HISTOLOGY: General His. of Alimentary Canal; His. of GI Tract

MUCOSA: What epithelium types are found in the mucosa of the GI tract?

- *Stratified squamous*: tough epithelium found in mouth, esophagus, & anus - Simple columnar: found in the rest of the GI tract

General features of *MUSCULARIS EXTERNUS*?

- Contains same VAN-L of the mucosa and submucosa. Serves muscles and deeper structures - Contains Auerbach's plexus (myenteric nerves) - both sympathetic and parasympathetic nerves

MUCOSA: Function of the *surface epithelium* and types of cells in the epithelium?

- Function: *secretes* enzymes and/or *absorbs* nutrients - Specialized (*goblet*) cells secrete mucous onto cell surfaces - *Enteroendocrine cells* - secrete *hormones* controlling organ functions

What is the *SEROSA*?

- The *SEROSA* is an example of a serous membrane (visceral & parietal membranes). It is the "wrapper" that covers all organs and walls of cavities that are not open to the outside of the body. - It secretes *serous fluid* and consists of *connective tissue* covered with *simple squamous epithelium*

Difference between *SEROSA* & *ADVENTITIA*? Organs covered with serosa / adventitia?

- The *adventitia* is a CT layer which *binds structures together* rather than reducing friction between them. - In the GI tract, *intraperitoneal organs* (stomach, spleen) are covered in serosa. The *retroperitoneal organs* (esophagus, rectum) are covered in adventitia (loose CT)

What are the general features of the *SUBMUCOSA*?

- The *submucosa* is loose loose connective tissue that contains the same blood vessels (VAN-L), glands, and lymphatic tissue (GALT/MALT) as the lamina propria of the mucosa. - Also contains meissner's plexus (nerves) - parasympathetic innervation responsible for vasconstriction and vocal movement performed by muscularis mucosa (smooth muscle)

Stomach: Mucosa - Secretory cells of gastric pits and their function: *parietal cells, chief cells*

1. *Parietal cells*: secretes *HCl* to destroy harmful bacteria in food, reacts with pepsinogen; *gastric intrinsic factor*, a protein necessary for absorption of vitamin B12 2. *Chief cells*: secrete *pepsinogen* which is activated into pepsin when it encounters acid. Begins the breakdown of proteins in food. *Gastric lipase* functions in fat digestion

What are the 3 sublayers of the *MUCOSA*?

1. Surface/lining epithelium 2. Lamina proper - CT below basement membrane 3. Muscularis internus (mucosae) - smooth muscle

Components of the *MUSCULARIS EXTERNA*?

1. The *muscularis externa* is made up of *skeletal muscle* which is found in the mouth, pharynx, upper esophagus, and anus. It's voluntary muscle that provides control over swallowing and defecation. 2. The ME also contains *smooth muscle* which is made up of *inner circular* and *outer longitudinal* fibers. This muscle is involuntary which propels food along tract via peristalsis/segmentation

Stomach: Mucosa - Secretory cells/tubular glands of gastric pits and their function: *mucous cells, other cells/glands*

3. *Mucous cells*: mucous secreted contains a bicarbonate-buffer that protects the walls of stomach from effects of acid and pepsin. Protects stomach against self digestion. 4. *Other cells / glands*: GALT / MALT, *enteroendocrine cells*(hormone-secreting cells), undifferentiated stem cells for rapid replacement of epithelium lining due to harsh acidic environment

Label the following structure(s) on the diagram: mucosa

A

Label the following structure(s) on the diagram: submucosa

B

Label the following structure(s) on the diagram: muscularis externa

C

Label the following structure(s) on the diagram: outer serosa

D

HISTOLOGY OF THE GI TRACT: *Esophagus*

Histology: 1. *mucosa*: keratinized *stratified squamous epithelium* with Goblet cells (mucus), MALT 2. *submucosa*: VAN-L, vessels, nerves, lymph tissue 3. *muscularis externa*: consists of skeletal muscle superiorly and smooth muscle (inner circle and outer longitudinal layers) inferiorly - smooth composes remaining musculature in the GI tract. 4. *serosa*: no serosa, adventitia (external layer of the esophagus)

HISTOLOGY OF THE GI TRACT: *Stomach*

Histology: 1. *mucosa*: varies depending on regions of stomach (epithelial cell types: mucous cells, parietal, chief cells, G-cells, undiferentiated stem cells) 2. *submucosa*: varies 3. *muscularis externus*: three layers 4. *serosa*: serosa

MUCOSA: Immune function of *lamina propria*?

Lymphatic nodules or *GALT* (gut associated lymphoid tissue) or *MALT* (mucosa associated lymphoid tissue) defend against invasion of bacteria and other microorganisms in the alimentary canal

What are the 4 basic tissue layers found throughout the alimentary canal?

The 4 basic tissue layers of the alimentary canal from the lumen outward: 1. Mucosa 2. Submucosa 3. Muscularis Externa 4. Serosa (or Adventitia)

Stomach: Mucosa - Internal surface of stomach

The internal surface of the stomach is lined with *simple columnar epithelium* that secretes mucous and is dotted with *gastric pits*

Stomach: Muscularis Externa - Layers of Muscle

The muscularis externa has three layers of muscle: 1. Outer: longitudinal muscle layer 2. Middle: circular muscle layer 3. Innermost: oblique muscle layer

MUCOSA: What is the function of the *muscularis mucosae (internus)* in the mucosa?

The muscularis mucosae is a thin layer of of *smooth muscle* that causes folds to form in mucosal layer which increases local movements

MUCOSA: Components of *lamina propria*?

Thin layer of loose *connective tissue* that contains *blood vessels* (veins, arteries, nerves, lymph vessels) and *lymphatic tissue* - Blood vessels nourish the epithelium lining; absorb digested nutrients