DIGESTION AND ABSORPTION Flashcards
What do glands produce and what is their function
enzymes that hydrolyse large molecules into smaller ones for digestion
Why can’t large biological molecules be absorbed into the blood from the gut and give examples
too big to cross cell membrane, e.g. starch and proteins
What are carbohydrates broken down into during hydrolysis
disaccharides and then monosaccharies
What are fats broken down into during hydrolysis
fatty acids and monoglycerides
What are proteins broken down into during hydrolysis
amino acids
What does amylase catalyse
conversion of starch into maltose
Where is amylase produced and released
salivary glands (into mouth) and pancreas (into small intestine)
What are the major parts of the digestive system
1) oesophagus
2) stomach
3) ileum
4) large intestine
5) rectum
6) salivary glands
7) pancreas
What is the job of the oesophagus
carry food from mouth to the stomach
What is the stomach
muscular sac with an inner ayer that produces enzymes
What is the role of the stomach
to store and digest food, especially proteins
What is the ileum
long muscular tube
What is the role of the ileum
to further digest food by enzymes that are produced in its walls and by glands that release them into it
What adaptation does the ileum have
the inner walls are folded into villi to increase SA:V, which are then folded further into microvilli on the epithelial cells of each villus - means that there is a larger SA for absorption into blood stream
What is the role of the large intestine
to absorb water, mainly water secreted from the digestive glands
What is the role of the rectum
to store the faeces until being removed via the anus through egestion
Where are the salivary glands situated
near the mouth
What do salivary glands secrete via a duct into the mouth
enzyme amylase that hydrolyses starch into maltose
Where is the pancreas situated
below the stomach
What is the role of the pancreas
to secrete pancreatic juice that contains proteases, lipase and amylase
What are the 2 stages of digestion
1) physcial breakdown
2) chemical breakdown
What is physical breakdown
the break up of large pieces of food into smaller ones via structures such as the teeth or stomach wall
What does physical breakdown mean
the food is possible to ingest, and there is a larger SA:V for chemical breakdown
What is chemial breakdown
hydrolysis carried out by enzymes of large, insoluble molecules into smaller soluble ones
What are the 3 main types of digestive enzymes and what do they hydrolyse
1) carbohydrases (carbohydrates-monosaccharides)
2) lipases (lipids-fatty acids and glycerol)
3) proteases (proteins-amino acids)
What is the usual events that occur when hydrolysing a carbohydrate
enzymes hydrolyse the molecule into smaller sectioons, and other enzymes hydrolyse them into their monomers
Explain the general process of starch digestion
1) amylase is produced in the mouth and pancreas which hydrolysis the alternate glycosidic bonds of the starch molecule, to produce maltose
2) Maltose is hydroyled by maltase (produced by lining of ileum) into alpha glucose
How does starch digestion occur in humans
1) saliva that contains salivary amylase and mineral salts enters mouth from salivary glands and mixed with food, which hydrolyses it into maltose (salts help to maintain neutral pH= optimal for enzyme)
How does starch digestion occur in humans 2
food enters stomach where conditions are acidic, whcih denatures amylase and stops further hydrolysis
How does starch digestion occur in humans 3
passed into small intestine where it mixes with pancreatic juice which contains pancreatic amylase that hydrolyses any remaining starch into maltose. pH is maintained at neutral by alkaline salts produced by pancreas &intestinal wall (so amylase can function)
How does starch digestion occur in humans 4
muscles in intestinal wall push food along the ileum whilst its epithelial lining produces maltase. Here it is a membrane bound disaccharidase, which hydrolyses maltose to alpha glucose
Why is the maltase in ileum describedc as membrane-bound disaccharidase
it is not released into the lumen of the ileum but is part of the cell-surface membranes of the epithelial cells that line the ileum
What are 2 other common disaccharies that are hydrolysed and what are they found in
1) sucrose - natural foods, fruits
2) lactose - milk
What hydrolyses sucrose and descrbe
sucrase, breaks the single glycosidic bond to produce glucose and fructose
What hydrolyses lactose and describe
lactase, breaks single glycosidic bond to produce glucose and galactose
What are lipids hydrolysed by
lipases
Where are lipases produced and where do they function
in the pancreas, work in small intestine
How do lipases work
they hydrolse the ester bond found in triglycerides to form fatty acids and monoglycerides
What is a monoglyceride
glycerol molecule with a single fatty acid molecule attached
How and why are lipids emulsified
by bile salts, as it increases the lipids surface area
Where are bile salts produced by
the liver
What are micelles
the molecules formed after the monoglycerides fatty acids stick with the bile salts
What do peptidases hydrolyse
proteins
What are the types of peptidases
1) endopeptidases
2) exopeptidases
3) dipeptidases
What do endopeptidases do
hydrolyse bonds WITHIN a protein - hydrolyse the bonds between amino acids in the central region of a protein molecule to form a series of peptide molecules
Give 3 examples of endopeptidases and where theyre fromed/released
trypsin and chymotrypsin - synthesised in pancreas & secreted into small intestine
pepsin - released into stomach by cells in stomach lining
What conditions does pepsin work best in and how are these met
acidic - provided by hydrochlorica acid in the stomach
What do exopeptidases do
hydrolyse the bonds AT THE END of the protein molecules (terminal amino acids) meaning they progressively release dipeptides and single amino acids (remove single amino acids from proteins)
What do dipeptidases do
hydrolyse bond between 2 amino acids of a dipeptide by hydrolysing the peptide bond between them
Where are dipeptidases often located
in the cell-surface membrane of epithelial cells in the small intestine
Are dipeptidases membrane-bound
yes
What causes lactose intolerance
the production of very little/no lactase so the lactose cannot be hydrolysed
What are the villi of the ileum located
between the lumen of the intestines, & the blood and other tissues inside the body
How do villi increase efficiency of absorption
1) increase SA:V for diffusion
2) very thin walled = short diffusion distance
3) contain muscle so are able to move, so can maintain diffusion gradients by mixing the content of the ileu
4) well supplied with blood vessels so blood can carry away absorbed molecules and hence maintain diffusion gradient
5) epithelial cells possess microvilli, further increase SA:V
How are amino acids and monosaccharides absorbed across cell membranes (w glucose, galactose, fructose)
diffusion and co-transport
glucose = absorbed via active transport with sodium ions via co-transporter protein
galactose = co-transport
fructose = facilitated diffusion
How big are micelles
small, 4-7nm in diameter
How do monoglycerides and fatty acids transport across cell membranes
micelles come into contact with epithelial cells lining villi of ileum and break down, releasing the non-polar lipid-soluble monoglycerides and fatty acids which diffuse across the membrane
What happens to monoglycerides and fatty acids once they are inside the epithelial cells
transported to endoplasmic reticulum where they are recombined to form triglycerides
What are chylomicrons
special particles adapted for the transport of lipids
What happens to the triglycerides after the endoplasmic reticulum
continue in the golgi apparatus where they associate with cholesterol and lipoproteins to form chylomicrons
How do chylomicrons move out of the epithelial cells
exocytosis
What happens to the chylomicrons after they move out of the epithelial cells
enter lymphatic capillaries called lacteals that are found at the centre of each villus, then into the bloodstream
How are amino acids absorbed across cell membranes
(similar way to glucose and galactose), sodium ions actively transported out of the epithelial cells into the ileum then diffuse back into the cells through sodium-dependant transporter proteins and carry amino acids with them
What substance plays a role in the digestion and absorption of fatty acids
bile salts
