Cleavage and Blastula PDF

Cleavage and Blastula Justhine R. Delos Reyes 1 - MB  Embryogenesis Is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe later s...

Cleavage and Blastula Justhine R. Delos Reyes 1 - MB  Embryogenesis Is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. Embryogenesis starts with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon).  Fertilization The fertilization process in animals can occur either internally or externally, a difference which is largely determined by the method of birth. Animals which use viviparous and ovoviviparous reproduction (embryos develop within the animal’s body), and oviparous animals which lay hard shelled eggs, use internal fertilization. Early Observations Karl Ernst von Baer - was a Baltic German scientist and explorer, renowned for his pioneering work in embryology. Born on February 28, 1792 and died in November 28, 1876, he made several significant contributions to biology and other fields. Early Observations Christian Heinrich Pander - (1794- 1865) was a prominent biologist and embryologist of Baltic German origin, often hailed as the "father of embryology. Born in Riga, Latvia, Pander made significant contributions to various scientific fields, including osteology, zoology, geology, and anatomy. Cleavage Cleavage in developmental biology was first observed and recorded by the Dutch microscopist and naturalist, Jan Swammerdam. Born on February, 12 1637 and died on February 17 1680.  Cleavage What is Cleavage? Refers to the early stages of embryonic development where a fertilized egg, or zygote, undergoes rapid cell divisions without increasing in overall size. The process by which cellular division occurs during the zygotic phase of development that ends with a multicellular embryo. Cleavage  Cleavage can take place in two ways. Holoblastic Meroblastic Cleavage Cleavage Holoblastic Cleavage ~Involves the division of the entire cell into blastomeres. ~Occurs when there is minimal or moderate yolk. ~Complete Cleavage  Who undergo Holoblastic Cleavage? ~Mammals ~Amphibians ~Echinoderms Holoblastic Cleavage Moroblastic Cleavage ~Generally occurs in fertilized eggs that contain a greater quantity of yolk. ~Incomplete Cleavage  Who undergo Moroblastic Cleavage? ~Reptiles ~Birds ~Fish Meroblastic Cleavage Holoblastic and Meroblastic  Embryo divided into two Hemispheres Animal Pole Vegetal Pole  Animal Pole ~Located at the upper hemisphere of the embryo ~ It contains smaller cells that divide rapidly. ~This region is more metabolically active and is involved in forming the future embryo. Embryo  Vegetal Pole ~Found at the lower hemisphere of the embryo ~ It contains larger, yolk-rich cells that divide more slowly ~This region is less active and primarily provides nutrients to the developing embryo, Embryo  Cleavage Patterns Isolecithal Radial Cleavage - Seen in echinoderms and amphibians, where cells divide symmetrically around the axis  Cleavage Patterns Isolecithal Spiral Cleavage - Found in mollusks and annelids, where cells divide at oblique angles.  Cleavage Patterns Isolecithal Bilateral Cleavage - Found in tunicates and some other invertebrates, where the embryo’s left and right sides are mirror images.  Cleavage Patterns Isolecithal Rotational Cleavage - Typical in mammals, including humans, where the first division is along the meridian, and the second division is perpendicular to the first.  Cleavage Patterns Radial mesolecithal cleavage - is a type of embryonic development seen in certain animals, such as amphibians.  Cleavage Patterns Telolecithal Bilateral cleavage - the first few cleavages are meridional (vertical), but they do not extend far into the yolk. Subsequent cleavages create a disc-like layer of cells on top of the yolk, forming a structure called the blastodisc.  Cleavage Patterns Centrolecithal Superficial cleavage - is a type of embryonic development seen in certain eggs, particularly those of arthropods like insects. In these eggs, the yolk is centrally located within the cytoplasm. This central placement of the yolk influences how the cell divides during early development. Cleavage Patterns  Morula What is Morula? Is an early stage in embryonic development. It is a solid ball of cells (blastomeres) formed by the division of a fertilized egg (zygote). Morula is usually produced in those species the eggs of which contain little yolk and, consequently, undergo complete cleavage. Morula  Blastula What is Blastula? Is an early stage of embryonic development in animals. It forms after a fertilized egg (zygote) undergoes multiple rounds of cell division, a process known as cleavage. The blastula is typically a hollow ball of cells, with a fluid-filled cavity called the Blastocoel. Blastula Thank You!