Gametogenesis and Fertilization Flashcards
primordial germ cells
- progenitors of gametes
- from yolk sac endoderm, migrate to genital ridge and become indifferent gonad
intermediate mesoderm
-urogenital organs: leydig cells, sertoli cells, follicular cells, ovary, testis, ducts, uterus
urogenital sinus endoderm
-terminal internal parts of genital organs: vesicular, prostate and bulbourethral glands
Mullerian (paramesonephric) ducts
- develop into fallopian tubes, uterus, cervix
- in male they disappear under the influence of anti-paramesonephric duct hormone
prepuberal testis
- seminiferous cords consisting of: sertoli cells, primordial germ cells (stem cells for spermatogenesis-stay dormant until puberty)
- inactive interstitial cells of leydig
cryptochidism
testes fail to descend into scrotum, inherited as a sex-limited autosomal recessive trait
types of cryptorchidism
- unilateral
- bilateral: sterile but has normal sexual behavior
scrotal hernia
type of inguinal hernia=congenital weakness in the abdominal wall
primitive sex cells
spermatogonia, oogonia- have complete DNA complement.
spermatogonia and oogonia Mitosis
results in more spermatoginia and oogonia
spermatocye and oocyte meiosis
insure variation and provide 1/2 of chromosomes (haploid number) both in male (1N) and female (1N) sex cells (gametes)
fertilization
joining of sex cells, create zygote, restores DNA complement (2N) initiates cleavage
mitosis
results in formation of 2 daughter cells each having DIPLOID set of chromosomes, same number as in the mother cell
Meiosis
comprised of 2 meiotic divisions, results in daughter cells which have half the parental number of chromosomes (haploid), called gametes
goals of meiosis
- reduction of diploid set chromosomes into haploid gametes
- exchange of genetic material between male and female chromatids in prophase of meiosis (crossing over)
- results in 4 daughter cells with 4 different genetic makeups
common features of gametogenesis
- multiplication of spermatogonia and oogonia
- meiosis
- extensive morphological differentiation
- incapacity of surviving for long if ferrtiization does not occur
characteristics of sperm
- continually renewed
- one spermatocyte produces 4 sperm
- initial large cell results in small cells
- motile cells
- x or y sex chromosomes
characteristics of ovum
- all oocytes present at birth
- one oocyte produces 1 ovum and 2-3 polar bodies
- initial small cell grows to large cell
- immobile
- x chromosome only
oogenesis
occur in ovary
1. oogonia-prenatal mitosis and differentiation
2. all are primary oocytes (4N) arrested in meiosis 1 until puberty
-at ovulaton, meiosis 1 is completed except in dogs and mares
3. secondary oocyte awaits fertilization in uterine tubes
-meiois 2 completed on sperm contact
result is ovum (1N) and 2nd polar body (2N)
ovulation
results from hormone influence on folliculogenesis at puberty
folliculogenesis: primordial (resting) follicles
oocyte1 + single layer of squamous follicular cells
folliculogenesis: primary follicles
activated or growing follicles, zona pellucida forms
folliculogenesis:secondary follicles
secretory/antral follicles, fluid filled spaces are formed among the granulosa cells
folliculogenesis: tertiary mature (Graafian) follicle
one antrum containig liquor folliculi, have eccentric cumulus oophorus, contain primary oocyte
zona pellucida
acts as immunologic protective barrier for developing egg and early embryo
corpus hemorrhagicum
after ovulation the follicular space fills with blood and clots, will be replaced by luteal calls and become corpus luteum
corpus luteum
yellow body, produces progesterone and some estrogen
- granulosa luteal cells: large
- theca luteal cells: small
progesterone
helps maintain the pregnancy, stimulate mammary development, and locally down regulates the immune system
corpus albicans
corpus luteum regresses during diestrus, connective tissue scar
atrectic follicle
follicle that is not selected to complete maturation, undergo programmed destruction, common
ovulation
oocyte departs the ovary and leave behind corpus hemorrhagicum that becomes the corpus luteum of thecal and granulosa cells
spermatogenesis
- spermatogonium mitosis: differentiate
- primary spermatocyte: meiosis 1 (crossover)
- 2 secondary spermatocytes: meiosis 2
- 4 sermatids do not divide but undergo spermiogenesis (metemorphosis)
- 4 spermatozoa
functions of sertoli cells
- activated by FSH
- secrete AMH during fetal development to inhibit uterus formation
- secrete inhibin and activins after puberty to regulate FSH secretion from pituitary
- secrete androgen binding protein (ABP) to bind testosterone increase concentration in seminiferous tubules and stimulate spermatogenesis
sperm cell maturation
spermatogonia (2N) –> spermatocytes: primary (4N) undergo st meiosis to secondary (2N) undergo 2nd meiosis–>spermatids (1N) undergo metamorphosis to spermatozoa
round spermatid
undergoes metamorphosis to elongated spermatids
sperm head
nucleus and acrosome
sperm head shape
- ruminants: disc like
- man, stallion: pear shaped
- rodents: hook like
- guinea pig: spoon like
- birds: filiform
axonema
core of cilia & sperm flagellum (tail)
structure of axonema
-derived from modified centriole
-pair of central microtubles
+ outer ring of 9 doublets with dynein arms
-each doublet has a microtuble A with dynein arms + an incomplete microtubule B
characteristics of spermatogenesis
- continuous process: throughout the year except for seasonal breeders
- highly organized process, fixed length of time
- takes place in orderly waves
- very sensitive to: temperature, x ray irradiation, nutrition, infection & non-infectious diseases, stress, drugs
spermatogenesis vs oogenesis: sperm
- spermatogonia remain dormant until puberty, the proliferate by mitotic division
- meiosis completed within testis
- each spermatogonium give rise to multiple
- spermatids undergo metamorphosis
- spermatogenesis may continue throughout the whole life of the animal
spermatogenesis vs oogenesis: oogenesis
- complete their proliferation in the early embryonic stage
- by birth all oogonia entered meiosis 1 but development arrested until puberty
- one oocytes give rise to one ovum
- ova do not undergo metamorphosis
- meiosis is completed in fallopian tube
- oogenesis stops after overy exhausted of germ cells
fertilization-sperm
-capacitation: occurs in uterine environment, gain ability to fertilize the oocyte
-acrosome reaction: release acrosomal enzymes to digest through zona pellucida
sperm contacts oocytes
-fusion of sperm plasma membrane with plasma membrane of oocyte
capacitation and acrosome reaction
plasma membrane over acrosome is destabilized and breaks down together with outer acrosomal membrane, acrosomal enzymes are released
fertilization-ovum
- cortex of oocytes below oolemma contains cortical granules
- sperm contact with oocyte plasma membrane causes release of proteases which modifies zona pellucida
- zona pellucida is then a barrier to other sperm penetration
pronuclei
nuclear material of sperm and ootid
syngamy
union of male and female pronuclei
