the digestive system i. type of food -...
TRANSCRIPT
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.
By: Hanadi Al- Shafee
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
By: Hanadi Al- Shafee
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.
By: Hanadi Al- Shafee
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)
By: Hanadi Al- Shafee
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
By: Hanadi Al- Shafee
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.
By: Hanadi Al- Shafee
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.
By: Hanadi Al- Shafee
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
By: Hanadi Al- Shafee
Digestion of carbohydrates
Starch digestion happens slightly in mouth & continues in the small intestine.
By: Hanadi Al- Shafee
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.
By: Hanadi Al- Shafee
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.
By: Hanadi Al- Shafee