Biology of Germ Layers and Epithelial Tissues

Germ Layers

• There are three primary germ layers: Ectoderm, Endoderm, and Mesoderm
• These germ layers form during organogenesis

History of Germ Layers

• Heinz Christian Pander discovered three primordial germ layers in 1817 while studying chick embryos
• Between 1850 and 1855, Robert Remak refined the germ cell layer concept
• T.H. Huxley introduced the terms "mesoderm" in 1871, and Lankester introduced "ectoderm" and "endoderm" in 1873

Formation of Germ Layers

• Gametogenesis: production of sperms (male) and ova (female)
• Fertilization: transmission of genes from parents
• Cleavage: rapid mitotic cell divisions of the zygote to form the Blastula
• Blastulation
• Gastrulation: rearrangement of cells to form a three-layered embryo (gastrula)
• Neurulation
• Organogenesis: formation of organs

Establishment of Somatic Cells

• Three classes of somatic cells: Ectoderm, Endoderm, and Mesoderm (also known as the three germ layers)

Gastrulation

• The blastula becomes a three-layered embryo (gastrula) through gastrulation
• Cells become arranged in three distinct germ layers: Ectoderm, Endoderm, and Mesoderm
• Each germ layer develops into specific parts of the embryo

Ectoderm

• Forms the outermost layer of the embryo
• Develops into:
  • Central Nervous System
  • Lens of the eye
  • Cranial and sensory
  • Ganglia and nerves
  • Pigment cells
  • Epidermis
  • Hair and mammary glands

Endoderm

• Forms the innermost layer of the embryo
• Develops into:
  • Flattened cells that become columnar

Mesoderm

• Forms the middle layer of the embryo
• Develops into:
  • Coelom (body cavity)
  • Generation of chimeric mice

Types of Animals

• Sponges: single germ layer
• Diploblastic animals (Cnidaria and Ctenophores): two germ layers (endoderm and ectoderm)
• Triploblastic animals: three germ layers (ectoderm, endoderm, and mesoderm)

Tissues

• A group of closely associated, similar cells that carry out specific functions
• Four kinds of animal tissues: epithelial, connective, muscle, and nervous tissue
• Each type of tissue is specialized to perform a specific function or group of functions

Epithelial Tissues

• Consists of cells fitted tightly together to form a continuous layer of cells
• One surface is exposed, while the other surface attaches to underlying tissue by a noncellular basement membrane
• Functions include:
  • Protection (epidermis)
  • Absorption (digestive tract)
  • Secretion (glands)
  • Sensation (sensory receptors)

Germ Layers

• There are three primary germ layers: Ectoderm, Endoderm, and Mesoderm
• These germ layers form during organogenesis

History of Germ Layers

• Heinz Christian Pander discovered three primordial germ layers in 1817 while studying chick embryos
• Between 1850 and 1855, Robert Remak refined the germ cell layer concept
• T.H. Huxley introduced the terms "mesoderm" in 1871, and Lankester introduced "ectoderm" and "endoderm" in 1873

Formation of Germ Layers

• Gametogenesis: production of sperms (male) and ova (female)
• Fertilization: transmission of genes from parents
• Cleavage: rapid mitotic cell divisions of the zygote to form the Blastula
• Blastulation
• Gastrulation: rearrangement of cells to form a three-layered embryo (gastrula)
• Neurulation
• Organogenesis: formation of organs

Establishment of Somatic Cells

• Three classes of somatic cells: Ectoderm, Endoderm, and Mesoderm (also known as the three germ layers)

Gastrulation

• The blastula becomes a three-layered embryo (gastrula) through gastrulation
• Cells become arranged in three distinct germ layers: Ectoderm, Endoderm, and Mesoderm
• Each germ layer develops into specific parts of the embryo

Ectoderm

• Forms the outermost layer of the embryo
• Develops into:
  • Central Nervous System
  • Lens of the eye
  • Cranial and sensory
  • Ganglia and nerves
  • Pigment cells
  • Epidermis
  • Hair and mammary glands

Endoderm

• Forms the innermost layer of the embryo
• Develops into:
  • Flattened cells that become columnar

Mesoderm

• Forms the middle layer of the embryo
• Develops into:
  • Coelom (body cavity)
  • Generation of chimeric mice

Types of Animals

• Sponges: single germ layer
• Diploblastic animals (Cnidaria and Ctenophores): two germ layers (endoderm and ectoderm)
• Triploblastic animals: three germ layers (ectoderm, endoderm, and mesoderm)

Tissues

• A group of closely associated, similar cells that carry out specific functions
• Four kinds of animal tissues: epithelial, connective, muscle, and nervous tissue
• Each type of tissue is specialized to perform a specific function or group of functions

Epithelial Tissues

• Consists of cells fitted tightly together to form a continuous layer of cells
• One surface is exposed, while the other surface attaches to underlying tissue by a noncellular basement membrane
• Functions include:
  • Protection (epidermis)
  • Absorption (digestive tract)
  • Secretion (glands)
  • Sensation (sensory receptors)

This quiz covers the formation and function of primordial germ layers, comparison of epithelial tissues, and the two basic classes of cells in animals, somatic and germ cells. It is part of the BGY 3202 course for Sem 2 2023/2024.