This document summarizes membrane digestion and absorption in the small intestine. It discusses how enzymes digest substrates in the mucus, glycocalyx, and on enterocyte membranes. Key points include the large surface area and efficiency of membrane digestion, as well as its close connection to absorption. Absorption involves both passive diffusion and active transport across enterocyte membranes and within microvilli. The major nutrients - proteins, carbohydrates, fats, vitamins and minerals - are absorbed primarily in the duodenum and jejunum through these membrane transport processes.

1. Membrane digestion &
absorption

2. Membrane digestion
Goes in succession in three zones:
In mucus
In glycocalyx
On the apical membrane of enterocytes
Was discovered by prof. Ugolev A.M.

3. Ugolev experiment
Amylase+
starch
Amylase+
starch
+intestine piece
Amylase+
starch
+boiled intestine piece
48-52 h
48-52 h3-4 h

4. muscels
Nervous fibres
Blood vessels
epithelium
lymphatic capillaries
villae

5. Sponsored
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USMLE Exam (America) – Practice

6. Substrates depolymerization
I the cavity & on the surface
of the intestines

7. Membrane with
adsorbed enzymes
МФ – memnbrane enzymes
ПФ – pancreatic enzymes
КЦФ – active centers of enzyme
РЦФ – regulatory
centers of enzymes
ТСМ – membrane transport syst

8. Brush boarder region
microvilli –
Up to 3000 on one
enterocyte – increase
the square up to
30 times
0,01-0,02 10-6
m
Membrane enzymes
Enzymes active centers
1-2мкм

9. Enteral medium
• Thin water film above the glycocalics
which isn’t mixed up
• Its content is homeostated
water film
Enteral cavity
blood

10. Characteristic properties of
membrane digestion
1. Large catalytic surface
2. Highly effective
3. Sterile
4. Closely connected with absorption

11. 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

12. Membrane digestion and
absorption

13. Absorption in small
intestine

14. 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

15. Methods of studying
absorption in the
intestines

16. Acute methods
Lymphatic vessels studying
vividiffusion
v. portae
печень
solution

17. Chronic methods
Isolated loop of small intestine
Thiry’s mehod Thiry-Vella method

19. 1.Polyfistule method
intestine
skin
fistuli
2.London’s angiostomy
- Fistula of vena
cava

20. macrovilli
Macrovilli & cript are
structural & functional
component of intestine

21. muscels
Nervous fibres
Blood vessels
epithelium
lymphatic capillaries
villae

22. Macrovilli contents
• arteriola
• Capillary net
• venula
• Lymphatic capillary
• Muscle fibres
• Nervous ending
• Enterocytes with brush boarder
• Surface of absorption is about 200 m2

23. macrovilli
water
Dissolved in wate
substances
arteries veins

24. Types of transport
passive:
• filtration
• osmosis
• diffusion
Goes along the gradients
created by macrovilli
contraction
15-20 ml of fluid is
absorbed per 1 minute
Active
• Primary active
(sodium-potassium
pump)
• Secondary active
(glucose & amino
acids transport)

25. enterocyte
Renewed very quickly
Non-differentiated cylindrical cells rise up
from cripts to the top of the villi in 24-36
hours

26. 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

27. jejunum ileum
p
e
r
Large intestines
permeability

28. Via cells
•Protein-carrier
•Energy requering
activepassive
Via cells
•diffusion
•convection
Via cell gaps
•diffusion
•convection

29. Water transport
Goes via gaps between the enterocytes
along the gradients:
• Hydrostatic
• Osmotic (created additionally by sodium
absorption)
• Dissolved in water substances are
absorbed

30. Water can be secreted from blood
into the intestinal cavity
1. Active secretion of anions
2. Decrease of active absorption
3. High osmotic pressure in the intestinal
cavity
4. Increased hydrostatic pressure in the serose
layer
5. Increased permeability of intracellular gaps
for ions

31. Dehydroxyle derivatives of bile acids & laxatives increase
permeability of intracellular junctions.
Magnesium sulphate increases osmotic pressure in the
intestinal cavity
Hydrostatic
pressure
“leaking” junction

32. 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

33. 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

34. Digestion & absorption of proteins

35. Amino acids absorption
• Goes in duodenum (50-60%) & jejunum
(30%) by means of secondary active sodium
dependent transport
• Protein-carriers are selective for:
Neutral АA
Двухосновных АA
Dicarbonic АA
Glycin

36. Carbohydrates
Daily dose 250-280 g:
• 60% vegetable starch
• 30% saccharase
• 10% lactose, glucose, fructose, glycogen
Enzymes:
• In the cavity – alpha-amylaze
• On the villi – olygosacharidazes:
lactatdehydrogenaze (lactase), glycosidase

37. 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

38. Transport of carbohydrates
monomers
Monomers:
• Glucose
• Galactose
• Fructose
Absorbed by means of secondary active
sodium dependent transport in
duodenum (30%) & jejunum (50-60%)

39. Scheme of secondary active
transport
ATP
К+
Na+
Na+
glucose
Apical membrane
Basilar membrane

40. Fats
• 60-100 g of fat per day
90% of them are thryglcerides
5-7 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

41. Lipids absorption
lipid
Bile acid blood
chilomicrone
TG lipoproteins
lymph

42. Relative volumes of absorption
Duodenum
30 сm
jejunum
120 сm
ileum
130 сm
95%
50% 30%
30% 50-60%
fats
Amino acids
glucose

43. Large intestine
Absorption 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.