Digestive System Flashcards
how exactly does the digestive system break down food? (3)
- digestive juices are produced by the gland cells of the digestive system
- they release hydrolytic enzymes and other molecules that facilitate digestion
- these enzymes hydrolyse large insoluble food molecules into smaller soluble molecules, which can then be absorbed through the lining of the intestine
carbohydrates are hydrolysed into ________ ________ by ________________
simple sugars
carbohydrases
fats are hydrolysed into __________, __________ _______ and _______________________ by ____________
glycerol
fatty acids
monoglycerides
lipases
polypeptides and proteins are hydrolysed into _________ _________ by ______________
amino acids
proteases
list the four key organs in the digestive system
salivary glands
stomach
pancreas
small intestine
FUNCTION: salivary glands
secrete salivary amylase which hydrolyses starch into maltose
FUNCTIONS: stomach (3)
- food is mixed with gastric juice, which is acidic
- kills micro-organisms
- contains endopeptidases and exopeptidases which hydrolyse polypeptides to dipeptides
FUNCTION: pancreas
secretes pancreatic juice containing amylase, endopeptidases, exopeptidases and lipases
FEATURES: small intestine (3)
- large surface area
- maltase enzymes embedded in the epithelium cell membrane
- sucrase, lactase, dipeptidase
describe the process of starch digestion step by step (6)
- food enters the mouth and is broken up by teeth (mechanical digestion), then mixed with saliva
- salivary amylase starts to hydrolyse glycosidic bonds in the starch, producing maltose (chemical digestion)
- salivary amylase is denatured in the stomach due to acidic pH
- in the small intestine, pancreatic amylase continues to hydrolyse the starch to maltose
- maltose is then hydrolysed into glucose by the membrane bound maltase
- this glucose can then be absorbed into the ileum
“only _______________________ can be transported across the epithelial cell membrane”
monosaccharides
what is the process called by which monosaccharides are absorbed into epithelial cells?
co-transport
describe the co-transport of monosaccharides step by step (4)
- Na+ (sodium ions) are actively transported out of the epithelial cells into the blood (by the sodium potassium pump)
- creates a concentration gradient of Na+ (between lumen of the ileum and the epithelial cells)
- Na+ and glucose enter cell by facilitated diffusion using complementary co-transporter proteins (have one site specific to Na+ and one specific to glucose)
- glucose moves into the blood by facilitated diffusion
how does Na+ diffuse into the cell?
down its concentration gradient
how does glucose diffuse into the cell?
against its concentration gradient
where does the process of protein digestion begin?
in the stomach
endopeptidases (2)
- hydrolyse internal peptide bonds within polypeptide chains
- this produces many shorter polypeptide chains and increases the surface area for the next enzyme
exopeptidases (3)
- hydrolyse the peptide bonds at the terminal ends of the polypeptide chain
- this produces dipeptides
- SPECIFIC: one group complementary to the N terminal end, another to the C terminal end
what are dipeptidases?
what is their function? (2)
- enzymes embedded in the cell surface membrane of epithelial cells
- hydrolyse the single peptide bond in the dipeptide
- produce single amino acids
what is the process called by which amino acid absorption occurs?
cotransport
what is the ONLY place wherein lipid digestion occurs?
within the lumen of the ileum
what happens to lipids in the stomach?
they are churned into fat droplets
describe how lipids can eventually become lipoproteins (chylomicrons) step by step (8)
include what happens at the SER and the golgi apparatus
- lipid droplets are mixed with bile salts to form smaller droplets (emulsification)
- these smaller droplets increase surface area for faster hydrolysis
- triglycerides hydrolysed into glycerol, fatty acids, and monoglycerides
- bile salts, glycerol, and fatty acids form micelles
- micelles make fatty acids soluble in water and bring them to the epithelial cells*
- fatty acids enter the epithelial cell by simple diffusion
at the SER
- fatty acids and glycerol are recombined to form triglycerides
at the golgi apparatus
- triglycerides are modified; proteins are added to form lipoproteins (called chylomicrons); packaged into vesicles
what subsequently happens to the chylomicrons?
they are transported into a lymph vessel by exocytosis, before entering the blood
