MNSR 38 - Human Reproduction: Spermiogenesis, Spermatozoa, Oogenesis

Question 1

Spermatogenesis

Answer 1

specialised meiotic division which leads to development of mature spermatozoa in the male

Question 2

when does spermatogenesis begin and what hormone influences that process

Answer 2

begins at puberty

under the influence of pituitary hormone FSH

Question 3

spermatogenesis

Answer 3

type A1 Spermayogonium (44XY) |
       Mitosis
            | 
type B spermatogonium (44XY)
          (Mitosis)
          /.              \ 
DIES                 primary (44XY)
                    spermatocytes
                    /.              \ 
            22X              22Y
     (Secondary spermatocytes)
           /   \                     /.     \ 
    22X.  22X.           22Y.  22Y
                (Spermatids)

Question 4

2 types of somatic cells in seminiferous tubule

Answer 4

(1) Myoid smooth muscle cell; (2) Sertoli/sustentacular ce

Question 5

sertoli cells

Answer 5

extend from basement membrane to lumen forming desmosome-like contacts with germ cells (especially) spermatogonia and primary spermatocytes… may play a role in translocating them towards lumen

Question 6

blood testis barrier

Answer 6

Sertoli cells form tight junctions (‘blood-testis barrier) between each other, dividing the intercellular spaces into a basal compartment (containing spermatogonia) and an intercellular adluminal compartment (containing primary spermatocytes).

Question 7

importance of barrier between sertoli cells

Answer 7

the barrier is important in preventing proteins and especially antibodies coming in contact with the germ cells and giving rise to the possibility of autoimmune reactions

Question 8

what occurs in ordinary when spermiogenesis happens and where does it occur

Answer 8

Involves cytoplasmic remodelling of each spermatid which starts as ordinary round cell
Occurs in close association with Sertoli cells
Takes place in deep adluminal compartments
No cell division takes place

Question 9

what occurs in adluminal compartment of seminiferous tubule

Answer 9

in the adluminal compartment they enter meiotic division stages producing secondary spermatocytes and spermatids;

Question 10

describe microtubule arrangement of axoneme

Answer 10

the axoneme or axial filament consists of the usual 9 + 2 microtubular arrangement surrounded by 9 coarse outer fibres;
the remainder of the middle piece is occupied by a helix of mitochondria lined up end-to-end

Question 11

what is principle piece covered in

Answer 11

the principal piece with the axial filament is covered by a fibrous sheath;

Question 12

describe formation of primordial follicle in fetus life

Answer 12

In early fetal life it is now believed that germ cells migrate into the genital ridge from the yolk sac forming primordial follicles containing oögonia (which are therefore only found in early foetal life

Question 13

through what process does oogonia divide

Answer 13

mitosis to make primary oocytes

Question 14

layers of seminiferous tubules from outer layer to inner layer (lumen)

Answer 14

leydig cells and capillaries
myoid smooth muscle cell 
basement membrane
spermatogonium 
blood testis barrier
primary spermatocyte
(sertoli cells interspersed)
secondary spermatocyte
spermatid
sperm cell/spermatozoon
lumen

Question 15

germ cells

Answer 15

spermatogonium (2n)
primary spermatocyte (2n)
secondary spermatocyte (n)
spermatid (n)
sperm cell/spermatozoon
lumen (n)

Question 16

spermatocytogenesis - processes of cell division (mitosis and meiosis)

Answer 16

in basal compartment
type A1 spermatogonia 
                 |
            mitosis
                 |
                V 
type B spermatogonia
                  |
            mitosis
                  |
                 V
primary spermatocytes - move into adluminal compartment through tight junctions between sertoli cells
                    |
              MEIOSIS I
                    |
                   V
secondary spermatocytes
                    |
              MEIOSIS II
                    |
                   V 
            spermatids

Question 17

when spermiogenesis occurs how does the organelles in the spermatid change

Answer 17

1. nucleus of cell condense into dark hetrochromatin
   2.golgi apparatus -> acrosomal vesicle -> acrosome -> acrosomal cap
2. mitochondria assemble to form a helix in upper region of tail called middle piece
3. centriole moves to bottom of cell as the nucleus moves to the top and elongates to form the axoneme in the centre of the sperm tail
   now mature spermatozoon and leaves lumen of seminiferous tubule

Question 18

how is the primordial follicle formed in early fetal life

Answer 18

germ cells move to genital ridge from yolk sac to form primordial follicle containing oogonia

Question 19

when does formation of primordial follicle containing oogonia occur in early fetal life

Answer 19

between 4 to 8 weeks

Question 20

how does oogonia divide and what does it produce

Answer 20

divides by mitosis to produce primary oocytes

Question 21

when is there a sudden drop in the number of germ cells in fetal life

Answer 21

in the 7th month

Question 22

after the sudden drop in oogonia in fetal life what happens to the remaining oogonia

Answer 22

enter first meiotic division

meiotic prophase is initiated in the 3rd month of gestation

Question 23

at what stage do the primary oocyte stop its meiotic division and when does it restart

Answer 23

stop at diplotene stage of meiotic prophase but stops until ovarian cycle starts when puberty begins

Question 24

what does each primary oocyte produce when it undergoes oogenesis per ovarian cycle

Answer 24

completes meiosis I and produce 2 haploid cells of unequal size

Question 25

after oogenesis occurs of primary oocyte during the ovarian and produces 2 cells of uneven size what is the name and what happens

Answer 25

1. first polar body - discarded nuclear material

2. secondary oocyte - containing the yolk and most of cytoplasm

Question 26

what events following the penetration of the egg by a spermatozoan

Answer 26

second meiosis division resumes
second meiosis may or may not occur in first polar body to make 2 more polar bodies
second meiosis division always occurs in secondary oocyte to make second polar body and ovum

Question 27

layers of the secondary oocyte the spermatozoon must penetrate

Answer 27

corona radiata - from gelatinous remains of membrana granulosa from cumulus oophorus
glycoprotein layer - zona pellucida
fluid filled perivitelline space - contains first polar body
plasma membrane
ooplasm - yolky vitellus

Question 28

fertilization

Answer 28

genetic material from a haploid sperm cell and a haploid secondary oocyte merging into a single diploid cell.

Question 29

how many spermatozoa manage to reach the ampulla of the fallopian tube and how long does the journey take

Answer 29

~200

takes 4-7 hours

Question 30

how long can the spermatozoa survive upon ejaculation

Answer 30

45-48 hours

Question 31

capacitation

Answer 31

the removal of a glycoprotein coat, cholesterol, proteins from plasma membrane from head of the sperm cell membrane surface by enzymes present in the uterus

Question 32

spermatozoan capacitation results in

Answer 32

change in area of acrosomal cap so acrosome reaction is possible
hyperactivity of spermatozoon

Question 33

where does acrosome reaction occur

Answer 33

occurs in fallopian tube

Question 34

what is an acrosome reaction

Answer 34

the acrosome starts to swell and fuses with the plasma membrane of the sperm, which causes small perforations to appear in the sperm head

Question 35

what does acrosome reaction result in

Answer 35

release of hyaluronidase and a trypsin-like enzyme called acrosin;

Question 36

what facilitates fertilisation of ovum by spermatozoa

Answer 36

Acrosomal enzymes which digest a pathway

Strong tail movements by the sperm which push it onwards

Question 37

how long does the first phase fertilization last

Answer 37

10-20 mins