Reproduction


REPRODUCTION IN ANIMALS

How do humans reproduce? They do it through sexual reproduction. A human fetus develops for nine months in the mother´s uterus before being born.

MAKING CELLS :

There are two ways by which new cells can be made. The first way is called mitosis, which happens when organisms are growing or replacing old or damaged cells.
Meiosis is the other way in which new cells can be made. Meiosis happens in the production of sex cells. Sex cells are called gametes.
Fertilisation involves the nucleus of a female sex cell fusing with the nucleus of a male sex cell giving the fertilised egg 46 chromosomes again.

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SEX CELLS:


The female egg is called the ovum and the male cell is called the sperm. Both of them are adapted to their functions.
The female cell has large food reserves in the cytoplasm so it is big and round.
The male sex cell has a long tail and streamlined body because it needs to swim.
During fertilisation each sex cell has a nucleus containing 23 chromosomes



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MALE REPRODUCTIVE SYSTEM:

Sperm, the male sex cells, are made in testes. The testes hang outside the body in a bag called scrotum. The testes are not inside the becausebody temperature is too high for sperm production. Each tesis is connected to the penis by a tube called sperm duct. before sperm leave the body they are mixed with a liquid which comes from two small glands called seminal vesicles. Together sperm and the liquid are called semen. The penis has a tube running through it called the urethra. Semen and urine from the bladder both leave the penis through the urethra. theurethra can carry either semen or urine but not both at the same time.
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FEMALE REPRODUCTIVE SYSTEM:



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The main female reproductive organs are oviduct, ovary, uterus and cervix and vagina.
The ova are made in two ovaries. These are found inside the abdomen. They are connected to the uterus by tubes called oviduct. An oviduct carries the ovum from the ovary to the uterus. The uterus is like a bag with a thick muscular wall where a fertilised egg cell can grow and develop. It takes between four and five days for the ovum to reach the uterus from the ovary. The uterus connects to the outside of the body by a muscular tube called the vagina. the neck of the uterus is called the cervix. When a man and a men have sex the penis is inserted into the vagina. Sperm may be released at the neck of the uterus.


MENSTRUATION:


external image Symptoms-of-Menstrual-Cycle.jpgEach month, women of reproductive age who aren't pregnant, go through a cycle of fertility that results in pregnancy or menstruation. This cycle takes place each 28 days more or less...

DAYS 1-5
The first day of a woman's period is considered the first day of the menstrual cycle. If an egg hasn't been fertilised it disintegrates. The lining of the uterus breaks down and leaves the body in the form of menstrual blood. Bleeding lasts an average of 5 days. Then the cycle starts again.

DAYS 6-13
The uterus lining starts to thicken ready for a fertilised ovum.

DAY 14
Ovulation: a mature ovum is released from an ovary.

DAY 15
The ovum is passed along the oviduct.

DAYS 16-21
The lining of the uterus remains thick waiting for the frtilise ovum. The hormones in the female's body start to change.

DAYS 22-28
The lining of the uterus stops developing.

This menstrual cycle can vary in lenths for different women. It can also be painful for some females because the muscles in the uterus wall contract. This may result in cramps and cause stomach and back pains. Sometimes water collectin body tissues which makes them swell up, resulting in swelling of the ankles and fingers. After menstruation the uterus grows a fresh lining for each new ovum. The cycle of making a new lining and a new ovum is called the menstrual cycle. I fan ovum is fertilised on day 14 then the lining of the uterus remains and the placenta develops, partly from the fertilised egg and partly from the mother, to feed and protect the developing embryo. The lining of the uterus doesn't break down this time.



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FERTILISATION:

The sperm are mixed with a small amount of fluid and squeezed along the sperm duct into the urethra. They are released as semen out of the end of the penis and deposited at the neck of the uterus, the cervix. From here the sperm swim through the uterus and up into the oviducts. This takes about 48 hours. Once in the oviduct they may meet an ovum. Only one sperm can fertilase the ovum.Ova(plural of ovum) are much larger than sperm. More than 300 million sperm enter a female during sexual intercouse. Approximately 100 of them reach the ovum but only one occasionally gets in. When one sperm enters the ovum the surface membranes of the ovum change to stop any more sperm getting in to it. After the sperm enters the ovum, the nucleous of the sperm (which contains genetic mateial) fuses with the nucleous of the ovum. The fusion of the two gametes is called fertilisation. A fertilised ovum contains two sets of genetic material. One set comes from each parent so that the new individual will have characteristics from both of the parents and will be unique.



Twins
Twins can be formed in two ways:
1. Sometimes a woman's ovaries release two or more ova at the same time. If they all become fertilised they all develop into babies. Sometimes a woman's ovaries release two or more ova at the same time. If they all become fertilised they all develop into babies. Twins formed in this way are non-identical. They develop from different ova fertilised by different sperm.
2. Sometimes, after fertilisation, the fertilised ovum splits and divides into two balls of cells. Twins formed in this way are identical. They develop from the same ovum.


PREGNANCY

Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the womb of a female.The term embryo is used to describe the developing offspring during the first 8 weeks following conception, and the term fetus is used from about 2 months of development until birth In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Childbirth usually occurs about 38 weeks after conception; i.e., approximately 40 weeks from the last normal menstrual period (LNMP) in humans.



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PREGNANCE SIGNS


Some women feel pregnant even before the test turns positive. The earliest signs include:

• Tender, swollen breasts :Many women say the tenderness they feel is an exaggerated version of how their breasts feel before a period.
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• Fatigue :Feeling tired all of a sudden — no, make that exhausted? Increased levels of the hormone progesterone and the extra effort required to start making a baby can make you feel as if you've run a marathon when all you've done is put in a day at work.

• Frequent urination :Shortly after you become pregnant, you may find yourself hurrying to the bathroom at an alarming frequency.

• Heightened sense of smell :Many newly pregnant women find they're overwhelmed by gag-inducing smells early in pregnancy. This may be a side effect of rapidly increasing levels of estrogen in your system.

• Food aversions :Food turn-offs are even more common than cravings during pregnancy. You may suddenly find that certain foods you used to enjoy are now completely repulsive to you.
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• Nausea or vomiting :Morning sickness usually doesn't start for a few weeks, but some women feel queasy earlier.

• Your basal body temperature stays high :If you've been charting your temperature and it stays elevated after you've ovulated, you're probably pregnant.

• Bleeding or spotting :Some women notice a small amount of red spotting or pink or reddish brown staining around the time they should get their period. (If you have pain along with spotting or bleeding, call your caregiver immediately since this can be a sign of an ectopic pregnancy.)


PREGNANCY PERIODS

Perinatal period defines the period occurring "around the time of birth", specifically from 22 completed weeks (154 days) of gestation to 7 completed days after birth.
Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.
The postnatal period begins immediately after the birth of a child and then extends for about six weeks. During this period the mother's body returns to prepregnancy conditions as far as uterus size and hormone levels are concerned.


DURATION
The actual pregnancy duration is typically 38 weeks after conception. Though pregnancy begins at conception, it is more convenient to date from the first day of a woman's last menstrual period, or from the date of conception if known. Starting from one of these dates, the expected date of delivery can be calculated.
Pregnancy is considered "at term" when gestation attains 37 complete weeks but is less than 42 (between 259 and 294 days ). Events before completion of 259 days are considered preterm; from 294 days events are considered postterm. When a pregnancy exceeds 294 days, the risk of complications for woman and fetus increases significantly.
Fewer than 5% of births occur on the due date; 50% of births are within a week of the due date, and almost 90% within 2 weeks. It is much more useful, therefore, to consider a range of due dates, rather than one specific day, with some online due date calculators providing this information.