Category Zoology

What happens after fertilization?

                    The fertilized egg begins to divide as it travels down the fallopian tube towards the womb. By the time it enters the womb it has divided into a ball of about 100 cells. It settles on the wall of the womb and sinks into the surface, becoming firmly fixed. At this point, the female is pregnant.

What is an embryo?

                     For the first eight weeks of a pregnancy, the developing egg is called an embryo. A liquid-filled bag develops around the embryo to protect it. By the fourth week of pregnancy the embryo is the size of a grain of rice. It has a head and a tail, and the beginning of limbs, and its tiny heart begins to beat. The placenta is the embryo’s life-support system. It is a red, flattened organ that becomes deeply embedded in the wall of the womb. The placenta extracts food substances from the mother’s blood and passes waste material from the embryo back to the mother for disposal. The placenta is connected to the developing baby by a thick umbilical cord, which contains large blood vessels.

What is a period?

                          Each month, an egg cell is released from a female’s ovaries. When this happens, the lining of the womb changes so that it is ready to receive the egg if it is fertilized.

                           If the egg is not fertilized, the womb lining breaks down, and blood and tissue pass out through the vagina. This process is called a period, and it happens about every 28 days. The time from one period to the next is known as the menstrual cycle. Hormones from the pituitary gland and the ovaries control the menstrual cycle, which may he irregular. However, it usually settles into a regular cycle.

How does fertilization take place?

                         It takes two days for an egg cell to travel along the Fallopian tube. During this time it may be fertilized. The male’s penis places sperms in the vagina, and about 300 million sperms are released. Some sperms pass through the neck of the womb and swim up into the uterus. They enter the Fallopian tube where some will meet the egg. Only one sperm may wriggle inside and fuse its own nucleus with the nucleus of the egg.

What is contraception?

                       Contraception prevents fertilization from taking place. There are several different contraceptive methods. One method involves a contraceptive device called a condom. It is a rubber covering, or sheath, that is worn over the penis to stop the escape of sperms. The contraceptive ‘pill’ is a drug taken regularly by a female. It prevents the ovaries from producing ripe eggs, or stops the eggs from developing.

How are sperms made?

                        Sperms, the male sex cells, develop in the testes. They are stored for several days until needed. The testes contain long tubes called the seminiferous tubules, which are tightly coiled. Sperms are produced continuously in these tubes, then passed to the epididymis and stored in a large duct called the vas deferens. Here liquid is added to the sperm to make a milky fluid called semen. It is stored in pouches called seminal vesicles. During sexual intercourse the seminal vesicles contract and force out the sperm. It passes out of the penis and into the female sexual organs.

How many sperms are there?

                     Up to 100 million sperms are produced every day by the male. If they are not released, they are soon destroyed and replaced. Sperms look like tiny tadpoles, with rounded heads and long lashing tails. They use their tails to swim at a speed of about one cm per minute. The head of the sperm contains the nucleus, which will join with the egg cell during fertilization.

What is a human egg cell?

                         The ovaries of a newborn baby girl contain about 250,000 egg cells. By the time she reaches maturity, there will be about 10,000 remaining. However, only a few of these eggs will be used — one each month throughout the years when she can have a baby. Every 28 days, a swelling appears on an ovary. This releases the egg cell in a process called ovulation. The egg cell then enters the fallopian tube. The swelling it emerged from produces hormones to prepare the womb to receive the egg.

What are the female sex organs?

                        The female sex organs are inside a woman’s lower abdomen. The womb, or uterus, is a pear-shaped muscular organ from which two ‘horns’ run out sideways, ending with the Fallopian tubes. The neck of these tubes is funnel-shaped, and the funnels are cupped around the ovaries where the egg cells are produced. The neck of the womb leads to a short tube called the vagina, leading outside the body. Urine passes out through a short tube, the urethra, near the mouth of the vagina.

What are the male sex organs?

                         The male sex organs are the testes and the penis. The two testes are contained in a skin sac called the scrotum, hanging beneath the groin. A tube called the urethra, which is connected to both the bladder and the testes, runs through the middle of the penis. The urethra is used to pass urine and also, at a different time, to pass sperms out of the man’s body. During intercourse the penis becomes stiff as blood is pumped into a cavity called the corpus cavernosum.

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Which gland helps with digestion?

                         The pancreas is an important gland that helps with digestion. It also controls sugar levels within the body. The pancreas produces digestive enzymes that flow into the intestine during the process of digestion. The pancreas also functions as an endocrine gland, releasing the hormone insulin into the blood. Insulin helps the body’s cells to use glucose, which is essential in the production of the energy that powers cells.

Which hormone affects growth?

                        Growth hormone, one of the most powerful hormones in the body, is produced in the pituitary gland. Growth hormone causes growth throughout childhood and adolescence, and it also affects the way that food substances are used to build new tissues. It stimulates cells throughout the entire body, and also causes the liver to produce special substances that activate bone and muscle growth.

                        Growth hormone is produced in differing amounts during adolescence, which is why children have a series of ‘growth spurts’ when they grow very rapidly. In adults, growth hormone acts mainly to maintain and repair the tissues.

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What is diabetes?

                     Diabetes is an illness that is caused when the body does not produce enough insulin. The result is that large amounts of glucose build up in the blood and the person has to urinate frequently to get rid of it. At the same time the loss of fluid makes the person very thirsty. A diabetic person may lose weight, because the body breaks down body fat when it cannot get energy from glucose, Sometimes the insulin shortage can be corrected by drugs or, in the case of severe diabetes, by having regular insulin injections of insulin.

What happens when I am frightened?

                        When you are frightened, hormones help to prepare you to fight or to run away. This is a primitive reaction that all human beings still have, and it can affect our day-to-day behaviour. A hormone called adrenalin is released from the adrenal glands, which are small glands attached to the kidneys. Adrenalin readies the body for instant action. It makes your heart beat faster and you breathe more deeply. The increased blood flow releases energy from the stored food materials, ready to provide power for the muscles to work.

                        Adrenalin causes the pupils of the eye to open wider, improving vision. Also, it makes digestive processes stop, allowing energy and blood to be channelled to other important areas. Blood is channelled away from the skin, so you become pale, and tiny muscles in the skin contract making your hairs stand on end, causing ‘gooseflesh’.