Only epithelium and lamina propria, no muscularis mucosae. The epithelium is stratified squamous epithelium with keratinization only in the hard palate. The connective tissue of the lamina propria protrudes into the epithelium to form papillae, which are rich in capillaries, so the mucosa is red. There are many sensory nerve endings in the nipple and epithelium. The epithelium at the floor of the mouth is thin and highly permeable, which is conducive to the absorption of certain chemicals. There are minor salivary glands in the lamina propria, and the lamina propria is connected to the skeletal muscles or periosteum.

Lingual tonsils

tongue papilla

Dentin

enamel

cementum

dental pulp

periodontal ligament

gums

Mucous membrane

Muscle layer

adventitia

Stratified squamous epithelium, the lamina propria is a fine connective tissue, and forms papillary epithelium. A small number of mucosal gonads can be seen in the lamina propria at the upper and lower ends of the esophagus. The mucosal muscle layer is composed of longitudinal smooth muscle bundles.

The connective tissue contains more mucinous esophageal glands, and the ducts penetrate the mucosa and open into the esophageal lumen.

The upper third of the inner circular and outer longitudinal layers is skeletal muscle, the lower third is smooth muscle, and the middle third is mixed. The inner circular muscles at both ends of the esophagus are slightly thicker, forming the upper and lower esophageal sphincters respectively.

for fiber membrane

epithelium

lamina propria

muscularis mucosa

Dense connective tissue, containing thick blood vessels, lymphatic vessels and nerves, and groups of fat cells can also be seen

The muscular layer of the stomach wall is thicker and generally consists of three layers of smooth muscle: internal oblique, middle circular, and external longitudinal smooth muscles. serous membrane

Mucous membrane

submucosa

muscularis and adventitia

The lumen is small and irregular, the large intestine glands are short and few, and the lamina propria is rich in lymphoid tissue. A large number of lymph nodes can be continuously layered and protrude into the submucosa, resulting in incomplete mucosal muscle layer, thin muscle layer, and outer covering. Serosa

The two ends of the digestive tract (oral cavity, pharynx, esophagus and anus) are composed of stratified squamous epithelium, whose main function is protection, while the rest are single-layer columnar epithelium, whose main function is digestion and absorption.

Loose connective tissue has more cellular components, denser fibers, and rich capillaries and lymphatic capillaries. The gastrointestinal lamina propria is rich in glandular and lymphoid tissue

It is a thin layer of smooth muscle. Its contraction can promote the discharge of glandular secretions and blood circulation in the lamina propria, which is beneficial to the absorption and transportation of substances.

serous acini

mucinous acini

mixed acini

Leap tube

striate duct

interlobular duct and common duct

The largest salivary gland in the human body is a pure serous acini with long intercalary ducts and short striate ducts. There are many fat cells in the glandular interstitium, and the secretion contains salivary amylase.

It is a mixed gonad with many serous acini, short intercalary ducts, well-developed striate ducts, secretions containing less salivary amylase and more mucus.

Mixed gonads, mainly composed of mucinous acini and mixed acini, without intercalary ducts, short striatal ducts, and the secretions are mainly mucus