© 2003 Science Press Internet Services FISIOLOGIA DIGESTIVA Clase 5: Secreción y digestión...

© 2003 Science Press Internet Services

FISIOLOGIA DIGESTIVAFISIOLOGIA DIGESTIVAClase 5: Secreción y digestión gástricaClase 5: Secreción y digestión gástrica

Dr. Michel Baró AlisteDr. Michel Baró Aliste


Nutrients provided by animal and vegetable products


Digestive process is initiated by sensory signals


The effect of discussion, sight, and smell of food


Oral cavity has important functions in initial processing

TABLE 2 - 4. DIGESTION STARTS IN THE ORAL CAVITY

Mastication–Mechanical disruption of solid food

Increased salivary secretion–Moistening of food particles and mixing withsalivary amylase, R - factors, and lingual lipase

Taste of food–Increased stimulation of gastric secretion

Swallowing of food bolus


Secreción salivalSecreción salival

Estímulos gustativos (amargos)Tactiles (lisos)


Fases de la secreción gástrica

Fase cefálica (30%)

Fase gástrica (70%)-reflejos vago-vagales-reflejos entéricos locales-gastrina

Fase intestinal Acetilcolina mocoGastrina pepsinógenoHistamina HCl


The arrival of a swallowed food bolus in the stomach

(20-30% de la digestión total)


The emptying of food from the stomach


Passage of acidic, hyperosmolar gastric chyme into duodenum


Glándulas de la mucosa gástrica

-80% oxínticas (cuerpo y fondo gástrico)-ácido clorhídrico-pepsinógeno I y II-factor intrínseco-moco

-20% pilóricas-moco-pepsinógeno-gastrina

Otras enzimas-lipasa gástrica(tributirasa)-amilasa gástrica-gelatinasa

capa de moco protector 1mmrico en bicarbonato


Célula parietal u oxíntica

(H+) = 160 mmol/L

pH = 0,8

(H+)lum = 3.000.000(H+)pl

1500 cal/L

mitocondrias

pepsinógeno (42500)

pepsina (35000)

activa a pH 1,8 a 3,5


Producción de ácido clorhídrico

anhidrasa carbónica


Central nervous system: Regula células secretoras

NMD del vago

n. tracto solitario

hipoglicemiaaferentes del gustoy viscerales

fondoantro

fondo

antro

SSTR2= receptor somastostatina CCK-B= receptor CCK y gastrina

pepsinógenoácido clorhídricomucus


The parietal cell


Stimulation of acid secretion


Peptides that affect gastric acid secretion

TABLE 2 - 29. PEPTIDES THAT AFFECT GASTRIC ACID SECRETION

Stimulants Inhibitors

Gastrin Somatostatin

Gastrin - releasing peptide (GRP) Cholecystokinin (CCK)

Peptide YY

Calcitonin gene - related peptide (CGRP)

Secretin

Neurotensin

Vasoactive intestinal peptide (VIP)


Gastrin effects on ECL cells are shown

HDC: histidina decarboxilasa


Sources of gastric histamine

TABLE 2 - 25. SOURCES OF HISTAMINE IN THE STOMACH

Enterochromaffin - like cells (ECL cells)

Mast cells

Neurons(?)


Interaction between histamine and other hormones

CélulaParietal


Enterochromaffin-like (ECL) cell receptor


Histamine-producing (enterochromaffin-like) cell (a)


Histamine-producing (enterochromaffin-like) cell (b)


Gastrin: chronology of discoveries

TABLE 2 - 3. GASTRIN: CHRONOLOGY OF DISCOVERIES

1902 EdkinsPostulated existence of a humoral substance released bydigested food that stimulates gastric secretion[2]gic302rfref02.

1938 KomarovShowed that antral mucosa extracts from which histaminehad been completely extracted continued to stimulategastric acid secretion when injected.

1948Grossman, etal.

Showed that distention of denervated antral pouchstimulated acid secretion from transplanted gastric pouch.

1964Gregory andTracy

Isolated and purified two gastrins from antra mucosa(gastrin I and II).


Gastrin has multiple physiologic effects

TABLE 2 - 7. GASTRIN: GASTROINTESTINAL FUNCTIONS

Stimulation of gastric acid secretion

Stimulation of histamine release from enterchromaffin - like (ECL) cells

Regulation of mucosal growth–most pronounced in nonantral gastric mucosa, ECL -cells, and proliferative zone of mucous neck cells

Contraction of lower esophageal sphincter (pharmacologic effect)

Stimulation of smooth muscle contraction

Regulation of antral motor activity

Possible role in regulation of glucose - stimulated insulin release

Release of somatostatin from fundic endocrine cell culture


Stimulations of gastrin release

TABLE 2 - 13. STIMULANTS OF GASTRIN RELEASE

Dietary products Beta - 2 adrenergic agonists

proteins, peptides, amino acids,amines

Fat

Gastrin - releasing peptide (GRP) Sham feeding

Luminal neutralization Truncal vagotomy

Antral distention

Major physiologic role


Depressant factors of gastrin release

TABLE 2 - 14. DEPRESSANTS OF GASTRIN RELEASE

Luminal acid

Somatostatin

Starvation

Major physiologic role


Human antral gastrin-producing (G) cell (a)


Human antral gastrin-producing (G) cell (b)


Human antral gastrin-producing (G) cell (c)


The G cell


Inhibition of gastrin release

gastrina

(+)


Chronology of gastrin-releasing peptide

TABLE 2 - 15. GASTRIN RELEASING PEPTIDE CHRONOLOGY

1970 Ersparmer, et al. Discovered bombesin in skin of amphibians (Bombinabombina and Bombina variegata)

1973/1974 Bertaccini, et al.Showed that bombesin stimulates gastric acid secretionin dogs and rats. Showed gastrin release by bombesin indogs.

1978 McDonald, et al.Discovered mammalian counterpart of bombesin, gastrin- releasing peptide (GRP), in porcine stomach


GRP-releasing nerves in human gastric mucosa (a)


Gastrin-releasing nerves in human gastric mucosa (b)


Gastric distribution of gastrin-releasing peptide

TABLE 2 - 19. DISTRIBUTION OF GASTRIN - RELEASING PEPTIDEIN THE STOMACH

Gastric mucosa Plexuses

Oxyntic (higher density) Myenteric***

Antral (lower density)** Submucosal?*,**

Muscular layer***

Circular (higher density)

Longitudinal (lower density)

Involved n regulation of acid secretion, perhaps using somatostatin**Involved inregulation of gastrin release***Involved in regulation of motor function


Somatostatin chronology, chemistry, and localization

TABLE 2 - 20. SOMATOSTATIN CHRONOLOGY

1973 Brazeau, et al.Isolated peptide from hypothalamus of sheep, whichinhibited secretion of growth hormone from pituitary(growth hormone inhibitory factor).

1975 Arimura, et al.Demonstrated abundance of somatostatin in ratstomach and pancreas by immunocytochemistry.

1976 Schally, et al.Isolated and determined tetradecapeptide structure ofsomatostatin from porcine hypothalamus.

1980 Godman, et al.Isolation and closing of anglerfish islets cDNA encodingfull amino acid sequence of preprosomatostatin.


Human somatostatin-producing (D) cell (a)


Human somatostatin-producing (D) cell (b)


Human somatostatin-producing (D) cell (c)


Somatostatin functions and receptors

TABLE 2 - 23. ACTIONS OF SOMATOSTATIN IN THE STOMACH

Reduced exocrine secretion

Hydrochloric acid

Pepsin

Reduced neuroendocrine secretion

Gastrin (from G cell)

Histamine (from enterochromaffin - like cell)

Gastric motility

Inhibitory

Late phase emptying

Migrating motor complexes (MMCs)

Excitatory

Early phase emptying

Food intake

Inhibition (in fed animals)

Stimulation (in fasted animals)

Somatostatin has the opposite effect in the intestine andstimulates MMCs.


Combination that regulates gastric acid secretion


Digestión GástricaDigestión Gástrica


Carbohydrate is the major energy source in the diet

+ sucrosa lactosa

%5 boca

30-40%En estómago(Maltosa)

50%

Endoglucosidasa


Lipids have highest energy content of 3 macronutrients

a-grasos esenciales:ac.linoleicoac.linolénico


The initial event in lipid digestion in the stomach

Formación de gotasde emulsión

Más relevante en elPeríodo de lactante

pH óptimo 4-5,5

Tributirasa: tributirinao grasa de la mantequilla

Gotas de emulsión


Average daily protein intake is about 70-100 g in adults

pH óptimo 2 – 3Inactiva a pH 5

Digestión del colágenode la carneProteosas, peptonas, polipéptidos


Protein digestion begins in the stomach


Vitamin B12 is one of water-soluble vitamins

(1 ug diario)


FIN

© 2003 Science Press Internet Services FISIOLOGIA DIGESTIVA Clase 5: Secreción y digestión...

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