Cells that secrete mucous layer

highest concentration of mucous in ....

Goblet cells

Stomach and colon (due to bacteria concentration)

Villi length and effect on surface area

0.5-1.5 mm

10X

microvilli length and effect on surface area

1um long, 0.1 um diameter

200X

Reserve capacity of pancreatic lipase

9 folds

Reserve capacity of glucose transport

duodenum and 30 cm jejunum

Safety Margin

capacity / load

extent of uptake of (CHO, Fe, Ca)

CHO 98%

Fe 10%

Ca 30%

Immunostaining in immunohistochemistry and confocal imaging measures?

Intestinal fatty acid-binding protein , amount of transporters

Methods used to develop ORS

perfusion of human small intestines

Hydrophobic AA

alpha helix

Functions of Aquaporins and Aquaglyceroporins

Transporting:

1. Water
2. Glycerol
3. Urea
4. NH3
5. H2O2

What concentration of Na drive water uptake?

90mmol/l

Models of water flow

1. Simple osmotic flow (fastest)
2. Paracellular
3. Aquaporins (40-60%)

Duplication of digestive enzymes

• Pancreatic amylase & brush-border glucoamylase
• Lingual and pancreatic lipase
• Gastric, pancreatic and brush-border peptidases

Duplication of absorptive functions (transporters)

• GLUT2 and SGLT1
• PEPT1 and Amino Acid transporters
• Flip-flop and Fatty Acid Binding Proteins

Types of transporters

Facilitative or non-active transporters (UT1, GLUT1)

Ion-coupled transporters (SGLT1)

ATP dependent transporters (MDR1)

uptake by the BB depends on

1. Number of cells
2. Number of transporters
3. Electrochemical driving force (SGLT1 needs a Na gradient maintained by the Na+/K+ ATPase

homozygous C292Y-SGLT1 mutation lead to

Glucose galactose malabsorption

Inhibitors can be used to unravel the transporters involved in intestinal glucose transport

Phloretin

Phloridzin

Km values of transporters (SGLT1, GLUT2)

SGLT1 > 0.5 low Km works best even at low glucose concentrations (fasting)

GULT2 > 17 high Km works best at high glucose concentrations (eating)

Intestinal glucose and fructose transporters

1. GLUT5 (necessary for fructose but not glucose)
2. GLUT2

effects of stress on glucose absorption

Stress decreases SGLT1 mediated transport

increase GLUT 2 mediated transport

Lipids Absorption

Transport systems highest FA uptake during fasting when lumen concentrations of FA low

1. Scavenger receptor CD36 (SR-B2)
2. scavenger receptor B1 (SR-B1) – CD36 family
3. FA transport protein 4 (FATP4)

Via diffusion is highest during feeding when FA concentrations in the lumen are high

AA transporters

1. Na dependent
2. IMINO
3. Na independent
4. Proton-energised peptide transporters (PEPT-1)

Lactalbumin absorption %

61%

Lactalbumin hydrolyate absorption %

91%

Milk protein components

75-80% Casein

20-25% Whey

Whey Protein properties

• Globular with defined tertiary structures
• Exist in milk serum
• Remain soluble at pH 4.6 > Stable
• Not incorporated into cheese curd

Classification of fibers (non-starch polysaccharides )

1. Cellulose (Carboxymethylcellulose)
2. Non-cellulose (hemicellulose, pectin, plant gums & mucilage, inulin, Guar)

How are SCFA and organic acids absorbed?

SCFA and organic acids - by organic anion transporter

SCFA – by passive diffusion?

Fermentation Capacity in Humans

• Lactitol - 74g/d
• Sorbitol - 71g/d
• Cellulose – much higher. WHY?
• Polydextrose [high melt, randon copolymer of glucose and citric acid] – 120g/d WHY?
• Most soluble and fermentable fibres - about the same as lactitol
• The kinetics of fermentation are variable

Non fermentable fiber effects on the gut

increase stool weight

Which SCFA is beneficial for blood flow? And which for cell turnover?

blood flow (acetate) and cell turnover(butyrate)

The enteric nervous system has two major ganglionated plexuses

Myenteric plexus - lies between the outer longitudinal and the circular muscle layers

Submucosal plexus - lies between the muscularis mucosae and the circular muscle layer

Food in the stomach causes .... release which stimulates.......

gastrin release which stimulates acid secretion

Fatty foods in the duodenum causes 2 things to happen:-

1.Secretin release – bicarbonate and pancreatic secretions

2.Cholecystekinin release CCK– gall bladder contracts, pancreatic secretions

Three phases of pancreatic stimulation

1 Cephalic (vagal, seeing, smelling, and thinking about food (20%))

2 Gastric (vagal, gastrin, acid, peptides (10%))

3 Intestinal (CCK, secretin, cholinergic vagal, serotonin 70%)

Pancreatic inhibition

1- Ghrelin

2- Leptin

3- Head break PYY, GLP-1

Reduction in duodenal and ileal motility when...

1. lipids in the duodenum
2. head of the meal reaches ileum

Presence of SCFA in caecum promotes ...

ileo-caecal motility increased – prevents reflux of colonic contents into ileum