As mentioned above, sperm are made in the testes. During sexual intercourse, smooth muscles contract and propel mature sperm from the end portions of the epididymis through a long tube (vas deferens or ductus deferens) inside the body, just beneath the bladder. From there, the sperm get mixed with nutrient-rich fluids from the seminal vesicles and a milky secretion from the prostate gland. This combination of sperm and fluids is called semen. The semen does three things:
Provides a watery environment in which the sperm cells can swim while outside the body
Provides nutrients for the sperm cells (fructose, amino acids, vitamin C)
Protects the sperm cells by neutralizing acids in the female's sexual tract
Once the semen is made, it passes through another tube (urethra) within the penis, exiting the body through the opening of the penis.
One last male organ is a tiny, pea-sized set of glands inside the body at the base of the penis, called the bulbourethral or Cowper's glands. During sexual excitation, and just prior to the ejection of sperm (ejaculation), the Cowper's glands secrete a tiny amount of fluid that neutralizes any traces of acidic urine that may be leftover in the urethra. It is also believed that these secretions are designed to lubricate the penis and female tract during sexual intercourse.
Wednesday, September 23, 2009
Female Sex Organs
All of the female's sexual organs are located within her body except the vulva. The vulva consists of two sets of folded skin (labia major, labia minor) that cover the opening to the reproductive tract, and a small nub of sensitive, erectile tissue (clitoris), which is the remnant of the fetal penis (see next page).
The two ovaries are the major female sex organs, the counterpart of the male testes. The ovaries make the eggs, or oocytes, which are the female gametes, and produce estrogen, the female sex hormone. Estrogen causes female secondary sexual characteristics such as pubic hair, breast development, widening of the pelvis and deposition of body fat in hips and thighs. The ovaries are located in the abdomen.
Female sex organs
Eggs develop inside the ovary and are released upon ovulation into a tube (the oviduct or Fallopian tube) lined with fingerlike projections. The egg travels through the Fallopian tube, where fertilization can take place, to a muscular chamber called the uterus.
Click the play button to see an animation of egg production.
If the animation above isn't working, click here to get the Shockwave player.
The uterus is where the baby develops. It is made of smooth muscle and is normally about the size and shape of a small pear turned upside down. During pregnancy, it can stretch to about the size of a basketball to hold the developing baby. The base of the uterus (neck of the pear) is a muscular wall called the cervix. In the cervix is a tiny opening, about the size of a pinhead, called the external os. The external os is filled with a thick plug of protein (mucus) that serves as a barrier to the entrance of the uterus. The cervix leads into a smooth-muscle-walled tube called the vagina, or birth canal.
The vagina connects the uterus to the outside of the body, and its opening is covered by the labia. The vagina receives the male's penis during sexual intercourse and delivers the baby during childbirth. The vagina is normally narrow (except around the cervix), but can stretch during intercourse and childbirth.
Finally, two sets of glands, the greater vestibular gland (Bartholin's gland) and the lesser vestibular gland, are located on either side of the vagina and empty into the labial folds of skin. The secretions from these glands lubricate the labial folds during sexual excitation and intercourse.
The two ovaries are the major female sex organs, the counterpart of the male testes. The ovaries make the eggs, or oocytes, which are the female gametes, and produce estrogen, the female sex hormone. Estrogen causes female secondary sexual characteristics such as pubic hair, breast development, widening of the pelvis and deposition of body fat in hips and thighs. The ovaries are located in the abdomen.
Female sex organs
Eggs develop inside the ovary and are released upon ovulation into a tube (the oviduct or Fallopian tube) lined with fingerlike projections. The egg travels through the Fallopian tube, where fertilization can take place, to a muscular chamber called the uterus.
Click the play button to see an animation of egg production.
If the animation above isn't working, click here to get the Shockwave player.
The uterus is where the baby develops. It is made of smooth muscle and is normally about the size and shape of a small pear turned upside down. During pregnancy, it can stretch to about the size of a basketball to hold the developing baby. The base of the uterus (neck of the pear) is a muscular wall called the cervix. In the cervix is a tiny opening, about the size of a pinhead, called the external os. The external os is filled with a thick plug of protein (mucus) that serves as a barrier to the entrance of the uterus. The cervix leads into a smooth-muscle-walled tube called the vagina, or birth canal.
The vagina connects the uterus to the outside of the body, and its opening is covered by the labia. The vagina receives the male's penis during sexual intercourse and delivers the baby during childbirth. The vagina is normally narrow (except around the cervix), but can stretch during intercourse and childbirth.
Finally, two sets of glands, the greater vestibular gland (Bartholin's gland) and the lesser vestibular gland, are located on either side of the vagina and empty into the labial folds of skin. The secretions from these glands lubricate the labial folds during sexual excitation and intercourse.
Male sex organs
Male Sex Organs
From the outside, the male has two visible sex organs, the testes and penis. The testes (singular: testis) are the primary male sexual organs in that they make sperm and produce testosterone. The sperm cell is the male sex cell (gamete). Testosterone is the hormone that causes male secondary sex characteristics such as facial and pubic hair, thickened vocal cords and developed muscles.
The testes are housed outside of the main part of the male's body, in a sac called the scrotum. This location is important because in order for the sperm to develop properly, they must be kept at a slightly lower temperature (95 to 97 degrees Fahrenheit, 35 to 36 degrees Celsius) than normal body temperature (98.6 F, 37 C).
The immature sperm travel from each testis to a coiled tube on the outer surface of each testis called the epididymis, where they mature in about 20 days. The sperm exit the body through the penis.
The penis is made of soft, spongy tissue (see How Viagra Works for details). When engorged with blood during sexual excitation and intercourse, the spongy tissue stiffens and causes the penis to become erect, which is important for the penis's main function -- to place the sperm inside the female.
From the outside, the male has two visible sex organs, the testes and penis. The testes (singular: testis) are the primary male sexual organs in that they make sperm and produce testosterone. The sperm cell is the male sex cell (gamete). Testosterone is the hormone that causes male secondary sex characteristics such as facial and pubic hair, thickened vocal cords and developed muscles.
The testes are housed outside of the main part of the male's body, in a sac called the scrotum. This location is important because in order for the sperm to develop properly, they must be kept at a slightly lower temperature (95 to 97 degrees Fahrenheit, 35 to 36 degrees Celsius) than normal body temperature (98.6 F, 37 C).
The immature sperm travel from each testis to a coiled tube on the outer surface of each testis called the epididymis, where they mature in about 20 days. The sperm exit the body through the penis.
The penis is made of soft, spongy tissue (see How Viagra Works for details). When engorged with blood during sexual excitation and intercourse, the spongy tissue stiffens and causes the penis to become erect, which is important for the penis's main function -- to place the sperm inside the female.
How Sex Works
From the time we are teenagers through mid-life or longer, we are capable of sexually reproducing. Sex plays a major role in much of our culture -- we see it in our fashion, literature, music, television and movies.
From a biological standpoint, the goal of sex is to merge two sets of genetic information, one from the father and one from the mother, to make a baby that is genetically different from either parent.
Fertilization
The primary goal of sex is to merge the sperm and egg (fertilization) to make a baby. In many organisms, sex occurs outside of the body. For example, in most fish or amphibians, females lay eggs somewhere (usually on the sea/river bed), the male comes along and sprays the eggs with sperm and fertilization takes place.
In reptiles and mammals (including humans), fertilization takes place inside the body of the female (internal fertilization). This technique increases the chances of successful sexual reproduction. Because we use internal fertilization, our sexual organs are specialized for this purpose. Let's take a closer look at the sexual organs in males and females.
From a biological standpoint, the goal of sex is to merge two sets of genetic information, one from the father and one from the mother, to make a baby that is genetically different from either parent.
Fertilization
The primary goal of sex is to merge the sperm and egg (fertilization) to make a baby. In many organisms, sex occurs outside of the body. For example, in most fish or amphibians, females lay eggs somewhere (usually on the sea/river bed), the male comes along and sprays the eggs with sperm and fertilization takes place.
In reptiles and mammals (including humans), fertilization takes place inside the body of the female (internal fertilization). This technique increases the chances of successful sexual reproduction. Because we use internal fertilization, our sexual organs are specialized for this purpose. Let's take a closer look at the sexual organs in males and females.
Biotechnology
So what is biotechnology and genetic engineering? There are three major developments that act as the signature of biotech, with many more surprises coming down the road:
Bacterial production of substances like human interferon, human insulin and human growth hormone. That is, simple bacteria like E. coli are manipulated to produce these chemicals so that they are easily harvested in vast quantities for use in medicine. Bacteria have also been modified to produce all sorts of other chemicals and enzymes.
Modification of plants to change their response to the environment, disease or pesticides. For example, tomatoes can gain fungal resistance by adding chitinases to their genome. A chitinase breaks down chitin, which forms the cell wall of a fungus cell. The pesticide Roundup kills all plants, but crop plants can be modified by adding genes that leave the plants immune to Roundup.
Identification of people by their DNA. An individual's DNA is unique, and various, fairly simple tests let DNA samples found at the scene of a crime be matched with the person who left it. This process has been greatly aided by the invention of the polymerase chain reaction (PCR) technique for taking a small sample of DNA and magnifying it millions of times over in a very short period of time.
To understand some of the techniques used in biotechnology, lets look at how bacteria have been modified to produce human insulin.
Insulin is a simple protein normally produced by the pancreas. In people with diabetes, the pancreas is damaged and cannot produce insulin. Since insulin is vital to the body's processing of glucose, this is a serious problem. Many diabetics, therefore, must inject insulin into their bodies daily. Prior to the 1980s, insulin for diabetics came from pigs and was very expensive.
To create insulin inexpensively, the gene that produces human insulin was added to the genes in a normal E. coli bacteria. Once the gene was in place, the normal cellular machinery produced it just like any other enzyme. By culturing large quantities of the modified bacteria and then killing and opening them, the insulin could be extracted, purified and used very inexpensively.
The trick, then, is in getting the new gene into the bacteria. The easiest way is to splice the gene into a plasmid -- a small ring of DNA that bacteria often pass to one another in a primitive form of sex. Scientists have developed very precise tools for cutting standard plasmids and splicing new genes into them. A sample of bacteria is then "infected" with the plasmid, and some of them take up the plasmid and incorporate the new gene into their DNA. To separate the infected from the uninfected, the plasmid also contains a gene giving the bacteria immunity to a certain antibiotic. By treating the sample with the antibiotic, all of the cells that did not take up the plasmid are killed. Now a new strain of insulin-producing E. coli bacteria can be cultured in bulk to create insulin.
For more information on cells, bacteria, enzymes and related topics, check out the links on the next page.
Bacterial production of substances like human interferon, human insulin and human growth hormone. That is, simple bacteria like E. coli are manipulated to produce these chemicals so that they are easily harvested in vast quantities for use in medicine. Bacteria have also been modified to produce all sorts of other chemicals and enzymes.
Modification of plants to change their response to the environment, disease or pesticides. For example, tomatoes can gain fungal resistance by adding chitinases to their genome. A chitinase breaks down chitin, which forms the cell wall of a fungus cell. The pesticide Roundup kills all plants, but crop plants can be modified by adding genes that leave the plants immune to Roundup.
Identification of people by their DNA. An individual's DNA is unique, and various, fairly simple tests let DNA samples found at the scene of a crime be matched with the person who left it. This process has been greatly aided by the invention of the polymerase chain reaction (PCR) technique for taking a small sample of DNA and magnifying it millions of times over in a very short period of time.
To understand some of the techniques used in biotechnology, lets look at how bacteria have been modified to produce human insulin.
Insulin is a simple protein normally produced by the pancreas. In people with diabetes, the pancreas is damaged and cannot produce insulin. Since insulin is vital to the body's processing of glucose, this is a serious problem. Many diabetics, therefore, must inject insulin into their bodies daily. Prior to the 1980s, insulin for diabetics came from pigs and was very expensive.
To create insulin inexpensively, the gene that produces human insulin was added to the genes in a normal E. coli bacteria. Once the gene was in place, the normal cellular machinery produced it just like any other enzyme. By culturing large quantities of the modified bacteria and then killing and opening them, the insulin could be extracted, purified and used very inexpensively.
The trick, then, is in getting the new gene into the bacteria. The easiest way is to splice the gene into a plasmid -- a small ring of DNA that bacteria often pass to one another in a primitive form of sex. Scientists have developed very precise tools for cutting standard plasmids and splicing new genes into them. A sample of bacteria is then "infected" with the plasmid, and some of them take up the plasmid and incorporate the new gene into their DNA. To separate the infected from the uninfected, the plasmid also contains a gene giving the bacteria immunity to a certain antibiotic. By treating the sample with the antibiotic, all of the cells that did not take up the plasmid are killed. Now a new strain of insulin-producing E. coli bacteria can be cultured in bulk to create insulin.
For more information on cells, bacteria, enzymes and related topics, check out the links on the next page.
Genetic Diseases
Many genetic diseases occur because a person is missing the gene for a single enzyme. Here are some of the more common problems caused by missing genes:
Lactose intolerance - The inability to digest lactose (the sugar in milk) is caused by a missing lactase gene. Without this gene, no lactase is produced by intestinal cells.
Albinism - In albinos, the gene for the enzyme tyrosinase is missing. This enzyme is necessary for the production of melanin, the pigment that leads to sun tans, hair color and eye color. Without tyrosinase, there is no melanin.
Cystic fibrosis - In cystic fibrosis, the gene that manufactures the protein called cystic fibrosis transmembrane conductance regulator is damaged. According to Encyclopedia Britannica:
The defect (or mutation) found in the gene on chromosome 7 of persons with cystic fibrosis causes the production of a protein that lacks the amino acid phenylalanine. This flawed protein somehow distorts the movement of salt and water across the membranes that line the lungs and gut, resulting in dehydration of the mucus that normally coats these surfaces. The thick, sticky mucus accumulates in the lungs, plugging the bronchi and making breathing difficult. This results in chronic respiratory infections, often with Staphylococcus aureus or Pseudomonas aeruginosa. Chronic cough, recurrent pneumonia, and the progressive loss of lung function are the major manifestations of lung disease, which is the most common cause of death of persons with cystic fibrosis.
Other genetic diseases include Tay-Sachs disease (damage to the gene for the enzyme hexosaminidase A leads to an accumulation of a chemical in the brain that destroys it), sickle cell anemia (improper coding of the gene that produces hemoglobin), hemophilia (lack of a gene for a blood-clotting factor) and muscular dystrophy (caused by a defective gene on the X chromosome). There are something like 60,000 genes in the human genome, and over 5,000 of them, if damaged or missing, are known to lead to genetic diseases. It is amazing that damage to just one enzyme can lead, in many cases, to life-threatening or disfiguring problems.
Lactose intolerance - The inability to digest lactose (the sugar in milk) is caused by a missing lactase gene. Without this gene, no lactase is produced by intestinal cells.
Albinism - In albinos, the gene for the enzyme tyrosinase is missing. This enzyme is necessary for the production of melanin, the pigment that leads to sun tans, hair color and eye color. Without tyrosinase, there is no melanin.
Cystic fibrosis - In cystic fibrosis, the gene that manufactures the protein called cystic fibrosis transmembrane conductance regulator is damaged. According to Encyclopedia Britannica:
The defect (or mutation) found in the gene on chromosome 7 of persons with cystic fibrosis causes the production of a protein that lacks the amino acid phenylalanine. This flawed protein somehow distorts the movement of salt and water across the membranes that line the lungs and gut, resulting in dehydration of the mucus that normally coats these surfaces. The thick, sticky mucus accumulates in the lungs, plugging the bronchi and making breathing difficult. This results in chronic respiratory infections, often with Staphylococcus aureus or Pseudomonas aeruginosa. Chronic cough, recurrent pneumonia, and the progressive loss of lung function are the major manifestations of lung disease, which is the most common cause of death of persons with cystic fibrosis.
Other genetic diseases include Tay-Sachs disease (damage to the gene for the enzyme hexosaminidase A leads to an accumulation of a chemical in the brain that destroys it), sickle cell anemia (improper coding of the gene that produces hemoglobin), hemophilia (lack of a gene for a blood-clotting factor) and muscular dystrophy (caused by a defective gene on the X chromosome). There are something like 60,000 genes in the human genome, and over 5,000 of them, if damaged or missing, are known to lead to genetic diseases. It is amazing that damage to just one enzyme can lead, in many cases, to life-threatening or disfiguring problems.
Viruses
Viruses are absolutely amazing. Although they are not themselves alive, a virus can reproduce by hijacking the machinery of a living cell. The article How Viruses Work describes viruses in detail -- below is a summary.
A virus particle consists of a viral jacket wrapped around a strand of DNA or RNA. The jacket and its short strand of DNA can be extremely small -- a thousand times smaller than a bacterium. The jacket normally is studded with chemical "feelers" that can bond to the outside of a cell. Once docked, the viral DNA (or RNA, depending on the virus) is injected into the cell, leaving the jacket on the outside of the cell.
In the simplest virus, the DNA or RNA strand is now floating freely inside a cell. RNA polymerase transcribes the DNA strand, and ribosomes create the enzymes that the viral DNA specifies. The enzymes that the viral DNA creates are able to create new viral jackets and other components of the virus. In simple viruses, the jackets then self-assemble around replicated DNA strands. Eventually the cell is so full of new viral particles that the cell bursts, freeing the particles to attack new cells. Using this system, the speed at which a virus can reproduce and infect other cells is amazing.
In most cases, the immune system produces antibodies, which are proteins that bind to the viral particles and prevent them from attaching to new cells. The immune system can also detect infected cells by discovering cells decorated with viral jackets, and can kill infected cells.
Antibiotics have no effect on a virus because a virus is not alive. There is nothing to kill! Immunizations work by pre-infecting the body so it knows how to produce the right antibodies as soon as the virus starts reproducing.
A virus particle consists of a viral jacket wrapped around a strand of DNA or RNA. The jacket and its short strand of DNA can be extremely small -- a thousand times smaller than a bacterium. The jacket normally is studded with chemical "feelers" that can bond to the outside of a cell. Once docked, the viral DNA (or RNA, depending on the virus) is injected into the cell, leaving the jacket on the outside of the cell.
In the simplest virus, the DNA or RNA strand is now floating freely inside a cell. RNA polymerase transcribes the DNA strand, and ribosomes create the enzymes that the viral DNA specifies. The enzymes that the viral DNA creates are able to create new viral jackets and other components of the virus. In simple viruses, the jackets then self-assemble around replicated DNA strands. Eventually the cell is so full of new viral particles that the cell bursts, freeing the particles to attack new cells. Using this system, the speed at which a virus can reproduce and infect other cells is amazing.
In most cases, the immune system produces antibodies, which are proteins that bind to the viral particles and prevent them from attaching to new cells. The immune system can also detect infected cells by discovering cells decorated with viral jackets, and can kill infected cells.
Antibiotics have no effect on a virus because a virus is not alive. There is nothing to kill! Immunizations work by pre-infecting the body so it knows how to produce the right antibodies as soon as the virus starts reproducing.
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