Small Intestine Diseases

15 Small Intestine Diseases



Anatomy of the Small Intestine



image

Greater Omentum and Abdominal Viscera



Duodenum



• See Chapter 10, Gastroduodenal Diseases.


Jejunum



• 40% of small intestine

• Few large vascular arcades (loops)

• Long vasa recta

• Large, tall, and closely packed plicae circulares

• Less fat in mesentery than ileum

• Locus of maximum water (90%) and nutrient absorption, except for B12, bile acids, iron, and folate

• 95% of water absorbed


Ileum



• 60% of small intestine

• Many small vascular arcades (loops)

• Short vasa recta

• Large, low, and sparse plicae circulares, none distal

• More fat in mesentery than jejunum

• Maximum absorption of nonconjugated bile acids, with conjugated bile acids absorbed in terminal ileum

• B12 and folate maximally absorbed in terminal ileum


Microscopic Anatomy



image

Jejunum and Ileum: Mucosa and Musculature


• Mucosa
image Epithelium: enterocytes (absorptive), goblet cells, Paneth cells, enterochromaffin cells

image Lamina propria: contains Peyer’s patches
image Lymphoid aggregations with B cells in germinal centers and T cell in interfollicular zones

image Densest patches are in ileum.

image Muscularis mucosa

• Submucosa: strongest layer, connective tissue, Meissner’s plexus (parasympathetic ganglion cells and neuronal network)

• Muscularis
image Inner circular muscle

image Outer longitudinal layer

image Auerbach’s plexus: myenteric neurons and parasympathetic ganglion cells

• Serosa: peritoneum

• Mucosal surface area specializations: microvilli, villi, plica circulares (valvulae conniventes)

• Total absorptive surface for water and nutrient transfer: 200-550 cm2

• Water and nutrients absorbed across mucosa


Endocrine Gut Functions



• Cholecystokinin (CCK): secreted by cells of proximal intestine

• Secretin: secreted by S cells of proximal intestine

• Motilin: secreted by M cells of proximal intestine

• Somatostatin (SMS): secreted by D cells throughout gut

• Peptide YY (PYY): secreted by L cells of distal intestine

• Glucagon-like peptide 2 (GLP-2): secreted by L cells of distal intestine

image

Nerves of Small Intestine



Innervation



• Parasympathetic: vagus
image Preganglionic fibers: posterior branches of right and left vagus distributed through celiac and superior mesenteric plexus

image Ganglion cells are located in myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses.

• Sympathetic
image Preganglionic fibers from T8-T10 lateral column distributed via splanchnic nerves to celiac and superior mesenteric ganglia

image Postganglionic fibers distributed through celiac and superior mesenteric plexuses along arterial branches

• Sensory fibers, general visceral afferent
image Vagal afferents distributed through celiac and superior mesenteric plexuses

image Segmental afferents travel back (parallel to sympathetics) through celiac and superior mesenteric plexuses and splanchnic nerves to dorsal root ganglia and thoracic spinal cord segments.


Vessels and Lymphatics



image

Arteries of Small Intestine

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  4. Liver Diseases

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Aug 12, 2016 | Posted by in ANATOMY | Comments Off on Small Intestine Diseases

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