Digestion 1 Flashcards
what are the 3 parts of the small intestine?
duodenum
jejunum
ileum
the villi of the small intestine is covered by? 2
mature cells - enterocytes
mucus secreting goblet cells
what shape of cell are enterocytes?
columnar epithelial cells
what are present on the luminal surface of enterocytes? why?
microvilli
to increase SA for absorption
enterocytes are responsible for? 2
absorption
some digestion
each villus of the small intestine contains? 2
a capillary network
a lacteal/lymph vessel
do enterocytes and goblet cells have a short or long life?
short
enterocytes are replaced by?
stem cells that migrate from the crypts (pits between vili)
what is primary active transport?
movement is directly linked to energy use
what is secondary active transport?
indirectly linked to an electrochemical gradient set up using energy
what is receptor mediated endocytosis?
movement into the cell via a specific receptor
what is pinocytosis?
‘cell drinking’
cell takes in extracellular fluid and soluble molecules
what does an antiporter integral membrane protein do?
transports two different molecules/ions across a membrane in different directions
what does a symporter integral membrane protein do?
transports two different molecules/ions across a membrane in the same direction
what does a uniporter integral membrane protein do?
moves one type of molecules across a membrane in both directions
what must happen to fat before digestion can occur?
emulsification
what enzyme hydrolyses lipids in the stomach?
gastric lipase
the triacylglycerides are hydrolised, the released fatty acids act as surfactants. what do surfactants do?
reduce surface tension
what does the hormone cholecystokinin do? 2
stimulates the release of pancreatic digestive enzymes and bile into the small intestine
lipases secreted by the pancreas are? 3
pancreatic lipase
carboxyl ester lipase
phospholipase A2
how are fat globules exposure to enzymes maximised?
mixed with bile salts and pancreatic juice containing lipases to form an aqueous suspension of fatty droplets
bile acids/salts are made in the ? from?
liver from cholesterol
bile acids/salts are stored where?
gall bladder
bile salts are composed of? 2
cholic acid
glycine or taurine
what does a micelle do?
allows transport of lipids to the brush border of the enterocyte where they are absorbed by diffusion
what is the structure of a micelle?
hydrophilic cholic acid face outward
hydrophobic glycine/taurine face inwards
bile salts emulsify fats by forming micelles
inside the cell TAGs triglycerides are?
resynthesised at the ER by acyltransferases
inside the cell phospholipids are? 2
acylated to form phosphatidic acid
converted to TAGs
in the cell cholesterol is?
acylated to form cholesterol esters
chylomicrons enter circulation through the lymph, they are formed from? 3
TAGs, cholesterol esters and apolipoprotein B
understand the absorption of lipids
where are chylomicrons assembled?
within enterocytes one the RER
how do chylomicrons leave the enterocyte cells into the lymphatic system?
exocytosis
disaccharides are broken down by what?
disaccharidases
starch and glycogen require what to digest them? 2
salivary and pancreatic amylases
how is glucose absorbed? 2
sodium potassium pump - Na+ out, K+ in using ATP
symport of glucose and Na+
how is glucose and galactose absorbed? 3
sodium potassium pump - Na+ out, K+ in using ATP
symport of glucose and Na+
glucose leaves cell via uniporter into the blood
how is fructose absorbed? 2
by GLUT5 sodium-independent facilitated diffusion into enterocyte
may be exported by GLUT2
absorbed nutrients from the intestine go where? 2
portal vein (circulatory system)
thoracic duct (lymphatic system)
