Digestion 1 Flashcards
What are the 6 types of membrane transport?
- Simple Diffusion
- Facilitated Diffusion
- Active Transport
- Receptor Mediated Endocytosis
- Pinocytosis (cell drinking like pint)
- Exocytosis
What is the action of an antiporter?
EXCHANGE - A goes in, B goes out
What is the action of a symporter?
COTRANSPORT - A and B simultaneously go in/out
Endocytosis is _______ and therefore is ________.
receptor mediated and therefore is specific and saturable.
Where do endosomes originate?
The golgi aparatus
What is endo/exocytosis fundamental to and what is it exploited by?
Fundamental to neurotransmission, signal transduction and regulation of plasma membrane activities
Exploited by viruses, bacteria and toxins to gain entry into the cell
What is the key structural component of the human small intestine?
Villi
What 2 types of cells are villi covered in?
Mature cells (enterocytes) and mucus producing goblet cells
Histologically, what type of cells are enterocytes?
Columnar epithelial cells
Thousands of what are present of on the luminal surface of each enterocyte?
Thousands of Microvilli
What are enterocytes responsible for?
Absorption and some digestion
What do the microvilli provide?
A large surface area to facilitate absorption
What must happen to large globules of dietary fat before digestion can occur?
globules must be emulsified
By which enzyme does partial lipid hydrolysis occur in the stomach?
gastric lipase
Why is partial lipid hydrolysis in the stomach slow?
due to separate aqueous and lipid phases
What is the abbreviation for a triacylglyceride molecule?
TAG
Where does emulsification happen?
In the stomach
What does the fat globule contain?
TAGs, Cholesterol esters, phospholipids
What 2 major components of bile are necessary for the breakdown on the fat globule?
Bile salts and phospholipids
What component of bile breaks down the big fat globule into the small fat droplet?
Phospholipids
What does the breakdown into small fat droplets allow for?
Allows the small fat droplets to interact with the watery secretion (intestinal chyme)
What component of bile facilitates the binding of the co-factor for pancreatic lipase and also the breakdown of the small fat droplet into the even smaller micelle?
Bile salts
What is the name of the co-factor which helps pancreatic lipase to further break down the small fat droplet?
Co-lipase
What does pancreatic lipase break the small fat droplet into?
FFAs and MAGs
What are the other pancreatic enzymes which breakdown the cholesterol esters and the phospholipids of the big fat globule?
PLA2 and Carboxyl Ester Lipase
What hormone stimulates the release of bile and pancreatic enzymes for digestion of big fat globules in the small intestine?
CCK
What occurs when the small fat droplets start to get broken down into FFAs and MAGs?
Fat soluble vitamins are absorbed and micelle formation occurs
What are the 5 products of lipid digestion?
- Fatty Acids
- MAGs and DAGs
- Cholesterol
- Phospholipids
- Glycerol
What is the function of micelles?
To deliver the products of lipid digestion to the brush border of the enterocytes where they diffuse into the cell
How are TAGs and CEs formed again inside the enterocyte?
- TAGs are re-synthesised by acyltransferases
- phospholipids are acylated into phosphatic acid and then into TAG
- Cholesterol is acylated by acyltransferases to form cholesterol esters
What do the TAGs and CEs inside the enterocyte join with and to produce what?
TAGs and CE join with apolipoprotein to produce a chylomicron
Where do these chylomicrons go next?
Lacteal –> lymph –> back into circulation at the thoracic duct
Give examples of MONOSACCHARIDES
glucose, galactose, fructose
Give examples of DISACCHARIDES
maltose, sucrose, lactose
Give examples of POLYSACCHARIDES
starch, glycogen
What must happen to di- and polysaccharides before absorption?
Digestion
How are disaccharides digested/broken down and where?
Disaccharides are broken down by specific disaccharidases on the intestinal brush border
How are polysaccharides digested/broken down?
Polysaccharides require salivary and pancreatic enzymes for digestion
What are the names of the specific disaccharidases for the examples of disaccharides already given?
maltase, sucrase, lactase
What is the one disaccharidase that is non-inducible?
Lactase
What is the rate limiting step for the absorption of disaccharides with inducible disaccharidases?
Transport of the monomeric sugars
What is the rate limiting step for the absorption of disaccharides with non-inducible disaccharidases?
hydrolysis
By what mechanism are primary monosaccharides (glucose, galactose, fructose) absorbed?
Carrier-mediated mechanisms
What is the function of the Sodium-Dependent Glucose Transporter?
To transport glucose (and galactose) into the enterocyte across the brush border.
What is the function of the Sodium-Independent GLUT5?
To transport fructose into the enterocyte across the brush border.
What is the function of the GLUT2?
To transport glucose, galactose and fructose into the blood from the enterocyte.
What maintains the concentration of sodium for the sodium-dependent glucose transporter?
Na+/K+ ATPase
Give 1 example of why the relationship between sodium and glucose has vast clinical consequences
Dehydrated patients where found to absorb sodium much better when glucose was also provided
The GLUT family have been looked at when the studying the pathogenesis of which disease?
Diabetes Melitus
