Spermatogenesis and oogenesis

1. By:
Rani I. Gurudasani
M.Pharm (Pharmacology)

2.  Spermatogenesis occurs in the seminiferous tubules that form the bulk of each
testis.
 The process begins at puberty, and continue constantly throughout a man’s
life.
 One production cycle, from spermatogonia to sperm, takes approximately 64
days.
 The process of spermatogenesis begins with mitosis of the diploid
spermatogonia (germ cells)

3. There are three phases of spermatogenesis:
(1) Spermatocytogenesis (Mitosis),
(2) Meiosis, and
(3) Spermiogenesis.

5. 1. Spermatocytogenesis (Mitosis):
Germ cells (spermatogonium) divide mitotically
to replace themselves and to produce cells that
begin differentiation. (As shown in fig.)

6. 2. Meiosis:
 Cells in prophase of the first meiotic division are primary
spermatocytes.
 Primary spermatocytes go through the first meiotic division and
become secondary spermatocytes.
 The cells quickly proceed through this stage and complete the
second meiotic division
 Meiosis is the process by which the diploid number of
chromosomes present in spermatogonia (the germ cells) is
reduced to the haploid number present in mature
spermatozoa.
 The products of the second meiotic division are
called spermatids.

7. 3. Spermiogenesis:

This is the metamorphosis of spherical spermatids into
elongated spermatozoa. No further mitosis or meiosis
occurs.
 During spermiogenesis, the acrosome forms, the flagellar
apparatus forms, and most excess cytoplasm (the residual
body) is separated and left in the Sertoli cell.
 Spermatozoa are released into the lumen of the
seminiferous tubule

8. Role of sertoli cell in spermatogenesis:
 Sertoli cells secrete signaling molecules that promote sperm
production.
 Sertoli cell has also been called the "mother" or "nurse" cell.
 Sertoli cells form blood–testis barrier.
 Sertoli cells provide factors necessary for the successful progression of
spermatogonia (germ cells) into spermatozoa (sperm).
 Helps in development and maturation of sperm cells.
 Provide protection to germ cells.
 Sertoli cells have receptors for follicle stimulating hormone (FSH) and
testosterone which are the main hormonal regulators of
spermatogenesis.

9. Hormones involve in spermatogenesis:
 Hormones such as testosterone, FSH and luteinizing
hormone (LH) are known to influence the germ cell fate.
 FSH, by its ability to stimulate Sertoli cell mitosis during
testicular development, can influence the spermatogenic
capacity of the adult testis.
 Both FSH and testosterone exert synergistic actions on
germ cells, but Testosteron has a specific action on the
later stages of spermatid maturation.

10.  Gametogenesis in females is called oogenesis.
 The process begins with the ovarian stem cells, or
oogonia
 Oogonia are formed during fetal development,
and divide via mitosis

12. Steps of oogenesis
1. Oogonia are formed during fetal development, and
divide via mitosis
2. oogonia produce primary oocytes in the fetal ovary
prior to birth.
3. These primary oocytes are then arrested in this stage
of meiosis I
4. Meiosis-I resumes at puberty and continuing until the
woman is near menopause.
5. After Meiosis-I, two cells are produce Secondary
oocyte and first polar body.

13. Steps cont…
6. This cell division does not result in two identical cells. Instead, the
cytoplasm is divided unequally, and one daughter cell is much larger
than the other.
7. This larger cell (the secondary oocyte), eventually leaves the ovary
during ovulation.
8. If fertilization occurs, then Meiosis of a secondary oocyte is
completed. ie Meiosis II then resumes, producing one haploid ovum
that fertilization by a (haploid) sperm and produce diploid (two cell)
zygote.
9. If fertilization does not occur, the secondary oocyte fails to complete
the 2nd meiotic division, and degenerates in about 24 hours after
ovulation

15. Follicular Development

16. Follicular development (stepwise)
1. Each primary oocyte is surrounded by follicular cells and
is called as Primordial follicle.
2. At puberty, the primordial follicle start growing under
influence of FSH and LH and developed into primary
follicle.
3. As the primary follicle grow, the follicular cell
surrounding to primary oocyte start growing, and that
newly growing cells are called as granulosa cells.
4. The glycoprotein layer is start developing between
granulosa cell and primary oocyte that layer is called as
zona pellucida.

17. Steps Cont…
5. As the follicle grow, the theca cells (also called as theca externa) are
developed that encircle the granulosa cells. At this stage granulosa
cells start secreting follicular fluid which develop the cavity called as
antrum.
6. When antrum is developed in follicle, the follicle is termed as
secondary follicle.
7. Theca cells work with the granulosa cells to produce estrogens.
8. Follicles in which the antrum has become large and fully formed are
considered tertiary follicles
9. Once the follicle is mature, it ruptures and releases the oocyte. Cells
remaining in the follicle then develop into the corpus luteum.