Andrology lecture 11 spermatogenesis

This tutorial decribes the process of spermatogenesis in male domestic animals and is available at YouTube channel Govind Narayan Purohit

1. SPERMATOGENESIS IN MALE
ANIMALS
Prof. Dr. G.N Purohit
MVSC, PhD, MNVAS
Dean Post Graduate Studies and University Head Dept. Veterinary
(Gynecology & Obstetrics)
College of veterinary & Animal Science, RAJUVAS
Bikaner, Raj., India.
Email: [email protected]
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2. About Me : Professor G N Purohit, MVSc, Ph.D, MNVAS
Head, Department of Veterinary
Gynecology and Obstetrics, Veterinary
College, Bikaner, Rajasthan, India
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3. Todays Topic –SPERMATOGENESIS
■<Topic 1>Spermatogenesis
■<Topic 2>Spermatocytogenesis,
Spermiogenesis and Spermiation
■<Topic 3>Spermatozoa in different species
■<Topic 4>Factors affecting
spermatogenesis
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4. The male reproductive system has
often been referred to as a
“manufacturing plant,” largely
because of the continuous
production of fertile spermatozoa.
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5. Spermatogenesis
■Spermatogenesis is a finely regulated process of germ cell multiplication
and differentiation leading to the production of spermatozoa in the
seminiferous tubules(ST).
The germ cells of the ST undergo a series of cellular division and cellular
changes
■Spermatogenesis has been divided into 2 or 3 stages (Some
consider 1 & 2 together)
■(1) Spermatocytogenesis (Mitosis)
■(2) Meiosis
■(3) Spermiogenesis
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6. Spermatocytogenesisis the proliferative stage in which
primitive germ cells (spermatogonia) are multiplied by a series
of mitotic divisions to produce the primary spermatocytes.
The primary spermatocytes undergo meiotic divisions
which produce the haploid stage spermatid. The primary
spermatocyte divides meiotically (Meiosis I) into two
secondary spermatocytes; each secondary spermatocyte
divides into two equal haploid spermatids by Meiosis II
(spermatidogenesis).
Spermiogenesisis the differentiative phase in which the
nucleus and cytoplasm of spermatid undergo morphologic
changes to form the sperm cells. Metamorphosis of
spermatid into spermatozoa, is called asSpermiogenesis.
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8. SPERMATOCYTOGENESIS
Five mitotic
divisions produce
16primary
spermatocytes
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Meiosis (Primary spermatocyte to Spermatids) (Spermatidogenesis)
Two meiotic
divisions
produce 64
haploid
spermatids
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Nuclear condensation: thickening and reduction of
the nuclear size, condensation of the nuclear
contents into the smallest space
Acrosome formation: Forming a cap (acrosome)
containing enzymes that play an important role in
the penetration through the pellucid zone of the
oocyte.
Flagellum formation: generation of the sperm cell
tail.
Cytoplasmic reduction: elimination of all
unnecessary cytoplasm.
SPERMIOGENESIS (Spermateliosis) morphological conversion of round
spermatid into spermatozoa without a division
The major changes that occur during spermiogenesis
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13. Golgi granules coalesce to form acrosome
One centriole gives rise to flagellum, other
gives rise to basal plate
Nucleus moves to periphery and
chromatin condenses
Spermatid rotates so tail sticks out into
lumen
Mitochondria congregate around
flagellum and become localized in mid-
piece
Most of cytoplasmic mass is engulfed by
Sertoli cells when spermatozoa are
released into lumen of seminiferous
tubule, small amount remains at neck
(proximal cytoplasmic droplet)
Proximal droplet moves to distal end of
mid-piece during epididymal passage
Distal droplet is lost during storage in the
epididymis or during ejaculation
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19. SPERMIATION
Release of mature
elongated spermatozoa
into lumen of the
seminiferous tubules is
known as spermiation.
The elongated spermatids,
which are oriented
perpendicularly to the
tubular wall are gradually
extruded into the lumen of
the tubule.
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21. Sperm Maturation
Epididymis
Maturation and storage of sperm
Head
Not motile -swim in circular motion
Not fertile
Proximal droplet
Low disulfide linkage
Fluid absorption
Body
First see some forward motility in body
Some fertility
Droplet moving down
More disulfide linkage
Tail
Normal motility
Fertile
Distal droplet
Hiighdisulfide linkage
Transport takes 9-13 d depending on
species
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22. DURATION OF SPERMATOGENESIS
■Entire spermatogenesis takes about 50-60
days in boars, 60-70 days in bull and ram.
■The daily sperm production would depend
on the age of the bull, breed and many other
factors and can range from 3 billion to 6
billion sperms per day.
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23. Spermatogenic cycle and wave.
A spermatogenic cycle is defined as the time it takes
for the reappearance of the same stage of
spermatogenesis within a given segment of the tubule
(Observed in cross sections). Each stage of the cycle
follows in an orderly sequence along the length of the
seminiferous tubule.
The spermatogenic wave is a sequence of segments
showing the complete series of cell associations
corresponding to the stages of the cycle of the
seminiferous epithelium.
Or in other words the distance between the same
stage is called the spermatogenic wave. One tubule can
contain numerous complete waves. Adjacent segments
of the tubule evidently communicate in some unknown
manner.
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24. These cycles of spermatogenesis are
essential for continuous sperm production
The wave is to space what the cycle is to time
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25. The number of stages
within a spermatogenic
cycle and the number of
cycles required for the
completion of
spermatogenesis varies
between species. There
are 12 different stages of
the cycle in the bull of
about 14 days each;
approximately four cycles
within a given region of
the tubule occur before
an A1 spermatogonia is
transformed into a
spermatozoa.
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26. The consistency of these cellular associations results
from two phenomena:
(i)At one point of the tubule, new spermatogonia begin
their divisions and engage in spermatogenesis at
time intervals of constant duration.
(ii) Once the germinal cells are involved in
spermatogenesis, their rate of differentiation
is always the same and each step has a fixed
and constant duration.
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33. Seminiferous tubules Rete testis Caput Epididymis
Corpus Epididymis
CaudaEpididymis
(Sperms Stored here)
Sperm Transport
Vas Deferens
Mating
Secretions of Accessory glands
Ejaculation
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34. The production of spermatozoa does not cease in sexually inactive males.
The two most likely ways of disposal of surplus spermatozoa are
i)that they are voided in the urine or
ii)that that they are resorbed in the epididymis or vas deferens.
It has been hypothesized that, in the normal
androgen-maintained epididymis, degradative
pathways are present in the luminal fluid that
are constitutively inhibited by survival signals
emanating from the epithelium.
Fate of unejaculated spermatozoa
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35. Hormonal Regulation of spermatogenesis
Hormonal effects on sperm cells are not direct, but are mediated through Sertoli cells.
Estradiol and DHT are also involved in the spermatogenic process.
FSH controls the secretory activity of Sertoli cells and is responsible for
the synthesis of androgen binding protein that binds the androgen
protein and stabilizes the concentration of testosterone.
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36. Sertoli cells have receptors for
follicle stimulating hormone (FSH)
and testosterone which are the
main hormonal regulators of
spermatogenesis. Hormones such
as testosterone, FSH and
luteinizing hormone (LH) are
known to influence the germ cell
fate. Their removal induces germ
cell apoptosis
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37. Sertoli cells convert testosterone to Dihydro-testosterone
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38. Spermatocytogenesis is
completely arrested at
the primary
spermatocyte stage in
hypophysectomized
animals
Meiosis II is hormonally-independent
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39. Physical factors-
Irradiation,
Hyperthermia,
Photoperiod in
seasonal animals
Chemical factors-Cadmium
salts, Alkylating agents,
diamines, hydroxyurea, DDT,
diethyslibesterol, environmental
pollutants etc.
Nutritional factors-Low or
High plane of nutrition,
Vitamin A deficiency
Hormonal factors-
Exogenous steroids, stress
FACTORS AFFECTING SPERMATOGENESIS
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40. Genetic factors-hereditary conditions such as
testicular hypoplasia, freemartin, inbreeding and
hybridization
Pathological factors-
Cryptorchid, testicular
degeneration, fibrosis,
scrotal or inguinal hernia
etc.
Age factors-Bulls can
remain in service until they
are 10 or 12 years of age.
However, this is not the
norm and usually remain in
the herd for 4 to 5 years.
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41. Re-cap –What we learned
■Spermatogenesis involves three phases namely spermatocytogenesis, meiosis and spermiogenesis
■Spermatocytogenesis involves activation of spermatogonia and mitotic division to yield 16 primary
spermatocytes.
■The primary spermatocytes undergo 2 meiotic division to yield 64 spermatids
■In spermiogenesisthe spermatids undergo morphogenicchanges without further division to form
spermatozoa.
■Spermiogenesis involves 4 phases the Golgi phase, Cap phase, Acrosomal phase and maturation phase
during which there is nuclear condensation, acrosomal and flagellarformation and cytoplasmic
reduction,
■Spermiation is the release of mature sperm from Seminiferous
tubules in to the lumen.
■The spermatozoa mature in the epididymis and stored in the tail of epididymis.
■Factors that affect spermatogenesis include age, nutrition,
genetics and pathological factors
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42. Contact me
Prof. Dr. G.N Purohit
MVSC, PhD, MNVAS
Head Dept. Veterinary (Gynecology & Obstetrics)
College of veterinary & Animal Science, Bikaner, Raj.India.
Email:[email protected]
Linked in :linkedin.com/in/dr-govind-narayan-purohit-13a04a17
YouTube Channel link : https://www.youtube.com/user
/gnpobs61/videos
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