Blastocyst 14 Days

Extraembryonic Visceral Mesoderm

The embryoblast differentiates into two distinct cell layers, the epiblast and hypoblast, forming a bilaminar embryonic disk. A. Epiblast. Clefts develop within the epiblast to form the amniotic cavity. B. Hypoblast cells migrate along the cytotrophoblast, forming the yolk sac. C. The prochordal plate, formed by the fusion of epiblast and hypoblast cells, marks the future site of the mouth. A. The syncytiotrophoblast continues its growth into the endometrium to make...

Vnerves Brachial Plexus

Trapped Nerve

Local molecular messages produced at the base of the limb bud guide the early nerve fibers into the limb bud the muscles themselves do not provide, any specific target messages to the ingrowing nerve fibers. B. Ventral primary rami from C5, C6, C7, C8, and Tl arrive at the base of the limb bud and join in a specific pattern to form the upper trunk, middle trunk, and lower trunk. C. Each trunk will divide into posterior divisions and anterior divisions. 1. Posterior divisions grow into the...

Clinical Correlations

Congenital Lens Opacities

Note the cleft in the iris (black spot at arrow). (B) Congenital cataracts. Note the lens opacities in both eyes. (C) Congenital glaucoma (buphthalmos). Note the enlarged left eye and the normal right eye. (D) Detached retina. Note rhe retina (arrow) detached from the choroid and sclera. L lens. (A, From Bergsma D ed Birth Defects Atlas and Compendium. Baltimore, Williams & Wi kins, 1973, Fig. 6.47. B-D, From Gilbert-Barness E Potters Atlas of Fetal and...

Vnerves Lumbosacral Plexus

New Herpes Breakthrough Ebook

Local cell biologic messages produced at the base of the limb bud guide the early nerve fibers into the limb bud the muscle themselves do not provide any specific target messages to the ingrowing nerve fibers. B. Ventral primary rami from L2, L3, L4, L5, SI, S2, and S3 arrive at the base of the limb bud and divide into posterior divisions and anterior divisions. a. These divisions grow into the posterior condensation of mesoderm. b. Posterior divisions will form the superior gluteal nerve...

Digestive System

Foregut Hindgut Midgut Duodenum

The primitive gut tube is divided into the foregut, midgut, A. Formation. The primitive gut tube is formed by the incorporation of a portion of the yolk sac into the embryo during craniocaudal and lateral folding. B. Histology. The epithelial lining and glands of the mucosa are derived from endoderm, whereas the lamina propria, muscularis mucosae, submucosa, muscularis externa, and adventitia serosa are derived from mesoderm. The epithelial lining of the gut tube...

Selected Photomicrographs

Syndrome Cat Cry

Chromosome 4P deletion Woilf-Hirschhorn syndrome and chromosome 5p deletion cri-du-chat syndrome Figure 23-1 B. Prader-Willi syndrome, Angclman's syndrome, DiGeorge syndrome, Miller-Dicker syndrome Figure 23-2 C. Robertsonian t 13ql4q , Robertsonian t 14q21q , acute promyelocyte leukemia t 15 17 q21 q21 , chronic myeloid leukemia t 9 22 q34 ql 1 Figure 23-3 Figure 23-1. Deletion abnormalities. A Chromosome 4p deletion Wolf-Hirschhorn syndrome . The deletion at 4pl6 is shown on chromosome 4....

Category X Drugs Absolute Contraindication In Pregnancy

Thalidomide is an antinausea drug that was at one time prescribed for pregnant women for morning sickness. It is no longer used. This drug can cause fetal limb reduction e.g., meromelia, amelia , ear and nasal abnormalities, cardiac defects, lung defects, pyloric or duodenal stenosis, and gastrointestinal atresia. B. Aminopterin and methotrexate are folic acid antagonists used in cancer chemotherapy. If used during pregnancy, these drugs can result in small stature, abnormal cranial...

Reproductive System

Mesonephric Tubule

Between weeks 1 and 6, female and male embryos are phe-notypically indistinguishable, even though the genotype XX or XY of the embryo is es-tablished at fertilization. By week 12, some female and male characteristics of the external genitalia can be recognized. By week 20, phenotypic differentiation is complete. A. Phenotypic differentiation is determined by the Sry gene, which is located on the short arm of the Y chromosome. 1. The Sry gene encodes for a protein called...

Respiratory System

Esophageal Fistula Adults

The first sign of respiratory system development is the formation of a respiratory di verticulum in the ventral wall of the foregut. B. The distal end of the respiratory diverticulum enlarges to form the lung bud. C. The lung bud divides into two bronchial buds that branch into the primary, sec ondary, and tertiary bronchi. D. The respiratory diverticulum is initially in open communication with the foregut, but eventually this communication is obliterated by the formation of the tracheoe...

Head and Neck

Foramen Cecum Tongue

PHARYNGEAL APPARATUS Figure 114 consists of pharyngeal arches, pouches, grooves, and membranes, all of which contribute greatly to the formation of the head and neck region. The Hox complex and retinoic acid appear to be important in the early stages of head and neck development. A lack or excess of retinoic acid causes striking facial anomalies. A. Pharyngeal arches 1, 2, 3, 4, 6 contain mesoderm somitomeric and neural crest cells. In general, the mesoderm differentiates into muscles and...

Week 1 Days

Conjoined Twins Diagram

Figure 2-1 summarizes the events that occur during week 1, following fertilization. II. FERTILIZATION occurs in the ampulla of the uterine tube. A. The sperm binds to the zona pellucida of the secondary oocyte and triggers the aero-some reaction, causing the release of acrosomal enzymes e.g., acrosin . B. Aided by the acrosomal enzymes, the sperm penetrates the zona pellucida. Penetration of the zona pellucida elicits the cortical reaction, rendering the secondary oocyte...

Positional Changes Of The Spinal Cord Figure 123

Fetal Conus Medullaris

At week 8, the spinal cord extends the entire length of the vertebral canal as spinal nerves exit the intervertebral foramina near their level of origin. This condition does not persist owing to the disproportionate growth of the vertebral column during the fetal period. Neural Tube Vesicles and Their Adult Derivatives Neural Tube Vesicles and Their Adult Derivatives Cerebral hemispheres, caudate, putamen amygdaloid, claustrum, lamina terminalis, olfactory bulbs, hippocampus Epithalamus,...

Urinary System

Formation Intermediate Mesoderm

Intermediate mesoderm forms a longitudinal elevation along the dorsal body wall called the nephrogenic cord, which forms the pronephros, mesonephros, and metanephros adult kidney . The homeobox genes, Lim-1 and Pax-2, appear to be important in this early stage of kidney development. A. The pronephros is not functional and completely regresses. B. The mesonephros is functional for a short period and completely regresses, except for C. The metanephros adult kidney...

Ivclinical Correlations

Flat Abdomen

Esophageal hiatal hernia is a herniation of the stomach through the esophageal hiatus into the pleural cavity, caused by an abnormally large esophageal hiatus. Esopha- visceral Intraembryonic Pleuropericardial membrane fibrous pericardium Pleuropericardial membrane fibrous pericardium Intraembryonic coelom pleuroperitoneal canal Intraembryonic coelom pleuroperitoneal canal Figure 15-1. Formation and partitioning of the intraembryonic coelom IC . A-C Cross-sections show various stages of IC...

Eye

Coroid Fissure Hyloid Artry

DEVELOPMENT OF THE OPTIC VESICLE Figure 141 . The optic vesicle begins to develop at day 22 with the formation of the optic sulcus. The optic sulcus evaginates from the wall of the diencephalon as the optic vesicle, consisting of neuroectoderm. The optic vesicle invaginates and forms a double-layered optic cup and optic stalk. A. The optic cup and its derivatives Table 14-1 . The double-layered optic cup consists of an outer pigment layer and an inner neural layer. a. The outer pigment layer...

Integumentary System

Epithelial Mammary Ridge

The skin consists of two layers the outer layer, or epidermis, and the deeper, connective tissue layer, or dermis. Skin functions as a barrier against infection, serves thermoregulation, and protects the body against dehydration. A. Epidermis. The epidermis is derived from the ectoderm. a. Initially, the epidermis consists of a single layer of ectodermal cells that give rise to an overlying periderm layer. b. The epidermis soon becomes a three-layered structure consisting of the...

Teratology

INTRODUCTION- A teratogen is any infectious agent, drug, chemical, or irradiation that alters fetal morphology or fetal function if the fetus is exposed during a critical stage of development. A. The resistant period week 1 of development is the time when the conceptus demonstrates the all-or-none phenomenon i.e., the conceptus will either die as a result of the teratogen or survive unaffected . B. The maximum susceptibility period weeks 3-8 embryonic period is the time when the embryo is...

Endocrinology Of Pregnancy

Human chorionic gonadotropin HCG 1. Definition. HCG is a glycoprotein hormone produced hy the syncytiotrophoblast. It stimulates the production of progesterone by the corpus luteum i.e., it maintains the function of the corpus luteum . HCG is detectable throughout a pregnancy. 2. Pregnancy tests. HCG can be assayed in maternal blood at day 8 or in maternal urine at day 10 using a radioimmunoassay with antibodies directed against the 3-subunit of HCG. The presence of HCG in maternal urine is...

Numerical Chromosomal Abnormalities

Trisomy Zygote

POLYPLOIDY is the addition of extra haploid sets of chromosomes i.e., 23 to the normal diploid set of chromosomes i.e., 46 . A. Triploidy is a condition in which cells contain 69 chromosomes. It results in spontaneous abortion of the conceptus or only brief survival of the liveborn infant after birth. Triploidy occurs as a result of either a failure of meiosis in a germ cell e.g., fertilization of a diploid egg by a haploid sperm or dispermy two sperm that fertilize one egg . B. Tetraploidy...

Vbones Of The Limbs And Limb Girdles

Upper Limb Bones Moore

Development in general see Chapters 19 and 20 1. The bones of the limb and limb girdles develop from condensations of lateral plate mesoderm within the limb buds. The limb buds are visible at week 4 of development the upper limb appears first. The limbs are well differentiated at week 8. 2. The limb tip contains the apical ectodermal ridge, which exerts an inductive influence on limb growth and development. 1. Amelia, an absence of one or two extremities, may result from the use of the...

Skeletal System

Spina Bifida Occulta Skeletal

The skull can be divided into two parts the neurocianium and the A- Neurocranium. The neurocranium consists of the flat bones of the skull cranial vault and the base of the skull. The neurocranium develops from neural crest cells, except for the basilar part of the occipital bone, which forms from mesoderm of the occipital sclerotomes. B. Viscerocranium. The viscerocranium consists of the bones of the face involving the pharyngeal arches, which have been discussed in...

Skeletal Muscle

Limb Bud Somitomeres

Mesodermal mesenchymal cells within somites become committed to a muscle-forming cell line through a poorly understood mechanism to form myogenic cells. 2. Stimulated by fibroblast growth factor FGF and transforming growth factor TGF-P , myogenic cells enter the cell cycle i.e., undergo mitosis . 3. Myogenic cells begin to express MyoD a helix-loop-helix transcription factor , which removes the myogenic cells from the cell cycle i.e., micosis stops and switches on muscle-specific genes to...

Ear

Corti And Viii

OVERVIEW- The ear is the organ of balance and hearing. It consists of an internal, a middle, and an external ear. II. INTERNAL EAR Figure 13-1 . The internal ear develops in Week 4 from a thickening of the surface ectoderm called the otic placode. A. Otic vesicle. The otic placode invaginates into the mesoderm adjacent to the rhombencephalon and becomes the otic vesicle. The otic vesicle divides into utricular and saccular portions. 1. Utricular portion. This portion of the otic vesicle...

Table 111

Terminal Sulcus Tongue

Adult Derivatives of the Pharyngeal Arches Mesoderm Muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, tensor tympani Neural crest cells Maxilla, zygomatic bone, squamous portion of the temporal bene, palatine bone, vomer, mandible, incus, malleus, sphenomandibular ligament Mesoderm Muscles of facial expression, posterior belly of the digastric, stylohyoid, stapedius Neural crest cells Stapes, styloid process, stylohyoid ligament, lesser horn and upper body of...

Placenta Amniotic Fluid and Umbilical Cord

Smooth Chorion

The maternal component of the placenta consists of a portion of the endometrium called the decidua basalis. 2. The fetal component of the placenta consists of tertiary chorionic villi, which are collectively called the villous chorion. B. Afterbirth appearance of the placenta 1. The maternal surface of the placenta is characterized by 15-20 cotyledons that impart a cobblestone appearance. The surface is dark red and oozes blood after birth owing to torn maternal blood vessels. 2. The fetal...

Cardiovascular System

Vsd Muscular Membranous

DEVELOPMENT OF THE PRIMITIVE HEART TUBE. A pair of endocardial heart tubes mesodermal in origin form within the cardiogenic region. A. As lateral folding occurs, the endocardial heart tubes fuse to form the primitive heart tube, which develops into the endocardium. B. Mesoderm surrounding the primitive heart tube develops into the myocardium and epicardium. C- The primitive heart tube forms five dilatations truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus...

Prefertilization Events

Achondroplasia Bone Histology

GAMETES oocytes and spermatozoa , descendants of primordial germ cells, are produced in the adult by either oogenesis or spermatogenesis, processes that involve meio-sis. Primordial germ cells originate in the wall of the yolk sac of the embryo and migrate into the gonad region. II. MEIOSIS Figure 1-1 , which occurs only during the production of gametes, consists of two cell divisions meiosis I and meiosis II and results in the formation of four gametes containing 23 chromosomes and IN...