Características do Intestino Delgado: adaptações morfofuncionais para a digestão e absorção

1. Características do Intestino Delgado: adaptações morfofuncionais para a digestão e absorção Adaptações da mucosa intestinal (pregas, vilosidades e microvilosidades) amplificam a superfície de contato entre o epitélio absortivo e os nutrientes.

2. Área total do intestino delgado de humanos: 200m2 É equivalente à área de uma quadra de tênis!!! Características do Intestino Delgado: adaptações morfofuncionais para a digestão e absorção Pregas, vilosidades e microvilosidades multiplicam em 600 vêzes a superfície absortiva e digestiva do intestino delgado pregas circulares vilos microvilos

3. Características do Intestino Delgado Duodeno This is a low power image of the first part of the Small Intestines, the Duodenum. It also has the basic layers of the GI system like the Mucosa, (blue arrows) , Submucosa, (red arrows), and the Muscularis Externa (green arrows). The small intestines has many adaptations to increase it's surface areaa. First it has Plicae Circulares (valves of kerckring),which are extensions of the submucosa, indicated by the yellow arrow. The next adaptation is the Villi, which are extensions of the mucosa indicated by the black arrows. Of important identification clues about the duodenum is the presence of Brunner's Glands which are very abundant in the submucosa. No other part of the intestines has these glands so once you see these you can be sure you are looking at the duodenum. http://www3.umdnj.edu/histsweb/lab20/lab20duodenum.html

4. INTESTINO DELGADO E AS ADAPTAÇÕES ABSORTIVAS The panels below depict the bulk of this surface area expansion, showing villi, epithelial cells that cover the villi and the microvilli of the epithelial cells. Note in the middle panel, a light micrograph, that the microvilli are visible and look something like a brush. For this reason, the microvillus border of intestinal epithelial cells is referred to as the "brush border". http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/anatomy.html

5. Características do Intestino Delgado: adaptações morfofuncionais para a digestão e absorção Existência de uma densa rede de capilares, vênulas e ductos lacteais que permeiam os vilos intestinais permitindo, assim, o aporte de substâncias e a drenagem dos nutrientes, água e eletrólitos absorvidos pelo epitélio intestinal. http://www.mc.vanderbilt.edu/histology/index.php?page=searchresult&category_name=intestine&cur_type=1

6. VOLUMES DIÁRIOS INGERIDOS, SECRETADOS, ABSORVIDOS E EXCRETADOS PELO TGI Overall fluid balance in the human gastrointestinal tract. About 2 L of water is ingested each day, and 7 L of various secretions enters the gastrointestinal tract. Of this total of 9 L, 8.5 L is absorbed in the small intestine. About 500 ml is passed on to the colon, which normally absorbs 80% to 90% of the water presented to it. (From Vander AJ, Sherman JH, Luciano DS: Human physiology, ed 6, New York, 1994, McGraw-Hill.) Levy et al., 2006

7. Segmentation in the Small Intestine • Purpose of segmentation is to mix & churn not to move material along as in peristalsis

8. Peristalstismo

9. Digestão e absorção de carboidratos Digestão do amido (amilopectina) ~glicogênio Structure of a branched starch molecule and the action of α-amylase. The colored circles represent glucose monomers linked by α-1,4 linkages. The black circles represent glucose units linked by α-1,6 linkages at the branch points. The α-1,6 linkages and terminal α-1,4 bonds cannot be cleaved by α-amylase. Berne et al., 2004

10. Digestão final de polissacarídeos pelas enzimas da borda-em-escova (constitucionais) do intestino delgado Veja aula online sobre absorção em: http://people.bu.edu/fgarcia/lectures/gi/index.htm

11. Carbohydrate Digestion in Small Intestine • Salivary amylase stops working in acidic stomach(if 4.5) • 50% of dietary starch digested before it reaches small intestine • Pancreatic amylase completes first step in 10 minutes • Brush border enzymes act upon oligosaccharides, maltose, sucrose, lactose & fructose • lactose indigestible after age 4 in most humans (lack of lactase)

12. Digestão e absorção dos derivados da digestão do amido (amilopectina) ~ glicogênio enzimas e transportadores presentes nos microvilos (borda-em-escova) Amido glicogênio salivar e pancreática (SGLT1) Functions of the major brush border oligosaccharidases. The glucose, galactose, and fructose molecules released by enzymatic hydrolysis are then transported into the epithelial cell by specific transport proteins. The glucose-galactose transporter is also known as SGLT1 and the fructose transporter as GLUT5. G, Glucose; Ga, galactose; F, fructose. Berne etal., 2004

13. Digestão e absorção de dissacarídeos da dieta LACTOSEeSACAROSE enzimas e transportadores presentes nos microvilos (borda-em-escova) Lactose Sacarose Amido glicogênio salivar e pancreática (SGLT1) Fig. 33-2 Functions of the major brush border oligosaccharidases. The glucose, galactose, and fructose molecules released by enzymatic hydrolysis are then transported into the epithelial cell by specific transport proteins. The glucose-galactose transporter is also known as SGLT1 and the fructose transporter as GLUT5. G, Glucose; Ga, galactose; F, fructose. Berne et al., 2004

14. Absorção de glicose/galactose nas microvilosidades (borda-em-escova) do intestino delgado http://faculty.uca.edu/~johnc/trans1440.htm veja animação online: http://www.stolaf.edu/people/giannini

15. Carbohydrate Absorption Liver • Sodium-glucose transport proteins (SGLT) in membrane help absorb glucose & galactose • Fructose absorbed by facilitated diffusion then converted to glucose inside the cell

16. Digestão de proteínas e absorção de polipeptídeos e aminoácidos

17. Início da digestão das proteínas: estômago (pepsina) extraído de: Vander, Sherman & Luciano, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270

18. extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270

19. extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270

20. extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270

21. Digestão final de polipeptídeos pelasenzimas da borda-em-escova (constitucionais) do intestino delgado

22. Fig. 33-6 The hierarchy of proteases and peptidases that functions in the small intestine. The pancreatic proteases convert dietary proteins to oligopeptides. Brush border peptidases then convert the oligopeptides to amino acids (about 70%) and dipeptides and tripeptides (about 30%). The amino acids are taken up across the brush border membrane by amino acid transporters and the small peptides by a peptide transporter. In the cytosol of the enterocyte, dipeptides and tripeptides are cleaved to single amino acids. (From Van Dyke RW: Mechanisms of digestion and absorption of food. In Sleisenger MH, Fordtran JS, editors: Gastrointestinal disease, ed 4, Philadelphia, 1989, WB Saunders.) Berne et al., 2004

23. Digestão e absorção de polipeptídeos e aminoácidos (enterócitos) Fig. 33-7 A wide variety of dipeptides and tripeptides is taken up across the brush border plasma membrane by a single type of H+-powered secondary active transport protein. The H+ gradient is created by Na+-H+ exchangers in the brush border membrane. In the epithelial cell cytosol, peptidases cleave most of the dipeptides and tripeptides to single amino acids, which leave the cell at the basolateral membrane by facilitated transport. Berne et al., 2004

24. Digestão e absorção de gorduras

25. Resumo da digestão e absorção de gorduras Cristina, 1999 modificado de Johnson, 1999

26. Digestão e absorção de triglicerídeos Cristina, 1999 modificado de Johnson, 1999

27. Sais biliares e a emulsificação das gorduras: a formação das micelas para a digestão pela lipase pancreática MICELA extraído de: Vander, Sherman & Luciano, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270 Vander, Sherman & Luciano, 1997

29. Fat Digestion & Absorption

30. extraído (enquanto disponível em 2002) de: http://www.mds.qmw.ac.uk/biomed/kb/metabolism/Micronutrients_files/frame.htm

32. Anatomy of Large Intestine

33. Absorption and Motility • Transit time is 12 to 24 hours • reabsorbs water and electrolytes • Feces consist of water & solids (bacteria, mucus, undigested fiber, fat & sloughed epithelial cells • Haustral contractions occur every 30 minutes • distension of a haustrum stimulates it to contract • Mass movements occur 1 to 3 times a day • triggered by gastrocolic and duodenocolic reflexes • filling of the stomach & duodenum stimulates motility • moves residue for several centimeters with each contraction

34. Bacterial Flora & Intestinal Gas • Bacterial flora populate large intestine • ferment cellulose & other undigested carbohydrates • synthesize vitamins B and K • Flatus (gas) • average person produces 500 mL per day • most is swallowed air but it can contain methane, hydrogen sulfide, indole & skatole that produce the odor

36. Defecation • Stretching of the rectum stimulates defecation • intrinsic defecation reflex via the myenteric plexus • causes muscularis to contract & internal sphincter to relax • relatively weak contractions • defecation occurs only if external anal sphincter is voluntarily relaxed • parasympathetic defecation reflex involves spinal cord • stretching of rectum sends sensory signals to spinal cord • splanchnic nerves return signals intensifying peristalsis • Abdominal contractions increase abdominal pressure • feces will fall away

37. Neural Control of Defecation 1. Filling of the rectum 2. Reflex contraction of rectum & relaxation of internal anal sphincter 3. Voluntary relaxation of external sphincter

38. Reflexos do sistema nervoso entérico 3. LONG-RANGE REFLEXES - altogether different types of rflexes which involve co-ordinated response of one region of the gut wall following activation in other parts of the GIT. 1. Gastro-enteric reflex - distension of stomach increase the excitability (motor and secretory) of the small intestine. 2. Gastro-ileal reflex - distension of stomach intesifies the activity of the terminal ileum and opens the ileo-cecal sphincter 3. Gastro- and duodeno-colic reflexes (with participation of extrinsic innervation and also hormonal (gastrin)`). Distension of stomach or duodenum initiate 'mass movements' of the colon. 4. Ileo-gastric reflex - distension of an ileal segment inhibits gastric motility. 5. Intestino-intestinal reflex - cessation of intestinal motility upon excessive distention (adynamic ileus), or rough handling (surgery) or peritonitis (severe irritation) extraído, enquanto disponível, de: http://medweb.bham.ac.uk/research/toescu/Teaching/GIT/OutlineDetailsMeds.htm#anchor225964