Embryology: Overview and Terminology Flashcards
Where does spermatogenesis occur?
in the seminiferous epithelium of the testis
Where does oogenesis occur?
in the cortex of the ovary
What is meiosis I called?
The reductional division (takes weeks)
What is the longest phase of meiosis 1 and why?
Prophase 1, where crossing over occurs (exchange of genetic material between homologous chromatids). Each homologous chromatid becomes unique. This phase can last weeks
What happens after completion of prophase 1?
Completion of meiosis 1 is rapid, the chromatids do not separate but rather one homolog of each chromosome goes into each of the daughter cells
What is meiosis II called?
The equatorial division (happens rapidly, in hours)
What happens in meiosis II?
chromatids separate from the centromeres like in mitosis. One chromatid in each daughter cell. Daughter cells are haploid
Is a germ cell haploid or diploid?
diploid - it is the precursor to spermatogenesis or oogenesis
what are the two functions of the testes?
- Spermatogenesis
2. Steroidogenesis - Leydig cells (testosterone)
Where are sperm stored?
Ductus (vas) deferens
What is a quiescent primordial follicle?
Structures containing oocytes arrested in meiosis 1. Every month, 10-20 are stimulated to develop, but only one reaches full maturity.
What does an ovarian follicle contain?
- Oocyte - developing gamete
- Granulosa and theca internal cells - Steroid-secreting cells which mainly produce estrogen during follicle development.
During ovulation, what stage of meiosis is the mature egg in?
Metaphase II - does not resume meiosis until fertilization
What is the myometrium?
The thick layer of smooth muscle around the uterus. Contraction is prevented during pregnancy by progesterone levels
What does estrogen cause in the uterine cycle?
High estrogen levels cause the endometrium of the uterus to rebuild and prepare itself for possible implantation (proliferation)
What is the function of the corpus luteum?
Maintains the endometrium during the secretory phase by releasing progesterone. If fertilization does not occur, it degenerates, blood progesterone falls, and the endometrium is sloughed off (menses)
What is the function of hCG?
Produced by the embryo, it maintains the corpus luteum so it continues to produce progesterone
What is the menstrual phase of the uterine cycle?
Corpus luteum degenerates in the ovary, blood progesterone and estrogen levels drop. The endometrium degenerates and is sloughed off
What is the proliferative / follicular phase?
Follicles develop in the ovary, blood estrogen rises, endometrium is rebuilt
What is the secretory / luteal phase?
Corpus luteum is present in the ovary, blood progesterone levels are high. Endometrium of uterus prepares for implantation
What are the two sub-periods of embryonic development (0-8 weeks)?
0-3 weeks post fertilization - early development including cleavage and gastrulation
4-8 weeks post fertilization - embryonic organogenesis - organ primordia are established
Remember this period is where all the precursors of the organs are developed
What are the effects of teratogens in the developmental periods?
0-3 weeks: not sensitive to malformation -> spontaneous miscarriage / lethal
4-8 weeks: most susceptible, especially 4 to 6 weeks. Big congenital defects
Fetal period: 9-38 weeks. Organ systems are maturing, may cause many congenital malformations but they tend to be minor
What is the difference between fertilization age and menstrual age?
Fertilization age - dates pregancy from time of fertilization (ovulation). This is 38 weeks full term
Menstrual age - dates pregenancy from start of last menstrual period (LMP). This is 40 weeks full term
What are three ultrasound measurements to determine age of embryo or fetus?
- Gestational sac diameter - also called chorionic cavity, used when embryo is too small to see
- Crown rump length - measurement from top of head to buttock. Best in the first trimester
- Size of head or femur length in later pregnancy
