Lecture 1 (8/26) Flashcards
What are the two daughter cells produced when the fertilized ovum divides?
Blastomeres
What is the spherical mass of cells that forms when the blastomeres repeatedly divide?
Morula; Latin for mulberry
Compaction?
When cells become more tightly packed
What is the name of the epithelial layer that superficial cells (cells that end up on the outside) gives rise to?
Trophoblast (trophoectoderm)
What are the cells on the inside of the blastocyst?
Inner cell mass (embryoblast)
Blastomeres give rise to what?
Blastocyst
The morula makes fluid which separates the cells and forms what?
The blastocyst cavity (blastocoele; primitive yolk sac)
The morula is surrounded by what?
The zona pellucida (a layer that surrounds the female egg)
What is the layer of trophoblasts overlying the inner cell mass?
Rauber’s layer (will eventually degenerate and go away to form the embryonic disc)
What are the outer cells of the inner cell mass?
Epiblasts
What do the cells of the embryonic disc become?
Ectoderm and mesoderm
What are the inner cells of the inner cell mass?
Hypoblasts
Which cells migrate around to line the blastocyst cavity and lay just inside the trophoblast layer to become the endoderm?
Hypoblasts
The blastocoele can be called what?
The yolk sac
Apoptosis?
Programmed cell death
Up to what percentage of blastomeres undergo apoptosis?
10%
Early on the blastomeres are considered embryonic stem cells then as division continues they are known as specific cell types. Why?
Early on they can differentiate into anything, but as division. Continues they become more specialized and can only differentiate into specific cell types.
During the division of the blastomeres, what disappears?
The zona pellucida
The shape of the blastocyst (blastula) varies considerably between species. Give examples of this.
Pear-shaped to spherical: dogs, horses Elongate: ruminants, pigs
What is gastrulation?
The stage where the three primary germ layers are formed: Ectoderm, Mesoderm, Endoderm
What are the three types of ectoderm? Discuss their differences.
Neural Ectoderm: comprises brain, spinal cord, retina, olfactory epithelium, pineal gland, posterior pituitary & Non-neural Ectoderm: comprises the epidermis and associated glands, lens of the eye, tooth enamel, and the inner ear & the Neural Crest
What primary germ layer comprises the urogenital, circulatory, and supportive muscular and skeletal systems?
Mesoderm
What primary germ layer comprises the lining of the gastrointestinal system, the lining of the respiratory system, the lining of the bladder, middle ear, and auditory tube, the liver, the pancreas, and the thyroid and parathyroid?
Endoderm
What is the primitive streak?
The midline indentation on the surface of the embryonic disc.
How are the three germ layers formed during gastrulation?
The epiblasts (most superficial layer) migrate to the primitive streak and invaginate (be turned inside out or folded back on itself to form a cavity or pouch). These cells that invaginate become the mesoderm. The epiblasts that do not migrate in and remain on the surface now become the ectoderm. The inner hypoblast layer then becomes the endoderm. After the 3 layers are formed gastrulation is complete and the primitive streak disappears.
How is the notochord formed? What does it eventually become?
Some of the epiblast cells that migrate in to become mesoderm migrate cranially to form the notochord (a midline tube of mesoderm). The primitive node moves to drag the notochord the full length of the embryo. The lumen of the notochord eventually becomes part of the axis of the axial skeleton (vertebral column).
How is the neuroectoderm formed?
The ectoderm directly above the notochord proliferates (rapidly multiples) to become the neuroectoderm (neural plate).
How is the neural tube formed? What does it eventually become?
The neural plate invaginates to form the neural groove and then pinches off to form the neural tube, which becomes the brain and spinal cord.
How are neural crest cells formed?
Some neuroectodermal cells go rogue and migrate laterally to become the neural crest cells.
The mesoderm differentiates further into what three zones?
Paraxial Mesoderm, Intermediate Mesoderm, Lateral Mesoderm
The paraxial mesoderm forms aggregates known as __ first cranially, then caudally.
Somitomeres
The first 7 somitomeres become the head. What do the more caudal somitomeres become?
Somites
Somites are further subdivided into what three categories?
Sclerotome: becomes cartilage and bone; Myotome: becomes skeletal muscle; Dermatome: dermis (part of skin)
What does the Intermediate Mesoderm become?
The urinary and reproductive systems; also the adrenal cortex
The Lateral Mesoderm splits into what two layers?
Somatic Layer and Splanchnic Layer
What do the somatic and splanchnic mesoderm layers form?
Somatic: lateral and ventral body wall, extra-embryonic membranes (placenta): amnion and chorion; Splanchnic: wall of the gut tube, extra-embryonic membranes (placenta): allantois, yolk sac, the Vascular System: endothelium, blood cells, spleen, and heart
What layer is formed when the somatic mesoderm layer fuses with the ectoderm?
Somatopleure
What layer is formed when the splanchnic layer fuses with the endoderm?
Splanchnopleure
What is the space between the splanchnopleure and somatopleure called?
The embryonic coelem
What two regions is the embryonic coelem divided into? What do they form?
Extra-embryonic coelem: forms the yolk sac and allantois (parts of the placenta); Intra-embryonic coelem: becomes the body cavities (pleural space, pericardial space, pertonenal cavity –> the mesodermal cells lining these cavities are squamous (flattened) and called mesothelium.
What is implantation?
The process where the trophoblast portion of the blastocyst attaches to the uterine lining.
What are the three stages of implantation?
Apposition, Adhesion, Attachment
What are the three different forms of implantation?
Interstitial, Eccentric, Centric
What is also known as the wall of the uterus?
Myometrium
Describe the Interstial form of implantation. Which species are involved?
Blastocysts burrow into the endometrium and are completely engulfed/covered; primates, guinea pigs (TOP of picture)
Describe the Eccentric form of implantation. Which species are involved?
Blastocysts hide in the folds in the endometrium (lining of the uterus) and are almost completely covered; Rodents (MIDDLE of picture)
Describe the Centric form of implantation. Which species are involved?
The blastocyst attaches to the endometrium, but doesn’t burrow (very little implantation); horses, cattle, sheep, pigs, dogs, cats, rabbits (BOTTOM of picture)
Some species have delayed implantation. What does this mean and what species are involved?
The embryo hangs out in the uterine horn (in limbo) for a variable amount of time prior to implantation. Theoretically this is so the babies are born at the ‘right’ time of the year; mink, ferrets, bears, badgers, seals
Placenta is Latin for what?
Cake
What are the 6 functions of the placenta?
- Supply or storage of nutrients 2. Respiratory exchange 3. Excretion of wastes 4. Mechanical protection of the embryo 5. Transfer of maternal antibodies (passive immunity) 6. Hormone production (mammals *non-mammals don’t have placentas)
What are the four extra-embryonic membranes?
Amnion, Chorion, Allantois, Yolk Sac
On the dorsal surface, the outer trophoblastic layer extends up around and over the embryo forming ___ (chorioamniotic folds) which eventually fuse at the chorioamniotic raphe.
amniotic folds
What is the inner membrane that results from the formation of the amniotic folds?
Amnion: directly surrounds the embryo throughout gestation; avascular; lined by ectoderm (which is surrounded by somatic mesoderm = somatopleure)
What is the outer membrane that results from the formation of the amniotic folds?
Chorion: forms the outermost layer of the extra-embryonic membranes (placenta) and surrounds the entire concepus, including the amnion and yolk sac; avascular; the outer surface of the chorion is ectoderm = somatopleure
What is the space between the amnion and the chorion (the two layers of somatopleure)?
the extra-embryonic coelem
What are the functions of the yolk sac?
Important for early hematopoiesis, source of primordial germ cells
What is the blastocyst cavity (blastocoele) in a blastocyst also called?
a bilaminar yolk sac
What are the two layers of the bilaminar yolk sac?
Endoderm: lining of the yolk sac; Outer trophoblastic layer/ectoderm
As the embryo develops the yolk sac becomes linded by what?
splanchnopleure (splanchnic mesoderm and endoderm)
After the yolk sac becomes lined by splanchnopleure the splanchnopleure then fuses with the somatopleure of the chorion to form the ___.
choriovitelline membrane
As the embryo develops the yolk sac gets pinched into what two portions?
- The portion that remains within the embryo that forms the gut. 2. The portion that remains outside the embryo that is the definitive sac.
What do the two portions of the pinched off yolk sac remain connected to, which is part of the umbilical cord?
vitello-intestinal duct
When the choriovitelline membrane contacts with the uterus it becomes a ___.
Choriovitelline placenta: the contact with the uterus is minimal; In mammals, the choriovitelline placenta is a temporary structure - it regresses as the chorioallantoic placenta develops; in marsupial, the choriovitelline placenta persists
