Digestive System Notes

1. Digestive System Notes January 27, 2016 *Record Notes in your Body Systems Booklet*

2. Digestive System • Functions: • Breaks down food into molecules the body can use. • Molecules are absorbed into the blood & carried throughout the body (by the circulatory system). • Wastes are eliminated from the body (by the excretory system) BrainPop Video – Digestive System

3. Roles of Organs • Mouth – mechanical & chemical digestion starts here • Mechanical – physically breaking down food (teeth) • Chemical – breakdown of molecules of food (saliva) • Esophagus – muscular tube connecting the mouth to the stomach • Peristalsis (muscle contraction) moves the food

4. Roles of Organs • Stomach • Most mechanical digestion takes place • Some chemical with the help of digestive juices (enzymes & acids) • Small Intestine • Most of the chemical digestion takes place • Absorption of nutrients from digested food into the bloodstream

5. Roles of Organs • Large Intestine • Water is absorbed into the bloodstream • Remaining material is readied for elimination from the body • Rectum • Waste material is compressed into solid form

6. Process of digestion (simplified) • 1. Ingestion: The MOUTH Food enters the gastrointestinal tract through the mouth. • 2. Digestion: A) MOUTH – both physical (mechanical) and chemical digestion begins here v Physical - Two main structures involved: teeth and tongue • i) TEETH - four types (normal adult has 32 teeth on average)

7. Digestion • ii) TONGUE - both tongue and teeth help to physically break apart food • Chemical digestion: using ENZYMES to break up food In the mouth, • SALIVARY glands produce SALIVA which contains the enzyme AMYLASE which acts on starch, breaking it into maltose. • BOLUS: the resulting ball of food in the mouth made by the actions of the teeth, tongue, and saliva • PERISTALSIS: the rhythmic muscular contractions that push digested food in one direction through the gastrointestinal tract The bolus is swallowed and travels down the esophagus into the stomach. It moves down the esophagus by peristalsis.

8. Digestion • B. STOMACH: physical and chemical digestion • The bolus passes through the CARDIAC SPHINCTER, the top opening in the stomach. • Sphincter: a muscle that controls the opening • i) cardiac: esophagus & stomach ii) pyloric: stomach and duodenum v • Physical: the stomach is a muscular storage organ that churns the food • Chemical: GASTRIC juice mixes with bolus - stomach contents now called CHYME • GASTRIC juice contains: a) HCl – hydrochloric acid b) pepsin – enzyme that breaks down PROTEIN • HCl: - helps breakdown fibrous tissue - kills bacteria - helps pepsin work properly (ph = 2 optimal pH for pepsin) • PEPSIN: - enzyme begins to break down PROTEIN into smaller polypeptides • MUCUS: - also made by stomach to protect itself from STRONG ACID • Chymestays in stomach until adequate protein digestion has occurred. This is why you feel less hungry between meals if you have eaten some protein. The chyme is kept in the stomach by the pyloric sphincter.

9. Digestion • Chemical: GASTRIC juice mixes with bolus - stomach contents now called CHYME • GASTRIC juice contains: a) HCl – hydrochloric acid b) pepsin – enzyme that breaks down PROTEIN • HCl: - helps breakdown fibrous tissue - kills bacteria - helps pepsin work properly (ph = 2 optimal pH for pepsin) • PEPSIN: - enzyme begins to break down PROTEIN into smaller polypeptides • MUCUS: - also made by stomach to protect itself from STRONG ACID • Chyme stays in stomach until adequate protein digestion has occurred. This is why you feel less hungry between meals if you have eaten some protein. The chyme is kept in the stomach by the pyloric sphincter.

10. Digestion • C. SMALL INTESTINE Final area where MOST digestion occurs and ABSORPTION begins. · • Physical – villi and microvilli help separate food particles · • Chemical – where many enzymes complete the digestive process - many enzymes from accessory glands (liver, gall bladder, pancreas) are dumped into the SI to help with digestion • The small intestine is a long tube (7 m) in length and 2.5 cm in diameter with a total inner surface area of 30 m2 (due to the villi and microvilli). The SI is also divided into three sections: a) duodenum b) jejunum c) ileum

11. Digestion • 3. ABSORPTION OF NUTRIENTS • Stomach: - small amounts of water - alcohol - some medicines, e.g. aspirin • Small intestine: jejunum - where most of the absorption takes place • ileum: where the remaining nutrients are absorbed Absorption is greatly aided by the folded interior structure of the intestine, particularly due to the presence of the villi and microvilli. • Structure of Villi: - tiny finger like projections lining the interior of the intestines • Small molecules like vitamins, minerals, natural glucose and amino acids do not need to be digested and are easily absorbed by the small intestine.

12. Digestion • The COLON – the LARGE INTESTINE (the BOWEL) • Structure: - 1.5 m in length, 5 cm in diameter (twice the diameter of SI) - made up of four sections: ascending transverse descending sigmoid process -the colon ends with the rectum • Function: - main job is to reabsorb water - bacteria here produce vitamins K and some B

13. Digestion • 4. EGESTION OF WASTE • CELLULOSE: main component of feces, along with living and dead bacteria and water – • FIBRE, found in plant cell walls, cannot be digested by humans • FECES: - waste is stored in rectum - removed by body removing possible toxic materials v • Egestion controlled by anal sphincter which allows feces to leave rectum through the anus. Toilet training is learning how to control the anal sphincter.

14. Path of food through Digestive System mouth esophagus stomach small intestine large intestine rectum eliminated from body

15. Summary • How does the digestive system work with the respiratory system to provide energy for the body?

16. Procedures for Today’s Activity • 1. Build your model. • 2. “Eat” (place in the mouth/sandwich bag) cracker. Slowly “drink” ( add the water to the bag). • 3. Close your “mouth” (you should not chew with your mouth open!) by zipping the bag shut, and then “chew” (smash all the ingredients until no more clumps are present) in your snack. • 4. Move the food to one side of the bag, toward the opening, and down the esophagus. • 5. Swallow your food by squeezing the esophagus in rhythmic waves to move the food along. • 6. Keep squeezing the esophagus until all of the food makes it way into the stomach. • 7. From the stomach, the snack needs to pass into the small intestine. Squeeze the contents of the “stomach” into the small intestine. Place toe end of the panty hose inside the cup labeled “nutrients”. To simulate the removal of nutrients from the food, squeeze the liquid from the contents in the panty hose [Note: Removal of the liquid actually occurs in the large intestine.] into the cup. • 8. Once most of the liquid has been squeezed from the food, take the panty hose out of the cup. Squeeze the food from the small intestine into the large intestine. • 9. Once in the “large intestine” things should really be squeezed hard with a paper towel to remove the water. • 10.Cut the toe end of the nylon (“the colon” – the end part of the large intestines) and squeeze the remaining solids out of the “rectum” (opening at the bottom of the panty hose) into the paper cup (the toilet).