Human Body Systems I Digestive System The Digestive

Human Body Systems I) Digestive System

The Digestive System • The purpose of the digestive system is to bring in nutrients from the outside and convert it into a form that the body can use.

Two parts of the Digestive System Digestive Tube Accessory Organs • The tube through which the food actually passes. • It has an opening through which food enters the body and an opening through which food exits the body. • These are organs that produce chemicals that digest the food. • These organs dump these chemicals into the Digestive Tube but the food does not actually enter these organs. • Examples include the liver, gallbladder and pancreas.

Order of the Digestive Tube 1. 2. 3. 4. 5. 6. 7. Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum/Anus Pharynx Mouth

Polymers Monomers • Digestion means the breakdown of large nutrients into smaller pieces. • This means breaking polymers into monomers: • Large fat molecules -> small lipid molecules • Proteins / polypeptides -> amino acids • Polysaccharides -> monosaccharides • After digestion is complete, the body will then build these building blocks into the polymers that it needs to survive.

1 - Mouth • The mouth performs two different jobs that help the body begin to digest the food. 1. Mechanical Breakdown – the teeth break up the food into smaller pieces so they can be swallowed. (“mechanical” means that it is done through force).

1 - Mouth 2. Chemical Breakdown – saliva contains the enzyme salivary amylase, which breaks starch, a polysaccharide, into monosaccharides (“chemical” means that it is done through enzymes and chemical reactions).

Demonstration • Starch, the polysaccharide, does not taste sweet. • Sugars, the monosaccharide, do taste somewhat sweet. • What should happen as you continue to chew food containing starch? It should become sweeter as starch is converted into sugars. DEMONSTRATION

2 - Pharynx • The pharynx is the soft area at the very back of the throat. • After the food is chewed, the tongue pushes the food to the back of the throat- the pharynx. • When the food touches the pharynx, it stimulates the automatic swallowing reflex.

Pharynx = Gateway • The pharynx is the gateway to two tubes. 1. The trachea. This is the tube from the mouth to the lungs. It is nearer to the front of the body and can be felt by the outside. 2. The esophagus. This is the tube from the mouth to the stomach. It is behind the trachea and cannot be felt.

Danger! • Food is not the only thing to pass through the pharynx - air also passes through the pharynx. • The body needs to direct the food to the esophagus (the tube to the stomach) and the air to the trachea (the tube to the lungs). • How can the body prevent food from going down the wrong tube?

Epiglottis • The epiglottis is a piece of tissue that covers the trachea when swallowing. • This prevents food and liquid from getting down the wrong pipe and guarantees that food cannot get into the trachea. DEMONSTRATION: Try to breath and swallow at the same time. You cannot. That is because of the epiglottis!

• Question: What happens if liquid/food goes down the trachea? • Answer: It is brought up again by coughing. This is what people mean when they say “it went down the wrong pipe”.

• Question: How does the body prevent air from going down the esophagus? • Answer: If there is no food passing down the esophagus, it is closed (unlike the trachea, which is constantly open). Therefore, when air is being pulled into the trachea, the esophagus is closed so air does not go there. (not responsible).

• Question: What happens if air accidently goes down the esophagus? • Answer: This can happen, for example, if you put air in your mouth and you swallow saliva. Then air will be forced down the esophagus. This air is brought back up by burping. People who can make themselves burp are just forcing air into the esophagus, which is then brought out by burping.

3 - Esophagus • The swallowing reflex pushes the food out of the pharynx and into the esophagus. • The esophagus is the tube that leads from the throat down to the stomach.

Peristalsis • The esophagus forces food to travel down the digestive tube (in the correct direction) through peristalsis. • Peristalsis is the contraction of the muscles behind the food and the relaxation of the muscles in front of the food, forcing it forward. • Peristalsis is what allows a person to swallow even if a person is upsidedown and gravity is working against the food.

Oh so now I understand…Vomit • The body will vomit when the stomach is irritated or it detects something poisonous in the contents of the food. • Vomiting is done through REVERSE PERISTALSIS. • Instead of the muscles directing the food down the digestion tube, it will direct the food in the opposite direction and bring it back up. = Throwing up

Esophageal Sphincter • The Esophageal Sphincter is a ring of muscle at the bottom of the esophagus that prevents the food and the acid in the stomach from getting back up into the esophagus.

Oh, so now I understand… Heartburn • It actually has nothing to do with the heart – it is just located in the area of the heart, so it feels like pain in the heart. • Heartburn is caused by acid from the stomach seeping back into the esophagus, which has not protective layer, like the stomach. • This can be caused by a weak esophageal sphincter that does not properly close. • The acid irritates the esophagus, causing pain.

4 - Stomach • The stomach is where much of the digestion takes place. • The stomach produces gastric juices, which digests the food. Gastric juice contains: 1) Acid – this kills any bacteria in the food and helps break up the food into smaller pieces. 2) Pepsin – this breaks down proteins into individual amino acids.

4 - Stomach • The stomach also produces mucus, which lines the inside of the stomach wall, protecting it from the acid.

5 - Small Intestine • From the stomach, the food passes into the small intestine. • The small intestine is called “small” because it is the thinnest of the tubes, but it is about 20 feet long! • It is coiled up so that it can fit into the abdomen. Large Intestine Stomach Small intestine

5 - Small Intestine • The small intestine has two roles: 1. It performs the final digestions of the food. 2. It absorbs the broken-down nutrients.

5 - Small Intestine (Digestion) • The small intestine is the mixing-bowl for three different digestive chemicals: 1. Bile- from liver and gallbladder (will explain) 2. Pancreatic Juice- from pancreas 3. Intestinal Juice- from small intestine

Functions of the three digestive chemicals in the small intestine • Bile is produced in the liver and stored in the gallbladder. It breaks up fat globules into tiny droplets. • Pancreatic Juice is produced and stored in the pancreas. It contains amylase (breaks polysaccharides into disaccharides) and trypsin (breaks large polypeptides into small polypeptides) and lipase (breaks tiny fat droplets into fatty acids and glycerol). • Intestinal Juice is produced and stored in the small intestine. It breaks disaccharides into monosaccharides (glucose) and small polypeptides into amino acids.

Digestion in the Small Intestine Name of Chemical Where is it from Function Bile Liver (produced) /gallbladder (stored) Breaks fat globules into tiny droplets. Pancreatic Juice Pancreas Breaks large polypeptides into small polypeptides and polysaccharides into disaccharides and tiny fat droplets into fatty acids and glycerol. Intestinal Juice Small Intestine Breaks small polypeptides into amino acids and disaccharides into monosaccharides (glucose).

Digestion in the Small Intestine Nutrient Step 1 Step 2 Final form Fat globules -> tiny droplets (bile) Tiny droplets -> glycerol and fatty acid (pancreatic juice) Glycerol and fatty acids Protein Large polypeptides - Small polypeptides - Amino acids > Small > amino acids polypeptides (intestinal juice) (pancreatic juice) Carbohydrate Polysaccharides -> disaccharides (pancreatic juice) Disaccharides -> monosaccharides (intestinal juice) Monosaccharides

Homework Questions. Small Intestine Digestion • What are three digestive juices in the small intestine? • Where do each of them come from? • What does bile do? • What does pancreatic juice do? • What does intestinal juice do? • What is the final, most broken-down form of fat, carbohydrates and proteins?

5 - Small Intestine (Absorption) • At this point, the food is completely broken down into its monomer (smallest) form. • Key to remember: Until now, the food has been isolated in the digestive tube. Now the body begins to absorb from the digestive tube to the blood stream and from there to feed the rest of the body. • Absorption begins in the small intestine, as well.

5 - Small Intestine: Villi • The small intestine is not a smooth tube on the inside. It has many ridges and indentations. Inside these indentations are tiny little fingerlike structures called villi (plural of villus). • This gives the small intestine enormous surface area to come into contact with the food it contains.

5 - Small Intestine- Villi • The villi contain tiny blood vessels called capillaries. The food in the small intestine is very rich in amino acids, fatty acids and monosaccharides. • These diffuse from the small intestine (high concentration) through the villi and into the capillaries (low concentration) • The nutrients travel from the capillaries to arteries to the rest of the body.

6 - Large Intestine (Colon) • It is called “large” because it is much wider than the small intestine. It is actually shorter, only 5 feet long.

6 - Large Intestine (Colon) • The large intestine does not do any digestion at all. Its role is purely absorption. 1. Water absorption 2. Bacteria / Vitamin K production

6 - Large intestine – Water Absorption • The large intestine reabsorbs water from the food mass (very liquidy) into the blood supply through villi that line the intestine. • If not enough water is reabsorbed, the result is that the food mass is too liquid when it is expelled (diarrhea). • If too much water is reabsorbed, the result is that the food mass is too solid when it is expelled (constipation).

6 - Large Intestine – Vitamin K production • The second function of the large intestine is that it contains bacteria that live off the undigested food particles. • The body allows these bacteria to live there because they are beneficial to the body. They produce Vitamin K (necessary for blood clotting). • This Vitamin K is then absorbed along with the water into the capillaries in the villi of the large intestine.

Waste Products • At this point, the important nutrients, vitamins and water have all been absorbed from the food mass into the body. • All that remains in the food mass is indigestible plant fiber, bacteria (that fall off the large intestine wall), bile, worn out cells from the digestive tract and other waste products. • The body must now remove these waste products.

7 - Rectum/Anus • When the food mass travels through the large intestine and the last useful nutrients are removed, it is called feces, or stool. • Feces is stored in the last part of the large intestine, the rectum. • It is periodically removed, or defecated, through the anus.

Summary Questions #1 Tiny, finger-like structures that line the inside of the intestines. • What are villi? • How do villi help the small and large intestine absorb nutrients from the food? The villi increase the surface area of the intestine so that it can come into direct contact with the food mass. • What three types of nutrients does the small Monosaccharides 2) Glycerol/Fatty intestine absorb? 1)Acids 3) Amino Acids • How do those nutrients enter the blood stream? They diffuse into the villi and then into the capillaries (small blood vessels) and then into the arteries.

Summary Questions #2 • How does the large intestine help digest the Trick Question! The large intestine does not food? play a role in the digestion of food. • What nutrients does the large intestine absorb? Water and vitamin K plant fiber, bacteria, bile, worn out • What is in feces? Indigestible cells, other waste products • What is the difference between the rectum and the anus? The rectum is the name of the last piece of the large intestine. The anus is the opening of the rectum through which feces is expelled.

Pharynx Mouth Liver Pancreas Esophagus Stomach Gallbladder Small intestine Large Intestine Rectum Anus

Summary of Digestion • http: //www. youtube. com/watch? v=yb. Y 1 d 5 v 0 b 4 E&feature=related

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