Small Intestine and Associated Structures

A.    Gross Anatomy of Small Intestine

1.     It extends from the pyloric sphincter to the ileocecal valve where it joins the large intestine. It has three subdivisions: the duodenum, the jejunum, and the ileum.

        B. Microscopic Anatomy of Small Intestine

               1. Modifications for absorption

        a. It is highly adapted for absorption with three microscopic modifications: plicae

circulares, villi, and microvilli [brush border]

2. Histology of the wall

        a. Simple columnar epithelial tissue with tight junctions and goblet cells

        b. Theintestinal crypts, or the crypts of Lieberkühn, secrete intestinal juice that

serves as a carrier fluid for absorbing nutrients from chyme.

c. Enteroendocrine cells and the enterogastrones secretin and cholecystokinin

        d. Intraepithelial lymphocytes [IELs]

        e. Paneth cells: defensins and lysozyme

                f. Peyer's patches: part of GALT

C.   The liver

               1. Functions [more than 200 functions!]

                        a. Metabolic regulation: regulation of blood composition,  removes and stores              nutrients, mobilizes stored reserves, performs synthetic activities, plays a role in                  carbohydrate, lipid & protein metabolism, waste removal, vitamin [A, D, E, K &                                B₁₂] and mineral [converts iron reserves to ferritin], drug inactivation

                        b. Hematological regulation: phagocytosis and antigen presentation [Kupffer cells],                                     synthesis of plasma proteins, removal of circulating hormones, removal of                                                    antibodies, removal or storage of toxins

                        c. Synthesis and secretion of bile [mostly water, with minor amounts of ions,                  bilirubin, cholesterol and an assortment of lipids known as bile salts, that function                                    in the emulsification of lipids

               2. Gross Anatomy

        a. Hepatic portal vein

3. Microscopic Anatomy

        a. Hepatocytes, liver sinusoids, Kupffer cells

        D. Gallbladder

        1. Stores and concentrates bile

        E.   Pancreas

               1. Functions: secretion of a watery buffer solution of a pH of 7.5-8.8 and a "bucket full

of enzymes" [pancreatic amylase, lipase, nucleases and proteases]

        F. Regulation of Bile and Pancreatic Secretion and Entry into the Small Intestine

A. Functions

                1.Absorption of water, bile salts, and bacterial-generatedvitamins K, biotin [glucose                           metabolism] & vitamin B₅ (pantothenic acid) [manufacture of steroids and some                             neurotransmitters]

        B. Gross Anatomy

                1. Teniae coli, haustra, &epiploic appendages

                2. Subdivisions: cecum, appendix, colon, rectum, anal canal

                3. Colon: ascending, transverse, descending, sigmoid