Sperm are tiny male sex cells that carry half of the chromosomes needed in all other normal cells, and as humans each of our cells have 46 chromosomes; 23 of them come from the mother’s egg and the other 23 are from a sperm, and when these join and fuse during fertilization a new life begins. The word ‘sperm’ is from the Greek ‘sperma’ for ‘seed’ and the medical term ‘spermatozoon’ simply means a moving sperm.
Sperm are the smallest of all human cells and they have three parts to them: a head, a midpiece and a tail.
- The tip of the head is called the acrosome and this contains enzymes that break down the outer layer of the egg (which is essential for the sperm to fuse with the egg), the rest of the head contains the nucleus with the DNA on 23 chromosomes
- The midpiece is wrapped with mitochondria, and these provide the energy to the tail for the journey through the uterus and fallopian tubes
- The tail lashes from side to side to push the sperm forward
Sperm production starts at puberty, from which point it’s normally a continual process that takes about three months that typically produces around 200 to 300 million sperm a day. There are lots of cases of men fathering children in their 70’s and 80’s, and the oldest authenticated father was a man of 94!i However not all men can father children in their later years, and sperm production significantly reduces after the age of 60.
Sperm are produced in two stages:
- The initial stage (in the testes) takes about 74 days and this is when the head is formed
- The second stage (in the epididymis) is when the tail develops, the sperm reach full maturity, and this takes a further 16 to 20 days
When sperm are fully mature they’re called spermatozoons, and after they’re ejaculated the contact with the woman’s fertile mucus activates them and ‘triggers’ them to swim like tadpoles, but just how long they survive after sex depends on the pH in the vagina. During a woman’s fertile phase her vagina has an alkaline environment, and once sperm make it into the uterus and fallopian tubes they can survive for up to 5 days. However outside the fertile phase the vaginal environment becomes acidic, which makes sperm clump together like frog spawn and they’ll only survive for about two hours.
For the woman the advantage of the acidity when she’s not able to conceive is it’s antibacterial and prevents unwanted infections. Leading up to ovulation the cervix produces increasingly ‘sperm friendly’ alkaline mucus, which is why checking cervical mucus is a good way to predict a woman’s ‘fertile window’, as explained in optimising fertility.
- Sperm are the smallest of all human cells and are continuously produced in an 80 to 90 day cycle.
- For healthy sperm the testes need to be 0.5°C (1°F) lower than the rest of body
- Exposure to toxins will reduce a man’s fertility about 3 months later
- The quality and quantity of sperm are reduced by cigarettes, alcohol, heat, cycling, tight clothing, motorbikes, drugs and caffeine
- Usually two and five ml of seminal fluid are released at ejaculation, each containing around 40 million sperm
- It takes about 40 sperm to break down the “shell” of tissue that surrounds the egg
- Sperm survive for 3-5 days or even longer when there’s fertile mucus
- During the infertile phase of a woman‘s cycle a mucus plug blocks the cervix and sperm die in 2 to 4 hours in the acidic environment (pH 4–5 compared to the sperm pH of 7.2–8.0)
- ‘Azoospermia’ (a semen sample with no sperm) affects about 1% of the male populationii and may affect up to 20% of men in male infertility situationsiii, and although azoospermia is associated with very low fertility (or even sterility), there’s hope as many forms of azoospermia respond well to both Western and Chinese medical treatment