Both gastrulation and neurulation are critical events that occur during the 3rd week of embryonic development. Gastrulation is the process by which the bilaminar disc Bilaminar disc Embryoblast and Trophoblast Development differentiates into a trilaminar disc, made up of the 3 primary germ layers: the ectoderm, mesoderm, and endoderm. During this process, a structure called the notochord is formed in the midline in the mesodermal layer; the notochord is critical in inducing neurulation. Neurulation is the process by which some of the ectoderm in the trilaminar embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week develops into the neural tube and neural crest Neural crest The two longitudinal ridges along the primitive streak appearing near the end of gastrulation during development of nervous system (neurulation). The ridges are formed by folding of neural plate. Between the ridges is a neural groove which deepens as the fold become elevated. When the folds meet at midline, the groove becomes a closed tube, the neural tube. Hirschsprung Disease cells, which will go on to form all of the neural tissue in the body. This process is completed by the end of the 3rd week.
Last updated: 22 Jun, 2022
Progression of early human development from
fertilization
Fertilization
To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur.
Fertilization and First Week through the
blastocyst
Blastocyst
A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper.
Fertilization and First Week stage:
During these stages, the
embryo
Embryo
The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus.
Fertilization and First Week is surrounded by a layer of
extracellular matrix
Extracellular matrix
A meshwork-like substance found within the extracellular space and in association with the basement membrane of the cell surface. It promotes cellular proliferation and provides a supporting structure to which cells or cell lysates in culture dishes adhere.
Hypertrophic and Keloid Scars known as the
zona pellucida
Zona pellucida
A tough transparent membrane surrounding the ovum. It is penetrated by the sperm during fertilization.
Fertilization and First Week.
Development of the
bilaminar disc
Bilaminar disc
Embryoblast and Trophoblast Development as the
embryo
Embryo
The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus.
Fertilization and First Week is invading into the uterine wall:
As the
cytotrophoblast
Cytotrophoblast
Embryoblast and Trophoblast Development cells divide, cells on the uterine side begin losing their membranes, releasing hydrolytic
enzymes
Enzymes
Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules.
Basics of Enzymes and allowing the
embryo
Embryo
The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus.
Fertilization and First Week to “digest” some of the uterine lining to facilitate
implantation
Implantation
Endometrial implantation of embryo, mammalian at the blastocyst stage.
Fertilization and First Week. These “free nuclei” are the
syncytiotrophoblast
Syncytiotrophoblast
Embryoblast and Trophoblast Development cells.
Implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week of the blastocyst Blastocyst A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper. Fertilization and First Week:
At this stage, the embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week exists as an outer cell mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast and an inner cell mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast. Note how, as the blastocyst Blastocyst A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper. Fertilization and First Week digests the uterine wall, a layer of endometrium Endometrium The mucous membrane lining of the uterine cavity that is hormonally responsive during the menstrual cycle and pregnancy. The endometrium undergoes cyclic changes that characterize menstruation. After successful fertilization, it serves to sustain the developing embryo. Embryoblast and Trophoblast Development (pink cells) grows over and surrounds the embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week, securing it to the uterine lining.
Image: “ Implantation Implantation Endometrial implantation of embryo, mammalian at the blastocyst stage. Fertilization and First Week” by Phil Schatz. License: CC BY 4.0, cropped by Lecturio.Relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship of the bilaminar disc Bilaminar disc Embryoblast and Trophoblast Development, yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development, and amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development in the early embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week:
As the embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week invades further, the endometrial lining covers the embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week, securing it to the uterine wall. The primary yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development develops “beneath” the hypoblast Hypoblast Embryoblast and Trophoblast Development, while the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development begins growing “above” the epiblast Epiblast Embryoblast and Trophoblast Development. The syncytiotrophoblast Syncytiotrophoblast Embryoblast and Trophoblast Development surrounds endometrial capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: Histology, which rupture, forming lacuna, which will ultimately become the maternal component of the placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity. A layer of extraembryonic mesoderm Extraembryonic mesoderm Embryoblast and Trophoblast Development grows outside both the yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development and the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development; ultimately the chorionic cavity will develop in this area.
Image by Lecturio. License: CC BY-NC-SA 4.0Gastrulation is the process by which the bilaminar disc Bilaminar disc Embryoblast and Trophoblast Development develops into the trilaminar disc.
Process of gastrulation:
Cells from the
epiblast
Epiblast
Embryoblast and Trophoblast Development migrate down through the primitive streak and displace most of the
hypoblast
Hypoblast
Embryoblast and Trophoblast Development cells, becoming the endoderm. Cells that remain in the middle become the mesoderm. Cells that remain in the
epiblast
Epiblast
Embryoblast and Trophoblast Development layer become the ectoderm.
Beginning of gastrulation:
The primitive streak and primitive groove form in the
bilaminar disc
Bilaminar disc
Embryoblast and Trophoblast Development.
Migration of
epiblast
Epiblast
Embryoblast and Trophoblast Development cells through the primitive groove:
These
epiblast
Epiblast
Embryoblast and Trophoblast Development cells displace the
hypoblast
Hypoblast
Embryoblast and Trophoblast Development to become the endoderm and create a middle layer known as mesoderm.
Epiblast
Epiblast
Embryoblast and Trophoblast Development cells that remain on the dorsal surface differentiate into ectoderm.
Neurulation is the process by which ectoderm in the trilaminar embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week develops into the neural tube.
Beginning in the 3rd week, a group of ectodermal cells progresses through the following structures:
Development requires folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12; folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12 deficiency → neural tube defects Neural tube defects Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed NTD) to very severe malformations of the spine or brain (open NTD). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects
The process of neurulation:
Neural crest
Neural crest
The two longitudinal ridges along the primitive streak appearing near the end of gastrulation during development of nervous system (neurulation). The ridges are formed by folding of neural plate. Between the ridges is a neural groove which deepens as the fold become elevated. When the folds meet at midline, the groove becomes a closed tube, the neural tube.
Hirschsprung Disease cells (green) are derived from the neural plate (gray), which folds upwards and inwards towards the midline to create the neural tube.
Neurulation:
Differentiation and growth of the neural plate into the neural tube during the 1st trimester of gestation
Spontaneous abortion Spontaneous abortion Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks’ gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Spontaneous Abortion ( miscarriage Miscarriage Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks’ gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Spontaneous Abortion): abnormalities of gastrulation typically result in multiple congenital Congenital Chorioretinitis anomalies. These embryos are typically incompatible with life, and the result is a spontaneous loss of the pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care, usually in the 1st trimester.
Neural tube defects Neural tube defects Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed NTD) to very severe malformations of the spine or brain (open NTD). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects ( NTDs NTDs Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed ntd) to very severe malformations of the spine or brain (open ntd). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects): caused by the failure of the neural tube to close properly during embryologic development, potentially resulting in protrusion of neural tissue. Neural tube defects Neural tube defects Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed NTD) to very severe malformations of the spine or brain (open NTD). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects may involve the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy and/or cranium Cranium The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy and may be open (involving the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy and/or neural tissue) or closed (involving the bony vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy). Prenatal diagnosis by ultrasonography and maternal α-fetoprotein level is common. Management of open NTDs NTDs Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed ntd) to very severe malformations of the spine or brain (open ntd). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects is mainly surgical.