GI Digestion and Absorption Flashcards
What does digestion entail?
Decreasing size (all of the gut)
What does absorption entail?
Passing nutrients to cells (small intestine)
Where does absorption of lipids occur?
At the level of the brush border
Top: digestion
Bottom: defense mechanism
What causes the defense mechanism for absorption to change?
Age: # of cells reduce and rate of regeneration decreases
Methods of transport
Simple diffusion
Active diffusion
Facilitated diffusion
Pinocytosis
Types of Digestion
Luminal (cavities)
Membrane (contact)
Luminal Digestion
Digestive enzymes
Sources: mouth, stomach (least impt.), intestinal/ pancreatic (most impt.)
Membrane digestion
Hydrolytic enzymes
Source: apical membrane of enterocytes
What are the 3 types of nutrients?
Carbs
Proteins
Fats
What is the end product of the digestion of carbs?
Glucose, fructose and galactose
Digestion process of carbs
- Starch at luminal digestion
- Amalayse converted starch into carbs
3.Carbs turned into sugars at membrane digestion
Which carbs are digested?
- Trehalose –> trehalase –> glucose
- Lactose –> lactase –> glucose and galactose
- Sucrose –> sucrase –> glucose and fructose
What does the absorption of carbs involve?
Enterocytes with special carries for molecules
What are the special carriers for carb absorption?
GLUT-5: fructose
SGLT-1: Glucose and galactose
GLUT-2: fructose, glucose and galactose (carries to blood stream)
T/F Newborns don’t have special carriers for absorotion
TRUE
What is the end product for the digestion of proteins?
Amino Acids
Luminal digestion of proteins
Endopeptidases (eats inside of protein molecule)
Exopeptidase (eats out)
Absorption of proteins
Free amino acids, di- and tripeptides (simple diffusion)
Large proteins: pinocytosis (decreases with age)
What are the end products of the digestion of lipids?
Cholesterol, free fatty acids, monoglycerides, glycerol
Steps of fat digestion
- Gut motility creates fat droplet formation
- Hydrolysis allows enzymes to work
- Emulsification by bile salts/ phospholipids (prevents aggregation of lipid droplets)
- Micelle formation (water soluble, no glycerol)
How are micelles formed?
Water soluble molecule formed by
1. Bile Acid
2. Cholesterol OR Fatty Acid OR Monoglyceride
Bile salts will take FFA–> bind them from Micelle –> transport (adding charge onto a fat)
Steps of lipid absorption
- Micelle formation
- Chylomicrons formation
Chylomicrons formation
Mostly from long chain FA
Short and medium chain FA
Absorbed directly in the blood
(lacteals)
Cholesterol
95% reabsorbed and 5% feces (intestinal/ bile)
Blood vessels are carriers
Good and bad cholesterol
Good cholesterol: High density lipoproteins
Bad cholesterol: (low density lipoproteins)