Vertebrate Development: Birds Flashcards
Microlecithal
Little yolk
Mesolecithal
Moderate yolk
Macrolecithal
Large yolk
Cleavage
Restricted to a small region at the animal pole of the zygote and produces the blastodisc (cleavage)
Blastodisc
Flat disc of cells (cleavage)
Blastula Formation
Blastodisc cells form the epiblast and the hypoblast (blastula formation)
Epiblast
Dorsal layer (blastula formation)
Hypoblast
Ventral layer (blastula formation)
Blastocoel
Space between the epiblast and the hypoblast (blastula formation)
Gastrulation
- Some epiblast cells migrate inward through the primitive streak to form endoderm (dorsal surface) and mesoderm (gastrulation)
- Remaining epiblast cells form ectoderm (ventral surface)
Primitive Streak
Groove in the epiblast layer
Formation of 3 Embryonic Germ Layers
Ectoderm, mesoderm, and endoderm (gastrulation
Neurulation
- Neural plate ectoderm bends along the dorsal midline and sinks ventrally into the embryo to form the neural groove and the neural folds on either side
- Neural folds fuse to form the hollow neural tube
- Neural crest cells separate from the dorsal region of the neural tube
(neurulation)
Central Nervous System Development
Anterior region of the embryo:
1. Neural tube of the head region starts to swell and expand into the brain
2. Neural tube posterior to head gives rise to spinal cord
(post-neurulation)
Somatic Hypomere Mesoderm
Hypomere mesoderm closer to ectoderm
Splanchnic Hypomere Mesoderm
Hypomere mesoderm closer to endoderm (within the chorioallantoic membrane) and forms allantoic vessels, vitelline vessels, and the heart
Coelom
Space between the somatic hypomere mesoderm and the splanchnic hypomere mesoderm (neurulation)
Lumen
Space of the digestive tract formed by:
1. Endoderm folds dorsally into the embryo
2. Folds come closer together and fuse to form the lumen of the digestive tract (in chicks)
(neurulation)
Extra-Embryonic Membranes
Produced and by the embryo and grow outward from the embryo (amnion, chorion, allantois, and yolk sac)
Amniotes
Have amnion, chorion, allantois, and yolk sac (mammals, reptiles, and birds)
Anamniotes
Yolk is already in the cells of frogs (fish and amphibians)
Amnion
Arise from somatopleure and is a waterproof membrane that surrounds the embryo in a capsule filled with amniotic fluid
Advantages of Amnion
- Slows cooling of remaining heat from adult
- Prevents desiccation (drying out)
- Prevents external things from getting in (embryonic fluid has anti-infection properties)
- Cushioning (fluid acts as a shock absorber)
- Buoyancy (prevents collapse under the weight of gravity)
Chorion
Arise from somatopleure and fuses with the outer section of the allantois to form the chorioallantoic membrane
Chorioallantoic Membrane
Vascular respiratory membrane used to exchange gases with the environment (through the shell) and also transports calcium from the shell to the embryo (located close to the shell)
Note: in most mammals, the chorioallantoic membrane (and/or yolk sac, depending on the species) produces the umbilical cord and the embryonic region of the placenta while amnion surrounds the embryo in a fluid-filled capsule
Somatopleure
Ectoderm and somatic hypomere mesoderm
Yolk Sac
Arise from splanchnopleure, grows ventrally to surround the yolk, and forms the vitelline vessels
Vitelline Vessels
Blood vessels that transport nutrients from the yolk to the embryo
Allantois
Arise from splanchnopleure and sequesters (hides/isolates) nitrogenous metabolic wastes away from the embryo (stores wastes in a large garbage bag)
Note: making and breaking proteins (metabolic activities) produce nitrogenous metabolic wastes (ex. ammonia/NH3)
Splanchnopleure
Endoderm and splanchnic hypomere mesoderm
