Anorectal junction (4x objective lens)

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This image is a composite of 20 low magnification images of the anorectal junction of a monkey. Uppermost in the image is the anal orifice (AO), which is the opening between the outside world and the anal canal (AC). It is lined by normal skin that is continuous with the integument that covers the external surface of the body. The skin is composed of a layer of epidermis (Ep), with a surface of keratinized cells, resting on a dermis (De) of dense connective tissue. Hair follicles (HF) and sweat glands (SG) are also present. The anal orifice is bounded by the external anal sphincter (EAS), a muscular ring composed of numerous fascicles of skeletal muscle. The terminal portion of the anal canal (AC) proper is also lined by epidermis. About half way through the anal canal there is a transition from keratinized stratified squamous epithelium (KSSE) to the anal mucosa (AM), consisting of nonkeratinized stratified squamous epithelium (NSSE) resting on a lamina propria (LP) of loose connective tissue. Within the connective tissue of the anal canal are large, thin-walled veins called the hemorrhoidal veins (HV). Beneath the connective tissue of the anal canal is the internal anal sphincter (IAS), composed of smooth muscle, which is a continuation of the inner (circular) layer of the muscularis externa of the rectum. At the anorectal junction (ARJ), which marks the point where the anal canal connects to the rectum (Re), the anal mucosa becomes the rectal mucosa (RM), which is structurally similar to the mucosa of the colon. It consists of: (1) a mucosa (Mu) of simple columnar epithelium composed of goblet cells and enterocytes (absorptive cells) supported by a lamina propria of loose connective tissue and bounded by a muscularis mucosae (MM). Like the rest of the intestine, the mucosa is characterized by the presence of tubular glands, called crypts of Lieberkuhn, which are seen both in longitudinal and cross section; (2) a submucosa (SM) of loose connective tissue; and (3) a muscularis externa (ME) consisting of an inner circular layer and an outer longitudinal layer. Aggregations of lymphoid cells (LC) may be found in the connective tissue of the anal or rectal mucosae.

Stain = H&E

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	the mucosa	the anal epidermis	anal orifice	the anal sphincter

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