Digestion and Absorption of Nutrients Flashcards
What happens in the absorption of small molecules in the intestines?
They are absorbed into the vasculature
They travel to the liver via the hepatic portal system
What happens in the absorption of long chain fats in the intestine?
They form mixed micelles with bile salts in the GI tract
They enter they enterocytes and are processed into chylomicrons
They enter the lymphatics via lacteals and eventually enter the circulation via the lympho-venous portal
What are the X4 layers of the GI tract?
What does each layer contain?
Mucosa
- epithelium
- lamina propria
- muscularis mucosae
Submucosa
Muscularis propria
- circular muscle
- longitudinal muscle
Adventitia or serosa
What is the general overview of lymphatic drainage of the small intestine?
Lymph nodes (multiple types) —> cisterna chyli —> thoracic duct —> Left lympho-venous portal
Once carbohydrate has been broken down and is in the small intestine, how is it absorbed?
Which channels are used for which monosaccharides?
Na co-transporters use the Na gradient to import glucose and galactose via SGLT-1 channels
Fructose is absorbed via GLUT-5 channels
GLUT-2 is on the basolateral membrane to aid facilitated diffusion of all X3 monosaccharides into the interstitial space.
What is located on the basloateral surface of intestinal epithelium that is vital for the absorption of carbohydrates?
Na/K ATPase to maintain the Na gradient exploited by SGLT-1 transporters on the luminal surface.
What is the first stage of peptide breakdown?
the enzyme pepsin releases as pepsinogen in the stomach and activated by HCl
What is another protease to act on the peptides further along the GI tract?
Where is this enzyme released from and how is it activated?
Tripsin in the duodenum
Is released from the pancreas as the pro-enzyme tripsinogen
What happens to peptides that have been broken down to single amino acids in the GI tract, how are they absorbed?
There exists many Na/amino acid co-transporters in the luminal membrane of enterocytes
What happens to peptides that have been broken down to di- and tripeptides in the GI tract, how are they absorbed?
There is a H ion co-transport which uses a H ion gradient to aid with H/peptide co-transport via transporters in the luminal surface of the enterocytes.
What happens to small peptides once absorbed into enterocytes via H/peptide co-transport?
They are hydrolysed into single amino acids
How are the amino acids absorbed into the enterocytes further absorbed into the interstitial space to reach the blood?
They move via facilitated diffusion via their own concentration gradients.
What is another name given to a peptide with only a small number of AA residues?
Oligopeptides
Name an example of a H/oligopeptide co-transporter?
PEPT-1 (PEPT = for peptide)
How are the sodium and hydrogen ion gradients in the lumen of the GI tract maintained?
1) Na/K ATPase on the basolateral enterocytes membrane (for Na ion gradient)
2) Na/H exchanger on the luminal surface (for H ion gradient)
What is hartnup disease?
An inability to absorb the amino acid L-phenylaline
What is cystinuria disease?
A lack of ability to absorb the amino acid L-cysteine and L-argenine
How are hartnup and cystinuria overcome?
They are unable to be absorbed as single AA’s but oligopeptide dipeptide transporters exist which can absorb dipeptides which include these AA’s.
How are vitamins A, E and K absorbed?
Into enterocytes via Na co-transport
Then into chylomicrons and via the same method/pathway as long chain fatty acids
What is another name for vitamin B12?
Colbalamin
How does colbalamin (B12) enter the body?
Attaches to dietary protein
What is the first step in colbalamin (B12) absorption?
HCl and pepsin release colbalamin (B12) from the dietary protein
What do the gastric glands secrete to help with colbalamin (B12) absorption?
What do gastric parietal cells secrete to help with colbalamin (B12) absorption?
What happens to these X2 molecules?
Gastric glands = hapticorrin
Parietal cells = IF (intrinsic factor)
Haptocorrin binds to colbalamin (B12), IF does not
What happens to colbalamin (B12) once haptocorrin has bound to it in the stomach?
It enters the small intestine with IF where released pancreatic proteases remove haptocorrin and allow IF to bind?
What eventually happens to colbalamin (B12) bound to IF?
It is absorbed by the Ileum
