Embryology Lab Notes

Overview of Embryology Lab (LAB 8)

• Purpose: Understand the three-dimensional development of vertebrate embryos.
• Model Organisms: Frogs and chicks.
• Methods: Classroom models, microscopic cross-sections, and live observations.

Introduction to Development

• Definition: Development is the process where undifferentiated cells become specialized, forming organs and systems.

• Approaches to Study Development:

• Observational Approach: Focused on visual changes in the organism over time.

• Experimental Approach: Manipulation of organisms to uncover underlying processes.

Frog Development Stages

• Key Terms:
• Cleavage: Division of the zygote into smaller cells without increasing overall mass.
• Blastula: A ball of cells with a central cavity (blastocoel) formed at the end of cleavage.
• Gastrula: The stage where major groups of cells begin to migrate to their destined positions.

Frogs (Rana pipiens)

• Cleavage and Blastulation:

• Animal Pole: Darker, smaller cells.

• Vegetal Pole: Heavier, yolk-filled cells.

• Blastula Formation: Ball of cells with blastocoel; three germ layers:

  • Ectoderm: Blue
  • Mesoderm: Red
  • Endoderm: Yellow

• Gastrulation:

• Begins with an indentation called the blastopore marking the entry of cells into the embryo.

• Formation of the dorsal lip of the blastopore which directs development regions.

• Leads to stratification into ectoderm, mesoderm, and endoderm.

Observations with Microscopes

• Procedure: Dissect embryos; focus on cell boundaries and layers; label structures in sketches.

Chick Development Stages

• Why Study Chick Embryos?: Developmental similarities with mammals make them ideal for research.

Early Development in Chick

• Cleavage occurs in a small region (blastodisc) due to yolk volume.
• Gastrulation:
• Organized along a primitive streak.
• Cells from the epiblast migrate inward at the primitive groove, forming endoderm and mesoderm.

Observations for Chick Development

• Use live embryos or cross-sections; note structures as they progress from 33 hours to 5-7 days.

Procedure for Observing Living Embryos

• Handling: Shell cracking, yolk pouring into saline solution, and gentle movement to avoid damage.

• Somite Counts: Indicator of developmental stage (e.g., 33-hour: 8-9 pairs).

• 34-hour Stage Observations:

• Identify heart, lobes of the brain, wing and leg buds, and circulatory functions.

Advanced Observations (5-7 Day Embryos)

• Increased size and complexity compared to earlier stages.
• Structures to notice:
  • Amnion: Cushions the embryo.
  • Allantois: Collects waste; more vascularized.

General Questions for Understanding:

1. Compare gastrulation in frogs vs. chicks.
2. Describe the sequence from primitive groove to spinal cord development.
3. Define somites and their role in embryonic growth.
4. Identify how the embryo acquires oxygen and releases carbon dioxide through vascular systems.

Conclusion

• Objective: Illustrate developmental stages and their ramifications for understanding vertebrate biology.