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
what helps a villi have efficient exchange?
- thin epithelial layer that absorbs materials rapidly.
- dense network of capillaries for rapid movement of absorbed nutrients
- microvilli on surface of epithelial cells to increase SA
- lacteals that absorb lipids into the lymphatic system
how do villi absorb monomers formed by digestion? and what do they absorb?
- they are permeable enough to allow useful nutrients to pass through the membranes but also a barrier against harmful substances.
- they absorb:
- monosaccharides: glucose, fructose and galactose
- amino acids
- fatty acids, monoglycerides and glycerol
- nitrogen bases from nucleotides
- mineral ions
- vitamin c
nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - simple diffusion
- lipids are absorbed as they are hydrophobic molecules
nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - facilitated diffusion
- hydrophilic substances like glucose, amino acids, some vitamins and minerals and fructose.
nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - osmosis
- allows water moles to diffuse across membrane in response to the movement of ions and hydrophilic monomers.
nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - active transport
- atp to pump sodium ions into the lumen from epithelial cell to maintain a concentration gradient
- the passive re-entry of sodium ions is joined by nutrients including amino acids, glucose and mineral ions to pass from epithelial cells to capillaries
nutrient absorption methods to pass from lumen to capillaries or lacteals in villi - endocytosis
- the bulk transport of materials
- pinocytic vesicles are formed around fluid containing dissolved materials in the lumen by endocytosis
digestion of starch in the small intestine.
- starch is found in plants and composed of many a-glucose monomers linked together by condensation reactions
- can’t pass through membranes it must be digested in the small intestine
- cant be in stomach bc its too acidic for the enzymatic reactions needed
how starch is digested.
- 2 starches:
amylose is unbranched with a-glucose linked by 1, 4 bonds
amylopectin is branched and has 1, 6 bonds - amylase begins digestion, 1, 4 bonds in amylose and amylopectin are broken to form maltose and maltotriose
- 1, 6 bonds need maltase, glucosidase and dextrinase to breakdown maltose, maltotriose and dextrins into glucose monomers
- glucose can be absorbed by villi with sodium ions
- then moved by facilitated diffusion into the interstitial spaces inside villus
- then into blood where it flows via hepatic portal vein to liver where stored as glycogen
experiment 1 - meniscus levels
- bit of dialysis tubing is filled with starch solution
- a second bit of dialysis tubing is filled with amylase solution
- both placed in separate beakers of water
- over time water moves into tubing via osmosis toward solute and causes meniscus to rise
experiment 2 - maltose diffusion
- a bit of dialysis tubing is filled with starch solution and put in a beaker of water
- a second bit of dialysis tubing is filled with starch and amylase solution and put in beaker of water
- the amylase digests starch into maltose and diffuses out to beaker
