Day 13, Lecture 1 (Sept 8): Human Development 1: The first week of development Flashcards Preview

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Flashcards in Day 13, Lecture 1 (Sept 8): Human Development 1: The first week of development Deck (44)
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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
9
Q

What are the key processes that must occur for a fertilized egg to give rise to the adult

A
  1. Proliferation
  2. Growth
  3. Differentiation
  4. Pattern Formation
  5. 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
13
Q

Pluripotent

A
  • Differentiate into many cell types
    • examples
      • Inner cell mass
      • Epiblast
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
Q

Apoptosis is an example of

A
  • Morphogenesis
26
Q

Syndactyly is a malformation due to

A
  • Altered Morphogenesis
  • Lack of apoptosis in interdigital regions
27
Q
A
28
Q

Egg at Fertilization

A
29
Q

Cleavage

A
  • 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
Q

Morula

A
  • 12-16 cell stage
  • formed on 3rd day
31
Q

Compaction of Morula

A
  • 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
Q

Blastocyste formation

A
  • 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
Q

Hatching of Blastocyst

A
  • Weakening of Zona Pellucida
  • Blastocyste squeezes out of zona pellucida
    • Formation of floating blastocyst (6th day of development)
34
Q
A
35
Q

Implantation

A
  • 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
Q

Reorganization of the inner cell mass

A
  • occurs at the end the first week of development
  • Delaminates into:
    • Hypoblast layer- forms extraembryonic structures
    • Epiblast- Forms embryo proper
37
Q
  • Review of 1st week of Development
A
38
Q

Spontaneous Abortion

A
  • 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
Q

Abnormal Implantation sites

A
  • 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
Q

Lithopedion

A
  • Abdominal pregnancy
  • results in fetus becoming calcified if it remains in abdomen
41
Q

Multiple pregnancy

A
  • Natural cycle:
    • Twins
      • 1:90
    • Triplets
      • 1:902
    • Quadruplets
      • 1:903
  • ​2/3 of twins dizygotic
  • 1/3 monozygotic
42
Q

Monozygotic Twinning

A
  • 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
Q

In Vitro Fertilization

A
  • 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
Q

Preimplantation Genetic Diagnosis

A
  • 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

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