Chapter 6

Digestion

6.1 – The Molecules of Living Systems

In this section we will:In this section we will:

1.1. Describe the nature of Describe the nature of carbohydrates, lipids & proteinscarbohydrates, lipids & proteins

2.2. Explain how carbohydrates, lipids Explain how carbohydrates, lipids & proteins are synthesized and & proteins are synthesized and broken downbroken down

3.3. Describe and perform tests to Describe and perform tests to identify macromoleculesidentify macromolecules

Macromolecules

Macromolecules are large, Macromolecules are large, complex organic moleculescomplex organic molecules

These include carbohydrates, These include carbohydrates, lipids, proteins, and nucleic acidslipids, proteins, and nucleic acids

These macromolecules are all These macromolecules are all created from smaller subunitscreated from smaller subunits

Assembling & Disassembling Molecules

MacromoleculMacromolecules are es are assembled assembled through through dehydration dehydration synthesissynthesis

They are They are broken down broken down through through hydrolysis hydrolysis reactionsreactions

Carbohydrates

Carbohydrates contain carbon, Carbohydrates contain carbon, oxygen and hydrogenoxygen and hydrogen

They can be classified as simple They can be classified as simple sugars (made up of one or two sugars (made up of one or two individual sugar units), or individual sugar units), or polysaccharides (which are long polysaccharides (which are long chains of simple sugars)chains of simple sugars)

Production of a Disaccharide

Note that this is a form of Note that this is a form of dehydration synthesisdehydration synthesis

Examples of Polysaccharides

All of these are All of these are examples of examples of polysaccharidespolysaccharides

The way that the The way that the individual sugar individual sugar units are units are arranged arranged determines their determines their shape and shape and functionfunction

Lipids Lipids consist of glycerol (a 3-Lipids consist of glycerol (a 3-

carbon chain) and fatty acids carbon chain) and fatty acids (whose composition may vary)(whose composition may vary)

Proteins Proteins make up most cellular Proteins make up most cellular

structuresstructures They are formed from tiny amino acid They are formed from tiny amino acid

molecules that are put together in long molecules that are put together in long chainschains

These amino acids vary due to their These amino acids vary due to their RR group group

The interactions between these The interactions between these RR groups can cause changes in the shape groups can cause changes in the shape of a protein (they may coil or twist)of a protein (they may coil or twist)

Protein Synthesis

The human body can synthesize The human body can synthesize 11 of the 20 amino acids11 of the 20 amino acids

We must then obtain the other 9 We must then obtain the other 9 (known as essential amino acids) (known as essential amino acids) from our dietfrom our diet

Protein Shapes

As you As you can can see, see, proteinproteins can s can have have many many shapesshapes

Nucleic Acids

These compounds make up DNA These compounds make up DNA and RNAand RNA

They contain phosphate, a sugar, They contain phosphate, a sugar, and a nitrogen baseand a nitrogen base

Vitamins and Minerals

Both vitamins and minerals are Both vitamins and minerals are key components of chemical key components of chemical reactions in the bodyreactions in the body

Vitamins are organic compounds Vitamins are organic compounds that often help enzymes functionthat often help enzymes function

Minerals or inorganic compounds Minerals or inorganic compounds that make up essential that make up essential components of hemoglobin, components of hemoglobin, hormones, enzymes and vitaminshormones, enzymes and vitamins

Enzymes

Enzymes are biological catalystsEnzymes are biological catalysts They increase reaction rates by They increase reaction rates by

reducing the amount of energy is reducing the amount of energy is required to start a reactionrequired to start a reaction

How an Enzyme Works:

Factors That Affect Enzymes

1.1. TemperatureTemperature2.2. pHpH3.3. Competitive Competitive

Inhibitors (fit into Inhibitors (fit into active sites)active sites)

4.4. Non-competitive Non-competitive Inhibitors (fit into Inhibitors (fit into other sites & other sites & change the shape change the shape of the enzyme)of the enzyme)

6.2 – The Digestive System

Importance of Digestion

We need to obtain our nutrients We need to obtain our nutrients from the foods we eatfrom the foods we eat

However, the food that we eat However, the food that we eat contain the nutrients in forms that contain the nutrients in forms that we may not be able to use directlywe may not be able to use directly

Therefore, our digestive system Therefore, our digestive system breaks down the food into units breaks down the food into units that our cells can usethat our cells can use

The Mouth

Physical digestion begins in the Physical digestion begins in the mouth where food is formed mouth where food is formed into a “bolus”into a “bolus”

AmylaseAmylase enzymes that begin enzymes that begin the digestion of starches are the digestion of starches are secreted from the salivary secreted from the salivary glandsglands

Taste

Our tongue is covered with taste Our tongue is covered with taste budsbuds

These chemical receptors identify These chemical receptors identify the taste of specific chemicals in the taste of specific chemicals in our foodour food

The Esophagus

The tongue pushes The tongue pushes the bolus of food into the bolus of food into the esophagusthe esophagus

The smooth muscle The smooth muscle in the esophagus in the esophagus creates waves of creates waves of muscle contractions muscle contractions (known as (known as peristalsisperistalsis) ) that push the food that push the food towards the stomachtowards the stomach

The Stomach

The stomach both serves as The stomach both serves as a food storage site and the a food storage site and the site of initial protein site of initial protein digestiondigestion

The stomach can hold about The stomach can hold about 1.5 L of food and contains 1.5 L of food and contains about 500 mL of corrosive about 500 mL of corrosive gastric juicesgastric juices

Mucous secreted from cells Mucous secreted from cells lining the stomach protect lining the stomach protect the stomach wall from being the stomach wall from being digested by its contentsdigested by its contents

Protein Digestion

Proteins and polypeptides Proteins and polypeptides are very large moleculesare very large molecules

An enzyme known as An enzyme known as pepsinpepsin is produced by is produced by peptic cells in the stomachpeptic cells in the stomach

This enzyme works along This enzyme works along with the hydrochloric acid with the hydrochloric acid in the stomach to break in the stomach to break down the polypeptides into down the polypeptides into smaller unitssmaller units

Another enzyme, Another enzyme, renninrennin, is used to , is used to slow the movement of milk slow the movement of milk through the digestive systemthrough the digestive system

If the mucous lining of the If the mucous lining of the stomach breaks down, an ulcer is stomach breaks down, an ulcer is formedformed

This is dangerous because This is dangerous because beneath the stomach lining there beneath the stomach lining there are many capillariesare many capillaries

Absorption in the Stomach

Because very little of the thick Because very little of the thick liquid called liquid called chymechyme that is that is produced in the stomach is produced in the stomach is absorbed thereabsorbed there

The stomach absorbs small The stomach absorbs small amounts of salts, water, anti-amounts of salts, water, anti-inflammatory medicines such as inflammatory medicines such as Aspirin, and alcoholAspirin, and alcohol

The Small Intestine

The first 30 cm of the small The first 30 cm of the small intestine is known as the intestine is known as the duodenumduodenum

The presence of acids from The presence of acids from the stomach here cause a the stomach here cause a release of bicarbonate ions release of bicarbonate ions from the pancreasfrom the pancreas

These bicarbonate ions These bicarbonate ions neutralize the acid (pH of the neutralize the acid (pH of the fluids goes from 2.5 to 9.0)fluids goes from 2.5 to 9.0)

Absorption

The stomach absorbs The stomach absorbs some water, vitamins and some water, vitamins and alcoholalcohol

Most absorption takes Most absorption takes place in the small place in the small intestineintestine

The interior of the small The interior of the small intestine is lined with intestine is lined with villivilli, , which are small finger-which are small finger-like projectionslike projections

The villi increase the surface area The villi increase the surface area of absorptionof absorption

The cell membranes of the lining The cell membranes of the lining of the small intestine also have of the small intestine also have folds, known as folds, known as microvillimicrovilli

The villi contains capillaries that The villi contains capillaries that absorb carbohydrates and amino absorb carbohydrates and amino acidsacids

The larger lipid molecules are The larger lipid molecules are absobed by the lymph vesselsabsobed by the lymph vessels

The pancreas also produces enzymes The pancreas also produces enzymes for digestionfor digestion

TrypsinTrypsin and and chymotrypsin chymotrypsin act on act on partially digested proteins, breaking partially digested proteins, breaking them down to shorter chainsthem down to shorter chains

Other peptidases are also produced by Other peptidases are also produced by the pancreas and small intestinethe pancreas and small intestine

Enzymes that break down nucleic acids Enzymes that break down nucleic acids are also produced by the pancreas and are also produced by the pancreas and small intestinesmall intestine

The breakdown of carbohydrates The breakdown of carbohydrates is due to amylase (which breaks is due to amylase (which breaks down starch), maltase (breaks down starch), maltase (breaks down maltose) and lactase (which down maltose) and lactase (which breaks down milk sugar)breaks down milk sugar)

Lipase Lipase enzymes break down lipids enzymes break down lipids into their fatty acids and glycerolinto their fatty acids and glycerol

The Liver and Gallbladder

The liver produces The liver produces bile bile saltssalts, which emulsify , which emulsify the fat (cause it to form the fat (cause it to form tiny globules)tiny globules)

These tiny globules of These tiny globules of fat have a large surface fat have a large surface area to volume ratio, area to volume ratio, and the lipase enzymes and the lipase enzymes work on them more work on them more effectivelyeffectively

Occasionally, a Occasionally, a gallstone will form, gallstone will form, which is crystallized bile which is crystallized bile saltsalt

This gallstone prevents the bile This gallstone prevents the bile salts from aiding in fat digestion salts from aiding in fat digestion and causes pain and causes pain

The pigments in bile are what give The pigments in bile are what give feces their characteristic brown feces their characteristic brown colorcolor

The liver also stores glycogen and The liver also stores glycogen and vitaminsvitamins

Digestion & Absorption of Macromolecules

Regulation of Small Intestine Processes

The small intestine is regulated by the The small intestine is regulated by the nervous and endocrine systemsnervous and endocrine systems

In the stomach, proteins in the food In the stomach, proteins in the food stimulate the production of gastrin, stimulate the production of gastrin, which stimulates hydrochloric acid which stimulates hydrochloric acid productionproduction

The movement of chyme into the The movement of chyme into the duodenum inhibits muscular contrations duodenum inhibits muscular contrations in the stomach, preventing more chyme in the stomach, preventing more chyme from entering the small intestinefrom entering the small intestine

A hormone known as secretin A hormone known as secretin stimulates the pancreas to produce stimulates the pancreas to produce bicarbonatebicarbonate

CCK and GIP are both released when CCK and GIP are both released when high-fat foods enter the duodenumhigh-fat foods enter the duodenum

Secretin, CCK and GIP reduce motility in Secretin, CCK and GIP reduce motility in the stomach, preventing more food the stomach, preventing more food from entering the small intestinefrom entering the small intestine

CCK also increases the release of bile CCK also increases the release of bile from the gall bladderfrom the gall bladder Hormone Animation

The Colon

By the time food reaches By the time food reaches the large intestine, it is the large intestine, it is completely digestedcompletely digested

The colon stores wastes The colon stores wastes long enough to absorb long enough to absorb waterwater

As well, bacteria that As well, bacteria that synthesize vitamins B & K synthesize vitamins B & K are found hereare found here

The buildup of waste in the The buildup of waste in the colon triggers nerve colon triggers nerve impulses that initiate a impulses that initiate a bowel movementbowel movement

6.3 – Health and the Digestive System

Many disorders of the digestive Many disorders of the digestive system will affect the health of the system will affect the health of the whole body whole body

These disorders may be These disorders may be physiological in nature, or they physiological in nature, or they may also be psychological may also be psychological

Ulcers

Ulcers are holes in the wall of the Ulcers are holes in the wall of the stomach and intestinestomach and intestine

These are often caused by a These are often caused by a breakdown of the mucus lining the breakdown of the mucus lining the GI tractGI tract

This is often caused by bacterial This is often caused by bacterial infectionsinfections

Inflammatory Bowel Disease

This is a general class of disorders This is a general class of disorders that result in an inflammation of that result in an inflammation of the GI tractthe GI tract

Some types of these diseases may Some types of these diseases may cause ulcers to appear, and the cause ulcers to appear, and the presence of blood in the stoolpresence of blood in the stool

In some cases, surgery may be In some cases, surgery may be required to remove diseased required to remove diseased portions of the digestive tractportions of the digestive tract

Accessory Organ Disorders

Hepatitis: Inflammation of the Hepatitis: Inflammation of the liverliver

Cirrhosis: A chronic liver disease Cirrhosis: A chronic liver disease where healthy liver tissue is where healthy liver tissue is replaced by fat and scar tissuereplaced by fat and scar tissue

Gallstones: Crystals of cholesterol Gallstones: Crystals of cholesterol and minerals build up in the gall and minerals build up in the gall bladder or duct, preventing the bladder or duct, preventing the flow of bileflow of bile

Psychological Disorders

Anorexia nervosaAnorexia nervosa BulimiaBulimia ObesityObesity PicaPica

The End