Sperm!
|
|
The doctor gave the man a jar and said, "Take this jar home and bring me back a semen sample tomorrow."
The next day the seventy-five-year old man reappeared at the doctor's office and gave him the jar, which was as clean and empty as he had received it on the previous day.
"Where's the sample?" said the Doctor.
"Well, doctor, it's like this," the man explained. "First I tried with my right hand, but that didn't work. Then I tried with my left hand, but still nothing. Then I asked my wife for help. She tried with her right hand, then her left, still no joy. She even tried with her mouth, first with the teeth in, then with her teeth out, and still nothing."
"I see.." said the Doctor dubiously. "Then what did you do?"
"Well, I asked my sixteen year old neice to lend a hand, but she failed too, even when she took it between her legs and squeezed it really hard."
"Her legs!" exclaimed the doctor, appalled.
"So I went next door to Eileen, and she tried too, first with both hands, then both armpits in turn and she even tried rolling it between her knees, but still nothing.
"You asked your neighbour?" cried the shocked doctor.
"The old man replied, "Yes, but no matter what we tried we still couldn't get the damn jar open!"
Sperm
Different types of sperm cells: A) spermatozoon (motile), B) spermatium (non-motile), C) fertilization tube with sperm nucleiThe term sperm is derived from the Greek word spermos (meaning "seed") and refers to the male reproductive cells. Sperm cells are the smaller gametes involved in fertilization in anisogamy and oogamy. In these types of sexual reproduction, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. A uniflagellar sperm cell that is motile is also referred to as spermatozoon, whereas a non-motile sperm cell is referred to as spermatium. Sperm cells cannot divide and have a limited life span, but they can fuse with egg cells during fertilization to form a totipotent zygote with the potential to develop into a new organism. Sperm can live for up to 3 days inside the female unless it is exposed to air or is mixed with another liquid.The spermatozoa of animals are produced through spermatogenesis inside the male gonads (testicles) through meiosis. Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) through mitosis. In flowering plants, sperm nuclei are produced inside pollen.
Motile sperm cells
Motile sperm cells of algae and seedless plants. Motile sperm cells typically move via flagella and require water in order to swim toward the egg for fertilization. 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).
In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.
Non-motile sperm cells
Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in a spermatangium.Because spermatia cannot swim, they depend on their environment to carry them to the egg cell. Some red algae, such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.
Fungal spermatia (also called pycnidiospores) 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 with 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.In some protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.
Sperm quality
A study by the University of California has suggested that folate may protect sperm cells from aneuploidy.Sperm Market
In the western world, sperm banks sell human sperm samples to licenced doctors to perform artificial insemination or research. The price is around $300 in the US and less in Europe. On the global market, Denmark has a well developed system of sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality and, in contrast with the law in the other Nordic countries, gives donors the choice to remain anonymous to the receiving couple. More than 50 countries worldwide are importers, including Paraguay, the US, Kenya and Hong Kong.
