Structural characteristic of small intestine 4. small intestinal glands located in the lamina propria.

Model H.E. staining villus Longitudinal section of villus and glands A Core of villus epithelium villus Smooth m.f. gland A gland L V Longitudinal section of villus and glands

Structures increasing surface area of small intestine *Plica : a fold of mucosa and submucosa in the lumen of digestive tract. *intestinal villus : the projection of mucosa of small intestine. *microvillus: the minute projection of cell membrane.

plicae microvilli villus

microvilli plica Villus epithelium

Structure of Intestinal Villus: *small finger projection of the mucosa, found only in the small intestine; *varying in the form and height in different region. 1. being covered by s. c. epith. 2. having a core of lamina propria with capillary network, central lacteal, a few smooth muscle f. and some lymphoid tissue.

capillary network central lacteal smooth muscle f. lymphoid tissue

Structure of Intestinal Villi: Simple Columnar Epith. *cellular types in simple columnar epith. of intestinal villi are as follow: * Absorptive cell Goblet cell Endocrine cell

Absorptive cell * a tall columnar cell with ovoid nucleus located toward the base. * striated border(LM) formed by closely packed, parallel microvilli (EM). tight junction near the apex between adjacent cells. * function as absorption of sugar, amino acid and lipid. * involving in secretion of IgA and producing enterokinase.(肠致活酶)

striated border

intestinal villi (SEM)

SEM Absorptive cell 微绒毛 LM(model) EM Microvilli Striated border Tight Junction SEM 微绒毛 LM(model) EM

Model of villi and gland H.E. staining Core of villus epithelium villus Smooth m.f. gland A gland L V Longitudinal section of villus and glands Model of villi and gland

Small intestine gland *infolding the epithelium to the lamina propria at the base of villus *cellular components are as same as that in the villous epith., except two types of cells: Goblet c. Absorptive c. Paneth c. Stem c. Endocrine c.

Paneth cell * found only in the base of the gland. * pyramidal shape with a broad base and a narrow apex. * having all features of protein- secreting cells. * acidophilic granules in the apical cytoplasm (LM). * secreting defensin, lysozyme which involved in the control of infection. Paneth c.

Paneth cell Section (HE)

Paneth cell (EM) Paneth cell (LM)

Regional difference in the small intestine duodenum jejunum ileum Villi shape leaf-like finger-like becoming smaller ++ Goblet C. + +++ scattered L.C. Same as in solitary L.N. duodenum Lymphatic tissue aggregated L.N. Glands in submucosa Present none none

ileum

Large intestine colon cecum rectum appendix anal canal

Large intestine * primary function is reabsorption of water and salt. * three main sections: cecum including the appendix colon rectum with the anal canal * primary function is reabsorption of water and salt. * secreted mucus acts as a lubricant during transport of the intestinal contents .

Longitudinal section of colon Structural characteristic of cecum, colon & rectum *absence of villi & plicae circulares. *the glands are longer, and straighter. *surface and gland epith. with numerous goblet c. Longitudinal section of colon

*absence of villi & plicae circulares. Structural characteristic of cecum, colon & rectum *absence of villi & plicae circulares.

Structural characteristic of cecum, colon & rectum *the glands are longer, and straighter. *surface and gland epith. with numerous goblet c.

Colon

Appendix

Structural characteristic of appendix * small lumen with usually irregular outline. * surface epith. with few goblet cells. * rare intestinal glands. * numerous lymphoid tisues located in the lamina propria and the submucosa. * muscularis mucosa usually incomplete. * thin muscularis. * serosa.

Appendix(transverse section) L.N. L.N. Appendix(transverse section)

Mucous neck cell *located in the neck of the gland in small groups; * flatten nucleus located in the base of cell; * mucin granules lie in the supranuclear position; * secreting acid mucus.

Stem cell Endocrine cells *a group of undifferentiated cells located in the neck region of the gland; *differentiating into surface mucous cells, chief cells and parietal cells; Endocrine cells *ECL cell：secreting histanine stimulated the acid production. *D cell: secreting somatostatin inhibited secretion of parietal cells and other endocrine cells.

Regional difference in the small intestine duodenum jejunum ileum Villi shape leaf-like finger-like becoming smaller ++ Goblet C. + +++ scattered L.C. Same as in solitary L.N. duodenum Lymphatic tissue aggregated L.N. Glands in submucosa Present none none

Goblet cell *scatted between the absorptive cells. *increasing from the duodenum to the terminal ileum. *secreting mucus formed a protective film and functioned as lubrication.