6. Digestion Flashcards
Name all the structures (e.g. stomach) involved in digestion and their role.
- mouth - ingestion and chewing
- esophagus - swallowing
- stomach - killing pathogens and protein digestion
- gall bladder - stores bile
- liver - secretes bile
- pancreas - secretes digestive enzymes
- small intestine - digestion and absorption
- large intestine - absorption of water
- anus - egestion of faeces
Draw and label the cross sectional structure of the small intestines.
outside to in:
- circular muscle layer
- longitudinal muscle layer
- submucosa
- mucosa
- villi
How does food move through the small intestine?
- waves of muscle contraction, called peristalsis, pass along the intestine
Explain how circular muscle contraction and longitudinal muscle contraction moves food through the small intestine.
What additional effect do these contractions have?
- contraction of circular muscle behind the food constricts the gut to prevent food from being pushed back towards the mouth
- contraction of longitudinal muscle where the food is located moves it on along the gut
- mixes food with enzymes in the small intestine
What is the role of enzymes in digestion?
enzymes digest most macromolecules in food into monomers in the small intestine
Give examples of some macromolecules that enzymes digest in the small intestine.
proteins, starch, glycogen, lipids, and nucleic acids
Give an example of a macromolecule that enzymes in the small intestine cannot digest.
cellulose
Name three types of enzyme the pancreas secretes to digest macromolecules.
- lipase
- endopeptidase
- amylase
Where does the pancreas secrete its enzymes?
into the lumen, the top part of the small intestine
What is lipase? What does it break down? What are the products of this reaction?
- an enzyme
- lipids
- fatty acids + glycerol
What is endopeptidase? What does it break down? What are the products of this reaction?
- an enzyme
- polypeptides
- shorter peptides
What is amylase? What does it break down? What are the products of this reaction?
- an enzyme
- starch
- maltose
State the two types of molecule in starch.
- amylose
- amylopectin
Compare amylose and amylopectin.
- molecules of starch
- polymers of a-glucose
- linked by 1,4 bonds
Contrast amylose and amylopectin.
- amylose: 1,4 bonds therefore chains are unbranched
- amylopectin: 1,4 bonds and has some 1,6 bonds that make the molecule branched
How does amylase break 1,4 bonds? Comment on the significance of this?
- in chains of four or more glucose monomers
- it can digest amylose into maltose but not glucose
What does the specificity of the active site of amylase mean?
amylase can break 1,4 bonds, but cannot break 1,6 bonds in amylopectin
What are dextrins?
fragments of the amylopectin molecule containing a 1,6 bond that amylase cannot digest
What is digestion of starch completed by?
enzymes in the membranes of microvilli on villus epithelium cells. The enzymes are maltase and dextrinase that digest maltose and dextrins into glucose
What else, apart from the enzymes maltase and dextrinase, are in the membranes of microvilli in the small intestine?
protein pumps that cause the absorption of the glucose produced by digesting starch
Outline the path glucose takes on its way to being stored, once it is in the blood.
- blood carrying glucose and other products of digestion flows through villus capillaries to venules in the submucosa of the wall of the small intestine
- blood in these venules is carried via the hepatic portal vein to the liver, where excess glucose can be absorbed by liver cells and concerted to glycogen for storage
