Unit 4 Digestion and absorption of food

Learning objectives

1. Explain why animals need to digest food and distinguish between chemical and mechanical digestion.

2. Be able to locate the position of and describe the function of the following organs and structures: salivary glands, esophagus, stomach, small intestine (duodenum and ileum), large intestine (colon, appendix, rectum), anus, pyloric sphincter, anal sphincter, gallbladder, bile duct, pancreas, liver.

3. Explain the role of these digestive secretions, enzymes and other chemicals: saliva, stomach secretions, pancreatic juice and bile.

4. Explain the role and properties of enzymes as biological catalysts.

5. Explain why enzymes are very specific using the 'Lock and Key' model of enzyme action.

6. Explain the effects of changing temperature and pH on enzyme activity.

7. Describe peristalsis.

8. Explain how the structure of the ileum is adapted for absorption, and list the mechanisms by which food molecules are absorbed.

9. Describe how the gut microbiome is important for health.

10. Describe the role of the liver in processing absorbed food (in particular sugars and amino acids), and destroying poisons.

11. State the order in which the body’s energy stores are used when a person is deprived of food.

Lo.1 Explain why animals need to digest food and distinfuish between chemical and mechanical digestion.

Digestion is important as out body needs nutrients from food and drink to stay healthy and the digestive system breaks nutrients down into smaller parts to be absorbed across the cells of the small intestine and into the blood.

Example.

Proteins are broken down into peptides by the enzyme trypsin

The peptides are then broken down into amino acids by the nzyke peptidase.

Minerals and vitamins are already so small that they don’t need to be digested(and water). Humans cannot digest cellulose (fiber) as we do not contain the enzyme cellulase

Enzymes mostly end with -ASE

Lo.2 Be able to locate the position of and describe the function of the following organs and structures: salivary glands, esophagus, stomach, small intestine (duodenum and ileum), large intestine (colon, appendix, rectum), anus, pyloric sphincter, anal sphincter, gallbladder, bile duct, pancreas, liver.

Types of digestion

1. Mechanical digestion:

   When we physically break food down into smaller pieces. It mostly happens when chewing by both teeth and muscular contractions of the tongue and gut.

2. Chemical digestion:

When chemicals break down food molecules into smaller, simple nutrients that can be used by the cell, this happens through enzymes, bile, and acid.

Enzymes break down carbohydrates into glucose

Proteins are broken down into amino acids

Oils are broken down into glycerol and 2 fatty acids

Stages of digestion

• Food is digested into the mouth and small intestine

• Digested food is then absorbed into the bloodstream through the small intestine.

• Excess water is stored in the large intestine

• Any undigested food passes out of the anus through the form of feces.

The Locations of nutrient digestion mouth, stomach, and small intestine

The location of nutrient absorption is the small intestine.

Organ structure and functions

• Salivary glands

Function: secretes saliva for moistening food and releasing the enzyme amylase to start digestion.

• Esophagus

Function: a tube connecting the mouth to the stomach, surrounded by muscles which contract (peristalsis)

• Stomach

Function: Secretes gastric juice containing HCL( kills bacteria) and the enzyme pepsin (for digestion )

• Small intestine (long and thin)

Function: secretes intestinal juice containing many enzymes for digestion and absorbs digested food into the bloodstream

• Large intestine (short and thick)

Function: Absorbs water from food and forms feces(indigested food, dead cells, and bacteria)

• Pyloric sphincter

Function: (sphincter is a ring of muscles) controls the release of food to the small intestine(allowing enough time to digest)

• Anal sphincter

Function: Controls the release of feces from the rectum

• Gall bladder

Function: Stores bile from the liver (bile surrounds fats and breaks it down into smaller pieces/for chemical digestion)

• Bile duct

Function: Connects to gall bladder to the small intestine

• Pancreas

Function (right behind the stomach): makes enzymes for digestion, secretes pancreatic enzymes, makes sodium bicarbonate to neutralize stomach acid, and makes insulin to control blood sugar levels

• Liver

Function: Makes bile (liquids turning fats into smaller pieces) and amino acids, and stores excess sugar

Lo.. 3 Explain the role of these digestive secretions, enzymes, and other chemicals: salivary, stomach secretions, pancreatic juice, and bile.

In chemical digestion, food is broken down by chemicals such as bile, enzymes, and acids.

Enzymes help for digestion occur faster

Examples :

Starch is broken down by amylose into maltose

Polypeptides broken down by the enzyme pepsin break down into peptides.

Emulsification is the mixing 2 immiscible liquids

Bile breaks fat down into smaller balls of fat to speed up digestion

Which changes both surface area (+) and size (-)

Why does this help?

• The larger surface area allows lipases to work better

Work equation examples

(a) The enzyme amylase found in saliva and pancreatic juice breaks down starch into maltose.

Starch -(amylase)—> maltose

(B) Fats are broken down into fatty acids and glycerol by lipase. This occurs into the small intestine.

Fat—(lipase) —> fatty acids and glycerol

Lo 4: Explain the role and properties of enzymes as biological catalysts.

Most chemical reactions occurring in the body would be impossible, for example, the body temperature of most organisms is too low for reactions to occur quickly enough to carry out life processes.

Lower temperature VS higher temperature

More collisions occur as the temperature increases(you can’t directly heat organisms)

As the concentration of reactants increases, the number of successful collisions increases

Since these two cannot just randomly increase, we need a catalyst

A catalyst is a chemical that speeds up chemical reactions.

In organisms, catalysts are called enzymes. An enzyme is a protein that acts as an enzyme to speed up the rate of reaction.

Enzymes have a part called the active site, which binds to the substrate molecule.

Which is then broken down into products.

The active site and the substrate match each other in both shape and chemical properties; only specific substrates can bind to an enzyme’s active site.

Enzymes are particular and catalyze only 1 reaction for example.

Lipase breaks down lipids(fats). Lipase cannot break down starch or proteins.

Enzymes are never used up and are reused

Lo. 5 Explain why enzymes are specific using the lock and key model of enzyme acyion

The lock and key model

Claims that the substrate will fit into a specific enzyme’s active site as a key fits into a particular lock.

If the enzymes’ shape were to change, it will not be able to bind with the active site.

Lo. 6 Explain the effects of changing temperature and pH on enzyme activity.

Enzymes are held together in a specific 3D shape by chemical bonds.

Things affecting Enzyme activity

• Extreme temperature changes

• pH levels

This is because extreme temperatures and pH levels can break bonds and alter the shape of the enzyme, thereby reducing its ability to catalyze reactions.

What is denaturation

Denaturation is when the enzymes’ shape has changed so they lose their ability to bond with the substrate, losing their function.

The effect of temperature on enzyme activity

1. Low temperatures slow down chemical reactions due to insufficient energy

2. Increasing temperature speeds up the movement, leading to more enzyme-substrate interaction

3. Enzyme activity is highest at its optimal temperature.

4. Too much heat can break bonds, changing the shape of the enzyme (denaturation), stopping it from working

The effects of pH on Enzyme activity

1. Enzymes have charged amino acids helping them maintain shape(if the environment changes, their bonds break)

2. At optimal pH, enzyme activity is at its highest

3. Changing pH disrupts charges, altering enzymes’ shapes (denaturation)

   Decreasing pH below the optimal temperature will denature and past the optimal temperature will denature

In pH levels, if anything is above or below the optimal pH, it will denature

Enzymes work best in the environment they are normally found.

Lo.7 Describe Peristalsis

Food moves through the digestive system by peristalsis. Which is where muscles contract and release pushing food forward.

Persistalsis happens in the esophagus, stomach, and intestines, moving one way from mouth to anus.

Lo 8 Explain how the structure of the small intestine is adapted for absorption, and list the mechanisms by which food molecules are absorbed.

Function of the small intestine:

complete digestion

Digested nutrients(amino acids, fatty acids, glycerol, and glucose) and minerals/vitamins are absorbed into the bloodstream.

Adaptation of the small intestine

1. Increased surface area- the intestine has villi, which increase surface area, allowing more absorption

2. Thin walls- the villi walls are thin, allowing quick absorption into the blood via facilitated diffusion and active transport

3. Blood supply - rich supply network of capillaries carries glucose and amino acids away from the intestine

4. Lacteals for fat absorption- Every villus has a lacteal which transports fatty acids and glycerol into the lymphatic system. Fats enter the lacteals through simple diffusion

Diagram of the Villi which are located in lymph vessels

(learn the parts of it)

Absorption of fats

End products of digesstion

• glucose

• amino acids

• minerals

• vitamins

How are they absorbed into the bloodstream?

• Absorbed into the capillary in the villi

Transport mechanism(S)

• Simple diffusion

• Facilitated diffusion

• active transport

End products of digestion

• Fatty acids

• glycerol

How are they absorbed into the bloodstream?

• Absorbed into the lacteal inside the villi

  Transport mechanism

• Simple diffusion

Lo 9: Describe how the gut microbiome is important for health

Microbiome means a collection of microorganisms (bacteria, fungi, and viruses) in a specific environment

Most bacteria live in the small intestine, as the stomach’s acidity prevents their growth

The bacteria help by

• producing vitamins

• Preventing harmful bacteria from growing

• breaking down toxins in the large intestine

• Digesting fiber, starch, and sugars, which the body cannot do on its own

• Without these bacteria, nutrition could be lost

We have a symbiotic relationship with bacteria

L 10 Describe the role of the liver in processing absorbed food

All blood from the small intestine flows along the hepatic portal vein

The livers function

• Makes bile

• Stores excess sugar

• makes amino acids

The liver converts nutrients in our diets into substances that the body can use, stores them, and supplies cells when needed.

The processing of absorbed food molecules by the liver:

Sugars

1. Excess glucose is converted into glycogen and stored inside liver cells

2. If glycogen stores in the liver are full, any further excess of glucose is turned into fat and stored around the body.

Amino acids

1. The liver can make nonessential amino acids from other amino acids eaten.

2. Excess amino acids are not stored in the body but broken down into 2 parts;

Amino acids (CHON) part containing N atoms are excreted in urine

Part containing CHO is converted into sugars + fats

Why does blood need to be taken to the liver before being distributed around the body.

This is because the liver plays a critical role in processing nutrients, detoxifying harmful substances, and regulating blood glucose levels before the blood circulates to other organs.

Lo 11 State the order in which the body’s energy stores are used when a person is deprived of food

Basic ways we use energy: Basic metabolism(digestion), movement

In a fasting state, energy stores are used in the order

1. Glycogen stores in the liver get used up first in short-term fasting

2. Fat stores in fat cells are used for longer-term needs such as an undernourished diet

3. Muscle protein is used for energy only during starvation as it causes harm to the body