1. Parotid Gland
As an exocrine gland, the parotid gland is composed of a lobular system of branching ducts that are separated by connective tissue septa. Like its fellow major salivary glands, the parotid gland is also surrounded by a dense connective tissue capsule. It also has a pseudocapsule arising from the deep investing layer of the cervical fascia. It produces watery, serous saliva as opposed to seromucous secretions like the other two major salivary glands, or mucous secretions like the minor glands.
The parotid gland is rich in serous cells, which are pyramidal cells with circular nuclei. These cells are polarized and rich in rough endoplasmic reticulum and secretory granules towards the apex of the cells. The cells are tightly adhered to each other at the respective tight junctions and are arranged in grape-like clusters known as serous acini (singular, “acinus”). They are also rich in alpha-amylase, which promotes hydrolysis of carbohydrates and protein abundant in proline.

2. Lip

The external surface of the lip:
• is covered with thin skin formed of epidermis and dermis with the associated hair follicles, sebaceous glands and sweat glands.
• underneath the skin, bundles of circular skeletal muscle of the orbicularis oris ms., are present.
The internal surface of The lip:

Lines by mucous membrane which is formed of:
• stratified squamous non-keratinized epithelium (thicker than that of epidermis of the external surface)
• lamina propria: formed of C.T. contain; Bl.Vs. , lymphatic Vs. , nerves and group of labial minor salivary glands (mucous acini)

The Vermilion (red) margin of the lip:
is continuous with the thin skin of the ext. surface of the lip covered by modified skin characterized by:
• transparent epithelium; formed of stratified squamous non-keratinized epithelium without hair follicles, sebaceous glands or sweat glands.
• deeply and heavily vascular dermal papillae (giving the red color of the lip margin), highly supplied with nerves.

3. Esophagus

Esophageal Mucosa
• Esophageal Epithelium: The esophageal epithelium is an unkeratinized stratified squamous epithelium designed to protect the esophagus as it conducts food downwards.
• Esophageal Lamina Propria: Fairly thin and contains a few lymphoid aggregates
• Esophageal Muscularis Mucosa: Is also fairly thin and insignificant

Esophageal Submucosa
• The collagenous esophogeal submucosa is fairly loose and can be significantly distended in order to accommodate passing food boluses. Small glands are also visible in this layer that secrete mucus which lubricates the passage of food.

Esophageal Muscularis Propria:
• The muscularis of the esophagus is the most prominent layer and allows for powerful peristalsis. The upper third of the esophageal muscularis is composed of skeletal muscle cells while the lower third is made of smooth muscle cells.

Esophageal Adventitia:
• Is a relatively thin layer histology layer of collagenous tissue which invests the entire esophagus.