Besides being highly advanced as compared to that of the other higher vertebrates, the human reproductive system has many mysterious and amazing facts associated with it. The interesting human reproductive system facts, described below, will not only add to your existing knowledge about it but also serve as a source of amusement.

• Unlike the majority of other structures and systems found in your body (which show structural as well as functional similarities in both the genders), the repro-ductive system happens to be relatively strange in this regard as structurally dif-fering organs perform different functions in either gender.
• Both in males and females, there are two major structural divisions of genitals: the former have penis and testes while in the latter you find vagina & uterus, and ovaries.
• On average, the total length of an erect human male penis varies between 12 and 15 centimeter, but occasionally it may measure up to 19 cm in some individ-uals.
• Did you ever imagine that a single seminal ejaculation in an adult human male may contain as many as two and a half billion sperm cells?
• It is one of the most interesting human reproductive system facts that, in most of the cases, out of billions of sperm cells found in semen, only one is used for fertilization of ovum in the ovary of a female.
• You can have an idea about the ultra-elasticity of the uterus from the fact that, when not in use, it measures just 3 and 2 inches in length and width, respective-ly. By about 36 weeks into pregnancy, the expanding uterus reaches all the way to the navel and to the lower edge of the rib cage.
• The medium of the vagina is as acidic as beer or tomatoes, averaging about 4 on the pH scale.
• Lactobacilli are a group of lactic acid-producing bacteria which dominate the ecosystem in many women’s vaginas and maintain its high acidity to keep nasty bugs from moving in and colonizing the place.
• The hymen is really just a small piece of tissue that rings the vaginal opening and serves as an indicator of virginity.
• Besides sexual intercourse, any other penetration into the vaginal opening or a minor physical injury may result in breakage, tearing or stretching of the hymen. So, you must be sure that the presence or absence of a hymen says nothing about whether a woman has experienced sexual intercourse.
• In very rare cases, at the time of birth, a girl’s hymen is imperforate with no hole in the tissue to allow menses or discharge to pass through, and this condition re-quires minor incision to correct the problem.
• The G-spot refers to an area in the vagina that has since long been a place of great contention owing to its controversial nature as being extra-sensitive to erotic stimulation.
• Many studies have shown that a large number of women report "G-spot Or-gasms" but the anatomical knowledge of the area still remains thin.
• In the process of urination, as your bladder is emptied, it gets collapsed, but it is inflated again as more urine enters through the ureters.
• Lungs also play a vital excretory role in the life of an individual as excess carbon dioxide is eliminated from the body which may, otherwise, lead to severe consequences.
• In very rare cases, a female human baby is born with not one, but two uterus-es a condition known as didelphys.
• There are also chances of a female’s vagina getting duplicated during the early developmental stages of the fetus, thus creating a forked path to each uterus.
• The stones found in your kidneys can move throughout your body while flowing along the blood stream.
• The color of your urine may be either pale straw or amber, while 95 percent portion of your blood is contributed by the universal solvent water.
• It is not usually possible for a woman to remember the day she actually con-ceived and doctors start measuring pregnancy from the first day of the last men-strual period.
• Various obvious physical changes take place in the body of a female during the tenure of pregnancy, such as the swelling of belly and feet.
• Placenta is the only transient organ in human body which grows with the devel-oping embryo in the womb and is expelled out of the body with the birth of the baby.
• Besides forming a porous barrier between the mom's and baby's blood, placenta also acts as an endocrine organ and excretes hormones, which play a vital role in the maintenance of pregnancy.
• The hormones secreted by the transient organ, placenta, include Homan Chori-onic Gonadotropin (hCG), estrogen and progesterone.
• The urethra in human male is longer than that of a female because in the former, it has to run along the entire length of penis and in the latter, it ends just above the vaginal opening.
• The placental hormonal secretions are crucial for maintaining pregnancy and preparing the mammary glands for nursing the new born.
• The amount of relaxin hormone secreted during pregnancy increase by ten times the normal level and serves to relax the cartilage that holds bones together.
• At the time of delivery, it is relaxin which makes the labor a lot easier than it would have been without it by loosening the pubic symphosis, a place on the pubic bone located in front of the bladder where a ring of cartilage anchors the bone together.
• Along with its immense benefits, the relaxin hormone also causes some troubles as during the course of pregnancy women experience joint and back pain and their foot size increases.
• During the second and third trimesters of pregnancy, the human females also encounter difficulty in remembering things and perform worse on the spatial memory tests than their non-pregnant sisters.
• Besides causing joint & back pain and memory issues, the pregnancy-triggered hormonal secretions also bring abnormal mood changes.
• Pregnancy is also associated with causing morning sickness and nausea & vomit-ing which can strike a pregnant woman by any time of the day.
• It is very fortunate that the crucial phase of vomiting and nausea passes by the twelfth week of pregnancy.
• The women passing through the phase of pregnancy are also very likely to expe-rience heartburn because of two basic reasons. Firstly, the release of progester-one hormone causes loosening in the cardiac sphincter, thus letting the gastric juice in stomach flow back to esophagus. Secondly, as the baby in the womb grows larger, more pressure is exerted against the stomach and esophagus, re-sulting in heartburn.
• As the unborn baby presses down on the bladder, the latter gets squished and a cough, sneeze and giggle can cause leakage of urine.
• It is one of the most surprising female reproductive system facts that by the 20th week of pregnancy, the quantity of blood in the body of a woman gets doubled.
• The pregnancy-triggered blood increase, in the body, also involves some strange side effects, such as nosebleeds, nasal stiffness, varicose veins and hemorrhoids, etc.
• It is very unfortunate to know that the pregnancy swelling may also trigger the onset of carpal tunnel syndrome, which is characterized by numb and tingling hands.
• You will be surprised to know that the extra fluids produced during pregnancy are responsible for the 25% of weight gain in female's body.
• At the fetal stage, the ovaries of human females contain as many as 6 to 7 mil-lion eggs, and after this stage, there occurs no further production of eggs.
• So surprisingly, the vast majority of egg cells (6-7 million) undergo death and their total depletion marks the onset of menopause.
• Of all the seven million eggs, present during the fetal stage, only one million have remained alive at the time of the baby’s birth.
• The death of egg cells doesn't stop even after birth and, as the female reaches puberty, only three hundred thousand are left behind.
• It is one of the really amazing female reproductive system facts that out of the whopping ten million originally produced eggs, 300 to 400 are ovulated during the reproductive lifetime of a woman.