Oogenesis + Spermatogenesis, fertilisation

Question 1

where are sperm cells made and mature

Answer 1

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.

Question 2

What are the 4 main stages of gametogenesis?

Answer 2

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.

Question 3

Q2 What happens during migration (PHASE1)?
* At week 3?

• At week 6?

Answer 3

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

Question 4

What happens if the cells migrate incorrectly and settle at extragonadal sites?

Answer 4

Teratomas (germ cell tumours); specifically extragonadal germ cell tumours

Question 5

When do oogenia enter first meiotic division?

Answer 5

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

Question 6

What stage of meiosis occurs in the oogonia in the early months after birth?

Answer 6

Diploid phase of prophase 1; this continues to puberty

Question 7

When does Primary oocyte complete meiosis1?

Answer 7

During the menstrual cycle (a secondary oocyte and polar body form)

(aka after u hit puberty when u start having period)

Question 8

At what stage does the secondary oocyte halt at?

Answer 8

Metaphase 2 and only continues if fertilisation occurs

Question 9

What are primordial follicles surrounded by?

Answer 9

primordial follicles are surrounded by multiple pre-granulosa cells

Question 10

What does the oocyte and granulosa cells later contribute to?

Answer 10

zona pellucida

Question 11

What do thecal cells secrete?

Answer 11

theca cells secrete angiogenic factors

Question 12

The granulosa cells respond to [] and produce oestrogen

Answer 12

The granulosa cells respond to follicle stimulating hormone (FSH) and produce oestrogen

Question 13

What regulates secondary follicle/ oocyte stimulation and maturation.

Answer 13

• 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

Question 14

What does a tertiary follicle (graafian follicle) do?

Answer 14

Pushes against ovary surface and then antrum enzymes break down follicular wall so wall bursts.

Question 15

Where does spermatogenesis begin?

Answer 15

Seminiferous tubules of testes after puberty

Question 16

What are the 2 types of precursory spermatogonia?

Answer 16

Type A (mitotically active to continue supplying germ cell precursos)

Type B cells that can enter meiosis.

Question 17

How are spermatogonia kept separate from blood?

Answer 17

Outside blood testis barrier formed by interlocking sertoli cells
If broken can result in infertility
Kept at base of seminiferous tubules.

Question 18

function of primary spermatocytes

Answer 18

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

Question 19

What do secondary spermatocytes immediately enter?

Answer 19

Meiosis 2 and then known as spermatids

Question 20

What is the process of spermatogenesis characterised by?

Answer 20

• 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

Question 21

What is capacitation of sperm?

Answer 21

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.

Question 22

What are the hormones associated with sperm production?

Answer 22

• 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

Question 23

hydrolytic enzymes from the acrosome of the sperm break down the [] surrounding the oocyte

Answer 23

hydrolytic enzymes from the acrosome of the sperm break down the zona pellucida surrounding the oocyte

Question 24

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)

Answer 24

sertoli cells consume the residual body of the spermatid; now we have a spermatozoon

Question 25

the capacitated spermatozoon + oocyte meet in which part of the fallopian tube

Answer 25

the capacitated spermatozoon + oocyte meet in the ampulla of the fallopian tube

Question 26

How does the sperm know where to go?

Answer 26

*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)

Question 27

what is the tunica albuginea
*in males
*in females

Answer 27

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.