Embryo Pt.1 Flashcards
What can human development be divided into?
Two periods/main stages:
- Prenatal development
- Postnatal development
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What does the postnatal development period include?
Commences at birth and continues to maturity, the state of full development or
completed growth.
What can the prenatal development period be divided into?
The prenatal period contains a number of sub periods:
- Germinal stage
- Embryonic period
- Fetal period
When is the germinal stage of development?
The first two weeks (including fertilization) are termed germinal stage
When is the embryonic stage of development?
Starts at the 3rd week until the end of the 8th week
What is a human termed at the embryonic stage?
Embryo
What is a human termed at the fetal stage?
Fetus
When is the fetal stage of development?
Starts from the beginning of the 9th week to birth
How long is the germinal stage of development?
Two weeks
How long is the embryonic stage of development?
8 weeks (if you include germinal stage in it which can be done?)
How long is the fetal stage of development?
30 weeks
What is a fertilized human egg known as?
Zygote
When does the germinal stage start and end?
Begins with fertilisation and ends with implantation in the uterus
Which major events occur in the germinal stage include?
Fertilisation, cleavage, blastulation, and implantation
Describe briefly what is the result of the embryonic stage?
- By the end of the embryonic stage, most of the organs have started to form and continue to develop, mature and differentiate during the fetal stage
- By the 8th week the embryo shows all basic organs except for sex organs.
What can the fetal stage be divided into?
It can be divided into 3 different periods for simplicity:
- 9-15 weeks
- 16-26 weeks
- 27-38 weeks
What are the most notable events that occur from weeks 9-15?
- Reproduction organs develop rapidly
- Maturation of thyroid gland and hormone production
- Urinary system develops
- Kidney starts to function
- Facial development
- Appearance of lanugo
What is lanugo?
Soft fine colourless (unpigmented) hair on the foetus, especially the face
What are the most notable events that occur from weeks 16-26?
- Embryo develops sensory responses to touch. The first sensory receptor develops…
- Face and eye continues to develop
- Alveoli formation in the lung
- Muscle development
- Intestine development for preliminary ability to absorb small molecules like sugars from amniotic fluid.
What are the most notable events that occur from weeks 27-38?
- Appearing of hair
- Diaphragm movement
- Pupil reaction to light, if you give stimuli to the embryo with some light you can see a reaction
What can the embryonic stage be divided into?
23 Carnegie stages
What do carnegie stages take into consideration?
The development of the embryo is described only in the sense of the morphological changes, we are not talking about the age (not dependent on the chronological stages of the embryo) or the size but only the morphological features
What does each week of the embryonic stage correspond to in terms of carnegie stage?
- Week 1: 1,2,3,4
- Week 2: 5,6
- Week 3: 7,8,9
- Week 4: 10,11,12,13
- Week 5: 14,15
- Week 6: 16,17
- Week 7: 18,19
- Week 8: 20,21,22,23
What are the main stages of the embryonic stage?
Morula, blastula, gastrula and organogenesis
When does carnegie stage 1 start and end?
Stage 1 starts at the beginning of fertilization, when an oocyte is penetrated by a sperm, and ends with the intermingling of the paternal (male) and maternal (female) chromosomes on the spindle at metaphase of the first mitotic division of the single cell
How long is carnegie stage 1?
Requires just over 24 hours to complete
What can carnegie stage 1 be divided into?
Three substages; a, b and c
What is carnegie stage 1a also known as?
Primordial embryo or the “penetrated oocyte”
What is carnegie stage 1b also known as?
Pronuclear embryo or ootid
What is carnegie stage 1c also known as?
Syngamic embryo’ or zygote
What are the characteristic signs of carnegie stage 1?
They include:
- Fertilized oocyte
- Polar bodies
- Male and female pronucleus
- Formation of the zygote
What are the characteristic signs of carnegie stage 2?
They include:
- Formation of the blastomeres
- Separation of blastomeres
- Morula stage (12-16 cells)
- Compaction (8-16 cells)
- The polarization of the blastomere becomes slowly visible
What are the characteristic signs of carnegie stage 3?
- Blastocyst formed (16-32 cells)
- Segmentation into inner (embryoblast) and outer cell mass (trophoblast)
- Embryonic and abembryonic poles
When does carnegie stage 2 occur?
On approximately the 2nd to 3rd day
When does carnegie stage 3 occur?
On approximately the 3rd to 4th day
What are the characteristic signs of carnegie stage 4?
- Free blastocyst
- Hatching of the blastocyst through degeneration of the zona pellucida
- Epiblast and hypoblast are formed (from embryoblast) and thereby the didermic embryonic disk
