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.