Ch.27 - Digestive System

nutrition

the way in which organisms get chemicals and energy (in the form of food) form their environment

human nutrition involves

• ingestion - taking in food

• digestion - breaking down food

• absorption - absorbing nutrients (taking food into body)

• egestion - removing unabsorbed waste

associated glands

salivary gland

liver

pancreas

alimentary canal

the digestive system consists of a tube running from the mouth to the anus

2 types of digestion

• mechanical digestion - physical breakdown of food e.g teeth

• chemical digestion - breakdown of food using enzymes e.g amylase breaks down starch into maltose

e.g of chemical digestion

amylase breaks down starch into maltose

mouth

• incisors - cut, slice, + bite (chisel shape)

• canines - grip + tear (long and pointed)

• premolars - crush, grind and chew (flat surface)

• molars - crush grind an chew (large and flat surface)

dental formula

2(I2/2C1/1P2/2M3/3)

pharynx

throat containing 2 tubes

• oesophagus - food pipe

• trachea - windpipe

the epiglottis automatically closes over the trachea when we swallow

peristalsis

involuntary wave of muscular contractions that moves food

• fibre - stimulates it

stomach

• muscular bag

• hydrochloric acid (ph2) kills most bacteria

• stores food to soften it and kill bacteria

stomach - mechanical and chemical digestion

• mechanical - churning of the stomach mixes all the contents and forms chyme

• chemical - contains HCL which kills most bacteria

HCL in the stomach

• breaks down some bonds in proteins

• this allows protein-digesting enzymes (proteases e.g pepsin) to break down proteins into smaller chains of amino acids

protein digestion in stomach

proteases (e.g pepsin) break down protein into polypeptides and peptides

small intestine

pH 7-8

• duodenum - digestion (25cm)

• ileum - absorption (5.5m long)

duodenum

where most food is digested

• mechanical digestion - by peristalsis

• chemical digestion - using enzymes

e.g iipase breaks down lipids into fatty acids and glycerol

pancreas

• produces sodium hydrogen carbonate (alkaline) which neutralises chyme

• produces and releases enzymes (e.g lipase and amylase) into the duodenum via pancreatic duct

• apart from its role in digestion, it also produces insulin

liver

largest organ in the body

• breaks down red blood cells to form bile (which emulsifies lipids

• makes sodium hydrogen carbonate (neutralises acid from stomach)

• detoxifies chemicals in body e.g drugs or alcohol

• breaks down extra amino acids to form urea - DEAMINATION

• converts glucose to glycogen

• stores vitamins (e.g Vit.D) and minerals (e.g iron, zinc, copper)

• makes proteins to help blood clots

• makes cholestrol, used to form many hormones

• produces heat to warm body

urea and other wastes leave the liver in the hepatic vein - heart - kidneys converting it to urine

gall bladder

• stores bile

• flows from the gall bladder into the duodenum through the bile duct

functions of bile

• bile salts - emulsify lipids, which helps them be easily digested by enzymes in the duodenum (mechanical digestion)

• neutralises chyme, as it contains sodium hydrogen carbonate

• responsible for the pigment of faeces

end products of digestion

• carbs - monosaccharides (such as glucose )

• proteins - amino acids

• lipids (or fats) - fatty acids and glycerol

learn the table on Pg. 368

ileum

• contains infoldings called villi (sing. villus) - soft velvety feeling

• each villus has smaller infoldings called microvilli

• the villi an microvilli increase the surface area for absorption of nutrients (glucose, amino acids, vitamins + minerals)into blood stream

adaptations of the ileum and villi

• about 5.5m long

• large numbers of villi

• each villi has a microvilli and a lacteal (gets rid of fats)

• lining of the villi 1 cell thick

• villi have a rich blood supply

absorption of water-soluble nutrients

• blood (and nutrients) are carried away from ileum to liver via the hepatic portal vein

• liver stores carbs in the form of glycogen

• liver breaks down unwanted amino acids into urea (deamination)

large intestine

1.5m long

main function = reabsorbing water

• caecum

• appendix

• colon

• rectum

• anus

parts and funtions of the large intestine

• caecum and appendix - may be vestigial and store microorganism

• colon - (longest part of LI) reabsorbs water and contains many microorganisms which are beneficial to us

• rectum - stores faeces

• anus - egests faeces

balanced diet

contains all the food types (carbs, lipids, proteins, minerals, vitamins, water, fibres) in the correct proportions, necessary to supply the nutrients needed to maintain good health

malnutrition

outcome of not having a balanced diet

our choice of diet has implications for

• health

• age

• gender

• activity

• our need for variety of food

• sufficient water and fibre

diagrams to learn!

human digestive system

• mouth

• salivary glands

• pharynx

• oesophagus

• stomach

• duodenum

• ileum

• pancreas

• liver

• gall bladder

• bile duct

• colon

• caecum

• appendix

• rectum

• anus

Villus

• villus

• microvilli

• capillaries - with arrows, including outer arrow to hepatic portal vein

• lacteal

• muscular wall of ileum