Membrane digestion & absorption
Membrane digestion Goes in succession in three zones:In mucusIn glycocalyxOn the apical membrane of enterocytes Was discovered by prof. Ugolev A.M.
Ugolev experiment
Amylase+starch
Amylase+starch+intestine piece
Amylase+starch+boiled intestine piece48-52 h
48-52 h3-4 h
muscelsNervous fibres
Blood vessels
epithelium
lymphatic capillaries
villae
Substrates depolymerization I the cavity & on the surface of the intestines
Membrane with adsorbed enzymes
МФ – memnbrane enzymesПФ – pancreatic enzymesКЦФ – active centers of enzymesРЦФ – regulatorycenters of enzymesТСМ – membrane transport systems
Brush boarder regionmicrovilli – Up to 3000 on one enterocyte – increase the square up to30 times
0,01-0,02 10-6 m
Membrane enzymes
Enzymes active centers
1-2мкм
Enteral medium
• Thin water film above the glycocalics which isn’t mixed up
• Its content is homeostated
water film
Enteral cavity
blood
Characteristic properties of membrane digestion
1. Large catalytic surface 2. Highly effective 3. Sterile4. Closely connected with absorption
Enzymes• Secreted by enterocytes• Fixed on the apical membrane of the
enterocyte• On enterocyte destruction get into
glycocalyx, mucus & enteric juice• Break down olygo- & dimers to form
monomers
Membrane digestion and absorption
Absorption in small intestine
absorption• Это сложный физиологический процесс
проникновения различных веществ через биологическую мембрану в кровь и лимфу
• В результате организм получает питательные вещества, воду, соли, витамины и лекарственные вещества
Methods of studying absorption in the
intestines
Acute methodsLymphatic vessels studying
vividiffusionv. portae
печень
solution
Chronic methodsIsolated loop of small intestine
Thiry’s mehod Thiry-Vella method
1.Polyfistule method
intestineskin
fistuli
2.London’s angiostomy- Fistula of vena cava
macrovilli
Macrovilli & cript are structural & functional component of
intestine
muscelsNervous fibres
Blood vessels
epithelium
lymphatic capillaries
villae
Macrovilli contents• arteriola• Capillary net• venula• Lymphatic capillary• Muscle fibres• Nervous ending• Enterocytes with brush boarder• Surface of absorption is about 200 m2
macrovilli
waterDissolved in water substances
arteries veins
Types of transportpassive:• filtration• osmosis• diffusionGoes along the gradients
created by macrovillicontraction15-20 ml of fluid is
absorbed per 1 minute
Active• Primary active
(sodium-potassium pump)
• Secondary active (glucose & amino acids transport)
enterocyteRenewed very quicklyNon-differentiated cylindrical cells rise up
from cripts to the top of the villi in 24-36 hours
Blood supply of small intestine• Upper mesenterical artery• Coeliac artery• Lower mesenterical artery
Small intestines get 10-15% of Q (MBF)400 ml/min
During digestion blood supply increases by 30-130% 750 ml/min
5% submucous
20%muscle layer 75%
mucous
jejunum ileum
per
Large intestines
permeability
Via cells•Protein-carrier•Energy requering
activ
epa
ssiv
e
Via cells•diffusion•convection
Via cell gaps•diffusion•convection
Water transport
Goes via gaps between the enterocytes along the gradients:
• Hydrostatic• Osmotic (created additionally by sodium
absorption)• Dissolved in water substances are
absorbed
Water can be secreted from blood into the intestinal cavity
1. Active secretion of anions2. Decrease of active absorption3. High osmotic pressure in the intestinal
cavity4. Increased hydrostatic pressure in the serose
layer5. Increased permeability of intracellular gaps
for ions
Dehydroxyle derivatives of bile acids & laxatives increase permeability of intracellular junctions.Magnesium sulphate increases osmotic pressure in the intestinal cavity
Hydrostatic pressure
“leaking” junction
Bacterial toxins (Cholera toxin, coletoxin)
Hormones (prostaglandies,secretin, VIP)
C-AMP
Calcium concentration in the enterocytes changes,Chlorine permeability increases
Chlorine gets into the cavity, sodium follows along the electrical gradient , water follows along the osmotic gradient
Proteins • 70-90 g per day with food 60 г белка с
пищеварителными соками ( ферменты и энтероциты).
• В полости 30% расщепляется до нейтральных и основных АК – 70% до олигопептидов
• Ологипептиды расщепляются до АК в щеточной кайме (10%) и в цитоплазме
Digestion & absorption of proteins
Amino acids absorption• Goes in duodenum (50-60%) & jejunum
(30%) by means of secondary active sodium dependent transport
• Protein-carriers are selective for:Neutral АAДвухосновных АADicarbonic АAGlycin
Carbohydrates Daily dose 250-280 g:• 60% vegetable starch• 30% saccharase• 10% lactose, glucose, fructose, glycogenEnzymes:• In the cavity – alpha-amylaze• On the villi – olygosacharidazes:
lactatdehydrogenaze (lactase), glycosidase
Lactase deficit
• In Europe – 15% of population• In Africa – 80% of population• In Muslim states of India – 15% of population• In Hindu states of India– 80% of population
Lactose increases osmotic pressure in the cavity & can cause dyarhea
Transport of carbohydrates monomers
Monomers:• Glucose• Galactose• FructoseAbsorbed by means of secondary active
sodium dependent transport in duodenum (30%) & jejunum (50-60%)
Scheme of secondary active transport
ATP
К+
Na+
Na+glucose
Apical membrane
Basilar membrane
Fats• 60-100 g of fat per day90% of them are thryglcerides5-7 g are excreted with faeces• Emulsified in duodenum (fat drop in stomach
is 100 nm in diameter, I the intestines – 5 nm)• Absorbed in the form of fine emulsions or
micells with bile acids 95% in duodenum
Lipids absorption
lipid
Bile acid blood
chilomicrone
TG lipoproteins
lymph
Relative volumes of absorptionDuodenum 30 сm
jejunum120 сm
ileum130 сm
95%
50% 30%
30% 50-60%
fats
Amino acids
glucose
Large intestineAbsorption is completed here & faeces are formed:
• 400 g of chyme per day enters from small intestine
• 150-200 g of faeces is formed – 70-80% of water; 20-30% of dry matter (cellulose, non-organic substances; fats)
• The number of microorganisms is exceptionally great— up to tens of milliards per kg of contents.