Digestion Grade 9

Video Demo digestive-system-stomach- video.htm Bill Nye

Jelly Bean Digestion What biochemical compound makes up this jelly bean? Eg. lipids, carbohydrates, proteins or nucleic acids What happens when you put the jelly bean into your mouth? Than what happens? …

Teeth Tear, rip and chew food to physically break it into smaller pieces. (Mechanical Digestion). Let’s look at the internal structure of teeth.

Teeth The crown is the part of the tooth above the gum line The root is the part of the tooth below the gum line The enamel is the white part you can see covering the crown. Enamel is the hardest substance in the human body It covers the dentine and stops bacteria getting inside the tooth

Teeth The crown is the part of the tooth above the gum line The root is the part of the tooth below the gum line The dentine is the major component within the tooth. It is made from softer material than enamel so is easier to decay.

Teeth The crown is the part of the tooth above the gum line The root is the part of the tooth below the gum line The pulp contains the nerves and blood vessels of the tooth. It is underneath the dentine. This is the part that hurts when you have a toothache!

Teeth The crown is the part of the tooth above the gum line The root is the part of the tooth below the gum line The cementum is found outside the dentine in the root. It cements (holds) the tooth into the jaw bone.

Bacteria Our mouths are busy places, full of friendly bacteria that coat our teeth Sometimes unfriendly bacteria, including one called Porphymonas gingivalis, will overgrow the friendly bacteria and cause damage to the gums and the jawbone. This bacterium is one of the main causes of gum disease.

Porphymonas gingivalis To fend off the attack, the body will send immune cells to kill the bacteria. The bacteria are difficult to kill so the immune cells can cause even more damage to your gums.

Mouth: What happens Food is crushed and ground up by teeth The salivary glands secrete saliva which makes the food moist and easy to swallow (Semi-solid lump now called Bolus). Amylase enzyme (in saliva) breaks the carbohydrate starch down into glucose.

Enzymes Remember : Large particles cannot be absorbed in the small intestine starch G G G GUT INSIDE THE BODY (BLOOD) Large particles (e.g. starch) are left in the gut and small particles (e.g. glucose) pass into the bloodstream. G G G BUT large particles can be broken down into small particles. This is called DIGESTION

Enzymes Large particles need to be broken down chemically by ENZYMES. Enzymes are biological catalysts. They speed up chemical reactions in the body. Digestive enzymes cleave (cut) the larger molecules into smaller ones.

Digestive Enzymes Mouth: Amylase breaks starch down into glucose. Stomach: Protease (Pepsin) breaks protein down into peptides.

Digestive Enzymes Amylase Starch Glucose Protease Protein Peptides

Enzymes and pH Enzymes work best at one pH. This pH is different for each different enzyme. If the pH goes too low (more acidic) or too high (more alkaline), the enzyme will not work as effectively. However, changes to pH will NOT denature enzymes.

Epiglottis Is the flap of cartilage lying behind the tongue and in front of the entrance to the larynx (voice box). At rest, the epiglottis is upright, allowing air to pass into the trachea (for breathing).

At Rest

During Swallowing The tongue pushes the bolus toward the pharynx (throat). The epiglottis folds back to cover the entrance to the trachea, protecting the larynx. This allows food to enter into the esophagus. *The epiglottis acts as a lid*

Swallowing

Esophagus A muscular tube that leads from the throat to the stomach. The smooth muscle of the esophagus pushes the bolus toward the stomach using wave-like contractions. This is called Peristalsis.

Peristalsis

Entering the Stomach From the esophagus, the bolus enters the stomach through the Cardiac sphincter (muscular ring). -Sphincters help move digested material in one direction.

Entering the Stomach

The Stomach A hollow, sac-like organ that stores, mixes, sterilizes and continues the digestive process. Storage: walls have folds called Rugae which allow the stomach to expand. Food spends 3-4 hours in here!

The Stomach Mixes: The stomach walls contain three layers of smooth muscle arranged in longitudinal, circular, and oblique (diagonal) rows. These muscles allow the stomach to squeeze and churn the food (mechanical digestion).

Muscles and Rugae

The Stomach Sterilizes and Chemically Digests: Secretes gastric juice & hydrochloric acid The acid kills germs in the food (pH 2) The gastric juice contains the protease enzyme PEPSIN to digest protein into peptides Protease Protein Peptides

Mucus A thick mucus layer lines the stomach walls to prevent the stomach from digesting itself.

Mucus

What do you think may happen when mucus is limited?

Ulcer Peptic ulcer disease occurs when the protective mucus layer wears away in certain areas, allowing damage to occur from the natural acids of the stomach.

Ulcer- 60% to 80% of gastric ulcers caused by bacteria Helicobacter pylori is a spiral shaped bacterium that lives in the stomach and duodenum (section of intestine just below stomach) The stomach is protected from its own gastric juice by a thick layer of mucus that covers the stomach lining. Helicobacter pylori takes advantage of this protection by living in the mucus lining.

Helicobacter pylori Once H. pylori is safely ensconced in the mucus, it is able to fight the stomach acid that does reach it with an enzyme it possesses called urease However, the immune system will respond to an H. pylori infection It may not be H. pylori itself which causes peptic ulcer, but the inflammation of the stomach lining; i.e. the immune response to H. pylori.

Continuation of Digestion The chyme is slowly transported from the stomach through the pyloric sphincter and into the small intestine where further digestion and nutrient absorption occurs.

DIGESTION

Definitions Gland: an organ or group of cells which secretes enzymes or hormones Peristalsis: muscle contractions that push food through a tube Bolus: chewed food

Definitions continued Chyme: nutrients in semi-liquid form Uvula: component that stops food from entering nasal cavity Epiglottis: component that stops food from entering the trachea

Digestive Tract and Functions 1) Mouth 2) Pharynx 3) Esophagus 4) Stomach 5) Small intestine 6) Large intestine 7) Rectum 8) Anus  Decomposition of food  Absorption of nutrients  Elimination of waste

Digestive Glands and Functions Salivary glands In mouth Gastric glands In walls of stomach Pancreas Liver Intestinal glands In small intestine Secretion of:  saliva  Gastric enzymes  Digestive juices  Bile

Physical/Mechanical Breakdown Food DOES NOT change its molecular makeup, just its shape and size, looks different 1. Mouth- chewing and swallowing 2. Esophagus- peristalsis 3. Stomach- churning, grinding and peristalsis 4. Small intestine- peristalsis and churning 5. Large intestine- peristalsis and churning

Chemical Breakdown Food changes its molecular makeup, looks and is different See handout*

Absorption Through folds called villi by diffusion Small intestine – amino acids, glucose, glycerol and fatty acids Large intestine – vitamins, minerals and water