Biological Differences Between Men and Women
We all know that the male and female human are obviously anatomically different. Furthermore, the male and female body behave differently when it comes to the manifestations and treatments of various diseases. These differences are due to biological and genetic reasons. Upon closer examination, the presence of several hormones and other chemicals, especially the quantity of the two major ones present in both sexes, androgens and estrogens make all the difference.
The Biological Difference Between Men and Women in Fertility
Fertility is one of the major differences between men and women. On one hand, men are continuously fertile from puberty to almost up to 100 years of age even though by that time they are physically unable to engage in sexual activities. Their sperms are still viable but poor in quality. Men are fertile this long because there is a continuous production of sperms through the process called spermatogenesis. The process begins with germ cells which are essentially immortal. The cells are haploid since they have only half the number of chromosomes, 23 in this case. In the male all of these cells are not used at once during the reproductive process, only some will become a mature germ cell to compete in the arduous task of uniting with a female germ cell, an ovum.
Women on the other hand, are fertile for roughly 12 hours each month from menarche up until they are in their fifties when menopause begins for most women. Fertility for them are limited because they have a set number of eggs. During fetal development there are initially 3 million to 4 million follicles or eggs present but through the process of apoptosis (cell death) that number drops to about 1 million eggs by the time of birth. This cell depletion will continue throughout the female's life. By menarche there are only 500,000 eggs available to continue this monthly cycle for the next five decades until menopause. After about 50 years a women releases about 7,000 eggs and only 1 in 12 is available for fertilization while the remaining approximately 492,000 eggs that are never released for fertilization go to waste.
Even though the fertility process for men and women are basically hormone driven with both beginning with the release of a hormone from the hypothalamus. The fertility process is a little more complicated for women and involves several critical steps with other hormones to progress from beginning to end of the menstrual cycle. These are the steps as follow:
- Release of gonadotropin releasing hormone from hypothalamus causes an increase in follicle-stimulating hormone (FSH). This is the beginning of the menstrual cycle.
- Ten to twelve ovarian follicles ripen due to the increase in FSH level.
- One of the follicles become the dominant one which causes an increase in estrogen level.
- The gonadotropin releasing hormone level rises even more which causes an increase in luteinizing hormone and FSH levels thus triggering ovulation. This is the midpoint in the menstrual cycle.
- After the egg is released, the dominant follicle becomes what called a corpus luteum. The corpus luteum will be active for two weeks while secreting estrogen and progesterone. Both of these hormones get the uterus ready for to receive a fertilized egg.
- If the egg is not fertilized during the 12 hour window in the two week period, the corpus luteum degenerates and the estrogen and progesterone levels drop. This drop in the hormones level starts the menstrual period thus ending the menstrual cycle.
The Quantity of the Hormones Make the Differences in Secondary Sex Characteristics
The obvious physical differences between the sexes are influenced by the quantity of androgens and estrogens, two chemicals from the steroid family of chemicals, released into our bloodstream. The biggest differences occur during the development of our secondary sex characteristics beginning at puberty. We know what they are and I will not go into any details about them here.
All the sex hormones in men and women originate from acetate and cholesterol molecules present in their bloodstream. The estrogens present in both sexes, more so in women than in men, are produced from the chemical breakdown of testosterone which is also present in the blood of both sexes. In case you didn't know testosterone is produced in both the testis and ovaries because the testis in the human male were once ovaries during fetal development until a chemical in the male body triggers the sequence to cause them to descend to the lower level into the scrotum to become the testis.
The testis make about 7 mg of testosterone a day and 1.75 mg of it is converted to small amounts of estradiol present in the blood of men while the ovaries in women only makes about 0.3 mg of testosterone and a little more than 0.15 mg of that is converted to estradiol. As we can see here it is the ratio of testosterone to estradiol and the potency of the two hormones that make the big differences between the sexes. Estrogens are 1000 times more potent than testosterone. The ratio of the amount of testosterone to estradiol found in men is 3 to 1 while the ratio of these two hormones in women is 1 to 1. Also, men make about 20 times more testosterone than women but the amount of testosterone converted to estrogens in women is 200 times more than men. It doesn't take much of either of these hormones to change the physical appearance of each sex to its opposite appearance.
The Non-Sexual Functions of the Sex Hormones
These hormones not only exert their effects on the reproductive organs but they also affect the physiological functions of non-reproductive tissues as well. These tissues are generally called the somatic cells since they essentially make up the rest of the tissues in the body ("soma" is the latin word for "body"), such as the muscles, eyes, bones, etc.
Estrogen plays a critical role in our growth rate during puberty. It controls the growth of the cartilage and bone tissues. The rapid growth spurt generally occurs in girls earlier than in boys when they reach puberty due to the higher level of estrogen in the female body. This is why girls are taller than boys in the first year or so as teens. Boys catch up later in height.
Estrogen also has a strong influence on the cardiovascular system. Estrogen decreases the incident of heart attacks, kidney diseases and other cardiovascular ailments in women since they have more of it than men. However, that benefit in women disappear once they reach menopause since estrogen level drop and their testosterone level go up. Decrease in estrogen level in both sexes causes an increase in the incident of osteoporosis or bone loss since estrogen controls the rate of bone loss and resorption of calcium to produce bone tissue. When estrogen level drops the rate of bone loss is greater than the rate of bone resorption and the problem is worst in women since their bones are generally less dense than men.
The Genetic Differences Between Men and Women
If you were to look at chromosome pair 23, XX for female and XY for male, the differences between the sexes are apparent. The "Y chromosome" is much shorter than it's corresponding "X chromosome". Despite its size the "Y chromosome carries two of the most important genes for a male. One of these genes is called SRY that determine the maleness of the human species. This is the gene that triggers the sexless gonads to become testis in the male otherwise they stay up in the abdomen to become ovaries for the female. In other words it is chromosome pair 23 from the male that determines what sex the developing embryo will ultimately become after conception. The other gene controls the production of sperms.
The other genetic difference between the sexes are the inheritance of the mitochondrial DNA in the female. Mitochondria are present in all the cells of both sexes but are passed from one generation to the next exclusively through the mother. The genes they carry are replicated and do not go through any recombination as the rest of genes do during fertilization. Maternity testing is based on this knowledge of the mitochondrial DNA properties. Paternity testing is generally performed using the nuclear DNA present in all non-reproductive or somatic cells.
The above information clearly shows that the physiological differences in the sexes are biological as well as chemical driven. It is the quantity of the testosterone and estrogen in the blood of both sexes and the ratio of the two hormones present that affect the physiological activities in both sexes as well as the physical attributes of the male and female human body.
© 2011 Melvin Porter
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