Digestion of Carbohydrates, Proteins and Lipids Flashcards
What drives the entire absorption process of carbs and proteins? What is the one exception to this?
- Na+/K+ ATPase
- Fructose is only one not dependent on ATPase, and has it’s own channel
Describe glucose absorption.
- Glucose absorption is not directly dependent on energy
- Glucose absorption is secondary to active transport
How does insulin affect glucose transport in the stomach and kidney?
It does not
What does insulin primarily affect?
Adipose tissue
resting muscles
Where is protein digested?
The lumen
Does glucose require digestion for absorption?
Nope
What digests sucrose prior to absorption?
Brush border enzymes
These are directly absorbed by cell then broken down inside cell, what are they?
Oligopeptides
These are broken down before absorption cell then resynthesize original molecule. What are they?
TAGs
All chemical digestion and nutrient absorption occurs in the small intestine, what developments allow for greater surface area?
- Circular folds of mucosa
- Villi
- Microvilli
Juice secreted by small intestine does not contain any digestive enzymes. The synthesized enzymes act within the brush-border membrane of epithelial cells. What are the three enzymes we covered?
- Enterokinase
- Disaccharidases
- Aminopeptidases
Peptidase
breaks down peptides into amino acids
Sucrase, maltase, lactase
break down disaccharides into monosaccharides
Lipase
breaks down fats into fatty acids and glycerol
Enterokinase
converts trypsinogen to trypsin
Somatostatin
hormone that inhibits acid secretion by stomach
Cholescystokinin
hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile
Secretin
stimulates pancreas to release bicarbonate ions in pancreatic juice
What does the small intestine absorb?
- 80 % ingested water
- Electrolytes
- Vitamins
- Minerals
- Carbonates
- active/facilitated transport
- monosaccharides
•Proteins
- di-/tripeptides
- amino acids
•Lipids
- monoglycerides
- fatty acids
- micelles
- chylomicrons
Fill in the boxes with the appropriate enzymes
What are the two steps of carbohydrate digestion?
- Intraluminal hydrolysis of starch to oligosaccharides by amylases
- membrane digestion of oligo to mono by brush border disaccharidases
What are the four brush border oligosaccharidases?
- Lactase
- Glucoamylase
- Sucrase
- Isomaltase
What are the two steps of carbohydrate absorption?
- Uptake across apical membrane into epithelial cell
- coordinated exit across basolateral membrane
Where does protein digestion begin?
In the stomach, when pepsin digests proteins to form polypeptides
What are the endopeptidases of the duodenum and jejunum?
(3)
- Trypsin
- Chymotrypsin
- Elastase
What are the exopeptidases of the duodenum and jejunum?
- Carboxypeptidases
- Aminopeptidase
What are the brush border enzymes responsible for breaking down protein?
- Carboxypeptidase
- Aminopeptidase
- dipeptidase
Fill in the boxes with the correct enzymes or compounds.
How are aminoacides and polypeptides transported across the basolateral membrane of enterocytes?
Facilitated or simple diffusion
What type of transporter is PepT1? What does it move?
H+/oligopeptide cotransporter
•dipeptides, tripeptides and tetrapeptides into enterocytes across apical membrane
What is the defect responsible for Hartnup disease?
Impaired a.a. transport in the SLC6A19 transporter across the apical brush border membrane of the small intestine. (Also impacts transport in the proximal tubule of the kidney)
What are the symptoms of Hartnup disease?
- Pellagra like skin eruptions
- cerebellar ataxia
- gross aminoaciduria
How does Hartnup disease manifest in infancy?
- failure to thrive
- photosensitivity
- intermittent ataxia
- nystagmus
- tremor
PepT1 also plays a major role in supplying what compound to the body?
Nitrogen
Fill in the blanks with the appropriate compounds or enzymes.
Describe steps 1-7 of the image.
Dietary fat (TGs) emulsified by
bile salts into fat droplets
- Lipase hydrolyses TGs into
mono-glycerides & free FAs
- These water insoluble products
are carried in interior of water-
soluble micelles to luminal
surface of S.I. epithelial cells
- Micelle in epithelial surface,
mono-glycerides & free FAs
leave micelles & passively diffuse
through luminal membranes
- Mono-glycerides & free FAs
resynthesized into TGs inside
epithelial cells
- TGs aggregate & coated with
lipoprotein to form water
soluble chylomicrons
- Chylomicrons enters lacteals
What does the large intestine secrete into the colonic lumen?
K+ and HCO3-
Hartnup disease can be overcome by a high protein diet. Why is this is possible?
The presence of PepT1 allows for the uptake of dietary di and tripeptides from the small intestinal lumen.
