Every second, the average man produces 1,500 sperm adding up to over 500 billion over the course of his life. The machinery that makes sperm is a marvel of biology with a single goal in mind – creating life. This article explores the micro world of sperm production and the key factors that affect proper sperm development.
Meet the Sperm
A wonder in its own right, the sperm cells is the single densest cell in the male body. It is lean and mean with all systems focused on optimizing its ability to swim to and fertilize the egg. The sperm cell is only in 0.05mm long (about 2 thousandths of an inch) but has to swim over 152 mm (around 6 inches) from the base of the woman’s cervix to the fallopian tube where it will fertilize the egg. If scaled to human size, this is a distance of almost 3 1/2 miles. The fastest sperm cells can cover this distance in 30-60 minutes, overcoming daunting obstacles along the way. To accomplish this feat, the sperm cell is engineered to be one of natures’ great wonders.
Spermatogenesis: Sperm Production Step-by-Step
Start to finish, it takes 72 days or 2 ½ months to make a sperm. During that time, the it will travel through over 25 ft of microtubes in the testicle. Each sperm starts as a germ cell which divides and undergoes meiosis to become a baby sperm, or spermatid. The spermatid is nourished by nurse cells in the testicle and it slowly grows a tail. After it is fully developed, it is released from the nurse cells and sent into a long tube, called the epididymis, where it learns to swim and is stored until it is ejaculated out of the body.
Sperm production (spermatogenesis) starts in the brain where the hypothalamus constantly monitors blood testosterone levels as an indicator of testicular activity. As blood testosterone levels droop, the hypothalamus fires up and begins secreting GnRH (gonadotropin-releasing hormone) which flows directly to the pituitary gland causing it to produce luteinizing hormone (LH) and follicle stimulating hormone (FSH).
Luteinizing hormone travels from the pituitary gland to the testicle where it stimulates leydig cells to secrete testosterone. FSH then concentrates that testosterone into the seminiferous tubule where sperm are made. Germ cells lining the inner walls of the tubules undergo a special process called meiosis that splits the parent cell DNA in half and rearranges it into new, unique combinations. Each one of these new cells will become a sperm cell.
Sertoli cells absorb testosterone that has been concentrated in the seminiferous tubule. Then, much as a mother nurses a young child, they provide testosterone and key micronutrients to baby sperm cells (spermatid). As they develop, the spermatids are pushed towards the center (lumen) of the seminiferous tubule to make room for new cells that are created at the edge. Upon reaching the center of the tubule, the adolescent spermatids grow tails and are released to be carried out of the testicle and into the epididymis. In the epididymis they finish maturing, learn to swim and are stored until they are ejaculated out of the body. Sperm can live in the epididymis for about three weeks. If not ejaculated within that time, they will die and be reabsorbed by the body.
Sperm DNA: How your genes are passed on
Sperm cells are sophisticated packages for delivering DNA to the egg to create a new genetically unique person. As awesome of a specimen as you are, Mother Nature does not simply pass along an exact duplicate of your genes on to your offspring. Instead, your DNA is rearranged into millions of unique combinations, so that each sperm cell carries a slight (and hopefully improved) variation of you.
To understand how, you need to take a closer look at your own DNA. You have 46 chromosomes that contain all your genes. Each chromosome is paired, so there are 23 sets or pairs of chromosomes. One set of 23 chromosomes are given to you by your father and the other set by your mother. Each cell in your body contain all 23 pairs.
In the normal life of the cell, the DNA is unwound in a long chain of spaghetti so that the cell can use it to create proteins that enable the body to function properly. You can think of genes as instructions to the cells for how to build proteins. Slight alterations in genes cause slight alterations to the proteins they create. For example, there are several genes that instruct the cells in your scalp to create proteins that become the hair on your head. Alterations to those genes will alter color, texture and shape of your hair. They can also cause disposition to baldness. Each of your cells contains two copies of every gene, one from your mom and one from your dad. When the genes are different from each other the cell has two options. It can follow the instructions given by a dominant gene or it can blend the instructions given by the both genes much as a cook improvises using two recipes to make a new dish.
When sperm cells are created, DNA is taken through two steps. First the two pairs of chromosomes are brought together, chopped up and reassembled causing some of the chromosomes to have a mixed set of genes coming from both parents. Then, the pairs are divided so that one of the chromosomes goes into one sperm cell and the other goes into a second sperm. The resulting sperm will end up with some genes that are entirely from your mother, some from your father, and some that are a blend of the two. The last chromosome is known as the sex chromosome and contains an X from your mom and a Y from your dad. When the pairs split during the formation of sperm, the X goes into one sperm and the Y goes into another. The means that half of the sperm are female and half are male.
Optimal Environment for Sperm Maturation
Fine-crafted machines need precise environments to ensure proper function. Sperm are incredibly sensitive to alterations in temperature. For proper development, they require an average temperature of approximately 93.5 degrees Fahrenheit. The scrotum is cleverly engineered for temperature control. The outermost layer is thin, stretchy skin specially designed to allow for movement and air cooling. The next layer in is a thin muscular sac called the cremaster muscle that contains and supports the testicle like a hammock. As it relaxes allowing the testicle to hang lower, the cremaster thins out allowing air to cool things off. If the scrotum gets too cold or when the testicle is threatened, the cremaster contracts drawing the delicate organ in towards the body and forms a thicker, more protective layer around it.
Read more about heat and male infertility.
As motile cells, sperm generate a significant amount of metabolic bi-product known as reactive oxygen species (ROS). Similar to exhaust that comes out of a car, ROS is the bi-product from the sperm’s engine burning sugars and nutrients to generate energy. Small amounts of ROS help sperm in the process of fertilization, but large amounts of ROS can injure and even kill sperm cells. The body’s natural defense against reactive oxygen species is the release of antioxidants. Antioxidants, such as vitamin C and vitamin E, are typically molecules that contain double-bonded carbon that enables them to easily bond to and neutralize reactive oxygen species.
Micronutrients & Sperm Production
There are a number of key nutrients that are important for proper DNA replication and sperm cell development. Here are some of the top nutrients that support proper sperm development
Coenzyme Q10: Converts food into an energy source for cells & serves as an antioxidant
Folic Acid: Provides critical molecules needed for DNA replication
Selenium: Helps to regulate hormones, serves as an antioxidant & supports the structural integrity of the sperm neck-piece that connects the head to the tail.
Vitamin E: Fat soluble antioxidant
Vitamin C: Supports the development of key amino acids necessary for cell division & serves as a powerful antioxidant.
Zinc: A building block for testosterone, semen, sperm and the prostate. Perhaps the manliest nutrient on earth
Learn more about nutrients that support sperm health.