Digestion And Absorbtion (Finished Apart From Visking Tubing) Flashcards
What happens during digestion
Large molecules are hydrolysed into smaller molecules that can be absorbed across the cell membrane
Outline how carbohydrates are digested
SAM:
Starch is hydrolysed by the salivary amylase (which is secreted by the salivary glands into the mouth) into maltose
PAM:
The pancreas releases pancreatic enzymes into the small intestine. This contains amylase which hydrolyses any remaining starch into maltose
MEG:
The enzyme maltase which is embedded In the epithelial cells in the small intestine hydrolyses the maltose into glucose, which can then be absorbed into the bloodstream through the epithelial lining
Give 2 places amylase is made
The salivary glands
The pancreas
What does amylase hydrolyse
Amylase hydrolyses glycosidic bonds in starch to produce maltose (a disaccharide made from 2 glucose molecules)
What is maltase and where is it found
One of the membrane - bound disaccharidases, found embedded on the cell surface membrane of the epithelial cells of the ileum
What is the ileum? Outline it’s structure (2) and what this structure adds
The ileum is the final section of the small intestine.
The lining of the ileum is folded, The cells that line the ileum also have microvilli present (to increase the surface area, allowing more membrane bound disaccharides to fit and faster absorbtion of the products of digestion)
The epithelial lining is only one cell thick, which decreases the diffusion distance therefore increases rate of absorbtion into the bloodstream
Give 3 features that effect the rate of diffusion in the small intestine (and how they help)
Microvilli - large surface area: volume ratio
Thin epithelial lining - low distance for molecules to diffuse across
Good blood supply - maintains the concentration gradient
Outline how protein digestion occurs
1) Protein digestion begins in the stomach using pepsin. This enzyme is secreted with HCl, giving an acidic pH of 2.
2) as this mixture enters the small intestine from the stomach, it is mixed with bile salts to neutralise the HCl.
3) Pancreatic juices are secreted into the small intestine. Pancreatic juice contains endopeptidase and exopeptidase enzymes.
4) Endopeptidases hydrolyse internal peptide bonds within the polypeptides to form smaller polypeptide chains. This gives them more ends, increasing the surface area for exopeptidases to act on.
5) exopeptidases then hydrolyse peptide bonds at the end of a polypeptide to remove terminal amino acids
6) membrane bound dipeptidases found within the cell surface membrane of epithelial cells hydrolyse peptide bonds in the resulting dipeptides, releasing 2 amino acids (which can then cross the cell membrane and be absorbed)
What are endopeptidases and what is their function
Enzymes that hydrolyse internal peptide bonds within a polypeptide to form smaller polypeptide chains.
This creates more ends (increasing the surface area) for exopeptidases to act on
What are exopeptidases and what is their function
Enzymes that hydrolyse peptide bonds at the ends of a polypeptide chain to remove terminal amino acids, releasing a single amino acid, dipeptide or tripeptide
What are terminal amino acids
Amino acids at the end of the polypeptide chain
Give the names of 4 mechanisms for the absorption of the products of digestion by cells lining the ileum
Simple diffusion
Facilitated diffusion
Active transport
Co-transport
Outline how amino acids and monosaccharides are absorbed
1) Sodium ions are actively transported out of the epithelial cells of the ileum and into the bloodstream (using the sodium potassium pump and ATP)
2) this creates a concentration gradient, with a higher concentration of sodium in the lumen than in the ileum cell.
3) this allows sodium to diffuse in from the lumen into the ileum cell, via a co-transport protein for either a monosaccharide/ amino acid
4)The co-transporter carries the monosaccharide/amino acid into the cell against its concentration gradient, resulting in a high concentration of monosaccharide/ amino acid in the cell. (This process is known as co-transport
5)Because of the concentration gradient, the monosaccharide/ amino acid can then be absorbed into the bloodstream via facilitated diffusion.
Where are bile salts made and stored
Bile salts are made by the liver and stored in the gallbladder until secreted into the small intestine.
Outline lipid digestion and absorbtion
Digestion:
1) bile salts are made by the liver and stored in the gallbladder until they are secreted into the small intestine.
2) the bile salts bind to large lipids to form lipid droplets, known as emulsification.
3) The lipid droplets have a higher surface area for lipase action, so it can quickly hydrolyse triglycerides
4) lipase is produced by the pancreas then secreted into the small intestine, where it hydrolyses ester bonds in the triglycerides to form monoglycerides and fatty acids
Absorbtion:
1) The monoglycerides and fatty acids can’t diffuse through the epithelial cell membrane alone-they must first be surrounded by bile salts to form micelles (this makes them more soluble)
2) the micelles transport the monoglycerides and fatty acids to the epithelial cell membrane
3) the fatty acids and monoglycerides (without the bile salts) are then absorbed by simple diffusion into the epithelial cells
4) the triglycerides are then reformed in the golgi apparatus into chylomicrons (combining proteins with the triglycerides).
5) the chylomicrons are then packaged into vesicles for release into lacteals via exocytosis as the vesicles move to the cell membrane and are carried away in the lymphatic system
What are Micelles
Circular formations that are made up of phospholipid tails
Give 3 components of micelles of Micelles
Bile salts
Fatty acids
Monoglycerides
What are dipeptidases
Enzymes that hydrolyse the glycosidic bond holding dipeptides together, producing 2 amino acids
Where are dipeptidases found
Embedded in epithelial cell membranes
What is the name of the protein via which sodium can diffuse into the epithelial cell with an amino acid
Amino acid co-transport carrier protein
Give 2 functions of bile in lipid digestion and how they help
Emulsifies large fats into droplets- this creates a larger surface area for lipase to hydrolyse
Neutralises stomach contents - this allows for the optimum pH for enzymes in the small intestine to be reached
What is visking tubing
A partially permeable membrane which allows smaller molecules to pass through but not larger ones
Where are lipases made and used
Made in the pancreas
They work in the small intestine
Give three examples of endopeptidases
Trypsin
Chymotrypsin
Pepsin
