The term sperm is derived from the Greek word (σπέρμα) sperma (meaning "seed") and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, whereas a non-motile sperm cell is referred to as a spermatium. Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a new organism begins developing, starting as a totipotent zygote.
The spermatozoa of animals are produced through spermatogenesis inside the male gonads (testicles) via meiotic division. They are carried out of the male body in a fluid known as semen. Mammalian sperm cells can survive within the female reproductive tract for more than 5 days post coitus.
Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) via mitotic division. In flowering plants, sperm nuclei are produced inside pollen.
Etymology
The term "sperm" probably comes from
sperma which in Greek is "seed" or Latin "something sown". Other terms for sperm include "prostatic fluid" and "seminal fluid" and "seed".
Origin
Sperm originates solely from the
testicles, and this is where sperm develop. The initial
spermatozoon process takes around 70 days to complete. The
spermatid stage is where the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when its called a
spermatozoan.
Subsequently, the semen wherein the sperm is carried is produced in the seminal vesicles, prostate gland and urethral glands.
Anatomy
The sperm cell consists of a head, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. The midpiece has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus and uterine tubes. The tail or "flagellum" executes the lashing movements that propel the spermatocyte.
During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centrosome, which is responsible for maintaining the microtubule system.
Motile sperm cells
Motile sperm cells typically move via flagella and require water 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) produced in most animals are referred to as spermatozoa, and are known to vary in size.
Motile sperm are also produced by many protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes, they are multi-flagellated (carrying more than one flagellum).
Non-motile sperm cells
Non-motile sperm cells called
spermatia lack flagella and therefore cannot swim. Spermatia are produced in a
spermatangium.
Fungal spermatia (also called pycniospores, especially in the Uredinales) may be confused with conidia. Conidia are spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.
Sperm nuclei
In many
land plants, including most gymnosperms and all
angiosperms, the male
gametophytes (
pollen grains) are the primary mode of
dispersal, for example via wind or insect
pollination, eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the
stigma of a receptive flower, it germinates and starts growing a
pollen tube through the
carpel. Before the tube reaches the
ovule, the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei which are then discharged through the tube into the
ovule for fertilization. (see
paternal age effect).
Market for human sperm
On the global market,
Denmark has a well-developed system of human sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high
quality Furthermore, Nordic sperm donors tend to be tall and highly educated and have altruistic motives for their donations, The
prevalence of mad cow disease is one in a million, probably less for donors. If prevalence was the case, the infectious proteins would then have to cross the
blood-testis barrier to make transmission possible.
History
Sperm were first observed in 1677 by
Antonie van Leeuwenhoek using a
microscope, he described them as being
animalcules (little animals), probably due to his belief in
preformationism, which thought that each sperm contained a fully formed but small human.
Forensic Analysis
Ejaculated fluids are detected by
ultraviolet light, irrespective of the structure or colour of the surface. Sperm heads, e.g. from vaginal swabs, are still detected by
microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining
.
See also
Ejaculation
Female sperm
Female sperm storage
Polyspermy
Semen
Sperm competition
Sperm donation
Spermatogenesis
Spermatozoon
References
External links
The Great Sperm Race pdf
Human Sperm Under A Microscope
Category:Fertility
Category:Germ cells
Category:Male reproductive system
Category:Reproduction
Category:Semen
