Lecture 7: Embryology Flashcards
What is the difference between mitosis and meiosis?
Mitosis: replication of somatic cells to produce 2 genetically identical daughter cells
Meiosis: replication of gametes to produce 4 genetically unique daughter cell
What is gametogenesis and what are the 2 types
Formation of germline cells
→ Oogenis : 2 million primary oocytes at birth
→spermatogenesis : formation of sperm
What are the 2 phases of the menstrual cycle?
Follicular phase → Maturation and development of follicle which leads to ovulation
Luteal Phase→ maturation of the egg cell
Identify key events during the first week of development?
- Sperm pass slowly through the female reproductive system and is viable for 48 hours.
- Several sperm begin to penetrate the Corona Radiata and Zona Pellucida. ONLY ONE IS SUCCESSFUL
- Fertilization occurs in the ampulla of the fallopian tube
After fertilization occur the secondary oocyte turns into a _________
ZYGOTE
2 secondary oocytes are produced by the ovaries and are both fertilized by 2 different sperm cells. What phenomenon is produced.
Dizygotic twins (FRATERNAL)
Describe the 3 situations that could occur for monozygotic twins.
→ zygote splits before implantation : separate placentas and separate inner sacs
→zygote implants first and then splits: Same placenta and separate inner sacs
→Zygote implants first and then splits LATER: Same placenta and same inner sac
What occurs if separation of the zygote does not occur within 2 weeks of feritlization?
Conjoined twins!
What happens to the zygote in the first week of development after fertilization?
Undergoes mitotic cell division of zygote called CLEAVAGE
New cells formed = blastomeres
2 cell → 4 cell → morula (clump) → Blastocyst
How does a morula turn into a blastocyst?
As the morula enters the uterine cavity the fluids secreted by the uterine glands form between the blastomeres making an internal cavity.
This hence makes it known as a blastocyst.
What even occurs after a blastocyst has formed?
Blastocyst will implant itself onto uterine wall in the endometrium lining. Area under the implanted blastocyst is called the decidua
What is the first thing that occurs in the 2nd week of development?
Trophoblast → Differentiates into 2 layers
/= syncytiotrophoblast (outer layer of cell, produces HCG hormone)
/=cytrotrophoblast (layer behind syncytiotrophoblast and in front of amniotic cavity and amnion
How do early pregnancy tests work?
Syncytiotrophoblast produces HCG hormone which can be detected in urine and indicates pregnancy.
What is the placenta and what is its function?
Organ of pregnancy; will deliver gas, nutrients and exchange waste products between the mother and foetus.
Produces hormones to sustain the pregnancy and is come about from foetal and maternal sources.
Other than the trophoblast, what other part of the implanted blastocyst will differentiate during the second week of pregnancy?
Cells of the embryoblast will differentiate into the bilaminar embryonic disc made up of:
→ Epiblast: Amnion development
→ Hypoblast: yolk sac develops
What is the first process that occurs in the third week of development of the embryo
GASTRULATION
Bilaminar embryonic disc will differentiate into the trilaminar embryonic disc
→Endoderm
→Mesoderm
→Ectoderm
What is the process after gastrulation that produces the spinal chord and brain.
Neurulation!
How do somite’s develop and what are the main types?
Mesoderm form paired columns which segment into cube shaped structures.
→ Myotome: Develops into skeletal muscle of neck, trunk, limbs
→Dermatome: CT & dermis of skin
→Sclerotome: vertebrate and ribs
How is the cardiovascular system developed from the embryo?
→ Early development is necessary
→ Develops from the splanchnic mesoderm as a result of cell differentiation + angiogenesis (heartbeat detected after the 3rd week)
What is the most noticeable feature in the 4th week of development?
→ Along the head and neck region of embryo, their are 5 pharyngeal arches which develop and give rise to
→ skeletal components
→ muscles
→ Nerve + blood vessels in head and neck
What is the period called between the 4th and 8th weeks of development?
Orthanogenetic period
EMBRYO TRIPLES IN SIZE
INTERNAL AND EXTERNAL STRUCTURES ESTABLISHED
MAIN BODY SYSTEM DEVELOPED BUT MINIMAL
What is the well known period after 9 weeks of development to birth
Foetal Period
