6.1 - digestion and absorption Flashcards
what is the digestive system?
- the system that humans use to digest food
- where food passes from mouth to anus
- broken from macromolecules to monomers and ions that can be absorbed
- macromolecules are broken down through different ways but mainly through enzyme action.
what does the mouth do?
- mechanical digestion of food by chewing, mixing with saliva and start starch digestion by enzymes
what does the oesophagus do?
moves food from the mouth to the stomach by peristalsis
what does the stomach do?
- churning and mixing of food with secreted water and acid to kill foreign bacteria and other pathogens
- start of protein digestion by enzymes
what does the small intestine do?
- final stages of digestion of carbs. lipids, proteins and nucleic acids
- neutralising of stomach acid and absorption of nutrients
what does the pancreas do?
- synthesis and secretion of lipase, amylase and protease enzymes
what does the liver do?
- produces bile which is used to break up or emulsify lipid droplets
what does the gall balder do?
- it is storage and release of bile
what does the large intestine do?
- reabsorbs water
- further digests carbs by gut bacteria
- forms and stores faeces
what and why is the structure of the small intestine?
- the wall is made of circular and longitudinal muscle instead of strained muscle
- contractions occur unconsciously or involuntarily as controlled by the enteric nervous system
- its moderate force and some vigorous contractions move the food along the gut
- contractions are called peristalsis
what happens in peristalsis?
- circular muscle contracts from back to front to move food and avoid backflow
- longitudinal muscle moves food forward
- movement is slow
- mixes partially digested food with enzymes to speed up the digestion process
what is partially digested food moving from mouth to stomach called?
bolus
what is food that has been mixed with enzymes in the stomach called?
chyme
what is the serosa of the small intestine?
the fibrous connective tissue that acts as a protective outer covering of small intestine
what is the muscle layer of small intestine?
the longitudinal muscle used for peristalsis and the inner circular muscle for contractions
what is the submucosa in the small intestine?
made of connective tissue and separates the muscle from the mucosa
what is the mucosa in the small intestine?
has the highly folded inner layer called villi that absorbs materials from the intestinal lumen
where are digestive enzymes secreted from?
- the pancreas mainly but also the salivary gland and stomach
- location and type of enzyme secreted depends on the specific substrate being hydrolysed (catabolic reaction)
what does the pancreas secrete and/or synthesise?
- hormones insulin and glucagon into blood from small groups of cells
- the hormones regulate blood glucose levels
- the rest of the pancreas synthesises and secretes digestive enzymes into the gut after food
- this response is supported by hormones synthesised and secreted by the enteric nervous system and stomach.
how are digestive enzymes synthesised?
- by pancreatic gland cells on the rER
- processed by the Golgi apparatus
- secreted by exocytosis to the duct that delivers the digestive enzymes to the small intestine
(pancreatic juice)
what is pancreatic juice?
- it contains enzymes that break down the three macromolecules ready for absorption of its monomers:
- amylase (starch)
- Lipase (triglycerides and phospholipids)
- proteases (proteins and peptides)
how do the digestive enzymes secreted by the pancreas chemically break down macromolecules into monomers?
- in the small intestine
- Amylase digests starch into maltose
- lipase breaks down triglycerides into fatty acids and glycerol
- phospholipase breaks down phospholipids into fatty acid, glycerol and phosphate
- protease breaks down proteins and polypeptides into shorter peptides
how do the enzymes that are immobilised on the plasma membrane chemically break down macromolecules into monomers?
- nucleases digest DNA and RNA into nucleotides
- maltase digests maltose into glucose and galactose
- lactase digests lactose into glucose and fructose
- exopeptidase digests peptides by removing one amino acid
- dipeptidase digests dipeptides into amino acids
Cellulose from plants remains undigested and passes to the large intestine
how is the absorption of nutrients highly efficient in the small intestine?
- inner epithelial lining of the intestine is highly folded into villi that stick into the lumen.
- they increase surface area available for absorbtion of material by diffusion or Active Transport - increase rate absorb