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Veterinary Embryology 8.1 - 8.4

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Veterinary Embryology 8.1 - 8.4


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Field of study concentrated on pregnancy, childbirth and the postpartum period

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Veterinary Embryology 8.1 - 8.4 - Details



113 questions
Field of study concentrated on pregnancy, childbirth and the postpartum period
3 Phases of Embryology
1. Pre-Embryonic Period 2. Embryonic Phase 3. Fetal Phase
4 Stages of the Embryonic Phase
1. Fertilization 2. Cleavage 3. Gastrulation 4. Development of body form
Average length of the Embryonic Phase
2-8 weeks (Depending on specie)
Sperm and ovum fuse to form a Zygote. (haploid + haploid = diploid)
Corona Radiata
Layer of follicular cells that surround the Zona Pellucida; does not impede fertilization; gradually desquamates to uncover nutrient pores in ZP
Zona pellucida
Glycoprotein layer that surrounds the ovum; becomes impermeable to sperm after fertilization
Factors that affect the rate at which cleavage occurs
1) Quantity 2) Distribution of yolk in the ovum The presence of a large amount of yolk mechanically retards cleavage because yolk cannot divide as rapidly as cytoplasm can
Type of ova with a small amount of yolk (Mammalian Ova)
Type of ova with yolk that is evenly distributed and nucleus is positioned centrally (Mammalian ova; resultant blastomeres are all the same size = cleavage is equal)
Complete cleavage that divides the whole egg into distinct and separate blastomeres (e.g. mammals)
Incomplete cleavage as a result of the presence of an impeding mass of yolk material (e.g. eggs of birds)
Blastocyst cavity
Fluid filled cavity within the blastomere (Fluid filled spaced develop between the cells in the centre of the morula, they coalesce to form the blastocyst)
1. The membrane that forms the wall of the blastocyst in early development; aids implantation in the uterine wall Gives rise the the placenta
Central cells (mainly from the animal pole) group together against the trophoblast to form the inner cell mass known as the Embryoblast Subsequently forms the embryo
A structure formed in the early development of mammals. It possesses an inner cell mass (embryoblast) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocyst cavity.
When is the Zona Pellucida lost in Ungulates?
After the Morula has been transformed into a blastocyst (Blastocyst looses is spherical shape after the loss of the ZP)
When is the Zona Pellucida lost in Carnivores?
After the commencement of gastrulation - at the stage when the somites start to form (Blastocyst looses is spherical shape after the loss of the ZP)
From what structure does the Embryonal Disc develop?
Embryoblast (The embryonal disc will later develop into the Embryo Proper)
Covering layer of Rauber
The part of the trophoblast that lies over the embryoblast. (Develops slower than the rest of the trophoblast)
Placental Mammals
Differentiation of the 3 germ layers Transforms the unilaminar blastocyst into a trilaminar gastrula
Cleavage is controlled by...
Properties transferred by the maternal nucleus to the cytoplasm of the the zygote.
What does the Ectoderm layer differentiate into?
Reception of stimuli and protection of the organism
What does the Mesoderm layer differentiate into?
Support, movement, excretion and reproduction
Name the 4 stages of Gastrulation
1. Formation of the Hypoblast and Embryonal disc 2. Primitive Streak Formation 3. Cell involution and Notochord Formation 4. Neurulation and Initial differentiation of the Mesoderm
When does Gastrulation commence?
After formation of the embryoblast
Hypoblast Formation
The hypoblast is a tissue type that forms from the inner surface of the embryoblast. It lies beneath the epiblast and consists of extended squamous epithelium. The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion.
Embryonal Disc Formation
After the loss of the Covering Layer of Rauber the exposed Embryoblast is transformed into a slightly convex layer of cells known as the Embryonal Disc. The Embryonal Disc is continues with the Trophoblast
Primitive streak formation
A dull, thickened stripe develops in the middle of the epiblast in the caudal half of the embryonal disc. It is formed by the medial and caudal migration of proliferating epiblast cells Continued cell migration causes cranial elongation of the primitive streak until it extends over all but the cranial third of the embryonal disc.
Primitive node
The caudal migration of proliferating epiblast cells from the cranial part of the embryonal disc causes a discrete aggregation of cells at the cranial end of the primitive streak; this thickening is known as the primitive node
Cell Involution
Proliferating cells immediately adjacent to the primitive streak are involuted into the area between the epi- and hypoblast The process of involution physically alters the primitive streak and it changes into a primitive groove, flanked on either side by a primitive fold.
Endoderm Formation
Some of the involuted cells invade the hypoblast and, multiply and form a layer on the deep surface of the embryonal disc known as the Embryonic Endoderm.
Extraembryonic Endoderm
Development if the endoderm displaces the hypoblast to the periphery of the Embryonic Disc. The Hypoblast now only lines the yolk sac and is now referred to as the EEE.
Mesoderm Formation
The remaining involuted cells (i.e. those that did not invade the hypoblast to form the endoderm) now constitute the mesoderm.
In what anatomical directions does the mesoderm expand with continued cell involution and proliferation?
Cranially, caudally and laterally (excluding the area immediately cranial to the primitive node, the prechordal plate and the cloacal membrane. It expands beyond the periphery of the embryonal disc and between the trophoblast and extraembryonic endoderm of the entire yolk sac.
Embryonic Mesoderm
Mesoderm within the embryonal disc
Extra-embryonic mesoderm
Mesoderm beyond the periphery of the Embryonic Disc
The mesoderm is prevented from invading the prechordal plate and the cloacal membrane by firm adhesion between the ________ and _______
Epiblast and Endoderm (The area in front of the prechordal plate is, however, eventually invaded by the expanding mesoderm)
Where does the pleuropericardial coelom develop?
The area in front of the prechordal plate
Notochordal canal
Lumen of the Notochordal Process
Notochord-induced transformation of ectoderm into nervous tissue
Notochord Formation
The notochord develops from the primitive node located at the cranial end of the primitive streak. From the node, cells proliferate and migrate forward into the future head region where they become the rod-shaped notochord.
Neurenteric canal
Temporarily connects the future amniotic cavity and yolk sac (Previously Notochordal canal)
Ectoderm Formation
All the epiblast cells that did not involute constitute the ectoderm
The ectodermal cells on the dorsal midline Destined to form the future brain and spinal cord.
Neural Plate
Thickening of the Neuro-ectoderm cranial to the Primitive Node Wide, flat cranially = Future Brain Narrower in the middle, caudally = future spinal chord
Neural Groove
Dorsal surface of the neural plate invaginates forming the NG
Neural Folds
Borders the Neural Groove on either side
Neural Tube
Neural folds fuse along the dorsal midline to form the NT The lumen of the NT is the Neural Canal
Neural Canal
Lumen of the Neural Tube Temporarily communicates with the amnotic cavity via the rostral and caudal neuropores. The rostral neuropore closes last.
Rostral or Caudal opening of the Neural Tube Temporarily communicates with the amniotic cavity. (Rostral opening closes last.)
Sulcus Limitans
From the level of the mesencephalon, a longitudinal groove develops bilaterally in the walls of the neural canal.
Paraxial Mesoderm
Distinct longitudinal columns adjacent to the Notochord (Originates from mesoderm)
Lateral Mesoderm
Mesoderm peripheral to Paraxial Mesoderm