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Mammalian Nutrition
Requirement for food
To maintain good health, human beings
consume a balanced diet from the main
food groups.
The main food groups are; carbohydrates,
fats, proteins, vitamins and minerals.
Energy requirements vary from person to
person.
Someone who leads an active lifestyle will
need more energy than someone who is
inactive.
CHEMICAL STRUCTURE
• Carbohydrates, fats and proteins all
contain the chemical elements carbon
(C);hydrogen (H) and oxygen (O).
• Proteins contain all the above elements
but also nitrogen (N).
CARBOHYDRATES
• Energy rich compounds
• E.g. sugars, starch, glycogen, and
cellulose.
CARBOHYDRATES
Glucose is the most common simple sugar.
Excess glucose is stored as starch in
plants and glycogen in the liver in
humans
A maltose molecule has 2 molecules of glucose
stuck together.
Starch is made up of lots of repeating units
CARBOHYDRATES
Glycogen
CARBOHYDRATES
Cellulose
Cellulose is a complex carbohydrate made up of
thousands of glucose molecules arranged into long
chains. (Cell walls are made of cellulose)
People are unable to digest cellulose but it is good
‘roughage’ and gives bulk to faeces!
FATS
• Release twice as much energy as
carbohydrates and proteins.
• A molecule of fat is made up of 1 glycerol and
3 fatty acids.
G
L
Y
C
E
R
O
L
FATTY ACID
FATTY ACID
FATTY ACID
PROTEINS
• Each molecule of protein is made up of many
different sub-units called amino acids.
• There are about 20 different types of amino
acids.
VITAMINS
• Are complex chemical compounds required for good
health. E.g. Vitamins A,B, C and D.
• They do not provide energy but are essential.
• Stick in table of importance of vitamins.
Vitamin
Function
A
Component of
visual pigment in
retina; needed to
maintain epithelial
tissues
Night blindness; dry
skin
Carrots and other yellow vegetables
B1
Plays essential
role in removal of
CO2 made during
tissue respiration
Weakening of heart;
beri-beri (paralysis
of limbs)
Liver, yeast and un-refined cereal grains
Essential for
development of
new red blood
cells
Anaemia
Meat, eggs and milk
C
Needed for
growth and repair
of the skin and
mucous
membranes
Scurvy (poor healing
of wounds; soft
bleeding gums)
Citrus fruits and green vegetables
D
Required for
absorption of
calcium and
phosphate from
small intestine
Rickets (soft bones
that become
deformed easily)
Fish liver oil, butter, milk and egg yolk
B12
If deficient, what
happens?
Rich sources
MINERALS
• Refers to certain chemical elements essential in
small quantities for a wide range of functions.
• E.g. Calcium for strong bones and teeth.
• Stick in the importance of minerals table
Mineral
Calcium
Function
Rich sources
Needed for hardening of bones and
teeth, clotting of blood and
contraction of muscles
Milk, cheese and green
vegetables
Acts as a structural component of
haemoglobin and some enzymes.
Meat, eggs, cereals and green
vegetables
Needed for the formation of bones
and teeth, and synthesis of DNA and
ATP
Milk, fish, meat, nuts and
cereals
Iodine
Required for formation of hormones
produced by thyroid gland
Sea foods and iodised salt
Sodium
Essential for contraction of muscles
and transmission of nerve impulses
Fish, meat, milk and salt
Potassium
Essential for contraction of muscles
and transmission of nerve impulses
Present in almost all foods
Iron
Phosphorous
FOOD TESTS FOR STARCH,
GLUCOSE, PROTEIN AND FAT
• You need to know the food tests for starch,
glucose, protein and fats.
FOOD TYPE
TEST
OUTCOME
Starch
Iodine
Brown to blue-black if
starch present
Glucose
Benedict’s
Blue to orange brick-red if
glucose present (heat
required)
Protein
Biuret
Blue to lilac if protein is
present
Fat
Translucent spot
Drop of fat on filter paper
makes a translucent spot
Energy Content of Food
• Different food groups have different energy
contents.
• Fat contains twice as much energy (kJ)
than protein and carbohydrate.
-> Read pg 225 and complete Q1.
The Need for Digestion
• Digestion involves the breakdown of
large, insoluble food molecules into
smaller soluble food molecules in the
gut.
• This allows absorption of the food
molecules into the bloodstream through
the lining of the small intestine.
Large particles of
insoluble food
Insoluble food
digested to soluble
state
Small soluble
molecules of food
absorbed into
bloodstream
Undigested waste
passed out
Experiment
The purpose of digestion and
absorption using Visking tubing as
a model gut
• Food passing along the alimentary
canal is a mixture of large particles of
carbohydrates, protein and fat.
• Every cell in the human body needs a
supply of food from a nearby blood
vessel. The food must first gain
access to the bloodstream from the
gut.
In this experiment:• The visking tubing acts as the wall of the gut.
• Starch and glucose acts as the food in the gut.
• Water in the boiling tube acts as the blood
surrounding the gut.
Visking tubing
Water
Starch +
glucose
Method
1)
2)
3)
4)
5)
Mix starch and glucose solution together.
Knot 1 end of Visking tubing
Pour in starch and glucose solution
Tie other end of visking tubing
Rinse the Visking tubing sausage under the
tap.
6) Put into boiling tube and top up with water.
7) Place in water bath (37ºC – body temperature)
8) Start clock – take sample of water and test for
glucose and starch.
9) Test again at 10, 20 and 30 minutes.
10) Record your results in a table
Results
Time (mins)
0
10
20
30
Starch present (x or )
Glucose present (x or )
Think Questions??
1) Which food was unable to pass out of the
Visking tube ‘sausage’ through tiny pores
in the membrane because its molecules
are too large?
2) Which food was able to pass out of the
Visking tube ‘sausage’ because its
molecules are too small?
Conclusion
Starch molecules are large and insoluble
and so are unable to pass through the gut
wall.
Glucose molecules are small and soluble
and so are able to pass through the gut wall.
Alimentary Canal and Associated
Organs
The alimentary canal is a long tube running
from the mouth to the anus.
The salivary glands, liver and pancreas are
connected to the alimentary by ducts.
Label your
diagram
A
B
F
C
G
D
H
I
J
E
K
L
The passage of food along the alimentary canal
• Food is broken down mechanically in the mouth by the
action of the teeth.
• The salivary glands secrete saliva which mixes with
food.
• The saliva contains the enzyme amylase which digests
the starch into maltose sugar.
AMYLASE
Starch  Maltose
• Mucus in the saliva keeps the mouth moist and
lubricates the food, making the food easier to swallow.
• Once chewed, the food is swallowed. It moves
along the oesophagus (gullet). This is a
muscular tube that connects the back of the
mouth to the stomach.
• It moves along the oesophagus by a mechanism
called peristalsis.
• Note that peristalsis occurs throughout the
length of the alimentary canal not just down the
oesophagus.
• Label your diagram of what happens
Muscular gut wall
Circular muscles form a ring
that contracts and squeezes
the food from behind
Food
Food
Circular muscles in front
relax and allow the food to
pass
Direction of food
• Peristalsis will happen even if you are standing
on your head!
• It is a wave-like motion since the gut wall
muscles contract and relax alternately along the
entire length of the alimentary canal.
• It ensures that food once swallowed is actively
carried to the stomach and once in the large
intestine, keeps unwanted wastes on the move
to exit the body.
• The food then reaches the stomach.
• The stomach is a muscular bag whose wall
contains longitudinal and circular muscles.
• These muscles contract and relax to bring about
churning of the contents of the stomach.
• The contents of the stomach are mixed with
gastric juices inside the stomach.
You do not need to
know the parts of the
stomach in this detail.
Just realise that the
churning happens as a
result of the contraction
and relaxation of the
longitudinal and circular
muscles.
• The inner lining of the stomach is folded
and contains gastric glands which
posses 3 types of cells.
• 1) Mucus-secreting cells
• 2) Acid-secreting cells
• 3) Enzyme-secreting cells
• (Stick in diagram 11.4)
• The slimy mucus sticks to the stomach lining and
protects it from being damaged by digestive enzymes.
• Hydrochloric acid is secreted by the acid-secreting
cells which creates acidic conditions inside the stomach.
• The enzyme-secreting cells secrete inactive
pepsinogen. The acidic conditions then convert it to
active pepsin.
• The pepsin then breaks down insoluble protein into
soluble peptides.
pepsin
Protein  peptides
• The partially digested food will then pass from
the stomach to the small intestine by the
action of peristalsis.
• Fat is digested by the enzyme lipase and
protein is further digested by the enzyme
trypsin.
• Once the food is digested into small, soluble
molecules the food can then be absorbed by
the process of diffusion from the small intestine
into the bloodstream.
•
Structure of the small intestine
The structure of the small intestine is suited
to its function in 3 ways:1)
It is long and has a folded inner lining with many
finger-like villi. A large surface area is provided for
absorbing digested food.
2)
The lining of each villus (epithelium) is only 1 cell thick
allowing nutrient molecules to pass through easily.
3)
A blood capillary network and a central lacteal are
present in each villus to allow efficient transport of
substances.
Thin epithelium
Absorption of substances from
the small intestine
• Glucose and amino acids are absorbed into
the epithelial cells and then pass directly into
the blood capillaries.
• The products of fat digestion are also
absorbed into the epithelial cells but do not
pass into the blood capillary. They pass into
the lacteal instead.
• (the lacteal is part of the lymphatic system
which will drain into the blood circulation
through ducts in the upper chest region.)
Fate of Absorbed Materials
• Blood rich in amino acids and glucose from the
small intestine is transported in the hepatic
portal vein to the liver.
• Enough glucose is is released into the blood
circulation for use as an energy source.
• Excess glucose is converted in the liver to
glycogen and is stored there until needed.
• Enough amino acids is released into the blood
circulation to be used in protein synthesis
during growth and tissue repair.
• Excess amino acids are broken down in the
liver to urea. (The kidneys deal with this later)
• The process of breaking down amino acids is
called deamination. This happens in the liver
• Some of the products of fat digestion (fatty
acids and glycerol) are used as an
energy source.
• Excess fatty acids and glycerol are
converted to fat and stored in the body’s
fatty tissue until required.
The role of the pancreas
• The pancreas produces pancreatic juices which
contains lipase, trypsin and amylase all being
digestive enzymes.
Fat
lipase
fatty acids + glycerol
trypsin
Peptides
Starch
amino acids
amylase
maltose
The role of the gall bladder
• The gall bladder stores bile which
emulsifies* fats to aid digestion.
• * just means to disperse fat into tiny
globules, this allows the enzyme to get
close enough to break down the fat.
The role of the large intestine
• Material that passes into the large
intestine consists of undigested material,
bacteria and dead cells.
• The large intestine absorbs water from this
leaving behind faeces.
• The faeces are passed into the rectum
and are later expelled through the anus.