4 layers of the GI tract

Mucosa – a mucous membrane composed of a layer of epithelium in direct contact with GI tract contents, lamina propria, and muscularis mucosae. It lines the inside of the stomach as surface cells and forms numerous tiny invaginations called gastric pits.

Submucosa – a thick layer of connective tissue that is flexible and mobile. Aside from rich vasculature and lymphatics, this layer also holds the submucosal plexus which carries parasympathetic intervention to the blood vessels and smooth muscle of the stomach walls

Muscularis – smooth muscle located deep in the submucosa which consists of 3 layers – oblique, middle circular, and outer longitudinal. It produces movements required for mechanical digestion

Serosa – consists of a simple squamous layer called mesothelium and underlying connective tissue. This lubricates the outer wall of the stomach and ensures its movement in the abdominal cavity.

Wall of the stomach with rugae

Rugae is the lining of the stomach at rest which forms into thick, velvety folds. These contain microscopic invaginations called gastric pits, that each open into gastric glands. It allows for expansion of the stomach after the consumption of food and liquid.

Tooth

A tooth is composed of four dental tissues. Three of them – enamel, dentine, and cementum – are hard tissues. The 4th tissue is called the pulp, which contains nerves, blood vessels, and connective tissue. Besides being essential for chewing, the teeth play an important role in speech. A normal adult has 32 teeth.