The anal glands or anal sacs are small glands near the anus in many mammals. [1] They are situated in between the external anal sphincter muscle and internal anal sphincter muscle. [2] In non-human mammals, the secretions of the anal glands contain mostly volatile organic compounds with a strong odor, and they are thus functionally involved in communication. Depending upon the species, they may be involved in territory marking, individual identification, and sexual signalling, as well as defense. [3] [ better source needed ] Their function in humans is unclear. [4]
Sebaceous glands within the lining secrete a liquid that is used for identification of members within a species. These sacs are found in many species of carnivorans, [2] including wolves, [5] bears, [6] [7] sea otters [8] and kinkajous. [9]
The human anal glands are situated within the wall of the anal canal [10] and communicate with the lumen of the canal via ducts that open at the anal valves, just proximal to the pectinate line. Humans have 12 anal glands on average (which are evenly distributed around the circumference of the anal canal). [4] The glands are situated at varying depths in the wall of the anal canal; some between the layers of the internal and external sphincter (the intersphincteric plane). [11] [12]
In humans, the glands secrete mucin (which differs in composition from that secreted by the rectal mucosa). Their function is unclear. [4]
Anal glands are the most common cause of anal fistula. Large fistulae present a surgical challenge as resection of larger sections of the anal sphincter may result in anal incontinence. [4] The cryptoglandular theory states that obstruction of these ducts[ clarification needed ], presumably by accumulation of foreign material (e.g. fecal bacterial plugging) in the crypts, may lead to perianal abscess and fistula formation. [11] [12]
Entry of bacteria into the lumen of the glands can cause infection (which may then spread), and inflammation can prevent drainage of the glands. [13]
Dogs and cats primarily use their anal gland secretions to mark their territory, and generally will secrete small amounts of fluid every time they defecate. Many will often express these glands when anxious or frightened as well. Dogs who are healthy can usually have a wide variety in the appearance of their sac's content. [14] Anal sac fluid varies from yellow to tan or brown in color. The consistency of the fluid ranges from thin, watery secretions to thick, gritty paste. There can also be a range in the malodorousness, or how strongly the contents smell. [14] These factors can all be different from animal to animal. [14]
The inability to effectively express this fluid can lead to anal sacculitis. This is characterized by a build-up of fluid in the anal sac, an uncomfortable condition that can lead to pain and itching. Dogs and cats of any age may be affected, but dogs are far more likely to suffer from anal sacculitis than cats. Dogs and cats with anal glands that do not express naturally may exhibit specific signs, such as scooting the backside upon the ground, straining to defecate, and excessive licking of the anus. Cats may also defecate in areas outside the litter box. [15]
Discomfort may also be evident with impaction or infection of the anal glands. Anal sac impaction results from blockage of the duct leading from the gland to the opening. The sac is usually non-painful and swollen. Anal sac infection results in pain, swelling, and sometimes abscessation and fever.
Initial treatment usually involves the manual expression of the anal sacs, most often by a veterinary professional. The frequency of this procedure depends on the patient's individual degree of discomfort but can range from weekly to every few months. [15] Treatment may include lancing of an abscess or antibiotic infusion into the gland in the case of infection. The most common bacterial isolates from anal gland infection are E. coli , Enterococcus faecalis , Clostridium perfringens , and Proteus species. [16] Increasing dietary fiber is also commonly recommended. [15]
Anal sacs may be removed surgically in a procedure known as anal sacculectomy. This is usually done in the case of recurrent infection or because of the presence of an anal sac adenocarcinoma, a malignant tumor. Potential complications include fecal incontinence (especially when both glands are removed), tenesmus from stricture or scar formation, and persistent draining fistulae. [17]
Opossums use their anal glands when they "play possum". As the opossum mimics death, the glands secrete a foul-smelling liquid, suggesting the opossum is rotting. Opossums are not members of the order Carnivora, and their anal sacs differ from those of dogs and their relatives. [9]
Skunks use their anal glands to spray a foul-smelling and sticky fluid as a defense against predators.[ citation needed ]
Both female and male beavers (Castor canadensis) have a pair of castor sacs and a pair of anal glands between the pelvis and tail. The physiology of the castor sac is unique to the beaver and contains an outer, vascular layer of connective tissue, a thicker layer of epithelial cells, and an inner packed layer of epithelial sheets. [18] Castoreum is the chemical compound that is secreted from the castor sacs and is originally a thin, yellowish liquid. It is composed of a mixture of varied metabolic compounds, from the sacs and other bodily systems, and excreted urine. [18] An extraction of castoreum, the scent glands from the male and female beaver are used in perfumery and as a flavor ingredient.
The vestibule of the anal glands are connected to the ducts of the castor glands. The anal glands of beavers are characterized as holocrine sebaceous glands, which means they secrete substances by disintegrating cells in the process. [19] Variations in color of anal glands range from a light straw color to brown. Compared to the castor sacs, anal glands secrete a much more sharp odor. [19] Beavers do have a presence of bacterial flora in their anal glands, with the most abundant being B. fragilis and E. coli. These two bacteria are common in the digestive tracts of mammals and are seen across all beaver populations regardless of sex, colony, age, class, and other factors. [19] This gives evidence to the idea that beavers do not have varied bacterial flora or significant varied odors within a family. Furthermore, this opposes the bacterial fermentation hypothesis that is common among a number of mammalian species. [18]
Beavers create scent mounds, which are essentially “mud pies”, where they deposit castoreum and other secretions on top of them. As scent communication is a common method across many species, beavers use scent mounds as a way to alert that a region is inhabited by a family of beavers and to mark territory. [20] The frequency of scent mounding is typically highest during the spring and after winter when the ice has melted. This is prevalent as the water sources are more available from which beavers can gather mud. [20] Scent mounding is highest during intergroup interactions, vicinity of abutting beaver populations, and gestation periods. [20] Scent mounds are mainly a medium of communication against adjacent beaver populations and it prevents the exploitation of food resources, marks distinct family territories, and prevents extreme colonization of a habitat. [20]
The European badger (Meles meles), a nocturnal carnivore, has a powerful olfactory system. [21] Anal gland secretions (AGS) of badgers are not commonly studied but contribute to key information for communication due to volatile organic compounds (VOCs). [21] Like many other carnivorous mammals, such as mongoose, bears, and otters, they can detect sex differences from the different ratios of compounds of VOCs. [21] VOCs in AGS of badger samples have individual-specific information, including health, fitness, reproductive status, and group membership. [21] Male badgers react differently to VOCs in AGS from fertile females versus non-fertile females. [21] The VOCs can change yearly based on diet and environmental factors, and seasonal changes of VOCs are influenced by breeding season. [21]
The subcaudal gland is right next to the anal sac. [22] The subcaudal gland contributes to individual-specific communication, much like the AGS. [22] Subcaudal glands of badgers had 56 operational taxonomic units (OTU) used to classify the different bacteria found into four different phyla. [22] Based on a study by Yung Wa Sin 2012, conducted on 79 subcaudal secretions from summer and spring, OTUs fall into four bacterial phyla: Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes. [22] Actinobacteria was the dominant phyla as it represented >76% of all bacterial communities in the badger adults. [22] Cub secretion microbial communities were significantly more diverse; Firmicutes were the most abundant bacterial phyla in adult badger microbial communities. [22] This bacterial dominance shift may be due to puberty in the cubs. [22] In the spring, a breeding female versus a non-breeding female had significant microbial community differences, but they did not see significant differences in bacterial communities in the summer months. [22] Secretions from the subcaudal gland are shown to be rich in short and medium-chain fatty acids likely produced by pheromone active products from actinobacteria long-chain fatty acids. [22]
In the majority of mammals, group integration is performed by the adult. However, in badgers cubs begin this gradual process (14–16 weeks). [23] Badgers have the reputation of being aggressive towards one another and cubs are often victims to infanticide. [23] To lower aggression within a group of badgers, members will allogroom (a form of social grooming) or allomark (transferring scents between other group members) more frequent and intense during spring months. [23] Maturing cubs rub themselves against adult badger's subcaudal region via allomarking. [23] This is also referred to as “scent theft” as cubs that do this have the same group scent. [23] Badger cubs do not have the subcaudal gland secretion ability until approximately four months old . [23]
Volatile compounds found in the anal sac secretions of intact males, intact females, castrate males, ovariectomized females, and anosmic/ pinealectomized males and females were analyzed using gas chromatography. [21] The volatile compounds found in the anal-gland secretions were largely alcohols, aldehydes, and ketones. [21] Of the volatile compounds that were analyzed, the relative quantities of volatile compounds present in the test subjects’ anal sac secretions varied significantly between secretions collected outside and during mating season. [21] This indicates that the volatile compounds in the anal sac secretions are used to signal information like gender and reproductive status. [21] Results of this study indicated that some of the volatile compounds, specifically 2-octenal, 2-octen-1-ol and indole, were produced by microbes. [21]
The anal gland of the Indian mongoose consists of large sebaceous glands that surround the anus, called the anal sac. [24] The anal sac remains covered in sebum and remains closed when the tail of the mongoose is down but opens when the tail is raised. [24] Inside the anal sacs are the ducts of the two anal pockets that lie on either side of the anus. [24] The mongoose marks objects in its habitat by rubbing that object with the anal area leaving behind the distinct scent of carboxylic acids. [24] Contents of the anal pocket secretions revealed 6 saturated carboxylic acids: acetic, propionic, isobutyric, butyric, isovaleric and valeric. [24] There are currently no notable differences in the chemicals found in the anal pocket secretions between the sexes. [24]
Evidence shows that the carboxylic acids found in the anal pocket secretions are produced by bacterial metabolism of contents inside the sebum. [24] The bacteria isolated from anal sac secretions have been identified as Peptococcusspp., Peptostreptococcus plagarumbelli, Bacillus cereus and Eubacterium or Catenobacteriumspp. [24] These bacterial species have been found to produce carboxylic acids within the anal pocket. [24]
Hyenas are known to engage in “pasting” which is a type of scent marking behavior. This paste is rich in lipid sebum and epithelial cells, and is produced by sebaceous glands which then go directly into the anal glands and on top of a grass stalk. [25] The organ that provides this paste, the anal glands, are occupied by microbes. Although both species of hyena contain fermentative bacteria, the microbes found in the anal gland of spotted hyenas (Crocuta crocuta) differ from the microbes found in striped hyenas. [26]
The spotted hyena paste holds many populations of coccus and rod shaped bacteria. A survey found that Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria are the most common bacteria found in the hyena paste. [25] Although many bacteria have been identified, around half are still unidentified. [25]
Microbiome populations also vary by sex and age. The adult and juvenile hyenas’ anal glands have the least diverse microbiota of their whole body. For females, the most common bacteria found in their paste was Anaerococcus, Anaerovorax, Corynebacterium, Eubacterium, Helcococcus, Porphyromonas, and Propionibacterium. [25] Compared to the male hyenas which have a different microbiota than female hyenas. Juvenile males have more Prevotella and Firmicutes, while juvenile females have more Corynebacterium and Clostridiales. There is also a difference between adult female hyenas and juvenile hyenas. Juvenile female hyenas have more Erysipelotrichaceae and Helicobacter than the adult hyenas. These bacteria are common to the milk that hyenas feed their young. [27]
The bacteria found in the feces and anal glands of dogs and cats are also found in their mouths due to the consistent exposure to their backsides (licking and chewing). [28] In a healthy dog or cat the bacteria normally found in their feces are Streptococci and Enterococci, more specifically, Enterococcus faecium, Streptococcus bovis, and Enterococcus faecalis. [28]
Dogs have two anal sacs which are located in the connective tissue off the anus. [14] There are many glands in dogs that secrete into the sac's lumen, filling them with fluid. [14] The anal-sacs are usually made up of about 88% water, 11.5% organic and 0.5% inorganic matter. [14] The secretion of anal gland content contains mucin, that is rich in sialic acid and other anti-microbial proteins, like lysozyme, immunoglobulin A, and lactoferrin. [14] There is also an abundance of gram-positive cocci since they are part of the anal glands normal flora. [14] The organic components mainly consist of short-chain fatty acids and trimethylamine. [14] The anal-sac fluid can be secreted or expressed into the anal channel to serve as a scent marker for an individual's territory through their feces. [14]
The aardwolf is an insectivorous hyaenid species, native to East and Southern Africa. Its name means "earth-wolf" in Afrikaans and Dutch. It is also called the maanhaar-jackal, termite-eating hyena and civet hyena, based on its habit of secreting substances from its anal gland, a characteristic shared with the African civet.
Beavers are large, semiaquatic rodents of the Northern Hemisphere. There are two existing species: the North American beaver and the Eurasian beaver. Beavers are the second-largest living rodents, after capybaras, weighing up to 50 kg (110 lb). They have stout bodies with large heads, long chisel-like incisors, brown or gray fur, hand-like front feet, webbed back feet, and tails that are flat and scaly. The two species differ in skull and tail shape and fur color. Beavers can be found in a number of freshwater habitats, such as rivers, streams, lakes and ponds. They are herbivorous, consuming tree bark, aquatic plants, grasses and sedges.
Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or ginger colored, but all have warning coloration.
Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small compounds that the body can use.
The bulbourethral glands or Cowper's glands are two small exocrine and accessory glands in the reproductive system of many male mammals. They are homologous to Bartholin's glands in females. The bulbourethral glands are responsible for producing a pre-ejaculate fluid called Cowper's fluid, which is secreted during sexual arousal, neutralizing the acidity of the urethra in preparation for the passage of sperm cells. The paired glands are found adjacent to the urethra just below the prostate, seen best by screening (medicine) MRI as a tool in preventative healthcare in males. Screening MRI may be performed when there is a positive prostate-specific antigen on basic laboratory tests. Prostate cancer is the second-most common cause of cancer-related mortality in males in the USA.
Saliva is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells, enzymes, and antimicrobial agents.
A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet. In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Surrounding the female nipple, areolar glands are specialized sebaceous glands for lubricating the nipple. Fordyce spots are benign, visible, sebaceous glands found usually on the lips, gums and inner cheeks, and genitals.
The spotted hyena, also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus Crocuta, native to sub-Saharan Africa. It is listed as being of least concern by the IUCN due to its widespread range and large numbers estimated between 27,000 and 47,000 individuals. The species is, however, experiencing declines outside of protected areas due to habitat loss and poaching. Populations of Crocuta, usually considered a subspecies of Crocuta crocuta, known as cave hyenas, roamed across Eurasia for at least one million years until the end of the Late Pleistocene. The spotted hyena is the largest extant member of the Hyaenidae, and is further physically distinguished from other species by its vaguely bear-like build, rounded ears, less prominent mane, spotted pelt, more dual-purposed dentition, fewer nipples, and pseudo-penis. It is the only placental mammalian species where females have a pseudo-penis and lack an external vaginal opening.
Areolar glands, also known as glandulae areolares, Montgomery glands, and tubercula areolae, are 10-15 elevations found on the areola. They are usually arranged in a circle around the nipple, and can be particularly visible when the nipple is erect. Their role is to promote adequate breastfeeding of the infant.
Body odor or body odour (BO) is present in all animals and its intensity can be influenced by many factors. Body odor has a strong genetic basis, but can also be strongly influenced by various factors, such as sex, diet, health, and medication. The body odor of human males plays an important role in human sexual attraction, as a powerful indicator of MHC/HLA heterozygosity. Significant evidence suggests that women are attracted to men whose body odor is different from theirs, indicating that they have immune genes that are different from their own, which may produce healthier offspring.
Sweat glands, also known as sudoriferous or sudoriparous glands, from Latin sudor 'sweat', are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial surface by way of a duct. There are two main types of sweat glands that differ in their structure, function, secretory product, mechanism of excretion, anatomic distribution, and distribution across species:
Castoreum is a yellowish exudate from the castor sacs of mature beavers and platypuses. Both animals use castoreum for various purposes; beavers use it in combination with urine to scent mark their territory, while platypuses use it in reproductive communication.
Scent gland are exocrine glands found in most mammals. They produce semi-viscous secretions which contain pheromones and other semiochemical compounds. These odor-messengers indicate information such as status, territorial marking, mood, and sexual behaviour. The odor may be subliminal—not consciously detectable. Though it is not their primary function, the salivary glands may also function as scent glands in some animals.
The violet gland or supracaudal gland is a gland located on the upper surface of the tail of certain mammals, including European badgers and canids such as foxes, wolves, and the domestic dog, as well as the domestic cat. Like many other mammalian secretion glands, the violet gland consists of modified sweat glands and sebaceous glands.
Dogs, as with all mammals, have natural odors. Natural dog odor can be unpleasant to dog owners, especially when dogs are kept inside the home, as some people are not used to being exposed to the natural odor of a non-human species living in proximity to them. Dogs may also develop unnatural odors as a result of skin disease or other disorders or may become contaminated with odors from other sources in their environment.
An apocrine sweat gland is composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle. In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits), areola and nipples of the breast, ear canal, eyelids, wings of the nostril, perineal region, and some parts of the external genitalia. Modified apocrine glands include the ciliary glands in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk. They are distinct from eccrine sweat glands, which cover the whole body.
Margaric acid, or heptadecanoic acid, is a saturated fatty acid. Its molecular formula is CH3(CH2)15CO2H. Classified as an odd-chain fatty acid, it occurs as a trace component of the fat and milkfat of ruminants. Salts and esters of margaric acid are called heptadecanoates.
Male accessory glands (MAG) are the seminal vesicles, prostate gland, and the bulbourethral glands. These glands are found only in mammals. In insects, male accessory glands produce products that mix with the sperm to protect and preserve them, including seminal fluid proteins. Some insecticides can induce an increase in the protein content of the male accessory glands of certain types of insects. This has the unintended effect of increasing the number of offspring they produce.
The biochemistry of body odor pertains to the chemical compounds in the body responsible for body odor and their kinetics.
Wolves communicate using vocalizations, body postures, scent, touch, and taste. The lunar phases have no effect on wolf vocalisation. Despite popular belief, wolves do not howl at the Moon. Gray wolves howl to assemble the pack, usually before and after hunts, to pass on an alarm particularly at a den site, to locate each other during a storm or while crossing unfamiliar territory, and to communicate across great distances. Other vocalisations include growls, barks and whines. Wolves do not bark as loudly or continuously as dogs do but they bark a few times and then retreat from a perceived danger. Aggressive or self-assertive wolves are characterized by their slow and deliberate movements, high body posture and raised hackles, while submissive ones carry their bodies low, sleeken their fur, and lower their ears and tail. Raised leg urination is considered to be one of the most important forms of scent communication in the wolf, making up 60–80% of all scent marks observed.
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