Lecture 29 - Prenatal Development Flashcards
Define -Embrynology
Embryology: the study of developmental events during the prenatal period
When is the prenatal period?
Prenatal period = conception -> delivery
What are the 3 stages of prenatal development?
Overview
1) Pre-embryonic development
- fertilization to 2 weeks
- ends after implantation
- cleavage
- “pre-embryo”
2) Embryonic development
- week 3-8
- organogenesis
- “embryo”
3) Fetal development
- week 9 - delivery
- “fetus”
After 1 week egg =
pre embryo
after 4 weeks egg =
embryo
after 9 weeks egg =
fetus
Define - Fertilization
Fertilization: sperm fusing with egg to produce a zygote
What is the first cell of a new indiv called?
zygote = first cell of a new indiv
How long does fertilization take?
Takes 30 minutes - 2 hours from penis to ampulla
then the sperm has to hang out for 6-8 hours waiting for capacitation to occur
Define - Capacitation
Capacitation: transition of sperm cap from tough membrane to weak and fragile membrane bc secretions of enzymes from the female genital tract
- only capacitated sperm are fertile
only ____ sperm are fertile
only capacitated sperm are fertile
What are the layers of cells surrounding the egg that must be penetrated by the sperm
1) corona radiata = cells surrounding the secondary oocyte
2) Zona pellucida = glycoproteins
What happens after capacitation
after capacitation acrosomal reactions occur
Define - Acrosomal reaction
Acrosomal reaction : dozens of sperm rupture releasing enzymes from their head
What is the function of the enzymes released from the acrosomal reaction?
Enzymes from the acrosomal reaction breakdown the material that holds together the cells of the corona radiate then digest a hole thru the zona pellucida
What is the end result of the acrosomal reaction
As a result of the acrosomal reaction the surface of the egg is exposed to 1 sperm which will make contact with the egg
What triggers the egg to be “activated” and what does that mean?
The process of membrane fusion triggers the egg to become “activated”
Activation causes changes to the egg membrane which prevent fertilization by another sperm
Where in the egg do the sperm wait while it unpacks its chromosomes
the sperm waits in the peripheral cytoplasm of the egg while it unpacks its chromosomes
Describe the end part of fertilization when the chromosomes meet
1) The egg nucleus and sperm nucleus swell and form a female and male pronuclei which will start to approach each other while the mitotic spindle forms btwn them
2) Then the pronuclei membrane ruptures releasing the chromosomes into the vicinity of the spindles
3) The moment of fertilization occurs when the maternal chromosomes combine to form a diploid zygote with 46 chromosomes
Define - clevage
Cleavage: period of cell division of the zygote
- division of the zygote into blastomeres
What is a pre-embryo
2 identical blastomeres
How long after fertilization does the first cleavage occur
30 hours after fertilization the first cleavage occurs producing 2 identical blastomeres = pre-embryos
What is the thing called 72 hours after cleavage
how many cells
when/where
72 hours = morula
16 cells
The morula reaches the uterus on the 4th day after fertilization. goes into lumen of uterus
A fluid penetrates the zona pellucida what/from where
A fluid penetrates the zona pellucida which rearranges the blastomere around a fluid filled central cavity
Fluid = uterine milk,
- secreted by glands of the endometrium
What is the result of the fluid penetrating the zona pellucida
Bc the milk penetrates the zona pellucida, it causes the layers of glycoprotein to breakdown and then the ball of cells inside can escape = Blastocyst
Blastocyst
When:
Where:
What:
Blastocyst
When: 5 days after fertilization
What: fluid filled hollow space composed of trophoblasts and embryoblasts
- is ready for implantation
Blastocytes are composed of trophoblasts and embryoblasts … what do they become
Trophoblasts -> form placenta
Embryoblast -> embryo
What ends pre-embryonic development?
implantation
Define - Blastocoele
Blastocoele = cavity inside blastocyst
When does implantation occur>
Implantation = 6 days after fertilization
Describe the steps of implantation
1) Trophoblast adheres to and embeds into the endometrium
2) The trophoblast cells release human gonadotropin which is the basis of a pregnancy test
3) Trophoblast divides into:
- cellular trophoblast (inner layer)
- synctiotrphoblast (outer layer)
4) Has lost membrane so can burry into the uterine walls until the blastocyst is fully barried
5) Takes 1 wee, completed 14 days after fertilization
Which hormone is used for pregnancy test
Human gonadotropin
What does the trophoblast divide into during implantatino
- cellular trophoblast = inner layer
- syncytiotrophoblast = outer layer
How long does implantation take
1 week
9 days after fertilization … is implantation complete?
No, implantation starts 6 days after fertilization and takes 1 week to complete
What happens 8 days after fertilization?
- The embryo divides into a 2 layer bilaminar disc composed of hypoblasts and epiblasts
What are the cell layers of the bilaminar disc called
hypoblasts and epiblasts
Btwn what cells layers is the amniotic cavity
The amniotic cavity is btwn the hypoblast and the epiblast
Define - Dizygotic fraternal twins
Fraternal Twins = 2 oocytes each fertilized by a diff sperm
Define - Monozygotic twins
Monozygotic = identical
When is is common for twins to form>?
2 Cell Stage
- zygote divides giving rise to 2 indiv blastocytes
- each get own amniotic cavity
Level of Inner Cell Mass - Blastocyst stage
- Most common
- common placenta, diff amniotic cavity
Level of bilaminar disc
- each form an embryo
- share amniotic cavity
When do twins share amneiotic cavity
when spit at level of the bilaminar disc
when does the bilaminar disc become a trilaminar disc
week 3
When does gastrulation occur
15 days after fertilization
Define - Gastrulation
Gastrulation: the process where the bilaminar embryonic disc, consisting of the epiblast and hypoblast is transformed into a trilaminar embryonic disc consisting of 3 layers:
- ectoderm
- mesoderm
- endoderm
Begins the formation of the primitive streak
What are the 3 layers of the trilaminar embryonic disc formed from primitive streak?
- ectoderm
- mesoderm
- endoderm
Define - Primitive streak
Primitive streak = narrow midline groove on the surface of the epiblast
What happens immediately following the formation of the primitive streak
As soo as the streak forms:
- some epiblast cells on either side of the streak migrate to the middle where they invaginate into the primitive streak and slide down the epiblast layer displacing the original hypoblast forming a mesoblast
What happens on day 16-18
Day 16-18
- cells combine and form the notochord which is the basis of the axial skeleton
Define - notochord
Notochord: axis around which the vertebral column forms
What happens in week 3-8
embryonic folding
What causes malformations in babies
tetragens
What are the derivatives of the ectoderm germ layer (9)
= forms structures that maintain contact with the external environment
- NS
- Epithelium of ear, nose, eye
- epidermis of skin
- epidermal derivatives (hair, nails, sweat glands, mammary glands)
- enamel of teeth
- pituitary gland
- lens of eye
- adrenal medulla
What are the derivatives of the mesoderm? (9)
-> forms supporting tissues
- ct including cartilage and bone
- muscle (striated and smooth)
- subcutaneous tissue of skin
- blood and bv
- kidney and ureters
- gonads and their ducts
- spleen
- adrenal cortex
- heart
-> medial mesoderm segments into somites which give rise to:
- skull
- vertebral column
- skeletal muscle
- dermis of skin
What are the derivatives of the endodermal germ layer?
-> Forms the epithelial lining of:
- GI tract
- Respiratory tract
- Bladder
- Middle Ear
-> Forms parenchyma of:
- liver
- pancreas
- thyroid
- parathyroid
- thymus
- tonsils
When is the fetal period?
Week 9 - birth
By which week are all adult organs formed?
By week 13 all adult organs are in place
What does the fetus grow to during the fetal period?
Grows form 22 mm -> 360 mm
1 g -> 2.7-4.4 kg
22 inches at birth
