BIU Lesson 04 Week 4 Human Development PDF

Human Embryology Lesson No. 04 Week of Embryo Development BIU Medical Science Program Professor Dr. Ejaz Ahmed Khan BIU Medical Science Program  Learning Outcomes After completion of this session students will be able to:...

Human Embryology Lesson No. 04 Week of Embryo Development BIU Medical Science Program Professor Dr. Ejaz Ahmed Khan BIU Medical Science Program  Learning Outcomes After completion of this session students will be able to: – Explain the process of neural tube and neural crest cells formation in nervous system development. – Explain the formation of the key structures that develop from somites, such as vertebrae, ribs, and skeletal muscles. – Discuss the primitive heart tube formation and initiation of blood circulation and its transition into a functional organ. – Illustrates the development of first two pairs of pharyngeal arches and head and neck structures, such as the mandible and facial muscles. – Describe the early stages of limb development, including the formation of limb buds and their potential to develop into arms and legs.  Neurulation: Neural Tube Formation (Week 4)  Neural Tube Formation is a crucial step of the development of CNS.  The Neural Plate folds into Neural Tube, to form brain and spinal cord. o Cranial Closure: Begins at the cranial end of the neural tube. o Caudal Closure: Begins towards the caudal end.  Neural Crest Cells form from the folds of the neural tube and will form various structures, including peripheral nerves and facial bones.  Summary of Key Processes Process Structure Formed Clinical Correlation Neural tube → Brain and spinal Spina bifida, Neurulation cord anencephaly Peripheral nerves, craniofacial Neural Crest Hirschsprung bones, melanocytes, adrenal Cells disease, cleft palate medulla Brain Holoprosencephaly, Forebrain, midbrain, hindbrain Development microcephaly Neurulation: Neural Tube Formation (Week 4)  Somite Formation (Week 4)  Around 20-25 somites form during Week 4, which give rise to various tissues and structures.  Somites are blocks of mesoderm that develop alongside the neural tube. o They contribute to the formation of the axial skeleton (vertebrae and ribs) and skeletal musculature. Somites determine the segmented body plan of the embryo.  Summary of Key Processes Somite Structure Formed Region Component Vertebrae, ribs, and Sclerotome Axial skeleton intervertebral discs Segmental body Dermatome Dermis of the skin regions Skeletal muscles of back, trunk, Epaxial and hypaxial Myotome and limbs muscles Somite Formation (Week 4)  Heart Development (Week 4) The Primitive heart tube begins to beat in Week 4, marking the initiation of blood circulation. – The heart tube initially forms as a Linear structure but will soon begin to loop and develop the chambers of the heart. Blood Circulation starts as blood is pumped from the primitive heart to various parts of the developing embryo. – The beating of the heart and initiation of circulation is crucial for delivering nutrients and oxygen to the growing tissues. Heart Development (Week 4)  Pharyngeal Arches (Week 4)  In Week 4, the first two pairs of Pharyngeal Arches appear. o The pharyngeal arches will eventually give rise to various structures in the Head and Neck, including bones, muscles, and nerves.  The First arch forms the Maxilla, Mandible, and muscles of mastication.  The Second arch contributes to structures like the Stapes of the Ear and Muscles for Facial expression.  Pharyngeal Arches (Week 4) Cartilage Derivatives Nerve Supply Arterial Pharyngeal Derivatives Muscle Derivatives Arch Malleus, Incus, Mastication muscles, 1st Arch Mandible, Ligaments Mylohyoid, Tensor Mandibular (CN V3) Maxillary artery muscles 2nd Arch Stapes, Styloid process, Facial expression, Facial (CN VII) Stapedial and Hyoid (lesser horn) Stapedius, Stylohyoid Hyoid arteries Pharyngeal Arches (Week 4) Pharyngeal Arches (Week 4)  Limb Bud Formation (Week 4)  In Week 4, Limb buds begin to form, marking the early stages of Limb development. o Upper limb buds appear slightly earlier than Lower limb buds. o The limb buds are primarily composed of Mesoderm and covered by Ectoderm, with the mesoderm giving rise to the Bones and Muscles, while the ectoderm forms the Skin. These Limb buds will elongate and differentiate into Arms and Legs, developing Fingers and Toes in the later stages of embryonic development. Limb Bud Formation (Week 4)  Summary of Key Events in Week 4 of Embryonic Development Neurulation: Neural tube formation begins, which will form the brain and spinal cord. Somite Formation: 20-25 somites form, contributing to the axial skeleton and musculature. Heart Development: The primitive heart tube begins to beat, and blood circulation starts. Pharyngeal Arches: The first two pairs of pharyngeal arches appear, contributing to the development of head and neck structures. Limb Buds: The limb buds begin to form, initiating the development of arms and legs. Zygote 2 Cells 4 Cells 8 Cell Marula Blastocyst Gastrulation 04 Weeks