Question

Immediately after the cells differentiate—become particular kinds of cells—they begin to form tissues. When does heart tissue first form in a human?

Answer 1

during the first trimester of pregnancy

Step-by-step explanation:

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Answer 2

19-22 days after fertilization of egg by sperm

Step-by-step explanation:

The heart is the first organ to be formed in a developing embryo. This is because it is a vital organ and responsible for the circulation of blood (with oxygen and nutrients) to the other developing tissues. It begins to be formed at around 18 days from fertilization and begins to function after day 21.