Human development begins at fertilization when a sperm fuses with an oocyte to form a single cell, the zygote . This highly specialized, totipotent cell (capable of giving rise to any cell type) marks the beginning of each of us…
Human development is a continuous process that begins when an oocyte (ovum) from a female is fertilized by a sperm (spermatozoon) from a male to form a single-celled zygote ( Fig. 1.1 ). Cell division, cell migration, programmed cell death…
Chapter 1 1 Health-care professionals are expected to give intelligent answers to the questions people ask, such as, “When does the baby's heart start to beat?” “When does it move its limbs?” “When is the embryo most at risk for…
During embryonic development, undifferentiated precursor cells differentiate and organize into the complex structures found in functional adult tissues. This process requires cells to integrate many different cues, both intrinsic and extrinsic, for development to occur properly. These cues control the…
Birth defects (anomalies) are developmental disorders present at birth. As a global problem, it has been estimated that annually almost 8 million children worldwide are born with a serious birth defect. Birth defects are the leading cause of infant mortality…
The integumentary system consists of the skin and its appendages: sweat glands, nails, hairs, sebaceous glands, and arrector muscles of hairs. The system also includes the mammary glands and teeth. Development of Skin and Appendages The skin, the outer protective…
Development of Eyes and Related Structures 17 The eyes are derived from four sources: Neuroectoderm of brain Surface ectoderm of head Mesoderm between the above layers Neural crest cells of the prosencephalon and mesencephalon Early eye development results from a…
The nervous system consists of three main regions: The central nervous system (CNS), which includes the brain and spinal cord and is protected by the cranium and vertebral column The peripheral nervous system (PNS), which includes the neurons outside the…
Skeletal System As the notochord and neural tube form in the third week, the intraembryonic mesoderm lateral to these structures thickens to form two longitudinal columns of paraxial mesoderm ( Fig. 15.1 A and B ). Toward the end of…
The cardiovascular system is the first major system to function in the embryo. The primordial heart and vascular system appear in the middle of the third week ( Fig. 14.1 ). The heart begins to beat at approximately day 22…