"" Functional Adaptability of the Tunica Media of the Atriopulmonary Junction

Original Article

Austin J Anat. 2015;2(2): 1034.

Functional Adaptability of the Tunica Media of the Atriopulmonary Junction

Poonamjeet Kaur Loyal*, Kevin Ongeti, Pamela Mandela and Paul Odula

Department of Human Anatomy, University of Nairobi, Kenya

*Corresponding author: Poonamjeet Kaur Loyal,Department of Human Anatomy, University of Nairobi,School of Medicine, 30197-00100- Nairobi, Kenya

Received: March 03, 2015; Accepted: May 04, 2015; Published: May 04, 2015

Abstract

Introduction: The histoarchitecture of the tunica media of the Atriopulmonary Junction (APJ) has not been extensively studied and yet the tunica media is the backbone, which provides the structural strength for optimum function. This study therefore strives to unravel the structural components of the tunica media of the APJ.

Methods: The study design was a descriptive cross-sectional study. Histological studies were done on tissues from the APJ of 20 hearts using light microscopy. The proportion of elastic fibers in the tunica media of the APJ was determined using the point intercept method by dropping a grid in ImageJ software.

Results: The smooth muscle cells were concentric and more prominent in males extending the entire extent of the tunica media compared to females where they were confined to the intimal side of tunica media. The collagen bundles were mainly longitudinal. The elastic fibers showed a diverse pattern of organization and side and sex differences in orientation and quantity.

Conclusion: Gender and regional variations in the histology of the tunica media of the pulmonary veins suggest a mechanism for controlling hemodynamic forces at the APJ.

Keywords: Tunica media; Atriopulmonary junction

Introduction

The Atriopulmonary Junction (APJ) is an interface between the Left Atrium (LA) and the Pulmonary Veins (PVs) [1]. It is subjected to various forces including hemodynamic stress of the blood as it flows from the lungs to the left atrium; translational forces of the lung through the pulmonary veins; and retrograde pressure forces during systolic contractions of the left atrium [2]. The tunica media of a blood vessel consists of smooth muscle, elastic fiber and collagen bundles [1], but there is paucity of information regarding the histoarchitecture of the APJ. This study was therefore designed to investigate the functional adaptability of the tunica media of the APJ in the face of the volume of forces that it withstands.

Materials and Methods

Ethical approval was sought from the Kenyatta National Hospital- University of Nairobi Ethics and Research Committee before commencement of the study. Permission and requisite authority was obtained from the administration of Chiromo Funeral Parlor for acquiring histological tissues from autopsy specimens. Twenty hearts were used for histomorphology with 10 being from male and 10 from female subjects for a fairer representation. Since a large proportion of the victims of cardiovascular disease are from the adult age group [3], hearts from subjects ranging from 20-40 years were used as study specimens. All specimens were from individuals of black Kenyan descent.

Heart specimens from both sexes and of adult age group (>18 years) were included in this study. With the help of the pathologist, heart specimens with any observable pathology or congenital defects were excluded. Autopsy specimens that had stayed for more than 48 hours post mortem were also excluded from histological study.

Data collection procedure

At autopsy, with the help of the pathologist, a Y-incision was made from the acromio-clavicular joints to the xiphoid process. The thoracic cage was opened by incision of the costal cartilages. The sternum was then removed carefully and pericardium was incised longitudinally to expose the heart. The hearts were categorized according to sex and longitudinal and transverse sections of APJ were cut. This allowed regional histoarchitectural changes from the LA, APJ, and proximal part of PV to be studied. The tissues were fixed for a period of 72 hours in 10% formal saline after which they were dehydrated in ethyl alcohol of increasing concentrations, starting with 70% alcohol to absolute alcohol (1hour in each solution). Toluene was used as a clearing agent for 1.5 hours followed by wax impregnation for 12hours at 58°C. After tissues were embedded in freshly molted wax, 7 micron thick sections were prepared using a sledge microtome (Leica Model SM2400, Leica Microsystems, Nussloch GmbH, Germany). These were then floated in warm water at 37°C to enhance spreading upon which they will be fixed on slides using egg albumin. The slides were left to dry in an oven at 38°C for 12 hours. Dewaxing was done using xylene and the segments rehydrated using xylol (prepared from xylene and isopropyl column), absolute alcohol and descending concentrations of alcohol to 70% then running water. The sections were stained with Masson’s Trichrome (MT) stain to demonstrate connective tissue and myocardial sleeve organization and Weigert’s resorcin fuschsin with van Gieson counterstaining (WT) to demonstrate elastic fibers. Mounting of the cover slips onto specimens was done using D.P.X mountant (Unilab Kenya).The slides were examined with a light microscope (Leica model BME, Leica Microsystems, Nussloch GmbH, Germany) at x40, x100, x400 magnifications and the histological features were recorded on data sheets.The slides were photographed using a ZeissTM digital photomicroscope (Carl Zeiss AG, Oborkochen, Germany) at various magnifications and were then downloaded for further computer analysis. The photographs were edited using Photoscape Image Editor ™version 3.5. The proportion of elastic fibers in the tunica media of the APJ was determined using the point intercept method by dropping a grid in ImageJ software:

Results

Salient features of the tunica media of the APJ were flattened fusiform shaped smooth muscles amidst dense regular connective tissue consisting of collagen bundles and elastic fibers. The Smooth Muscle (SM) cells were concentric and more prominent in males (Figure 1) compared to females (Figure 2). Whereas the SM cells occupied almost the entire extent of the tunica media in the males (Figure 1A, 1B), in females they were confined to the intimal side of the tunica media (Figure 2A, 2B). The collagen bundles were mainly longitudinal but changes in orientation were observed towards the adventitial side of the tunica media as they became less densely packed (Figure 1, 2).