BGY3202 2 Anatomy of Germ layers (1).ppt

BGY 3202 Sem 2 2023/2024 Germ layers by Asssoc Prof Dr. Mashitah Shikh Maidin LO’s 1.Describe the layers and formation of primordial germ layers 2.Identity the function of germ layers 3.Comparison between the main types of epithelial tissues.  Cell types Two basic classes o...

BGY 3202 Sem 2 2023/2024 Germ layers by Asssoc Prof Dr. Mashitah Shikh Maidin LO’s 1.Describe the layers and formation of primordial germ layers 2.Identity the function of germ layers 3.Comparison between the main types of epithelial tissues.  Cell types Two basic classes of cells in animals – somatic cells – germ cells Somatic cells 2N - almost everything we see and use, skin, muscle, blood, etc. Germ cells N - the cells that are responsible for reproduction, propagation of the species. Stem cell - neither fish nor fowl. Can in some cases do both. Histogenesis - the formation of different tissues from undifferentiated cells. HISTOLOGY - The science of the microscopic structures of the tissues formed within histogenesis. These cells are constituents of three primary GERM LAYERS through organogenesis : 1. Ectoderm 2. Endoderm 3. Mesoderm What the history of GERM LAYERS?? 1. In 1817, Heinz Christian Pander discovered 2. three primordial germ layers while studying chick embryos. 3. Between 1850 and 1855, i. Robert Remak had further refined the germ cell layer concept, i. Huxley introduced the terms "mesoderm" (1871) ii. Lankester introdueced and "ectoderm" and "endoderm“(1873)  7 steps 1. Gametogenesis - spermatogenesis (male) in testes produce sperms. oogenesis (female) in Ovary produce ova 2. Fertilization -Transmit genes from parents 3. Cleavage -process of repeated rapid mitotic cell divisions of the zygote (unicellular structure) to form the Blastula (multicellular structure). 4. blastulation 5. Gastrulation -rearranges the cells of a blastula into a three- layered 6. neurulation 7. Organogenesis -formation of the organs Establishment of somatic cells Three classes of somatic cells Ectoderm (outside) Endoderm (inside) Mesoderm (in between) – frequently called the 3 germ layers  Gastrulation The blastula becomes a three-layered embryo (gastrula) by the process of gastrulation Cells become arranged in three distinct germ layers, or embryonic tissue layers: – Ectoderm, the outermost layer – Endoderm, the innermost layer – Mesoderm, the middle layer Each germ layer develops into specific parts of the embryo ECTODERM A tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers. It will formed: Central Nervous System Lens of the eye Cranial and sensory The ganglia and nerves Pigment cells Epidermis Hair and mamary glands  ENDODERM Cells migrating inward along the archenteron form the inner layer of the gastrula. Flattened cells, which subsequently become columnar Mesoderm During gastrulation, some of the cells migrating inward The formation of a mesoderm led to the development of a coelom (body cavity). Generation of chimeric mice Sponges are the only animals that have a single germ layer Diploblastic animals, Cnidaria and Ctenophores : - more complex than sponges - having two germ layers (endoderm and ectoderm) Diploblastic animals are organized into recognizable tissues. Triploblastic ???  Tissues A tissue consists of a group of closely associated, similar cells that carry out specific functions There are four kinds of animal tissues: epithelial, connective, muscle, and nervous tissue Each kind of tissue is composed of cells with characteristic sizes, shapes, and arrangements; and each type of tissue is specialized to perform a specific function or group of functions  Animal tissues can be derived to 4 Epitelial Connective Muscular Neuron  Epithelial Tissues Epithelial tissue (epithelium) Consists of cells fitted tightly together to form a continuous layer of cells One surface is exposed – it covers the body (outer layer of skin) or lines a cavity in a hollow organ, such as the lumen of the intestine The other surface attaches to underlying tissue by a noncellular basement membrane  Epithelial Tissues Everything that enters or leaves the body must cross at least one layer of epithelium – epithelial tissues regulate exchange between the body and the external environment Epithelial tissues perform many functions, including protection (epidermis), absorption (digestive tract), secretion (glands), and sensation (sensory receptors) The epithelial layer of the skin (epidermis) covers and protects the entire body