Chapter 43, Problem 1Q

Summary Introduction

To review:

The relationship of defects in various bones, muscular system, and cardiovascular system of an infant with the deficiency of vitamin A.

Introduction:

The zygote is formed after the fertilization of an egg with the sperm. It further divides to form blastula that gets implanted into the uterine wall of the mother for its further growth. Formation of three germ layers occurs, from which various organs and organ systems of the fetus originate (organogenesis).

Explanation of Solution

The three germ layers: ectoderm, endoderm, and mesoderm arise from the embryo as a result of gastrulation that is sequentially positioned and organogenesis occurs in a coordinated manner. Some cells migrate anteriorly and becomes the part of endoderm. Another group of cells that migrate towards the midline of the embryo becomes the mesoderm and rest of the cells present above the mesoderm at the periphery forms the ectoderm.

Organs such as epidermis, nervous system, hairs, nails, and mouthparts arise from the ectoderm. The mesoderm also contributes to the formation of nervous system and other organs such as mesenchyme, cardiac and skeletal muscles, and gonads development. Digestive system, respiratory system and other vital organ systems such as endocrine system and urinary system develops from the cells of the endoderm layer.

This differentiation of three layers occurs during the first trimester of the gestation period. Several chemicals, as well as the environmental factors, affect the development of the embryo during this time. Deficiency or increased levels of these chemicals such as vitamins, folic acids, and valproic acid may yield detrimental results for the developing fetus. The deficiency of vitamin A has ill effects on the organs originating from the ectoderm and if present in excess amount then it can result in mesenchymal defects.

Thus, if an infant show defects in cardiovascular system, muscular system, bones, and mesenchyme that is due to the presence of excess levels of vitamin A and not due to deficiency of vitamin A. The reason behind this is deficiency of vitamin A causes defects in the organs originating from the ectoderm layer, whereas the cardiac system, muscular system and mesenchyme are mesodermally originating organs. However, excess level of vitamin A does affect the mesenchyme, which is mesodermally derived.

Conclusion

Therefore, the deficiency of vitamin A do not affect the mesenchyme, bones, cardiac and muscular systems in the infant rather the presence of excess levels of vitamin A cause these defects. Vitamin A deficiency causes defects in the ectodermal derived tissues and organs.