Gametogenesis & Fertilization Flashcards
When are precursors of gametes recognizable by?
The 4th week of gestation
Where do primordial germ cells develop?
In the endoderm of the yolk sac
What do primordial germ cells associate with to form primordial gonads?
With somatic cells
What do primordial germ cells divide by?
Standard mitosis
What hypothalmic/pitutary influences affect male and female gametes?
Hypothalmus - GnRH
Pituitary - LH, FSH
Sex Steroids
What sex steroids are used in males and females?
Males use testosterone
Females use estrogen and progesterone
What is initiated by week 12?
Meiosis I, primary oocytes are beginning to develop, aquirered layer of epithelial cells called primordial follicles
What do follicular cells secrete?
OMI or oocyte maturation inhibitor which arrests the follicle at prophase I
How many oocytes at birth, puberty and maturity?
~2.5 million at birth
~70,000 at puberty
~400 at maturity
What does GnRH do to oocytes at puberty?
Increases FSH & LH secretion
What does FSH do to oocytes at puberty?
Stimulates follicle maturation; maturing oocyte termed “Graafian follicle”
What does LH do to oocytes at puberty?
Stimulates ovulation
What does Estrogen do to oocytes at puberty and what is it secreted by?
Secreted by follicular cells, stimulates maturation
What is Progesterone secreted by?
By the corpus luteum
At what stage are oocytes arrested at until the menstrual cycle?
They are arrested as primary follicles which is an oocyte plus a single columnar layer of epithelial cells.
What does an oocyte progress to during a menstrual cycle?
A secondary follicle which is a primary oocyte + zone pellucida and multi-layer epithelial cells
What does the innermost layer of the secondary follicle attach too?
The corona radiata attaches to the zona
What is the Zona pellucida made of?
3 glycoproteins (ZP 1,2,3)
What does the epithelial layer of the oocytes differentiate into?
Into the interna and external of the theca follicle.
What is the antrum?
Fluid filled cavity in center of follicle
What does the LH surge trigger?
Proteolytic breakdown of ovarian wall granulose-secreted enzymes
What prohibits the enzyme breakdown triggered by LH?
Theca cells
When does meiosis resume for oocytes?
Just prior to ovulation
What is OMI maintained by?
PK-A
What does the LH surge cause?
An increase in IP3 and Ca2++ in granlosa cells which is transmitted via gap junctions to oocyte
How does signaling for oocytes change when cAMP phosphodiesterase is increased?
[cAMP] goes down resulting in PK-A losing activation and OMI loses function. When PK-A mediation is shut off PK-C mediation begins.
What is MPF?
Maturation Promoting Factor
What does MPF target?
Nuclear laming and triggers germinal vesicle breakdown and completion of meiosis I.
What increases MPF activity?
PK-C
At what stage does the secondary oocyte arrest until fertilization?
Meiosis II, metaphase II
Where are spermatogonia located?
As dormant cells in testicular seminiferous tubules
What does GnRH do to spermatogenesis at puberty?
Increases FSH and LH
What does FSH do to spermatogenesis at puberty?
Stimulates Serotoli cell secretion of androgen binding protein (ABP) and inhibin
What does LH do to spermatogenesis at puberty?
Stimulates Leydig cell secretion of testosterone
What do testosterone and DHT do to spermatogenesis at puberty?
Stimulate final steps of spermatogenesis
How many lobules and seminiferous tubules are in the testes?
2-300 lobules each with 2-3 seminiferous tubules
How does Sperm Differentiate?
Histones replaced by protamines; intensive condensation
Golgi builds acrosomal
Axoneme organizes flagella
What type of genome does spermiogenesis require?
A diploid hormone
How long does it take for the differentiation process of converting spermatids to mature sperms take?
~64 days total
How many mature sperm are produced each day?
~300 million
Are sperm and egg cells large or small?
Sperm = small Egg = huge
Are sperm and egg cells motile or immotile?
Sperm = motile Egg = nonmotile
Do sperm and egg cells have accessory cells?
Sperm = no Egg = Yes
Do sperm and eggs have lots of cytoplasm or sparse cytoplasm?
Sperm = sparse Egg = Lots
How many types of sperm and egg cells are there?
Sperm = 2 types: 23X, 23Y Egg = 1 Type: 23X
How do oocytes go from the the ovaries to the fallopian tube?
Oocyte and follicular fluid are swept in the fallopian tube via fimbriae and mucosal cell cilia
How does the oocyte get move toward the ampulla of the fallopian tube?
Via peristaltic waves
Define emission in terms of sperm transport?
Semen is delivered to posterior urethra via peristalsis of ductus deferens
Define ejaculation.
Semen is expelled through urethra via bulbospongiosus muscle contractions
How much volume is expelled during ejaculation and what is the approximate sperm concentration?
About 2.5 - 5 ml with a sperm concentration of 50-150 x 10^6 / ml
Where do the components of seminal fluid come from?
60% - seminal vesicles
25% - prostate
10% - bulbourethral (Cowper’s) gland
What do the seminal vesicles contribute to seminal fluid?
Fructose
Prostaglandins
Unique clotting proteins
What does the prostate contribute to seminal fluid?
Citrate
Prostate specific antigen (PSA)
What does the Cowper’s gland contribute to seminal fluid?
Buffer
Mucous
What happens in post ejaculation sperm maturation?
Capacitation
What happens in capacitation?
Acrosome is cleared of glycoprotein coat and seminal proteins
Sperm become more actively motile
What is capacitation dependent on and who long does it take?
Calcium dependent
Takes 7-10 hours
What happens post-fertilization?
Oocyte completes 2nd meiotic division and female and male pronuclei form
Sperm parts breakdown
Pronuclei breakdown
Mitotic spindle organizes using centriole components from sperm tail; chromosomes arrange on spindle
Mitosis begins
What are some ways to assist fertilization?
IVF: in vitro fertilization
GIFT: gamete intrafallopian transfer (sperm + egg transfer)
ICSI: intracytoplasmic sperm injection (sperm only transfer)
What are some reasons for male infertility?
Sperm count
Sperm motility
Sperm morphology
What sperm count threshold is considered to be infertile?
< 20 X 20 ^6 / ml
What is preimplantation genetic diagnosis (PGD) via blastomere dissection used for?
For diagnosis of heritable disease in 8-cell embryo
What is the “manster” test?
Tests the ability of human sperm to penetrate zone-free hamster egg
