St. Paul's Analogy of the Body Updated (#1)

"Just as a human body, though it is made up of many parts, is a single unit because all these parts, though many, make one body, so it is with Christ."
[1 Cor 12:12 Jerusalem Bible]

The Heart

"The mammalian embryo, having practically no yolk available as food, is dependent for its survival and growth on the prompt establishment of relations with the circulation of its mother. This implies the neceesity of a very early development of the embryonic cardio-vascular system, for the maternal circulation remains confined within the uterine walls and the embryonic circulation must grow to meet it. Until this is accomplished the embryo is dependent on what food material it can obtain by direct absorption from the fluid within the uterine cavity..."
[B. M. Patten, Foundations of Embryology, 289]

How poetic is is to note that the hemopoietic centers - that is, the places where blood is made - begin to form around the third week of life. But these are not the red blood cells of adulthood called erythrocytes - those marvels which bring the outer air to every part of the body, which do not have a nucleus, and so do not divide and never have offspring, but exhaust themselves in service to the body...

Thus, let it be noted that never again can someone say that the celibate priesthood is unnatural! It is curious to also note that there are two other early forms of red blood cells which do have nuclei.

But these servants of the body will not go anywhere unless they are sent [See Romans 10:15]...

As a mammalian embryo advances [through the early stages of life] it satisfies all its metabolic needs by simple, diffusive interchanges with the fluid medium in which it is immersed. But as the embryo continues to gain size and begins to take form, a functioning circulatory system becomes necessary in order to make use of the required food and oxygen obtainable from the mother's blood. Hence it is that the heart and blood vessels are the first organ system to reach a functional state. [at about 4 weeks]
[L. B. Arey, Developmental Anatomy 375]

It is the heart which sends forth the blood, and so enables growth.

Most Sacred Heart of Jesus, have mercy on us.