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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. Área total do intestino delgado de humanos: 200m 2 - PowerPoint PPT Presentation
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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.
vilos
microvilos
Características do Intestino Delgado:adaptações morfofuncionais para a digestão e absorção
Pregas, vilosidades e microvilosidades multiplicam em 600 vêzes a superfície absortivae digestiva dointestino delgado
pregas circulares
Área total do intestino delgado de humanos: 200m2
É equivalente à área de uma quadra de tênis!!!
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 area a. 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
Características do Intestino DelgadoDuodeno
INTESTINO DELGADO E AS ADAPTAÇÕES ABSORTIVAS
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/anatomy.html
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".
Características do Intestino Delgado:adaptações morfofuncionais para a digestão e absorção
http://www.mc.vanderbilt.edu/histology/index.php?page=searchresult&category_name=intestine&cur_type=1
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.
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
VOLUMES DIÁRIOS INGERIDOS,
SECRETADOS, ABSORVIDOS E
EXCRETADOS PELO TGI
Segmentation in the Small Intestine
Purpose of segmentation is to mix & churn not to move material along as in peristalsis
Peristalstismo
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
Digestão do amido (amilopectina) ~glicogênio
Digestão e absorção de carboidratos
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
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)
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
Amidoglicogênio
Digestão e absorção dos derivados da digestão do amido (amilopectina) ~ glicogênio
enzimas e transportadores presentes nos microvilos (borda-em-escova)
(SGLT1)
salivar epancreática
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
(SGLT1)
SacaroseLactose
Amidoglicogênio
Digestão e absorção de dissacarídeos da dietaLACTOSE e SACAROSE
enzimas e transportadores presentes nos microvilos (borda-em-escova)
salivar epancreática
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
Carbohydrate Absorption
Sodium-glucose transport proteins (SGLT) in membrane help absorb glucose & galactose
Fructose absorbed by facilitated diffusion then converted to glucose inside the cell
Liver
Digestão de proteínas e absorção de polipeptídeos e aminoácidos
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
extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270
extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270
extraído de: Saladin, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270
Digestão final de polipeptídeos pelas enzimas da borda-em-escova (constitucionais) do intestino delgado
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
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
Digestão e absorção de polipeptídeos e aminoácidos (enterócitos)
Digestão e absorção de gorduras
TG
BOCAESTÔMAGO
INTESTINO DELGADO mucosa ID linfa
TG sais biliares(fígado)
Lipase (PAN)
ChlFlp
TG: TriglicerídeosChl: colesterolFlp: fosfolipídeos
MG AGL
QUILOMÍCRONS
MG: monoglicerídeosAGL: ác. graxos livres
Flp(8%)
Apoproteína B (2%)
Chl(2%)
88%+
Chl Flp
MICELA
sais biliares
RER
Resumo da digestão e absorção de gorduras
Cristina, 1999 modificado de Johnson, 1999
MICELAsais biliares
TGLipase pancreática
MG AGL Glicerol
Fígado
Íleo
Chl
Flp
Quilomícrons
vasos lacteais (linfa) capilares
RER
Digestão e absorção de triglicerídeos
Cristina, 1999 modificado de Johnson, 1999
Vander, Sherman & Luciano, 1997
MICELA
Sais biliares e a emulsificação das gorduras:a formação das micelas para a digestão pela lipase pancreática
extraído de: Vander, Sherman & Luciano, 2002 – WEBsite original: http://www.biocourse.com/mhhe/bcc/domains/quad/topic.xsp?id=000270
Fat Digestion & Absorption
extraído (enquanto disponível em 2002) de: http://www.mds.qmw.ac.uk/biomed/kb/metabolism/Micronutrients_files/frame.htm
Anatomy of Large Intestine
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 motilitymoves residue for several centimeters with each
contraction
Bacterial Flora & Intestinal Gas
Bacterial flora populate large intestine ferment cellulose & other undigested
carbohydratessynthesize vitamins B and K
Flatus (gas)average person produces 500 mL per daymost is swallowed air but it can contain
methane, hydrogen sulfide, indole & skatole that produce the odor
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
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
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 sphincter3. 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)
Reflexos do sistema nervoso entérico
extraído, enquanto disponível, de: http://medweb.bham.ac.uk/research/toescu/Teaching/GIT/OutlineDetailsMeds.htm#anchor225964