Components of food

  • Carbohydrates, Proteins, Fats, Vitamins, Fibbers, Water and minerals


  • made up of carbon, hydrogen and oxygen
  • they provide energy and structural material
  • eg sadza, cassava, bannanas, cereals and their products, sweet potatoes, honey….
  • in plants- starch and in humans- stored as glycogen
  • cell membranes have carbohydrates with fats


Nutrient Uses
Carbohydrates Energy
Fats Source of energy, building materials, energy store, insulation, buoyancy, making hormones
Proteins Energy, building materials, enzymes, haemoglobin, structural material (muscle), hormones, antibodies
Vitamin C Protect cells from ageing, production of fibres
Vitamin D Absorption of calcium
Calcium Development and maintenance of strong bones and teeth
Iron Making haemoglobin
Fiber Provides bulk for faeces, helps peristalsis
Water Chemical reactions, solvent for transport


  • made of carbon, hydrogen oxygen, nitrogen and rarely Sulphur
  • for growth and repair of worm out tissues
  • eg milk, chicken, fish, egg, meat, peas, beans……
  • hormones production eg insulin
  • transport of oxygen by hemoglobin (made from proteins)



  • contains carbon, hydrogen and oxygen
  • energy providers and reserve food material
  • eg margarine, avocado, butter, fats, meat …
  • insulation beneath skin
  • structural purposes eg cell membranes



  • protective and proper body function
  • eg green vegetables, sea foods, iodized salts, milk, eggs ….


Deficiency effects of some vitamins

Name Source Function Effects
Vitamin A Green vegetables, milk, carrots, liver, milk.. improves eyesight and resistant to cold poor sight, upper respiratory tract infections
Vitamin C fresh fruits, vegetables strengthening teeth and bones poor healing of wounds, scurvy, swelling of gums
Vitamin D Fatty foods, fried foods Absorption of calcium from the intestines. formation of bones and teeth rickets, poor teeth and bone formation

Deficiency effects of some Mineral salts

Name Source Function Effects
Calcium milk, vegetables bone and teeth formation, proper muscle function, blood clotting poor bone and teeth formation muscle cramps
Iodine sea fish, iodised salt hormones formation mental and physical growth, goitre in adults
Iron broad leaved vegtables eg spinach, dried fruits, pumkin formation of haemoglobin Anaemia


  • gain; metabolic water; eating; drinking loss; sweating; urination; exhalation etc


Uses of water

  • cooling
  • transport of material
  • reactant for photosynthesis
  • lubrication
  • used during hydrolysis


Deficiency effects of water

  • dehydration
  • thickening of blood
  • drying mouth



Balanced diet

Is a diet containing required nutrients in their correct proportions

Food and energy requirements

  • it depends on age, sex, activity and conditions eg pregnancy
  • infants need some energy than their grandparents due to activity(high) and for growth
  • boys need more energy than girls of their age
  • a pregnant woman needs more energy than an ordinary woman for the fetus growth
  • sedentary workers need less energy than manual workers
  • each individual needs a minimum amount of energy to stay alive ie basal metabolic requirement


  • bad feeding either over or under feeding
  • underfeeding leads to kwashiorkor (protein energy malnutrition-PEM)
  • overfeeding leads to a condition called obesity


Effects of Malnutrition

  • Starvation: losing strength & finally dying because of lack of food
  • Coronary heart disease: eating too much fats which are rich in saturated fatty acids and cholesterol, may lead to heart attack
  • Constipation: lack of roughages in food causes constipation because roughages are indigestible and form bulks. Friction between bulks and walls of intestine stimulate the peristalsis
  • Obesity: Eating too much fats and carbohydrates leads to their storage in the body mainly in the forms of fats and causing an increase in body weight. This can cause; heart attack, stroke, joint pain, mobility impairment, high blood pressure


Symptoms of kwashiorkor
  • thin limbs
  • hair acquires reddish colour
  • poor growth
  • skin cracks
  • miserable and restless
  • distended stomach


Human alimental canal


is the breaking down of large molecules into smaller ones that can be absorbed into our body system. It can be chemical or mechanical digestion.

Types of Digestion

Mechanical digestion

Involves the breaking down of large food molecules by means of teeth and churning of food in the stomach

Chemical digestion

it involves the breaking down of large food molecules in simple one by means of enzymes. It starts in the mouth; cooked starch is acted upon by salivary amylase into sugars(maltose)


This is the introduction of food into the human alimental canal through the mouth. Food is chowed by means of teeth into small pieces to increase surface area for enzyme activity and to be easily swallowed. Some mucus in saliva helps in the movement of the food down the gullet. Tongue helps in the swallowing of food.

Human teeth and dental decay

Structure of a tooth

  • crown
  • part exposed to the mouth cavity
  • enamel- the strongest tissue inn the body made from calcium salts
  • The neck
  • part surrounded by the soft gum between the crown and root
  • The root
  • Part embedded in the jaw bone
  • pulp cavity-contains tooth-producing cells, blood vessels and nerve endings which detect pain

Types of teeth

chisel shaped teeth at the front for biting and cutting of food pieces
Cone shaped and pointed to cut and tear tough food
have two flat projections for crushing and grinding
found at the back of the mouth, have four projections/cusps for chewing

Dental Decay


Food remains in the mouth forms a layer on teeth- plaque. Bacteria inn the mouth act on the plaque too produce lactic acid(fermentation). Lactic acid is corrosive ie it corrodes the enamel and the the destine to form a cavity. When the cavity reaches the nerves severe pain if felt

Care for the teeth

  • brush your teeth regularly
  • dietary fibres
  • dental discloses
  • reduce the consumption of surgery foods eg seets
  • eat foods rich in calcium, phosphorus and vitamin D to strengthen them
  • use of fluoridated/ alkaline toothpastes
  • use dental floss to remove debris between the teeth
  • Regularly visit a dentist for check ups
  • eat balance diet



One food is chewed and swallowed it moves along alimental canal by peristalsis is pushed through the esophagus by waves of contraction of circular muscles in the esophagus and relaxing of longitudinal muscles

Digestion in the stomach

Gastric juices produced by the stomach walls contains enzymes pepsin and renin and hydrochloric acid.The stomach walls also mix food and gastric juices to form chyme. It moves into the duodenum.


  • break down proteins into peptides


  • Clot milk in young children

Hydrochloric acid

  • creates proper medium for the enzyme pepsin
  • Kill harmful bacteria in food
  • stops the action of the salivary


Digestion in the Doudenum.

  • Juices from the pancreas contains;
  • Amylases- act on stomach converting it tot maltose then to glucose
  • Trypsin- act on proteins breaking them into peptides then into amino acids
  • Lipase- acts on fats to break them down into fatty acids and glycerol.
  • Fat digestion is added by bile from the gall bladder in the liver. Bile emulsifies fats.


Digestion in the ileum

  • Digestion of food by enzymes from doudenum continues
  • unchanged peptides are changed into amino acids
  • unchanged fats are changed into fatty acids and glycerol
  • Unchanged maltose are changed into glucose.
  • Soluble foods is absorbed into the blood stream in the ileum – so it ahs greater surface area to volume ratio.


Adaptation of the small intestines for the absorption

  • they are very long and coiled to increase the surface area.
  • presence of villi increase surface area
  • villi have a dense network of blood capillaries to carry the absorbed food
  • walls of the small intestines are very thin to allow easy food diffusion.
  • food moves from the ileum into blood stream by diffusion and active uptake
  • the absorbed food is transported by the blood to the rest of the body.



The absorbed food is transported by blood to the liver and to the body where it is used. The making use of absorbed food by the body eg for growth, energy, repairing tissues..- assimilation. Diffusion rate is affected by the surface are, thin membrane, partially permeable membrane and continous flow of materials.

Large intestines- colon

  • No food digestion takes place in the large intestines.
  • Escherichia coli, E-coli breaks down cellulose to produce vitamiin B.
  • Water and vitamin B are absorbed into the blood stream.
  • the remaining wastes are passed to feaces where they are ejected at intervals.



  • Is the realize of waste from digestion through the anus.


Caecum and Appendix

  • These contain E-coli which breaks down cellulose into vitamin B and gases.
  • In humans the appendix may be blocked as a result of collection of hard materials leading to a appendicitis
  • This can lead to the removal of the appendix.


Region Digestive juice Enzyme Food acted upon End product
Mouth Saliva salivary amylase cooked starch maltose
Stomach gastric pepsin
peptides and amino acids
Duodenum pancreatic juices Trypsin
amino acids
fatty acids-glycerol
Ileum intestinal juices Trypsin
Amino acids
fats acids & glycerol.
Pancreatic enzymes Maltose
glucose + fructose


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