Medulla of kidney – A Postmortem Grossmorphological Study in Bangladeshi People

Introduction: The kidneys maintain the balance of sodium and water in blood plasma, they also excrete toxic wastes. On coronal section the kidney presents two parts-outer renal substance and inner renal sinus. Renal substance consists of outer cortex and inner medulla. Cortex is granular in appearance and medulla presents renal pyramids which are conical masses. Cortex which contains the glomeruli and the convoluted tubules can be distinguished from the medullary pyramids which has the loops of Henle, collecting ducts and collecting tubules. In apex of pyramid 16-20 ducts of Bellini open. The apices of several pyramids open together into a renal papilla, each of which projects into a minor calyx. Although the kidneys constitute 0.5% of the total body mass, they receive about 25% of the cardiac output. This richness of blood supply also makes the kidneys susceptible to toxic injuries by drugs and toxins. Of the amount of blood going to each kidney, 90% or more is distributed to the cortical area. Thus the exposure to circulating toxic substance, culminating in loss of renal cells is greater for the cortex than medulla. Renal mass increases from about 50gm at birth to more than 400gm during the third and fourth decades and it decreases approximately one fifth of it between fourth to eighth decade of life. An increase in interstitial fibrosis may conceal some

of the loss of substance.After the seventh decade, interstitial fibrosis becomes particularly pronounced in the medulla 12 .
Available articles are the evidences that human kidney has been widely studied in different races by various investigators.By studying kidney of different age groups, it is found that there are considerable structural and functional changes.These studies show normal growth process as well as degenerative changes after certain age 10-13, But regarding medullary pyramid, very few research works have been performed on kidneys collected from Bangladesh.So this study was intended to evaluate the number of medullary pyramid of kidney with changes of it in relation to age.

Materials and Methods:
The present study was performed on 70 kidneys of both sexes and sides in the Department of Anatomy of Mymensingh Medical College.The samples were collected from unclaimed fresh dead bodies that underwent routine postmortem examination in the morgue of the Department of Forensic Medicine, Mymensingh Medical College, Mymensingh from January 2004 to June 2005 due to accidental and unnatural death.Mymensingh is one of the largest districts in Bangladesh.Here people, who were migrated from all over Bangladesh live for various purposes.From this corner of views, the study of 70 samples of kidneys collected from Mymensingh can be taken into consideration that it might represent the status of 2 kidneys of whole Bangladeshi people.Moreover it is hardly possible to study the kidneys collected from the morgues of all over Bangladesh within the limited time during thesis period.The Kidneys of decomposed bodies, poisoned cases, kidneys with gross anatomical anomalies and known cause of renal death were excluded.The collected samples were divided into three age groups (Table-I).The samples preserved in 10% formol saline were washed to avoid irritation of the eyes and nasal mucosa.Then the samples were taken in metallic tray and the surrounding fat and other unwanted structures were removed carefully.After these by a sharp knife, coronal section of kidney was done through the lateral border to the hilum passing from upper to lower pole.Then medulla of the kidney was observed.After gross dissection mentioned above, the number of medullary pyramid in each half of the kidney was counted and noted 14 .

Results:
Out of total 70 study samples the average number of medullary pyramid was approximately 9. The highest mean number of pyramids was found in group B. Highly significant (<0.001) differences were found in the number of medullary pyramid between groups as well as among groups when analyzed statistically (Table IIa and Table IIb).

Table-IIb: Statistical analysis of table IIa
Discussion: Snell 4, Junqueira 15 , Ross 16 , Inke 17 found medullary pyramids 12,8-15,8-18,4-19 respectively.In this study, number of medullary pyramids ranged from 5 to 14 which is considerably lower than the findings reported by the investigators mentioned above.This may be due to the higher body weight as well as greater body surface area of western people and the kidney mass being more dependent on the individual's body built 18 .For this reason, in the present study number of medullary pyramids was dissimilar to that of kidney of western people.However the & Alam 19 that the kidney mass increases with increasing age upto 35 years and gradually decreases along with the increase of age particularly after 40 years, which may be a reflection of senile changes of the kidney and this was also correlated with the find-ings reported by Maclachlan 12 .Renal mass increases from about 50 gm at birth to more than 400 gm during the third and forth decades 13 .So in our study, presenting lowest number of medullary pyramid at younger age group could be explained by the relation of kidney mass to one's body built; with smaller individuals having generally small kidney mass than larger individuals 18 .
In this study number of medullary pyramid of the kidney in relation to various age groups was established as well as changes of it among the age groups had been marked.The cause of increase or decrease of the number of medullary pyramid at different periods of life might be related to the increase or decrease in body surface area as well as renal mass with age.