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Biology Topic 2 - Nutrition in humans (Functions and source of components…
Biology Topic 2 - Nutrition in humans
Balanced diet
Protein - people
Lipids - like
Minerals - Many
Carbohydrates - carrots
Vitamins - Very
Water - with
Dietary fibre - dinner
digestion
Mouth
There are two types of digestion in the mouth
Mechanical – teeth
Chemical – saliva – amylase (works best at pH7) – starch – maltose/glucose (simple sugars)
Amylase is a carbohydrase
oesophagus
Circular and longitudinal muscles used for peristalsis
It takes 6-10 seconds for food to pass through the oesophagus to the stomach
Stomach
Made up of three tissues: Muscular, glandular and epithelial
Glandular secretes two things: digestive juice (protease – pepsin) and hydrochloric acid
Hydrochloric acid kills microbes and is antiseptic
Protease breaks down protein into amino acids (pepsin works best at pH2)
Epithelial is used for protection
duodenum
Where digestion takes place and food is broken into tiny molecules small enough to be absorbed into the blood
Villi – they increase the surface area, where absorption takes place and food moves into the bloodstream.
Pancreas, liver and gall bladder
The gall bladder is contained in the liver and bile is produced here (bile is made in the liver and stored in the gall bladder).
Bile is alkaline and neutralises stomach acid and emulsifies fat
The pancreas secretes digestive juices into the duodenum: lipase, pancreatic amylase and protease – trypsin (Works best in alkaline solutions)
Large intestine
Water is reabsorbed
Rectum
Where the faeces is stored
Functions and source of components of the diet
Protein
Growth & repair
Meat, fish
Lipid
A source of energy and insulation
Butter, lard
Carbohydrates
A source of energy
Pasta, bread
Vitamin A
An important role in eyesight
carrots
Vitamin C
formation of connectives tissues
Citrus fruit, green vegatables
Vitamin D
Helps calcium absorption in small intestine
Oliy fish
Calcium
Builds bones and teeth
Milk
Component
Function
Source
Iron
Formation of haemoglobin
Liver, spinach
Energy Requirements
Age
Young children and adolescents need more carbohydrates as the energy is required to help the growth and development of their bodies.
Pregnancy
Pregnant women need more carbohydrates, mainly to provide the extra energy for her muscles to carry the extra weight of the foetus.
Activity Levels
A more active lifestyle (e.g. regularly playing sport) requires intake of more carbohydrates to provide the glucose that can be respired to produce energy for muscle contractions.
Villi
Microvilli
Increases surface area for absorption.
Lacteal
Absorbs glycerol and fatty acids which are quickly transported away to maintain concentration gradient.
Elonagated shape
Increases surface area for absorption.
Blood supply (Capillaries)
Absorbs glucose, amino acids,vitamins, minerals which are quickly transported away to maintain concentration gradient.
Feature
Function
Smooth muscles
Allows villus to sway to come into contact with food.
How does food move through the gut by peristalsis?
This means movement of the food in the gut doesn't depend on gravity and can occur with the body in any position.
The walls of the alimentary canal has two layers of muscle: Circular and longitudinal muscle.
This wavelike movement squeezes food along the alimentary canal.
Circular muscle consists of fibres running in rings around the canal.
Peristalsis is the alternative contraction and relaxation of circular and longitudinal muscles lining the alimentary canal.
Longitudinal muscle consists of fibres running along the length of the canal.
Role of digestive enzymes
The substances which our body needs cannot be absorbed into our blood until they have been broken down further and converted into small soluble chemicals.
All digestive enzymes speed up catabolic reactions (breaking apart reactions.)
Starch - Starch is broken down by the amylase to maltose. Maltose is broken down to glucose by the enzyme maltase.
Starch-----(Amylase)---- Maltose
Maltose ----(Maltase)---- glucose
Proteins - Proteins are broken down by proteases such as pepsin to amino acids.
Protein ---- (Proteases) ---- Amino acids
Lipids - Lipids are broken down by lipases to glycerol and fatty acids.
Lipid ---- (Lipases) ---- glycerol + fatty acids
Sources of enzymes
Enzyme
Secreted from the salivary glands (saliva)
Secreted from the stomach (gastric juice)
Secreted from the pancreas (Pancreatic juice)
Secreted from the small intestine (intestinal juice)
Amylase
✓
x
✓
x
Maltase
x
x
x
✓
Proteases
x
✓
✓
✓
Lipases
x
(✓) has a little effect
✓
x
Bile
Bile is produced by the liver and stored in the gall bladder.
To increase the efficiency of lipase, lipids first need to be emulsified.
This is done by bile, a substance produced in the via the bile duct when food is passing through the duodenum.
Bile disperses lipids into droplets (An emulsion) and so increases the surface area for the action of lipase.
NOTE: Bile is NOT an enzyme.
Bile salts also neutralise the stomach acid and help to create optimum pH conditions for enzymes in the small intestine.
