BIU Human Embryology Lesson 05 Week 06 Development PDF

Human Embryology Lesson No. 05 Week 06 of Embryo Development BIU Medical Science Program Professor Dr. Ejaz Ahmed Khan BIU Medical Science Program  Learning Outcomes After completion of this sess...

Human Embryology Lesson No. 05 Week 06 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: – Describe key events of embryonic development during the sixth week, including the growth of the pharyngeal arches, nasal pits, maxillary and mandibular processes. – Explain the cardiac morphogenesis, including the process of atrial and ventricular septation and the significance of the foramen ovale in fetal circulation. – Describe the formation of hand and foot plates and explain apoptosis in digit separation for upper limb differentiation. – Illustrate the herniation process of the midgut into the umbilical cord and discuss the formation of cranial and caudal limbs and their role in future small and large intestine development.  Facial Development: Week 6  Overview: o Rapid morphological changes in the face. o Contributions from the pharyngeal arches, frontonasal prominence, and maxillary/mandibular processes.  Key Events: o Nasal Pits Form:  Depressions appear on the frontonasal prominence and represents early stages of nostrils and nasal cavities.  Surrounding mesenchyme gives rise to the nasal structures. o Maxillary and Mandibular Processes:  Maxillary processes expand medially, forming the upper jaw and cheeks.  Mandibular processes merge to form the lower jaw and chin. Facial Development: Week 6 Facial Development: Week 6  Cardiac Development: Week 6 Overview: o Heart continues morphogenesis, becoming more structurally defined and functional. Key Events: o Septation of Atria and Ventricles:  Atrial Septation:  Septum primum and septum secundum continue to grow and refine the separation between the right and left atria.  Foramen ovale allows blood flow bypassing the non-functional fetal lungs.  Cardiac Development: Week 6 Ventricular Septation: – Interventricular septum develops, dividing the ventricles into right and left chambers. Heartbeat Detection: – Coordinated contractions visible via ultrasound (transvaginal). – Heart rate typically between 100-160 beats per minute. Cardiac Development: Week 6 Limb Differentiation: Week 6 Overview: o Limb buds become more defined, and segmentation for fingers begins. Key Events: o Hand Plates Form:  Distal ends of upper limb buds flatten into paddle-like structures.  Precursor to the hands.  Limb Differentiation: Week 6 o Digital Rays Appear:  Thickened ridges in the hand plates mark the future fingers.  Controlled by apoptosis in the interdigital regions to sculpt the digits. o Lower Limbs: o Lag slightly behind upper limbs but show initial signs of elongation and differentiation Limb Differentiation: Week 6 Upper Limb Bud Lower Limb Bud  Formation of Hand Plates in Upper Limbs 1. Hand Plates Formation: o At week 6, the distal ends of the upper limb buds begin to flatten, forming paddle-like structures known as hand plates. o These plates are the precursors to the hands and mark the early stages of digital development. 2. Significance: o The hand plates serve as the foundation for further limb differentiation, including the development of fingers, thumbs, and palms. o They provide a structural basis for the digit formation. Formation of Hand Plates in Upper Limbs  Digital Rays and Apoptosis in Upper Limbs 1. Digital Rays: o Thickened ridges appear in the hand plates, which will eventually form the future fingers. These ridges are referred to as digital rays. o The digital rays indicate the beginning of finger segmentation and help organize the future digits. 2. Apoptosis: o The interdigital regions between the digital rays undergo apoptosis (programmed cell death), which helps to sculpt and separate the digits, forming individual fingers. o Apoptosis is crucial for digit formation. Digital Rays and Apoptosis in Upper Limbs Lower Limb Development in Week 6 1. Lag in Development: o The lower limb buds appear slightly later than the upper limb buds and lag behind in differentiation. o However, by week 6, they begin to show initial signs of elongation and differentiation. 2. Formation of Foot Plates: o The lower limb buds begin to elongate and start to flatten at their distal ends, forming the foot plates, precursor to the feet. Lower Limb Development in Week 6 Development of the Intestinal Loop: Week 6 Overview: o The midgut elongates and forms a loop that temporarily herniates into the umbilical cord, accommodating rapid growth. Key Events: o Herniation of the Midgut:  Occurs due to insufficient space in the abdominal cavity.  Herniated loop remains connected to the yolk sac via the vitelline duct.  Development of the Intestinal Loop: Week 6 o Future Structures Form: Cranial limb of the midgut loop develops into parts of the small intestine.  Caudal limb forms parts of the large intestine. o Rotation Begins:  Initial 90-degree counterclockwise rotation of the midgut loop around the axis of the superior mesenteric artery. Development of the Intestinal Loop: Week 6 Herniation of the Midgut 1. Herniation Occurrence: o The midgut becomes elongated and bulges out of the abdominal cavity into the umbilical cord due to insufficient space in the developing abdomen. o The midgut herniates into the umbilical cord around week 6 to accommodate its rapid growth. 2. Connection to the Yolk Sac: o The hernial loop remains connected to the yolk sac through the vitelline duct (also known as the omphalomesenteric duct), which serves as a conduit for nutrients and waste exchange. Herniation of the Midgut Formation of Future Intestinal Structures 1. Cranial Limb of the Midgut: o The cranial limb of the midgut loop will develop into parts of the small intestine, including the duodenum, jejunum, and part of the ileum. o This segment is responsible for nutrient absorption and early digestive functions. 2. Caudal Limb of the Midgut: o The caudal limb forms the large intestine, including the cecum, appendix, and part of the colon. o This segment will eventually handle water absorption and the formation of fecal matter. Formation of Future Intestinal Structures Rotation of the Midgut Loop 1. Initial 90-Degree Counterclockwise Rotation: o The midgut loop begins to rotate 90 degrees counterclockwise around the axis of the superior mesenteric artery (SMA) during week 6. o This rotation is crucial for the proper positioning of the small and large intestines within the abdominal cavity. 2. Impact on Organ Positioning: o The cranial limb moves to the right side of the body, while the caudal limb moves to the left side. Rotation of the Midgut Loop