The tissue that forms a loose-fitting sac around the heart is the

Explanation:

Pericardium is the fibrous tissue that surrounds the heart and the roots of the great blood vessels

The pericardium's outer coat is called the parietal pericardium which is tough and thickened, loosely cloaks the heart, and is attached to the central part of the diaphragm and the back of the breastbone

Its inner coat is called the visceral pericardium or epicardium which is double, with one layer closely adherent to the heart and the other lining the inner surface of the outer coat

The intervening space between these layers is filled with pericardial fluid

This small amount of fluid acts as a lubricant to allow normal heart movement within the chest

Explanation:

The word "pericardium" means around the heart.

The parietal pericardium  serve  to protect the heart from damage and it reduce friction, and is made of the serous membrane.

It is made from thick connective tissue and  it is attached to diaphragm. It holds the heart in place in the chest cavity and protects from infections.  

Functions of  parietal pericardium

Parietal pericardium protects the heart from various type of infections. Parietal pericardium is the layer situated between the fibrous pericardium and visceral pericardium.

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