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Dr Sundus Tariq

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Terminal food digestion, nutrient absorption, and endocrinesecretion.

The small intestine is relatively longapproximately 7 m.

Three segments:

duodenum,

jejunum

ileum.

SMALL INTESTINE

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Plicae circulares:Permanent circular or

semilunar folds

Valves of Kerckring

Mucosa and submucosa

Best developed in thejejunum

SMALL INTESTINE

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Intestinal villi

0.5 to 1.5-mm-long

Mucosal outgrowths (epithelium plus core of lamina

propria)

Duodenum they are leaf-shaped,

Ileum fingerlike shape.

Mucosa

EpitheliumLamina propria

Intestinal glands

Peyers patches.

Muscularis Mucosae

SMALL INTESTINE

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Epithelium

SMALL INTETINE

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Enterocytes, Absorptive cells.

Tall columnar cells, an ovalnucleus in the basal half ofthe cell.

Striated (or brush) border . A homogeneous layer at apexof cell.

E/M the striated border isseen to be a layer of denselypacked microvilli.

Microvilli Cylindrical protrusion of theapical cytoplasm

1 m tall and 0.1 m indiameter

Actin filaments.

3000 microvilli on each cell. 1 mm2 of mucosa = 200

EPITHELIUM

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Plicae increase the intestinal surface three-fold,

Villi increase it 10-fold

Microvilli increase it 20-fold.

Together, these processes are responsible for a 600-foldincrease in the intestinal surface, resulting in a totalabsorptive area of 200 m2!

ABSORPTION

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Goblet cells

Interspersed between theabsorptive cells

Less abundant in the duodenum

More numerous in the ileum.

Produce glycoprotein mucins

hydrated and cross-linked to form

mucus protect and lubricate the lining of

the intestine.

EPITHELIUM

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Paneth cells

located in the basal portion of theintestinal crypts

Exocrine cells with large,

eosinophilic secretory granules intheir apical cytoplasm

Exocytosis to release

lysozyme,

phospholipase A2,

defensins (hydrophobicpeptides)

Bind and breakdown membranes ofmicroorganisms and bacterial walls.

Important role in innate immunity

and in regulating themicroenvironment of the intestinal

EPITHELIUM

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Enteroendocrinediffuse neuroendocrinesystemGastro-entero-pancreatic

system.EC cells = Somatostatin

GLI cells = Glicentin

I cells = Cholecystokinin

S cells = Secretin

K cells = GIPMo cells = Motilin

the control of peristalsis,regulation of secretions necessaryfor food digestion, and the sense ofbeing satiated after eating.

EPITHELIUM

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M (microfold) cells

Specialized epithelial cells in theileum overlying the lymphoid folliclesof Peyer patches.

Basal membrane invaginations orpockets containing manyintraepithelial lymphocytes andantigen-presenting cells.

Selectively endocytose antigens

Transport them to the underlyingmacrophages and lymphocytes, whichthen migrate to lymph nodes whereimmune responses to foreign antigensare initiated.

Serve as sampling stations wherematerial in the lumen of the gut istransferred to immune cells of the

EPITHELIUM

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Loose connective tissue

Blood and lymph vessels, nervefibers, and smooth muscle cell.

Penetrates core of villus,bringing with itmicrovasculature, lymphatics,and nerves.

Smooth muscle fibers inside thevilli are responsible for their

rhythmic movements, which areimportant for efficientabsorption. The muscularismucosae also produces localmovements of the villi andplicae circulares.

LAMINA PROPRIA

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Lymphocytes

Plasma cells, Mast cells, Macrophages

Lymphoid aggregates

Peyer patches

Big lymphoid masses

Ileum

May extend in submucosa

50 lymphoid nodules

LAMINA PROPRIA

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Smooth muscles

Inner circular

Outer longitudinal

MUSCULARIS MUCOSAE

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Loose, coarse connective tissue

Blood vessels

Lymphatics

Meissners plexus

Duodenum

Brunners gland

Simple branched tubulo-alveolar glands

Alkaline mucus

Urogastrone

SUBMUCOSA

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Smooth muscles

Inner circular

Myenteric plexus

Outer longitudinal

MUSCULARIS EXTERNA

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Thin layer of connective tissue

Mesothelium

Duodenum

Adventitia on posterior surface

SEROSA

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Histological differences between Duodenum, Jejunum andIleum

ASSIGNMENT