Chapter 1 1 The secondary sexual characteristics develop, reproductive functions begin, and sexual dimorphism becomes more obvious during puberty. The pubertal changes are not the same in males and females. In females, the age of presumptive puberty is after 8…
During the process of embryonic development, undifferentiated precursor cells differentiate and organize into the complex structures found in functional adult tissues. This intricate process requires cells to integrate many intrinsic and extrinsic cues for development to occur properly. These cues…
Birth defects (anomalies) are developmental disorders present at birth. Defects are the leading cause of infant mortality (fetal outcome). They may be structural, functional, metabolic, behavioral, or hereditary. Birth defects are a global problem; close to 8 million children worldwide…
The integumentary system consists of skin and its appendages: sweat glands, nails, hairs, sebaceous glands, arrector muscles of hairs (arrector pili muscles), mammary glands, and teeth. Development of Skin and Appendages The skin is a complex organ system, and it…
Development of Eyes and Related Structures 17 The eyes begin to develop in 22-day embryos when optic grooves appear ( Fig. 18.1 A and B ). The eyes are derived from four sources: Neuroectoderm of the forebrain Surface ectoderm of…
The nervous system consists of three main regions: The central nervous system (CNS) consists of the brain and spinal cord and is protected by the cranium and vertebral column. The peripheral nervous system (PNS) includes the neurons outside the CNS…
Early Stages of Limb Development 15 The upper limb buds are visible by day 24, and the lower limb buds appear 1 or 2 days later, with the activation of a group of mesenchymal cells in the somatic lateral mesoderm…
The muscular system develops from mesoderm , except for the muscles of the iris of the eye, which develop from neuroectoderm (neural crest cells) , and the muscles of the esophagus, which are thought to develop by transdifferentiation from smooth…
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. 14.1 A and B ). Toward the end of the third…
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. 13.1 ). This precocious cardiac development occurs because the rapidly growing…