Lecture 9- Digestion and absorption Flashcards
CHOs are
chanins of sugar
polysacchairdes
long chains of monosaccharides
disacharides
2x sugar
- lactose
- glucose and galactose
- Sucrose
- glucose and fructose
- maltose
- glucose and glucose
*
- glucose and glucose
monosacchairdes
1 sugar
only ……….. can be absorbed (CHO)
monosacharides
glucose can only be absorbed with
sodium
Carbohydrates of plant origin that cant be digested
–> past onto large colon and digested by microbes–> good for microbiome and gut health
Goal of CHO digestion –>
to get monosaccharides
- Glucose
- Galactose
- Fructose
common dietary starch
starch
lactose
sucrose
starch
- Polysaccharide (long chain of glucose)
- Consists of
- Straight chains of glucose- amylose
- Held together by alpha 1-4 bonds
- Branched chains of glucose- amylopectin
- Held together by alpha 1-6 bonds
- Straight chains of glucose- amylose
amylose digestion
Use pancreatic and salivary amylase to breakdown the 1-4 alpha bond of amylose–> liberating disaccharide maltose
amylopectin digestion
Break down 1-4 bond- leaves us with shorter but still branched molecule –>alpha dextrin- due to amylase not having an effect on 1-6 bonds
- Need isomaltose to breakdown alpha 1-6 binds
products of starch digestion
malrtose digestion
maltase breaks this down to 2 glucose
Alphadextrins digestion
(isomaltose break this down to amylose)
amylose digestion
amylase break this down to glucose
lactose digestion
- Disaccharide found in milk
- Galactose and glucose
- Enzyme to break down lactose = lactase (brush border enzyme)
- Disaccharide
1.
- Glucose and fructose
- Enzyme= sucrase
Monosaccharide produces from the digestion of common dietary CHO
*
- Glucose
- Galactose
- Fructose
Absorption of monosaccharides
- On the basolateral side of the enterocyte (blood)
-
Sodium potassium ATPase
- Moves sodium out of enterocyte into the blood in exchange for potassium
- Therefore low cytosolic sodium
- Sets up gradient for moving sodium and other things (monosaccharides) into the enterocyte
-
GLUT2 transporter
- Transports glucose, galactose, fructose into the blood
Absorption of monosaccharides
- On the apical side of the enterocyte (lumen)
-
SGLT1 transporter- sodium glucose transporter
- Co-transporter
- Moves sodium and glucose or galactose
- Glucose or galactose can only bind if sodium is bound already
-
Glut5 transporter
- For moving Fructose into the enterocyte
Blood rich in glucose, galactose, fructose is transported to the liver via
the portal system.
protein digestion happens in the
stomach, intestinal lumen, brush. border, cytosol
digestion of protein in the stomach
- Chief cells release inactive protease called pepsinogen
- Gets converted to pepsin in the lumen of the stomach by HCL
- Pepsin acts on protein molecules in the stomach
- We get shorter chains of proteins (oligopeptides) and amino acids
protein digestion in the intestinal lumen
- Chains of proteins (oligopeptides) and amino acids enter the intestine
- Zymogen (inactive protease) are release from the pancreas and activated in the lumen of the gut
- trypsinogen –>trypsin (converted by enteropeptidase= brush border enzyme)
- trypsin can then go on and activate other zymogens
which other zymogens does trypsin activate
- More trypsinogen–> trypsin
- Chymotrypsinogen –> chymotrypsin
- Proelastase –> Elastase
- Procarboxypeptidase A –> Carboxypeptidase A
- Procarboxypeptidase B –> Carboxypeptidase B
These enzymes can be grouped into: Endopeptidases or Exopeptidases
Endopeptidases
- produce smaller polypeptides- break down bonds in the middle of the chain
- Trypsin
- Chymotrypsin
- Elastase
exopeptidases
- break off bonds at the end of the chain
- Carboxypeptidase A and B
digestion of proteins in the intestinal lumen yields
amino acids and short proteins
protein digestion on the brush border
- Work on the short proteins (di/tripeptides)
- Have more enzymes on brush border to produce amino acids
- Amino acids are cotransporter with sodium
- Also have transporters which can transport di and tripeptides across the apical membrane of the enterocyte (PepTi)
- Have more enzymes on brush border to produce amino acids
protein digestion in the cytosol
-
Cytosolic peptidases
- Small peptides (di and tri) are then broken down into amino acids in the cytosol by cytosolic peptidases
- Water can move both out and into the enterocyte
- can move:
- paracellularly – through tight junctions
- transcellular- through the cell
Water only moves
down its osmotic gradient
- Na/K+ ATPase pumps sodium out into the paracellular region –> pulling water paracellularly
- Water follows sodium absorption- transcellularly
- Na+ being pump out of cells into the blood vessels drives sodium absorption from the lumen of the gut
- Why oral rehydration treatment works- uses water, sodium and glucose to help enhance absorption of water
water follows …….. when being secreted into the lumen
chloride
water secretion
- Chloride moves into the enterocyte on the basolateral membrane via the sodium/chloride/potassium channel
- If cAMP rises
- Cl- secreted into the lumen via the CFTR (cystic fibrosis transmembrane conductance regulator)
- This causes Sodium to follow paracellularly through tight junctions into the lumen
- Causes water to move into the lumen
Vitamin B12 deficiency- Symptoms
- Neurological
- Megablastic anaemia
Vitamin B12 deficiency- causes
-
Lack of intrinsic factor
- Released by parietal cells
- Bound to B12 which helps transportation to ileum where most is absorbed
-
Hypochlorhydria
- Gastric atrophy
- Proton pump inhibitors
- Not enough B12 in food
- Inflammation of terminal ileum
- Crohns disease
Irritable bowel syndrome (IBS)
- Diagnosis
- in the absence of documented abnormalities
- Affects 10-15% of adults
- More common in female 2:1
- 20-40s most common
- Associated with psychological disorders
IBS symptoms
Symptoms
- Abdominal pain
- Bloating
- Flatulence
- Diarrhoea/ constipation
- Rectal urgency
lactose intolerance is caused by
defiicency in lactase–> lactase usually diminishes after age of 2
Mechanism of lactose intolerance
- Disaccharide found in milk cannot be broken down
- Can only absorbed monosaccharides
- Disaccharide stays in lumen- high osmotic pressure–> draws water into lumen –> diarrhoea
- Disaccharide passes to colon–> fermented–> gases released –> flatus
coeliac disease is an immunological response to which fraction of gluten
Gliadin fraction found in wheat, rye, barley
coeliac disease and the gut
- Damaged mucosa- flattening of villi, hypertrophy of crypts, lymphocytes in epithelium in lamina propria –>impaired digestion and malabsorption
cause sof coeliac disease
- Genetic factor
- Under diagnosed
symptoms of coeliac disease
- Malabsorption symptoms
- Diarrhoea (due to osmotic pressure
- Weight loss
- Flatulence à distension = pain
- Anaemia
- Neurological symptoms (hypocalcaemia)
treatment of coeliac disease
- Strict gluten free diet –> clinical improvements quite quickly
- Repeat endoscopy will look for improvements
