THE HUMAN DIGESTIVE SYSTEM Flashcards
why is food digested? (2)
- insoluble/too big to cross membrane and be absorbed into blood
- polymers must be broken into monomers to be rebuilt into useful molecules
gut (4)
- where digestion occurs
- long hollow muscular tube
- movement in one direction by peristalsis
- several sections of unique mechanical/chemical digestion and absorption
functions of the gut (4)
- ingestion, taking food in
- digestion, break down of molecules by mechanical/chemical digestion
- absorption, passage of useful molecules into gut wall into blood
- egestion - elimination of waste not made by the body
types of digestion (2)
- mechanical - chewing/crushing
- chemical - secreted enzymes
function of parts table 223
function half
structure of the gut wall (4)
- serosa - tough connective tissue, reduces friction
- muscle - two layers (circular/longitudinal), make waves of contractions (peristalsis) to push food along
- submucosa - connective tissue w/ blood/lymph vessels, remove ab
unlabelled gut
label lumen, serosa, longitudinal muscle, circular muscle, epithelium,
what must the gut wall do before absorption
- break down macromolecules into smaller molecules
how are carbohydrates digested? (4)
- digested from polysaccarides to disaccarides to monosaccarides
- amylase hydrolyses starch into maltose
- maltase digests maltose into glucose
- sucrase digests sucrose, lactase digests lactose`
how are proteins digested? (4)
- they are very large molecules so digested into polypeptides, into dipeptides, into amino acid
- protein digesting enzymes = protease, peptidase
- endopeptidases hydrolyse peptide bonds in the protein
- exopeptidases hydrolyse peptide bonds at the end of the polypeptides
how are fats digested?
- into fatty acids and monoglycerides by lipase
buccal cavity (3)
- where mechanical digestion begins (the mouth)
- food is mixed with saliva and chewed by the teeth
- increases foods surface area for enzymes to access
what is in saliva? (3)
- amylase
- HCO3- and CO3^2- so the pH is akaline for amylase
- mucus to lubricate the food’s passage down the oesophagus
oesophagus
- carries food from the mouth to the stomach
the stomach (3)
- food is digested in the stomach
- kept there by contraction of two sphincters/rings of muscle
- stomach wall muscles contract rhythmically and mix food with gastric juice secreted by the glands in the wall
what does gastric juice contain?
- peptidases, secreted by zymogen/chief cells at the base of the gastric pit
- hydrochloric acid, secreted by oxyntic cells to lower the pH for enzymes
- mucus, secreted by goblet cells, at the top of the gastric pit, forms a lining to protect the stomach wall from enzymes and lubricate food
how are peptidases secreted?
- as inactive pepsinogen from the zymogen cells and activated by H+ to pepsin, an endopeptidase
gastric pit picture p225
labels: gastric pit, goblet cells, submucosa, immature goblet cells, zymogen cells, oxyntic cells
what are the regions of the small intenstine (2)
- the duodenum
- the ileum
how is partially-digested food allowed into the duodenum?
- relaxation of pyloric sphincter muscle at the base of the stomach, allowing food through in small doses
bile (3)
- made in the liver
- stored in the gallbladder
- passed into the duodenum by the bile duct
what is in bile? (3)
- no enzymes
- amphipathic bile salts, emulsify lipids in food by lowering surface tension and increasing surface area by breaking globules into smaller globules
- is alkaline and neutralises acid from stomach, makes pH suitable for small intestine
amphipathic
- contain both hydrophilic and hydrophobic parts
pancreatic juice (2)
- secreted by islet cells (exocrine glands in the pancreas)
- enters duodenum through pancreatic duct
what is in pancreatic juice?
- enzymes
- sodium hydrogen carbonate
enzymes in pancreatic juice? (4)
- endopeptidases, to hydrolyse protein to peptides
- amylase, to digest any remaining starch to maltose
- lipase, lipids to fatty acids and monoglycerides
- trypsinogen, inactive enzyme converted into protease trypsin by enterokinase (duodenal enzyme)
purpose of sodium hydrogen carbonate in pancreatic juice? (3)
- raises pH
- neutralises acid from the stomach
- providing pH for pancreatic enzymes
what happens to food coming from the stomach? (2)
- lubricated by mucus
- neutralised by alkaline secretions from cells at the base of the crypts of Lieberkühn, called Brunner’s glands
enzymes associated with villi (3)
- endo/exopeptidases secreted by cells at villus tips to digest polypeptides
- enzymes on epithelial cell membranes that digest dipeptides into amino acids
- carbohydrases digest disaccarides and they are absorbed into epithelial cells of the villi
how is the ileum well-adapted (4)
- very long with folded lining
- villi on the surface of the folds
- microvilli on the epithelial cells
- all produce large SA for absorption
how does absorption occur? (2)
- by diffusion, facilitated diffusion and active transport
- epithelial cells have many mitochondria for ATP
how are amino acids absorbed? (3)
- absorbed into epithelial cells by active transport
- pass into capillaries by facilitated diffusion
- water-soluble and dissolve in plasma
how is glucose absorbed? (4)
- passes into epithelial cells w/ glucose by co-transport
- move into capillaries, sodium by active transport, glucose by facilitated diffusion
- dissolve in plasma
- diffusion/facilitated diffusion are slow so active transport is used for some to prevent it being lost in faeces
how are fatty acids / monoglycerides absorbed? (2)
- diffuse into epithelial cells into lacteals, ending lymph capilaries in villi
- lacteals transport fat-soluble molecules through lymphatic system to left subclavian vein near heart
how are minerals absorbed? (2)
- into the blood by diffusion/facilitated diffusion/active transport
- dissolve in plasma
how are vitamins absorbed? (2)
- B/C water soluble and absorbed into blood
- A,D,E fat soluble absorbed into lacteals
how is water absorbed? (2)
- absorbed into epithelial cells in ileum
- into capillaries via osmosis
what happens to lipids after absorption (2)
- used in membranes and to make hormones
- excess is stored
where do glucose and amino acids go after absorption?
- taken to the liver by the hepatic portal vein
what happens to glucose in the liver? (2)
- taken to body cells and respired for energy or stored as glycogen in liver/muscle cells
- excess stored as fat
what happens to amino acids in the liver? (3)
- taken to body cells for protein synthesis
- excess not stored so liver deanimates and converts amine groups to urea and carried in blood, excreted at kidney
- remains of amino acid conversed into carbohydrate for storage or conversion to fat
what is the large intestine made up of? (4)
- the caecum
- the appendix
- the colon
- the rectum
what passes into the colon? (4)
- undigested food
- mucus
- bacteria
- dead cells
how does the colon work? (6)
- less villi with a major role in water absorption
- vitamin K and folic acid secreted by mutualistic microorganisms living there
- minerals absorbed from colon
- as material passes along, water absorbed
- reaches the rectum semi-solid
- passes along rectum and egested as faeces in defecation
