Histology

Histology

The Common Vein Copyright 2007

Ashley Davidoff Cristina Cesaro

The aortic wall, with its high elastic content supported by muscle and collagen, allows for transmission of a more or less steady blood pressure within the circulation by providing a tensile strength that can be adjusted to conform to the pumping strength of the heart muscle.

Normal Smooth glistening Endothelial Surface of the Neonatal Aorta

This is a post mortem specimen of the aorta of a patient with pulmonary atresia and bronchial collaterals. Overlaid in red are the enlarged orifices of the origins of the bronchial arteries. In yellow is the entrance of the PDA (patent ductus arteriosus) to the aorta Note in addition the normal appearing shiny appearance of the neonatal intima. Courtesy Ashley Davidoff MD 32628c a79-8

 

The composition of the aortic walls attributes its elastic nature. The innermost layer of the artery is the tunic intima. This layer is coated by a single sheet of endothelial cells which line the lumen of the artery. The intima’s subendothelial layer consists of a complex network of cells which aid in the dilation and contraction of the walls. They include fibroblasts, macrophages and elastic fibers surrounded by in an extracellular matrix. These membrane-bound elastic fibers run in parallel directions, causing the striated appearance of the layer.

Directly below the intima lies the tunica media. Composed primarily of smooth muscle and elastic fibers, this is the layer primarily responsible for the aorta’s distensible strength.  The elastic fibers are discretely packaged in circulatory lamellae separated by an intercellular medley of elastic fibers, collagen and undifferentiated cells. Such a radial arrangement of fibers characterizes this middle layer.

The last and outermost layer of the aorta is the tunica adventitia. Extending to the outer wall of the aorta, this layer serves not only as a protective covering for the aorta but also a supplier of oxygen to the distal layers of the wall. This function is achieved by the vasa vasorum—an extensive network of miniscule arterioles dispersed between the media and adventitia interface. It should be noted that these branches vary along the sections of the aorta. They are most dense in the thoracic region and nearly absent in the abdominal region. Without the vasa vasorum, only the proximal aortic layers would receive substantial oxygen from the lumen. In comparison with the tunica media, the tunica adventitia contains a smaller amount of smooth muscles cells. It is primarily made up of collagen-dispersed connective tissue, fibroblasts and a network of nerves relaying mostly adrenergic responses. These fibers protect the aorta from overstretching and comprise the aorta’s protective outer shell.

Elastic Artery
47678b04.800 artery aorta histology character normal endothelium media adventitia tunica elastica tunica muscularis.

Elastic Aorta

histologic section of the wall of the aorta shows the thin intima, the thick elastic media characterised by the white wavy bands, and the media which consists of strong collagenous fibres.

 

Elastic Aorta

47678.800 artery aorta histology character normal endothelium media adventitia tunica elastica tunica muscularis Davidoff art Davidof MD

Shock and the Small Aorta Ability of the Smooth Muscle

This patient presents with cardiogenic shock In image a, the right ventricle and right atrium are enlarged and thereare bilateral pleura; effusions. Image b shows stasis of contrast into the IVC and the column is relatively stattic due to peripheral constriction and slow return. There is reflux into the hepatic veins due to tricuspid regurgitation and the reflux extnds all the way to the periphery indicating poor forward flow in the hepatic circulaltion again due to operipheral constriction. Note how small the aorta due to contraction of the muscular media in this life threatening situation.. In image c the celiac axis with branches hepatic artery and splenic artery show severe vasoconstriction. In d the reflux of contrast from tricuspid regurgitaion (TR)extends deep into the renal parenchyma for the reasons outlined above.   The patient subsequently developed shocked liver.

73796c01 Courtesy Ashley Davidoff MD