Structure, Function of the Salivary Glands: Lesson 55

Function of salivary glands

Saliva has digestive, lubricating and protective functions; as well as important buffering functions

Salivary glands

Exocrine glands in the mouth which produce saliva

Three pairs of major salivary glands and several minor salivary located throughout

the oral mucosa

Major salivary glands in the mouth

parotid, mandibular, and sublingual glands

Minor salivary glands

named according to their location → labial, lingual buccal, palatine, molar and zygomatic

Parotid Salivary Gland

Structurally similar in all species and composed of numerous lobules separated by a thin CT septa

Roughly triangular, relatively thin, and molded around the ventral portion of the auricular cartilage

Occupies a depression between the masseter, the wing of the atlas, and the auricular cartilage.

Parotid salivary gland in the horse

partially overlays the lateral wall of the guttural pouch, and should be considered when using an external surgical approach to the guttural pouch

Image of the parotid gland

Parotid Duct: trajectory and termination varies amongst species

Close proximity to the external carotid artery, maxillary vein and branches of the facial and trigeminal nn. L

The parotid duct terminates on a papilla, located opposite an upper third to fourth cheek tooth

Parotid duct in carnivores and sheep

In carnivores and sheep, it crosses the lateral surface of the masseter muscle

The parotid duct terminates on a papilla, located opposite an upper third to fourth cheek tooth

❑ Dog- opposite premolar 4

Parotid duct in horse, ox, goat and pig

it courses medial to the angle of the jaw and travels along the ventral surface of the masseter muscle

The parotid duct terminates on a papilla, located opposite an upper third to fourth cheek tooth

❑ Horse, small ruminant and pig- 3rd or 4th superior cheek teeth

❑ Ox- opposite the 5th superior cheek tooth

Species difference in the parotid duct

Mandibular Salivary Gland

Located close to the angle of the jaw and partially covered by the parotid salivary gland.

largely ovoid gland in carnivores and situated subcutaneously and caudal to the monostomatic salivary gland between the linguofacial(a) and maxillary vein(b).

Contained within a strong fibrous capsule which continues rostrally into the monostomatic (compact) part of the sublingual gland.

mandibular salivary gland relations

rostrally, close to the angle of the jaw with the mandibular lymph nodes, sublingual gland, masseter and digastricus muscles

medially with the digastricus, medial retropharyngeal lymph node and external carotid artery.

caudally the muscles of the neck

Image of the canine mandibular salivary gland

Conditions with the mandibular salivary gland

In the dog the mandibular and monostomatic salivary glands are of practical importance since they undergo cystic changes (ranula) which require removal

May Result in the disruption of mastication swallowing, prehension and can cause excess salivation (ptyalism)

Mandibular duct

drained by a single duct that travels ventral to the mucous membrane floor of the mouth, close to the frenulum, and opens on the sublingual caruncle

Sublingual Salivary Gland: Monostomatic (compact)

Situated more caudally

Drains by a single duct

Shares a common opening with the mandibular salivary duct on top of the sublingual caruncle

Sublingual salivary gland: polystomatic(diffuse)

Situated more rostrally, Drained by several ducts

openings are located on a longitudinal fold in the lateral sublingual recesses

In cattle: on top the conical papillae located on the fold

The only part present in the horse

Salivary glands

Comprise a series of secretory units(glandular epithelium) that originate from the oral ectoderm and grow into the underlying mesoderm as large aggregates of compound glands

The secretory component of each gland is the parenchyma, and the supporting connective tissue is the stroma.

Types of secretion by salivary glands

serous, seromucous, or mucous, depending on its mucin content

Each salivary secretory unit is composed of?

three epithelial cell types

Serous cells, Mucous cells, Myoepithelial cells

Serous cells

Pyramidal shape protein(enzyme) secreting cells

Contain spherical nucleus, numerous RER and apical secretory granules

Joined apically by tight junctions and adherent junctions creating a spherical unit called an acinus

Mucous cells

Columnar shaped cells with more compressed basal nuclei.

Contain apical granules with hydrophilic mucins that provide lubricating properties in saliva

Can be organized in acini but often are found in cylindrical tubules

Histology of mucous cells

Composition of the parotid salivary gland

Compound acinar gland composed of numerous lobules separated by thin connective tissue septa

Each lobule consists of acini formed by pyramid-shaped cells with basal nuclei

Myoepithelial cells are located between the secretory cells and the basement membrane

Parotid salivary gland duct system

Description of the parotid salivary gland duct system

The lumen of the acinus opens into a short intercalated duct, simple cuboidal epithelium → joins a larger striated duct which extend to the edge of the lobule

At the edge of the lobule, they join interlobular ducts located in the CT septa between the lobules.

The interlobular ducts then converge to form the parotid duct

Interlobular ducts within the duct system

Interlobular ducts are lined by simple columnar epithelium which changes to stratified columnar epithelium as the ducts become larger and fuse with similar ducts draining other lobules.

Mandibular Salivary Gland produces?

two-thirds of all saliva.

Seromucous (mixed) compound tubuloacinar gland

Mandibular salivary gland: mixed salivary gland

In this type of gland, the serous and mucous units may be separate, or the serous cells may form a halfmoon shaped cap on one side of the mucous unit called a serous demilune.

Myoepithelial cells are present around the secretory units

Sublingual salivary gland composition

Seromucous (mixed) compound tubuloacinar gland(Similar to the mandibular) Smallest of the major glands

In addition to the typical mucous acini and demilunes, the glands of dogs and cats contain clusters of serous acini.

The mucous cells form tubular secretory units that connect the serous acini with the intercalated ducts

Striated and intercalated ducts are present but not prominent

Sublingual glands in large animals

Sublingual glands of cattle, sheep and pigs are almost entirely mucous, with relatively few serous demilunes

Minor salivary glands in the cat

Lingual glands

located in the submucosa between the intrinsic muscles of the tongue

Gustatory glands

associated with the vallate and foliate papillae and are entirely serous

Labial, palatine, buccal and pharyngeal glands

also contribute mucous and serous secretory products to the saliva

Zygomatic salivary gland

is only present in carnivores

Molar salivary gland is similar to the zygomatic salivary gland

Saliva has numerous functions relating to metabolic and nonmetabolic activities

including

Providing a medium for dissolved and suspended food materials that chemically stimulate taste buds.

Buffering the content of the oral cavity, because of its high concentration of bicarbonate ions

Digesting carbohydrates with the digestive enzyme alpha amylase, which breaks down one to four glycosidic bonds and continues to act in the esophagus and stomach

Parasympathetic innervation of the salivary glands

Parasympathetic innervation → cranial nerves VII and IX

PS originate from two salivatory nuclei(rostral salivatory nucleus and caudal salivatory nucleus located) in the brainstem

The mandibular and sublingual glands receive parasympathetic innervation via

cranial nerves VII

The parotid gland receives parasympathetic innervation via

cranial nerves IX

Sympathetic innervation of the salivary glands

originate from the caudal thoracic segment of the spinal cord from synapses in the cranial cervical ganglion and reaches the salivary glands in the tunica adventitia of the arteries

Arterial supply to the head

leaves the aorta through the brachiocephalic and then the left and right common

carotid arteries.

The common carotid arteries terminate near the body of the hyoid bone by dividing into the internal and external carotid arteries

The internal carotid artery is smaller and runs through the deep structures of the head and brain.

The external carotid is the main continuation of the common carotid and supply either half of the head:

Its branches consists of; occipital, cranial laryngeal, ascending pharyngeal, lingual, facial, caudal auricular, parotid, superficial temporal and maxillary arteries.

The two terminating branches of the external carotid: a. Superficial temporal artery (smaller)

the branches of the artery are; the messeteric, transverse facial, rostral auricular, temporal, superior and inferior palpebral arteries.

The two terminating branches of the external carotid: b. Maxillary artery (larger)

gives branches that supply the deep structures of the head lying outside of the brain. It is considered the main continuation of the external carotid.

Can be divided intro three portions:; mandibular:, pterygoid: and Pterygopalatine:

Anatomy of the arterial supply to the head

Anatomy of the venous drainage of the head

Arterial and venous drainage of the parotid salivary gland

The main blood supply to the gland is via the parotid artery (blue) a branch of the external carotid.

Minor branches are sent to the gland by the caudal auricular, masseter, transverse facial and rostral auricular arteries.

The primary veins draining the gland are radicles of the superficial temporal (green) and great auricular veins

Anatomy of Arterial and venous drainage of the parotid salivary gland

Arterial and Venous Drainage of the Mandibular Salivary Gland

The largest artery supplying the gland is the facial artery (red) and smaller branches from the caudal auricular artery (green)

The chief vein draining the gland terminates in the lingual vein

(yellow) which then drains into the external maxillary vein. A smaller vein also drains the gland an terminates either in the facial, maxillary or lingual vein.

Anatomy of Arterial and Venous Drainage of the Mandibular Salivary Gland

Arterial and Venous Drainage of the Sublingual Salivary Gland

The main supply to the monostatic potion is via the glandular branch of the facial artery and the polystomatic portion the sublingual artery

(grey) a branch of the lingual artery

The satellite veins of the arteries drain the gland

Anatomy of Arterial and Venous Drainage of the Sublingual Salivary Gland

Rate of Saliva Secretion

horse produce ~50L of saliva daily.

The pig produces ~15 L/day

The cow produces ~ 100-200 L/day: flow rate increases during rumination and helps to buffer the fatty acids that are produced