DigestionTopic 6.1

Assessment Statements

6.1.1 Explain why digestion of large food molecules is 6.1.1 Explain why digestion of large food molecules is essential.essential.

6.1.2 Explain the need for enzymes in digestion.6.1.2 Explain the need for enzymes in digestion. 6.1.3 State the source, substrate, products and 6.1.3 State the source, substrate, products and

optimum pH conditions for one amylase, one protease optimum pH conditions for one amylase, one protease and one lipase.and one lipase.

6.1.4 Draw and label a diagram of the digestive 6.1.4 Draw and label a diagram of the digestive system.system.

6.1.5 Outline the function of the stomach, small 6.1.5 Outline the function of the stomach, small intestine and large intestine.intestine and large intestine.

6.1.6 Distinguish between 6.1.6 Distinguish between absorptionabsorption and and assimilationassimilation.. 6.1.7 Explain how the structure of the villus is related 6.1.7 Explain how the structure of the villus is related

to its role in absorption and transport of the products to its role in absorption and transport of the products of digestion.of digestion.

Series of events

1.1. IngestionIngestion

2.2. DigestionDigestion

3.3. AbsorptionAbsorption

4.4. TransportTransport

Why digestion of large molecules is essential

Large molecules are too big to pass Large molecules are too big to pass across any cell membraneacross any cell membrane

Any food we eat must be chemically Any food we eat must be chemically digested to a suitable sizedigested to a suitable size

Molecule type Molecular form ingested

Molecular form after digestion

Protein Protein Amino acids

Lipids Triglycerides Glycerol and fatty acids

Carbohydrates Polysaccharides monosaccharides

Nucleic acids DNA, RNA nucelotides

Digestion allows you to turn molecules into ‘your own’

Example:Example: You eat an eggYou eat an egg The egg white (albumin) The egg white (albumin)

contains an amino acid contains an amino acid called serinecalled serine

Your stomach/small Your stomach/small intestine digests the intestine digests the albuminalbumin

Serine diffuses through Serine diffuses through the cells of the small the cells of the small intestine and then into a intestine and then into a capillarycapillary

Serine is enters a Serine is enters a pancreas cellpancreas cell

The cell uses the genetic The cell uses the genetic code of your DNA to build code of your DNA to build serine into insulinserine into insulin

Benefits of Benefits of digestion:digestion: Serine is able to Serine is able to

leave the albumin leave the albumin and enter the and enter the bloodstreambloodstream

Serine helps to Serine helps to synthesize your synthesize your own protein under own protein under the control of your the control of your DNADNA

Need for enzymesTo lower activation energyTo lower activation energy

Enzymes are protein Enzymes are protein molecules which act as molecules which act as catalysts for reactionscatalysts for reactions

They lower the activation They lower the activation energy of the reactions energy of the reactions that they catalyzethat they catalyze

Reactions occurring with Reactions occurring with an enzyme can occur with an enzyme can occur with a lower input of energy a lower input of energy than the same reaction than the same reaction without the aid of an without the aid of an enzymeenzyme

To catalyze hydrolysis To catalyze hydrolysis reactionsreactions Converts large Converts large

macromolecules to smaller macromolecules to smaller molecules that can be molecules that can be absorbed and then usedabsorbed and then used

Amylase puts stress on Amylase puts stress on bonds of glucose held bonds of glucose held together in a starch together in a starch moleculemolecule

Surrounding thermal Surrounding thermal energy provides molecular energy provides molecular motion to break the bondsmotion to break the bonds

Examples of digestive enzymes

Salivary amylase

Pepsin (a protease)

Pancreatic lipase

Source Salivary glands

Stomach cells Pancreas cells

Substrate Amylose (starch)

Proteins Lipids

Products Maltose/glucose

Amino acids Glycerol/fatty acids

Optimum pH Neutral (pH 7) Acidic (pH 3) Neutral (pH 7)

Digestive system

Any foods you Any foods you ingest must ingest must eithereither be be digested and digested and absorbed for use absorbed for use by the body by the body oror remain remain undigested and undigested and be eliminated as be eliminated as solid waste solid waste (faeces)(faeces)

Stomach

Food brought to Food brought to stomach by stomach by oesophagusoesophagus

When you swallow, the When you swallow, the food is forced down to food is forced down to your stomach by your stomach by peristalsisperistalsis

Once in the stomach, Once in the stomach, the food is held for a the food is held for a period of time in order period of time in order to mix it with a variety to mix it with a variety of secretions of secretions collectively known as collectively known as gastric juicesgastric juices

PepsinPepsin – a protease – a protease enzyme most active in enzyme most active in acidic pHacidic pH

Hydrochloric acidHydrochloric acid – – helps degrade and helps degrade and break down foods and break down foods and creates the acidic pH creates the acidic pH necessary for pepsin to necessary for pepsin to be activebe active

MucusMucus – lines the – lines the inside of the stomach inside of the stomach wall to prevent stomach wall to prevent stomach damage from the damage from the hydrochloric acidhydrochloric acid

The muscular wall The muscular wall of the stomach of the stomach creates a churning creates a churning motion in order to motion in order to mix the food with mix the food with the gastric juicethe gastric juice

After a period of After a period of time, a valve at the time, a valve at the lower end of the lower end of the stomach opens and stomach opens and the food enters the the food enters the small intestinesmall intestine

What are you eating in a day?

How to read food labels Record the nutrition facts for all of Record the nutrition facts for all of

the food that you consume in one the food that you consume in one mealmeal

Small intestine

11stst portion is called the portion is called the duodenumduodenum Secretions are emptied here in Secretions are emptied here in

order to continue the digestive order to continue the digestive process:process: Bile from liver and gall bladderBile from liver and gall bladder Trypsin (a protease), lipase, amylase Trypsin (a protease), lipase, amylase

and bicarbonate from the pancreasand bicarbonate from the pancreas

Small intestine villi

Molecules are produced that are Molecules are produced that are small enough to be absorbedsmall enough to be absorbed

Inner wall of small intestine is made Inner wall of small intestine is made up of thousands of finger-like up of thousands of finger-like extensions called extensions called villivilli which functions which functions to increase surface area for to increase surface area for absorptionabsorption

Each villus contains a capillary bed Each villus contains a capillary bed and a and a lacteallacteal (a small vessel of (a small vessel of lymphatic system)lymphatic system)

AbsorptionAbsorption Molecules taken into Molecules taken into

capillary bed and capillary bed and lacteallacteal

Taken to a wide Taken to a wide variety of body cellsvariety of body cells

Used for energyUsed for energy

AssimilationAssimilation Molecules taken into Molecules taken into

capillary bed and capillary bed and lacteallacteal

Taken to a wide Taken to a wide variety of body cellsvariety of body cells

Used for building Used for building larger moleculeslarger molecules

Large intestine

Vast majority of food is absorbed in SI

What remains is undigested

Much of the water we drink or that is found within food is still present

Escherichia coli and other naturally occurring bacteria are mutualists

We provide nutrients, water, and a warm environment

They synthesize vitamin K and maintain and overall healthy environment

Any undigested food is eliminated from the body as solid waste or faeces

Vitamin K

Vitamin K is essential in humans and most animals as we cannot synthesize the compound ourselves

vitamin K is used by the liver to synthesise prothrombin, which in turn is processed to form the enzyme thrombin; a key enzyme involved in the blood clotting process

there is increasing evidence that vitamin K has additional roles in maintaining in bone health

There are two forms of vitamin K vitamin K1 – comes from our diet and is found in soybean

oil and dark green veggies vitamin K2 - which can come from the bacteria in the gut

and indeed E. coli can synthesise menaquinone because it uses it during respiration. As E. coli lives and dies in the gut, the dead cells release vitamin K2, which can then, theoretically, be absorbed and utilised by the body.