Question

What is the name of the thick, membranous sacs that surrounds and protects the heart?

Answer 1

The pericardium

Explanation:

The pericardium is a thin, but tough and fibrous sac that protects the myocardium (heart muscle).

It is described as being double-layered, in that the innermost surface is called the visceral pericardium, this is attached to the outermost layer of the heart, the epicardium. There is then a gap between the visceral pericardium known as the pericardial cavity and a second layer, known as the parietal pericardium. The purpose of the gap is to provide a space for lubrication. The heart is continuously beating, and if there was no lubrication, the pericardial layers would rub against one another, resulting in pain and inflammation (pericarditis).

The best way to imagine the layers of the pericardium is to get a partially inflated balloon, and press your fist into it. Imagine that your fist is the heart muscle. The layer of balloon that is covering your fist is the visceral layer, and the layer that is touching the table is the parietal layer. The gap that is formed between the visceral and parietal layers is the pericardial cavity.

The sides of the membranes that face one another to form the pericardial cavity are very smooth. To feel them in your hands feels much like how I imagine two thin pieces of balloon sliding against one another covered in washing-liquid must feel like. Go ahead, experiment if you like. This is what the heart needs in order to beat continuously, without friction.

At this point, I have no idea what your level is, but I'd like to point out that the anatomical nomenclature used here is exactly the same for the pleural membranes that surround the lungs, the meningeal membrane that surrounds the brain, and the peritoneal membrane that surrounds the abdominal organs. Wherever there is a cavity containing organs, there is usually a membrane surrounding them. Just as long as you can remember that another term for organs is viscerae, you'll always know that the visceral layer attaches to the organ; the outer layer must then be the parietal layer.