Chemical Digestion Breaking food into useable pieces for the cell.

Chemical Digestion The body is VERY well suited to take food in all of its complex forms and break it down into its smallest pieces! This process of organic macronutrients returning back to their smallest pieces is known as chemical digestion.

The Goals Transform carbohydrates into mono- saccharides. Transform lipids (triglycerides) into fatty acids. Transform proteins into amino acids. Transform nucleic acids into a sugar, base and a phosphate group.

Mechanical versus Chemical Digestion Mechanical –C–C–C–Changes the physical form of food Chew Tear Grind Mash Mix

Chemical –C–C–C–Changes the chemical composition of food with the aid of digestive enzymes Carbohydrate into monosaccharides Protein into amino acids Lipids into fatty acids Nucleic Acids into sugar, base, phosphate group

How is it possible to break down complex food into simple molecules? –Digestive enzymes are special proteins that help break up large molecules of food into very tiny molecules that can be absorbed and used by the cells in the form of nutrition.

Phases of Digestion 1. Ingestion - mouth 2. Movement 3. Digestion – stomach and small intestine. 4. Absorption – small intestine, large intestine (water) 5. Further digestion

Accessory Parts of the Digestive System Organs that are not in the digestive tract but helps in the digestion –T–T–T–Teeth –T–T–T–Tongue –S–S–S–Salivary glands –L–L–L–Liver –G–G–G–Gall bladder –P–P–P–Pancreas

Mouth Functions: – F– F– F– Food enters in the mouth or oral cavity – T– T– T– Tasting – M– M– M– Mechanical breakdown of food – S– S– S– Secretion of salivary glands (salivary amylase)

Mouth Structures in the mouth that aids digestion: Teeth – cut, tear, crush and grind food. Salivary glands – 3 pairs produce and secrete saliva into the oral cavity. – P– P– P– Parotid (beneath the cheeks) – S– S– S– Submaxillary (below the jaw bone) – S– S– S– Sublingual (below the tongue)

Role of Saliva – the first chemical digestion site! To moisten the food and contains enzymes (salivary amylase) that begins digestion of starch (glycogen into small polysaccharides, or disaccharides) into smaller polysaccharides. Carbohydrate digestion is the only macronutrient digestion that begins in the mouth! Cool! Carbohydrate digestion isn’t complete in the mouth but it is a nice start!

Bolus! The bolus is the food that you eat that has been mechanically crushed with the tongue, teeth, hard and soft palate, and then mixed with saliva to start the beginning of chemical carbohydrate digestion.

Cracker Experiment Let’s build a bolus!

Mechanism of Swallowing Swallowing is a coordinated activity of the tongue, soft palate, pharynx and esophagus. Phases –F–F–F–Food is pushed into the pharynx by the tongue. (voluntary) –T–T–T–Tongue blocks the mouth –S–S–S–Soft palate closes off the nose –L–L–L–Larynx (Adam’s Apple) rises so the Epiglottis (a flap of tissue) can close the opening of the trachea.

Esophagus To pass through the esophagus the bolus must travel down the 10 inch tube, this takes 8 seconds. The wall of the esophagus contain smooth muscles that contracts in wavy motion (Peristalsis).

What is PERISTALSIS? Peristalsis propels food and liquid slowly down the esophagus into the stomach. Cardiac Sphincter (ring-like valve) relaxes to allow food into the stomach.

Video of Peristalsis….SO COOL! Peristalsis

Peristalsis

Once a bolus is made it needs to travel to the stomach In the stomach the bolus is mixed with GASTRIC JUICE! In the Gastic juice there is HCl – hydrochloric acid that has a pH of 2 and Pepsin. The HCl disrupts the extracellular matrix and kills the bacteria that was living on the food. The acidic environment created by the HCl turns ON or activates Pepsinogen into PEPSIN.

Inside the Stomach Churns and grinds together the bolus into smaller pieces. Food is mixed with gastric juices (hydrochloric acid and enzymes) secreted by the stomach walls. HCl helps break down food and kills bacteria that came along with the food.

Stomach

Enzymes in the Stomach Pepsin and HCl are the major enzymes in the stomach. Pepsin – converts proteins into peptides in the presence of HCl. Converts the bolus into a liquid (chyme) after 4 hrs of mechanical and chemical digestion Chyme passes through the pyloric sphincter into the small intestine.

Movements in Stomach

Small Intestine Inside the small intestine, triglycerides, carbohydrates, proteins and nucleic acids are all broken down into smaller digestible products. Remember that we want the macronutrients to become smaller so they can slip across the cell membrane into the bloodstream.

Fats in the Small Intestine Site of greatest amount of digestion and absorption Triglycerides are broken down using bile from the liver and the gallbladder into emulsified fats. Pancreatic lipase from the pancreas takes the emulsified fats and breaks them into fatty acids and then down further into glycerol. Fat digestion is complete in the small intestine thanks to the actions of the bile and the pancreatic lipase.

Carbs in the Small Intestine Carbohydrate digestion also happens in the small intestine. Pancreatic amylase from the pancrease breaks polysaccharides down into disaccharides. The Disaccharides can then be broken into monosaccharides with the help of intestinal enzymes. We are talking about HYDRATION SYNTHESIS Maltose is broken into glucose Sucrose is broken into glucose Lactose is broken into glucose

Protein in the Small Intestine Peptidases from the pancrease help convert polypeptides into dipeptides. The intestinal enzymes from the intestinal walls break dipeptides into amino acids. Amino acids are the smallest part of a protein. When the protein has been digested into amino acids in the small intestine, protein digestion is complete!

Nucleic Acids in the Small Intestine We get nucleic acids from eating the DNA and the RNA contained in food. It is in the small intestine that we have nucleic acid digestion. Pancreatic enzymes from the pancreas break nucleic acids down into nucleotides The nucleotides are then converted into sugars, bases and phosphates with the help from many intestinal enzymes secreted from the intestinal walls. Nucleic acid digestion is completed in the small intestine.

Small Intestine Has folded inner walls covered with fingerlike projections (villi; sing. – villus) Each villus has tinier projections called microvilli that absorbs digested food. Villi and microvilli increases the surface area of the small intestine for greater absorption. Peristalsis moves the undigested food to the large intestine.

VILLI! VILLI!

Movement in small intestine: Mixing: Segmental contraction that occurs in small intestine Secretion: Lubricate, liquefy, digest Digestion: Mechanical and chemical Absorption: Movement from tract into circulation or lymph Elimination: Waste products removed from body

Large Intestine a.k.a. Colon larger diameter, but shorter (5 ft) Water is absorbed from the undigested food making the waste harder until it becomes solid. Waste stays for 10 – 12 hours.

Waste is pushed into the expanded portion (rectum) of the large intestine. Solid waste stays in the rectum until it is excreted through the anus as feces. Appendix hangs on the right side of the large intestine.

Accessory Organs Produce or store enzymes that helps in digestion. Liver –L–L–L–Largest gland of the body –S–S–S–Stores vitamins A,D,E,K –S–S–S–Stores sugar and glycogen –P–P–P–Produces bile (watery, greenish substance) –S–S–S–Secretes bile to the gall bladder via the hepatic duct and cystic duct.

Gall bladder – S– S– S– Stores bile in between meals – S– S– S– Secretes bile to the duodenum through the bile duct during mealtime. Bile contains bile salts, pigments, cholesterol and phospholipids. Bile is an emulsifier NOT an enzyme. Emulsifier – dissolves fat into the watery contents of the intestine.

Pancreas – P– P– P– Produces a juice that contains enzymes (amylase and insulin) to break down carbohydrates, fats and protein. – S– S– S– Secretes the juice into the duodenum through the pancreatic duct.

Path of Digestion Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Anus