Macro and Micronutrients: Digestion Flashcards
Three major food types:
- Macronutrients:
- Carbohydrates (CHO)
- Fats
- Proteins
Hydrolysis is a ——- reaction, where the reactant is ——
- decomposition
- water
CHO digestion:
- within CHO, starch is located and held together by
two forms of glucose polymers:
1) amylose: a chain of glucose bonded by alpha 1-4
glycosidic bonds
2) amylopectin: a chain and branch of glucose bonded
by alpha 1-4 glycosidic bonds as well as alpha 1-6
glycosidic bonds
The enzyme salivary alpha amylase provides hydrolysis of alpha 1-4 glycosidic bonds in starch to form maltose (disaccharide), maltotriose (trisaccharide), and alpha dextrins
Starch digestion does not occur —– and why
in the stomach
acidic nature of gastric secretions denatures salivary amylase hence starch digestion is halted
Locations in GI Tract where starch is digested:
- mouth
- small intestine
Two mechanisms of starch digestion in the small intestine:
1) due to pancreatic enzymes being secreted into the
small intestine (pancreatic alpha amylase); hydrolysis
alpha 1-4 glycosidic bonds
2) due to enterocyte brush border enzymes: secretes:
- maltase: hydrolysis of maltose into 2 glucose
- sucrase: hydrolysis of alpha 1-4 and alpha 1-6
glycosidic bonds - sucrose into
glucose+fructose
What are the eventual products of CHO digestion?
How are they absorbed?
What happens after absorption?
- glucose molecules
- glucose molecules are absorbed via the sodium
glucose co-transported on the apical surface of
enterocytes (2 Na+, 1 Glu). Na+ down conc grad,
creates an electrochemical gradient that pulls in
glucose AGAINST its conc grad - once within the cell, the glucose molecules is
transported via the GLUT2 (glucose transported type
2) on the basolateral membrane into the bloodstream
for energy use or storage as glycogen in the liver.
CHO digestion III
The digestion of fat commences in
the oral cavity
Two types of fat digestion occur in the oral cavity:
- mechanical via mastication
- chemical via lingual lipase
Fat digestion by lingual lipase
- secreted by the dispersed salivary glands of tongue
secrete - responsible for the hydrolysis of lipid triglycerides to
fatty acid and diglycerides
Fat digestion in the stomach:
- lingual lipase hydrolyses triglycerides to free fatty
acids and partial glyceride and gastric lipase secreted
by chief cells (exocrine) converts triglycerides to fatty
acid and diglycerides - gastric lipase converts triglycerides into diglycerides
and fatty acids - the stomachs contractions assist to disperse the fat
molecules, while the diglycerides derived in this
process act as further emulsifiers
Fat digestion and absorption in the small intestine:
- as the gastric contents enter the duodenum, they are
clustered together. Bile is secreted by the gallbladder
which emulsifies. This along with mixing of the gastric
contents via segmentation, leads to conversion of
larger fat globules into small droplets - the micelles are water soluble arrangements can now
pass through microvilli. Monoglyceride and fatty acids
cross the apical membrane of microvilli through
passive diffusion and lipid protein transporter
mechanisms. - inside the enterocyte, fatty acids and monoglyceride
are transported into the endoplasmic reticulum and
latterly the Golgi, where they are used to synthesize
triglycerides before being located with cholesterol and
lipoproteins lipids into particles called chylomicrons - chylomicrons then under go exocytosis via Golgi
vesicles to the basolateral aspect of the enterocyte
into a lacteal
Fat digestion and absorption in the small intestine III
What types of proteins are not absorbed?
dietary proteins
protein digestion by pancreatic enzyme
