3 Esophagus, Stomach, Small Intestine

Esophagus

Develops as a muscular tube, about 25 cm long in adults, which transports swallowed material from the pharynx to the stomach.

Nonkeratinized stratified squamous epithelium

Type of tissue in the esophageal mucosa

Esophageal glands

lubricate and protect the mucosa

Esophageal cardiac glands

secrete additional mucus in the esophagus

Swallowing

Begins with voluntary muscle action but finishes with involuntary peristalsis.

skeletal muscles, skeletal and smooth muscle fibers, smooth muscle

In approximately the upper one-third of the esophagus, the _____ consists exclusively of _______ like that of the tongue. The middle portion of the esophagus contains a combination of _____ and _____, and the lower third the muscularis has exclusively ______

Stomach

greatly dilated segment of the digestive tract

Chyme

Viscous mass of ingested food and contents

Lipase

Digestion of triglycerides begin with a secreted _____

Pepsin

Initial digestion is promoted by what enzyme?

cardia, fundus, body, and pylorus

Four major regions make up the stomach. What are these?

Cardia

makes up a narrow transitional zone, 1.5-3 cm wide, just beyond the esophagus

Pylorus

denotes the funnel-shaped region opening into the small intestine.

Cardia and pylorus

Both these regions have mucous glands primarily and are histologically similar.

Fundus and body

have similar microscopic structures and contain gastric glands releasing acidic gastric juice.

Rugae

The mucosa and submucosa of the empty stomach form large, longitudinally directed folds called ______ which flatten when the stomach fills with food

Simple columnar epithelium

Mucosa of stomach has what type of tissue?

gastric pits

The mucosa of the stomach wall contains invaginations called _____

Gastric glands

Gastric pits lead to _____

Surface mucous cells

Line the lumen and gastric pits and secrete a thick, highly viscous, and adherent mucous layer, which is rich in bicarbonate ions and protects the mucosa from both the abrasive effects of food and the corrosive effects of stomach acid.

Muscularis mucosae

Thin layer of smooth muscle which separates the mucosa from the underlying submucosa

Gastric glands

In the fundus and body, ____ fill most of the mucosa, with several such glands formed by branching at the neck of each gastric pit

Mucous neck cells

Present mainly as clusters but also singly among the other cells in the necks of gastric glands and include many progenitor and immature surface mucous cells

Parietal or oxyntic cells

Produce hydrochloric acid (HCl) and occur scattered among the mucous neck cells and throughout deeper parts of the gland.

intracellular canaliculus

A striking and unique ultrastructural feature of an active parietal cell is a deep, circular invagination of the apical plasma membrane to form an _______

Canalicular lumens

In the _____, the H+ and Cl – ions combine to form HCl

Intrinsic factor

Glycoprotein required for uptake of vitamin B12 in the small intestine.

Chief or zymogenic

Predominate in the deeper regions of gastric glands and have all the characteristics of active protein secreting cells.

Pepsinogen

Precursor of pepsin produced by chief cells

Gastric lipase

Chief cells produce ___ which digests many lipids

Enteroendocrine cells

Scattered among the epithelial cells deep in gastric glands, sense signals in the lumen of the gut and secrete factors with endocrine or paracrine functions

Serotonin

In the fundus, small enteroendocrine cells secreting ______ (5-hydroxytryptamine) become localized at the basal lamina of the gastric glands

G cells

What cells produce gastrin?

Amine Precursor Uptake and Decarboxylation

Digestive system cells are collectively called ____.

Cardiac glands and pyloric glands

In the cardia and pylorus regions of the stomach, the mucosa also contains tubular glands, with long pits, branching into coiled secretory portions, called ____ and ____ respectively

Submucosa

consists of connective tissue with large blood and lymph vessels and many lymphoid cells, macrophages, and mast cells.

Pyloric sphincter

At the pylorus the circular muscle layer thickens greatly to form the

Small intestine

Digestive processes are completed and the products of digestion (nutrients) are absorbed by cells of the epithelial lining.

Plicae circulares

Viewed macroscopically the lining of the small intestine shows a series of permanent circular or semilunar folds, the ________

jejunum

Plicae circularis best develops in _____.

Villi

Projecting into the lumen densely cover the entire mucosa of the small intestine

Simple columnar epithelium ; enterocytes; goblet cells

Villi consist of _____ epithelium of absorptive cells called _______ with many _____ cells.

intestinal glands or crypts (Crypts of Lieberkuhn)

Openings of short tubular glands called _____ occur between the villi, with the epithelium lining each crypt continuous with that covering the villi

Enterocytes

Tall absorptive cells of the small intestine

striated (or brush) border

The apical end of each enterocyte displays a region called _______

Goblet cells; mucins

Secrete specific antibacterial peptides and glycoprotein _____, which undergo hydration to form a mucus layer that functions to protect and lubricate the lining of the intestine.

Paneth cells

located in the basal portion of the intestinal crypts below the stem cells, develop as exocrine cells with large, eosinophilic secretory granules in their apical cytoplasm

Lysozyme, phospholipase A2, and hydrophobic peptides

Substances that Paneth cells produce

Microfold (M) cells

develop as unique cells specialized for transepithelial transport of particles and microorganisms, located mainly in the ileum’s mucosa overlying the lymphoid follicles of Peyer patches.

Enteroendocrine cells

Many of these exemplify the “open” type of enteroendocrine cells, in which the apical end of the cell contacts the intestinal lumen