the digestive system i. type of food -...

By: Hanadi Al- Shafee

The Digestive System

I. Type of food:

1- Carbohydrates 2- Proteins 3- Lipids 4- Water

5- Vitamins 6- Minerals 7- Fibers

1- Carbohydrates: are energy foods (sugars). They are made of C,H, and O

atoms. They are of 3 categories:

A- Simple sugars (Monosaccharides): made up of 1 simple unit,

soluble in water. Their molecular formula is C6H12O6. Example:

Glucose, Fructose and Galactose.

B- Compound/Double sugars (Disaccharides): made up of

2 simple units joined together.

They are soluble in water, their molecular formula is

C12H22O11. Example: maltose, Lactose and sucrose.

B- Complex sugars (polysaccharides): made up of more than 2 units joined

together. As an example, starch is made of more than 1000 glucose units.


2- Proteins:

Proteins are building up foods, they are made

of C,H,O, and N atoms.

The simplest units of proteins are amino acids.

Amino acids join to form a polypeptide.

Polypeptides join to form protein.

3- Lipids:

Are energy foods.

Lipids are made of fatty acids and

glycerol.

They are made up of C,H, and O.

Category Example Simplest Units Food Sources

Monosaccharides

1- Glucose - Grapes

2- Fructose - Honey & fruits

3- Galactose - Some seed

Disaccharides

1- Sucrose Glucose +

Fructose Sugar can

2- Lactose Glucose +

Galactose Milk

3- Maltose Glucose +

Glucose Barely

Polysaccharides Starch Glucose Bread

Proteins - Amino Acid Meat & egg

Lipids - Fatty Acid +

Glycerol oil


II. Identify Tests for Various Kinds of

Food:

1- Iodine Test:

-Used for the testing of starch

presence.

-Iodine is added to food and color

changes from brown to dark blue

color indicating the presence of

starch.

2- Fehling Test:

- Used for the presence of reducing

sugars.

- Fehling solution (blue) is added to

food and heat is applied then brick red

precipitate is observed indicating the

presence of reducing sugars (glucose).

Reducing Sugars are all simple sugars, maltose and lactose. Sucrose

is a non- reducing sugar.

3- Biuret Test: - Used to identify the presence of

proteins and peptides.

- Biuret solution is added and violet

color is observed if proteins or

peptides are present.


4- Coagulation Test: this test is used to distinguish between

proteins and polypeptides.

We apply heat to tubes, if solid structure 9coagulation) is

observed, then it os proteins.

If no change occurs, then the test tube contains polypeptides.

5- Rubbing on a paper: a translucent spot is observed,

identifying the presence of lipids.

III. Digestion: A General View:

Digestion is the process of gradual breaking down of complex food into simple

nutrients that the body can absorb and use.

Complex food is gradually broken down during digestion into simple nutrients.

Carbohydrates

(Complex food)

Monosaccharides

(Simple Nutrients)

Proteins

(Complex food)

Amino acids

(Simple Nutrients)

Lipids

(Complex food)

Fatty acids +

Glycerol

(Simple Nutrients)


Digestion could be two types:

Mechanical digestion (Mechanical transformation or simplification): is

breaking down of complex food into small food.

Example: mastication (chewing), churning and peristaltic movement.

Chemical digestion (Chemical transformation or simplification): is the

Change of food from complex molecules into simple molecules (nutrients). It

occurs under the action of biochemical substances called enzymes which are

contained in the digestive juices. Each juice contains one or more enzymes.

Example: proteins transformed into amino acids under the action of enzyme

called Trypsin present in the intestinal juice.

Organs of the digestive system: the

digestive tract (tract):

1. Mouth: chemical digestion (saliva)

and mechanical digestion (chewing

by teeth).

2. Pharynx: common pathway

between the respiratory and the

digestive system.

3. Esophagus: Mechanical digestion

only (peristaltic movement).

4. Stomach: chemical (Gastric juice)

and mechanical (churning).

5. Small Intestine: chemical (juice)

and mechanical (churning &

peristaltic movement).

6. Large Intestine.

7. Anus.

Mechanical Digestion

Chemical Digestion


Digestive glands

The digestive glands: are organs that produce chemicals called digestive

juices, containing enzymes, to help in digesting food. food doesn’t pass by

them.

1. Salivary Gland

2. Gastric Gland

3. Pancreas

4. Intestinal Gland

The liver, the pancreas, and the gall bladder are accessory organs that help in

digestion without letting food pass through them.

IV. Enzymes:

A- Introduction:

- Enzymes are substances secreted in the body they are known as biological

catalysts.

- They speed up the simplification of complex molecules into simple units.

- Enzymes transform food (substrate) into nutrients.

- Enzymes act on the substrate as key and lock.

- Enzymes are used in small amounts, and remain unchanged at the end of the

reaction.

B- Properties of Enzymes:

1- Specificity.

2- Medium or PH.

3- Temperature.

4- Time.

1- Specificity:

Enzymes act on specific substrates. This

means that every type of food needs a

specific enzyme to work on. This is called

the key-lock model, where the key is the

enzyme and the lock is the substrate.

Amylase acts only on starch.

Proteases digest only proteins.

Lipase acts only on lipids.


2- Enzyme work is only a suitable medium (pH):

PH is the scale from 1 to 14 used to know if a substance is acidic or basic or

neutral.

The PH of the mouth is neutral (PH=7). While, the PH of the stomach is acidic

(PH<7) and that of the small intestine is basic (PH>7).

3- Enzymes and Temperature:

The optimum temperature for enzymatic activity is at normal body

temperature= 37oC.

Enzymes are destroyed if temperature is greater than 60 oC, and cannot be

active again if we decrease the temperature.

Cold temperature (<37 o C) will stop the enzyme activity, but will not destroy it.

The enzyme is inactive at zero o

C and regains its activity if the enzyme activity

is regenerated if we increase the temperature to 37 oC.


V. From Food to Nutrients:

Digestive

Tube

Name of the

gland

Medium Juice Enzyme Action

Mouth Salivary

glands

Neutral

(pH=7)

Saliva Salivary

Amylase

Cooked starchmaltose

Stomach Gastric

glands

Acidic

(pH=2)

Gastric

juice

Pepsin

(protease)

Proteins polypeptides

Small

Intestine

Pancreas

Basic

(pH=8)

Pancreatic

juice

1- Lipase

2-

Protease:

Trypsin

3- Maltase

4-

Amylase

Lipidsfatty acid +

glycerol

Proteins Peptide

amino acid

Maltose glucose

Starch maltose

Intestinal

glands

Intestinal

juice

1- Lipase

2- Protease

3- Maltase

4-

Amylase

5- Surcase

6- Lactase

Lipids fatty acid &

glycerol

Proteins amino acids

Maltoseglucose +

glucose

Starch glucose +

fructose

Sucrose glucose +

fructose

Lactose glucose +

galactose


Digestion of carbohydrates

Starch digestion happens slightly in mouth & continues in the small intestine.


Lipids digestion begins in the stomach and ends in the small intestine.

Bile characteristics:

- It is a greenish liquid

- Bile secreted by the liver, stored in the gallbladder and released to the small

intestine.

Role of bile:

Emulsification of lipids (dispersion of lipids).

Provide a basic (alkaline) medium for pancreatic and intestinal

enzymes.

Facilitate (speed up) the action of lipase.

VI. The Route of Nutrients:

Nutrients are small and soluble molecules that result from the final and

complete digestion of food.


Small Intestine:

- Folded

- Its inner wall contains many ridges.

- Ridges are covered with several close villi (folds/projections).

- Villus is the unit of absorption.

Characteristics of Villi:

1- Its large surface area.

2- Thin wall favor absorption.

3- It is richly vascularized.

Nutrients leave the small intestine to the blood stream or to lymph, then joined

and distributed to the whole body organs.

The undigested food goes to the large intestine to form feces and to get it out of

the body.

Water and mineral salts are absorbed through the large intestine.

Absorption is the passage of nutrients from the small intestine to the blood or

the lymph through the villi of the intestinal wall.

Blood leaving the small intestine will be higher in glucose and amino-

acids concentrations due to intestinal absorption.

Characteristics of Villi:

1- Large surface area.

2- Highly vascularized.

3- Thin wall.

the digestive system i. type of food -...

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