CB Quiz 3 Flashcards
What is involved in the Pre-embryonic Period?
- Pre-embryonic Period (0-2 weeks):
A. Cleavage, Blastocyst Formation
B. Implantation, Placentation
C. Gastrulation (Bilaminar => Trilaminar
What is involved in Embryogenesis (Mainly)
- Embryogenesis (weeks 3-8 )
A. Three germ layers give rise to specific tissues & organs
B. Neural tube, Notocord, and Somites
C. Body Folding
What is Teratology
Study of Embryological Origins
Teratogenesis
Causes of Birth Defects
What is the origin of germ cells before Spermatogenesis and Oogenesis?
• Germ Cells:
◦ In yolk sac at 3 weeks of Intrauterine (Within the Uterus) life
◦ Migrate to developing Gonads (Organ that produces gametes) or Genital Ridges by 5 weeks
‣ In Female: Oogonia
‣ In Male: Spermatogonia
Outline the steps of spermatogenesis
• Spermatogenesis: In Spermatazoon: Spermatogonia -> Mitosis -> Some mature into Primary Spermatocyte -> Meiosis I -> Secondary Spermatocyte -> Meiosis II -> Spermatids -> Mature into Spermatozoa
Outline the process of Oogenesis
• Oogenesis: In Ovum: Oogonia -> Mitosis -> Some mature into Primary Oocyte —> Meiosis 1 (Arrested in prophase for up to 40 years as Primordial Follicles —> Secondary Oocyte & Polar Body —> Meiosis II (Arrested in metaphase and only completes if the cell is fertilized) —> Ovum + 3 polar bodies
Where do sperm and Ova typically meet and fertilize
Ampulla
What is polyspermy and how is it prevented
Polyspermy is the fertilization of an egg by more than one sperm.
Depolarization of the Zona Pellucida prevents polyspermy
What are the processes of fertilization and Implantation
Fertilization and Implantation:
1. Mature Ova is shed and gathered into the Fallopian tube
2. Capacitation of sperm in uterine tube
A. Removal of Glycoproteins coat from acrosome
B. Sperm and Ova typically meet and fertilize at the Ampulla
3. Acrosome Reaction: Enzyme released which allow
A. Phase 1: Penetration of Corona Radiata
B. Phase 2: Penetration of Zona Pellucida
C. Phase 3: Fusion of the oocyte and sperm cell membranes
a. Zona Pellucida depolarizes and becomes impenetrable preventing polyspermy
b. Resumption of meiosis 2 for the oocyte resumes
D. Male & Female pronuclei Merge - Zygote
E. Division begins 24-36 hours after fertilization with resulting cells getting smaller as no net-growth takes places
F. Morula is formed 3-4 days and still enclosed by Zona Pellucida
G. Cavity is formed in the cell mass - Blastocoel
H. Blastocyst emerges from the Zona Pellucida and begins to adhere to uterine wall
Where do Blastocysts emerge from, what do they adhere to, and what are they composed of?
They emerge from the Zona Pellucida, adhere to the uterine wall and are composed of a Trophoblast and Embryoblast
What are the types of trophoblasts
Syncytiotrophoblast
Cytotrophoblast
Describe the 2 types of Trophoblasts briefly
No need for full details just basic function
◦ Trophoblast: Outer cell mass with two types of cells:
‣ Syncytiotrophoblast: Externally
• Very invasive
• Eats into uterine wall
• No distinct cell boundaries
• Can’t proliferate (rapid cell division)
‣ Cytotrophoblast: Internally
◦ Cells divide by mitosis and migrate into Synctiotrophoblast
What are the two types of Embryoblasts
Hypoblast
Epiblast
Describe the two types of Embryoblasts briefly
◦ Embryoblast: Inner cell mass with two types of cells:
‣ Hypoblast:
• Cells close to blastocyst activity
• Primitive Endoderm
• Migrate around Blastocoel Cavity and eventually line it
• Fluid filled cavity which shapes the Primitive Yolk Sac
‣ Epiblast:
• Primitive Endoderm
• Fluid filled cavity which shapes the amniotic space or cavity
What is the purpose of the Bilaminar Disc
◦ Bilaminar Disc forms the embryo
Where does normal implantation take place?
Anterior/posterior uterine wall
What is an Ectopic implantation
Implantation in an abnormal positions
What happens when implantation occurs
• If implantation occurs:
◦ Developing placenta produces Human Chorionic Gonadotrophn (HCG) which makes Corpus Luteum persist
◦ Corpus Luteum continues to produce Progesterone
◦ Progesterone sustains endometrial lining
Explain the process of Gastrulation
Gastrulation: (Begins Day 15):
• Bilaminar Disc Formation including the Epiblast & Hypoblast
• Primitive Streak, Groove, and Node develop in Epiblast
◦ Indicates the main line/body axis
◦ Node is at Cranial or Cephalad end
• Epiblast migrate to streak and Invaginate
◦ Some completely displace Hypoblast - Embryonic Endoderm
◦ Some lie between Epiblast and Endoderm - Embryonic Mesoderm
◦ Cells remaining in Epiblast - Embryonic Ectoderm
What is the Trilaminar Disc composed of and briefly state their primitive role
• Trilaminar Disc:
◦ Ectoderm: All epidermis and the nervous system
◦ Mesoderm: Bone, muscle, connective tissue, dermis
◦ Endoderm: Inner lining of the gastrointestinal & respiratory tracts
‣ The Ectoderm and Endoderm are only continuous at the Oropharyngeal (mouth and pharynx) and Cloacal (anal) areas
What is the notochord and what is it’s significance
• Notochord:
◦ Distinguishing characteristic of vertebrates
‣ Lies underneath neural tube
‣ Becomes cartilaginous
Define the Notochordal process
◦ Notochordal Process:
‣ Develops in primitive node
‣ Hollow and grows cranially (towards skull)
Explain the overall significance of the Notochord including its formation
• No need for so much detail just describe the process
Notochord:
◦ Distinguishing characteristic of vertebrates
‣ Lies underneath neural tube
‣ Becomes cartilaginous
◦ Notochordal Process:
‣ Develops in primitive node
‣ Hollow and grows cranially (towards skull)
◦ Notochordal Plate: Notochordal Process then fuses with Endoderm, to form solid Notochordal plate
◦ Notochord: Notochordal Plate detaches from endoderm to form a solid rod called the Notochord
Define Caudal
Tail or posterior part of body
Explain the process of formation of the Neural tube
No need for so much detail, just be able to describe process
Neural Tube: (Begins day 17/18)
• Ectoderm overlying the notochord will thicken to form the Neural Plate
◦ It then begins to fold, forming neural tube
• Closure begins in the middle of the Dorsum of the embryo and then extends cranially and Caudally (tail or posterior part of body) until “Zipped up”
◦ The Zipping process begins at about day 22
• Tube closes completely at the cranial end a few days later and caudal end a few days after that
• Neurulation is then complete with the CNS being a closed tube
◦ Narrow Caudal End = Spinal Chord
◦ Broader Region at head region = Brain
What is the cranium
Skull
What are the different classifications within the mesoderm with a brief description of the Lateral Plate components
Mesoderm:
• Paraxial Mesoderm: Somitomeres & Somites
• Intermediate Mesoderm: Urogenital
• Lateral Plate:
◦ Somatic Mesoderm: Attached to Ectoderm and helps form body wall (Parietal). Bones, dermis, muscles, and connective tissue
◦ Splanchnic Mesoderm: Attached to Endoderm (Visceral). Gut Epithelium, Bladder, Urethra, and Lungs
Discuss the Paraxial Mesoderm including
Segmentation and Somites:
• Paraxial mesoderm organizes into segments Craniocaudally (from head to tail) called Somitomeres & Somites
• Somitomeres first appear in the Cephalad Region and are associated with neuromeres
• Somites appear Craniocaudally
Briefly describe the formation of vertebrae through induction
Induction:
• Neural Tube and Notochord Induce formation of vertebrae
◦ Neural tube & Sclerotome - Vertebral arch
◦ Notochord & Sclerotome - Vertebral body
◦ Notochord forms Nucleus Pulposus
Spina Bifidia
Neural Tube Defects
Describe the different ways the body of an embryo fold
Body Folding:
• Longitudinal Folding (Craniocaudal)
◦ Endoderm also layer becomes incorporated into the body of the embryo
◦ Connection with yolk sac narrows - Vitelline Duct
• Transverse Folding: Surface Ectoderm and Amniotic Cavity fold around laterally
• Development or incorporation of embryonic body cavity (Coelum)
What is an aneurysm?
Weakness in the arterial wall causing a bulge. There are often no symptoms. A ruptured aneurysm can be fatal.
Another variation is a false lumen that could redirect the blood
