Lectre 2 - absorption

Question 1

Digestion of proteins: stomach

Answer 1

Most dietary proteins from meats and vegetables
Stomach: pepsin digestion (pH of 2)
Special feature: pepsin also digests collagen (access to cellular/intracellular proteins)
Product: Large poly-peptides, protein chunks (proteoses, peptones)

Question 2

Digestion of proteins through pancreatic enzymes: small intestine

Answer 2

Exposure to pancreatic enzymes: trypsin, chymotrypsin, carboxypolypeptidase
Product: Polypeptides and amino acids

Question 3

Epithelial peptidases

Answer 3

Enterocytes at brush boarder contain several enzymes for peptide hydrolysis
Enzymes specific for given peptide linkages as energetic bond differs

Product: Dipeptides, amino acids

Question 4

Endo- and exopeptidases with defined specificity

Answer 4

depend on where hydrolytically cleave

Question 5

One protein - a multitude of enzymes

Question 6

1 protein-3 phases and loci of digestion

Question 7

Answer 7

• Epithelial peptidases at brush boarder
• brush border increases space for enzymes to break peptide bonds

Question 8

Intra-epithelial cell
Na+ symport, ATP dependent, H+ symport ATP dependent, passive cariers, endothelial diffusion (cave: blood brain barrier)

Question 9

Transcytosis

Answer 9

Finally: amino acids are available in the blood steam

Question 10

Answer 10

Gluten enteropathy (celiac disease): loss of enzymatic functions at brush boarder due to auto-immune condition
- Gluten: wheat, rye, barley, oats: causing malabsorption –> gluten-free diet

Question 11

Transport and storage of amino acids

Answer 11

Blood: 35-65mg/dl
2mg/dl per amino acid
As strong acids, they exist in the blood in ionized state, neg. charged ions

After entering the blood, excess amino acids are absorbed within 5-10 mins (especially by the liver, but also kidney and mucosaacting as “stores”)
Rapid amino acid turnover (many grams transferred/hour)
Significant quantities can only be transported through the cellular membrane by active transport (carrier mechanism poorly understood)
400g of body proteins are synthesized and degraded daily!

Question 12

Reversible equilibrium
There is a constant equilibrium between the plasma amino acids and most of the proteins in the cells in order to maintain constant amino acid plasma levels

Question 13

Transport and storage of amino acids
- The renal threshold

Answer 13

Prevent loss in urine
Upper limit of filtration/reabsorption rate (carrier/active transport!!)
Kidney disease: loss of protein!!! edema and plasma fluid accumulation!!!

Question 14

Thinking points

Answer 14

Vital functions: colloid osmotic pressure (malnutrition, vs liver disease, vs kidney disease)

Multistep digestion with a multitude of enzymes

Tissue equilibrium, 400 g of amino acid flux daily