parotid
The largest, slightly triangular wedge-shaped, is located in the anterior lower part of the external auditory canal, the posterior surface of the masseter muscle, and the posterior part of the gland is particularly thick, reaching the posterior mandibular fossa. The parotid duct starts from the front end of the gland near the upper edge, passes through the surface of the masseter muscle about one finger below the zygomatic arch, bypasses the front edge of the masseter muscle and turns deeper, and passes through the buccal muscle opening to the buccal mucosa, where a mucosal nipple is formed, facing the maxillary second molar.
submaxillary gland
Slightly oval, located in the mandibular triangle between mandibular body and hyoid muscle. The submandibular gland duct originates from the inner surface of the gland, extends along the deep surface of the mucosa at the floor of the mouth, and opens at the hypoglossal nerve caruncle.
sublingual gland
Smallest, slender, slightly flat. Located on the deep surface of the mucosa at the bottom of the mouth. There are about 5- 15 tubules in the excretory duct, which directly open to the mucosa at the mouth floor. Another part of the large duct often merges with the submandibular gland duct or opens separately at the hypoglossal nerve mound.
Salivary glands secrete saliva, which can moisten the mouth and facilitate swallowing and speaking. Human saliva contains amylase, which can preliminarily decompose starch in food.
Large salivary gland
There are three pairs of large salivary glands: parotid gland, submandibular gland and sublingual gland, and their ducts open in the mouth.
(A) the general structure of salivary glands
Salivary gland is a compound tubular vesicular gland with thin sac. The glandular essence is divided into many lobules, which are composed of terminal branch ducts and acini.
1. The alveoli are cystic or tubular, and consist of single-layer cubic or conical gland cells, which are the secretory parts of glands. There are myoepithelial cells between glandular cells and basement membrane and between some ductal epithelium and basement membrane. The cells are flat and have protrusions, and actin microfilaments are contained in the cytoplasm. The contraction of myoepithelial cells contributes to the excretion of acinar secretions. There are three types of acinus: serous, mucinous and mixed.
(1) Serous gonad: It is composed of serous gonad cells. In HE stained sections, the cytoplasm was deeply stained. The basal cytoplasm is basophilic, and there are many rough endoplasmic reticulum and ribosomes here under electron microscope. The nucleus is round and located at the base. There are many eosinophilic secretory granules in the apical cytoplasm, and the serous gonadal vesicles secrete thinly and contain salivary amylase.
(2) Mucous gonad: It is composed of mucinous gonad cells. In HE stained sections, the cytoplasm was lightly stained and secretory granules could not be displayed. The nucleus is oblate and located at the bottom of the cell. Under electron microscope, there are coarse secretory granules (mucinogen granules) at the top of cytoplasm. Mucous gonad vesicles secrete viscous, mainly mucus (glycoprotein).
(3) Mixed gonad: It consists of serous gonad cells and mucinous gonad cells. The common morphology is that acinus is mainly composed of mucinous gonad cells, and several serous gonad cells are located at the bottom of acinus or attached to the end of acinus, and the cross section is arranged in a half-moon shape, so it is called a half-moon shape. Semilunar secretions can be released into the acinar cavity through mucinous intercellular tubules.
2. Catheter is an epithelial catheter with repeated branches, which is the excretory part of gland and its end is connected with acinus. Salivary duct can be divided into the following sections:
(1) Sandwich catheter: directly connected with acinus, with thin diameter and single-layer cubic or single-layer flat epithelium.
(2) Transverse duct: or secretory duct, connected with intercalated duct. The wall of the catheter is a single layer of high columnar epithelium, with the nucleus at the top of the cell and the cytoplasm being eosinophilic. Vertical stripes can be seen at the cell base, and folds of plasma membrane and mitochondria can be seen vertically arranged under electron microscope. This structure increases the surface area of cell basement and promotes the transport of water and electrolyte between cells and interstitial fluid. Epithelial cells of striated duct can actively absorb Na+ in secretion, expel k+ into lumen, and re-absorb or expel water, so the electrolyte content and saliva quantity in saliva can be adjusted.
(3) Interlobular duct and common duct: the striated ducts meet to form interlobular ducts, which run in interlobular connective tissue. The interlobular duct is thick, and the wall of the duct is pseudostratified columnar epithelium. The interlobular ducts gradually converge and thicken, and finally one or several main ducts open to the oral cavity, and the ducts near the oral cavity gradually become stratified epithelium, which is continuous with the oral cavity epithelium.
Salivary gland protuberance
Salivary glands are hidden in the upper part of the throat, located on a cartilage called eustachian tube bulge, with an average length of about 1.5 inches (3.9 cm).