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Nutrition is the process by which living organisms obtain food they need to grow and repair body tissues. Food can be divided into 7 main classes: classes: (a) Carbohydrates (b) Proteins (c) Fats (d) Fibre (e) Water (f) Vitamins (g) Minerals
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Functions of Each Class of Food
Classes of food
Carbohydrates
Proteins
Fats
Sources
- Starch (nrad, rice, potato etc.) - Cellulose (vegetables & fruits) -Glycogen (stored in liver & muscle cells)
Meat, fish, egs, beans, lentils and vegetables which are rich in plant proteins
Butter, cheese, vegetable oils, nuts
Functions
Sources of energy for physical activities and keeping the body warm
- For the growth of new cells - Repair of damages tissues - Required for the formation of enzymes, hormones, haemoglobin and antibodies
-Sources of energy during extreme starvation - Fats underneath the skin act as an insulator and help to keep the body warm - Fats stored around the internal organs protect them against physical injury -As a medium of transport for fat-soluble vitamins (A, D, E, & K)
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Vitamins (a) are organic compounds that are essential for maintaining good health (b) are required in small amounts (c) do not provide any energy A deficiency in vitamins may cause deficiency diseases. There are 2 kinds of vitamins: (a) Fat-soluble vitamins: vitamin A, D, E & K (b) Water-soluble vitamins: vitamins B & C
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The main sources, functions and effects of vitamin deficiency
Vitamin
Main Source
Functions
Deficiency diseases
A
-Carrots, egg yolks, liver, fish
-Maintains healthy skin -For good night vision
-Dry, scaly skin -Night blindness
B
Cereals, lover, eggs, milk, yeasts, vegetables
-Maintains a healthy nervous system -Helps in the breakdown of carbohydrates to release energy -Helps in the formation of red blood cells
-Beri-beri (disease of the nervous system -Pellagra (skin disease) -Anaemia
C
Fruits & Vegetables
-Maintains healthy skin, teeth, and gums -Heals wounds -Increases the body’s resistance to diseases
-Scurvy
D
Liver, eggs, dairy products, formed in the skin under sunlight
-Helps in the absorption of calcium and phosphorus -Formation of strong teeth and bones
-Rickets (weak bones and dental decay)
E
Seeds, nuts. Whole germ, vegetable oils, whole grains
-Maintains fertility -Prevents cell damage
-Sterility -Poor nerve and muscle functions
K
Liver, egg yolk, green vegetables
-Promotes blood clotting
-Prolonged bleeding
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Minerals (a) are inorganic substances vital for maintaining good health (b) are needed in small amounts by the body (c) do not provide any energy
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A deficiency in minerals may cause deficiency diseases. Excess minerals are excreted through sweat and urine
The main sources, functions and effects of mineral deficiency
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Mineral
Main Source
Functions
Deficiency diseases
Calcium
-Milk, eggs, anchovies, yoghurt, green vegetables
-Build strong teeth & bones -Helps blood clotting -Form normal functioning of nerve and muscle activities
-Rickets in children -Osteoporosis in adults -Prolonged bleeding
Sodium
Table salt, cheese, processed food
-Maintains balance of body fluid -For normal functioning of nerves
-Muscle crapms
Potassium
Fish, bananas, meat, nuts
-For normal functioning of nerve and muscle activities -Maintains balance of body fluid
-Weak muscles -Paralysis
Iron
Liver, meat, seafood, green vegetables
-Needed for formation of haemoglobin in red blood cells
-Anaemia
Iodine
Seafood, iodised sale
-Needed to make the hormones of the thyroid gland
-Goiter (swollen neck)
Phosphorus
Cheese, milk, eggs, fish
-To make healthy bones and teeth -Helps in muscle contraction
-Rickets -Tooth decay -Weak muscle
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Dietary fibre (a) is made up of cellulose from plant call walls (b) cannot be digested by our digestive system (c) is obtained from cereals, fruits, and, leafy vegetables Importance of dietary fibre (a) Provide bulk to the contents in the large intestine (b) Stimulates peristalsis, the rhythmic muscular contractions along the alimentary canal (c) Prevents Constipation Water (a) water is very important to the body (b) About 70% of the body is made up of water (c) Water does not provide any energy (d) Importance of water: - Transport of digested food, respiratory gases and excretory products - As a solvent for chemicals to dissolve in - As a medium for biochemical reactions - Needed for the production of mucus - Helps to regulate body temperature (e) Water is lost through urine, sweat and exhaled air
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A Balanced Diet Diet refers to the daily food we eat. A balanced diet consists of all the seven classes of food taken in the right amounts to meet the daily requirements of the body. A balanced diet (a) provides energy for daily activities (b) prevents diseases (c) Provides nutrients needed for growth
1. Age A child needs more carbohydrates and proteins than an older person for continuous growth. A teenager needs plenty of carbohydrates to remain active. They also need plenty of proteins to make new cells and plenty of calcium to make strong bones and teeth. 2. Sex Men require a higher energy intake than a woman from the same age group. Heat loss is faster in men than in women because men have a lower body fat content. •
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3. Physical activity and occupation A more active person requires more energy. A person who does heavy work like a farmer requires more energy than a person who does lighter work like a clerk. 4. Body size A bigger-sized person needs more energy than a smaller-sized person because smaller-sized person have a bigger surface area per unit volume. 3. State of health A person recovering from illness needs more of certain nutrients. A pregnant woman requires more energy than a woman who is not pregnant. 4. Climate People living in cold countries need more energy to keep their body warm People living in warmer climates do not need as much energy. •
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Calorific value or energy value of food refers to the amount of energy released from one gram of food. The calorific value of food is measured in calories (cal) or joules (J). 1 calorie (cal) = 4.2 joules (J) Energy value of main food classes: Carbohydrates: 17kJ g-1 Protein: 18kJ g-1 Fat: 39kJ g-1 •
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Eaten in moderation, sugary and fatty foods can form part of healthy, balanced diet.
Milk and dairy products contain calcium, proteins and vitamins
Vegetables are important to every diet
Meat, poultry and fish are good sources of iron, zinc and vitamin B
Fruits supply most of our dietary vitamin C
Bread, cereals, and potatoes are the main sources of complex carbohydrate
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Digestion is the process of breaking down large complex food molecules into smaller and simpler molecules. Digestion takes place in the alimentary canal. There are two types of digestion: (a) Physical digestion is the breaking down of large pieces of food into smaller pieces using teeth and the churning actions of the alimentary canal. (b) Chemical digestion involves the breaking down of complex food molecules into small soluble molecules by digestive enzymes. These molecules are then transported by the blood circulatory system to every cell in the body. Enzymes are protein that speed up biochemical reactions in the cells. Complex food molecules are broken down into their smaller molecules so that these molecules can dissolve and diffuse through the wall of the small intestine. End products of digestion: (a) carbohydrates glucose (b) proteins amino acids (c) fats fatty acids and glycerol
Muscles relax
Sequence of the parts of the alimentary canal involved in food digestion and absorption:
Muscles contract
Mouth Oesophagus Stomach Small Intestine Large Intestine Rectum Anus
Bolus moves along oesophagus by peristalsis
Teeth- cut tear and grind food.
Salivary glands – Secretes amylase to break down starch.
Tongue – Helps swallow food.
Oesophagus- Tube connecting mouth to stomach.
Pancreas – Secretes pancreatic juice which contains enzymes to break down carbohydrates, proteins and fats.
Stomach – Secretes gastric juice to break down proteins. Hydrochloric acid kills bacteria.
Liver- Excess amino acids converted to urea. Produces bile. Small intestine – Food substances absorbed into blood.
Gallbladder – Stores bile. Bile neutralizes stomach acid. Duodenum – Receives pancreatic juice and bile.
Large intestine – Excess water reabsorbed into blood.
Rectum – Stores faeces Anus – Faeces removed.
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Process of Digestion along the Alimentary Canal
Gland/ organ
Secretion
Contents of secretion
Digestive action/ function
Salivary glands (mouth)
Saliva
-Salivary amylase
-Salivary amylase breaks down starch into maltose.
Gastric glands (stomach)
Gastric juices
-Hydrochloric acid
-Stop the action of the salivary enzymes. -Kills bacteria in the food. -Provides an acidic medium for the action of enzymes in the stomach.
-Proteases
-Break down proteins into polypeptides or peptones.
-Casein
-Coagulates liquid milk protein.
Liver
Bile (stored in the gall bladder)
Pancreas
Pancreatic juice
-Neutralizes the acid produced by the stomach. -Provides an alkaline medium for the action of the enzymes in the pancreatic juice. -Emulsifies fats and oil into small globules. This increases the surface area for the action of enzymes in the pancreatic juice. -Pancreatic amylase
-Break down starch into maltose.
-Proteases
-Break down proteins into polypeptides.
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Process of Digestion along the Alimentary Canal
Gland/ organ
Secretion
Contents of secretion
Digestive action/ function
Pancreas
Pancreatic juice
-Lipase
-Breaks down fats into fatty acids and glycerol.
Intestinal gland
Intestinal juice
-Maltase
-Break down maltose into glucose.
-Protease
-Breaks down polypeptides into amino acids.
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Absorption is the diffusion of end products of digestion through the walls of the small intestine into the blood capillaries. The characteristics of the walls of the small intestine adapted for absorption: (a) The small intestine is long (about 6 metres). This ensures that digested food is absorbed before it reaches the large intestine. (b) The inner surface of the ileum is covered with millions of finger-like projections called villi (singular: villus . The villi increase the surface area for the rapid absorption of digested end products. (c) The walls of the small intestine have many blood capillaries to transport digested food. (d) The intestinal wall is very thin so that digested food can diffuse easily into the blood capillaries. The digested food absorbed into the blood capillaries is then transported to the liver. From the liver, the nutrients are transported to the heart to be pumped to all parts of the body.
Large Intestine
2. In the large intestine, water is absorbed into the bloodstream.
1. The bulk of the undigested food that is not absorbed move along the large intestine.
4. The process off removing faeces from the body is called defecation.
Anus
3. The undigested food undergoes decay and becomes faeces. Faeces are stored temporarily in the rectum before being pushed through the anus.
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Roughage or dietary fibre helps undigested food to move along the large intestine. If there is lack of dietary fibre in the diet, undigested food moves very slowly through the large intestine and too much water will be reabsorbed into the blood. As a result, the faeces become hard and dry and this result in constipation. Practise healthy eating habits by: (a) eating a balanced diet (b) drinking at least 7 glasses of water a day (c) consuming less fats, sugars, and salt (d) eating plenty of vegetables and fruits (e) eating in moderation Unhealthy eating habits may lead to many diet-related diseases: (a) Consistently eating more than the daily requirement may lead to obesity. (b) Eating too much of oily food may lead to heart diseases. (c) A high intake of salt may lead to high blood pressure. (d) A high intake of sugar may lead to diabetes.
