Histology Lecture 3b -- Salivary Glands Flashcards
From what are glands derived?
Ectoderm or endoderm layers
3 steps in the development of glands
- The epithelium invaginates into the underlying connective tissue, bringing the epithelial basal lamina with it
- The invagination develops a lumen that communicates to the original surface
- The invagination differentiates into a secretory unit as its furthest part and a duct that connects the secretory unit to the epithelium
Define exocrine glands
Product made by the secretory unit of the gland and is delivered by the duct to the surface from which the invagination occurred
Define endocrine glands
The duct loses its connection with the secretory unit and the unit secretes into the connective tissue around it and ultimately into the blood vessels (ductless glands)
3 classes of exocrine glands based on the shape of secretory unit
- Tubular
- Acinar
- Alveolar
Define tubular exocrine glands
Unifrom diameter for the secretory unit and the duct (i.e. sweat gland)
Define acinar exocrine glands
A grape-like secretory unit is attached to a duct (i.e. salivary glands)
Define alveolar exocrine glands
A flask-shaped secretory unit, but is not often used because it can be confused with an alveolus of the lung
2 classes of exocrine glands based on the relationship between secretory unit and duct
- Simple = one secretory unit to one duct (i.e. sweat gland)
- Compound = a branching tree-like system with secretory units at the ends of all the branches (i.e. salivary glands)
4 classes of glands based on the manner in which cells secrete
- Holocrine
- Merocrine
- Apocrine
- Cytocrine
Define holocrine glands
- Entire cell is the secretion product
- The gland cells become filled with the secretory substance and the cell dies and disintegrates as it forms the secretion product
- Example = sebaceous glands of the hair
Define merocrine glands
- Secretion based on production of membrane-bound secretory granules that are exocytosed or secreted to the outside of the cell
- No loss of cell material as membrane is derived from the Golgi apparatus and retrieved by fusion with cell membrane
- Secretory product is made de novo for export
- Example = all salivary glands
Define apocrine glands
- A small part of the cell cytoplasm is lost as part of the secretion
- Example = matrix vesicles from hypertrophic chondrocytes in the cartilaginous growth plate
Define cytocrine glands
- Part of one cell containing the secretory granule is phagocytosed by another cell
- Example = melanosomes produced by melanocytes phagocytosed by keratinocytes in the skin
3 classes of glands based on the type of secretion product
- Serous
- Mucous
- Mixed
Define serous glands
Producition of a watery secretion, usually glycoproteins that are enzymes
Define mucous glands
Production of a secretion that is high in carbohydrates (about 50% protein, 50% carbs)
Define mixed glands
Acinus is composed of both serous and mucous cells, or there is a mucous acinus with a serous demilune
Describe the arrangement of serous cells
Usually arranged as acinar secretory units. Their pyramidal shapes are arranged in a spherical unit with the apices of the cells meeting to form a small lumen
How may the luminal surface area of serous glands by increased?
Interncellular canalicules between serous cells
Describe the cell base of serous cells
- Basophilic
- Occupied by abundant parallel cisternae of rER
Describe the apex of serous cells
- Filled with eosinophilic zymogen granules
- Under certain conditions of poor fixation, the granules may be dissolved, leaving empty vacuoles
Describe the nuclei of serous cells
- Spherical and located towards the base of the cells, usually surrounded by rER
- Prominent nucleoli (high protein synthesis)
What drains the acini of serous glands?
Intercalated duct
How are mucous cells arranged?
- As acinar or tubular secretory units
- Cuboidal cells arranged around a large lumen
Describe the rim and base of mucous cells
- Rim of darkly stained cytoplasm rich in rER at the base
- Flattened dark-stained nuclei at base
Describe the apex of mucous cells
Filled with large mucinogen droplets or granules, whose proteins have a high sugar content
Why might it be hard to see the lumen of a mucous gland despite it being larger than a serous gland?
The secretory product of mucous glands, mucin, fills the large lumen when released and hydrated
How are mucous acini drained?
By intercalated or larger ducts
Describe the distribution of cells in mixed acini
Most often composed of a mucous acinus capped by a serous demilune (a cap of serous cells sitting on a mucous acinus)
What empties a mixed acinus?
The secretions enter a common duct, which may be intercalated
Describe what immediately surrounds all secretory units of glands and why
Since all secretory units are epithelially derived, they are surrounded by a basal lamina, which is continuous with the duct and ultimately the epithelium of origin
What lies between basal lamina and the base of secretory units in some acini?
Epithelial cells with contractile properties (myoepithelial cells) and therefore contain actin and myosin