BL - Embryology Flashcards
What are the tubes called that connect the ovaries with the uterus?
Fallopian tubes
Briefly explain the process of oogenesis.
- oogonium splits into another oogonium and a primary oocyte
- primary oocyte splits into 1st polar body and secondary oocyte
- 1st polar body splits to form two more polar bodies (polar body still undergoes mitosis despite having no role)
- secondary oocyte splits to form secondary polar body and ovum
Where does fertilisation take place usually?
The ampullary region of the Fallopian tube
True or false - sperm must be introduced into the female reproductive tract within five days before ovulation?
True. Sperm are viable for five days, but secondary oocytes are only viable for 12-24 hours.
What is capacitation?
When the tail of the sperm moves faster causing the plasma membrane to alter.
Why is semen not rejected by the body?
The body only develops antigens for semen if it is exposed to the blood supply. This means that there are no antibodies for its antigens.
What is the difference between embryonic age and gestational age?
Embryonic age is time since fertilisation, while gestational age is time since last menstruation.
What is the “germinal stage”?
Time from fertilisation to the end of the second week.
What is the “embryonic period”?
Time from third week to end of eighth week
What is the “foetal period”?
Beginning of ninth week to birth at 38 weeks.
What is the zona pellucida?
A ‘shell’ that surrounds the egg, preventing it from adhering to the oviduct. It must be lost before the blastocyst can implant.
What does the fertilised egg form when it reaches the 16-celled stage?
A morula
What forms after the morula?
Blastocyst
Where does implantation usually occur?
The posterior wall of the upper part of the body of the uterus.
What is an ectopic pregnancy?
This occurs when the blastocyst implants in the wrong place, eg the fallopian tube.
What is placenta praevia?
This occurs when the placenta forms very close to (or even occluding) the vaginal opening.
Why is the second week of development known as the “week of twos”?
- the trophoblast differentiates into two layers
- the embryoblast forms two layers
- the hypoblast contributes to the formation of two cavities
During which stage of development is the foetus at greatest risk of congenital malformation due to environmental exposure?
The embryonic period
What appears in the dorsal surface of the epiblast at three weeks?
The primitive streak
What are the two layers of the “bilaminar disk”?
- epiblast
- hypoblast
What are the three layers of the “trilaminar disk”?
- ectoderm
- mesoderm
- endoderm
What do the two holes in the mesoderm go on to form?
The mouth and anus
What does the ectoderm form?
Organs and structures that maintain contact with outside world, eg nervous system, epidermis
What does the mesoderm go on to form?
Supporting tissues, eg muscle, cartilage, bone
What does the endoderm go on to form?
Internal structures eg epithelial lining of GI tract
What is situs inversus?
Complete mirror image viscera
How does the embryonic disk signal which side is left and which is right?
Action of ciliated cells at the node results in left-ward flow of signalling molecules. This causes side-specific signalling cascades to be initiated.
What is gastrulation?
The process of the bilaminar disk being converted to a trilaminar disk. Occurs in third week of development.
What is the notochord?
A solid rod of cells that runs down the midline, which directs conversion of overlying ectoderm to neurectoderm (beginning of central nervous system).
How does the ectoderm over the notochord form the neural tube?
- notochord signals cause overlying ectoderm to thicken
- neural plate edges elevate out of the plane of the disk and curl towards each other
- this creates neural tube
What are the four different sections of the mesoderm?
Paraxial, intermediate, somatic, splanchnic
What are somites?
Organisation of the parasail mesoderm into segments. The first pair appear at day 20 in the occipital region. There will be 31 in total
How do somites form myoterm?
- somites appear as regular block of mesoderm cells around small cavity
- followed by organised degeneration where ventral wall of somite breaks down and forms sclerotome
- organisation of dorsal portion forms combined dermomyotome
- myotome proliferates and migrates, dermatome disperses
What are the three somite derivatives?
- DERMATOME (“skin section”, dermis)
- MYOTOME (“muscle section”, muscles)
- SCLEROTOME (“hard tissue section”, bones)
What are the functions of segmentation?
- Organisation of mesoderm into somites forms repeating structures:
Vertebrae, ribs, intercostal muscles, spinal cord segments - It also guides innervation
What is achieved by folding of the trilaminar disk?
- creates a ventral body wall
- pulls amniotic membrane around the disk (leading to embryo being suspended within amniotic sac)
- pulls connecting stalk ventrally
