Food and Digestion

BALANCED DIET

Definition :A balanced diet contains all the nutrients required by the body in the right amounts (neither omitted nor in excess). It includes fats, proteins, carbohydrates, fibre, water, vitamins and minerals.

If balanced diet is not provided and food intake is only starch, like potatoes: Essential nutrients might be missing. A balanced diet is needed that contains all required nutrients in the right amounts.

·                Proteins are required for cell growth, enzyme manufacture and antibody production. A weak immune system results from protein deficiency.

·                Vitamins are needed by the body. Lack of vitamin causes deficiency diseases, such as,

·                Fats are required for cell membrane formation.

·                Minerals are required. Iron deficiency can cause anaemia.

Miners / Builders have greater energy demand, and hence, they need more carbohydrates and fats. They need more protein.

Sedentary workers, like office workers, need less proteins and minerals as they have lower energy demand. They have less wear and tear on their bodies.

CARBOHYDRATES

In Excess :

·                Excess carbohydrates are changed to fats

·                Obesity results as fat is stored around organs and under the skin.

·                Extra mass has to be moved around due to obesity, which puts strain on muscles, heart and skeleton

·                Increased risk of diabetes

·                Increased risk of coronary heart disease

Test for starch :

·                The test sample is grinded / chopped into small fragments with water.

·                Iodine solution is added to a solution of the test sample.

·                Colour changes from brown to blue – black.

·                A blue – black colouration confirms the presence of starch.

Cellulose digestion in herbivores :

·                Regurgitation occurs.

·                Symbiotic bacteria in the stomach / rumen digest cellulose to sugar.

Test for glucose :

·                The test sample is taken in a test tube and Benedict’s solution is added to it. It is boiled for one minute. Colour changes from blue to red, indicating presence of glucose. A brick red precipitate is seen.

·                Clinistix – colour changes from pink to purple / dark blue

Digestion of carbohydrates :

·                Food is mechanically digested by mastication in the mouth. Teeth chop food, increasing surface area for enzyme activity.

·                Food is mixed with saliva in the mouth. Salivary amylase digests starch to maltose.

·                Starch enters the stomach. There is no carbohydrate digesting enzyme in the stomach.

·                The food then enters the duodenum, where pancreatic amylase is added, to digest the remaining starch to maltose.

·                The maltose enters the ileum, where maltase is secreted. Maltase digests maltose to glucose.

Note :Blood glucose level does not rise as soon as a person finishes his / her meal as it takes time for the enzymes to work and to bring about digestion of starch. It takes time for food to reach the small intestine. Materials cannot pass into blood until it is soluble.

Amylase / ptyalin / diastase act on starch.

Assimilation of products of starch digestion :

·                Glucose is used for energy release by aerobic respiration to manufacture ATP. Energy is used for movement or for chemical reactions.

·                Some glucose is converted to glycogen for storage.

·                Some glucose is converted to fat for storage.

·                Some glucose is converted to amino acids for protein manufacture.

Note :Overweight people should avoid food like chips, that have more energy due to having more fats and carbohydrates, as this adds to obesity. The chances of weight loss are less.

Thin chips have a larger surface area. More fat is coated on the surface of the chips due to greater surface area. More energy / fat is taken into the body, adding to fat store in body / increasing obesity.

PROTEINS

Structure :Proteins are polymers of amino acids joined by peptide bonds. Amino acids are chain compoundscontaining carbon, hydrogen, oxygen and nitrogen. Proteins are large molecules.

Functions :

·                New cell growth as proteins make cytoplasm and protoplasm of cells and thus, cause growth of tissue.

·                Enzyme manufacture

·                Antibody production

·                Haemoglobin production

Deficiency :

·                Cells cannot form as cytoplasm is not made

·                Slow healing of wounds

·                Reduced immunity, so the person is more susceptible to disease. This causes early death.

·                Kwashiorkor causes swelling of the belly and hair to turn orange

·                Marasmas

·                The person is underweight due to poor growth

·                Oedema

Test for Proteins :         

·                The food sample is mixed with water.

·                Grind together.

·                Add Biuret Solution to the food sample.

·                Colour changes from blue to mauve / purple / lilac.

·                A mauve / purple / lilac colour indicates positive result.

·                If Millons reagent is used, colour changes to red.      

·                If albustix is used, colour changes to pink.

Digestion of Proteins :

·                Proteins are chewed in mouth.

·                They are passed to the stomach.

·                Pepsin in stomach acts on proteins to digest them to polypeptides.

·                Presence of HCl in stomach activates pepsin.

·                The chymethen passes to the duodenum.

·                In the duodenum, trypsin / pancreatic protease digests polypeptides to peptides.

·                The food then passes by peristalsis into the ileum.

·                In the ileum, peptidases / carboxypeptidase / erepsin digests peptides to amino acids.

Absorption and Assimilation of Proteins :

·                Proteins are absorbed as amino acids via villi into blood capillaries.

·                Amino acids are transported via hepatic portal vein to the liver.

·                The liver cells use some amino acids to form cell proteins, cytoplasm, protoplasm for growth and to produce fibrinogen, haemoglobin, hormones and enzymes.

·                Excessamino acids are deaminated in the liver.

·                Urea is excreted via kidney.

FATS

Use of fats in the body:

·                Fats act as a store of energy for use when the body requires extra energy. Fats have higher energy value.

·                Fats provide electrical insulation around axons and dendrons of neurones.

·                Fats act a solvent for uptake of vitamins A and D to allow them to pass across cell membranes.

·                Fats are a component of the cell membrane, so, they are needed to form new cells.

·                Fats protect internal organs, for example, pericardium around the heart, protects against mechanical injury. Kidneys are protected.

·                Fat layer under the skin in the hypodermis provides thermalinsulation, reducing heat loss to the environment, thus helping maintain a constant body temperature.

Note :Eat food having lower fat content as the chances of blocking arteries / causing heart attacks is reduced. Lower risk of obesity.

Deficiency :

·                The person finds it difficult to control body temperature in a cold environment. Fat layer under the skin in the hypodermis provides insulation. If that layer is lost, that is, used up if diet lacks fat, more heat is lost to the environment.

·                The body loses a source of energy from diet.

In Excess :

·                Obesity results as fat is stored around organs and under the skin.

·                Extra mass has to be moved around due to obesity, which puts strain on muscles, heart and skeleton. The heart muscle must also work harder.

·                Increased risk of diabetes

·                Increased risk of coronary heart disease as deposit of saturated fat, such as, cholesterol cause coronary arteries to be narrowed / blocked. This increases the risk of heart attack.

Problems linked to obesity :

·                Coronary Heart Disease

·                Varicose veins

·                Colon cancer

·                High blood pressure

·                Foot problems

·                Heart attacks

·                Increased pressure in the eye

Test for fats :

·                The food sample is chopped or grinded and is put in a dry test tube. Ethanol is added and the test tube is shaken. The liquid is decanted and a drop of cold water is added to it.A cloudy emulsion confirms the presence of fats.

·                Squash food on filter paper. Attempt to dry stain. If still transclucent, fat present.

·                Chop / squash food. Add (III or IV) dye. Leave for a few minutes and wash off. Look for orange / red colour in food.

Bile :

·                Bile is produced by the liver.

·                It has bile salts.

·                It is secreted into the duodenum by the bile duct when stomach acid enters the duodenum.

·                Bile emulsifies fats to increase surface area for efficient enzyme activity.

·                Bile is alkaline.

·                Bile helps neutralize stomach acids and increase pH.

·                It provides optimum pH for enzyme activity.

Digestion :

·                Fats are liquidised/ melt into oils in large droplets

·                Liver produces bile.

·                Bile passes into the duodenum along bile duct.

·                Bile emulsifies fats to increase surface area of fat droplets for action of lipase.

·                Lipase is provided by the pancreas in the ileum.

·                Alkaline conditions are provided by pancreatic juice and bile.

·                Bile neutralises stomach acids.

·                Lipase from pancreas digests fats into fatty acids and glycerol.

Absorption of Fats:

·                Fats are absorbed in the ileum of the small intestine.

·                Fatty acids and glycerol pass through the thin ileum wall via villus into lymph vessels / lacteals.

·                The lymph vessels join the blood circulation system near the heart.

Note :Fatty acids and glycerol are recombined in body cells to form fats.

VITAMINS

Why boiling reduces vitamin content of potatoes?

·                Heat breaks down vitamins.

·                Cell membranes may break down.

·                Vitamins diffuse out of cells / leach into water.

·                The vitamins may be water soluble.

Vitamin A (Retinol)

·                It is an antioxidant.

·                It is needed for the formation of pigment in the retina.

·                It is needed for black / white vision.

·                It helps regrowth of skin and thus helps maintain the skin.

·                It helps form melanin.

Source :

·                Carrots

·                Margarine

·                Butter

·                Milk

·                Fatty meats

Vitamin C

·                Prevents scurvy

·                Maintains health of skin

·                Mucous membranes

·                Helps wounds to heal

·                Is an antioxidant

Source :

·                Citrus fruits, such as, tomatoes

·                Blackcurrants

·                Raw vegetables

Vitamin D

·                It is needed for the uptake of calcium ions into blood in the small intestine

·                It is needed for the absorption of calcium ions into bones to form strong bones

·                It is needed for calcification of teeth

Source :

·                Milk

·                Cream

·                Margarine

·                Butter

·                Egg yolk

·                Fish liver

Teenagers need more vitamin D as they are still growing rapidly. Calcium ions are needed for formation of bones and teeth. Vitamin D is needed for uptake of calcium ions.

DIETARY FIBRE

Source

·                Brown rice

·                Spinach

·                Root vegetables

·                Fruits

·                Bran / wholegrain cereal

·                Wholemeal bread

Functions :

·                Dietary fibre increases / aids peristalsis as plant cell walls contain indigestible cellulose, which gives bulk to food. It gives grip to gut muscles as they contract during peristalsis.

·                It prevents constipation as faeces are removed easily. It retains water from faeces and, thus forms soft faeces.

·                It reduces risk of bowel cancer.

·                Less time is there for toxins to accumulate.

MINERALS

Iodine

·                For formation of thyroxine

Source

·                Fish, especially, shell fish

·                Algae

·                Table salt

Iron

·                Formation of haemoglobin in red blood cells to transport oxygen

·                Prevent anaemia

Note :Females need more iron as they lose blood during menstruation regularly on a monthly basis, during pregnancy and afterbirth.

An anaemic person has lower oxygen content in arterial blood than normal person as s/he has less haemoglobin (red blood cells) to carry oxygen.

Source

·                Red meat

·                Spinach

·                Lettuce

·                Cabbage

·                Green vegetables

·                Red peppers

WATER

Uses of water in the human body :

·                Water is a major component of blood plasma. Water is a good solvent and hence, acts as a transport medium. Glucose is transported in blood plasma. Oxygen dissolves in the film of moisture in the alveolar lining, and then diffuses into red blood cells.

·                Water is a major component of cytoplasm.

·                Water causes hydrolysis of food substances during digestion, like digestion of starch.

·                Sweat is made of water. It evaporates to carry body heat away as latent heat of vapourisation. Thus, body heat is lost. Sweat cools the body. So, water helps in temperature regulation.

Example and function of Body Fluids :

·                Blood plasma :transporting materials, such as, glucose

·                Saliva : lubricates food. It contains salivary amylase that digests starch to maltose

·                Sweat : reduces body temperature and acts as a coolant

·                Urine : excretes metabolic wastes, like urea

·                Tear fluid :removes foreign bodies from the eye

·                Mucus :removes particles from airways

·                Synovial fluid :acts as a lubricant

·                Amniotic fluid

·                Lymph

·                Tissue fluid

·                Pancreatic juice

·                Gastric juice

·                Bile

·                Semen

·                Cerebrospinal fluid

Role of water in digestion :

·                Enzymes need water to be active

·                Chemical reactions occur in solution

·                Absorption : water is needed to absorb digested glucose and amino acids into blood capillaries by diffusion

·                Peristalsis : water lubricates bolus of food, thus allowing easy swallowing

·                Water is needed for mucus formation

·                Water causes hydrolysis

Role of water in temperature regulation :

·                Sweat production can be increased or decreased.

·                When sweat is produced on the body surface, evaporation takes body heat away as latent heat of vapourisation.

·                Sweat increases cooling / heat loss from the body.

Uses of water :

·                Food preparation / cooking

·                Agriculture / horticulture

·                Industrial use

·                Washing clothes and bathing

·                Flushing toilets

·                Cleaning homes / clothing

ENERGY REQUIREMENTS

People, who tend to be more active, go through a lot of muscular activity, thus more energy is required. Differences in body size also matter.

Choose a diet that has lower energy content to reduce the risk of obesity.

During pregnancy, diet must contain

·                small increase in energy to provide calories for fetus

·                increase food containing iron needed for red blood cells of fetus

·                increase food containing calcium needed for bones and teeth of fetus

·                increase food containing protein needed for fetus

·                no / low alcohol as intake can damage fetal cells

·                increased vitamins or folic acid

Uses of energy :

·                Contraction of muscles for movement

·                Synthesis of materials / cell division / used in chemical reactions

·                Maintenance of body temperature by generating heat

·                Transmission of nerve impulses

·                Active transport

TEETH

Structure of Teeth :

·                Enamel is very hard and covers the crown / exposed part of the tooth.

·                Dentine – bulk of tooth

·                Enamel and dentine are made of calcium salts.

·                Pulp cavity contains living cells and nerves

·                Blood vessels supply nutrients to living cells

Types of Teeth:

·                Incisors :They are sharp, chisel shaped and are used for biting and cutting food.

·                Canines : Canines are sharp, conical and pointed for tearing food, like meat.

·                Premolars / Molars :Premolars / Molars have a large surface area as they have cusps / ridges on top, giving them a W or M shape, for grinding and crushing food. They have better attachments through a larger and deeper root, allowing sideways movement across one another.

Differences between Incisors and Molars :

Incisors	Molars
12 incisors	8 molars
Single root	Multiple roots
Cuts food	Grinds food
Chisel shaped	Square top with cusps
Small surface area	Large surface area

Tooth Decay :

·                Bacteria in plaque act on sugars and release acid.

·                Acid dissolves enamel and allows bacteria to enter the dentine and the living tissues.

Preventing Tooth Decay :

·                Brush teeth regularly to remove food particles collecting there and plaque / bacteria. No acid is produced. So, the enamel is not dissolved.

·                Use fluoride toothpaste or mouth wash or dental floss. Fluoride is alkaline that neutralisesmouth acid and is also bactericidal.

·                Regularly visit the dentist every 4 to 6 months to detect early signs and prevent further decay.

Changes in diet to reduce tooth decay

·                Reduce sugar in diet to reduce bacterial decay and thus, reduce acid production.

·                Eat fibrous fruits, having vitamin C, as this helps gum health and chances of gum infection, gingivitis and scurvy are reduced.

·                Increase dairy products, that have calcium as this hardens the enamel. So, there is less chance of bacteria breaking through.

·                Addition of fluoride to drinking water / toothpaste as this hardens the enamel.

Food for Healthy Teeth Formation: The diet of the person must contain adequate

·                Calcium to form bulk of tooth

·                Phosphates – teeth is formed from calcium phosphate

·                Proteins – formation of new cells / living part of tooth

·                Vitamin D for uptake of calciumsaltsinto the blood

·                Vitamin C for gum development

·                Fluoride makes teeth harder and more resistant to acid

DIGESTION

Definition of Digestion :Digestion refers to the mechanical and chemical breakdown of food from large, complex, insoluble molecules to small, simple and soluble ones to allow absorption of the substances into the blood by diffusion.

Mouth :

·                Saliva is added to lubricate food and digest starch.

·                Food is mixed with saliva by the tongue.

·                Food is rolled by the tongue into a bolus for swallowing it down the oesophagus.

·                Tongue tastes food.

·                Saliva contains the enzyme,salivaryamylase that breaks down starch to maltose.

·                Mastication occurs. Teeth chop food to increase surface area for more efficient enzyme activity.

·                Food is cut by incisors, torn by canines, grinded by molars and premolars.

Peristalsis :

·                Circular muscles behind the bolus of food contract and the circular muscles in front of the bolus of food relax, pushing the food forward in wave-like muscular contractions called peristalsis.

·                Cell walls of plants are made of cellulose, which is indigestible.

·                It gives bulk to food and gives grip to gut muscles when they contract during peristalsis.

·                This prevents constipation and retains water from food to form soft faeces.

·                Fibre lowers the risk of bowel cancer.

·                Peristalsis of ova occurs in the oviduct, urine occurs in the ureter and urethra, semen along urethra and arteries.

·                Peristalsis mixes food and maintains diffusion gradient.

Swallowing :

·                On swallowing, the epiglottis covers the entrance of the trachea, like a flap. So, food particles cannot enter the trachea.

·                If food particles do enter, they are coughed out as a reflex action.

Stomach :

·                Stomach muscles cause churning to occur.This mixes food with enzyme andincreases surface area of food particles. This also liquefies food.

·                Pepsin is secreted by the stomach wall.

·                Pepsin is contained in gastric juice.

·                Hydrochloric acid activates pepsin.

·                Pepsin begins breakdown of protein.

·                Proteins are digested to polypeptides.

·                Rennin

·                Chymase

Duodenum :Bile is secreted into the duodenum from the liver. Pancreatic juice is also secreted. Both are alkaline as they contain sodium hydrogencarbonate.

·                Peristalsis bringchymeinto the duodenum from the stomach.

·                Pancreas secretes juice to duodenum.

·                Pancreatic juice contains the enzymes : lipase, pancreatic amylase, trypsin

·                Lipase digests fats to fatty acids and glycerol.

·                Trypsin digests polypeptides to peptides.

·                Pancreatic amylase digests starch to maltose.

Adaptations of Duodenum for digestion :

·                It is long in structure and is internally folded, which provides a large surface area.

·                Bile enters the duodenum.

·                Enzymes are secreted

·                Villi are present

·                Muscles move food along by peristalsis and mix food

Villi :The villi absorbs the products of digestion.

·                Villi and microvilli are large in number and provide a large surface area for absorption of glucose and amino acids into bloodby rapid diffusion down concentration gradient.

·                They have a thin one celled epithelium for rapid diffusion across short distance.

·                The dense capillary network provides rich blood supply to each villus for absorption of glucose and amino acids.

·                Lymph capillaries transport fatty acids and glycerol.

Note : Large surface area in the ileum is provided by the following :

·                Villi

·                Microvilli

·                The ileum is folded

·                The ileum is long

Digestion in the small intestine:

·                Peristalsis brings chymeinto the duodenum.

·                Enzymes are activated by alkaline conditions, provided by sodium hydrogencarbonate in bile

·                Bile emulsifies fats

·                Lipase digests fats to fatty acids and glycerol

·                Pancreatic amylase digests remaining starch to maltose

·                Maltase digests maltose to glucose

·                Trypsin digests polypeptides to peptides

·                Peptidases digest peptides to amino acids

Absorption in the small intestine :

·                Amino acids and glucose are soluble and can be absorbed

·                Glucose and amino acids are absorbed into blood capillaries by diffusion down concentration gradient

·                Fatty acids and glycerol are absorbed into lacteals by diffusion down concentration gradient

·                Glucose and amino acids diffuse via villi and microvilli into capillaries.

·                They are transported in blood plasma.

·                Capillaries join to form hepatic portal vein.

Large Intestine

·                Water is reabsorbed in colon.

·                Solid food is compacted into faeces.

·                Faeces are stored in rectum.

·                Faeces are egested via anus.

LIVER

The liver metabolises the products of digestion:

·                Glucose is converted to glycogen for storage in liver

·                Proteins are absorbed as amino acids. Liver removes excess amino acids from blood in hepatic portal vein by deamination. Amino group from amino acids is removed to form toxic ammonia, which cannot be stored. Hence, it is changed to the less toxic urea as ammonia and carbon dioxide combine / react. The rest of the amino acid is converted to glucose. Urea is transported in blood plasma to the kidneys as it is very soluble, to be excreted in urine. Concentration of urea in urine rises.

·                Detoxification :Substances, like alcohol / drugs are broken down by oxidation.They become toxic if their concentrations build up in the body. Detoxification turns them into harmless products.

Bile formation:

·                Old red blood cells are destroyed by the liver.

·                The haemoglobin is broken down.

·                Iron is removed and stored.

·                The rest becomes bile pigments.

·                It contains bile salts.