Lecture 5 Nutrient Digestion and Absorption Flashcards
What is the majority of digested fat in the form of
Triacylglycerol
Where does all fat digestion occurs
In the small intestine by pancreatic lipase
What type of enzyme is lipase
Water soluble
Why is digestion a very slow process
It can only take place at surface level of droplet
Define Emulsification
dividing large lipid droplets into smaller droplets (~1mm diameter) which increases surface area and accessibility to lipase action and prevent them forming large droplets again
What are the requirements of emulsification
- Mechanical Disruption of large lipid droplets to small
- Smooth muscle contractions
- Emulsifying agents
How does emulsifying agents such as bile prevent large droplets reforming
Non-polar portions of amphiphatic molecules (bile salts and phospholipids) associated with non-polar interior of lipid droplet leaving polar portions exposed at water surface
What enhances absorption of fat
Formation of Micelles
What are micelles
Bile salt + monoglycerides + 2 fatty acids + phospholipids (smaller than emulsion droplets)
What forms the polar portion and non-polar portion of micelle
Polar portion of molecules at micelle surface; non-polar portion form micelle core
What is critical for the transport of fat soluble minerals
Bile acids
What does the breakdown of micelles lead to
Free fatty acids (FFA) and monoglycerides that diffuse across the plasma membrane
What happens when FFA and monoglycerides when they enter epithelial cells
They enter smooth Endoplasmic Reticulum where they are reformed as tricylglycerols by enzymes located there and processed through Golgi apparatus and exocytosed to ECF
What are chylomicrons
Extracellular fat droplets
Where do chylomicrons pass through
Lacteals (lymphatic vessels) as they cannot pass through capillary basement membrane
What are the 2 classes of Vitamins
Fat soluble -Follow same absorptive path as fat and
Water-soluble Vitamins- • Either absorbed by passive diffusion or carrier-mediated transport
Name Fat soluble vitamins
A,D,E,K
Name Water soluble vitamins
B group, C and Folic acid
How is Vitamin B12 absorbed
It is a charged molecule that binds to an intrinsic factor in the stomach to form a complex via a specific transport mechanism in the distal ileum
How much daily digested iron is absorbed into the blood
10%
How is iron absorbed
- Iron transported across brush border to membrane (via DMT1) into duodenal enterocytes (simple columnar epithelial cells which line the inner surface of the small intestine)
- Iron ions incorporated into ferritin (protein-iron complex intracellular iron store)
What is iron in the blood bound to
Transferrin
Define Hyperaemia
increased ferritin levels more iron bound to enterocytes
Define Anaemia in terms of iron
decreased ferritin levels- more iron released to blood
