Chemical Chemical DigestionDigestion

Breaking food into Breaking food into useable pieces for useable pieces for

the cell.the cell.

Chemical DigestionChemical Digestion

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

The GoalsThe Goals

Transform carbohydrates into mono-Transform carbohydrates into mono-saccharides.saccharides.

Transform lipids (triglycerides) into fatty Transform lipids (triglycerides) into fatty acids.acids.

Transform proteins into amino acids.Transform proteins into amino acids.

Transform nucleic acids into a sugar, base Transform nucleic acids into a sugar, base and a phosphate group. and a phosphate group.

Mechanical versus Chemical Mechanical versus Chemical DigestionDigestion

MechanicalMechanical– Changes the physical form Changes the physical form

of foodof food

Chew Chew

TearTear

GrindGrind

MashMash

MixMix

Mechanical versus Chemical Mechanical versus Chemical DigestionDigestion

ChemicalChemical– Changes the chemical composition of Changes the chemical composition of

food with the aid of digestive enzymesfood with the aid of digestive enzymes

Carbohydrate into monosaccharidesCarbohydrate into monosaccharides

Protein into amino acidsProtein into amino acids

Lipids into fatty acidsLipids into fatty acids

Nucleic Acids into sugar, base, Nucleic Acids into sugar, base, phosphate groupphosphate group

How is it possible to break down How is it possible to break down complex food into simple molecules?complex food into simple molecules?

– Digestive enzymesDigestive enzymes are special proteins are special proteins that help break up large molecules of that help break up large molecules of food into very tiny molecules that can food into very tiny molecules that can be absorbed and used by the cells in the be absorbed and used by the cells in the form of nutrition.form of nutrition.

Phases of DigestionPhases of Digestion

1. 1. IngestionIngestion - mouth - mouth2. Movement2. Movement33. Digestion. Digestion – stomach and small – stomach and small

intestine.intestine.4. 4. Absorption Absorption – small intestine, – small intestine,

large intestine (water)large intestine (water)5. Further digestion5. Further digestion

Accessory Parts of the Accessory Parts of the Digestive SystemDigestive System

Organs that are not in the digestive tract Organs that are not in the digestive tract but helps in the digestionbut helps in the digestion– TeethTeeth– Tongue Tongue – Salivary glandsSalivary glands– LiverLiver– Gall bladderGall bladder– PancreasPancreas

MouthMouthFunctions:Functions:

– Food enters in the mouth or oral Food enters in the mouth or oral cavitycavity

– TastingTasting

– Mechanical breakdown of foodMechanical breakdown of food

– Secretion of salivary glands Secretion of salivary glands (salivary amylase) (salivary amylase)

MouthMouthStructures in the mouth that aids digestion:Structures in the mouth that aids digestion:

TeethTeeth – cut, tear, crush and grind food. – cut, tear, crush and grind food.

Salivary glandsSalivary glands – 3 pairs produce and – 3 pairs produce and secrete saliva into the oral cavity. secrete saliva into the oral cavity.

– Parotid (beneath the cheeks)Parotid (beneath the cheeks)

– Submaxillary (below the jaw bone)Submaxillary (below the jaw bone)

– Sublingual (below the tongue)Sublingual (below the tongue)

Role of Saliva – the first chemical Role of Saliva – the first chemical digestion site!digestion site!

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

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

Cracker ExperimentCracker ExperimentLet’s build a bolus!Let’s build a bolus!

Mechanism of SwallowingMechanism of SwallowingSwallowing is a coordinated activity of the Swallowing is a coordinated activity of the tongue, soft palate, pharynx and esophagus.tongue, soft palate, pharynx and esophagus.

PhasesPhases

– Food is pushed into the Food is pushed into the pharynx pharynx by the by the tongue. (voluntary) tongue. (voluntary)

– Tongue blocks the mouthTongue blocks the mouth

– Soft palate closes off the noseSoft palate closes off the nose

– Larynx (Adam’s Apple) rises so the Larynx (Adam’s Apple) rises so the Epiglottis Epiglottis (a flap of tissue) can close the (a flap of tissue) can close the opening of the trachea.opening of the trachea.

EsophagusEsophagusTo pass through the esophagus the bolus To pass through the esophagus the bolus must travel down the 10 inch tube, this must travel down the 10 inch tube, this takes 8 seconds.takes 8 seconds.

The wall of the esophagus contain smooth The wall of the esophagus contain smooth muscles that contracts in wavy motion muscles that contracts in wavy motion ((PeristalsisPeristalsis).).

What is PERISTALSIS?What is PERISTALSIS?

Peristalsis propels food and liquid Peristalsis propels food and liquid slowly down the esophagus into the slowly down the esophagus into the stomach.stomach.

Cardiac Sphincter (ring-like valve) relaxes Cardiac Sphincter (ring-like valve) relaxes to allow food into the stomach.to allow food into the stomach.

Video of Video of PeristalsisPeristalsis….SO COOL!….SO COOL!

PeristalsisPeristalsis

Once a bolus is made it needs Once a bolus is made it needs to travel to the stomachto travel to the stomach

In the stomach the bolus is mixed with In the stomach the bolus is mixed with GASTRIC JUICEGASTRIC JUICE!!

In the Gastic juice there is HCl – hydrochloric In the Gastic juice there is HCl – hydrochloric acid that has a pH of 2 and Pepsin.acid that has a pH of 2 and Pepsin.

The HCl disrupts the extracellular matrix The HCl disrupts the extracellular matrix and kills the bacteria that was living on the and kills the bacteria that was living on the food.food.

The acidic environment created by the HCl The acidic environment created by the HCl turns ON or activates Pepsinogen into turns ON or activates Pepsinogen into PEPSIN.PEPSIN.

Inside the StomachInside the StomachChurns and grinds together the bolus into Churns and grinds together the bolus into smaller pieces.smaller pieces.

Food is mixed with gastric juices Food is mixed with gastric juices (hydrochloric acid and enzymes) secreted (hydrochloric acid and enzymes) secreted by the stomach walls.by the stomach walls.

HCl helps break down food and kills HCl helps break down food and kills bacteria that came along with the food.bacteria that came along with the food.

StomachStomach

Enzymes in the StomachEnzymes in the StomachPepsin and HCl are the major Pepsin and HCl are the major enzymes in the stomach.enzymes in the stomach.

PepsinPepsin – converts proteins into – converts proteins into peptides in the presence of HCl.peptides in the presence of HCl.

Converts the bolus into a liquid Converts the bolus into a liquid ((chymechyme)) after 4 hrs of mechanical after 4 hrs of mechanical and chemical digestionand chemical digestion

Chyme passes through the Chyme passes through the pyloric pyloric sphinctersphincter into the small intestine. into the small intestine.

Movements in StomachMovements in Stomach

Small IntestineSmall IntestineInside the small intestine, triglycerides, Inside the small intestine, triglycerides, carbohydrates, proteins and nucleic acids carbohydrates, proteins and nucleic acids are all broken down into smaller digestible are all broken down into smaller digestible products.products.

Remember that we want the Remember that we want the macronutrients to become smaller so they macronutrients to become smaller so they can slip across the cell membrane into the can slip across the cell membrane into the bloodstream. bloodstream.

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

Carbs in the Small IntestineCarbs in the Small IntestineCarbohydrate digestion also happens in the Carbohydrate digestion also happens in the small intestine. small intestine. Pancreatic amylase from the pancrease breaks Pancreatic amylase from the pancrease breaks polysaccharides down into disaccharides.polysaccharides down into disaccharides.The Disaccharides can then be broken into The Disaccharides can then be broken into monosaccharides with the help of intestinal monosaccharides with the help of intestinal enzymes. enzymes. We are talking about HYDRATION SYNTHESISWe are talking about HYDRATION SYNTHESISMaltose is broken into glucoseMaltose is broken into glucoseSucrose is broken into glucoseSucrose is broken into glucoseLactose is broken into glucoseLactose is broken into glucose

Protein in the Small IntestineProtein in the Small Intestine

Peptidases from the pancrease help Peptidases from the pancrease help convert polypeptides into dipeptides.convert polypeptides into dipeptides.

The intestinal enzymes from the intestinal The intestinal enzymes from the intestinal walls break dipeptides into amino acids. walls break dipeptides into amino acids.

Amino acids are the smallest part of a Amino acids are the smallest part of a protein. When the protein has been protein. When the protein has been digested into amino acids in the small digested into amino acids in the small intestine, protein digestion is complete!intestine, protein digestion is complete!

Nucleic Acids in the Small IntestineNucleic Acids in the Small Intestine

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

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

VILLI! VILLI!

Movement in small intestine:Movement in small intestine:

Mixing: Segmental contraction that occurs in small intestineMixing: Segmental contraction that occurs in small intestineSecretion: Lubricate, liquefy, digestSecretion: Lubricate, liquefy, digestDigestion: Mechanical and chemicalDigestion: Mechanical and chemicalAbsorption: Movement from tract into circulation or lymphAbsorption: Movement from tract into circulation or lymphElimination: Waste products removed from bodyElimination: Waste products removed from body

Large IntestineLarge Intestinea.k.a. Colona.k.a. Colon

larger diameter, but shorter (5 ft)larger diameter, but shorter (5 ft)

Water is absorbed from the Water is absorbed from the undigested food making the waste undigested food making the waste harder until it becomes solid.harder until it becomes solid.

Waste stays for 10 – 12 hours.Waste stays for 10 – 12 hours.

Large IntestineLarge Intestine

Large IntestineLarge IntestineWaste is pushed into the expanded Waste is pushed into the expanded portion (rectum) of the large intestine.portion (rectum) of the large intestine.

Solid waste stays in the rectum until it Solid waste stays in the rectum until it is excreted through the anus as is excreted through the anus as feces.feces.

Appendix hangs on the right side of Appendix hangs on the right side of the large intestine.the large intestine.

Accessory OrgansAccessory OrgansProduce or store enzymes that helps in Produce or store enzymes that helps in digestion. digestion. Liver Liver – Largest gland of the bodyLargest gland of the body– Stores vitamins A,D,E,K Stores vitamins A,D,E,K – Stores sugar and glycogenStores sugar and glycogen– Produces Produces bilebile (watery, greenish (watery, greenish

substance) substance) – Secretes bile to the gall bladder via the Secretes bile to the gall bladder via the

hepatic duct and cystic duct.hepatic duct and cystic duct.

Accessory OrgansAccessory OrgansGall bladder Gall bladder – Stores bile in between mealsStores bile in between meals– Secretes bile to the duodenum through Secretes bile to the duodenum through

the bile duct during mealtime. the bile duct during mealtime. Bile contains bile salts, pigments, Bile contains bile salts, pigments, cholesterol and phospholipids.cholesterol and phospholipids.Bile is an emulsifier NOT an enzyme.Bile is an emulsifier NOT an enzyme.Emulsifier – dissolves fat into the Emulsifier – dissolves fat into the watery contents of the intestine.watery contents of the intestine.

Accessory OrgansAccessory OrgansPancreasPancreas– Produces a juice that contains Produces a juice that contains

enzymes (enzymes (amylase and insulinamylase and insulin) to ) to break down carbohydrates, fats break down carbohydrates, fats and protein.and protein.

– Secretes the juice into the Secretes the juice into the duodenum through the pancreatic duodenum through the pancreatic duct.duct.

Path of DigestionPath of Digestion

MouthMouth

PharynxPharynx

EsophagusEsophagus

StomachStomach

Small IntestineSmall Intestine

Large IntestineLarge Intestine

AnusAnus