Human embryonic development Flashcards
(42 cards)
Describe what happens in first week of human embryonic development (fertilisation and pre-implantation).
Day 0: Oocyte is released from the ovary in the female reproductive tract and passes down the fallopian tubes.
Day 1-4:When fertilisation occurs -> sperm penetrates ovum, and first cleavage stage occurs in the oviduct.
Early embryo has egg cell uncompacted morula.
Day 5: Formation of blastocyst -> which develops when there’s cavity inside embryo. Group of cells located on one side (inner cell mass), a group of cells around the outside (trophoblast or trophoectoderm).
Day 6-7: Embryo hatches or emerges from zona pelucida (glycoprotsin coat) that surrounds embryo and then impants into the wall of uterus into the endometrium.
What happens in the weeks 1-3 (cleavage, implantation and gastrulation) stage?
Day 1 (Fertilisation): Male and female pronucleus meet.
Day 2 (Cleavage): Rapid cell division generates tight ball of cells during compaction.
Day 3 (Compaction: morula): Embryo as morula (solid ball of cells)
Day 4-5 (Blastocyst formation): Cavity appears in embryo (called blastocyst). Blastocyst has outer trophoblast and inner cell mass. Inner cell mass gives rise to entire embryo and embryonic stem cells. Trophoblast gives rise to embryonic portion of placenta.
Day 6 (Hatching): Hatching from zona pellucida from coat that surrounds early embryo.
Day 7 (Implantation): Implants into wall of uterus, into uterine epithelium shown here.
Then:
- Inner cell mass resolves into two cell groups; Upper epiblast, lower hypoblast, and trophoblast. Embryo forms from inner cell mass, trophoblast forms embryonic component of placenta.
- Hypoblast forms primitive yolk sac.
Day 8-12 (Bilaminar disc): Two layers; epiblast and hypoblast.
Day 12 (Gastrulation): Formation of 3 germ layers:
- Epiblast cell migrate through primitive streak, Displace hypoblast to form endoderm. - Second wave of cells migrate through primitive streak of epiblast to form mesoderm.
Day 18 (Mesoderm spreading): Mesoderm spreads out around embryo and contributes to chorion. Embryo has three tri-layers: - Epiblast -> ectoderm - Mesoderm - Endoderm
What specific body parts do the three germ layers form?
Ectoderm: brain, nervous system, epidermis
Mesoderm: muscles, bones, heart and blood vessels urogenital system
Endoderm: lining of gut, liver, pancreas
What is a pregnancy test? What hormone does the test rely on? How is it detected?
A biochemical test to determine if a woman is pregnant.
Modern tests rely upon the hormone, human chorionic gonadotrophin (hCG) secreted by placenta after embryo implantation and detectable in maternal blood and urine.
hCG cannot be detected until after implantation (day 7-8).
What happens in ectopic pregnancy:?
Embryo implants outside uterus. Rather than implanting into accommodating wall of uterus, it will implants in wall of fallopian tubes -> this causes bleeding and tubal miscarriage.
Also, early embryo can dislodge from fallopian tube. And be embedded somewhere else (e.g. gastrointestinal tract) -> failed pregnancy.
What is a hydatidiform mole?
Inner cells mass resolves into bilaminar disc, upper epiblast, and lower hypoblast.
Epiblast gives rise to embryo proper, but if that fails due to congenital malformation -> trophoblast can proliferate alone and not embryo.
Why does a pregnancy test show normal results despite of hydatidiform mole?
The trophoblast cells will secrete human chorionic gonadotropin (hCG), as in a normal pregnancy, and may appear maternally and by pregnancy test to be “normal”. Prenatal diagnosis by ultrasound analysis demonstrates the absence of a embryo.
What are the symptoms of Hydatiform mole?
Abnormal growth, vaginal bleeding, 80% are benign and are removed.
What is neurulation and neural tube?
Neurulation: formation of the neural tube (future brain and spinal cord)
Neural tube is specialised ectoderm on dorsal embryo surface
How does the groove of neural tube fold?
Induced by growth factors, or inductive signals from underlying notochord
What is the general process of neurulation?
1) . Groove invaginates -> tube folds, neural folds on either side.
2) . Notochord releases inductive signals -> induces invagination.
3) . Cells of neural crest border (neural crest cells) pinch off and migrate away.
When do neural tube defects occur:
Occurs early in pregnancy (first trimester).
What are some examples of neural tube defects?
Anencephaly: the cephalic part of neural tube fails to close, leading to absence of a major portion of the brain (babies can be born, but are deaf, blind, unconscious).
Spina bifida: incomplete closure of posterior neural tube: varies in severity : vertebrae remain open, part of spinal cord is exposed : causes neural disability : risk greatly reduced by folic acid supplementation before conception : familial or sporadic.
Sporadic = The sporadic form of the disease can affect anyone and is dependent on genetic changes acquired during the lifetime of the affected individual.
What are neural crest cells?
A population of cells derived from junction of neural plate and epidermis.
What is the process in which neural crest cells migrate?
- Neural plate folds and closes to form neural tube.
- Cells at this border junction will bud off and migrate away because they’re going from epithelian to mesenchyme transition.
What do neural cress cells contribute to?
Melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral & enteric neurons.
What are some derivatives of neural crest cells?
Neural crest cells give rise to craniofacial region (cartilage and bone), odontoblasts (dentine of teeth), melanocytes (pigment cells), parts of the heart, branchial arch derivatives (throat), parts of peripheral nervous system.
Check slide to see what cranial…. Neural crest cells give rise to.
What is the first organ to function in an embryo?
Heart
Briefly describe the formation of the heart during organogenesis (weeks 3-4)?
- Heart tubes fuse in midline to form early heart tube
- Heart fold upon itself to form 4 chambers of heart.
- Heart begins to beat at day 22-23.
What are two broad types of abnormalities in embryonic development?
- Genetic (inherited or de novo (from new; weren’t present in mother or father)
- environmental (effects of teratogens - toxins, these modify development.)
What are the three broad types of genetic defects that cause embryonic and postnatal abnormalities
- Single gene defects (about 4000 known diseases)
- Alterations in larger chromosomal segments (Multiple genes)
- Chromosomal defects (large scale; loss or gain of DNA)
Is single gene disorder (e.g. Duchenne muscular dystrophy) X-linked dominant or recessive? What is it caused by? What are the symptoms?
- X-linked recessive.
- Caused by a loss of function mutation of dystrophin gene, that encodes key structural component of muscle tissue.
- Results in muscle degeneration, difficulty walking ,breathing, death
What is Dystrophin?
Dystrophin is a rod-shaped protein that connects cytoskeleton of muscle fibre cell to surrounding ECM
What type of test is used to confirm if child has Duchenne muscular dystrophy or not?
Prenatal tests can tell whether their unborn child has the most common mutations. (only works if mutation known in family).
