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Embryology of Upper, lower limbs and the.pptx
- 1. Embryology/development of bones,muscles andvessels of the Upper, lower limbs and pelvis Presenter:- CHUBAKA BISHIKWABO Franck Facilitator:- Dr. Farouk
- 2.
- 3. 1.Basic terminology Embryology:science that studies formation and development of an organism. Reproduction: Sexual reproduction involves fusion of male and female gametes to produce an offspring. • It helps in maintenance of species. Ontogeny: science that deals with complete life cycle (prenatal and postnatal ) of an organism. Phylogeny deals with an evolutionary history and relationship among organisms
- 4. Terminology Development ofa human from a single cell stage of life involves growth and differentiation. increase in the number and size of cells. cell transformation to acquire specific character and function
- 5. PERIODS OF HUMANEMBRYOLOGY Clinicians divide human prenatal development as first, second and third trimesters but embryologically, prenatal growth is divided into: 1. Germinal/ovular period: First three weeks of development after fertilisation. 2. Embryonic period: From 4th to 8th week of development. 3. Foetal period (organ growth): From third month till the end sof the pregnancy.
- 6. Periods of humanembryology. Abbreviations: wk: Week; LMP: Last menstrual period
- 9. Week 1 postconception Zygote divides repeatedly moving down tube toward uterus (cleavage) The daughter cells are called blastomeres Morula: the solid cluster of 12-16 blastomeres at about 72 hours Day 4: late 60 cell morula enters uterus, taking up fluid becoming blastocyst
- 11. Blastocyst stage Twodistinct types of cells Inner cell mass: forms the embryo Trophoblast: layer of cells surrounding the cavity which helps form the placenta Floats for about 3 days Implantation on about day 6 post conception Trophoblast erodes uterine wall Takes 1 week to complete If inner cell mass of a single blastocyst divides: monozygotic (identical) twins _____inner cell mass ______trophoblast
- 12. Week 2 Innercell mass divides into epiblast and hypoblast 2 fluid filled sacs Amniotic sac from epiblast Yolk sac from hypoblast Bilaminar embryonic disc: area of contact (gives rise to the whole body)
- 13. Bilaminar totrilaminar disc Three primary “germ” layers: all body tissues develop from these Ectoderm Endoderm Mesoderm Week 3
- 14. Formation of the3 “germ” layers Primitive streak (groove) on dorsal surface of epiblast Grastrulation: invagination of epiblast cells Days 14-15: they replace hypoblast becoming endoderm Day 16: mesoderm (a new third layer) formed in between Epiblast cells remaining on surface: ectoderm
- 15. The three “germ”tissues “Germ” as in germinate, not germs Early specialization of cells Are precursors Ectoderm and endoderm are epithelial tissue (form sheets of tissue) Mesoderm is a mesenchyme tissue Mesenchyme cells are star shaped and do not attach to one another, therefore migrate freely
- 16. Notochord Days 16-18 Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells Rod defining the body axis is formed Future site of the vertebral column
- 17. Neurulation Notochord signalsoverlying ectoderm Formation begins of spinal cord and brain (neurulation) Neural plate to neural groove to neural tube: pinched off into body
- 18. Closure ofneural tube: begins at end of week 3; complete by end of week 4 (folic acid important for this step) Extends cranially (eventually brain) and caudally (spinal cord) Neural crest, lateral ectodermal cells, pulled along and form sensory nerve cells and other structures
- 19. Mesoderm beginsto differentiate Lateral to notochord, week 3 Extends cranially and caudally (from head to tail or crown to rump) Division of mesoderm into three regions Somites: 40 pairs of body segments (repeating units, like building blocks) by end week 4 Intermediate mesoderm: just lateral to somites Lateral plate: splits to form coelom (“cavity”)
- 20. Divisions of themesodermal lateral plate Somatic mesoderm: apposed to the ectoderm Splanchnic mesoderm: apposed to the endoderm Coelom in between will become the serous cavities of the ventral body cavity: Peritoneal Pericardial Pleural
- 21. Folding begins at week4 (main difference between the 3 week embryo and the adult body is that the embryo is still a flat disc)
- 22.
- 23. Day 23, beginning tofold Lateral folds will join ventrally
- 24. Cylindrical human body plan, day28 (about ½ cm) Simplified cross section through abdomen of an adult (essentially the same as above)
- 25. Major derivatives ofthe embryonic germ layers
- 26. 29 day embryo (thisis when the heart starts pumping, about 4 weeks or 1 month, ½ cm size)
- 27. month 3 month5 3 month fetus (6 cm) late 5th month (about 19 cm)
- 28. The Skeletal system The skeletal system develops from paraxial and lateral plate(somaticlayer)mesoderm and from neural crest. Paraxial mesoderm forms a segmented series of tissue blocks on each side of the neural tube, known as somitomeres in the head region and somites from the occipital region caudally.
- 29. The bone-formingcapacity of mesenchyme is not restricted to cells of the sclerotome, but occurs also in the somatic mesoderm layer of the body wall, which contributes mesoderm cells for formation of the pelvic and shoulder girdles and the long bones of the limbs. In most bones, however, mesenchymal cells first give rise to hyaline cartilage models, which in turn become ossified by endochondral ossification.
- 30. By thebeginning of the fifth week, forelimbs and hindlimbs appear as paddle-shaped buds. The former are located dorsal to the pericardial swelling at the level of the fourth cervical to the first thoracic somites, which explains their innervation by the brachial plexus. Hindlimb buds appear slightly later just caudal to attachment of the umbilical stalk at the level of the lumbar and upper sacral somites. End Fourth and Beginning of fifth week
- 31. Cells inthe dorsolateral wall of the somite form limb and body wall musculature, while cells at the dorsomedial portion migrate beneath the remaining dorsal epithelium (the dermatome) to form the myotome. At the end of the fourth week of development, limb buds become visible as out pocketing from the ventrolateral body wall.
- 32. Development of thelimb buds in human embryos. A. At 5 weeks. B. At 6 weeks. C. At 8 weeks. The hindlimb buds are less well developed than those of the forelimbs.
- 33. This ridgeexerts an inductive influence on adjacent mesenchyme, causing it to remain as a population of undifferentiated, rapidly proliferating cells, the progress zone. As the limb grows, cells far the from the influence of the AER begin to differentiate in to cartilage and muscle. In this manner development of the limb proceeds proximo-distally.
- 34. 6-week-old embryo Theterminal portion of the limb buds becomes flattened to form the handplates and footplates and is separated from the proximal segment by a circular constriction. Later a second constriction divides the proximal portion into two segments, and the main parts of the extremities can be recognized. Fingers and toes are formed when cell death in the AER separates this ridge into five parts.
- 36. With further growth,the terminal portions of the buds flatten and a circular constriction separates them from the proximal, more cylindrical segment. Soon, four radial grooves separating five slightly thicker areas appear on the distal portion of the buds, foreshadowing formation of the digits. Scanning electron micrographs of human hands. A. At 48 days. Cell death in the apical ectodermal ridge creates a separate ridge for each digit. B. At 51 days. Cell death in the interdigital spaces produces separation of the digits. C. At 56 days. Digit separation is complete. The finger pads will create patterns for fingerprints.
- 37. Human embryo (CRL25 mm, seventh to eighth week). The chorion and the amnion have been opened. Note the size of the head, the eye, the auricle of the ear, the well-formed toes, the swelling in the umbilical cord caused by intestinal loops, and the yolk sac in the chorionic cavity.
- 38. Development ofthe upper and lower limbs is similar except that morphogenesis of the lower limb is approximately 1 to 2 days behind that of the upper limb. Also, during the seventh week of gestation the limbs rotate in opposite directions. The upper limb rotates 90◦ laterally, so that the extensor muscles lie on the lateral and posterior surface and the thumbs lie laterally. Whereas the lower limb rotates approximately 90◦ medially, placing the extensor muscles on the anterior surface and the big toe medially.
- 39. The limbsreach their relative length in comparison with the rest of the body, although the lower limbs are still a little shorter and less well developed than the upper extremities. Primary ossification centers are present in the long bones and skull by the 12th week. While the external shape is being established, mesenchyme in the buds begins to condense and these cells differentiate into chondrocytes.
- 40. By the6th week of development the first hyaline cartilage models, foreshadowing the bones of the extremities, are formed by these chondrocytes. Joints are formed in the cartilaginous condensations when chondrogenesis is arrested and a joint interzone is induced. Cells in this region increase in number and density and then a joint cavity is formed by cell death. Surrounding cells differentiate into a joint capsule. Factors regulating the positioning of joints are not clear, but the secreted molecule WNT14 appears to be the inductive signal.
- 41. Ossification of Bones Ossification of the bones of the extremities, endochondral ossification, begins by the end of the embryonic period. Primary ossification centers are present in all long bones of the limbs by the 12th week of development. From the primary center in the shaft or diaphysis of the bone, endochondral ossification gradually progresses toward the ends of the cartilaginous model.
- 42. At birththe diaphysis of the bone is usually completely ossified, but the two ends, the epiphyses, are still cartilaginous. Shortly thereafter, however, ossification centers arise in the epiphyses. Temporarily a cartilage plate remains between the diaphyseal and epiphyseal ossification centers. This plate, the epiphyseal plate, plays an important role in growth in the length of the bones. Endochondral ossification proceeds on both sides of the plate. When the bone has acquired its full length, the epiphyseal plates disappear and the epiphyses unite with the shaft of the bone.
- 43. In longbones an epiphyseal plate is found on each extremity; in smaller bones, such as the phalanges, it is found only at one extremity; and in irregular bones, such as the vertebrae, one or more primary centers of ossification and usually several secondary centers are present.
- 49.
- 50. Bone Age Radiologistsuse the appearance of various ossification centers to determine whether a child has reached his or her proper maturation age. Useful information about bone age is obtained from ossification studies in the hands and wrists of children. Prenatal analysis of fetal bones by ultrasonography provides information about fetal growth and gestational age.
- 51. Limb Defects Meromelia,Amelia, Phocomelia, micromelia, Sirenomelia Polydactyly, ectrodactyly, syndactyly, synpolydactyly Cleft hand and foot (lobster claw deformity) Hand-foot-genital syndrome Clubfoot Congenital absence or deficiency of the radius- craniosynostosis– radial aplasia syndrome. Amniotic bands Congenital hip dislocation Achondroplasia
- 52. A. Three-month-old infantwith achondroplasia. Note the large head, short extremities, and protruding abdomen. B and C. Achondroplasia in a 15-year-old girl.
- 53. Sirenomelia (caudal dysgenesis).Loss of mesoderm in the lumbosacral region has resulted in fusion of the limb buds and other defects.
- 54. Infant showing limb amputationresulting from amniotic bands.
- 55. A. Child with unilateralamelia. B. Child with meromelia. The hand is attached to the trunk by an irregularly shaped bone.
- 56.
- 57.
- 58. Cleft hand andfoot (lobster claw deformity)
- 59.
- 61. Congenital absence ofthe radius
- 63. Time for questionsand reflection
- 64. References 1.Textbook of humanembryology 2. Langman 12th Edition 3. Before we are born 4. Med Pub (photos)
Editor's Notes
- #14 What does the hypoblast become later and the epiblast? Answer Endoderm and ectoderm
- #15 Why does the mesenchyme cells migrate freely? Answer Because of their stary shape
- #28 Somites differentiate into a ventromedial part, the sclerotome, and a dorsolateral part, the dermomyotome. At the end of the fourth week sclerotome cells become polymorphous and form a loosely woven tissue, the mesenchyme, or embryonic connective tissue . It is characteristic for mesenchymal cells to migrate and to differentiate in many ways. They may become fibroblasts, chondroblasts, or osteoblasts (bone-forming cells).
- #32 Initially they consist of a mesenchymal core derived from the somatic layer of lateral plate mesoderm that will form the bones and connective tissues of the limb covered by a layer of cuboidal ectoderm. Ectoderm at the distal border of the limb thickens and forms the apical ectodermal ridge (AER).
- #34 Further formation of the digits depends on their continued outgrowth under the influence of the five segments of ridge ectoderm, condensation of the mesenchyme to form cartilaginous digital rays, and the death of intervening tissue between the rays.
- #35 A. Longitudinal section through the limb bud of a mouse embryo, showing a core of mesenchyme covered by a layer of ectoderm that thickens at the distal border of the limb to form the AER. In humans this occurs during the fifth week of development. B. Lower extremity of an early 6-week embryo, illustrating the first hyaline cartilage models. C and D. Complete set of cartilage models at the end of the sixth and the beginning of the eighth week, respectively.
- #51 Limb malformations occur in approximately 6/10,000 live births, with 3.4/10,000 affecting the upper limb and 1.1/10,000, the lower. These defects are often associated with other birth defects involving the craniofacial, cardiac, and genitourinary systems.
- #52 Achondroplasia (ACH), the most common form of dwarfism (1/26,000 live births), primarily affects the long bones. ACH is inherited as an autosomal dominant, and 80% of cases appear sporadically. Hypochondroplasia, another autosomal dominant form of dwarfism, appears to be a mildertypeofACH. Note dwarfism of the short limb type, the limbs being disproportionately shorter than the trunk. The limbs are bowed; there is an increase in lumbar lordosis; and the face is small relative to the head.
- #53 In caudal dysgenesis (sirenomelia), insufficient mesoderm is formed in the caudal-most region of the embryo. Because this mesoderm contributes to formation of the lower limbs, urogenital system (intermediate mesoderm), and lumbosacral vertebrae, abnormalities in these structures ensue. Affected individuals exhibit a variable range of defects, including hypoplasia and fusion of the lower limbs, vertebral abnormalities, renal agenesis, imperforate anus, and anomalies of the genital organs. In humans, the condition is associated with maternal diabetes and other causes.
- #54 Occasionally, tears in the amnion result in amniotic bands that may encircle part of the fetus, particularly the limbs and digits. Amputations, ring constrictions, and other abnormalities, including craniofacial deformations, may result. Origin of the bands is probably from infection or toxic insults that involve either the fetus, fetal membranes, or both. Bands then form from the amnion, like scar tissue, constricting fetal structures.
- #55 Both infants were born to mothers who took thalidomide. In 1961 observations by Lenz linked limb defects to the sedative thalidomide and made it clear that drugs could also cross the placenta and produce birth defects.
- #56 A different category of limb abnormalities consists of extra fingers or toes (polydactyly). The extra digits frequently lack proper muscle connections. Abnormalities with an excessive number of bones are mostly bilateral. Polydactyly can be inherited as a dominant trait but may also be induced by teratogens. Abnormal fusion is usually restricted to the fingers or toes (syndactyly). Normally mesenchyme between prospective digits in the hand plates and footplates breaks down. In 1/2000 births this fails to occur, and the result is fusion of one or more fingers and toes . In some cases the bones actually fuse.
- #57 Absence of a digit such as a thumb (ectrodactyly) is usually unilateral.
- #58 Cleft hand and foot (lobster claw deformity) consists of an abnormal cleft between the second and fourth metacarpal bones and soft tissues. The third metacarpal and phalangeal bones are almost always absent, and the thumb and index finger and the fourth and fifth fingers may be fused. The two parts of the hand are somewhat opposed to each other and act like a lobster claw.
- #59 Clubfoot usually accompanies syndactyly. The sole of the foot is turned inward, and the foot is adducted and plantar flexed. It is observed mainly in males and in some cases is hereditary. Abnormal positioning of the legs in utero may also cause clubfoot.
- #61 Congenital absence or deficiency of the radius is usually a genetic abnormality observed with malformations in other structures, such as craniosynostosis–radial aplasia syndrome. Associated digital defects, which may include absent thumbs and a short curved ulna, are usually present.
- #62 Congenitalhipdislocationconsistsofunderdevelopmentoftheacetabulumandheadofthefemur.Itisrathercommonandoccursmostlyinfemales. Although dislocation usually occurs after birth, the abnormality of the bones develops prenatally. Congenital hip dislocation consists of under development of the acetabulum and head of the femur. It is rather common and occurs mostly in females. Although dislocation usually occurs after birth, the abnormality of the bones develops prenatally.