Pregnancy Week 3 – The Baby’s Progress

As you can see, in pregnancy week 3, this is when the first structural forms of the embryo begin to take shape. The 3 seperate germ layers on the embryo body now begin developing into their respective internal organ groups by undergoing a process known as Organogenesis (a Greek term meaning “that with which one works”). This process is defined as splits, folds and condensation of the evolving organs.

Pregnancy Stages Week By Week

2 vital structures in these early stages of pregnancy development are:

The Notochord – This is a flexible rod that appears in the body of the embryo and defines the structure of it’s central axis. It will be replaced later by the spinal column. There are many essential functions of the notochord at this stage. To understand the notochord in it’s simplest form then think of it as a primitive ‘control center’ to the embryo before the brain and nervous have evolved.

The notochord secretes growth proteins which instruct surrounding tissues of the germ layers to acquire particular differentiated fates and without these signals then the structures of the spinal cord, organs and muscles would not develop properly. The notochord plays an integral role next in the development of the neural tube.

The Neural Tube – Which folds over the notochord is the precursor to the central nervous system that includes the spinal cord and a brain bulge at one end. The spinal cord in a long, thin, tubular bundle of nerve tissue that extends from the brain. Together, the brain and spinal cord make up the nervous system.

Extensive bundles of cell formation, known as ‘Somites’ are distributed along both sides of the neural tube which later develop into skeletal muscle, spinal nerves and vertebrae (flexible bone). These vertebrae are the spinal column that ultimately protects the spinal cord.

The diagram below, defining pregnancy week 3, clearly shows the early fetal development stages of cell division in the separate germ layers (ectoderm, endoderm and mesoderm, see week 2) as they form into their respective organ groups. This week will also see the beginnings of a primitive heart tube forming.

Early Fetal Development

It’s astounding to think that by the time your next period was due you could already have a human embryo with the foundations of a heart, brain, spinal cord and nervous system already laid down and still you may not even realize that you’re pregnant. Equally astounding, is that all of this complexity is occurring within something that is no larger than the size of a pin-head.

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(See 3 Weeks Pregnant – The Mother’s Progress)

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