Embryology Flashcards
How long is in utero human development?
9 months (38-40 weeks)
What are weeks 0-3 called in human gestation?
conceptus/embryo
What are weeks 3-8 called in human gestation?
Embryonic period
What are weeks 9-40 called in human gestation?
fetal period
How many stages of embryogenesis are there?
6 (gametogenesis, fertilisation, cleavage, gastrulation, formation of a body plan and organogenesis)
What is the chromosome complement of a gamete?
23 chromosomes ( half of a typical somatic cell)
What are the two stages of gametogenesis?
Mitosis and meiosis
What does mitosis and meiosis lead to?
genetic variation
When does spermatogenesis occur?
At puberty and continues throughout life
How long does each cycle of spermatogenesis take?
around 64 days
What is the average production rate of sperm?
6.5 million sperm per gram of testicular tissue per day (decreases with age)
What is the outcome of spermatogenesis on the chromosomes in sperm ?
either 22 + X (will create female) or 22 + Y (will create male)
When does oogenesis start and end?
Starts in development and ends at menopause
When do primary oocytes begin meiosis?
week 28-30 but it is arrested in prophase until puberty
When is reproductive life span determined in females?
In foetal life ie dependent on number of ova produced during foetal development
What causes Trisomy 21 (Down Syndrome)?
An additional copy of chromosome 21 caused by non disjunction
What is fertilisation?
The fusion of a sperm and an oocyte
What does fertilisation produce?
A diploid zygote (single cell embryo)
What are the 2 options of sex determination in zygotes?
46 XX or 46 XY
What is cleavage?
A period of rapid mitotic cell division with no increase in size
What does cleavage form?
A morula (16+) cells then a blastocyst (days 1-4)
What is gastrulation?
The formation of the germ layers which establishes body axes
When does gastrulation happen?
Week 3
What are the 3 germ layers?
Ectoderm, Mesoderm and Endoderm
What is the formation of the body plan?
Embryonic folding (gut tube within a skin/body wall/tube)
What in organogenesis?
the formation of organs and organ systems
When is the basis of all organs/their systems in place by?
The end of the embryonic period but continues throughout the foetal period
What trimester does the foetus lengthen most?
2nd
What trimester is the most weight gained?
3rd
What are the main events that occur during the foetal period?
Tissues mature and become functional, overt sexual differentiation and bone laid down, connections in the central nervous system
What are some of the primary processes involved in development from zygote to human?
cell division, differentiation, cell attachment (eg tissue formation), apoptosis, induction (ability of one cell type to cause another to differentiate) and cell migration
What are some of the secondary processes involved in development from zygote to human?
axis formation/polarity (so cells know where they are in relation to one another and the whole embryo) and folding/rotation
What are the 2 types of control of development?
genetic control (gene expression) and epigenetic control
What is epigenetic control?
the preferential expression of either the maternal or the paternal copy of the gene
In humans, what does the sperm first bind to during fertilisation?
The zona pellucida glycoprotein (ZP3) - which tells cells to release calcium
What type of enzymes are released from the sperm head?
Acrosomal enzymes
