Bio-Insights- Sperms

Structure of Spermatozoon

A morphologically normal sperm cell is about 40-50 µm in length and consists of a head and tail. [2]

Head: It mainly consists of nucleus and acrosome. Sperm head performs two functions- genetic and activation. The genetic function is embodied in the sperm nucleus which consists of DNA and nuclear proteins and thus is responsible for the transmission of hereditary characters from the male. The major part of the sperm head is occupied by the nucleus about 65%, which determines the sperm head shape. The sperm head anterior end is covered by a cap-like structure called acrosome. The acrosome is represented by Golgi complex and it contains a number of hydrolytic enzymes, such as hyaluronidase and acrosin, which are required for fertilization. During fertilization, the acrosomal membrane fuses with the oocyte cytoplasmic membrane and followed by acrosomal reaction, an event where the acrosomal enzyme is released from the head tip. Sperm head measures between 4.0-5.5 µm in length and 2.5-3.5 µm in width. [1 and 2]

Structure of a Sperm

Neck: It is a short, slightly constricted segment made up of projections located between the head and the tail portion. Neck differs clearly from the head and also from the rest part of the tail. [1 and 2]

Tail: The tail measures 40-50 µm in length and provides motility for the cell. Sperm cell’s entire motility apparatus is contained in the tail. The tail can be divided into the mid-piece (anterior portion), principle piece, and end-piece (posterior portion). Mid-piece supports the head at exactly the center position. The mid-piece consists of tightly packed mitochondria surrounded by a sheath. The mitochondria in the mid-piece supply energy in the form of ATP for tail movement. The principle piece is the longest part of the tail and comprises most of the propellant machinery. Motility plays the main role in sperm transport through the cervix. [2]

Abnormal Sperm Morphology

Teratospermia is a condition characterized by the presence of sperm with an abnormal morphology that affects fertility in males. Normal sperm exhibits an oval-shaped head with a regular outline and a cap (acrosome) covering more than one-third of the head surface. The mid-piece is slender, less than one-third of the width of the head, straight and regular in outline. The tail is slender, uncoiled and should present a regular outline. Abnormal sperm morphology is classified as a defect in the head, midpiece or tail of the sperm.

Sperm Head Abnormalities

Head defects include large, small, tapered, pyriform, round, amorphous heads, heads with a small cap area and double heads, as well as any combination of these. Globozoospermia, where the sperm head appears small and round due to the failure of the acrosome to develop is one of the examples of a head defect.

Mid-piece defects include “bent” neck (where the neck and tail form an angle greater than 90% to the long axis of the head), thick/irregular mid-piece, abnormal thin mid-piece, as well as any combination of these.

Sperm Tail Abnormalities

Tail defects Include short, multiple, hairpin, broken or bent (>90⁰) tails, tails of irregular width, coiled tails, as well as any combination of these.

Sperm Defect	Possible related observations	Possible associated functional anomaly
Elongated head	Abnormally shaped head and abnormally condensed chromatin	Immature chromatin/fragmented DNA/increased aneuploidy
Thin head	Abnormally shaped head and abnormally condensed chromatin	Immature chromatin/fragmented DNA
Microcephalous head	Excessive shrinkage of the nucleus and abnormally condensed chromatin	Immature chromatin/fragmented DNA
Macrocephalous head	Insufficient shrinkage of the nucleus and abnormally condensed chromatin	Increased aneuploidy
Multiple heads	Two or more closed or dissociated heads with or without a common acrosome or midpiece	Handicaps migration through mucus and oocyte vestments/fragmented DNA
Abnormal acrosome region	Absent or abnormally shaped or sized acrosome, incomplete acrosome and/or abnormal appearance of the underlying nucleus	Abnormal acrosome reaction/fragmented DNA
Thin midpiece	Partial/absent mitochondrial sheath	No or reduced ATP available for cell propelling
Bent tail	Misaligned midpiece and head or sharply bent midpiece/tail	Impairment of syngamy and cleavage, abnormal cell propelling, handicaps migration through mucus and oocyte vestments
Absent tail	Various anomalies of the neck region	Fragility of the neck structure and sperm moving forward is not possible
Short tail	Abnormally shaped periaxonemal and sometimes axonemal structures/dysplasia of the fibrous sheath	Immotility or severe dyskinesia
Irregularly shaped tail	Abnormally shaped periaxoneamal and sometimes axonemal structures/dysplasia of the fibrous sheath	Abnormal motion
Coiled tail	Completely or partially coiled tail often within a huge cytoplasmic remnant	Sperm moving forward is not possible
Multiple tails more than one tail	Partially dissociated tails connected to a single or to multiple heads or tails knitted together over a variable length	Abnormal motion: handicaps migration through mucus oocyte vestments

Semen Analysis

This is an evaluation of a certain characteristic of male’s semen and the sperm. This helps in evaluating male fertility

Color: Normally semen appears in whitish-gray in color. As the man ages, it appears as a yellowish tint. Presence of blood in semen (hematospermia) a rare condition which results in brownish or red color ejaculate. Deep yellow or greenish color appearance of semen is due to medication. Other causes of unusual semen color are due to STI’s, genital surgery and injury to male sex organs.
Volume: Semen volumes between 2.0 ml and 5.0 ml are considered to be normal. WHO regards 1.5 ml as the lower reference limit.
pH: According to WHO the normal semen pH is in the range of 7.2-8.2. An acidic pH ejaculate indicates one or both of the seminal vesicles are blocked. A basic pH ejaculate indicates an infection. pH value outside of the normal range is harmful to sperm and affects their ability to penetrate the egg.
Viscosity: It measures seminal fluid’s resistance to flow. High viscosity may interfere with the determination of sperm motility, concentration and antibody of spermatozoa. Normally semen coagulates upon ejaculation and usually liquefies within 15-20 min. Liquefaction time within 60 min is considered as the normal range.
Motility: The efficient passage of spermatozoa through the cervical mucus is dependent on rapid progressive motility, that is, spermatozoa with a forward progression of at least 25 µm/s. Reduced sperm motility can be a symptom of a disorder related to male accessory sex gland secretion.

>Rapid progressive motility- Moves at >25 µm/s at 37⁰C and >20 µm/s at 20⁰C

>Non-progressive motility- Move at <5 µm/s

>Immotility

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