Biology - Other

Sexual Reproduction in Biology



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Life is very complex, but at one point in all of our lives we were only two things: a sperm from your dad and an egg from your mom. They were both very tiny. How did we grow up from that tiny sperm and an egg that is the size of one grain of sand to the size of six feet tall weighing hundreds of pounds? There are some key steps in the process.
It all starts in the male's testes or testicles, two small glands. These testes are located in the scrotum, which is an external sac below the penis. Sperm, male reproductive cells, is made and stored in these testes when you're not in sexual activity. Sperm is held in the scrotum because it must be outside of the body. Sperm can only live at certain temperatures. The scrotum goes closer and moves away from the body as the temperature goes up and down. Sperm is specifically located in small tubes called epididymis. During sexual activity males get erections, which changes the tube and valve called the vas deferens. This valve makes sure no urine comes out with the sperm.
The vas deferens tube connects the epididymis with the urethra. On the way through the vas deferens it passes the prostate gland that adds sticky liquid to the sperm, this helps the sperm to swim. When this is added to the sperm it is then called semen. The semen then goes through the urethra, which is the tube that goes out to the tip of the penis. The penis is the tube shaped organ right above the scrotum. Before puberty, males don't make sperm. Sterile means that you are unable to produce sperm even after puberty. The semen then comes out and goes from the penis to the vagina. But before we get into the fertilization process we must first learn about the female.
The female's reproductive cells are calls the egg or the ova. The uterus which is a hollow, muscular, pear shaped organ inside a females body that help nourish and protect the fertilized egg from fertilization to birth. The egg in a female's body is equal to sperm in the male's body. Unlike males, females are born with eggs. When they mature they start to release these mature eggs from the ovaries, or female sex glands that store the eggs. You are born with 400,000 eggs so you will never run out. One egg matures each month, beginning at puberty. Each month after puberty ovulation occurs, the process of releasing a mature egg into the fallopian tube. The fallopian tube is a tiny tube the size of a hair connecting the ovaries and the uterus. If the egg is not fertilized then the egg goes through the uterus and through the cervix or the opening from the uterus to the vagina.
Then menstruation occurs which is the shedding of the uterine lining. This only happens if the egg is not fertilized.
Finally we come to the miracle of life: the fertilization. During sexual activity thousands of sperm enter the vagina. The vagina is the first step for the sperm to travel through; it is a muscular, elastic passageway that extends from the uterus to the outside of the body. The sperm then travels through the uterus. Since there is a fallopian tube on each side they must split up. During this journey the sperm are constantly being attack by the female's defense system. Her body doesn't want the sperm in there so it tries to destroy it. While they swim down the fallopian tube they tend to bunch up to try and find the egg. The egg has its own layer of protection. It takes a lot of sperm to break through this layer. Finally sperm start hitting the egg. More and more sperm start running right into it, and one sperm finally reaches the core. When one sperm enters the egg immediately makes a layer so that no more sperm can enter. This joining of sperm and egg is called fertilization; the fertilized egg is now called a zygote. The zygote is finally a completed cell and it can start to reproduce. The cell of the zygote divides and makes new cells. By the time it travels to the uterus the zygote has divided many times. The zygote then implants it self into the uterine wall which is very thick. This process is called implantation. The zygote is now known as an embryo. The tissue that lines the walls during pregnancy that nourishes the embryo is called the placenta. After implantation, the umbilical cord connects the baby to the mother. The umbilical cord leaves its mark on everyone; this mark is known as your belly button. Also the amniotic sac forms around the baby. This is a thin fluid-filled membrane that protects the unborn baby. After about two months the embryo changes into a fetus, or an unborn baby. The fetus continues to grow for about seven more months. Around the eighth and ninth month of pregnancy the female starts having contractions and the uterus starts to push out the baby. Finally the mother goes into the labor or the final stage of pregnancy in which the uterus pushes the baby out of the female's body. When the baby is pushed out of the woman's vagina it is called birth. The umbilical cord is then cut and the baby is free to breath on its own. After the baby has come out, contractions continue until the placenta is pushed out all the way. This process is called the afterbirth. After all this is done the parents will take the baby home and another life has been made. The miracle of life is very fascinating.




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