Week 8 Lesson 62 Structure and Function of Salivary Glands_

Systems Overview

• Topic: Digestion, Metabolism & Nutrition

• Focus: Structure and Function of Salivary Glands

• Instructors: Dr. Crissy-Ann Harrylal, Dr. Rhea St. Louis

Learning Outcomes

• By the end of the session, students will be able to:

  • Describe the structure and function of salivary glands

  • Explain the process and control of saliva secretion

  • Analyze the relationship between saliva, food, and feeding habits of healthy animals

Importance of Salivary Glands in Domestic Animals

• Salivary glands are critical for:

  • Facilitating digestion through enzyme secretion

  • Lubrication of food for swallowing

  • Protection against pathogens

  • Buffering pH in the oral cavity

Salivary Glands Structure

• Classification: Exocrine glands that produce saliva

• Functions of Saliva:

  • Digestive function

  • Lubrication of food

  • Protective barriers against pathogens

  • Buffers for pH control

• Major Salivary Glands:

  • Parotid

  • Mandibular

  • Sublingual

• Minor Salivary Glands: Named according to location, including labial, lingual, buccal, palatine, molar, and zygomatic glands.

Morphology and Topography of Major Salivary Glands

1. Parotid Salivary Gland

• Structure:

  • Composed of lobules and connective tissue

  • Triangular shape, located near the auricular cartilage

• Duct System:

  • Varies by species in trajectory and termination

  • Terminates at a papilla opposite upper cheek teeth

  • In dogs, opposite the 4th premolar; in horses, small ruminants, and pigs, opposite 3rd or 4th superior cheek teeth; in oxen, opposite 5th superior cheek tooth

Fun Fact

• The parotid duct can be translocated to treat dry eye in dogs.

2. Mandibular Salivary Gland

• Location:

  • Near the jaw's angle, partially covered by the parotid gland

• Structure:

  • Largely ovoid, situated between veins

  • Encapsulated by strong fibrous tissue

• Clinical Relevance:

  • Cystic changes can occur leading to ranula, which may disrupt functions like mastication and swallowing

3. Sublingual Salivary Gland

• Structure:

  • Two parts: Monostomatic (single duct) and Polystomatic (multiple ducts)

  • Mainly mucous in cattle and sheep; mixed in dogs and cats

• Duct System:

  • Connects with mandibular duct on sublingual caruncle

Functionality of Salivary Glands

• Each gland comprises secretory units (glandular epithelium) from oral ectoderm growing into mesoderm.

• Cell Types:

  • Serous Cells: Protein-enzyme secreting, pyramidal shape

  • Mucous Cells: Column-shaped with hydrophilic mucins

• Salivary glands can produce:

  • Serous (mostly parotid)

  • Mucous (mostly sublingual and minor glands)

  • Mixed (mandibular)

Saliva Functions

• Diverse Functions:

  • Moisten oral mucosa and foods

  • Buffer oral cavity content (high bicarbonate concentration)

  • Digest carbohydrates via alpha-amylase

  • Control bacterial flora using lysosomes

  • Source of calcium and phosphates for teeth

Autonomic Innervation

• Nerve Supply:

  • Parasympathetic: Cranial nerves VII (mandibular/sublingual) and IX (parotid)

  • Sympathetic nerve fibers from spinal cord through cervical ganglion

Blood Supply

• Arterial Supply:

  • From the external carotid artery with branches serving the salivary glands including facial, caudal auricular, masseter, and others

Venous Drainage

• Veins parallel arteries; external jugular vein formed from linguofacial and maxillary veins.

Salivary Glands Contribution to Digestion

• Salivary fluid production varies:

  • ~50L/day in horses

  • ~15L/day in pigs

  • ~100-200L/day in cows especially during rumination

Lesson Summary

• Salivary Gland Types:

  • Parotid: Located by the ear; duct near cheek teeth.

  • Mandibular: Near jaw angle; duct opens floor of mouth.

  • Sublingual: Mixed; drains via different ducts.

• Saliva's importance: Digestive functions, lubrication, and protection.

• Nerve Supply: Both parasympathetic and sympathetic control functions, vital for regulation.