The rudimentary plant contained in the seed, consisting of cotyledon(s), radicle and plumule.
The prenatal stage of mammalian development characterized by rapid morphological changes and the differentiation of basic structures.
The rudimentary plantlet in the seed.
An undeveloped plant still inside the seed.
The fertilized egg from the moment of conception through the 8th week of prenatal development, which is the period during which primary tissues differentiate and organs develop.
An unborn baby during the first eight weeks after conception.
The earliest detectable stage of a seedling enclosed in the developing seed, shortly after fertilization; or the plantlet that can be observed when a mature seed is dissected.
Unborn child that is still developing and growing inside the mother’s body.
The initial stage of development of the fertilized egg; usually the first 12 weeks in human pregnancy.
Medical designation for the growing being during a pregnancy, from the time of implantation, when the fertilized egg attaches itself to the lining of the uterus, through the first eight weeks of gestation. After that point, the being is generally known as a fetus. Soon after implantation, some of the egg’s cells begin to develop the nourishing placenta. Also a sac filled with amniotic fluid begins to form, cushioning the developing embryo. (It is this fluid that is sampled in the genetic screening test called amniocentesis.) These early weeks of embryonic development are crucial to the new being; it is during this period that all of the major organs begin to develop (by the fifth week). And it is during this period, often before a woman even realizes that she is pregnant, that great damage can be done by ingestion of alcohol and drugs and exposure to radiation and other hazards that can lead to birth defects.
Early developing organism, from the zygote to the fetal stage; in humans, from week 3 to week 8 after conception, at which time the main organ systems have formed, at least in their early stages.
A fertilized egg from the time of conception until the eighth week of pregnancy. Pregnancy begins with fertilization, the process in which the egg is united with a sperm. After fertilization, the egg (zygote) begins to divide into a cluster of cells, or blastocyst, which continues to divide as it moves down the fallopian tube toward the uterus. Five to eight days after fertilization, the blastocyst implants itself in the wall of the uterus and becomes a developing embryo. After 8 weeks the embryo is called a fetus.
An animal at an early stage of development, before birth. In man the term refers to the products of conception within the womb in the first eight weeks of development, during which time all the main organs are formed.
The fetus in the womb prior to the end of the second month.
The young of any organism in an early stage of development.
A developing human, from fertilization through the first 8 weeks of development.
Name given to the blastocyst after it has attached itself to the wall of the uterus.
The initial phases of an organism’s development.
The developing entity within the womb during the initial eight weeks after conception is referred to as the “embryo.” After this period and for the remainder of the pregnancy, it is commonly known as the “fetus.”
The progression of the embryo’s development is regulated by a combination of internal factors, including genes inherited from the parents, and external influences, such as the mother’s diet and any medications taken during pregnancy.
The embryo originates from a fertilized ovum (egg) resulting from the union of sperm and egg. Initially, it begins as a single cell but undergoes multiple divisions while journeying through the fallopian tube towards the uterus (womb), eventually forming a spherical cluster of cells.
Approximately six days following conception, this cell mass becomes implanted in the lining of the uterus. At the point of attachment, the outer layer of cells draws nourishment from the woman’s blood, eventually developing into the placenta. Within the cell mass, a flat disc emerges, comprising layers of cells from which all the baby’s tissues will eventually arise. Concurrently, the amniotic sac begins to take shape around the developing embryo.
During the early part of the third week, the previously flat disc of cells transforms into a pear-shaped structure. The rounded end gives rise to the head of the embryo, while the pointed end becomes the lower spine. Simultaneously, a cluster of cells emerges along the embryo’s back, forming the notochord—a fundamental rod-like structure that serves as the foundation for the spine. From this stage onwards, the embryo exhibits two distinct halves, which develop in a more or less symmetrical manner.
Following its formation, the notochord undergoes furrowing, with its edges gradually moving towards each other. Eventually, they fuse together to create the neural tube. As development progresses, the neural tube will further mature and give rise to both the brain and the spinal cord.
In the fourth week, the back of the embryo experiences accelerated growth compared to its front, resulting in a C-shaped appearance. The neural tube also elongates towards the embryo’s head, where a noticeable fold begins to take shape, destined to develop into the brain in due course.
As the embryo progresses, it undergoes fascinating transformations. Ears take shape as small depressions, and basic eyes emerge as tiny stalks. Buds of tissue emerge within, destined to grow into vital organs such as the lungs, pancreas, liver, and gallbladder. The heart begins its development, initially resembling a tube. Meanwhile, the outer layers of the embryo give rise to limb buds, and on the sides of the neural tube, paired bulges appear. These bulges will eventually develop into the essential structures of the back, including cartilage, bone, and muscle.
By the fifth week of pregnancy, remarkable changes take place in the developing embryo. External ears become discernible, and tiny pits indicate the nascent position of the nose. The jawline begins to take shape, while limb buds continue to extend, gradually flattening at their ends, foretelling the emergence of hands and feet. Additionally, folds of tissue fuse together to form the front wall of the chest and abdomen. During this period, the crucial umbilical cord also starts to develop, establishing a vital connection between the growing embryo and the placenta.
Between weeks six to eight of pregnancy, remarkable transformations occur in the embryo’s development. The face starts to take on recognizable human features, giving a glimpse of the future appearance. The neck begins to form, providing a clear distinction between the head and the rest of the body. Moreover, the limbs undergo joint formation, allowing for greater flexibility and movement. During this period, the fingers and toes make their appearance, further emphasizing the emergence of the individual’s distinct characteristics.
Once the embryo reaches the eight-week mark, it measures approximately 2.5 cm in length, marking significant growth since conception. At this stage, the majority of internal organs have taken shape, setting the foundation for their respective functions. Additionally, all external features have developed, making the embryo’s appearance complete with recognizable characteristics. While still in the early stages of development, the embryo’s basic form is now evident and poised for further growth and refinement.
The initial phases of the fertilized egg’s growth within the uterus, where the embryo comprises three distinct layers: the ectoderm, serving as the outer layer, giving rise to the skin, hair, eyes, nails, and nervous system; the mesoderm, positioned as the middle layer, which forms the circulatory, muscular, and skeletal systems; and the entoderm, constituting the innermost layer, responsible for the development of the digestive system, liver, lungs, bladder, and thyroid gland.