Lecture 9- Digestion and absorption Flashcards
1
Q
CHOs are
A
chanins of sugar
2
Q
polysacchairdes
A
long chains of monosaccharides
3
Q
disacharides
A
2x sugar
- lactose
- glucose and galactose
- Sucrose
- glucose and fructose
- maltose
- glucose and glucose
*
- glucose and glucose
4
Q
monosacchairdes
A
1 sugar
5
Q
only ……….. can be absorbed (CHO)
A
monosacharides
6
Q
glucose can only be absorbed with
A
sodium
7
Q
Carbohydrates of plant origin that cant be digested
A
–> past onto large colon and digested by microbes–> good for microbiome and gut health
8
Q
Goal of CHO digestion –>
A
to get monosaccharides
- Glucose
- Galactose
- Fructose
9
Q
common dietary starch
A
starch
lactose
sucrose
10
Q
starch
A
- 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
11
Q
amylose digestion
A
Use pancreatic and salivary amylase to breakdown the 1-4 alpha bond of amylose–> liberating disaccharide maltose
12
Q
amylopectin digestion
A
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
13
Q
products of starch digestion
A
14
Q
malrtose digestion
A
maltase breaks this down to 2 glucose
15
Q
Alphadextrins digestion
A
(isomaltose break this down to amylose)
16
Q
amylose digestion
A
amylase break this down to glucose
17
Q
lactose digestion
A
- Disaccharide found in milk
- Galactose and glucose
- Enzyme to break down lactose = lactase (brush border enzyme)
18
Q
- Disaccharide
1.
A
- Glucose and fructose
- Enzyme= sucrase
19
Q
Monosaccharide produces from the digestion of common dietary CHO
*
A
- Glucose
- Galactose
- Fructose
20
Q
Absorption of monosaccharides
- On the basolateral side of the enterocyte (blood)
A
-
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
21
Q
Absorption of monosaccharides
- On the apical side of the enterocyte (lumen)
A
-
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
22
Q
Blood rich in glucose, galactose, fructose is transported to the liver via
A
the portal system.
23
Q
A
24
Q
protein digestion happens in the
A
stomach, intestinal lumen, brush. border, cytosol
25
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
26
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
27
which other zymogens does trypsin activate
1. More trypsinogen--\> trypsin
2. Chymotrypsinogen --\> chymotrypsin
3. Proelastase --\> Elastase
4. Procarboxypeptidase A --\> Carboxypeptidase A
5. Procarboxypeptidase B --\> Carboxypeptidase B
These enzymes can be grouped into: Endopeptidases or Exopeptidases
28
Endopeptidases
1. produce smaller polypeptides- break down bonds in the middle of the chain
1. Trypsin
2. Chymotrypsin
3. Elastase
29
exopeptidases
1. break off bonds at the end of the chain
1. Carboxypeptidase A and B
30
digestion of proteins in the intestinal lumen yields
amino acids and short proteins
31
protein digestion on the brush border
* Work on the short proteins (di/tripeptides)
1. Have more enzymes on brush border to produce amino acids
1. Amino acids are cotransporter with sodium
2. **Also have transporters which can transport di and tripeptides across the apical membrane of the enterocyte (PepTi)**
32
protein digestion in the cytosol
1. **Cytosolic peptidases**
* Small peptides (di and tri) are then broken down into amino acids in the cytosol by cytosolic peptidases
33
* Water can move both out and into the enterocyte
* can move:
* paracellularly – through tight junctions
* transcellular- through the cell
34
Water only moves
down its osmotic gradient
- Na/K+ ATPase pumps sodium out into the paracellular region --\> pulling water paracellularly
35
* 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
36
water follows ........ when being secreted into the lumen
chloride
37
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
38
**Vitamin B12 deficiency- Symptoms**
* Neurological
* Megablastic anaemia
39
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
40
**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
41
IBS symptoms
**Symptoms**
* Abdominal pain
* Bloating
* Flatulence
* Diarrhoea/ constipation
* Rectal urgency
42
lactose intolerance is caused by
defiicency in **lactase--\>** lactase usually diminishes after age of 2
43
44
**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
45
coeliac disease is an immunological response to which fraction of gluten
Gliadin fraction found in wheat, rye, barley
46
coeliac disease and the gut
* Damaged mucosa- flattening of villi, hypertrophy of crypts, lymphocytes in epithelium in lamina propria --\>impaired digestion and malabsorption
47
cause sof coeliac disease
* Genetic factor
* Under diagnosed
48
symptoms of coeliac disease
* Malabsorption symptoms
* Diarrhoea (due to osmotic pressure
* Weight loss
* Flatulence à distension = pain
* Anaemia
* Neurological symptoms (hypocalcaemia)
49
treatment of coeliac disease
* Strict gluten free diet --\> clinical improvements quite quickly
* Repeat endoscopy will look for improvements
