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Journal of the Anatomical Society of India

Comparative Study Of Ano-Rectal Region In Mammals

Author(s): Agarwal, K.K.; *Agarwal, A.K.; *Singh, P.J., **Sharma, S.N.

Vol. 51, No. 2 (2002-07 - 2002-12)

Department of Anatomy, MOIC Govt. Allopathic Hospital, Kathgodam *S.N. Medical College, Agra, **Malaria Researach Centre, Haldwani, INDIA

Abstract

Comparative macro and microscopic study of anorectal region in human beings, dogs and rabbits was carried out in the department of anatomy, S.N. Medical College, Agra. Results were compared with available literature. Results of macroscopic study of length of rectum, anal canal and types of mucosal folds revealed that the mean rectal length was more in rabbit (74.5 cm) as compared to human beings (9.46 cm) and dog (5.30 cm). The mean length of anal canal in human being was more (2.77 cm) in comparison to dog (1.4 cm) and rabbit (0.92 cm). The rectal mucosa of human being, dog and rabbit showed transverse folds, nodular swellings and temporary longitudinal folds respectively. While anal mucosa of human being and dog showed columns, valves and sinuses, these were absent in rabbit.

The microscopic study revealed mucosa of rectum of human being, dog and rabbit is lined with simple columnar epithelium and having intestinal glands, whereas mucosa of anal canal in human being is lined with simple columnar epithelium, stratified columnar epithelium and stratified squamous epithelium as one proceeds distally. Anal mucosa of dog and rabbit is lined with stratified squamous epithelium. In all the three species stratified squamous epithelium of anal region transform into skin structure.

The study has clinical significance in better understanding of structure during radiological and sigmoidoscopic examination.

Key words: Human, Dog, Rabbit, Anal canal, Folds and Mucosa, Epithelium.

Introduction:

In mammals, the anorectal region is an end piece of digestive tract related to concavity of sacrum & coccyx. It terminates externally into anus. Human anorectal region has attracted great attention from many anatomists because it has transverse mucosal folds, columns, valves, and sinuses. Pennigton (1900) attached particular importance to the folds from clinical point of view stating that they are often cause of constipation, Chalari (1878) described rectal sinuses. He believed that the fistula is produced by outward and downward extension of these structures. In mammals changing pattern of epithelium of mucosa is reported by various workers like Walls (1958), Park (1956) and Goligher (1955). Hence intense study of this region is required on top priority for devising control measures against diseases of this particular region.

Human being was selected for this study along with domestic pet animal dog having eating habbits similar to man & rabbit being a common laboratory animal.

Walls (1958) pointed out that highest part of anal canal is lined with small tubular prolongation having intestinal glands & solitary lymphoids present beneath the epithelium, while Robbin and Cadist (1874) stated that Pars analis recti differ from Pars ampullaris in having no intestinal glands. Similarly Hebrant (1899) found a close relationship of lymphoid nodule to anal mocosal membrane in dogs. In rabbit there are few studies in this region.

Hence this study was undertaken during the year 1995 to 1997. Results of this study are communicated in this paper.

Material and Method:

The present study of anorectal region was restricted to the class mammalia in which human being, dog and rabbit were chosen. For this 10 specimen of each species were taken for macroscopic and one each was used for microscopic studies.

All the animals were obtained from the animal house of S.N. Medical College, Agra. Autopsy was performed immediately after sacrificing the animal. Mid line incision was given in the anterior abdominal wall extending from the subcostal angle upto pubic symphysis. Then two transverse incisions were given starting from both the ends of first incision. The skin and muscles were cut along these lines and after incision of peritoneum, the peritoneal cavity was approached. Pubic symphysis was cut by bone cutter to expose pelvic cavity. Rectum and anal canal were mobilized and following points were observed.

  1. Extent of rectum and anal canal.
  2. Length of rectum.
  3. Length of anal canal.
  4. mucosal folds of rectum.
  5. Number of anal columns.
  6. Number of anal valves and sinuses.

Measurements of rectum and anal canal were Histological Slides were stained with H and E taken with the help of caliper. stain and studied under light microscope.

Preservation :

The anorectal canal was removed from the body, washed in running tap water and then kept in 10% formalin saline.

Lumen of rectum and anal canal were opened by sharp knife cutting longitudinaly and mucosal folds of rectum and anal canal were observed. For human beings gross anatomy of rectum and anal canal was studied in cadavers and for histology, the anal canal and rectum were obtained from the fresh accidental cases brought to the post mortum room of S.N. Medical College, Agra.

Histological Slides were stained with H and E stain and studied under light microscope.

Observations and Results:

Extent of rectum & anal canals observed in the present study is depicted in Table I.

Table-1 Extent of rectum and anal canal

Species Extent of rectum Extent of anal canal
Human being 3rd sacral vertebra to pelvic diaphragm Pelvic diaphragm to anal orifice
Dog Pelvic brim to 3rd coccygeal vertebra 3rd coccygeal vertebra to anal orifice
Rabbit End of pocket like structure (haustra) to 3rd coccygeal vertebra 3rd coccygeal vertebra to anal orifice

Table-2 Macroscopic measurements of rectum and anal canal in different mammals

Name of species and their no. Length of rectum (in cm) Length of anal canal (in cm) Mucosal folds of rectum Anal columns Anal Valve and sinuses
Human being
s.no.
Transverse mucosal folds Complete columns Incomplete columns
1- 9.5 2.5 2.0 12 Absent 6.0
2 - 10.5 3.0 2.0 15 - 6.0
3- 8.5 2.5 3.0 9 - 3.0
4- 9.0 2.5 4.0 22 - 10
5- 9.7 2.8 2.0 14 - 7
6- 10.0 2.9 2.0 14 - 6
7- 8.8 2.7 3.0 10 - 4
8- 8.2 3.0 3.0 18 - 8
9- 10.8 3.2 4.0 20 - 10
10- 8.6 2.6 2.0 8 - 4
Mean and S.D. 9.46±0.79 2.77±0.25 2.70±0.78 14.20±4.68   6.40±2.41
Dog
s.no.
Length of rectum (in cm) Length of anal canal (in cm) Mucosal
swelling
Complete
columns
Incomplete
columns
Anal Valve and sinuses
1- 5.5 1.5 100 9 11 5
2- 4.2 1.0 60 6 10 3
3- 6.0 1.6 110 10 12 5
4- 5.0 1.2 70 7 11 4
5- 5.4 1.4 90 8 12 4
6- 4.4 1.2 66 7 10 3
7- 5.9 1.6 100 11 13 5
8- 5.0 1.3 80 8 11 4
9- 5.6 1.5 100 10 11 5
10- 6.0 1.7 99 12 14 6
Mean and S.D 5.30±0.64 1.40±0.22 88.50±18.36 8.8±1.93 11.5±1.2 4.40±0.97
Rabbit s.no Length of rectum (in cm) Length of anal canal (in cm) Temprary
longitudinal
folds
Complete columns Incomplete
columns
1- 74 0.85 6 Absent Absent
2- 76 0.9 6 - -
3- 70 0.8 7 - -
4- 75 0.8 5 - -
5- 80 1.0 6 - -
6- 74 1.2 6 - -
7- 72 0.9 7 - -
8- 80 1.10 6 - -
9- 70 0.80 5 - -
10- 74 0.86 6 - -
Mean and S.D. 7.45 ± 3.50 0.92 ± 0.14 6.0 ± 0.67 - -

The other gross observations made on rectum & anal canal of different species are shown in Table II.

Length of rectum-The rectal length was more in rabbit (74.5 cm. ± 3.5 cm.) in comparison to human being (9.46 cm ± 0.79 cm). & dog (5.30 cm ± 0.64 cm).

Length of anal canal-In human being length of anal canal was longest (2.77 cm ± 0.25 cm) in comparison to dog (1.40 cm ± 0.22 cm) and rabbit (0.92 cm ± 0.14 cm).

Mucosal folds of rectum-In human beings, there were seen transverse folds ranging from 2 to 4 with mean of (2.70 ± 0.78) while rectal mucosa of dog consisted of nodular swellings ranging from 60 to 110 with mean of 88.50 through out the rectum where as that of rabbit consisted of temporary longitudinal folds ranging from 5 to 7 with mean of 6. These longitudinal folds were of variable length & scattered through out rectum.

Number of anal columns-The anal columns in human being were complete. Their average number was 14.20 ± 4.68. In dog, anal columns were of complete and incomplete types, their average no. being 8.8 ± 1.93 and 11.5 ± 1.2 respectively (Fig 1 & 2) In rabbit, anal columns were absent.

Number of anal valves and sinuses -The average number of anal valves and sinuses were 6.40 ± 2.41 and 4.40 ± 0.97) in human beings and dog respectively. (Fig 1 & 2). The above structures in rabbit were absent.

Microscopic observations:

Human being-The mucosa of rectum was lined with simple columnar epithelium having intestinal glands. The upper most part of anal mucosa where intestinal glands ended had simple columnar epithelium (figure-3). The part distal to this & upto the supero external surface of anal valve was lined with stratified columnar epithelium (figure-4). Region from supero external surface of valve including the part below it was lined with stratified squamous epithelium (figure-5).

Dog-The mucosa of rectum was lined with simple columnar epithelium and had intestinal glands while mucosa of anal canal was lined with stratified squamous epithelium having close relation to lymphoid nodules (fig. 6).

Rabbit Mucosa of rectum was lined with simple columnar epithelium having crypts of lieberkuhn while the mucosa of anal canal was devoid of anal valves and sinuses and lined with stratified squamous epithelium (fig. 7)

In all these three groups studied so far as proceeded further downwards from stratified squamous epithelium of anal canal, it took gradually structure of skin (confirmed by observing cornification, sebaceous glands, sweat glands and hair follicles).

Discussion:

Extent of rectum and anal canal-

Human specimens - The rectum extended from 3rd sacral vertebra to pelvic diaphragm and anal canal extended from the pelvic diaphragm to anal orifice. But Symington (1888) reported that the rectum extends from 3rd sacral vertebra to the end of coccyx and anal canal extends from coccyx to terminate as anus.

In dog -The rectum extended from pelvic brim to 3rd coccygeal vertebra and anal canal extended from 3rd coccygeal vertebra to anal opening. But Miller (1993) stated that the rectum begins at pelvic inlet and it ends ventral to 2nd or 3rd coccygeal vertebra continuing as anal canal.

In rabbit -The rectum extended from the pocket like pouch (haustra) to the 3rd coccygeal vertebra. But Kotpal (1989) described the rectum in rabbit as narrow terminal part and opening outside through anus.

Thus the extent of rectum of human beings is different from that of dog and rabbit.

Length of rectum-

In human beings-Williams et al, (1995) described that mean length of human rectum is 12 cm while we found the mean length of rectum was 9.46 cm ± 0.79 cm. The difference may be due to the racial variation of individuals studied.

In dog -Length of rectum of dog in present study was 5.30 cm ± 0.64 cm. This was similar to those reported by Miller (1993).

In rabbit -Kotpal (1989) mentioned the length of rectum in rabbit as 75 cm, which is again very close of present study figure of 74.5 cm ± 3.5 cm.

The length of rectum of rabbit is much more than that of human beings and dog. Long rectum might be because of rabbit being herbivorous.

Length of Anal Canal-

In human being-In present study the length of anal canal ranged from 2.5 cm to 3.2 cm with mean of 2.77 cm ± 0.25 cm which is close to observation by Symington (1888) but differs from the observation by Williams et al (1995).

In dog-Mean length of anal canal in present study is 1.40 cm ± 0.22 cm, which is more than 1.0 cm. as reported by Miller (1993).

In rabbit-Mean length of anal canal was 0.92 cm. However literature did not mention about the length of anal canal in rabbit.

Mucosal folds of Rectum-

In human being-Otis (1887) observed 2 or 3 transverse mucosal folds in his study. In this study we have found 2 to 4 transverse mucosal folds; 50% cases showed 2 folds while 30% cases showed 3 folds and 20% showed 4 transverse mucosal folds. Williams et al, (1995) mentioned the occurence of 4 transverse mucosal folds but nothing is mentioned about percentage of the cases.

In dog-In present study rectum of dog does not exhibit any mucosal folds but showed about 60 to 110 nodular swellings in the mucosa of the whole rectum. Miller (1993) observed about 100 solitary lymph nodules in the rectal mucosa of dog.

In rabbit-Present study showed 5 to 7 temporary mucosal folds of various length. Jordan and Verma (1999) said that the rectum of rabbit showed small folds.

Anal Columns:

In human beings-The present study showed 8 to 20 anal columns (average 14.20 ± 4.68). The number of anal columns in human beings were not mentioned by Robin and Cadist (1874).

In dog-The anal columns in dog are of two types complete and incomplete. The number of columns are 8.8 ± 1.93 & 11.5 ± 1.2 respectively. Miller (1993) reported that anal columns in dog are either longitudinal or oblique. The available literature does not mention about their number.

In rabbit-Present study did not show any anal columns

Number of Anal Valves and sinuses:

In human beings-The number of anal valves & sinuses varied from 3 to 10 in number. Brodenhamer (1888) and Robin and Cadist (1874) have studied the anal valves and sinuses, but they did not mention about their number.

In dog-The number of valves ranged from 3 to 6 in present study. Zimmermann (1904) though studied the structure in dog but did not mention their number.

In rabbits-Anal canal did not exhibit any valves or sinuses. Kotpal (1989) did not mention about the presence of anal valves and sinuses.

Microscopic Study In Human Being:

In present study mucosa of rectum was found lined with simple columnar epithelium and having intestinal glands. The upper most part of the anal canal was lined with simple columnar epithelium where intestinal glands end. Robin and Cadist (1874) stated that pars analis recti differs from pars ampullaris in having no intestinal gland.

In present study, region between simple columnar epithelium and up to the superoexternal surface of anal valves was lined with stratified columnar epithelium Park (1956) described the extent of stratified columnar epithelium between the bottom of crypts and commencement of intestinal mucosa. While Goligher et al (1955) found that this zone was lined by stratified squamous epithelium.

In the present series we have found that region from superoexternal surface of valves including the part below it, is lined by stratified squamous epithelium and as proceeded caudally from stratified squamous epithelium it takes gradually the structure of skin. According to Robin and Cadist (1874) stratified epithelium lines the internal wall of sinuses, that is superoexternal wall of valves. Distal to sinuses he described the region which takes more and more structure of skin when followed caudally. According to Walls (1958) the upper zone between line of valve and intersphincteric interval, lining is formed by squamous epithelium; but the hair follicles and sebaceous glands are absent in this zone. As this region merges into true skin of perianal region, hairs, sebaceous and sweat glands reappear.

In Dog:

In present study rectum was lined with simple columnar epithelium having intestinal glands. The mucosa of anal canal was lined by stratified squamous epithelium having close relationship with lymphoid nodules. As proceeded distally from stratified squamous epithelium, it took gradually the structure of skin. Zimmermann (1904) reported that this region is lined with stratified squamous epithelium, which took more and more structure of skin, while passing distally from one region to the next.

In Rabbit:

In the present study the rectum was lined with simple columnar epithelium and having crypts of leiberkuhn. The anal canal was lined with stratified squamous epithelium and as proceeded distalwards from stratified squamous epithelium of anal canal, it took gradually structure of skin. According to Kotpal (1989) the rectum is lined with columnar mucosa. The epithelium becomes stratified near anus and it is guarded by anal sphincter.

References:

  1. Brodenhamer, W (1888) : Observation on the normal saccual of anal canal, both in health and disease also on the pretre natural pouches of the same region as described by Dr. Physick, New York, medical record vol-33 pp. 569-573.
  2. Chalari (1878) : Unberdieanalen Divertikelder rectum Sschleimhaut undthre Berichung-Zuden Analtisteln medjahrb. pp-419-427.
  3. Goligher (1955) : Surgical Anatomy of Anal canal, British Journal of Surgery 43: 51-61.
  4. Hebrant (1899) : Sur les glandes anales duchien, anatomic, physiologic, pathologics, Ann de med. Vet tom 48: pp. 633644.
  5. Jordan, E.L. and Verma, P.S. : Chordate Zoology S. Chand and company Delhi. p-634 (1999)
  6. Kotpal, R.L. : Modern text book of Zoology In: vertebrate. Rastogi publication, Merut 318-499 (1989)
  7. Miller : Miller's Anatomy of The Dog - 3rd ed / Howard E. Evans Edr W.B. Saunders Company devision of Harcourt Brace & Company: 446 to 449 (1993).
  8. Otis (1887) : Anatomischel Untersuchungenam Mensch- Llchen Rectum Leip. Zig Pp. 1-18.
  9. Park (1956) :British Journal of Surgery 44, 337
  10. Pennigton (1900) : New point in the Anatomy and Histology of rectum and colon Journal of American Medical Association Vol. 35: 1520 to 1526.
  11. Robin and Cadist (1874) : Jurn. del' Ant et de la phys tom 10: 589-620.
  12. Symington (1888) : The rectum and anus Journal of Anatomy & Physiology 23: pp. 106-115.
  13. Walls, E.W. (1958) : Observation on microscopic anatomy of human anal canal British Journal of Surgery 45: 504-12.
  14. Williams, P.L; Bannister, L.H; Berry, M.M; Collins, P; Dyson, M; Dussek, J.E; Ferguson, M.W.J. Gray's Anatomy In: Alimentary System. Bannister, L.H. Edr. 39th Edn. Churchill Livingston, London: pp- 1778-85 (1995).
  15. Zimmermann (1904) :Uterschungenam Des Analtengumentedes hundes, Arch, F Tlerheik, 30: pp-472515.

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Fig. 1: Interior of rectum and anal canal of human being. Showing transverse mucosal folds, anal columns, anal valves and sinuses

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Fig. 2: Interior of rectum (having nodular swelling) and anal canal of dog showing anal columns

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Fig. 3: Longitudinal section of anorectal region of human being having simple columnar epithelial lining and disappearance of intestinal glands.

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Fig. 4: Longitudinal section of anal canal of human being showing stratified columnar epithelium up to anal valve.

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Fig. 5 Longitudinal section of anal canal of human being showing both surfaces of anal valves and lined by stratified squamous epithelium

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Fig. 6: Longitudinal section of anal canal of dog showing lymph nodule and crypts lined with stratified squamous epithelium

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Fig. 7: Longitudinal section of anal canal of rabbit lined by stratified squamous epithelium with cornification.

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