6.1 digestion and absorption Flashcards
why do we need to eat?
to provide our bodies with chemical energy, which can be converted to ATP to power processes in the body
what are essential nutrients and why do we need them?
they are nutrients not made by the animal and thus must be obtained from dietary sources
in digestion, assimilation is the….
synthesis of molecules in the body from the absorbed small molecular nutrients
label a diagram of the digestive system
-
the alimentary canal consists of organs in which food ____________ ________.
passes through
accessory organs are…
organs that aid in digestion but do not actually transfer food
what is the function of the mouth?
- ingestion and chewing to break down food to smaller pieces -> incr SA:VR
- salivary amylase secreted for the digestion of starch to maltose
- alkaline medium of saliva for enzymatic activity
what organs have peristalsis in the alimentary canal?
esophagus, stomach, small intestine, large intestine
which part of the esophagus prevents acid and food reflux?
the sphincter muscle
what is the function of the esophagus?
- transports food from mouth to stomach by peristalsis
- prevents food and acid reflux through the contraction of sphincter muscle
which organ produces and secretes bile into the gall bladder?
the liver
the gall bladder stores ______ which functions to aid digestion by…
- bile
- helping to emulsify fats for incr SA:VR for more efficient digestion by pancreatic lipase
what is the function of the stomach? (3)
- secretes HCl and pepsinogen
- acidic medium kills pathogens in food
- pepsinogen converted to pepsin due to HCl and digests proteins into amino acids
what does the pancreas do to aid digestion? (2)
- secretes digestive enzymes for proteins, fats and carbohydrates
- alkaline medium due to HCO3 ions for enzymatic activity
what happens in the small intestine? (2)
- further digestion of food into monomers
- absorption of monomers facilitated by intestinal folds to incr SA
what is the function of the small intestine? (3)
- digests food into monomers
- absorbs monomers across a 1-cell epithelium for quick movement into capillaries and lacteals
- intestinal folds e.g. villi, microvilli incr SA for absorption
the three sections of the small intestine are…
1. duodenum
2. jejunum
3. ???
ileum
what is the function of the large intestine? (3)
- absorption of water, vitamins and mineral ions
- house beneficial bacteria
- fermentation of undigested waste
the part of the body involved in egestion of undigested food is…
the anus
what part of the body stores undigested food?
the rectum
why are enzymes needed in digestion?
they are biological catalysts, meaning they speed up the rate of reaction at body temperature by lowering the activation energy of the catabolic reactions
intestinal enzymes are _______ ________ while pancreatic enzymes are _______________________ (ref to movement)
membrane-bound, carried along w food
what is peristalsis?
the rhythmic contraction of antagonistic circular and longitudinal muscles
how does peristalsis aid digestion
- it mixes chyme (semi-digested food) with enzymes
- it moves it along the gut
how is food moved along the gut? (3)
- through peristalsis; the alternate contraction of the longitudinal and circular muscles
- behind the food, the C muscle contracts and L muscle relaxes
- gut wall constricts to become narrow and longer
- prevents food from being pushed back while pushing food forward
- at the food, the C muscle relaxes and L muscles contract
- gut wall becomes wider and shorter
- relaxation of C dilates gut wall and enables food to be pushed forward
- contraction of L muscles shorten the distance to be travelled
what takes place at the duodenum, jejunum and ileum respectively?
duodenum, jejunum: digestion
ileum: absorption
identify the small intestine tissue layers
-
what is one feature of the serosa
it is a membrane coated with mucus to reduce friction with other organs
in the small intestine, the large blood and lymph vessels and nerves are contained in the…
submucosa
how does villi enhance the rate of absorption in the small intestine?
microvilli and villi increases the SA of the epithelium with numerous folds
what are 6 features of villi (mnemonic: MRS LIM)
- microvilli
- numerous folds increases SA
- rich blood supply
- rich supply of capillaries maintain conc gradient for diffusion
- single layer epithelium
- minimises diffusion dist btw lumen + blood
- lacteals
- absorbs lipids into lymphatic system
- intestinal glands
- exocrine pits release digestive juices
- membrane proteins
- facilitates transport of digested materials into epithelial cells
why does the villus epithelium have a lot of mitochondria?
to provide ATP for AT
fill in the list of membrane transport mechanisms:
1. ????
2. facilitated diffusion
3. ???
4. simple diffusion
- secondary active transport (co-transport)
- osmosis
what monomers undergoes secondary AT?
glucose and amino acids
how does glucose and amino acids enter the epithelial cell by secondary AT?
glucose and amino acids are co-transported across the epithelial membrane by the active translocation of Na+
where do amino acids and glucose go and by what vessel after being absorbed into the bloodstream?
to the liver by the hepatic portal vein
which monosaccharides enter by AT?
glucose and galatose
which molecules enter by simple diffusion?
fatty acids, monoglycerides
fructose enters by…
facilitated diffusion
how are peptides absorbed?
co-transport by active translocation of H+
fats enter the lacteal as…
chlyomicrons
how does facilitated diffusion work?
- through channel proteins
- channel proteins help hydrophilic food molecules pass through hydrophobic part of plasma membrane
what enters the epithelial cell by facilitated diffusion?
fructose, vitamins and some minerals
what molecules enter the epithelial cells by osmosis and what is this in response to?
water molecules, in response to the movement of ions and hydrophilic monomers
what type of materials can enter epithelial cells by simple diffusion?
hydrophobic materials
lipids enter the epithelial cell by _______
simple diffusion
what is linear-chain starch called?
amylose
what is branched starch called?
amylopectin
where is starch digested?
mouth and small intestines
what enzyme breaks down amylose and amylopectin?
amylase
what is the products of digestion of amylose and amylopectin?
- amylose: maltose
- amylopectin: limit dextrin
where is maltose and limit dextrin digested?
at the membrane of microvilli
what enzymes digest maltose and limit dextrin?
maltase and dextrinase
maltase and dextrinase are ____________ (ref to position and mobility)
membrane-bound
the hydrolysis of maltose and dextrin produce…
glucose monomers
how is glucose absorbed? (6)
- glucose is co-transported across the epithelial membrane by secondary AT
- uses energy from the movement of Na+ ions down their electrochemical gradient at the apical side of the epithelial cell to transport gluc against its concentration gradient
- glucose is transported out of epithelial cell from basolateral side by facilitated diffusion to the blood in villus capillaries
- blood from villus capillaries then drain into venules in submucosa layer
- glucose in venules will be brought to liver via hepatic portal vein
- excess is converted to glycogen for storage
