3. “HEALTHY SPERM” CONCEPT
"Healthy spermatozoa," or "viable
spermatozoa," should possess certain
abilities (Krawetz, 2005):
Reach the fertilization site.
Bind to and fertilize the oocytes (egg
cells).
Contribute to the initiation of early
embryo development.
CONCEPT OF HEALTHY VIABLE SPERM: MALE FERTILITY
POTENTIAL RELIES ON STRUCTURAL, MORPHO-FUNCTIONAL,
AND INTRINSIC SPERM FEATURES THAT SHAPE EQUALLY THE
CONCEPT OF VIABLE SPERM
4. SPERM MORPHOLOGY
Mature spermatozoon consists of two principal parts: head
and tail.
Head- acrosome and nucleus
The tail comprises four components: (Phillips, 1975).
• Neck- proximal centriole
• Midpiece- mitochondria, outer dense fibers (ODF) and
axoneme
• Principal piece- fibrous sheath and axoneme
• Terminal piece.
Continuous Plasma Membrane: Both the head and tail of the
spermatozoon are enclosed in a continuous plasma
membrane, similar to other living cells.
5. THE HEAD
Sperm Head Composition:
Contains limited cytoplasm, highly condensed DNA, and a well-defined acrosome.
Loss of cytoplasm occurs during spermiogenesis, the final steps of spermatogenesis (Gadea et al., 2013).
The remaining cytoplasm, known as the cytoplasmic droplet, is lost during sperm transit through the epididymis.
Genome Condensation:
During spermiogenesis, histones are sequentially
replaced by transitional proteins and then by
protamines (convey the hyper condensation of the
nucleus assisting sperm motility) within sperm
chromatin (Zini and Agarwal, 2011; Gadea et al.,
2013).
This process triggers genome condensation,
ensuring stability and protection of the genetic
material.
6. Acrosome Function:
Located at the top of the head, the acrosome contains specific enzymes with various functions:
Exposure of acrosome zona pellucida binding proteins during sperm capacitation.
Facilitation of sperm's ability to cross cumulus cells surrounding the oocytes.
Mediation of sperm binding to the zona pellucida and acrosome reaction.
Migration of IZUMO1 protein to ensure binding to the JUNO receptor on the oocyte (Satouh et al., 2012;
Bianchi et al., 2014).
Role in Fertilization:
Acrosome-reacted sperm retain the ability to penetrate the zona pellucida.
The role of enzymes released during the acrosome reaction in digesting the zona pellucida has been
revisited in different species, challenging previous paradigms.
7. Comprises the neck, midpiece, principal piece, and terminal piece.
1. Neck:
Neck- present between head and the middle piece.
Morphologically distinct from the head and the rest of the tail.
Contains two Centrioles, proximal (1st zygotic cleavage) and distal (forms axial
filament/tail-motility).
Two or three mitochondria present, establishing a close relationship with the Centrioles.
2. Middle Piece:
Located between the neck and the annulus- site of METABOLIC ACTIVITIES.
SPIRAL MITOCHONDRIA, providing energy (ATP) for sperm motility (22-75 in nos.)
ANNULUS at the junction of middle piece and principal piece, possibly preventing
displacement of mitochondria.
MANCHETTEE- thin sheet of cytoplasm mainly composed of microtubules at the
periphery of mid piece.
THE TAIL
Axoneme Structure:
Axoneme- Internal structure
along the entire flagellum.
Composed of nine
peripheral doublets and two
central single microtubules (9
+ 2 structure).
Integrated by the
intraflagellar transport (IFT)
system.
8. 3. Principal Piece:
Surrounded by a fibrous sheath composed of circumferentially oriented ribs and longitudinal columns.
Longitudinal columns composed of subunits attached to the axoneme, independent of the plasma membrane.
Gradual reduction in size of longitudinal columns towards the end of the piece.
4. End Piece:
Consists of central pair of axial fibrils and ring of nine doublet fibers, surrounded by the plasma membrane.
Retains the 9+2 pattern of axial filament complex, but arrangement of fibers changes towards the tip.
Successive termination of subfibers suggests progressive end of the tail structure.
CROSS SECTION OF MIDPIECE AND
PRINCIPAL PIECE
9.
10. WHAT IS CONSIDERED AS AN IDEAL SPERMATOZOAN
MORPHOLOGY?
• WHO (1999)- Oval shaped head
• 4.0-5.0 µm long and 2.5-3.5 µm wide.
• Acrosome- 40-70% of head area
• Length:width ratio of head- 1.50-1.75
• Symmetrical insertion of sperm tail- at the fossa
in base of head
• Broad head base (not arrow like)
• Tail length ~ 45 µm long, no coiling, nicked or
bent
• Midpiece- thickness ~ 1 µm; length ~ 7-8 µm long
• All borderline cases classifies- defective as per
‘Kruger Strict Criteria’
11. WHAT IF THE SPERM DOES NOT HAVE NORMAL
MORPHOLOGY?
The condition is called TERATOZOOSPERMIA.
Teratozoospermia is the medical term used to refer to abnormal sperm morphology, caused by either defects in the
head, midpiece, and/or tail.
MORPHOLOGY CRITERIA
Two types: World Health Organization guidelines (third edition) and
the Kruger strict criteria.
Kruger Strict Criteria:
Developed by Thinus Kruger in 1986.
Assumed sperm reaching upper endocervical canal post intercourse
had superior functional capacity.
Initially 15% for "normal" morphology; now 8-4%.
12. World Health Organization (WHO) Guidelines:
Since 1980, WHO has issued guidelines for "normal" semen morphologies.
Criteria for "normal" has become progressively more rigorous over time.
WHO Editions & Normal Morphology Range
1st Edition (1980): 80.5%.
2nd Edition (1987): 50%.
3rd Edition (1992): 30%.
4th Edition (1999): 14%.
5th Edition (2010): 4%.
Clinical Utility
WHO 5th edition deemed most relevant to fertility outcomes.
Some labs still use WHO 3rd edition (normal ≤ 30%), but its relevance in determining fertility potential is
questioned.
15. Fertility Assessment
Predicting Fertility Potential
Diagnostic Tool for Male Infertility
Guiding Treatment Strategies
Optimizing Assisted Reproductive Technologies (ART)
IMPORTANCE OF UNDERSTANDING SPERM
MORPHOLOGY
16. Semen consists of spermatozoa suspended in a fluid medium called SEMINAL PLASMA. (60-70% seminal
plasma; 30% sperms)
FUNCTIONS-
1. serves as a vehicle for transporting ejaculated spermatozoa from testis to oocyte.
2. provides protection and nutrition to the spermatozoa during their onward movement in the female
reproductive tract.
3. Seminal fluid contact during conception activates endometrial gene expression and immune cell changes.
4. This activation is crucial for robust implantation of the embryo.
5. It influences the quality of the pregnancy and the health of the offspring.
SEMINAL PLASMA
17.
18. EPIDIDYMAL SECRETION
Secretes Immobilin, a large glycoprotein. It immobilizes the sperm until ejaculation
Epididymosomes are extracellular micro vesicles found in the epididymal fluid. They are a type of exosome
released by the epididymal epithelium. They contain proteins, RNAs, and other metabolites, and are thought
to influence sperm function and embryonic development
Carnitine, concentrated from the blood by the epididymis, is also found in seminal plasma. This chemical is
involved in the metabolism of fatty acids, with the metabolites being used as another nutrient source for the
sperm.
Secretes Glycerylphosphocholine, HLA-G, CD52g, GPX5, ECM1, MIF, P34H, SPAM1, alpha-Glucosidase
19. SEMINAL VESICLE SECRETION
Secretion:
about 60-70% of the seminal plasma volume
constitutes the bulk of the seminal fluid (semen)
thick fluid yellowish secretion that contains the sugar fructose, proteins, vitamin c, protein kinase, citric acid,
inorganic phosphorus, potassium, and prostaglandins.
Functions:
Fructose provides an energy source for sperm motility and metabolism.
Alkaline pH helps neutralize the acidic environment of the male urethra and female reproductive tract, enhancing
sperm survival.
Prostaglandins promote smooth muscle contractions in the female reproductive tract, aiding in sperm transport.
Semenogelin- coagulation and subsequent liquefaction of semen after ejaculation.
20. HOW SEMENOGELIN WORKS?
Two types of semenogelins- SGI and SGII
Zinc ions- released from the prostate
their concentration in humans is ∼2 mM (Arver, 1982; Arver and Sjoberg, 1982), i.e. zinc ion concentration is ∼100 times higher than that in
blood plasma
1. Coagulation:
Zn+2- high binding affinity to SGs
A coagulum is formed by the binding of SGs with zinc ions from the prostate.
The coagulum is elastic, so the sperm are unable to move due to the pressure from the surrounding SGs-Zn complex.
2. Liquifaction:
Mediated by PSA (Prostate-specific antigen)
Inactive pro form in prostate- activated through the action of KLK2
Zinc ions have a strong inhibitory effect on the activity of PSA
On ejaculation, semen is exposed to the acidic pH of the vagina, due to the presence of lactic acid. In fertile couples, the final vaginal pH
after coitus approaches the 6-7 levels, which coincides well with reduced zinc inhibition of PSA. At these pH levels, the reduced PSA activity
is countered by a decrease in zinc inhibition. Thus, the coagulum is slowly liquefied, releasing the sperm in a well-regulated manner.
PSA cleaves the cross-links between proteins, breaking down the gel and leading to the release of entrapped sperm and seminal fluid
components.
21. PROSTATE SECRETION
Prostate gland- 20-30% of the seminal plasma secretion
The secretions of the prostate are thin, milky colored and acidic.
They function to enhance the motility of the sperm.
Prostate specific antigen (PSA/KLK3), a glycoprotein produced by the prostate gland; involved in the
liquefaction of seminal fluid
It is composed of several protein-splitting enzymes; fibrolysin, an enzyme that reduces blood and tissue
fibres
Citric acid and acid phosphatase, which help to increase the acidity; and other constituents, including ions
and compounds of sodium, calcium, and potassium.
Zinc is one of the most important compound of seminal fluid contributed by prostate gland, Zinc in seminal
plasma stabilizes the cell membrane and nuclear chromatin of spermatozoa.
22. BULBOURETHRAL GLAND
SECRETION
• Bulbourethral gland Contribute about 1% of seminal plasma.
• In response to sexual stimulation, the bulbourethral glands secrete an alkaline mucus-like fluid.
• This fluid neutralizes the acidity of the urine residue in the urethra, helps to neutralize the acidity
of the vagina, and provides lubrication during intercourse.
