Lecture 3 & 4- Embryology Flashcards
From which embryonic tissue are the three germ layers derived from?
Epiblast
What is the function of the hypoblast layer?
It lines the blastocyst cavity forming the yolk sac
Initial development of which system in the body is driven directly by the notochord?
CNS
Which tissue lines the intraembryonic coelom?
Mesoderm
What is the function of the notochord?
- Drives neurulation (formation of spinal cord, CNS)
- Is a hollow cord (becomes solid rod)
- Forms nucleus pulposus of intervertebral disc
- Has no function in adult life
- Acts as midline
What is a derivative for the splanchnic layer of the lateral plate mesoderm?
- Cardiac muscle
- Blood vessels
What is the difference between pluripotent and totipotent?
- Zygote is totipotent: Has the ability to differentiate into any type of cell.
- Pluripotent: Diff. into many but not all cell types (forms anything from the trilaminar disc)
Why does the buccopharyngeal membrane and the cloacal membrane have no mesoderm?
(mesoderm gives rise to all tissues of the CVS)
- Opening for mouth & anus
What can umbilical cord stem cells be used for?
- Multipotent (more specialised than pluri)
- Form haematopoetic blood cells
- Form mesenchymal stroma cells (multipotent adult stem cells)
- Used in blood transplants to cure blood cancers (leukemia), immune deficiency disorders
What are embryonic stem cells and what are the ethical issues posed by their use?
- Pluripotent
- Ethical issues: consent?
Why is C-section recommended in cases of placenta previa?
- Baby might not make it to term: placenta is unstable, less uterine tissue
- Increase risk of detachment: major blood loss
How can an ectopic pregnancy present clinically? And why are they life-threatening?
- Implantation in any other place except for uterine lining
- Signs: missed period, hemorrhage, brown watery discharge, lower abdominal pain on one side
- Can rupture blood vessels leading to internal bleeding (burst fallopian tube)
- 4-8 days after implantation
What are the most common causes of maternal mortality globally?
- Poverty: lack of resources
- Complications from delivery
- Pre-eclampsia: High BP during pregnancy
- Severe bleeding
- Infections
- Unsafe abortion
- Diabetes
In the UK, maternal mortality is due to…
- Stroke
- Pulmonary embolism
- Deep vein thrombosis
- Postnatal depression
How long is the different stages in pregnancy?
- Pre-embryonic (1-3 weeks)
- Embryonic (3-8 weeks)
- Fetal (9-38 weeks)
Where does fertilisation usually occur? What is the ideal site of implantation? And how long is oocyte/sperm viable for?
- Ooctye released from ovary –> fertilised in ampulla of Fallopian tube
- Endometrium ideal site of implantation
- Oocyte - 1 day, sperm - 3 days
What is cleavage and what is its results?
- First mitotic division
- Forms 2 blastomeres of equal size
- Zona pellucida (glycoprotein shell) prevent entry of sperm
What forms after blastomeres in day 3? Is it totipotent or pluripotent?
- Morula (16 cells)
- Totipotent: Capacity to form any type of cell
What is Pre-implantation Genetic Diagnosis (PGD)? Why is it preceded by IVF?
- Cell removed from morula tested for hereditary diseases prior to transfer of embryo to mother
- IVF, oocyte taken from mother, fertilised in vitro, morula then transferred for implantation
In week 1, compaction occurs. What happens in compaction?
- Formation of first cavity
- Blastocyst formed: Outer cell mass (trophoblast) –> form placenta, inner cell mass (embryoblast)
- After compaction, cells become pluripotent (diff into many type of cells)
On day 5, hatching occurs. Why?
- Blastocyst hatches from zona pellucida, free to divide
- Interact w uterine surface
What happens at the end of 1st trimester?
- Implantation (100 cells)
What occurs in differentiation?
Outer cell mass:
- Syncytiotrophoblast (outside)
- Cytotrophoblast
Inner cell mass:
- Epiblast
- Hypoblast
What is the significance of implantation?
- Implantation is interstitial: Conceptus implants itself within the endometrium
- Establishes maternal blood flow within the placenta (support, nutrients)
- Establishes basic structural unit for maternal-fetal exchange
Describe some implantation defects
- Placenta previa: Implantation occurs in lower uterine segment (cervix)
- Can cause haemorrhage
- Require C-section - Ectopic pregnancy: Implantation anywhere other than endometrium (peritoneal, ampulla)
- Life-threatening emergency
Summary of first lecture
- Zygote –> morula –> blastocyst
- Inner cell mass: epiblast & hypoblast –> germ disc
- Outer cell mass: Syncytiotrophoblast & cytotrophoblast –> placental membranes
What are some risk factors of ectopic pregnancy?
- IVF
- Past pelvic infections
- IUCD
- Becoming pregnant whilst on progesterone-only contraceptive pills
Symptoms of ectopic pregnancy
- Abdominal pain
- Pelvic pain
- Vaginal bleeding
- Breast tenderness
- Dizziness
Signs of ectopic pregnancy
- Pelvic/abdominal tenderness
- Pallor
- Enlarged uterus
- Tachycardia/Hypotension
Risk factors of placenta previa are?
- Previous history of P.P
- Previous caesarean section
- Age
- Smoking
- Cocaine use during pregnancy
Symptoms of placenta previa
- Incidental finding on ultrasound scanning
- Painless bleeding (sudden, X last long)
- Risk of preterm delivery
What are some teratogenic agents?
- Thalidomide
- Radiation
- Rubella virus
How deadly is the impact of teratogenic agents during pre-embryonic, embryonic & fetal phase?
- Pre-embryonic: lethal effects
- Embryonic: V. sensitive
(after embryonic period, risk of structural defects very low, except CNS) - Fetal: Less sensitive
State the 4 key events in order
Gonna Need Some Food
Gastrulation –> Neurulation –> Segmentation –> Folding
What is gastrulation?
- Epiblast diff. into 3 layers (endo,meso & ecto)
[bilaminar –> trilaminar disc] - Hypoblast displaces to form yolk sac
What are some derivatives of endo,meso and ectoderm?
Ectoderm: Organs & structures that have contact w outside world
- Nervous system
- Skin
Mesoderm: Supporting tissues
- Muscle
- Cartilage
- Liver (organs)
- Bone
Endoderm: Internal structures
- Epithelial lining of GI tract
- Respiratory tract
What is situs inversus and what causes it?
- Heart is on right side
- Caused by immotile cilia, no associated morbidity
(Action of ciliated cells on primitive node pushes cell signalling molecules to left)
When does gastrulation occur, how and why?
- Occurs in third week of development, start of embryonic period
- How? Primitive streak forms –> migration & invagination of epiblast cells
- Why? Ensure correct placement of tissues to allow for morphogenesis
What are somites and what forms them?
- Paraxial mesoderm (forms somatic [limbs,muscle] & splanchnic [heart muscles] mesoderm)
Extra: coelom form body cavities (mesoderm) - Somites are regular blocks of mesoderm cells
- Undergo organised degeneration (somite –> sclerotome –> dermatome & myotome)
What are derivatives of dermatome, sclerotome and myotome?
- Dermatome: Skin
- Sclerotome: (hard tissue) bone
- Myotome: muscle
How many somites are there? What do they give rise to?
- 31
- Form ribs, vertebrae, spinal cord segments
What does folding achieve?
- Creates margins of the disk (endo inside, ecto outside)
- Creates ventral body wall
- Makes embryo suspended in amniotic sac
