Spermatogenesis is the process by which male primary sperm cells develop into mature spermatozoa through stages including spermatocytogenesis, spermatidogenesis, and spermiogenesis, requiring hormonal regulation by testosterone, FSH, and LH. The process occurs in the seminiferous tubules and is sensitive to environmental factors and temperature, with mature sperm gaining motility in the epididymis. Ejaculation involves the coordinated contraction of reproductive structures to expel mature sperm, vital for male fertility.

1. SPERMATOGENESIS

2. Learning Objectives
• Define the processes of spermatogenesis and
spermiogenesis.
• Describe the stages of spermatogenesis in the seminiferous
tubule, including the roles of the sustentacular and Sertoli
cells and interstitial cells of Leydig.
• Describe hormonal regulation of spermatogenesis.

3. Spermatogenesis is the process by which male primary sperm cells
undergo meiosis and produce a number of cells calls spermatogonia, from
which the primary spermatocytes are derived. Each primary spermatocyte
divides into two secondary spermatocytes and each secondary
spermatocyte into two spermatids or young spermatozoa. These develop
into mature spermatozoa, also known as sperm cells. Thus, the primary
spermatocyte gives rise to two cells, the secondary spermatocytes, which
in turn produce four spermatozoa.
Spermatogenesis is the male version of gametogenesis and results in the
formation of spermatocytes possessing half the normal complement of
genetic material.

4. Spermatogenesis
• Haploid cells produced via spermatogenesis.
• Diploid spermatogonium in seminiferous tubules. (mitosis  2 diploid primary
spermatocytes).
• Primary spermatocyte  meiosis I  2 haploid secondary spermatocytes.
• Haploid secondary spermatocytes  meiosis II  4 haploid spermatids.
• Each spermatid grows a tail and a mitochondrial-filled midpiece,
• Chromatin is tightly packaged into an acrosome at the head.
• Maturation removes excess cellular material,
• Spermatids  inactive, sterile spermatozoa that are transported via peristalis to
the epididymus.
• The spermatozoa gain motility in the epididymus, but do not use that ability until
they are ejaculated into the vagina.
• Spermatogenesis requires optimal environmental conditions.

5. 2000 – 100,000 receptors
on each cell of target tissue
• On cell membrane 
Peptides &
catecholamine receptors
• In cytoplasm  Steroid
hormone receptors
• In nucleus  thyroid
Hormone receptors

6. Cont…….
• bind to specific receptors at the target cell
• initiates a cascade of reactions in the cell.
• Receptor proteins are inactivated / destroyed or reactivated on demand.
• different functions are elicited in different target cells
• adrenal , gonadal steroid hormones, thyroid hormones, retinoid hormones,
and vitamin D.
• Activated hormone receptor complex binds with a specific regulatory
(promoter) sequence of the DNA (hormone response element),
• activates or represses transcription of specific genes and formation of
messenger RNA (mRNA)
• May take minutes, hours, or even days after the hormone has entered the
cell due to genetic involvement.

7. • Steroid Hormones Increase Protein Synthesis, activates cells
functions.
• hormone enters cytoplasm , binds with receptor protein
• combined receptor protein–hormone diffuses into nucleus.
• Binds at specific points on DNA strands in chromosomes
• activates transcription of specific genes to form mRNA.
• mRNA diffuses into the cytoplasm
• promotes translation at ribosomes to form new proteins. E.g;,
aldosterone

10. Key Terms
• Spermatozoa: Motile sperm cell, moving form of haploid cell (male
gamete).
• Spermatocyte: Male gametocyte, from which a spermatozoon
develops.
• Axoneme: Cytoskeletal inner core structure of eukaryotic flagella.
• Spermatid: A haploid cell produced by meiosis of a spermatocyte
that develops into a spermatozoon.
• Spermatogonium: Any of the undifferentiated cells in the male
gonads that become spermatocytes.

11. Ejaculation
• Ejaculation is the forceful expulsion of semen from the male
reproductive tract.
• It involves coordinated contractions of the vas deferens,
seminal vesicles, and prostate gland.
• The urethra carries semen through the penis during
ejaculation.

12. Hormonal Control
Testosterone Produced by Leydig cells in the testes, testosterone stimulates
spermatogenesis and the development of male secondary sex
characteristics.
FSH Released by the pituitary gland, FSH is necessary for sperm
maturation.
LH (Luteinizing
Hormone)
Also produced by the pituitary gland, LH stimulates testosterone
secretion and androgen production.
Inhibin Acts as negative feedback to regulate FSH and GnRH release.

13. • Spermatogenesis is the process by which immature male
germ cells (spermatogonia) divide, undergo meiosis, and
differentiate into highly specialized haploid spermatozoa.
• Optimal spermatogenesis requires the action of both
testosterone (via androgen receptors) and Follicle-
Stimulating Hormone (FSH).
• Spermatogenesis takes place within the seminiferous tubules
of the testis.

14. Transport of Sperm
• Spermatozoa mature in the epididymis, where they gain motility and
the ability to fertilize an egg.
• During ejaculation, sperm travel through the vas deferens to mix with
seminal fluid.

15. • Spermatozoa (mature male gametes) formed.
• In testes and epididymis (approximately 64 days).
• Essential for sexual reproduction.
• Dependent upon optimal conditions to occur correctly.
• Starts at puberty ,continues till death, declines with age.

16. • of the steps of spermatocytogenesis, including type Ad spermatogonium, type Ap
Spermatogonium, type B spermatogonium, primary spermatocyte, and secondary
spermatocyte.
• Mitotic division of a diploid spermatogonium that resides in the basal
compartment of the seminiferous tubules, resulting in two diploid intermediate
cells called primary spermatocytes.
• Each primary spermatocyte then moves into the adluminal compartment of the
seminiferous tubules, duplicates its DNA, and subsequently undergoes meiosis I
to produce two haploid secondary spermatocytes.
.

17. • Secondary spermatocytes later divide into haploid spermatids. During this
division, random inclusion of either parental chromosome and
chromosomal crossover both increase the genetic variability of the gamete.
• Each cell division from a spermatogonium to a spermatid is incomplete; the
cells remain connected to one another by bridges of cytoplasm to allow
synchronous development. Not all spermatogonia divide to produce
spermatocytes; otherwise, the supply would run out. Instead, certain types
of spermatogonia divide to produce copies of themselves, thereby ensuring
a constant supply of gametogonia to fuel spermatogenesis

18. • Steps in Spermatogenesis
• Step 1: Spermatocytogenesis
• Step 2: Spermatidogenesis
• The creation of spermatids from secondary spermatocytes. Secondary
spermatocytes produced earlier rapidly enter meiosis II and divide to
produce haploid spermatids. The brevity of this stage means that
secondary spermatocytes are rarely seen in histological preparations.

19. • Step 3: Spermiogenesis
• At this stage, each spermatid begins to grow a tail and develop a
thickened midpiece where the mitochondria gather and form an
axoneme. Spermatid DNA also undergoes packaging, becoming highly
condensed. The DNA is packaged with specific nuclear basic proteins,
which are subsequently replaced with protamines during spermatid
elongation. The resultant tightly packed chromatin is transcriptionally
inactive. The Golgi apparatus surrounds the now condensed nucleus,
becoming the acrosome. One of the centrioles of the cell elongates to
become the tail of the sperm.

20. • The non-motile spermatozoa are transported to the epididymis in
testicular fluid secreted by the Sertoli cells with the aid of peristaltic
contraction. While in the epididymis, the spermatozoa gain motility
and become capable of fertilization. However, transport of the mature
spermatozoa through the remainder of the male reproductive system
is achieved via muscle contraction rather than the spermatozoon’s
recently acquired motility.

21. Physiology of Spermatogenesis
• Seminiferous Tubule
• Seminiferous Tubule: Micrograph showing seminiferous tubule with
maturing sperm.
• Maturation takes place under the influence of testosterone, which
removes the remaining unnecessary cytoplasm and organelles. The
excess cytoplasm, known as residual bodies, is phagocytosed by
surrounding Sertoli cells in the testes. The resulting spermatozoa are
now mature but lack motility, rendering them sterile. The mature
spermatozoa are released from the protective Sertoli cells into the
lumen of the seminiferous tubule in a process called spermiation.

22. • Spermatogenesis is highly sensitive to fluctuations in the environment,
particularly hormones and temperature. Seminiferous epithelium is
sensitive to elevated temperature in humans and is adversely affected by
temperatures as high as normal body temperature. Consequently, the
testes are located outside the body in a sack of skin called the scrotum. The
optimal temperature is maintained at 2 °C below body temperature in
human males. This is achieved by regulation of blood flow and positioning
towards and away from the heat of the body by the cremaster muscle and
the dartos smooth muscle in the scrotum. Dietary deficiencies (such as
vitamins B, E, and A), anabolic steroids, metals (cadmium and lead), x-ray
exposure, dioxin, alcohol, and infectious diseases will also adversely affect
the rate of spermatogenesis.

24. • Male sexual response is demonstrated by vasodilation and blood
engorgement of the penis, leading to an erection.
• The testes rise and grow larger and warmer as blood pressure rises.
• The muscles of the pelvic floor, the vesicles, and the prostrate contract,
injecting sperm into the urethra of the penis and resulting in the onset of
orgasm.
• Ejaculation continues with orgasm.
• Following orgasm, there is a gradual loss of erection and a feeling of
relaxation known as the refractory period.
• Cognitive factors involving visual stimuli and high levels of activity in the
amygdala and hypothalamus contribute to sexual arousal and sexual
response in males.

25. • erection: The physiological process by which a penis becomes engorged
with blood.
• sexual arousal: Changes that occur during or in anticipation of sexual
activity.
• refractory period: The period after excitation, during which a membrane
recovers its polarization and is not able to respond to a second stimulus.
• sex flush: Increased blood flow leading to reddening of the skin in response
to sexual arousal or orgasm.
• tumescence: The normal engorgement of the erectile tissue with blood.
• genitalia: Sex organs.

26. Sperm Physiology and Function
• In animals, most of the energy (ATP) for sperm motility is derived
from the metabolism of fructose carried in the seminal fluid. This
takes place in the mitochondria located in the sperm’s midpiece. This
energy is used for the journey through the female cervix, uterus, and
uterine tubes.
• Motile sperm cells typically move via flagella and require a water
medium in order to swim toward the egg for fertilization.These cells
cannot swim backwards due to the nature of their propulsion. The
uniflagellated sperm cells (with one flagellum) of animals are referred
to as spermatozoa.

27. • This sperm diagram indicates the acrosome, plasma membrane,
nucleus, centriole, mitochondria, terminal disc, axial filament, head,
midpiece, tail, endpiece, periacrosomal space, cell membrane,
acrosome, nuclear vacuoles, nucleus, nuclear envelope, subacrosomal
space, outer acrosome membrane, ecuatorial segment,
postacrosomal region, postacrosomal sheet, posterior ring,
connecting piece, redundant nuclear envelope, mitochondrial sheath,
outer dense fibers, central pair, and axoneme.