Anal glands
Glandulae anales
Definition
The anal glands of the columnar zone refer specifically to mucosal glands located within the columnar zone of the anal canal in domestic animals. These glands differ from the more commonly discussed anal sac (paranal sinus) glands and perianal (circumanal) glands, as they are embedded within the mucosa of the anal canal and function primarily in lubrication rather than scent marking.
Histological characteristics
Epithelium: The glandular ducts open onto the surface of the columnar zone, which is lined by mucus-secreting columnar epithelium rich in goblet cells.
Gland type: These are mucus-producing glands, classified histologically as tubuloalveolar glands in some species.
Distribution: The number and density of these glands vary among species, generally being more prominent in carnivores.
Species-specific features
Dog and cat
Mucosal glands in the columnar zone are well-developed, assisting in lubricating the anal canal.
They are separate from the ducts of the anal sacs, which open into the anal sinuses at the base of the anal columns.
These mucosal glands are not responsible for scent production, unlike the glands of the anal sacs.
Horse
Glands in the columnar zone are limited, and the mucosa is generally smooth with minimal folding.
Mucosal secretion is less important functionally compared to the rectum.
Ruminants (cattle, sheep, goats)
Poorly developed columnar zone glands. The transition from rectum to anal canal occurs with little structural elaboration.
Mucus production is primarily a rectal function.
Pig
Columnar zone glands are moderately developed, supporting a longer anal canal with some lubrication function.
Mucosal glands are present but not as prominent as in dogs.
Functional significance
These glands produce mucus that lubricates the anal canal during defecation, reducing friction and potential mucosal injury.
The mucus also helps protect the epithelium of the columnar zone from irritation by fecal matter.
They play no role in scent marking, which is the function of the apocrine and sebaceous glands in the anal sacs.
Clinical relevance
While not usually a direct source of disease, hyperplasia, inflammation, or obstruction of these glands could contribute to local irritation or minor infections.
These glands are not usually surgically targeted but may be encountered during anal sacculectomy or procedures involving the anal canal mucosa.
!! The term anal glands may sometime regroup this 3 types of glands :
Feature | |||
Location | Within the mucosa of the columnar zone of the anal canal | In the walls of the anal sacs, which are located between the internal and external anal sphincters | In the skin surrounding the anus, especially in the cutaneous zone |
Duct Opening | Directly onto the mucosal surface between anal columns | Into the anal sinuses at 4 and 8 o’clock positions of the anus | Directly onto the skin surface or adjacent hair follicles |
Gland Type | Tubular mucous glands | Modified apocrine (dogs); apocrine + sebaceous (cats) | Modified sebaceous glands with hepatocyte-like cells |
Secretion Type | Mucus | Oily, protein-rich secretion with species-specific odor | Sebaceous-type secretion |
Function | Lubrication of anal canal during defecation | Scent marking, communication, minor lubrication | Unknown; may have pheromonal or sexual signaling roles |
Presence in Species | Present in most mammals, more developed in carnivores | Present and functional in dogs and cats; absent in ruminants and horses | Prominent in dogs (especially intact males); absent or rudimentary in other species |
Histological Features | Simple columnar epithelium with goblet cells, mucus glands in submucosa | Lined by stratified squamous epithelium with apocrine glands in sac wall | Resemble hepatocytes, form lobules around hair follicles |
Clinical Relevance | Rarely involved in disease | Common site of impaction, infection, abscess, neoplasia | Common site for adenomas (benign tumors) in older male dogs |
Surgical Importance | Not typically targeted | Site of anal sacculectomy in recurrent infections | May require excision in cases of tumor growth |
References
Dyce KM, Sack WO, Wensing CJG. Textbook of Veterinary Anatomy. 5th ed. St. Louis: Saunders Elsevier; 2017.
König HE, Liebich HG. Veterinary Anatomy of Domestic Mammals: Textbook and Colour Atlas. 6th ed. Stuttgart: Schattauer; 2020.
Evans HE, de Lahunta A. Miller’s Anatomy of the Dog. 5th ed. St. Louis: Saunders Elsevier; 2013.
Sisson S, Grossman JD. The Anatomy of the Domestic Animals. 5th ed. Philadelphia: Saunders; 1975
