chapter 9 - the digestive system Flashcards
what are the associated organs
- pancreas, liver, gall bladder (accessory organs)
what is digestion
- carbohydrates, proteins and fats are broken down into units small enough to be absorbed into the blood and cells
what are the functions of the digestive system
- ingestion of food and water
- mechanical digestion
- chemical digestion
- movement along the alimentary canal
- absorption of food into the bloodstream
- elimination of food / defection of materials not absorbed
what do cells need
- vitamins, minerals, water, simple sugars, fatty acids, amino acids
what is the structure of the mouth
- human dental formula 2:1:2:3 (x4)
- 2 incisors: chisel shaped, cutting and biting
- 1 canine: conical, tearing
- 2:3 premolars and molars: broad crowns with cusps, crushing and grinding
mechanical digestion in the mouth
- ingestion, food enters the mouth
- teeth: breaks down food into smaller pieces
- mucous: lubricates food and with aid of tongue forms a bolus, pushed into pharynx
chemical digestion in mouth
- salivary glands: 3 pairs, secrete enzymes and mucous
- salivary amylase: breaks down starch into polysaccharides and disaccharides (pH 6.7)
structure of the oesophagus
- circular and longitudinal muscles
- causes wavelike contractions to move the bolus
mechanical digestion of the oesophagus
- the bolus moves down the oesophagus due to wavelike contractions (peristalsis)
- movement is lubricated –> secretion of the mucous
structure of the stomach
- longitudinal, circular and oblique muscles
- mucosa lining: specialised cells which secrete gastric juices
- holds food for 2-8 hours
mechanical digestion in the stomach
- churning of the food, contracts in different ways / directions
- provides chyme (soupy thick liquid)
chemical digestion in the stomach
- mucosa lining secretes gastric juices (mucous, pepsinogen, HCl) into gastric pits
- mucous: lubricates
- HCl: maintains low pH of 1.5-1.8, activates pepsinogen (becomes pepsin)
- pepsinogen: becomes pepsin –> breaks down proteins into peptides and polypeptides
absorption in the stomach
- nutrients are not absorbed in the stomach
- alcohol and some drugs (aspirin) are absorbed
what is the function of the pyloric sphincter
- allows for substances to enter the small intestine only once ready (after 2-8 hours)
structure of the small intestine
- 6m long, thin, duodenum, jejunum, ileum
- mucosa lining: folds internally (large SA)
- villi: projections that extend from folded surface, allow for absorption
what is the alimentary canal
- continuous tube that runs from the mouth to the anus (9m approx)
what are the villi in the small intestine
- 1mm long, single cell layer, contains lymph and blood capillaries
- lymph: absorption of fatty acids and glycerol, fat soluble substances
- -> carried to lymph nodes as fat -> lymphatic system -> blood drains into heart
- blood: absorption of amino acids, simple sugars, water, water soluble substances
- -> carried to liver via hepatic partial vein -> stored or continues to body cells
mechanical digestion in the small intestine
- movement: segmentation
- bile: secreted in the liver and stored in the gall bladder
- bile emulsifies fats (lipids -> fat droplets = easier to be broken down), this increases SA -> lipase can enter -> fatty acid and glycerol
chemical digestion in the small intestine
- pancreatic juices / enzymes (duodenum): produced in pancreas, digestion
- -> pancreatic amylase, lipase, protease, ribonuclease and deoxyribonuclease
- intestinal juices / enzymes (duodenum): produced in intestine, digestion
- -> intestinal amylase, lipase, protease
absorption in the small intestine
- takes place in the jejunum and ileum
- amino acids, simple sugars, fatty acids, glycerol, vitamins, minerals, water
- movement of small intestine wall promotes absorption
structure of the large intestine
- 1.5m long, thick
- ascending, transverse and descending colon, rectum, anus
mechanical digestion in the large intestine
- very slow
- 18-24 hours
absorption in the large intestine
- most of the water, minerals and vitamins are absorbed
what is the faeces made of
- undigested food material (cellulose, bile pigments, bacteria)
- bacteria breaks down in large intestine, sometimes converted into vitamins which are then absorbed
