At 3 weeks gestation, precursors of red blood cells are present in my yolk sac, and early blood vessels can be seen. These elements are important in supplying my tiny body with nutrients. At 5 weeks my liver is red because it is producing red cells, a process called hematopoiesis, and this is taking place within my body for the first time. B - lymphocytes can be found at 7 weeks. Lymphocytes are part of my immune system which help me fight invading infections, and after birth they produce antibodies to assist in this effort. By week 11 and 12, T - cells leave the thymus, and immunological competence occurs. At 15 weeks stem cells arrive in the bone marrow, where most of the blood production will occur in the future. A large lymphocyte, the natural killer cell, recognizes abnormal cells, such as those with viruses, and tumor cells. They defend against intracellular pathogens.
The clotting of the blood, and the lysis of the clot can be seen at the end of the embryonic period, and these are in constant balance. Megakaryocytes are found in my liver and spleen at week 12, and platelets are released when they disintegrate. Clotting factors play a role in this system, and are both vitamin K dependent, and vitamin K independent. The vitamin K independent factors are at 50% that of the normal adult, and the vitamin K dependent ones are only 10 - 30% of the adult. Vitamin K reserves are low at birth, the hepatocytes are immature, not able to produce the vitamin in sufficient quantities, and the milk from my mum contains very little vitamin K. For this reason, newborns are given 1 mg of vitamin K to prevent bleeding in the intestinal tract and brain. I have a young cousin who suffers from thrombocytopenia, too few platelets, but he has not experienced any severe bleeding problems. My father takes ‘poisons’ which make his platelets less ‘sticky’, allowing the blood to flow more easily through his old blood vessels filled with plaques.
My blood initially is formed in “blood islands”, then the blood-forming cells migrate to the liver, spleen, thymus and the bone marrow. My clavicle is the first bone to contain marrow, at 10 to 11 weeks. Blood vessel development is coupled to other system development, including bones and endocrine systems, to allow distribution of hormones. Vessels form from endothelium from mesoderm, and from pre-existing vessels. Stimulation and Inhibition of vessel growth is in balance, as is the differentiation of arteries, veins, lymph vessels, and capillaries. My mum’s blood volume increases 50% during pregnancy, and uterine flow increases 10 - 12 fold. No wonder mummy is tired! My blood doesn’t mix with Mum’s blood. My red cells keep their nuclei, but adults red cells lose their nuclei. Our hemoglobins are different, and the exchanges of gases, waste products, and nutrients take place across layers of membranes in the placenta.
Like most of our organs, we take them for granted, and we are unaware of the tasks they are performing. We can’t feel the blood flow, nor are we able to feel the blood clotting, the dissolving of clots, the constant battle combating infections and foreign invaders. We don’t have a sensation of the oxygen and nutrients being delivered to our vital organs, nor of the metabolic wastes and carbon dioxide being carried away, and disposed of properly. We forget that Jesus redeemed us by shedding His blood on the cross, providing us a path to salvation. Can you help my ‘cousins’, by praying for their safety in the womb, and working so they may be recognized as humans, and that their blood will not be sacrificed any longer.
For more information go to: www.ehd.org., www.embryology.med.unsw.edu.au, www.embryology.ch.
With love,
Rose M. Bryo
Jesus poured out his blood for us.