: 2.Food molecules may be too big to be absorbed: – Food molecules are absorb by the villi in our small intestines. – Thus food molecules must be broken down into small enough molecules that they can be absorbed by: Simple diffusion, facilitated diffusion or active transport.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase

Three types of food molecules that must be digested 1.Starch 2.Proteins 3.Triglycerides (Fats and Oils)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes of digestion AmylaseProteaseLipase Example of enzyme Salivary Amylase PepsinPancreatic Lipase SourceSalivary glands Wall of stomachPancreas SubstrateStarchProteinsTriglyerides (fats and oils) ProductsMaltoseSmall PeptidesFatty Acid and glycerol Optimum pH pH 7pH 1.5pH 7

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IB Learning Objective Explain the need for enzymes in digestions

Enzymes essential to digestion of food molecules Digestions of food molecules will happen naturally at body temperature BUT very slowly Thus, ENZYMES are essential to speed up the process.

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IB Learning Objective Outline the reasons for cellulose not being digested in the alimentary canal.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summary of digestion Some molecules cannot be digested (example: Cellulose) The enzyme cellulase digest cellulose, but humans lack the gene that codes for this enzyme. Undigested cellulose is an important part of dietary fibre, which has beneficial effects on the digestive system.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE Draw and Label a diagram of the digestive system. This diagram should include the following structures and clearly show the interconnections between these structures: – Mouth – Esophagus – Stomach – Small intestines – Large intestines – Anus – Liver, – Pancreas – Gall bladder

Parts of the Digestive System Mouth Salivary glands Stomach Pancreas Large intestine Small intestine Pharynx Esophagus Liver Gallbladder Rectum

Sequence of digestion – Food is digested as it passes along the alimentary canal from mouth to anus. – Food enters mouth, moves into the esophagus, the stomach, next small intestine, then large intestine, and finally anus.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video Of Digestions hill.com/sites/ /student_view0/chapter2 6/animation__organs_of_digestion.htmlhttp://highered.mcgraw- hill.com/sites/ /student_view0/chapter2 6/animation__organs_of_digestion.html FUNNY VIDEO:

Summary of digestion Longitudinal and circular muscle fibers along the walls of the alimentary canal contract and relax squeezing the food and breaking up large solid lumps. Digestive juices release by salivary glands, stomach and pancreas contain enzymes which help break food molecules

LE 41-15b Esophagus Stomach Liver Salivary glands Gall- bladder Pancreas Rectum Anus Large intestines Small intestines Mouth A schematic diagram of the human digestive system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE Outline the function of the stomach

The Stomach Summary The Stomach Food from the esophagus empties into the stomach. The stomach continues mechanical and chemical digestion. Alternating contractions of three smooth muscle layers churn food.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stomach

Function of Stomach Summary – Mechanical Digestion The stomach contracts to churn fluids and food, gradually producing a mixture known as chyme. After 1–2 hours, the pyloric valve between the stomach and small intestine opens and chyme flows into the small intestine.

The Stomach Summary – Chemical Digestion The stomach lining has millions of gastric glands that release substances into the stomach. – Some glands produce mucus, which lubricates and protects the stomach wall. – Other glands produce hydrochloric acid, which makes the stomach contents very acidic. – Other glands produce pepsin, an enzyme that digests protein.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Interior surface of stomach

Function of Stomach Before food reaches the stomach, gastric juices are being secreted, as a result of a involuntary reflex action. When food enters the stomach more gastric juices are released.

Function of Stomach When food enters the stomach a hormone gastrin is released. Gastrin signals for the stomach to increase the amount of hydrochloric acid (HCl) in the stomach The pH of the stomach is about 3 (very acidic) when food enters

Function of Stomach Bacteria which could cause food poisoning, are most killed by acid conditions.

Enzymes released by stomach. Enzyme released by stomach is pepsin. Pepsin functions has an optimum pH of 1.5 (very acid). Pepsin digests proteins.

Pepsin vs. Pepsinogen Since pepsin digests proteins, it could be harmful to the cell of the glands that secrete them. They are therefore secreted as an inactive pre- cursors called Pepsinogen. Pepsinogen is an inactive form of pepsin. Pepsinogen becomes pepsin when it is released in the hydrochloric acid (HCl) of the stomach

Structure of stomach LE Esophagus Cardiac orifice Pyloric sphincter Small intestine Folds of epithelial tissue Stomach Epithelium Pepsin (active enzyme) Pepsinogen HCl Pepsinogen and HCl are secreted into the lumen of the stomach. HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Parietal cellChief cell Chief cells Mucus cells Parietal cells Interior surface of stomach Gastric gland 5 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE Outline the function of the small intestine

Function of the Small Intestine The small intestine is the longest section of the alimentary canal It is the major organ of digestion and absorption

LE Stomach Pancreas Liver Gall- bladder Duodenum of small intestine Intestinal juice Bile Acid chyme Pancreatic juice

The Small Intestine As chyme from the stomach is pushed through the pyloric valve, it enters the duodenum. The duodenum is the first of three parts of the small intestine, and is where most digestive enzymes enter the intestine.

The Small Intestine Accessory Structures of Digestion Liver Gallbladder Duodenum Bile duct Pancreas Pancreatic duct To rest of small intestine

The Small Intestine – Accessory Structures of Digestion Just behind the stomach is the pancreas.

The Small Intestine During digestion, the pancreas: produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes of the Pancreas Amylase – completes breakdown of starches into maltose Protease – completes the breakdown of small polypeptides (proteins) to amino acids Lipase – converts fat to glycerol and fatty acids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pancreas Pancreas also produces sodium bicarbonate, a base that neutralizes stomach acid so that these enzymes can be effective. Sodium bicarbonate is released into the duodenum of the small intestine right after chyme enters it from the stomach.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LIVER Assisting the pancreas is the liver, which produces bile. Bile dissolves and disperses droplets of fat in fatty foods. This process is called emulsification Emulsification increases surface area of lipid droplets This enables enzymes (lipase) to break down smaller fat molecules.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Liver – Bile -- Digestion of Lipids Bile is stored in the gallbladder. – and released into the small intestines. – Lipid molecules tend to bond together and are only accessible to lipase (enzyme) at the lipid–water interface/ boundary.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parts of the small intestines

Absorption in the Small Intestine The small intestine is adapted for the absorption of nutrients. Most absorption occurs in the ileum of the small intestine

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE Explain the structure of the villus is related to its role in absorption and transport of products of digestions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption in the ileum of the Small Intestine The folded surfaces of the ileum are covered with fingerlike projections called villi.

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The Small Intestine Absorption in the Small Intestine

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Relationship between structure of villus and its function Villi increase surface area over view food is absorbed An epithelium consists of only one layer of cells, which is all that food have to pass through in order to be absorbed Protrusions of exposed plasma memebrance of the epithelium called microvilli, increase surface area for absorption.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Small Intestine Absorption in the Small Intestine

Cell surfaces of villi have more projections called microvilli. These provide an enormous surface area for the absorption of nutrient molecules. Slow, wavelike contractions of smooth muscles move the chyme along this surface. Relationship between structure of villus and its function

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Relationship between structure of villus and its function Protein channels and pumps in microvilli allow for rapid absorption of food by facilitated diffusion and active transport A lot of mitochondria in epithelium cell need for ATP in active transport.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Relationship between structure of villus and its function Blood capillaries inside villus are very close to epithelium so the distance for diffusion of food is very small. A lacteal (lymph vessel) in the centre of villus carries fat away after digestion.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Relationship between structure of villus and its function There are many pinocytic vesicles near the microvilli. Pinocytic vesicles are formed by endocytosis Each vesicles are formed from plasma membrane and so contain both: – Protein channels for facilitated diffusion – Protein pumps for active transport Digested food can be absorbed from vesicles into the cytoplasm of cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Small Intestine

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ileum of the small intestines

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings IB LEARNING OBJECTIVE Outline the function of the large intestine

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Large Intestine

The Large Intestine When the chyme leaves the small intestine, it enters the large intestine, or colon. The large intestine removes water from the chyme. Water is absorbed quickly, leaving undigested materials behind. Concentrated waste material passes through the rectum and is eliminated from the body.

The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins