PLMS 3

The _______ is the major structure of the circulatory system.

• brain

• heart

• lungs

• blood

The heart is surrounded by a thin fluid-filled sac called the ________.

• muscular organ

• pericardium

• Arteries

• Capillaries

The thin outer layer of the heart

(a)  

The right and left chambers are separated from each other by partitions called (a)  

The middle muscle layer of the heart is called (a)   .

The thin inner layer of the heart is called (a)   .

The upper chambers on each side of the heart are called (a)  

The lower chambers on each side of the heart are called (a)  

The valves at the entrance to the ventricles are called (a)  

The valves at the exit to the ventricles are called (a)