Lecture 2 - Basic Embryology and Developmental Periods Flashcards
Prenatal period divided into (2)
Embryonic period - fertilization through 8 weeks
fetal period - 9 weeks until birth
Major events of week 1
fertilized oocyte (zygote) –> morula (day 3-4) –> blastocyst (4-5) –> embryo (from layer of blastocyst)
Major events of week 2
produces 2 germ layers
- trophoblast - embryoblast
Major events of week 3
produces 3 germ layers and layers fold into recognizable 3D shape
define gastrulation
production of 3 germ layers
what are the two folds that happen in week 3
lateral and cranio-caudal folds
when does organogenesis happen
weeks 4-8
_______ refers to growth in size of organs
_______ refers to rapid increase in cell number
hypertrophy
hyperplasia
mature organ function is not achieved until after birth EXCEPT for which system?
cardiovascular (heart pumps blood to developing organs, which is necessary for their development_
______ axis gives top and bottom
______ axis gives us front and back
cranial-caudal
dorsal-ventral
pathway of sperm in male reproductive system
seminiferous tubules in testes –>(epididymis) –> ductus (vas) deferens –> ejaculatory duct –> urethra (3 parts) –> out
pathway of oocyte in female reproductive system
ovary –> uterine (fallopian tubes) –> uterus
meiosis in a nutshell
SINGLE duplication of DNA followed by TWO cell divisions
what happens in first meiotic division
1 cell divides into two - goes from diploid to haploid
crossing over of genetic material happens in prophase I
what happens in second meiotic division in sperm
secondary spermatocyte (23X, 23Y) –> spermatids x 4
Three reasons why meiosis is so important
constancy of chromosome number
random assortment of genetic material and paternal chromosomes
crossing over of chromosome segments (genetic variation)
Parts of mature sperm
Head - contains nucleus and covered by acrosome
Middle piece - contains ATP for energy
Tail - single flagella for locomotion
first division of oogenesis happens when?
2 million oocytes have completed prophase I by birth
remain in prophase I until right before ovulation, during puberty the rest of the phase is completed (40,000 oocytes)
second division of oogenesis happens when?
an ovulated egg or secondary oocyte (400 oocytes) is arrested at metaphase II
metaphase II is ONLY COMPLETED IF FERTILIZED
the secondary oocyte gets released from the ovary and contains the zona pellucida and corona radiata. What are these?
zona pellucida - protective glycoprotein layer
corona radiata - follicular cells from ovary that get “stuck” to oocyte with ovulation
when do the two polar bodies arise?
first polar body - arises from unequal cytoplasm division in meiosis I
second polar body - arises once egg is fertilized, in meiosis II
female reproductive cycle is controlled by (3)
hypothalamus - GRH
pituitary gland - FSH and LH
ovaries
what does follicle-stimulating hormone do?
development of ovarian follicles and produces estrogen
what does luteinizing hormone do?
stimulates the follicular cells and corpus luteum to produce progesterone
Describe the ovarian cycle
Many primary follicles (oocyte protected by follicular cells) start growing each month
Secondary follicles - have acquired fluid filled cavities (antrums) and zona pellucida
one lucky follicle is the mature follicle that is released during ovulation - which happens within 24 hours of a surge of LH production
follicle collapses and form corpus luteum
Describe the menstrual cycle (endometrium)
Day 1-5 - Menses (functional layer of endo is sloughed off to prepare for new tissue)
Day 5-14 - Proliferative phase (tissues increases and thickens, controlled by estrogen from follicles; spiral arteries elongate)
Day 14 - Ovulation
Day 14-28 - Luteal phase (tissue increases and progesterone surges from corpus luteum; if no pregnancy, endometrium becomes ischemic due to spiral arteries contracting)
where does fertilization happen?
Ampulla of uterine tubes
Describe steps of fertilization
sperm enters through corona radiata and lyses zona pellucida (acrosome)
cell membranes of oocyte and sperm fuse
- creates a change in zona pellucida layer and
no other sperm can enter
second meiotic division of oocyte happens - female and male pronuclei formed and fuse together = ZYGOTE
