Digestion 2 Flashcards
By what enzyme are proteins hydrolysed?
Pepsidases
What are the 2 different types of pepsidase?
Endopepsidase and Exopepsidase
What is the function of endopepsidase?
They cleave internal peptide bonds and breakdown large polypeptides into smaller oligopeptides
What is the function of exopepsidase?
They cleave from the ends of the protein/peptide and breakdown these oligopeptides into di- and tri- peptides and amino acids
What are the 3 products of protein digestion?
Tri-peptides
Di-peptides
Amino Acids
What does the low pH of stomach acid do for protein digestion?
Denatures the protein and causes unravelling of the peptide chain to make the protein more accessible to digestive enzymes
What do chief cells in the gastric mucosa secrete?
Pepsinogen
What is pepsinogen?
The inactive precursor of pepsin
What initially activates pepsinogen?
Low pH of stomach acid
What are the functions of pepsin?
- Autocatalyses further conversion of pepsinogen to pepsin
- Digests target protein into large peptide fragments and amino acids
- This then stimulates CCK hormone release in duodenum
What are the 2 hormones issued in the duodenum that are secreted?
Secretin and CCK
What stimulates the release of SECRETIN and what is its action?
Stimulated by: acidity of stomach acid into duodenum
Action: stimulates secretion of bicarbonate rich pancreatic fluid to neutralise acid
What stimulates the release of CCK and what is its action?
Stimulated by: breakdown of protein into large peptide chain and amino acids by pepsin
Action: causes contraction of gall bladder and relaxation of sphincter of Oddi and so promotes entry of bile and pancreatic juices into duodenum
What are zymogens?
pancreatic enzymes that are released as inactive precursors
What do duodenal enteropeptidases do?
Convert trypsinogen to trypsin
List 5 pancreatic zymogens and their active postcursors, N.B. trypsin activates the last 4 pathways
Trypsinogen --> trypsin Chymotrypsinogen --> chymotrypsin Proelastase --> elastase Procarboxypeptidase --> carboxypeptidase Prophospholipase A2 --> phospholipase A2
Where on the polypeptide chain does trypsin hydrolyse polypeptides?
On the carboxyl side or arginine and lysine residues
How do hydrophobic amino acids pass through the brush border of the small intestine?
Through passive diffusion
How do the rest of the amino acids pass through the brush border/basolateral border of the small intestine?
Against a concentration gradient so relies on active carrier mechanisms on the brush border AND the basolateral border of enterocytes
How many amino acid specific transporter are there on the bush border and how many are sodium dependent?
7 in total, 5 Na+ dependent
How many amino acid specific transporter are there on the basolateral border and are they sodium dependent or independent?
3, all 3 are Na+ independent
How are di- and tri-peptides transported into the enterocyte?
through secondary active transport by on H+ dependent co-porter
What are the fat soluble vitamins?
A, D, E, K
Answer these with regards to FAT SOLUBLE vitamins: Chemical Property? Excess is? Deficiency? Toxicity? Deficiency related to Malabsorption
hydrophobic stored in body slower onset more common yes
Answer these with regards to WATER SOLUBLE vitamins: Chemical Property? Excess is? Deficiency? Toxicity? Deficiency related to Malabsorption
hydrophilic excreted in urine faster onset less common no
How do FAT SOLUBLE vitamins get transported?
carried in micelles
How do WATER SOLUBLE vitamins get transported?
simple passive diffusion
What are cobalamins?
The 4 metabolically important forms of B12
What is the name for the active metabolite of Vitamin D?
Calcitriol
Where is calcium predominantly absorbed?
in the proximal small intestine
What are the two cellular calcium transport processes?
- Paracellular absorption - through the intracellular space
- Transcellular absorption - through the cell
What is iron important for?
the transfer of molecular oxygen
Where is 75% of the body’s iron found?
In haemoglobin and myoglobin
Where the other 25% of the body’s iron found?
tissues: bone marrow, liver and reticuloendothelial system
What type of iron is dietary iron?
The FERRIC form - Fe3+
What enzyme reduced the ferric form of iron to its ferrous form and where is this enzyme located?
Ferrireductase, found on the brush border of enterocytes
