Digestive System A closer look

Digestive Processes In order for our bodies to use the food we eat to grow, energize, and repair our cells, 5 digestive processes have to occur. These include: Ingestion Movement Digestion Absorption Egestion (excretion)

Digestive Processes These processes occur at different locations along the digestive tract, which is a continuous tube from mouth to anus. We are going to discuss what happens at each site as we go through the stages. It will be useful to copy the following concept map and to keep adding to it as we add more details to help you stay organized.

NOTE: This should be a straight line in your notes Small Intestine Stomach Large Intestine Esophagus Tongue Rectum/ Anus Mouth/ Throat Teeth Salivary Glands

Digestive System Includes organs which perform digestion tasks: Digestive Tract (Gastrointestinal Tract, G. I. Tract) includes: mouth, esophagus, stomach, small intestine, large intestine or colon, and anus. Accessory Structures include:, tongue, salivary glands, liver, gall bladder and pancreas.

Digestion The process in our bodies that breaks down food for use by our cells. This is done in two ways: Mechanical: our teeth chewing through the food Chemical: enzymes breakdown food into absorbable molecules.

Mouth (where it all begins) Hard Palate Four main parts of the mouth Teeth Tongue Salivary Glands Hard and Soft Palates Uvula

Mouth Teeth (Chewing) How many teeth in adult humans? Mechanical Digestion Are covered by enamel, the hardest structure of the body Their movements slice, tear, grind and mix food Incisors: snap off pieces of food Canine: tearing pieces apart Premolars & molars: grind food to a paste How many teeth in adult humans?

Tongue Floor of oral cavity Composed of voluntarily controlled muscle tissue Role: Guides food during chewing and swallowing Major taste buds are embedded here. Salty, sweet, sour, bitter

Salivary Glands Release saliva in response to the smell, taste, and thought of food First example of chemical digestion: Contains Amylase: an enzyme that begins breakdown of starch into simple sugars, like glucose or table sugar. Interesting Fact: We secrete about 1-2L of saliva per day!

Hard & Soft Palates Separate mouth from nasal cavity, so food doesn’t go up your nose! Located at the roof of your mouth. Uvula (dangles) Just beneath the soft palate Prevents food from entering nasal passages by raising up.

Soft Palate Hard Palate Tongue Uvula Epiglottis Trachea

Recap (Mouth) Food enters Teeth rip, tear, and chew into smaller pieces to swallow At the same time, Salivary Glands are stimulated to release saliva which contains amylase. Tongue pushes bolus to back of pharynx (throat) and the uvula elevates, closing off the nasal passage. The bolus now pushes the epiglottis which closes the opening of the larynx, preventing the food from entering the wrong tube, which results in choking

Esophagus Muscular tube which extends from pharynx (throat) to the stomach Swallowing initiates peristalsis, a wave of contraction which initiates just above the “bolus” (substance) and moves it towards the stomach. This movement also occurs in the stomach and in the intestines. http://pennhealth.com/health_info/animationplayer/

Esophagus Secretes mucus (along with the rest of the digestive tract) This lubricant decreases the likelihood of the esophagus getting damaged by any sharp edges from the food entering. Mucus also protects esophagus from acid and enzymes in gastric juice if reflux were to occur. http://digestive.niddk.nih.gov/ddiseases/pubs/gerd/

NOTE: This should be a straight line in your notes Small Intestine Stomach Mechanical: Peristalsis Large Intestine Esophagus Tongue Rectum/ Anus Mouth/ Throat Mechanical: Chewing Chemical: Starch/Amylase Teeth Salivary Glands

Stomach Separated from esophagus by the Gastro esophageal sphincter Expandable muscular J-shaped sac that can hold up to 2-4 liters of food and liquid Secretes mucous to protect lining cells Contents are held in the stomach by the pyloric sphincter, ring of circular muscle, which separates the stomach from upper small intestine

Stomach 3 Functions Stores food and releases it gradually into the small intestine Assist in mechanical breakdown of food by peristalsis and contractions of muscular walls Chemical breakdown of food by enzymes and other substances.

Stomach Secretions (continued) Gastrin: hormone that stimulates secretion of Hydrochloric acid (HCl) Pepsinogen: inactive form of enzyme is activated by HCl and transformed into pepsin which helps breakdown proteins into amino acids (smaller units).

Stomach Food is gradually converted into a thick liquid called chyme which consists of partially digested food and digestive secretions. Chyme is propelled towards small intestine The Pyloric sphincter lets a teaspoon of chyme into the small intestine during each contraction Takes around 2-6 hours to empty stomach

NOTE: This should be a straight line in your notes Mechanical: Muscle Contractions Mechanical: Peristalsis Small Intestine Stomach Mechanical: Peristalsis Chemical: Pepsin (Proteins), HCl Large Intestine Esophagus Tongue Rectum/ Anus Mouth/ Throat Mechanical: Chewing Chemical: Starch Teeth Salivary Glands

Small Intestine (S. I.) Narrow tube (1-2 inches in diameter) Longest part of digestive tract Split into three parts: duodenum, jejunum, and the ileum Function: to digest food into small molecules and absorb into blood stream and lymph vessels.

Small Intestine (S. I) Helped by three other sources: 1. Liver: Has many functions in our bodies. In digestion, it produces bile which is stored in the gall bladder, then released in the S. I. Bile is made up of bile salts, water, and other salts and assist in the breakdown of lipids. http://zap.intergate.ca/images/liver%20image.jpg

Small Intestine (S. I.) 2. Gall Bladder stores bile until it’s needed for digestion http://www.nlm.nih.gov/medlineplus/ency/imagepages/19260.htm

Small Intestine (S. I.) Located between stomach and S. I. 3. Pancreas Located between stomach and S. I. Cells produce pancreatic juice which neutralizes the acidic chyme it receives from the stomach Digests carbohydrates, proteins, and lipids Contains water, sodium bicarbonate, and many enzymes YouTube - Pancreas - "Weird Al" Yankovic http://www.nlm.nih.gov/medlineplus/ency/imagepages/17194.htm

Small Intestine (S. I) Pancreas (cont’d) Enzymes include: Amylase Carbohydrates Lipase Lipids Proteases Proteins and peptides

Small Intestine (S. I.) Specialized cells within the wall complete the process. At the same time, nutrients are absorbed into the blood stream. The numerous folds and projections, called villi, give the internal surface area a much larger surface for absorption. http://www.udel.edu/biology/Wags/histopage/wagnerart/anaglyphpage/anaglyph.html

Small Intestine (S. I.) The area of absorption is also increased by the millions of microvilli.

NOTE: This should be a straight line in your notes Mechanical: Peristalsis Bile emulsifies lipids Alcohol absorbed Chemical: Amylase-CH2O Lipase-Lipids Proteases-Proteins Mechanical: Muscle Contractions Peristalsis (3 layers) Small Intestine Stomach Macro & micronutrients absorbed Mechanical: Peristalsis Chemical: Pepsin-Proteins HCl: pH-2 (gastric juices) Large Intestine Esophagus Tongue Rectum/ Anus Mouth/ Throat Mechanical: Chewing Chemical: Amylase-Starch Teeth Salivary Glands

Are We There Yet? Almost… While the nutrients are being absorbed by these cells, chyme is being mixed back and forth by segmentation movements within the small intestine. When absorption is complete, undigested material moves into the large intestine.

Large Intestine (L. I.) Is about 5 feet long and 3 inches in diameter in adults Two parts: Colon (for most of its length) Rectum: the final 6” Receives leftovers of digestion: water mixture, undigested fat and proteins, indigestible fibers http://www.nlm.nih.gov/medlineplus/ency/imagepages/19220.htm

Large Intestine (L. I.) Contains large populations of bacteria that thrive on the unabsorbed nutrients and are also responsible for synthesizing important vitamins for the body (B12, riboflavin, K). Remaining water, salts, and vitamins are reabsorbed by cells in the L. I.

NOTE: This should be a straight line in your notes Mechanical: Peristalsis Bile emulsifies lipids Mechanical: Muscle Contractions Peristalsis (3 layers) Chemical: Amylase-CH2O Lipase-Lipids Proteases-Proteins Small Intestine Stomach Macronutrients absorbed Mechanical: Peristalsis Chemical: Pepsin-Proteins HCl: pH-2 (gastric juices) Large Intestine Esophagus Tongue Remaining water, salts and vitamins absorbed Rectum/ Anus Mouth/ Throat Mechanical: Chewing Chemical: Amylase-Starch Teeth Salivary Glands

Large Intestine (L. I.) Leftover material is condensed into semisolid feces which are transported to the rectum by peristaltic movements. Expansion of the rectum stimulates the urge to defecate which is initiated voluntarily after age 2.

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