Day 13, Lecture 1 (Sept 8): Human Development 1: The first week of development Flashcards
1
Q
Gestational Age
A
- Staging of the human embryo
- Determine age based on time from last normal menstrual period
- Normal time to parturition- 40 weeks
- Staging used clinically
2
Q
Fertilization age
A
- Staging of the Human Embryo
- Determine age based on time from fertilization
- Normal time ot parturition
- 38 weeks
- Staging used in embryology and in this class
3
Q
Staging of the Human Embryo
A
- Gestational age
- Determine age based on time from last normal menstrual period
- Normal time to parturition
- 40 weeks
- Staging used clinically
- Fertilization age
- Determine age based on time from fertilization
- Normal time to parturition
- 38 weeks
- Staging used in embryology in this class
4
Q
A
5
Q
The Embryonic period
A
- Weeks 1-8
- Organogenic period
- Time most vulnerable to teratogens
6
Q
Fetal Period
A
- Weeks 9-32
- Development of organs and organ systems
- Extensive growth
- (luns developed sufficienctly at approximately 24 weeks to allow survivla of fetus with extensive critical care)
7
Q
What makes the earliest an infant can survival premature birth
A
- Development of the lungs
- lungs developed sufficiently at approximately 24 weeks to allow survival of fetus with extensive critical care
8
Q
Postnatal develpment
A
- Development continues after birth
- Respiratory system
- Alveoli form in lungs
- Cardiovascular system
- Closure of fetal shunts and vessels
- Nervous system
- Continued neuronal development
- Respiratory system
9
Q
What are the key processes that must occur for a fertilized egg to give rise to the adult
A
- Proliferation
- Growth
- Differentiation
- Pattern Formation
- Morphogenesis
10
Q
What is differentiation
A
- Process by which cells or tissues become different from one another
- Progressive acquisition of structural and biochemical specializations leading to unique or highly developed cellular functions
11
Q
There are how many different specialized cells in adult human
A
200
12
Q
Totipotent
A
- Can differentiate into all cell types
- examples
- Zygote
- Morula
- examples
13
Q
Pluripotent
A
- Differentiate into many cell types
- examples
- Inner cell mass
- Epiblast
- examples
14
Q
Multipotent
A
Differentiate into restricted group of cells
15
Q
Unipotent
A
Determined as to differentiated cell to form
16
Q
Since all cells contain the same set of genes (genomic equivalence) how can genes direct development when same in all cells?
A
- Differential Gene Activity
- Different genes are turned on and off during development leading to specific genes being expressed in the differential cell
17
Q
Does differential gene acitvity lead to irreversibly turning off of genes?
A
- No
- Think about Dolly and iPS cells
18
Q
Induced Pluripotent Stem Cells (iPS cells)
A
- Reverse differentiated cell to pluripotent state
- Express factors found in pluripotent cells
- Another demonstration of genomic equivalence
- Provide possible pluripotent stem cells to be used clinically
- Genotype same as patient if use adult cell from patient
19
Q
Regulation of Differential Gene Activity occurs at Mutliple Levels
A
- Differential gene transcription
- Transcrption factors
- Histone Methylation
- DNA Methylation
- Selective Nuclear RNA processing
- Selective messenger RNA Proccessing
- Differential Protein Modification
20
Q
Cells must acquire _______ to determine what to form and when to undergo differentiation
A
- Positional Information
21
Q
Example of differntation with loss of pattern formation
A
Teratoma
22
Q
Positional Information
A
- Receive cues from environment
- Cell-Cell interactions
- Soluble factors including growth factors and cytokines
- Extracellular matrix
- Lineage
- Restricts response to positional information
23
Q
Specification of Little Verse Great Digit
A
24
Q
A
25
Apoptosis is an example of
* Morphogenesis
26
Syndactyly is a malformation due to
* Altered Morphogenesis
* Lack of apoptosis in interdigital regions
27
28
Egg at Fertilization
29
Cleavage
* Specialized cell division whereby daughter cells divide rapidly reducing size with each division
* Partition of cytoplasm of zygote into small cells (blastomeres) without an increase in cytoplasmic mass
* Reason for cleavage
* Zygote very large (1000 micrometers) compared to normal cell (10 micrometers)
30
Morula
* 12-16 cell stage
* formed on 3rd day
31
Compaction of Morula
* compaction occurs 4 days post fertilization
* first morphogenesis in the embryo
* Formation of tight junctions between outer blastomeres
* Tight junctions allow for the partitioning of inside and outside
* Dependent on the presence of **E-cadherin** in outer layers of blastomeres
* Forms two distinct lineages
* outer and inner cells
* Blastomeres no longer totipotential
32
Blastocyste formation
* 4 day post fertilization
* Following compaction
* Forms fluid filled cavity- blastocyst cavity
* First sorting of embryonic cells into lineages
* Inner cell mass cells will form embryo
* Pluripotenital
* Trophoblast
* will form protective membranes
* Extraembryonic membrane (chorion)
33
Hatching of Blastocyst
* Weakening of Zona Pellucida
* Blastocyste squeezes out of zona pellucida
* Formation of floating blastocyst (6th day of development)
34
35
Implantation
* end of the first week of development
* Floating blastocyste makes contact with the endometrial lining of the uterus
* Trophoblast will form two distinct layers of cells
* Cytotrophoblast
* Actively dividing
* gives rise to Syncytiotrophoblast
* Syncytiotrophoblast
* nuclei don't divide
* highly envasive into endometrium allowing for implantation
* Produces matrix metalloproteinases (MMPs) to promote invasion
* (note: the most invasive carcinoma known is **choriocarcinoma** similar process of invasion used during metastasis)
* Produces protein and steroid hormones
* ex. hCG, which stops the menstrual cycle
36
Reorganization of the inner cell mass
* occurs at the end the first week of development
* Delaminates into:
* Hypoblast layer- forms extraembryonic structures
* Epiblast- Forms embryo proper
37
* Review of 1st week of Development
38
Spontaneous Abortion
* Spontaneous abortion thought to be as high as 60%
* almost all are early in pregnancy
* only about 5% are after 8 weeks of development
* Many times women don't realize they are pregnant
* Found out due to careful monitoring of early pregancy that is now possible
* about 50% is due to chromosomal abnormalities
39
Abnormal Implantation sites
* any place place other than the normal (superior part of the body of the uterus)
* most frequent normal location is in the posterior part of the superior body of the uterus
* Placentia Previa
* implantation in the lower part of the uterus
* placenta is covering the internal os of uterus
* may result in early placential
* fetus must be delivered by cesarean section
* Tubal Implantation
* is the most common ectopic site (about 98%)
* Result of delayed transport along uterine tube
* In approximately 50% of tubal pregnancies if the embryo remains will result in rupture 6-8 weeks post-ferilization. leading to potential death of mother due to internal bleeding
* Ovarian and abdominal implantation
* Relatively rare
* Risk of internal bleeding high
40
Lithopedion
* Abdominal pregnancy
* results in fetus becoming calcified if it remains in abdomen
41
Multiple pregnancy
* Natural cycle:
* Twins
* 1:90
* Triplets
* 1:902
* Quadruplets
* 1:903
* 2/3 of twins dizygotic
* 1/3 monozygotic
42
Monozygotic Twinning
* Formation of Identical Twins from splitting of Blastomeres
* Twinning occurs during cleavage
* two morulas are formed forming two embryos demonstrates
* blastomeres are totipotential
* Blastomeres can regulate
* Formation of Identical Twins from splitting of inner cell Mass
* Twinning occurs at blastocyst stage
* inner cell mass divides forming two embryos demonstrates
* inner cell mass cells are pluripotential
* inner cell mass cells can regulate
43
In Vitro Fertilization
* Can be used as an effective treatment for infertility
* Indications for IVF
* Blocked fallopian tubes or pelvic adhesions
* Male factor infertility
* Failed 2-4 cycles of ovarian stimulation with intrauterine insemination
* Unexplained infertility
* Vasectomy or tubal ligation
* Preimplantation genetic diagnosis
* In Vitro Fertilization Protocol
* Usually have 10-15 blastocysts per cycle
* Implant no more than 3 blastocysts
* Freeze remaining blastocysts for subsequent use
44
Preimplantation Genetic Diagnosis
* Screening of embryos for genetic disorders
* Perform genetic diagnosis on embryos produced by IVF
* Implant embryos not carrying genetic disorde
* Can be screened for monogenic disorders, chromosomal structural aberrations, or X-linked diseases
* Frequently screened disorders
* Cystic Fibrosis
* Beta-thalassemia
* Fragile X syndrome
* Duchenne muscular dystrophy
* Procedure
* Remove one blastomere from morula
* possible because
* blastomeres are totipotent
* morula can regenerate
* Perform genetic analysis
* Only implant blastocysts not carrying genetic disorder
