Embryology Flashcards
Where does fertilisation normally occur?
Ampullary region of the fallopian tube
What surrounds the ovum?
A layer of cells called the corona radiata
What is the zone pellucida?
the thick transparent membrane surrounding a mammalian ovum before implantation
What lies between the corona radiata and the ovum?
The zone pellucida
What are the male and female nuclei called called just before they fuse within the ovum?
Pronuclei
What is embryonic age?
The time since fertilisation
What is gestational age?
The time since the last menstruation
So embryonic age plus 2 weeks
What is the Germinal stage of a pregnancy called?
The time from fertilisation to the end of the second week
What is the embryonic period of pregnancy?
The time from the the third to the end of the 8th week
What is the foetal period of pregnancy?
The time from the beginning of the ninth week to to birth at 38 weeks (38-embryonic age/40-gestational age)
What happens at the point of fertilisation and what type of zygote is formed as a result?
Immediate mitosis produces a 2 cell zygote
When does implantation of the blastocysts occur?
Day 6
After fertilisation the zygote begins to divide, what restricts the size of the ball of cells?
The zone pellucida
What is a morula?
a solid ball of cells resulting from division of a fertilized ovum
Within the zona pellucida the morula develops into two cell masses, what are these called?
Inner and outer cell mass
What does the outer cell mass become?
The trophoblast
What does the trophoblast become during the later stages of pregnancy?
The placenta and yolk sac
Where does normal implantation occur?
Superior posterior wall of uterus
What happens if the zygote implants in an abnormal site within the woman’s reproductive organ?
An ectopic pregnancy
During which period of pregnancy is there the most change?
The embryonic period (weeks 3-8)
What stgage of pregnancy is at the greatest risk o major congenital malformation and why?
The embryonic period because it is very sensitive to teratogenic agents and it is the stage where all major structures and systems are formed
What are the 4 main events/processes occurring in early development of a foetus following fertilisation and implantation?
Gastrulation
Neurulation
Segmentation
Folding
What appears on the epiblast in the third week of development and where exactly is this?
The primitive streak, pit and node appear on the dorsal surface of the epiblast
What forms the bilaminar disk in gastrulation?
Epiblast and hypoblast
How does the the bilaminar disc become the trilaminar disc?
The cells in the epiblast migrate and invaginate to form a mesoderm
What are the layers of the trilaminar disc in gastrulation?
Ectoderm, mesoderm, endoderm
Why are there two points at which there is no mesoderm?
So the endoderm and ectoderm are touching,
These points will become the future mouth and future anus
List some structures that will arise form the ectoderm (2)
Organs and structures that maintain contact with outside world:
Nervous system
Epidermis
List some structures that will arise from the mesoderm (4)
Supporting tissues: Muscle Bone Cartilage Vascular system (including heart and vessels)
List some structures that will arise from the endoderm (3)
Internal structures:
Epithelial lining of GI tract
Respiratory tract
Parenchyma of glands
What is situs inversus?
When someone has complete mirror image viscera
What can situs inversus commonly result from?
Immotile cilia
When might situs inversus be an issue?
If there is a mixture of both normal and mirror image dispositions
Prior to gastrulation what state is the embryonic disk in?
Bilaterally symmetrical
What type of cells can you find at the node on the trilaminar disk?
Ciliated cells
What do the ciliates cells present on the node of the trilaminar disk cause?
Leftward movement of signalling molecules which causes a sight specific signalling cascade
How would cells migrate toward the left and right side of the trilaminar disk through the action of the ciliated cells on the node?
Move to left=The cilia would be leftward
Move to right= absence of any cilia movement, meaning signalling molecules aren’t moved
Gastrulation marks the start of which period of pregnancy?
Embryonic period (3-8 weeks)
Name a key structure that appears as a result of gastrulation
The notochord (runs straight down the mid line of the embryonic disk)
What is neurolation?
The process by which we begin the develop the nervous system
What is the notochord? (In terms of structure?)
A solid chord of cells that lies in the mesoderm
What do the cells in the notochord do?
Release signalling molecules which directs conversion of overlying ectoderm to neurectoderm
How does ectoderm become neurectoderm? (3)
Ectoderm thickens
Slipper shaped neural plate is formed
Edges of the plate elevate up and curl towards each other creating the neural tube
During neurolation in pregnancy, what 4 types does the mesoderm differentiate into and where are the types found?
Paraxial mesoderm - next to the neural tube (next to the axial)
Intermediate mesoderm- lateral to the paraxial mesoderm
Somatic mesoderm- a fork of mesoderm just below the ectoderm (lateral to the intermediate mesoderm)
Splanchnic mesoderm- a fork of mesoderm just above the endoderm (lateral to the intermediate mesoderm)
What is the space created between the somatic and splanchnic mesoderm called?
Intraembryonic coelom
What does the paraxial mesoderm become?
Somites- body segments
Where do the 1st somites appear?
1st pair appear at day 20 in the occipital region
By the end of week 5 how many somites are there?
42-44 pairs
Which will eventually become 31 pairs
What doe somites give us?
The building blocks of the musculoskeletal system
How do somites initially appear? Structure.
As regular blocks of mesoderm cells arranged around a small cavity
What do the cells in somites undergo in order to become precursor cells?
‘Organised degeneration’
What the mesoderm undergoes ‘organised degeneration’ what are the two categories of cells formed?
Dermomyotome and sclerotome
What is sclerotome?
Precursor of bone
The dermomyotome (mesoderm cells in the somites of a developing embryo) separate into two groups. Name the groups and what they are precursors of
Dermatome- precursor for dermis
Myotome- precursor of skeletal muscle
What are two reasons for segmentation of the body during development?
Guides innervation
Gives rise to repeating structures (ie ribs/vertebrae)
What is the area of the mesoderm in the trilaminar disc that gives rise to the future heart and where would you find it?
Cardiogenic area- found right at the cranial end of the embryonic disc (even above the mouth!)
During development the embryonic disc needs to be folded in order to put structures in their correct place (the heart for example). In simple terms how is this achieved?
The formation of the neural tube causes folding at the head and tail end of the embryonic disc
And the formation of somites caused folding of the lateral edges
What is the head and tail folding of the embryonic disc called and why does it occur?
Cephalocaudal folding
Caused by the formation of the neural tube
What is the folding of the lateral edges of the embryonic disc called?
Lateral folding
What does folding of the embryonic disc achieve? (3)
Creates a ventral body wall
Pulls amniotic sac around embryo
Ensures structures are in the correct place
What is the lining of the uterus called?
Endometrium
What layer of the embryonic disc gives rise to the cardiac tissue?
Splanchnic mesoderm
