Human Embryology Lesson 4, Week 4 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: – Explain the proce...

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. 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. 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 Muscle Derivatives Derivatives Arch Mastication muscles, Malleus, Incus, 1st Arch Mylohyoid, Tensor Mandibular (CN V3) Maxillary artery Mandible, Ligaments muscles Stapes, Styloid process, Facial expression, Stapedial and 2nd Arch Facial (CN VII) 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  Introduction to Week 05  Key Highlights: o Rapid Brain and Head development. o Organ primordia become more defined. Approximate Size: 7-9 mm  Key Development in Week 05 1. Brain Development: o Division of the Primary Brain Vesicles: forebrain, midbrain, hindbrain. o Cranial nerves begin to form. 2. Eye and Ear Development: o Optic vesicles appear (future eyes). o Otic pits form (future inner ears). 3. Limb Development: o Upper limb buds become paddle-shaped and Lower limb buds appear. 4. Heart Development: Septation begins in the heart chambers. Key Development in Week 05  Summary of Week 5 Brain and Cranial Nerve Development  Brain Vesicles: o Forebrain: Telencephalon (cerebrum), Diencephalon (thalamus and hypothalamus). o Midbrain: Relay for sensory and motor functions. o Hindbrain: Metencephalon (pons, cerebellum), Myelencephalon (medulla). Brain Vesicles:  Cranial Nerves  Cranial Nerves: o CN I (olfactory) and CN II (optic) from the forebrain. o CN III–XII from the midbrain and hindbrain.  Significance: o Lays the foundation for higher brain functions, sensory pathways, and motor coordination.