Stomach Mucosa and Gastric Glands

Stomach Mucosa

• Lined by simple columnar epithelium and contains branched tubular gastric glands.

Gastric Gland Cells

• Simple columnar epithelium: mucous surface secreting and protects the stomach wall from HCL (pH 2.5).
• Chief cells (zymogen cells): produce pepsin for protein digestion.
• Parietal (oxyntic) cells: secrete hydrochloric acid and intrinsic factors.
• Gastric enteroendocrin cells: coordinate blood flow and smooth muscle movement.
• Stem cells: regenerate damaged cells.

Stomach Layers

• Mucosa: consists of three parts - epithelial lining, lamina propria of C.T. with fundic gland, and muscularis mucosa.
• Submucosa: contains Meissner's plexus of nerves and lymphatics, and fundic glands.
• Muscularis externa: smooth muscle layer with Auerbach's plexus, responsible for peristaltic contractions.
• Serosa: peritoneal or C.T. covering.

Function of Stomach

• Mixes food with gastric juice (HCL, mucosa protection, pepsin enzyme, and intrinsic factor for vitamin B12 absorption).
• Absorbs water and electrolytes.

Pylorus

• Muscular sphincter.
• Pylorus gland: contains mucus, stem cells, and enteroendocrin cells.
• Short, wide gastric pit.

Small Intestine

• Function: absorption of food.
• Length: 6 meters.
• Mucosa: forms villi, crypts, and simple columnar (absorptive) cells with goblet cells that lubricate food.
• Submucosa: contains mucous glands (Brunner's glands) and Peyer's patches of lymphatic nodules.
• Muscularis: smooth muscles with Auerbach's plexus, performs peristaltic contractions.
• Serosa: simple squamous peritoneum.

Small Intestine Mucosal Cells

• Surface simple columnar absorptive cells on villi with microvilli.
• Goblet cells.
• Paneth (exocrinocytes) cells: secrete antibacterial lysozymes and tumor necrosis factor.
• Caveolated cells: present in crypt.
• M-cells: transporting in crypt.
• Intestinal renewal stem cells: in base of crypt.
• Entero-endocrine cells: in crypt.

Large Intestine

• Function: absorbs water and stores fecal or residual part during defecation.
• No villi, only crypts.
• Mucosa: simple columnar (absorptive) cells with many goblet cells to soften stool.
• Enteroendocrin and stem cells.
• Submucosa: Meissner's plexus.
• Muscularis externa: teniae coli with three separate longitudinal ribbons.
• Serosa: fat cell appendices epiploicae and appendix.

The Digestive System

• The digestive system, also known as the gastrointestinal tract or alimentary canal, consists of the oral cavity, digestive tract, and digestive glands.

Oral Cavity

• The oral cavity consists of the lips, tongue, palate, and cheeks.
• The lips have three histological regions: the outer surface (thin hairy skin), the inner surface (mucous membrane), and the red margin (vermilion).
• The color of the lip margin can indicate health conditions: pale red (anemia), blue (cyanosis), or red (healthy).

The Tongue

• The tongue is a mass of lingual striated muscle covered by mucosa, which helps mix food during mastication and swallowing.
• The tongue has two surfaces: the dorsal surface (rough, covered by partially keratinized stratified squamous epithelium) and the ventral surface (smooth, covered by non-keratinized stratified squamous epithelium).
• There are four types of lingual papillae on the tongue:
• Filiform papillae (most common, with partially keratinized stratified squamous epithelium)
• Fungiform papillae (reddish in color, with few taste buds)
• Foliate papillae (on each side of the tongue)
• Vallate or circumvallate papillae (rich in taste buds, with Von Ebner glands)

Taste Buds

• Taste buds are neuro-epithelial organs found on the tongue, containing three layers: receptor taste cells (with microvilli), supporting cells, and basal cells.
• Taste buds have a taste pore where food enters to be tasted.

The Esophagus

• The esophagus is a 25 cm long muscular tube that connects the oral cavity and stomach, conducting food without digesting it.
• The esophageal wall consists of four layers: mucosa, submucosa, musculosa, and adventitia.
• The mucosa layer has three sublayers: non-keratinizing stratified squamous epithelium, lamina propria with cardiac glands, and muscularis mucosa.
• The submucosa layer contains esophageal glands that secrete mucus.
• The musculosa layer is composed of skeletal muscle in the upper 1/3, mixed in the middle 1/3, and smooth muscle in the lower 1/3.
• The adventitia layer is connective tissue covering the esophagus with blood vessels and lymphatic vessels.

The Stomach

• The stomach is a sac-like, muscular, and extended organ, acting as the first station for digestion.