NUTRITION
Balanced Diet


A balanced diet consists of all of the food groups in the correct proportions
The necessary food groups are:
o Carbohydrates
o Proteins
o Lipids
o Vitamins
o Minerals
o Dietary Fibre
o Water
Food Groups Table
Vitamin and Mineral Requirements Table
Varying Dietary Needs of Individuals Table
Scurvy & Rickets
Scurvy




Scurvy is the name for a severe vitamin C deficiency
o It is caused by a lack of vitamin C in the diet for over 3 months
Its symptoms include:
o Anemia
o Exhaustion
o Spontaneous bleeding
o Pain in the limbs
o Swelling
o Gum ulcerations
o Tooth loss
It is a condition that was commonly seen in sailors between the 15th to 18th centuries
o Long sea voyages made it very hard to access a ready supply of fresh produce
Scurvy can be treated with oral or intravenous vitamin C supplements
Rickets


Rickets is a condition in children characterised by poor bone development
Symtpoms include:
o Bone pain
o
o



Lack of bone growth
Soft, weak bones (sometimes causing deformities)
Rickets is caused by a severe lack of vitamin D
o Vitamin D is required for the absorption of calcium into the body
 Calcium is a key component of bones and teeth
Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish,
eggs and butter)
The treatment for rickets is to increase consumption of foods containing calcium and vitamin D
o Alternatively vitamin D supplements can be prescribed
Identifying Organs of the Digestive System
The human digestive system
Organs of the Digestive System: Function
Stages of food breakdown

Food taken into the body goes through 5 different stages during its passage through the
alimentary canal (the gut):
o Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth
o
o
o
o
o
Mechanical digestion - the breakdown of food into smaller pieces without chemical
change to the food molecules
Chemical digestion - the breakdown of large, insoluble molecules into small, soluble
molecules
Absorption - the movement of small food molecules and ions through the wall of the
intestine into the blood
Assimilation - the movement of digested food molecules into the cells of the body where
they are used, becoming part of the cells
Egestion - the passing out of food that has not been digested or absorbed, as faeces,
through the anus
Functions of the Digestive Organs Table
Physical Digestion



Physical digestion (sometimes referred to as mechanical digestion) is the breakdown of food into
smaller pieces without chemical change to the food molecules
The processes that take place during physical digestion help to increase the surface area of food
for the action of enzymes during chemical digestion
It is mainly carried out by the chewing action of the teeth, the churning action of
the stomach and the emulsification of fats by bile in the duodenum
Types of Human Teeth




Mechanical digestion is the breakdown of food into smaller pieces without chemical change to
the food molecules
It is mainly carried out by the chewing action of the teeth, the churning action of
the stomach and the emulsification of fats by bile in the duodenum
Teeth are held firmly in the bone of the jaw
o They are used for chewing to increase the surface area of the food so that it can be
exposed to saliva and other digestive juices and broken down more quickly
The differing shapes and sizes of teeth enable them to perform slightly different functions:
o Incisors - chisel-shaped for biting and cutting
o Canines - pointed for tearing, holding and biting
o Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and
grinding up food
Types of teeth
Structure of a Tooth
Structure of a typical tooth
The Stomach



The stomach is one of a number of organs that make up the digestive system
The role of the digestive system is to break down large insoluble molecules into smaller, soluble
food molecules to provide the body with nutrients
The stomach lining contains muscles which contract to physically squeeze and mix the food with
the strong digestive juices that are present
o Also known as "stomach churning"

Food is digested within the stomach for several hours
Three types of tissue found in the stomach are muscular, epithelial and glandular. These
tissues work together to allow the stomach to carry out its role.
Emulsification of Fats & Oils: Extended

Cells in the liver produce bile which is then stored in the gallbladder
Bile production and secretion
Bile has two main roles:



It is alkaline to neutralise the hydrochloric acid which comes from the stomach
The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the
stomach
It breaks down large drops of fat into smaller ones. This is known as emulsification. The
larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids
faster
Exam Tip
Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper.This
is an example of mechanical digestion, not chemical digestion – breaking something into
smaller pieces does not break bonds or change the chemical structure of the molecules which
make it up, which is the definition of chemical digestion.
Chemical Digestion
Stages of food breakdown

Food taken into the body goes through 5 different stages during its passage through the
alimentary canal (the gut):
o Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth
o

Mechanical digestion - the breakdown of food into smaller pieces without chemical
change to the food molecules
o Chemical digestion - the breakdown of large, insoluble molecules into small, soluble
molecules
o Absorption - the movement of small food molecules and ions through the wall of the
intestine into the blood
o Assimilation - the movement of digested food molecules into the cells of the body where
they are used, becoming part of the cells
o Egestion - the passing out of food that has not been digested or absorbed, as faeces,
through the anus
The role of chemical digestion is to produce small soluble molecules that can be absorbed
Enzymes in Digestion
Amylases


Amylases are produced in the mouth and the pancreas (secreted into the duodenum)
Amylases digest starch into smaller sugars
The digestion of starch
Proteases

Proteases are a group of enzymes that break down proteins into amino acids in the stomach
and small intestine (with the enzymes in the small intestine having been produced in the
pancreas)
The digestion of proteins
Lipases


Lipase enzymes are produced in the pancreas and secreted into the duodenum
They digest lipids into fatty acids and glycerol
The digestion of lipids
Hydrochloric Acid



The stomach produces several fluids which together are known as gastric juice
One of the fluids produced is hydrochloric acid
This kills bacteria in food and gives an acid pH for enzymes to work in the stomach
How is a low pH helpful in the stomach?



The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their
cells, meaning they cannot carry out any cell reactions to maintain life
Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH
- around pH 2
The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain
within the optimum range for pepsin to work at its fastest rate
Digestion of Starch: Extended


Amylases are produced in the mouth and the pancreas (secreted into the duodenum)
Amylases digest starch into smaller sugars
The digestion of starch


Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the
pancreas) and digests starch to maltose (a disaccharide)
Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium
lining the small intestine
Digestion of Protein: Extended

Proteases are a group of enzymes that break down proteins into amino acids in the stomach
and small intestine (with the enzymes in the small intestine having been produced in the
pancreas)
The digestion of proteins

Protein digestion takes place in the stomach and duodenum with two main enzymes produced:
o Pepsin is produced in the stomach and breaks down protein in acidic conditions
o Trypsin is produced in the pancreas and secreted into the duodenum where is breaks
down protein in alkaline conditions
Bile: Extended

Cells in the liver produce bile which is then stored in the gallbladder
Bile production and secretion
Bile has two main roles:



It is alkaline to neutralise the hydrochloric acid which comes from the stomach
The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the
stomach
It breaks down large drops of fat into smaller ones. This is known as emulsification. The
larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids
faster
Exam Tip
Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper.This
is an example of mechanical digestion, not chemical digestion – breaking something into
smaller pieces does not break bonds or change the chemical structure of the molecules which
make it up, which is the definition of chemical digestion.
Absorbing Nutrients


Absorption is the movement of digested food molecules from the digestive system into the
blood (glucose and amino acids) and lymph (fatty acids and glycerol)
Nutrients are absorbed in the small intestine
Absorbing Water

Water is absorbed in both the small intestine and the colon, but most absorption of
water (around 80%) happens in the small intestine
Adaptations of the Small Intestine: Extended


The ileum is adapted for absorption as it is very long and has a highly folded surface with
millions of villi (tiny, finger like projections)
These adaptations massively increase the surface area of the ileum, allowing absorption to take
place faster and more efficiently
Adaptations of the small intestine
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Microvilli on the surface of the villus further increase surface area for faster absorption of
nutrients
Wall of villus is one cell thick meaning that there is only a short distance for absorption to
happen by diffusion and active transport
Well supplied with a network of blood capillaries that transport glucose and amino acids away
from the small intestine in the blood
Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the
small intestine in the lymph
Exam Tip
The way in which the structure of a villus is related to its function comes up frequently in
exam questions so it is worth ensuring you have learned these adaptations.
Nutritive value of foods
Proteins
Sources
Functions
HBV: (All essential amino acids.)E.g.: Milk, Meat, Fish, Eggs, Cheese.
Growth (hair, nails,
skin)
LBV:(lack some essential amino acids.)E.g.: Cereals, pulses, nuts, some
vegetables.
Growth (hair, nails,
skin)
Chemistry: Oxygen, Carbon, Hydrogen, Nitrogen, Sulphur, Phosphorus.
Body maintenance
Deficiency: Kwashiorkor, Marasmus, and Kidney disease.
Providing energy
Symptoms: Kwashiorkor: Diarrhoea, Fatigue, Enlarged Belly.
Repair
Marasmus: Growth failure, sunken eyes, “old man’s” face.
Repair
Carbohydrates
Sources: Milk, yogurt, bread, rice, beans, cereals.
Classification:
Monosaccharides:
(carbohydrates that can’t be hydrolyzed to simpler carbohydrates.)
Fructose, Glucose, Galactose.
Disaccharides:
(consists of two Monosaccharides.)
Sucrose, Maltose, Lactose.
Polysaccharides:
(many glucose molecules joined together.)
Starch, Cellulose, Glycogen, Dextrin.
Functions:
Provide energy.
Aids fat metabolism.
Helps build body mass.
Prevents constipation.
Chemistry:
Oxygen, Carbon, Hydrogen.
Deficiency:
Marasmus.
Loss of stamina.
Symptoms:
Marasmus:
Growth failure.
Loss of hair.
Shrunken body.
Ribs stick out.
Skin hangs loose.
Sunken Eyes.
“Old man’s” face.
Fats
Sources:
Visible fat: (easy to detect in food.)
E.g.: Butter, Cooking oils/fats, fat on meat.
Invisible fat: (difficult to detect in food.)
E.g.: Lean meat, egg yolk, oily fish, nuts, seeds, fruits, fried foods, sweets.
Types:
Fats: Solid and Saturated.
Oils: Liquid and Unsaturated.
Functions:
Provides energy.
Stores energy for later.
Protects vital organs.
Insulation.
Provides texture and flavor.
Chemistry:
Oxygen, Carbon, Hydrogen.
Deficiency:
Growth Failure.
Eczema of skin.
In Excess.
Obesity.
CHD (coronary heart disease).
Cancer.
High blood pressure.
Stress
Vitamins
A:
Deficiency: Night blindness and Skin defections.
Sources: Vegetables & fruits, Milk, Liver & meats.
Functions:
Keeps skin &
mucus membrane healthy.
Prevents night blindness.
Promotes growth.
B:
Deficiency: Beri-Beri and Anaemia.
Sources: Eggs, Fish, Yeast, Broccoli, Lean meat.
Functions:
Releases energy from carbohydrates.
Healthy nervous system.
Healthy skin.
Aids in absorption.
C:
Deficiency: Scurvy (Bleeding gums).
Sources: Citrus fruits, Berries, Vegetables.
Functions:
Improves immune system.
Aids in wound healing.
Aids in absorption.
D:
Deficiency: Rickets (Soft bones & Dental decay).
Sources: Eggs, Fish, Yeast.
Functions:
Strong bones & teeth.
Maintain heart actions.
Maintains nervous system.
E:
Deficiency: Sterility.
Sources: Cereals and nuts, Green Vegetables, Wheatgerm
Functions:
Maintains reproductive system.
Aids in fighting diseases.
K:
Deficiency: Prolonged bleeding.
Sources: Cabbage, Spinach, Soybeans, Cauliflower.
Functions:
Clotting of blood.
Strong bones.
Vitamin B group
Thiamine (B1)
Functions:
Circulation.
Blood formation.
Brain function.
Sources: Organ meats, Yeast, Peas, Beans.
Riboflavin (B2)
Functions:
Blood formation.
Production of anti-bodies.
Sources: Meat, Poultry, Fish, Nuts, Liver.
Nicotinic acid (B3)
Functions:
Circulation.
Healthy skin.
Aids the nervous system.
Sources: Meat, Nuts, Potatoes.
Cobalamin (B12)
Functions:
Prevents anaemia.
Cellular longevity.
Digestion
Sources: Lamb, Beef, Eggs, Poultry, Liver.
Mineral elements
Calcium:
Deficiency: Osteomalacia and Rickets.
Functions:
Bones & teeth growth.
Nerve conduction/ muscle contractions.
Sources: Yoghurt, Milk, Cheese, Tofu.
Iron:
Deficiency: Anaemia.
Functions:
Haemoglobin production.
Production of enzymes for metabolism.
Sources: Liver, Soya beans, Apricots, Leafy vegetables.
Phosphorus:
Deficiency: Anorexia.
Functions:
For metabolism.
Bone development.
Muscles contraction
Sources: Fish, Milk, Meats, Nuts, Poultry.
Potassium:
Deficiency: Hypokalaemia.
Functions:
For nerve impulses.
Fluid balance.
Normal heart function.
Sources: Potatoes, Beans, Fruits, Vegetables, Squash.
Sodium:
Deficiency: High blood pressure.
Functions:
For nerve impulse conduction.
Muscle contraction.
Fluid balance
Sources: Salt, Canned food, Meat, Fish.
Fluoride:
Deficiency: Tooth decay.
Functions:
Development of bones & teeth.
Aids teeth to be resistant to decay.
Sources: Tea, Seafood, Drinking water.
Chloride:
Deficiency: Imbalance in blood P.H.
Functions:
For salivary amylase activation.
For gastric acidity.
Regulation of osmotic pressure
Sources: Eggs, Meat, Salt, Seaweed, Cheese, Celery, Olives.
Iodide:
Deficiency: Goitre.
Functions:
For production of hormones.
Maintaining metabolic rate.
Sources: Yoghurt, Milk, Eggs, Seaweed.
Water
Functions of water:
Forms saliva.
Regulates body temperature.
Flushes body waste; mainly in urine.
Prevents constipation.
Moistens oxygen for breathing.
Helps convert food to energy.
Protects body organs & tissues.
Lubricates joints.
Growth of cells.
Facilitates blood flow.
Keeps mucus membrane moist.
Helps dissolve minerals & nutrients.
NSP/ Dietary fiber
Sources and functions of non-starch polysaccharide (NSP)/dietary fiber:
Source: Cellulose & Pectin.
Functions:
Can’t be digested.
Aid removal of water from the body by peristalsis.
Absorb water.
Digestion and absorption
Digestion stages

Mouth:
Physical breakdown
Chemical breakdown
Teeth rip, tear & grind food to smaller pieces.
Protein & fat DO NOT break down here.
Tongue pushes food down the oesophagus.
Carbohydrate: Salivary amylase converts
starch to maltose.
Chemical breakdown
Physical breakdown
Salivary glands produce saliva and amylase to moisten
food for easy swallowing.

Stomach:
Chemical breakdown
Physical breakdown
Peristalsis moves food around; helps to break it
down.
Protein & fat DO NOT break down here.
Broken food pieces mix with gastric juices
produced in the stomach.
Carbohydrate: Salivary amylase converts
starch to maltose.
Chyme: term used to refer broken down food.

Duodenum:
Chemical breakdown only
Chyme mixed with bile (Bile produced from gall bladder) and pancreatic juice (from pancreas).
Protein: Trypsinogen (produced by pancreas) mix with enterokinase to form trypsin, this continues
to breakdown proteins to peptones.
Trypsinogen + Enterokinase -> Trypsin
Fat: Bile emulsifies fats to disperse them to small droplets.Pancreatic lipase breaks fat to glycerol and
fatty acids.
Carbohydrate: Amylase breaks down starch to maltose.

Ileum:
Chemical breakdown only
Protein: Erepsin converts peptones to amino acids.
Fat: are broken by lipase further.
Chemical breakdown only
Carbohydrate: Maltase breaks down maltose to glucose. Invertase breaks sucrose
to glucose + fructose. Lactase breaks lactose to glucose + galactose.
Enzymes in digestion

Amylase: breaks starch to maltose.

Erepsin: digest peptones to amino acids (found in intestinal juices).

Invertase: breaks sucrose to glucose + fructose.

Lactase breaks lactose to glucose + galactose.

Lipase: breaks fats (found in pancreatic juices/intestinal).

Maltase: breaks maltose to glucose.

Pepsin: breaks proteins to peptides then to peptones then polypeptides.

Renin: clots milk.

Trypsinogen: breaks proteins to peptones.
Role of bile in fat emulsification

The liver produces bile.

Bile emulsifies fats.

Breaks down fats to small droplets.

Small droplets create larger surface area.

Fat droplets are then digested by lipase.
Absorption of nutrients
Small intestine:
[Alcohol- the only substance that can be absorbed in the stomach.]

Villi:

Tiny finger-like projections.

Surrounded by a wall of single cells.


Single cells allow nutrients to move through and reach the lacteal.
Lacteal:

Connected to lymphatic system.

Surrounded by blood capillaries.

Monosaccharides, amino acids, water-soluble vitamins & minerals are absorbed into
blood capillaries.

Glucose is used for immediate energy or converted to glycogen

Converted glycogen is stored in the liver and muscles.

Glycerol and Fatty acids are absorbed into the lacteal to form fats which is converted to soluble
fats in the liver.
Large intestine (colon):

Food residues and water products pass here in liquid state.

Water is absorbed here making the food residues solid, forming faeces.

All actions here are assisted by NSP.
Meal planning and dietary guidelines
Factors affecting food requirements

Age.

Gender.

Health condition.

Daily activity.

Climate.

Likes and dislikes.

Time and facilities.

Food availability.

Financial ability.
Planning and serving of family meals

Plan dishes and create a shopping list.

Prepare dishes with a balanced portion of vegetables, meat, lentils in mind.

Store leftovers and use them the next day instead of throwing them.
Meals for different ages, occupations, cultures, and
religions
Who?
Meals (summary)
Lacto-Ovo
No meat. Consume fish products BUT Will eat dairy.
Lacto-vegans
No meat, fish, or eggs BUT Will eat other dairy products
Vegans
No animal-based foods/products. No dairy products.
Vegetarians
No meat, fish, and poultry. Consume dairy products. Fruits/vegetables.
Soya drinks/ yoghurt.
Religious groups
Foods eaten according to religious beliefs.
Cultures
Foods eaten according to cultural occasions.
Allergies
Foods must be checked for allergy-containing ingredients. Should read
labels on packaged food products.
Coeliac disease
Foods that do not contain gluten: Most dairy products, fruits/vegetables,
Rice, Potatoes.
Food intolerant
Should check labels on packaged foods and check for food intolerant
ingredients.
Pregnant/ lactating
women
Fruits/vegetables. Whole grains. Lean protein. Avoid raw foods (e.g., eggs
or fish).
Diabetics
Carbohydrate and fiber-rich foods: Fruits/vegetables, Whole grains, Beans/
lentils.
Infants
Breastfeeding. Bottle feeding. Weaning.
Who?
Meals (summary)
Toddlers
Protein foods. Calcium. Fluoride & Iron foods
School-aged
Foods should contain energy and nutrients for healthy growth.
Adolescents
Protein. Iron. Calcium, Vitamin D
Adults
Iron. Water & Sodium chloride. Energy-rich foods.
Seniors/ Elderly
Less energy-rich foods.· Vitamin D.· NSP/ Dietary fiber.
Convalescents
Vitamin D & C . Carbohydrates. Water.
Packed Meals

Should supply 1/3 of the daily intake of nutrients and energy.

Meal should be well obtained.

Easy to eat.

Should be carefully packed.

Must be placed in sufficient temperature.

Has variety of texture & flavours.

Meal should include a drink
Special occasions & Festivals


When preparing foods for special occasions, celebrations, or festivals, consider the following:

Where the food will be served?

Why is it being served? (if there is a special meaning behind the occasion.)

What should be served?
Examples of occasions:

Birthdays: can prepare a light meal as a starter then introduce the main course that
could be a cake or a
heavier meal with beverages.

Religious feast: food is prepared with tradition and culture being of main
importance.

Festivals: no special preparation needed as festivals usually have food stalls with
beverages.
Snacks & beverages

Snacks are small portions of foods eaten in between meals, throughout the day.

Beverages are drinks.

Snacks and beverages should be consumed limitedly as this can reduce hunger.

Excess consumption of snacks can cause problems such as weight gain, elevated cholesterol
levels, elevated sugar levels.

Eat healthy snacks like fruit salads, flavored yoghurt, mixed nuts, etc.

Lessen the consumption of carbonated and sugary beverages.

Drink water, milk, or fresh fruit juices as healthy alternatives to beverages.
Use of Herbs and Spices


Herbs:

Garlic - Stews, salads, soups.

Mint - Drinks, salads, ices.

Oregano - Pizza’s, pasta.

Parsley - Good source of vitamin C.

Thyme - Used for stuffing.

Basil - For salads
Spices:

Chilies - Spicy, used in curries.

Cinnamon - In cakes, pies, biscuits.

Vanilla - For essence, in cakes.

Turmeric - In curries, for coloring.

Paprika - Not very spicy, used to season dishes.

Ginger - In cakes, meat dishes.
Attractive presentation of food

Used in food advertising.

To make food visually appealing.

Presentation should take account of all senses.

Presentation should make food look appetizing.

Colour, design & decoration should be considered.
DRV and RDI

Dietary reference value: is a term for a set of reference values used to plan and assess nutrient
intakes of healthy people.

Reference daily intake: is the daily intake level of a nutrient considered to meet the requirements
of 97-98% of healthy people.
Use of nutritional tools

ABC’s of healthy eating: aim to achieve and maintain a healthy body weight.

RDI’s: Based on average needs of people of different age groups.

Healthy diet pyramid: Pictorial presentation helps children to understand better.

Food composition tools: Can be compared with RDA.
SUMMARY
Diet
Balanced diet
A balanced human diet contains all essential ingredients in the correct proportions
There are certain factors that affect diet such as:
– Children require more protein per kg of body weight than adults
 Gender – Males generally use more energy than females
 Activity – Higher levels of physical activity will increase demand for nutrients
 Pregnancy – Higher demands for nutrients in order to supply fetus with energy
for development
 Breast feeding mother – Higher requirements for vitamin and water
 Age
Malnutrition
Malnutrition is the lack of a balanced diet such as deficiencies, excesses or imbalances
in a person’s intake of nutrients.
Malnutrition can lead to consequences such as:
 Obesity (excessive
nutrients)
 Starvation (insufficient nutrients)
 Coronary heart disease (excessive saturated fat and cholesterol)
 Kwashiorkor (too much carbohydrates, too little protein)
 Constipation (lack of fibre)
Essential nutrients
Alimentary canal
Useful definitions
– Taking in of substances e.g. food and drink into the body through
the mouth
 Egestion – Passing out of food (as feces) that has not been digested or absorbed
via the anus
 Mechanical digestion – Break down of food into smaller pieces without
chemical change to food molecules
 Ingestion
digestion – Break down of large insoluble molecules into small,
soluble molecules
 Absorption – Movement of chemically digested food molecules through the
small intestine walls into the blood
 Assimilation – Movement of digested food molecules into the cells of the body
where they are used and become a part of the cells
 Chemical
Structure and function
Mouth
This is the location of ingestion. Mechanical digestion of food occurs as we chew on it
with our teeth. Chemical digestion occurs due to amylase enzymes in our saliva which
break down starch into maltose.
Esophagus
Round clumps of food (boluses) are passed down the esophagus via peristalsis from
the mouth to the stomach.
Peristalsis is the contraction and relaxation of the esophagus wall muscles which
creates a wave-like motion that pushes the food down the canal.
Stomach
Mechanical digestion occurs as the stomach walls squeeze the food to liquefy it.
Gastric juices contain pepsin (a protease) which chemically digests proteins. It also
contains hydrochloric acid which kill bacteria, but also maintains an optimum acidic
pH for pepsin.
Pancreas
The pancreas secretes pancreatic juice into the duodenum.
The juice contains a large variety of different enzymes involved in the chemical
digestion of food.
 Proteases
break down proteins
 Lipases break down lipids
 Amylases break down carbohydrates
Most enzymes in the pancreatic juice have an optimum pH of around 7. The pH of
pancreatic juice is slightly alkaline, and this is to neutralize the acidity of the food
coming from the stomach.
Duodenum
This is the first part of the small intestine. It receives pancreatic juice which contains
enzymes for the chemical digestion of food.
Ileum
This is the second part of the small intestine. The inner walls have finger-like
extensions called villi which massively increases the surface area for nutrient
absorption.
Liver
The liver produces a substance called bile which is stored in the gal bladder.
Bile has the function of emulsifying fat into droplets to increase the surface area for
lipases to come and digest them.
Bile is also basic which assists in neutralizing the acidity of the food coming from the
stomach.
Colon
This is the second part of the large intestine. The main function of the colon is to
reabsorb water from undigested food and also bile salts to return back to the liver.
Rectum
The rectum stores feces until it is egested
Anus
Muscles control egestion of feces
Cholera infection
Cholera bacteria releases toxins which causes chloride ions to be secreted into the
small intestine. This causes the osmotic movement of water into the gut, and leads to
diarrhea.
NOTE: Diarrhea is defined as the loss of watery feces
Diarrhea can be treated using oral rehydration therapy. It involves drinking water with
modest amounts of sugar and salts, specifically sodium and potassium.
Mechanical digestion
Types of human teeth
Mechanical digestion involves physically breaking food into smaller pieces, and our
teeth serve exactly that function!
There are four types of teeth:
 Molar





Located at back of mouth
4 or 5 cusps
2 or 3 roots
Used for chewing and grinding food
Used for chewing and grinding food
 Pre-molar




Behind canines
2 cusps
1 or 2 roots
Used to tear and grind food
 Canine



On either side of incisors
More pointy than incisors
Used to bite pieces of food
 Incisor



In front of the mouth
Chisel shaped
Used to bite off food pieces
Structure of human teeth
Dental decay
 Dental
decay is caused by bacteria which is present on the surface of our teeth.
 The bacteria and food deposits form a layer called plaque.
 Bacteria in plaque feed on sugars which produce acid that dissolves the enamel,
resulting in a hole.
 As the hole deepens it may eventually reach the nerves which result in pain i.e.
tooth ache.
Proper dental care
 Avoid
sugary food so that bacteria cannot make acid
cleaning to remove plaque
 Use floss to remove trapped food
 Visit the dentist regularly for treating early decay and removal of thick plaque
 Regular
Chemical digestion
Chemical digestion involves breaking down large, insoluble food into smaller soluble
nutrients that can be absorbed and used by the cells.
Chemical digestion is carried out by enzymes. A lot about chemical digestion has
already been covered above in regards to the alimentary canal, and what enzymes are
found where.
Summary of enzymes that you should be aware of:
Remember, the acidic pH of the stomach is maintained by hydrochloric acid which
also kills bacteria via denaturing their enzymes.
The alkaline conditions of the small intestine is maintained by pancreatic juice and
bile. The bile also has the function of emulsifying fats into droplets to increase the
surface area for digestion
Absorption
After large food molecules get digested by enzymes, the small soluble
nutrients diffuse into the small intestine walls and then into the blood.
Sometimes the concentration of nutrients i.e. glucose may be higher in the blood than
in the small intestine. In such cases diffusion cannot be relied upon. Instead, active
transport is used for absorption.
Absorption is defined as the movement of small food molecules and ions through the
wall of the intestine into the blood. It can either be done through diffusion or active
transport.
The inner walls of the small intestine have finger-like structures called villi which
greatly increases the surface area of absorption.
Structure of a villus
 Blood
vessels/capillaries
 Absorbs glucose and amino acids by diffusion
 Lacteal
 Absorbs fatty acids and glycerol
 Epithelial lining
 One cell thick to increase diffusion rate
 Microvilli increase surface area even further