Learn Romanian: Inima este organul care trimite sângele. - The heart is the organ that sends the blood.

While a pompa (to pump) is perfectly valid and medically accurate (inima pompează sângele), trimite is commonly used in everyday Romanian to describe the heart's function in a simpler way. It is a natural way to express that the heart sends or circulates blood throughout the body.

Sânge ends in -e. Why is its definite form sângele instead of taking a feminine article?

Sânge is a masculine noun, not feminine. Masculine and neuter nouns that end in -e take the definite article -le, making it sângele (the blood). This is a common pattern to remember for words like câine (câinele) or frate (fratele).

Is organ masculine or neuter, given it takes the -ul article here?

It is neuter. You can tell by its plural form: un organ, două organe. In the singular, neuter nouns behave exactly like masculine nouns, which is why it takes the standard masculine/neuter definite article -ul to become organul.

Could I omit the definite article on sângele and just say trimite sânge?

Yes, and it changes the nuance slightly in Romanian just as it does in English. Trimite sângele means it sends the blood (referring to the specific total volume of blood in the body), whereas trimite sânge simply means it sends blood in a general, uncountable sense. Both are perfectly natural.