Brianna Laplante

I really enjoyed learning about fertilization in last night’s lecture. I think it is amazing how a tiny ball of cells develops into a fetus with complex body systems. Pregnancy is measured in trimesters from the day of your last menstrual period, totaling 40 weeks. The first trimester is the period that really interests me. The first trimester of pregnancy includes weeks 1-12, or about 3 months.

Actual pregnancy begins at the time when the egg is fertilized by the sperm cell. During the following week the fertilized egg grows into a microscopic ball of cells (blastocyst), which implants on the wall of the uterus. This implantation triggers many hormonal and physical changes in the body. The third-eighth weeks are called the embryonic stage, during which the embryo develops most major body organs. During this stage the embryo is highly vulnerable to damaging substances such as alcohol, radiation, and infectious disease.

Having reached a little more than 1 inch in length by the 9th week of growth, the embryo is now called a fetus. By this time, the uterus has now grown from the size of fist to about the size of a grapefruit!!

What struck me as interesting during lecture was the discussion on Schwann cells. Schwann cells are a variety of neuroglia that mainly provides myelin insulation to axons in the peripheral nervous system. Schwann cells are named after the German physiologist, Theodore Schwann.

I found some additional information about Schwann cells today. Schwann cells appear under a light microscope when immunostained with an anti-S-100 antibody. Schwann cells begin to form the myelin sheath of mammals during fetal development and work by spiraling around the axon up to 100 revolutions. A well-developed Schwann cells is shaped similarly to a rolled up sheet of paper with layers of myelin between each coil. Many recent experimental studies are implanting Schwann cells into patients with multiple sclerosis to try to induce remyelination. In addition to creating myelin sheaths in the PNS, Schwann cells also aid in cleaning up of debris in PNS and guide the regrowth of PNS axons. Pretty cool!