características do intestino delgado: adaptações morfofuncionais para a digestão e absorção

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