bio: #7

human nutrition

importance of food

1. growth of new cells/tissues

2. source of energy

3. replacement of worn/damaged tissues

balanced diet

a diet that contains all essential nutrients in correct proportions to maintain good health

essential nutrients

carbohydrates, protein, fat, fibre, water, vitamins, minerals

carbohydrates

source of energy

examples of carbohydrates

rice, potato, sweet potato, cassava, bread, millet

protein

for growth, tissue repair, enzyme, some hormones, hair/nails, can be broken down to release energy

examples of protein

meat, fish, eggs, soya, groundnuts, milk

fat/oil

source of energy, heat insulation, part of hormones, in cell membranes, insulation of nerve fibres, eg. butter, milk, cheese, egg yolk

examples of fat/oil

butter, milk, cheese, egg yolk

fibre

this is cellulose, and adds bulk to undigested food passing through the intestines, maintaining peristalsis

peristalsis

a mechanism that helps moves food along the alimentary canal

water

formation of blood and cytoplasm, solvent for transport of nutrients and removal of wastes

vitamins and minerals

• not digested or broken down for energy

• essential in small quantities for health

importance of vitamin c

prevents scurvy

deficiency effects of vitamin c

1. bleeding gums

2. bleeding under skin

3. poor healing of wounds

• all due to fibres in connective tissue of skin/blood vessels not forming properly

examples of vitamin c

orange, lemon, tomato, fresh green vege

importance of vitamin d

prevents rickets/osteomalacia

deficiency effects of vitamin d

• vitamin d helps in absorption/deposition of calcium in bones

• lack causes soft bones/osteomalacia in adults

  • or rickets in children

examples of vitamin d

butter, milk, cheese, egg yolk, liver, fish-liver oil

importance of calcium

1. forms healthy bones and teeth

2. for normal blood clotting

3. helps in muscle contraction & nerve impulse transmission

deficiency effects of calcium

osteoporosis in older people

examples of calcium

milk, cheese, fish

importance of iron

1. formation of haemoglobin in red blood cells

2. needed by muscles and for enzyme systems in cells

deficiency effect of iron

iron-deficiency anaemia

iron-deficiency

• the decrease in red blood cells

• symptoms are feeling weak, tired, and irritable

examples of iron

red meat, liver, kidney, eggs, green vege (spinach, cabbage), chocolate

ingestion

taking of substances (eg. food, drink) into the body through the mouth

mechanical digestion

breakdown of food into smaller pieces without chemical change to the food molecules

chemical digestion

breakdown of large, insoluble molecules into small, soluble molecules

absorption

movement of digested food molecules through the wall of the intestine into the blood

assimilation

uptake and use of nutrients by cells

egestion

passing out of food that hasn’t been digested or absorbed, as faeces, through the anus

mastication

or chewing, is a form of mechanical digestion in the mouth done by teeth

types of teeth

incisor, canine, premolar, molar

incisor

front of mouth, chisel-chaped (sharp edge), for biting off pieces of food

canine

either side of incisors, slightly more pointed than incisors, for biting off pieces off food

premolar

behind canines, have 2 points (cusps), 1-2 roots, for tearing and grinding of food

molar

back of mouth, 4-5 cusps, 2-3 roots, for chewing and grinding of food

structures of a tooth

crown, gum, root, enamel, cement, dentine, pulp cavity

crown

the part visible above gum line

gum

tissue that overlays the jaws

root

other structures that are embedded in the jaw bone

enamel

covers the surface of the crown, very hard

cement

in the root, cement replaces the enamel, anchors the tooth into the bony socket of the jaw

dentine

below enamel, softer than enamel, contains pulp cavity

pulp cavity

contains nerves and blood vessels which enters the tooth through a small hole at the base of the root

mouth

1. ingestion of food

2. mechanical digestion by teeth

3. chemical digestion of starch by amylase

4. formation of a bolus for swallowing

bolus

a soft ball of chewed food mixed with saliva

salivary glands

contains:

1. amylase for chemical digestion of starch in food

2. liquid to lubricate food and make small pieces stick together

oesophagus (gullet)

transfers food from mouth to stomach by peristalsis

stomach

1. produces gastric juices containing pepsin

2. chemical digestion of protein

3. hydrochloric acid to kill bacteria

4. peristalsis churns food up into a liquid

duodenum

1. first part of small intestine

2. receives pancreatic juice for chemical digestion of proteins, fats and starch

3. neutralises the acid from the stomach

4. receives bile to emulsify fats (a form of physical digestion)

ileum

1. 2nd part of small intestine

2. enzymes in epithelial lining carry out chemical digestion of maltose and peptides

3. very long and has villi to increase surface area for absorption of digested food molecules

pancreas

secretes pancreatic juice into the duodenum via pancreatic duct for chemical digestion of proteins, fats, and starch

liver

1. makes bile, containing salts to emulsify fats (physical digestion)

2. assimilation of digested food such as glucose

3. deamination of excess amino acids

deamination

the process by which the liver breaks down excess amino acids because the body cannot store them

gallbladder

stores bile, made in the liver, to be secreted into the duodenum via the bile duct

colon

1. first part of large intestine

2. absorption of water from undigested food

3. absorption of bile salts to pass back to the liver

rectum

2nd part of large intestine that stores faeces

anus

egestion of faeces

chemical digestion

breaking down of large molecules into smaller, soluble molecules, occuring in stages

mouth digestive gland, secretion, enzyme, action

• salivary glands secrete saliva, contains salivary amylase

• salivary amylase digests starch → maltose

• pH 7

stomach digestive gland, secretion, enzyme, action

• gastric glands secrete gastric juice

• pepsin digests proteins → peptides

• pH 1-2

small intestine (duodenum) digestive gland, secretion, enzyme, action

• pancreas secretes pancreatic juice

• trypsin digests proteins → amino acids

• pancreatic amylase digests starch → maltose

• lipase digests fast → fatty acids & glycerol

small intestine (ileum) digestive gland, secretion, enzyme, action

• epithelial cells of intestine secrete intestinal enzymes

• protease digests proteins → amino acids

• maltase digests maltose → glucose

• lipase digests fats → fatty acids & glycerol

bile

• green, watery fluid produced in the liver

• stored in gallbladder

• delivered to duodenum through bile duct

bile functions

1. emulsifies fats (breaks fat globules → smaller fat droplets)

2. neutralises acidic mixture of food (bile is slightly alkaline)

hydrochloric acid

• provides ideal environment for protein-digesting enzymes

• destroys pathogens

adaptation of intestine

1. presence of many villi

2. epithelium/wall of villus is only one cell thick

3. presence of microvilli on cells of epithelium

4. each villus has many blood capillaries that allow blood to transport absorbed glucose & amino acids away

5. each villus has lacteal

6. epithelial cells have many mitochondria

presence of many villi

increases surface area for absorption

epithelium/wall of villus is only one cell thick

provides short diffusion distance for nutrients to pass through

presence of microvilli on cells of epithelium

further increases surface area for absorption

each villus has many blood capillaries that allow blood to transport absorbed glucose & amino acids away

maintains diffusion gradient

each villus has lacteal

transports fat away

epithelial cells have many mitochondria

provides energy for active transport of nutrients into villi

absorption of glucose & amino acids

epithelial cells (of villus) → capillaries (inside the villus) → venules/small veins → hepatic portal vein → liver → blood circulation

hepatic portal vein

transports deoxygenated blood from the gut to the liver

absorption of fatty acids and glycerol

combine into fats again in intestinal epithelium → lacteals → lymphatic system → bloodstream

absorption of vitamins & minerals

• water soluble vitamins → epithelium

• fat soluble vitamins → fat droplets

• mineral salts ion → active transport

epithelium

• type of body tissue covering all internal/external body surfaces, lines body cavities and hollow organs

• major tissue in glands

assimilation

the uptake and use of nutrients by body cells

assimilation of glucose

• glucose is oxidized to CO2 & water in respiration

• provides energy to cells

assimilation in fats

• built into cell membranes/etc

• oxidized to provide energy

• provides 2x as much energy as sugar

assimilation in amino acids

• built up into proteins like plasma proteins

• form cell membranes & enzymes

• unneeded amino acids are converted by the liver into glycogen

  • used for energy