Animal Embryology Flashcards
What are the three germ layers and what roles do they play?
Ectoderm, endoderm and mesoderm. Ectoderm is the outer layer of the embryo (forming the skin), endoderm is the pouch of the embryo and it forms the gut and organs like the pancreas, liver, lungs and the lining of the digestive tract and arch enteric. The mesoderm is the layer between the two other germ layers that forms the notochord, muscle, the lining of the coelom, skeleton, gonads, kidney and most of the circulatory system.
Talk about body symmetry types
Radial symmetry is when an organism has a top and bottom but no front or back. In bilateral symmetry, the organism has a top/bottom and front/back (dorsal, central, anterior and posterior). If you cut the organism with bilateral symmetry down the central axis, it should give equal halves. With radial symmetry, if you cut the organism from the top to the bottom it should give roughly equal halves along any axis.
Why do radiata not have a coelom and what is the role of the coelom? Define coelom too.
Radiata are diploblasts and do not have mesoderm. Coelom is a fluid filled space in mesodermal tissue that is lined with mesodermal epithelium. The coelom provides protection against mechanical shock for organs. It allows organs to move independently of the body wall and forms the hydrostatic skeleton.
Talk about the protostomes and deuterostomes and how they differ from each other in terms of definition, cell division and coelom
Protostomes have the mouth develop first and then the anus. Deuterostomes is vice versa. In protostomes, cell division happens spirally at an oblique angle to the embryo. In deuterostomes, it happens radially either at right angles or parallel to the embryo. Also, in protostomes the coelom is formed from splitter masses of mesoderm, whereas in deuterostomes it is foldings of the archenteron.
What are the four steps in animal development from a zygote to a multicellular organism?
Fertilisation, cleavage, gastrulation and organogenesis. Gastrulation and organogenesis make up morphogenesis.
Describe frog gastrulation
The mesoderm and endoderm invaginate to form a crease called the blastopore. The top of the crease is called the dorsal blastopore lip. The ectoderm at the same time is expanding over the outer surface of the embryo. The mesoderm and ectoderm migrate over the dorsal blastopore lip and towards the interior of the embryo in a process called involution. The blastopore lip becomes ring shaped. The ectoderm continues to expand and cover the embryo. The mesoderm and ectoderm continue involution around the ring. As the endoderm moves, the archenteron begins to form and the blastocoel shrinks. By the end of gastrulation, the embryo is covered by the ectoderm, the archenteron has formed and blastocoel has shrunk, two germ layers have folded inwards completely.
What is neurulation?
Neurulation is the process leading to the formation of the brain and spinal cord. In this, the dorsal mesoderm specialises into the notochord and the dorsal ectoderm forms a neural plate above the notochord. The neural plate folds inwards and pinches off to form the neural tube that creates the brain and spinal cord. The ectoderm develops a neural crest that migrated around the body and creates peripheral nerves, skull bones and teeth.
What are the four dichotomous branches used to classify organisms?
Tissue type, body symmetry, cavity and modes of development
Describe neurulation
The dorsal mesoderm specialises into the notochord an dorsal ectoderm creates the neural plate above the notochord. After that, the neural plate folds inwards and pinches off to form the neural tube that goes on to create the brain and spinal cord. The ectoderm also creates the neural crest which migrates around the body and forms peripheral nerves, skull bones and teeth.
