Oogenesis + Spermatogenesis, fertilisation Flashcards
where are sperm cells made and mature
Sperm production in the testes takes place in coiled structures called seminiferous tubules. Along the top of each testicle is the epididymis (a cordlike structure) where the sperm mature and are stored.
The sperm release process starts when the penis fills with blood/ becomes erect.
What are the 4 main stages of gametogenesis?
gametogenesis= takes place within the gonads (testes or ovaries in males or females, respectively); in males this process is called spermatogenesis and produces spermatozoa, while in females this is oogenesis and results in eggs or oocytes
4 main stages:
* Extra embryonic origin of germ cells and migration to gonads
*Increase in number of germ cells by mitosis
*Reduction in chromosome number by meiosis
*Structural and functional maturation into eggs and sperm.
Q2 What happens during migration (PHASE1)?
* At week 3?
- At week 6?
At week 3
* Primordial germ cells leave primary ectoderm and move to yolk sac wall
* Collect near the exit of the allantosis
* The cells are now extra-embryonal
* They are lying in the endoderm and mesoderm of the yolk sac wall
At week 6
* Primordial germ cells leave the yolk sac wall
* Migrate along the vitelline and the dorsal mesentery into the gonadal ridge
What happens if the cells migrate incorrectly and settle at extragonadal sites?
Teratomas (germ cell tumours); specifically extragonadal germ cell tumours
When do oogenia enter first meiotic division?
oogenia enter first meiotic division: Late foetal period (7th month of foetal development)
however, the number of germ cells drops precipitously. Most oogonia die during this period, while the remaining oogonia enter the first meiotic division
What stage of meiosis occurs in the oogonia in the early months after birth?
Diploid phase of prophase 1; this continues to puberty
When does Primary oocyte complete meiosis1?
During the menstrual cycle (a secondary oocyte and polar body form)
(aka after u hit puberty when u start having period)
At what stage does the secondary oocyte halt at?
Metaphase 2 and only continues if fertilisation occurs
What are primordial follicles surrounded by?
primordial follicles are surrounded by multiple pre-granulosa cells
What does the oocyte and granulosa cells later contribute to?
zona pellucida
What do thecal cells secrete?
theca cells secrete angiogenic factors
The granulosa cells respond to [] and produce oestrogen
The granulosa cells respond to follicle stimulating hormone (FSH) and produce oestrogen
What regulates secondary follicle/ oocyte stimulation and maturation.
- FSH stimulated oestrogen production by granulosa cells.
- Activin, LH and testosterone
LH and FSH induce ovarian follicle maturation (into a graafian follicle) and synthesis of ovarian steroids
What does a tertiary follicle (graafian follicle) do?
Pushes against ovary surface and then antrum enzymes break down follicular wall so wall bursts.
Where does spermatogenesis begin?
Seminiferous tubules of testes after puberty
What are the 2 types of precursory spermatogonia?
Type A (mitotically active to continue supplying germ cell precursos)
Type B cells that can enter meiosis.
How are spermatogonia kept separate from blood?
Outside blood testis barrier formed by interlocking sertoli cells
If broken can result in infertility
Kept at base of seminiferous tubules.
function of primary spermatocytes
primary spermatocytes produce mRNA which is stored till later
Each primary spermatocyte undergoes the first meiotic division to yield a pair of secondary spermatocytes, which complete the second division of meiosis.
n.b. Each secondary spermatocyte contains 23 chromosomes whereas primary spermatocyte contains 46 chromosomes.9
What do secondary spermatocytes immediately enter?
Meiosis 2 and then known as spermatids
What is the process of spermatogenesis characterised by?
- Reduction in nuclear size
- Golgi apparatus condensation into the Acrosome
- A flagellum grows out of the centriole
- Cytoplasm parts from nucleus and is phagocytosed by Sertoli cells
- Mitochondria form a spiral arrangement around flagellum
- Head partitions into domain
What is capacitation of sperm?
Acrosomal reaction that takes place in females genital tract to allow fertilisation i.e. the swimming
Sperm capacitation is the set of natural physical changes that a spermatozoon undergoes in order to be able to fertilise the ovum. This occurs in vivo following ejaculation when the spermatozoa come into contact with the different fluids in the female genital tract.
What are the hormones associated with sperm production?
- GnRH stimulates LH and FSH release from the pituitary
- LH stimulates testosterone production by Leydig cells
- Testosterone and FSH target sertoli cells
- Sertolli cells secrete androgen binding protein and tubular fluid
- Androgen binding fluid binds to testosterone and carries it to the location of (and stimulates) spermatogenesis
hydrolytic enzymes from the acrosome of the sperm break down the [] surrounding the oocyte
hydrolytic enzymes from the acrosome of the sperm break down the zona pellucida surrounding the oocyte
the bulk of the spermatids cytoplasm is cast off as a residual body leaving a thin rim of cytoplasm around the nucleus of the spermatozoon. What cells in the testes consume the residual body (old cytoplasm of spermatid)
sertoli cells consume the residual body of the spermatid; now we have a spermatozoon
the capacitated spermatozoon + oocyte meet in which part of the fallopian tube
the capacitated spermatozoon + oocyte meet in the ampulla of the fallopian tube
How does the sperm know where to go?
*thermotaxis= temperatue difference of 2degress exists between storage site + fertilisation site (temp guides them)
*rheotaxis- ability to align with or against fluid flow- positive rheotaxis means swimming against flow
*chemotactic gradients of progesterone from cumulus osphorus (granulosa cell ring outside ova innermost part is called the corona radiata) + fMLF (N-Formylmethionine-leucyl-pheylalanine)
what is the tunica albuginea
*in males
*in females
in males; The tunica albuginea is the fibrous layer covering of the testis. It is a dense blue-grey membrane, composed of bundles of white fibrous tissue which interlace in every direction.
in females;
The ovarian tunica albuginea, positioned beneath the surface epithelium, is a thin and hypocellular connective tissue sheath, which serves as a protective layer for the ovary. The tunica albuginea is collagen-rich and undergoes remodeling prior to ovulation.
