Sperm Cells

HOW ARE SPERM MADE?

  • Sperm are made in the seminiferous tubules of the male testes, via a process known as ‘Spermatogenesis’.
  • The main hormones that regulate spermatogenesis are Testosterone (from the testes) and FSH (from the brain’s pituitary gland).
  • In humans it takes 64 days for a sperm cell to fully develop.

STEP ONE – MITOSIS

  • Men only start making sperm when they hit puberty, but they are born with a pool of cells destined to become sperm cells.
  • At puberty, some of these cells multiply to make sure the pool doesn’t run out, and the rest develop into sperm.
  • The cells that develop into sperm also multiply as they develop.
  • The scientific name for cell multiplication is mitosis.

STEP TWO – MEIOSIS

  • As they develop, sperm cells undergo  a different type of cell division called ‘meiosis’ to halve the genetic information they contain.
  • That’s so they contain half the genetic information needed to make a baby. Female egg cells contain the other half.
  • This step is followed by a further two rounds of mitosis.

STEP THREE – SPERMIOGENESIS

  • Once a sperm cell has undergone meiosis, it changes into an oblong shape and forms a tail, or flagellum.
  • It also forms an ‘acrosome’ which is a cap on the top of the sperm full of chemicals the sperm uses to break into an egg cell.

Mature sperm can be stored in the epididymis (a long coiled tube in the scrotum) for up to two weeks before being ejaculated or broken down and reabsorbed by the body.

HOW MANY SPERM DO MEN PRODUCE?

  • Men produce 300-600 sperm per gram of testis per second!
  • That means there are between 200–500 million sperm in half a teaspoon of semen.
  • Anything under 20 million sperm in half a teaspoon of semen is considered abnormal.

 HOW DO SPERM FIND THE EGG?

  • Of the millions of sperm that are ejaculated into the vagina, most die during the journey, and only one can win the race to successfully fertilise the egg.
  • From a sperm’s point of view, the egg is miles away. It swims at about 2-4 milimetres per minute, and can sometimes manage to get there in under an hour.
  • Sperm meet the egg in one of the fallopian tubes, but how do they know which one? Well, we’re not entirely sure yet, but it looks like sperm swim towards the fallopian tubes because they’re warmer than the uterus, and the egg uses chemicals (chemo-attractants) to attract sperm.

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