Digestive System II

Stomach

Small intestine

Large intestine

Stomach

is an expanded part of the digestive tube lies beneath the diaphragm

Stomach functions

Mechanical and chemical treatment of a food bolus

⇓

chyme formation Digestion of

proteins begins

carbohydrates continues Chyme transport to the duodenum Absorption (minimal)

Stomach regions

Cardia Fundus Corpus Pylorus

Stomach tunics

Mucosa Submucosa Muscularis externa Serosa

Stomach mucosa

covering epithelium lamina propria muscularis mucosae (3 layers) gastric glands

Gastric surface epithelium

is simple columnar mucous

(glandular, secreting) arises from the endoderm

Gastric epitheliocytes lack tight junctions

some substances (water, salts, alcohol, aspirin)

may be absorbed between cells

⇔

Epithelium forms microrelief

gastric pits gastric areas

Gastric submucosa

moderately dense connective tissue blood vessels, submucosal nerve plexus

⇒

Gastric muscularis externa

consists of smooth muscle tissue

3 layers: inner oblique

middle circular

outer longitudinal is more developed in the pyloric region forms sphincters in the cardia and pylorus contains myenteric nerve plexus

Gastric serosa

LCT and mesothelium contains subserosal nerve plexus

GALT – gut associated lymphatic tissue

forms lymphatic nodules in

the mucosa and submucosa

Gastric fundic glands

are simple tubular slightly branched are subdivided into

neck

corpus

bottom occupy the lamina propria open into the gastric pits

Gastric glands produce gastric juice

⇔

Gastric juice content

mucus enzymes hydrochloric acid - HCl

promotes protein acid hydrolysis

activates enzymes

suppresses bacterium development intrinsic factor

provides vitamin B12 absorption

Gastric gland cell types

Mucous cells Chief cells Parietal cells Enteroendocrine cells Stem cells

Gastric gland mucous cells

are located in the gland neck regions secrete a soluble mucus

Gastric gland chief cells

are located in the deepest gland parts are typical protein-secreting cells

Chief cells secrete gastric enzymes

pepsin

digests proteins to peptones lipase

digests milk lipids

rennin and chymosin

digest milk proteins

gastric enzymes are activated by HCl

Gastric gland parietal cells

are most numerous in the gland bottoms are large triangular in shape their cytoplasm stains with Eosin

Parietal cell ultrastructure

tubulovesicular membrane system

intracellular canalicular system with microvilli

numerous mitochondria

Parietal cell produce hydrochloric acid HCl

⇔

Parietal cell produce intrinsic factor

is a glycoprotein complexes with vitamin B12

provides subsequent vitamin absorption its absence leads to anemia

Stimulation of the parietal cell secretion

Acetylcholine Histomine Gastrin

Gastric gland enteroendocrine cells

are more numerous in the gland bottoms their cytoplasm is rich in secretory granules produce peptide hormones release hormones into the lamina propria

Enteroendocrine cells

are revealed by staining with salts of silver and chromium

(enterochromaffin, argentaffin, or argyrophil cells)

DES and APUD system

Enteroendocrine cells are members of the diffuse endocrine system (DES) Some cells belong to APUD system (amino precursor uptake and decarboxylation) Cells produce hormones - gastrin, secretin, motilin, somatostatin etc. Hormones provide endocrine and paracrine (local) regulation of secretion, muscle

contraction, cell proliferation

Gastric gland G-cells

are main gastric endocrinocytes secrete hormone gastrin

⇓stimulates acid production

pepsin secretion

muscle contraction

Gastric gland undifferentiated (stem) cells

are located in the gland neck parts serve for epithelial cell renewal

mitotic anaphase ⇒

Gastric surface and glandular epithelium renewal

surface epithelial cells ⇒ every 4-7 days all gland cell types ⇒ several times in a year

Cardiac gastric glands

are tubular, tortuous, and branched contain a few chief and parietal cells

Gastric pyloric glands

are branched, coiled, tubular glands open into the deep gastric pits lack chief and parietal cells

Small intestine

forms loops in the abdominal cavity is divided into 3 anatomical segments:

duodenum

jejunum

ileum

Small intestine functions

Digestion of

proteins up to amino acids

carbohydrates up to monosaccharides

lipids up to glycerol and fatty acids

nucleic acids up to nucleotides Absorption Chyme transport

Small intestine wall structure

Mucosa Submucosa Muscularis externa Serosa

Small intestine mucosa

covering epithelium lamina propria – LCT muscularis mucosae

⇓

2 layers of smooth muscle cells:

inner circular

outer longitudinal

⇒

Intestinal mucosa epithelium

simple columnar striated (with the brush border) arising from the endoderm

Small intestine mucosa microrilief

Villi

finger-like mucosa projections Crypts

tubule-like epithelium invaginations

Villi amplify the mucosa surface

⇒

Small intestine submucosa

moderately dense connective tissue contains blood vessels, submucosal nerve plexus

⇒

Duodenal submucosa contains glands

duodenal (Brunner’s) glands are

compound

branched

tubular-alveolar

mucus-secreting protect intestinal mucosa

against acid gastric content

⇒

Small intestine muscularis externa

two layers of smooth muscle cells

inner circular

outer longitudinal contains myenteric nerve plexus

⇓

LCT and mesothelium contains blood vessels, subserosal nerve plexus

Small intestine serosa

⇒

Intestinal villus structure

covering – intestinal epithelium core – extension of the lamina propria

Intestinal villi contain

network of fenestrated sinusoidal capillaries blind-ending lymphatic capillary - lacteal smooth muscle cells derived from the muscularis mucosae

muscles accompany the lacteal

and permit lymph moves away

⇓

Villus epithelium cell types

Enterocytes Goblet cells Enteroendocrine

Enterocytes or absorptive cells

are columnar cells with apical microvilli microvilli form the brush border

the brush border amplifies the epithelium surface for absorption and membrane digestion

Enterocyte junctional complex

tight junctions establish a barrier between

the lumen and intercellular space

Enterocyte functions

Produce enzymes for terminal digestion Absorb substances from the lumen Resynthesize neutral fat from

absorbed glycerol and fatty acids

Enterocytes transport substances to the circulation

Into the blood

amino acids

monosaccharides

nucleotides

water

electrolytes Into the lymph (chyle)

lipids in chylomicrones

Goblet cells

produce mucus

Goblet cell ultrastructure

⇔

Enteroendocrine (DES) cells

produce hormones

secretin

motilin

cholecystokinin, etc.

⇓– increase the pancreas and gall bladder activity – inhibit the stomach secretion and motility

Crypt epithelium cell types

Enterocytes Goblet cells Enteroendocrine cells Paneth cells Intermediate (stem) cells

Paneth cells

are located in the crypt bottoms contain large acidophilic granules

in the apical cytoplasm

Granule content:

- antibacterial proteins (lysozyme)

- digestive enzymes (dipeptidases)

- zinc ions

Paneth cells functions

Regulation of the intestinal flora Digestion of proteins

Intermediate cells

are located in

the lower half of the crypts are capable of

division and differentiation give rise to

the all epithelium cell types

Gut-associated lymphatic tissue - GAlT

infiltrates the intestinal mucosa and submucosa forms lymphatic nodules and the Peyer’s patches serves as an immunologic barrier

cooperates with the overlying epithelial M-cells

M-cells or microfold epithelial cells

overlie lymphatic nodules and Peyer’s patches have numerous apical plasma membrane folds are associated with numerous lymphocytes

Functions

- transport antigens from the intestinal lumen

- represent antigens to lymphocytes

- stimulate antigen-depended GALT response

GALT immune response to antigens

activated lymphocytes migrate to the lymphatic nodules and regional lymph nodes

B lymphocytes undergo differentiation to the plasma cells plasma cells migrate back into the lamina propria

Secretory IgA are molecules of mucosal immunity

plasma cells release antibodies – IgA enterocytes

- produce secretory glycoprotein ⇒ complex with IgA

- transport complex to the lumen

plasma cells in ⇒ the lamina propria

Large intestine

Anatomical division

Cecum with appendix

Colon

ascending

transverse

descending

sigmoid

Rectum

Anal canal

Large intestine functions

Absorption of

water

electrolytes

monosaccharides Digestion of cellulose by

symbiotic bacteria Feces formation and evacuation

Large intestine wall

Mucosa Submucosa Muscularis externa Serosa

Large intestine mucosa

contains only crypts (villi are absent) ⇒

Large intestine mucosa epithelium

is simple, columnar, striated,

arising from the endoderm consists of

enterocytes

goblet cells (prevalent)

enteroendocrine cells

intermediate (stem)) cells

Large intestine lymphatic tissue

is well-developed reflecting the large number

and variety of microorganisms in the lumen

⇑appendix – “an intestinal tonsil”

Large intestine muscularis externa

outer layer forms three

longitudinal bands called teniae coli

⇒

The End

Thank you for attention!