Sabiston Anatomy Flashcards
(19 cards)
Anatomy , Lengths
duodenal length 20 cm
jejunal length at 100 to 110 cm
ileal length at 150 to 160 cm.
Anatomy , Jejunum Vs Ileum
jejunum :
larger circumference, thicker
can be identified during surgery by examining mesenteric vessels, only one or two arcades send out long, straight vasa recta to the mesenteric border
Ileum : blood supply to the ileum may have four or five separate arcades with shorter vasa recta
Mucosa of Small bowel
characterized by transverse folds (plicae circulares), which are prominent in the distal duodenum and jejunum
Blood Supply to Duodenum
Superior mesenteric artery > distal duodenum.
The celiac artery > proximal duodenum
Blood Supply to Small Bowel
-superior mesenteric artery (except for the proximal duodenum )
-SMA > courses anterior to the uncinate process of the pancreas and the third portion of the duodenum, it divides to supply the pancreas, distal duodenum, entire small intestine, and ascending and transverse colons.
-abundant collateral blood supply provided by vascular arcades coursing in the mesentery
Innervation
parasympathetic and sympathetic divisions of the autonomic nervous system
The parasympathetic fibers > the vagus nerve, traverse the celiac ganglion and influence secretion, motility, and probably all phases of bowel activity.
The sympathetic fibers > splanchnic nerves > located in a plexus around the base of the superior mesenteric artery
Location of myenteric (Auerbach) plexus and (Meissner plexus)
myenteric (Auerbach) plexus > muscularis propria (between the muscles)
(Meissner plexus) > networks of lymphatics, arterioles, and venules > in Submucosa
lamina propria Location and Role
between the epithelial cells and muscularis mucosae
Contains > plasma cells, lymphocytes, mast cells, eosinophils, macrophages, fibroblasts, smooth muscle cells, and noncellular connective tissue
protective role > rich supply of immune cells
Main functions of the crypt epithelium and Villous Epithelium
crypt epithelium > cell renewal, exocrine, endocrine, water, and ion secretion
villous epithelium > digestion and absorption.
What are the Four main cell types are contained in the mucosal layer
(i) absorptive enterocytes
(ii) goblet cells, which secrete mucus
(iii) Paneth cells, which secrete lysozyme, (TNF), and cryptdins, which are homologues of leukocyte defensin peptides related to the host mucosal defense system
(iv) enteroendocrine cells,produce the gastrointestinal hormone
What is the Main Cell in the Mucosa
Absorptive enterocytes
Function of The brush border of the small intestine
contains the enzymes
lactase, maltase, sucrase-isomaltase, and trehalase
split the disaccharides into their monosaccharides
Transport of the released hexoses (glucose, galactose, and fructose) is by
active transport.
The major routes:
sodium-glucose transporter 1 (SGLT-1), glucose transporter 5 (GLUT-5), and glucose transporter 2 (GLUT-2).
Protein Digestion
Pancreatic trypsinogen is secreted in the intestine by the pancreas in an inactive form > activated by the enzyme enterokinase, a brush border enzyme in the duodenum to an activated form of trypsin.
Bile Acid
-unconjugated bile acids absorbed into the jejunum by passive diffusion
-conjugated bile acids that form micelles are absorbed in the ileum by active transport
-then reabsorbed from the distal ileum and pass through the portal venous system to the liver for secretion as bile.
Vitamins Absorbtion
Calcium > duodenum and jejunum by active transport
facilitated by an acid environment and is enhanced by vitamin D and parathyroid hormone
Iron > as a heme or nonheme component > duodenum by an active process.
total absorption of iron is dependent on body stores of iron and the rate of erythropoiesis
Potassium, magnesium, phosphate, and other ions actively absorbed throughout the mucosa
Vitamin B1 > jejunum by an active process similar to the sodium-coupled transport system for vitamin C.
Vitamin B2 > the upper intestine by facilitated transport.
vitamin B12 > terminal ileum.
derived from cobalamin, freed in the duodenum by pancreatic proteases, binds to intrinsic factor
Vitamin B6 > simple diffusion into the proximal intestine
Motility
Sympathetic activity inhibits motor function
parasympathetic activity stimulates it.
motilin, its peak plasma level during phase III (intense bursts of myoelectrical activities resulting in regular, high-amplitude contractions) of migrating myoelectric complexes
The gut-associated lymphoid tissue is localized in four areas
-Peyer patches > activate and prime B and T cells
-lamina propria lymphoid cells
-Paneth cells
-intraepithelial lymphocytes > unique subtype of T cells.
major protective immune mechanisms for the intestinal tract is
the synthesis and secretion of IgA.
produced by plasma cells in the lamina propria
