3. Digestion & Absorption Flashcards
Suggest why the stomach does not have villi or microvilli.
- food in stomach x yet hydrolysed into soluble molecules
- x be absorbed
- villi would be futile
List 3 enzymes produced by thr epithelium of the ileum.
- maltase
- sucrase
- lactase
- Suggest the process by which microorganisms produce ‘a large volume of gas’ in lactose intolerant individuals.
/ - Suggest a reason why this gas is unlikely to be CO2.
- Respiration
- CO2 formed in aerobic respiration vs conditions in colon = anaerobic
Explain how lowering the water potential in the colon can cause diarrhoea.
- water moves from epithelial cells into lumen of colon
- water faeces
Describe digestion in the mouth.
- Mechanical: chewing- ↑ s.a. for stomach to work on in c. digestion –> quicker digestion
- Chemical: Saliva- 1. amylase hydrolyses starch 2. mineral salts maintains ~ neutral pH (optimum)
Why are polysaccharidases (eg. amylase) produced in the mouth?
- polysaccharides take longer to digest
- start earlier in mouth
- single molecules ready to be absorbed in the S.I.
Features of the oesophagus.
- muscular –> peristalsis
- rings of cartilage –> flexibility + protection
Digestion in the stomach.
C:
- HCl- kills pathogens in food
- releases protein (peptin- pH2)
- mucus- line stomach wall for protection
M:
- muscular- churns food–> ↑ s.a.
Digestion in the pancreas.
Pancreatic juice
- pancreatic amylase- cont. hydrolysis of starch (after stop in stomach ∵ denaturation of salivary amylase)
- alkaline salts (bicarbonates)- neutralises acid–> optimum pH for amylase (+enzymes) in the S.I. + x erode intestinal wall
Processes in the large intestine
- absorbs excess water
- bacteria w/ enzymes- break down complex carbs (eg. plant-based cellulose)
Describe the action of amylase
- produced in mouth & pancreas
- hydrolyses alternate g. bonds of starch molecule
- produce maltose (disaccharide)
Explain the importance of maltase being membrane-bound.
- in epithelial lining of ileum
- broken down –> directly absorbed after broken down
- ↓ diffusion distance for monos
Explain the importance of pancreatic amylase.
- ensures complete breakdown of polysaccharides
:)
* salivary amylase denatured in stomach
* broken down into smaller chains
* ↑ s.a. for disaccharidases to work on
* broken down into** monos for absorption**
Explain how a co-transporter of sodium and glucose works. (7)
- transporter faces into lumen- ✔️bind w/ Na+ ❌glucose
- Na+ binds –> CONFORMATIONAL CHANGE –> opens glucose binding site
- glucose binds
- protein reorients in mem –> sites holding glucose & Na+ face into epithelial cell
- Na+ dissociates –> cytoplasm ==> glucose binding destabilises
- glucose dissociates –> cytoplasm
- protein reorients back –> original position
Explain the action of endopeptidases using an example.
- hydrolyse internal peptide bonds in polypeptide chains
- to ↑ end points & ↑ s.a. for exopeptidases
Example: - pepsin made as pepsinogen (inactive form ∵ would damage stomach lining before release)
- acid (~pH2) –> CONFORMATIONAL CHANGE –> acitvated
- goblet cells- mucus lining stomach wall –> protects against HCl
- trpsin & chymotrypsin- in pancreatic juice
Describe the action of exopeptidases.
- hydrolyse terminal peptide bonds in a polypeptide chain (remove single a.a.)
Describe the action of dipeptidases.
- act on dipeptides
- hydrolyse peptide bond between 2 a.a.
- in cell-surface mem on epithelial cells in s.i.
Describe how lipids are digested into its component molecules.
- hydrolysed by lipases (produced in pancreas)
- only hydrolyse 2 ester bonds
- triglycerides –> 2x fatty acids + monoglyceride
Describe the actions of bile salts.
- emulsify lipids into smaller droplets (splitting x broken down ∵ x bonds broken)
- ↑ s.a.
Describe what micelles are and their functions.
- small droplets of monog & fatty acids w/ bile salts
Functions:
1. ↑ s.a. for lipase to work on –> broken down into monog + fatty acids (non-polar- easily diffuse)
2. transport products to mem of epithelium of s.i.
List 3 organelles that you would expect to be numerous &/ well-developed in an epithelial cell of the ileum, explain why.
- ER- resynthesise triglycerides from monog & fatty acids
- Mitochondria- ATP for co-transport of glucose & a.a.
- Golgi- form chylomicrons from triglycerides, cholesterol, lipoproteins
In addition to having microvilli, state one other feature of the epithelial cells of the ileum that would increase the rate of absorption of amino acids.
↑ no. of protein channels + carriers
Describe the path taken by monoglycerides and fatty acids after being absorbed into the epithelial cell.
- ER: reformed into triglycerides
- Golgi: + cholesterol + lipoproteins (+phospholipids) –> chylomicron (vesicle of triglycerides)
- chylomicron released by exocytosis (chylomicron fuses w/ mem)
- enter lacteal (lymphatic vessel) –> bloodstream
Explain how bile salts are able to split lipids into smaller droplets.
- 2 ends
- lipophilic (hydrophobic- soluble in fat)- arrange in fat droplets
- lipophobic (hydrophilic- soluble in water)- sticking out
- prevents fat droplets from sticking to each other to form a large droplet
Why is the importance that the blood is moving for the uptake of glucose?
- maintains conc. gradient
- glucose moves into blood by f. diffusion
