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Light microscopic study of epithelial histogenesis of the acini of the parotid gland.

INTRODUCTION: The parotid gland is a compound tubulolalveolar type of gland situated between mandible and sternocleidomastoid muscle projecting forwards on the surface of masseter muscle where a small part known as the accessory part of the parotid gland lies between parotid duct below and zygomatic arch above. (Bailey 1948). (1)

The largest of these salivary glands of human body is parotid gland, the gland around the ear (para-around, otic-ear). This is almost a serous gland. In humans, 25% salivary secretion is contributed by parotid gland. This secretion contains salts, proteins, and the enzyme ptyalin (Bloom and Fawcett, 1976). (2)

The complex mechanisms essential for the very existence of human life on the earth are dependent on the various secretions by exocrine and endocrine glands of the body. There is a group of larger glands situated anatomically outside the wall of the tract discharging into it, like pancreas the oropharyngeal region of human adult is beset with small gland in its mucous lining. Besides these minor salivary glands there are of course the major salivary glands including the parotids, the submandibulars and the sublinguals (Eorliss CE, 1976). (3)

The minimum physiological parenchymal unit of a salivary gland is referred to as a salivon which consists of an alveolus or acinus.

The proliferations form epithelial buds which later branch and further branch forming solid ducts with rounded ends. Ducts develop lumina within themselves and rounded ends differentiate into acini. Appearance of parotid duct anlage was observed at 14-18mms CRL Stage as an epithelial invagination in oral epithelium (Merida Velasco 1991). (9) At 7 weeks gestational age and unbranched parotid gland was seen as a bud from buccal cavity and extending towards ear (Gasser 2005). (6)

Salivary glands are therefore a classic model of organ development and differentiation. These begin as a solid proliferation of cells from the epithelium of the primitive mouth during 6th to 7th weeks (Moore et al 2008). (10)

MATERIAL and METHODS: 39 fetuses were collected from operation theatres and labor rooms of Government Medical College Jammu and various private hospitals, were preserved in 10% formalin followed by measurement of CR Lengths. The parotid glands of both right and left sides were dissected out and subjected to histological processing and sections of 5-7 microns were cut and stained with H and E stain and Masson Trichrome stain and then were seen under a binocular research light microscope and observations were made.

Assessment of the age of the fetuses was done according to the rule as described by Hamilton Boyd and Mossman (1976) (7) which states that at 32 days of intrauterine life, embryo is 5mms in CR length. For each additional day up to 55th day, the embryo grows at the rate of 1mm per day and after 55th day.

OBSERVATIONS:
TABLE III

GROUP NO.   CROWN RUMP LENGTH   NUMBER OF FETUSES

I              53 to 92 mm              4
II            97 to 120 mm              6
II            125 to 150 mm            16
IV            151 to 184 mm             8
V             187 to 250 mm             5


The study dealt was concerned with the development of acini of parotid gland. The parotid glands of both right and left sides of 39 fetuses ranging from 53 to 250 mm of crown rump lengths (10 to 29 weeks) were dissected and observations were made. For better understanding of the observations the fetuses were first arranged in ascending order, then divided into five groups and acini were described.

Group I:

[FIGURE 1 OMITTED]

a) Branching duct

b) Abundant connective tissue

c) Uncanalized acini

d) Canalized acini

Here parotid gland of a small fetus of 53mms size was taken for making observations. It was to be quite rudimentary seen as a small mass which was undifferentiated due to lack of lobulisation. Solid cords or clusters were seen spread over a sheet of mesenchyme and canalization in these solid cords or clusters was hardly visualized in initial stages though 1 to 2 linear cords of cells were seen which indicated initiation of branching.

These uncanalised clusters represent initial uncanalised tubules originated from main parotid gland. Formation of terminal end pieces as acini which are not showing significant canalization was seen in this group indicating that canalization of acini is not quite established in this initial group.

Group II:

[FIGURE 2 OMITTED]

a) Canalized acinus with lining of single layered pyramidal cells

b) Connective tissue

In this group, 6 fetuses of 97 to 120 mm CR Lengths were taken into consideration. The gland was observed to be still rudimentary in this group including parotid glands of small fetuses of various sizes. The further development and increased canalization of acini was observed as important milestone. Here at terminal ends the formation of acini was observed with linear ducts.

In this group acini were seen uncanalized at some places and canalized in some sections. Acini consisted of single layer of cells stained pink with H&E stain and were having central lumen. With progressively increasing CR lengths, the glandular component consisting of acini was seen slightly dominating over the ductal system.

Group III:

[FIGURE 3 OMITTED]

a) Acini with lumen

b) Connective tissue

In group III, 16 fetuses of CR Lengths ranging from 125mms to 150mms were considered and acini here were visualized as end pieces. Appearance of lumen was quite obvious in this group. Acini were seen in clusters or groups i.e. lobules separated by somewhat distinct connective tissue septae and together formed lobes of the gland. Acinar diameter was observed increasing as crown- rump length was increasing and glandular component was observed dominating the picture over the duct component.

Group IV:

[FIGURE 4 OMITTED]

a) Lymph node

b) Lobule with acini

In group IV, 8 fetuses of CR Lengths 151 mms to 184 mms were taken up for observation. Acini here were observed in clusters and further having arrangement of lobes and lobules. Therefore we could see the glandular component more distinctly in this group of fetuses. Acini were seen as terminal end pieces lined by single layer of cells and showed lumina clearly. So lobulisation formed a prominent feature with a quite distinct capsule.

Group V:

[FIGURE 5 OMITTED]

a) Blood vessel

b) Connective tissue septae

[FIGURE 6 OMITTED]

a) Intralobular duct between acini in lobules

In group V, 7 fetuses of CR Lengths 157mms to 250mms were seen again glandular component was seen dominating the picture as compared to the ductile system and connective tissue component and this dominance was quite significant in this group. Arrangement here could be compared to that of the adult parotid gland. The acini here were observed to be more closely packed as compared to the previous groups with clear and definite lobulisation.

DISCUSSION: The study under consideration has shown the changes during development of parotid gland in the intrauterine life.In fetuses with the smaller Crown Lump Lengths, we observed solid cords of cells over sheets of mesenchyme and ducts were seen forming prominent features branching and increasing proliferation. This is in accordance with the view given by Singh (11) that the salivary glands develop as outgrowths of the buccal epithelium and also in accordance with the findings of Fernandes et al (5) who state that by 10th week the invagination of parotid duct gives rise to several epithelial sprouts that proliferate and migrate posteriorly to form ducts. Work of Farr (4) also supports this stating that salivary glands arise as ectodermal buds that branch bush like into the deeper mesoderm.

In the present study, at 12 weeks gestational age, we observed the solid cords of cells along with linear clusters of cells forming linear ducts. These show canalization at only one or two places.

This differs with the view given by Merida Velasco et al (9) that canalization of intraglandular secretory ductules is completed by 11 weeks of gestation. Yaku (12) also described the formation of terminal tubules and also the lumina by 18 weeks. As the size of fetuses increased, the number of canalized acini increased significantly and the glandular component was seen dominating the picture with increasing Crown Lump Lengths. In the late developmental stage, acini histologically developed into a mature state similar to adult glands in accordance to the view expressed by Lee et al. (8)

CONCLUSION: The current study thus revealed the epithelial origin of the glandular component of the acini of the parotid gland. This has clinical implication in the later life when we come across the development of the salivary gland tumors. There we observe that this epithelial factor in histogenesis may contribute to the fact that most of the SATS are epithelial in origin as compared to the meager 25% of non-epithelial tumors of parotid gland later in adult life through the other associated causative factors are yet to be explored.

DOI: 10.14260/jemds/2014/2825

REFERENCES:

(1.) Bailey Hamliton. The surgical Anatomy of parotid gland. Br. Med. J 1948; volume 2. 245-248.

(2.) Bloom William and Fawcett DoN-W. Oral cavity & associated Glands. A text book of histology. W.B Sanders company. 1976; 8th edition; pp 605-612.

(3.) Eorliss clark Edward 'Glands of digestive tract', Patten's human embryology. McGraw Hill, New York 1976; 2ndedition; PP 291-292.

(4.) Farr Gary: Ectodermal derivatives. Human Embryology, epub, sept. 2003; Pp 1-8.

(5.) Fernandes ACS, Lima GR, Roosi AM. Parotid gland with double duct: An anatomic variation description. Int. J Morphol. 2009; 27(1); Pp 129-132.

(6.) Gasser Raymond F. "The early development of parotid gland around the facial nerve and its branches in man." Anat. Rec. 2005; vol. 167; Pp 63-67.

(7.) Hamilton WJ and Boyd J D and Mossman. Textbook of Human Embryology by Boyd, Hamilton and Mossman. William and Wilkins Company, 4th ed., 1976; Pg. 545.

(8.) Lee SK, Lim CY, Chi JG, Yamada K. Prenatal development of human major salivary glands and immmunohistochemical detection of keratins using monoclonal antibodies Acta. Histochem. 1990; 89(2); Pp 213-235.

(9.) Merida Velasco 1991, cited by Merida Velasco JR, Rodriguez Vazquoz JF, CDE LA CaudraBLANCO, I. Sanchez-Montesinos and Merida Velasco JA "Morphogenesis of juxtaoral organs in humans." J. Anat.2005; vol. 206 (2); Pp 155-163.

(10.) Moore Keith L, Persaud TVN and Torchea Mark G. The Developing Human. Saunders Philadelphia 2008, 8th edition; pg 179.

(11.) Singh Inderbir. Alimentary system1; Mouth, pharynx and related structures. Human Embryology, 8th edition 2007; Macmillon; Pg147.

(12.) Yaku Yuji. Ultrastructural studies of the development of human fetal salivary glands Archives of Histology and Cytology 2006 vol. 46 (5); Pp. 677-690.

AUTHORS:

[1.] Richa

[2.] Shahnaz Choudhary

[3.] Ashwani K. Sharma

PARTICULARS OF CONTRIBUTORS:

[1.] Demonstrator, Department of Anatomy, Government Medical College, Jammu.

[2.] Lecturer, Department of Anatomy, Government Medical College, Jammu.

[3.] Lecturer, Department of Anatomy, Government Medical College, Jammu.

NAME ADDRESS EMAIL ID OF THE CORRESPONDING AUTHOR:

Dr. Richa, H. No. 1, East Ext-D, Sainik Colony, Near Heritage School, Jammu.

E-mail: richadoctor@yahoo.com

Date of Submission: 23/04/2014.

Date of Peer Review: 24/04/2014.

Date of Acceptance: 05/06/2014.

Date of Publishing: 16/06/2014.
TABLE I

Age of the embryo/Fetus   Crown Rump Length

32 days                   5 mm
33-35 days                5mm+1mm per day
56 days onwards           Calculated age of fetus at 55
                            days + 1.5 mm per day

TABLE II: Embryonic growth is 1.5mm per day with respect to its CR
length

SL.     Crown Rump    Estimated     sex     No. of cases
NO.      Lengths     Age in Days              studied

I           53           72         Male         1
II          75           76        Female        1
III         87           94        Female        1
IV          92           98        Female        1
V           97           101        Male         1
VI         100           103        Male         1
VII        112           111       Female        1
VIII       115           113       Female        1
IX         120           116       Female        2
X          125           120       Female        2
XI         128           122       Female        1
XII        130           123        Male         1
XIII       134           126       Female        1
XIV        135           127        Male         2
XV         136           128       Female        1
XVI        140           130        Male         1
XVII       142           131       Female        1
XVIII      143           132        Male         1
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Title Annotation:ORIGINAL ARTICLE
Author:Richa; Choudhary, Shahnaz; Sharma, Ashwani K.
Publication:Journal of Evolution of Medical and Dental Sciences
Date:Jun 16, 2014
Words:1983
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