Embryology Flashcards
When is meiosis II of oogenesis complete?
On fertilisation
Where does fertilisation usually occur?
In the ampullary region of the Fallopian tube
How long are sperm viable for?
Five days
True or false: sperm are initially incapable of fertilisation
TRUE
What do sperm require to become capable of fertilisation?
Capacitation-tail of sperm moves faster, causing plasma membrane to alter
Define embryonic age
Time since fertilisation
Define gestational age
Time since last menstruation, so embryonic age plus 2 weeks
What is the germinal stage?
Time from fertilisation to the end of the second week
What is the embryonic period?
Time from third to end of eighth week
What is the foetal period?
Time from beginning of ninth week to birth at 38 weeks (gestational age)
Complete the sentences:
Before the blastocyst can implant, it has to lose the _____ _________. This is thought to prevent the morula/blastocyst adhering to the oviduct. The process of losing this structure is called __________.
Zona pellucida
Hatching
What does the zona pellucida stop?
Morula enlarging
What does the trophoblast become?
Yolk sac and placenta
What is the difference between histiotrophic and haemotrophic nutrition?
Histiotrophic-nutrition provided to embryo not from maternal blood, important up to 12th week
Haemotrophic-nutrition provided by mother’s blood, important from 12th week on
What is the normal site of implantation?
Upper part of the body of uterus, most often on the posterior wall
What is an ectopic pregnancy?
Embryo attaches outside uterus (eg ovaries, in Fallopian tube, interstitial, abdomen etc)
What is a syncytiotrophoblast?
Epithelial covering of embryonic placental villi which invades wall of uterus for nutrient circulation between embryo and mother
What is a cytotrophoblast?
Inner layer of trophoblast
How does the yolk sac deliver nutrient to the developing embryo?
Attaches outside the embryo and delivers via primitive aorta
Which layers does the trophoblast differentiate into in the second week?
1) cytotrophoblast
2) syncytiotrophoblast
Which two layers does the embryoblast form in the second week?
1) epiblast
2) hypoblast
Which two cavities does the hypoblast contribute to in the second week?
1) yolk sac
2) chorionic cavity
What is a conceptus?
Product of conception but unsure whether it is an embryo or foetus
True or false: the embryonic period is when all the major structures and systems are formed
TRUE
Give examples of teratogenic agents which interfere with development
Thalidomide
Rubella
Warfarin
What are the key events and processes in early development? (5)
1) fertilisation and implantation
2) gastrulation
3) neurulation
4) segmentation
5) folding
What is gastrulation?
Bilaminar disk is converted to trilaminar disk with three germ layers
Which layers make up the bilaminar embryonic disk?
Epiblast
Hypoblast
Which layers make up the trilaminar disk?
Ectoderm
Mesoderm
Endoderm
What does the ectoderm develop into?
Organs and structures that maintain contact with the outside world eg nervous system and epidermis
What does the mesoderm develop into?
Supporting tissues eg muscle, cartilage, bone, vascular system
What does the endoderm develop into?
Internal structures eg epithelial lining of GI tract, respiratory tract, parenchyma of glands
What is situs inversus?
Complete mirror-image viscera, commonly resulting from immotile cilia
How many lobes does the left lung have?
Two
How many lobes does the right lung have?
Three
What marks the start of the embryonic period?
Gastrulation
How does gastrulation occur?
Primitive streak forms in the caudal epiblast, leading to migration and invagination of epiblast cells
Why does gastrulation occur?
To ensure the correct placement of precursor tissues to allow subsequent morphogenetic to take place
What is the notochord?
Structure that runs down the midline
By which process does CNS development begin?
Neurulation
What is the role of the notochord in neurulation?
Important signalling role-signals overlying ectoderm to thicken and directs its conversion to neurectoderm
What are somites?
Organisation of paraxial mesoderm into body segments
Where and when do the first pair of somites appear?
At day 20 in the occipital region (skull)
How many somites are left in total at the end?
31
What forms when the ventral wall of the somites breaks down?
Sclerotome
What forms when the dorsal portion of the somites is organised?
Dermomyotome
What are the somite derivatives? (3)
1) dermatome
2) myotome
3) sclerotome
True or false: organisation of mesoderm into somites gives rise to non-repeating structures
FALSE - repeating structures such as vertebrae, ribs, intercostal muscles and spinal cord segments
What is cephalocaudal folding driven by?
Growth of neural tube
What is lateral folding driven by?
Growth of somites
What does folding achieve? (3)
1) Draws together the margins of the disk, creating a ventral body wall.
2) Pulls amniotic membrane around the disk so that the embryo is suspended within the amniotic sac
3) Pulls connecting stalk centrally
What occurs at the end of the fourth week of development?
Nervous system started to form
Segments appeared
Embryo folded
