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Digestion and Absorption (GI system pt. 2), ★Age and co-ingestion impact…
Digestion and Absorption
(GI system pt. 2)
Primarily we absorb
monosaccharides
3 main monosaccharides are:
Galactose
Fructose
Glucose
Starch/carb digestion
1st (salivary amylase in mouth) ➔ pancreatic amylase
lactose and sucrose (along brush border - villi)
final product of monosaccharides: glacatose,glucose,fructose
Glucose + Galactose
need
sodium
to cross membrane (
through SGLT-1 transporter)
Fructose
absorbed via
facilitated diffusion
Gluten sensitivity in relationship with fruits
Gluten has higher levels of FODMAP's (absorbed through gut, cause some GI discomfort in some people)
overall: Gluten (protein) only foods had fewer negative symptoms
True gluten sensitivity had abnormal immunse response in colon
food with high FODMAP's (fermentable, oligosaccharides, monosacc and polyols) will have an impact on gut
Protein digestion
Large peptides
Polypeptides
Pepsin (pH 1.6 -3.2)
trypsin,chymotrypsin (endopeptidases)
carboxypeptidases (some aa are freed in
lumen
others along
brush border
)
short peptides and amino acids ➔
absorb amino acids
Lipid (FAT) digestion
7 different transports
(5 require Na+/sodium cotransport)
Mutation in a SINGLE transporter = Hardins disease (absorptive condition)
Peptide transporter 1 (uses H+)
actively transport
dipeptides + tripeptides
Amino acids ➔ 50% from food
Protein ➔ 25% in digestive juice
Protein content from Mucosal cells ➔ 25%
1st lingual lipase + 2nd gastric lipase = FFA ➔ feedforward and release CCK
Most fat digestion happen in duodenum
emulsification by bile needed here = digestion of of these fatty acids until we get to triglycerides, FFA and monoglycerides togehter.
Emulsification by bile acid
= breaking fat into tiny pieces
"micelles"
Micelles (act as uber)➔ FA and monoglycerides
absorbed by
Enterocyte (SI cells)
Reassemble FA's into triglyceride (re-esterification)
Golgi packages these into chylomicrons ➔ into lymph
Micronutrient Absorption
Via duodenum, ilium and jejunum
ex: Vit B12 (needs stomach acid/intrinsic factor)
Iron: heme iron absorbed better than non heme
★Age and co-ingestion impact our ability to absorb and utilize protein
food matrix (amino acids in food)
amount of protein in food
physical activity prior to protein ingestion make it more efficient at being absorbed in bioavailable
food ingestion
disease - malabsorbed to conditions
Malabsorption conditions (reduced nutrient absorption = reduced energy availabilty)
celiac disease
crohns disease
short bowl syndrome
chronic diarrhea disorders
Even if enough calories taken in following happen
Poor absorption
GERD (acid reflux)
symptoms: heartburn, chest discomfort, throat irritation, nausea, regurgitation
Things that worsen reflux : supine/abdominal exercises, heavy lifting, bending forward, post meal exercise, ↑ intrabdominal pressure
some disaccharides as well
Focused more on end products now: Start will polysaccharide (like starch/carbs) ➔ monosaccharide
⬇︎
⬇︎
⬇︎
Next we absorb them
our rate limiting step in energy availability is digestion!!!
fun fact: lactose is a molecule of these 2 monosacc
rate limiting step is digestion
Now we have Protein absorption (amino acids)
Now we move to lipid absorption
⬇︎⬇︎
lipids absorbed via passive simple and facilitated diffusion
short/medium chain FA enter blood directly
Long chain FA
carbs ➔ less gycogen storage
iron/B12 ➔ fatigue and reduced O2 delivery
protein ➔ impaired muscle repair
calcium/vit D ➔ poor bone healing