Spermatogenesis and fertilisation

Question 1

what happens to males in phase II of gametogenesis

Answer 1

• Spermatogonia undergo mitosis in early embryonic testes

- Spermatogonia undergo periodic waves of mitosis form puberty onwards throughout life

Question 2

describe phase IV of gametogenesis for males

Answer 2

• Much more rapid than oogenesis, begins in seminiferous tubules of testes after puberty
• Type A spermatogonia are mitotically active throughout reproductive life
• Give rise to type B spermatogonia which enter meiosis
• Spermatogonia are kept at base of seminiferous epithelium by interlocking sertoli cells
• Connected by intercellular cytoplasmic bridges

Question 3

what are the two types of spermatogonia

Answer 3

type A and type B

Question 4

what id the difference between type A and type B spermatogonia

Answer 4

Type A spermatogonia are mitotically active throughout reproductive life
• Give rise to type B spermatogonia which enter meiosis

Question 5

where are spermatogonia kept

Answer 5

At Base Of Seminiferous Epithelium By Interlocking Sertoli Cells

Question 6

where does spermatogenesis happen

Answer 6

• the development the germ cells begins with the spermatogonia at the periphery of the seminiferous tubule and they advances towards the lumen they mature and they become primary spermatocytes I, and secondary spermatocytes, spermatids and finally mature sperm.

Question 7

what do sertoli processes form

Answer 7

• they form an immunological barrier

- if this is broken than autoimmune infertility can occur

Question 8

what is another word for type B spermatogonia

Answer 8

primary spermatocytes

- this happens when they enter meiosis

Question 9

what do type B spermatogonia cells do during early meiosis I

Answer 9

• they become immunologically district from other cells

- they move through the barrier to interior of seminiferous tubule

Question 10

how long do primary spermatocytes take to complete meiosis I

Answer 10

• primary spermatocytes take 24 days to complete meiosis I

Question 11

what do primary spermatocytes do in meiosis I

Answer 11

• making mRNA for later protein production.

- mRNA stored until required late

Question 12

what happens after completion of meiosis I what is produced

Answer 12

• secondary spermatocytes are produced

- these immediately enter meiosis II and produce spermatids

Question 13

what do spermatids become

Answer 13

• Spermatids undergo spermiogenesis to become spermatozoa

Question 14

what do spermatids need to have happen to them in order to become spermatozoa

Answer 14

• Reduction in nuclear size
• Golgi apparatus condenses to form acrosome
• Flagellum grows out of centriole
• Cytoplasm streams away from nucleus
• Mitochondria in spiral arrangement around flagellum
• Head partitioned into domains
- Cytoplasm moves to residual body which is phagocytosed by Sertoli cells

Question 15

in order to fertilise the egg what does a sperm need to undergo

Answer 15

capacitiation

Question 16

where does capacitation happen

Answer 16

• It takes place within the female genital tract and requires contact with the secretions of the oviduct.

Question 17

what happens in capacitation

Answer 17

• It is part of a series of physiological processes which allows the sperm to fertilise the egg.
• Only capacitated sperm are capable of the acrosome reaction and fusion with the oocyte.
- they become more sensitive to signalling from the uterus

Question 18

what does GnHR do

Answer 18

stimulates FSH and LH -release from the anterior pituitary

Question 19

what does LH do

Answer 19

• LH stimulates testosterone production by Leydig cells (which surround the seminiferous tubules) – they are not inside the seminiferous tubules

Question 20

what is the main target of testosterone and pituitary FSH

Answer 20

• Main target of testosterone and pituitary FSH are Sertoli cells

Question 21

what do Sertoli cells secrete

Answer 21

• Sertoli cells then secrete androgen binding protein (abp) and tubular fluid

Question 22

what does Abg do

Answer 22

• Abg binds to testosterone & carries it to area of seminiferous tubule where it stimulates spermatogenesis

Question 23

what do you need in order for fertilisation to take place

Answer 23

• Functioning hypothalamic-pituitary-gonadal axis
• Normal oogenesis & spermatogenesis
• Normal structure and function of reproductive tract
• Trouble free transport of gametes
• Gamete fusion
• Trouble free transport of embryo

Question 24

where is the sperm deposited

Answer 24

• in the cervical os

Question 25

how does the sperm travel towards the cervics and into the uterus

Answer 25

The ciliated surface of the cervical os help the sperm towards the cervical canal (over 99% spermatozoa do not get there)
• Transport into uterus & oviducts by sperm’s own propulsion & fluid currents caused by uterine cilia. It’s a distance of about 13-15cm & takes about 2-7 hours.
• During this journey sperm undergo capacitation
• Sperm become hyperactive & sensitive to surrounding signals.

Question 26

what is capacitation

Answer 26

– the removal of its glycoprotein coat.

Question 27

what happens to the cervix when ovulation happens

Answer 27

the properties of the cervix mucus changes from a sperm hostile to sperm friendly

Question 28

how is an egg fertilised

Answer 28

1. Sperm finds egg
2. Sperm recognises egg.
3. Sperm has acrosome reaction to penetrate extracellular layer
4. Sperm cell membrane fuses with egg cell membrane and triggers Ca2+ wave in egg.
5. Polyspermy is blocked.
6. Fertilisation cone forms around sperm head.
7. Movement and fusion of pronuclei.

Question 29

how does the acrosome reaction and egg sperm fusion happen

Answer 29

• The acrosome membrane fuses with the overlying plasma membrane
• Enzymes released that allow passage through zona pellucida
• Enzymes include hyaluronidase, which dissolves the intercellular matrix between the cumulus cells, and other enzymes dissolve the zona pellucida
• Sperm finishes its journey between the zp and the oocyte membrane (oolemma)
• Sperm becomes enveloped
• Fusion occurs - mechanism unknown
• Large increase in intracellular Ca2+ which forms a wave across the egg (mechanism uncertain – few candidates)

Question 30

How do the sperm and egg find each other

Answer 30

• Sperm attracted to egg via chemotaxis
• Only found in mature eggs and sperm
• Mechanisms vary depending on species

Question 31

how do cells fuse with each other in mammals

Answer 31

• A glycoprotein called ZP3
• Found in the zona pellucida
• Binds to β1, 4 galactosyl transferase receptor on the sperm plasma membrane
• Capacitated sperm are species-specific in their binding to ZP3
• Binding triggers changes in Ca2+ and pH in sperm and acrosome reaction

Question 32

how is the number of cell fusing restricted

Answer 32

Production of second messengers on sperm/egg binding triggers polyspermy blocking.
Slow block:
- release of calcium in a wave
- calcium triggers cortical granule
- release and activation of cell division

Question 33

where does the fertilised ovum travel

Answer 33

• travels down the oviduct
• it travels down the fallopian tube the fertilised oocyte or zygote will begin to divide and it undergoes cleavage to form two cells

Question 34

what happens at the 16-32 stage

Answer 34

1. The outer cells form one population and are trophoblast precursors.
2. The inner cells are the pluriblast cells.
   This is called a morula.

Question 35

what happens at the 32-64 stage

Answer 35

(4-5 days after ovulation) the cells which have been polarised start to differentiate into different cell types.
This is called the blastocyst.
– there is something stoping it from developing further, the zona pellucida has harderend therefore if it wants to grow it has to free itself from the zona pellucida
Around day 5 the blastocyst frees itself from the zona pellucida.
It does this through a series of expansion-contraction cycles and with the help of enzymes that dissolve the zona pellucida.
This is called ‘hatching’.
The blastocyst will attach to the uterine wall about 7-9 days post ovulation

Question 36

what stops the blastocysts from developing further

Answer 36

zona pellucida has harderend therefore if it wants to grow it has to free itself from the zona pellucida

Question 37

how does the blastocysts free itself

Answer 37

It does this through a series of expansion-contraction cycles and with the help of enzymes that dissolve the zona pellucida.
This is called ‘hatching’