Introduction and Gametogenesis Flashcards
When do primordial germ cells first appear following fertilization?
24 days after fertilization and they are found in the endodermal layer of the yolk sac
What is the migration route of primordial germ cells into the developing gonads from the yolk sac?
Yolk sac to hind gut epithelium through dorsal mesentery into the developing gonads
What is nondisjunction
Abnormal number of chromosomes
What is the difference between aneuploidy and euploidy?
Aneuploidy is an abnormal number of chromosomes. Such as monosomy or trisomy. Euploidy is changes in number of complete sets of chromosomes.
How many oocytes are present early in embryonic development and how many present at birth and then puberty?
7 million germ cells are present midway through embryonic term. 2 million are present at birth and by puberty around 400,000 made it.
Describe stages of follicular development from primordial follicle to mature follicle and ploidy of each stage.
- In the early fetal period the oogonium is diploid and not surrounded by follicle cells.
- In late fetal period through birth the primary oocyte has made it to the diplotene stage and primordial follicle with a few follicle cells. Has 2 chromatids/chromosome
- Birth to puberty oocyte is diploid and primary follicle with a single layer of follicle cells. Oocyte and follicle cells are connected through gap junctions. Zona pellucida separates primary oocyte and follicular cells. 2 chromatids/chromosome
- Secondary follicle with multiple layers of follicle cells and antrum formation begins
- tertiary follicle has multiple layers of follicle cells, corona radiata and a large antrum.
Ontogeny?
Study of all developmental processes from conception to death
Embryogeny?
Part of ontogeny from conception to birth
Embryology?
Study of embryo
Stages of gametogenesis?
1.Extraembryonic origin of germ cells by mitosis 2. Increase in number of germ cells by mitosis 3.Reduction in chromosomal number by meiosis 4.Structural and functional maturation of eggs and spermatozoa
Teratoma?
Growths from misdirected migrating primordial germ cells containing mixtures of highly differentiated tissues
What are the divisions of Prophase I?
Leptotene Zygotene Pachytene Diplotene Diakinesis
What are the major results of meiosis?
Increase in the number of cells sometimes. Daughter cells are not genetically identical. Daughter cells are haploid
Describe Leptotene stage.
First subdivision in prophase I. Chromosomes are threadlike and each chromosome consists of two chromatids. Chromosomes begin to coil
Describe Zygotene stage.
Second stage in prophase I. Homologous chromosomes pair and synaptonemal complex forms
Pachytene stage?
Third stage in prophase I. Maximum coiling occurs and tetrads form. Crossing over begins
Diplotene stage?
Fourth stage in prophase I. Crossing over continues and chiasmata is well defined
Diakinesis stage?
Fifth stage in prophase I. Crossing over is complete and terminalization occurs. The spindle apparatus is in place and the nuclear membrane is disrupted.
Metaphase I?
Tetrads line up and centromeres do NOT divide
Anaphase I?
Homologous chromosomes move to opposite poles and each homologue consists of two chromatids. Chromatids are not genetically identical because of crossing over. Haploid daughter cells.
Telophase I?
Cytokinesis occurs and nuclear membrane reforms. Spindle apparatus disassembles and chromosomes can uncoil.
What is the end result of telophase II?
Four genetically unique haploid daughter cells
What stage are the oocytes arrested in before puberty?
Diplotene stage of meiosis
What stage are oocytes arrested in after puberty at beginning of menstrual cycle?
Second metaphase
What cells produce estrogen and what stimulates them to do it?
Granulosa cells produce estrogen and FSH stimulates them to do so.
During oogenesis what allows meiosis to resume and then be arrested at metaphase II?
LH surge that shuts down gap junctions between granulosa cells and the oocyte
What are the 4 components of a tertiary follicle? (external to internal)
- Theca exgterna: produces angiogeneis factor
- Theca interna: secretes testosterone which is converted to estrogen by aromatase
- Membrana granulosa
- Mural granulosa cells: synthesizes aromatase in response to FSH
- Antrum
- Cumulus oophorus cells: facilitate release of ovum at ovulation
- Zona pellucida: involved in fertilization
- Oocyte
During spermatogenesis histone is repalced by which of the following to allow better packing of the condensed chromatin in the head of the spermatozoon?
A. Inhibin
B. Prostaglandin E
C. Testosterone
D. Proamine
E. Androgen-Binding protein
D. Proamines
What cell type is located outside the blood testis barrier?
Primary Spermatocyte
What stage does ovulation occur in?
Metaphase II
What happens after fertiliztion?
- Completion of second meiotic division
- Fertilized ovum and a second polar body
- One chromatid per chromosome
- Diploid number is reestablished after fertiliztion
What is necessary for pregnancy for the first few months?
Corpus Luteum
What factor leads to meiotic arrest at the diplotene stage of meiosis?
High concentation of cAMP from oocyte and the folliclular cells which inactivates maturation promoting factor (MPF)
What is the corona radiata?
Layer of ofllicle cells surrounding the oocyte and interacts with the oocyte through gap junctions and microvili.
What is the Zona pellucida?
Non cellular membrane that is secreted by the corona radiata and oocyte
How does the egg get transported through the uterine tube?
- Fimbriae of the tube moves close to ovary and sweeps
- Captures egg and surrounding follicle cell
- Transports of egg is through contractions of tubal sm. mm
- Transport time to uterus is around 3-4 days
What type of spermatogonia leave the mitotic cycle and enter the meiotic cycle?
Type B
What is the order of cells in spermatogenesis?
- Primordial germ cell (2N)
- Spermatogonia (2N)
- Primary Spermatocytes (2N) undergo meiosis I
- Secondary Spermatocytes (2N) undergo meiosis II
- Spermatids 4 1N cells
What do cells of leydig produce?
Testosterone
What are the four stages to spermiogenesis?
- Golgi phase: proacrosomal vesicles and acrosomal vesicle
- Cap phase: mature acrosome forms a cap over nucleus
- Acrosomal phase: rotate sperm so acrosomal pole faces wall of seminiferous tubule and cytoplasm towards tail
- Maturation phase: completion of flagellum and nuclear condensation
What acrosomal enzyme gets through the zona pellucida?
Zona lysin
What do sertoli cells do?
- Physical support and maintenance and secrete tubular fluid
- Maintain blood testis barrier
- Secrete estrogen inhibin and anti mullerian factor
- Phagocytize residual bodies of sperm cells
What male spermiogenesis cells are comparable with granulosa cells in the female?
Sertoli cells because they convert testosterone to estrogens and produce inhibin
Sperm transport after spermiogenesis?
- Passive transport through testicular fluid, sm. mm contractions and cilia from seminiferous tubules move the sperm because they are immotile.
- Through the rete testis
- Through the efferent ductules
- To the head of the epididymis
How long does it take for maturation of sperm to occur and where?
12 days in the head of the epididymis and changes in the glycoproteins in the PM of sperm head occur
What is the ejaculation path?
From the tail of the epididymis to the ductus deferens where addition of seminal vesicle fluid (fructose and prostaglandins) and prostate fluid ( citric acid, Zn,Mg, phosphatase) are added. To the urethra.
Sperm transport through female?
- Upper vagina where the sperm buffers the pH with seminal fluid
- Cervix, which is optimal pH for sperm motility
- Cervical canal
- Can go through rapid transport not as capable as fertilization, 5-20 min
- Can do slow transport through cervical mucous 2-4 days
- Isthmus: After release following capacitation sperm move up the oviduct and make it to the ampulla where fertiliztion occurs
