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Reproductive Systems Sexual activity is a basic drive and one that humans share with all other animals. It is necessitated by the need to reproduce in order for the species to survive. In humans, the reproductive organs and glands begin to develop during the phase of growth known as puberty. In women, a finely-tuned timing mechanism controls the major physical processes of reproduction and this is evident in the processes of menstruation, conception and pregnancy. Reproductive Organs The reproductive organs of the male and female are divided into two parts the external and internal genitals and the gonads. The gonads are represented in the male by the testes and in the female by the ovaries. It is during puberty that the gonad: begin to grow and become active under the influence of the gonado-tropic hormones which are producer in the pituitary gland. These hormones in turn stimulate the production of the sex hormones: testosterones, or androgens, in males and oestrogen: and progesterones in females. These sex hormones promote the growth of the genitalia as well as secondary sexual characteristics such as the growth of the larynx in the male (which produces the breaking of the voice), and the onset of menstruation or the menarche, in the female. The Male In men, the genitals consist of the penis and scrotum, which are situated outside the body, and the prostate gland, seminal vesicles and various tubes of the genital tract, which are found inside the abdominal cavity. The male genital system is designed to produce sperm and deposit them in the female. The penis consists of a central tube - the urethra - down which urine passes when a man relieves himself (urination or micturition), or down which semen passes during inter-course. The urethra connects the bladder, where urine is stored, to a hole at the tip of the penis (the meatus). Semen enters the urethra during inter-course through a pair of tubes called the seminal ducts or vas deferens which join it shortly after it leaves the bladder. A tight ring of muscle at the opening from the bladder into the urethra keeps the passage closed so that urine only emerges when this is intended. The penis usually hangs down in front of the scrotum, the wrinkled bag that contains the testes, in a slack or flaccid state. Its length varies from 6-12 cm (2%-5in). When sexually stimulated it becomes stiff and erect, usually pointing slightly upwards. It is then 10-20 cm (4-8 in) long. The tip of the penis - the glans or ‘helmet’ - is the most sensitive area. The valley behind the glans is the coronal sulcus, the main length of the penis is the body or shaft, and the area of the penis where it joins the lower abdomen is called the root. Erection The greater part of the penis is made up of three groups of tissue which are responsible for erection. These areas are supplied with a rich network of blood vessels, and when a man is sexually excited the amount of blood flowing into these areas increases enormously, while at the same time it is prevented from leaving. This engorgement with blood makes the penis longer, thicker and rigid; it also rises as the internal pressure increases. After ejaculation has taken place and sexual excitement has subsided, the blood flow diminishes to normal levels and the penis returns to its flaccid state as the extra blood causing the erection drains away. The Foreskin And The Glans The delicate glans is protected by a loose fold of skin called the foreskin or prepuce. As the penis enlarges during erection this peels back to leave the glans exposed to the stimulation that eventually leads to orgasm. The skin on the glans and foreskin make a greasy substance called smegma, which acts as a lubricant facilitating the movement of the foreskin over the glans. It is important to wash this away regularly: in some men smegma tends to accumulate, forming a smelly, cheesy mess which can cause soreness or inflammation of the foreskin - a condition called balanitis. Repeated or persistent balanitis is sometimes a medical reason for carrying out circumcision - which is normally a social or religious practice. The Testes The normal human male has two testes which develop in the embryo from a ridge of tissue at the back of the abdomen. When the testes have formed, they gradually move down inside the abdomen so that at the time of birth, each testis has usually arrived in its final position within the scrotum. The function of the testes is twofold. First, they provide the site where sperm is manufactured; each sperm contains all the genetic information for that particular male. Second, the testes contain cells which produce the male sex hormone testosterone and consequently the male characteristics such as the deep voice, male hair distribution and typical distribution of fat. These two functions are carried out by completely separate sets of cells within each of the testes; one function can fail without the other one necessarily doing so. The testes are oval structures. Attached to the back of each one is a smaller structure which is shaped like a long comma and is called the epididymis. The epididymis consists of a series of microscopically tiny tubes which collect sperm from the testis. These tubes connect together to form one tube, called the vas deferens, which transfers the sperm towards the base of the bladder. All these structures, with the exception of the vas deferens, are microscopic in size. Each testis is suspended in the scrotum by the spermatic cord, which consists of the vas deferens, the testicular artery and the testicular vein. These three structures are surrounded by a tube of muscle, called the cremasteric muscle. The spermatic cord, therefore, serves two purposes: first, to provide a blood supply to the testis; and second, to conduct the newly-formed sperm away from the testis. Sperm Sperm is the name given to the male reproductive cell. Its only purpose is to achieve fertilization by union with the female cell, the ovum. Each sperm is about 0.05 mm in length and is shaped like a tadpole. It has three main sections which consist of a head, a mid-section and a tail. The front of the head - the acrosome - contains special enzymes which enable the sperm to penetrate into the ovum and so achieve fertilization. The mid-section contains structures called mitochondria, which hold the vital source of energy needed by the sperm on its journey to the ovum. The tail’s only function is to propel the sperm, which it does by moving in a whip like fashion, generating a speed of about 3-3.5 mm per minute. The sperm is made up of a number of chemicals and genetic material. These are the chomosomes which carry the genetic blueprint of the father, and which will determine the paternally inherited characteristics of the child. It is the sperm which carries the genetic message that determines the sex of the child. The Manufacture Of Sperm The successful manufacture of sperm necessitates a temperature of about three degrees Centigrade lower than the rest of the body. Consequently, manufacture takes place outside the body, within the scrotum. Surrounding tissue helps to regulate the temperature of the testicles inside the scrotum by pulling them upwards to the body in cold conditions, and by a rich supply of blood vessels which dissipate the heat when the temperature gets too high. Sperm production - at the rate of 10 to 30 billion a month - takes place in the seminiferous tubules in the testicles. The newly formed sperm then pass through the seminiferous tubules into the epididymis which is located behind the testicles. This serves as a storage and development area, the sperm taking between 60-72 hours to achieve full maturity. In fact, the epididymis can be emptied by three or four ejaculations in twelve hours; it takes about two days to be refilled. If there is no ejaculation, the sperm disintegrate and are reabsorbed. Ejaculation Before ejaculation occurs, the sperm move along the vas deferens - two tubes connecting the testicles to the prostate gland - and into a further storage area, the ampulla. Here, the sperm receive a secretion from the seminal vesicles, two coiled tubes adjoining the ampulla. This secretion, called seminal fluid, stimulates the motility - the ability to move spontaneously - of the sperm, and helps them survive in the vaginal secretion. The prostate gland through which the sperm pass during ejaculation produces a small amount of a similar fluid, giving the sperm full motility. At the moment of ejaculation the sperm and seminal fluid are forced out of the ampullae, and epididymes, into the urethra by a series of muscular contractions. lf the sperm have been ejaculated into the vagina of a woman, they move as fast as they can through the cervix and into the uterus, where they make their way into the Fallopian tubes. It is in these tubes that fertilization may occur if an egg is present. The Prostate Gland The prostate gland is a walnut shaped structure found only in males. It is situated at the base of the bladder and surrounds the urethra. This gland produces the fluid that mixes with semen to make up part of the seminal fluid. Although the exact function of the prostatic fluid is unknown, it is thought that one of its roles is to help keep the sperm active so that fertilization can occur more easily. Owing to its position in the body, problems associated with this gland can often affect the normal functioning of the bladder - although this particular problem is more common among elderly men. The Female The female’s reproductive system must not only receive the sperm but also must produce ova (eggs) for fertilization and eventually nurture one egg if it is fertilised, so that a baby can develop. The external female genitals are the clitoris and the labia, which together are known as the vulva. Most prominent among the parts of the vulva are the two pairs of ‘lips’ or labia. The outer and larger labia majora consist of thick folds of skin that cover and protect most of the other parts. They become thinner at the base and merge with the perineum (the skin over the area between the vulva and the anus). At the top the outer lips merge with the skin and hair on the pad of fatty tissue that covers the pubic bone, the mons pubis or mons veneris often referred to as the Mount of Venus. Within the labia majora are the labia minora or ‘lesser lips’. They join at the top to form a protective hood over the sensitive clitoris, dividing into folds which surround it. They also protect the opening to the urethra or water passage. The area between the labia minora is largely taken up by a space called the vestibule. Before a women is sexually active, the space is mostly covered by the hymen, also known as the maidenhead. This varies in shape, size and toughness. The tags of skin which many women have around the vestibule are the remains of the hymen, and are called the carunculae myrtiformes. At the back, the labia minora join to form the fourchette, which is often ruptured during the first childbirth. The Clitoris And Glands The clitoris is actually similar in structure to the penis, even to the extent of having a hood of labia equivalent to the foreskin and a small connecting band of tissue called the frenulum. It is primarily an organ of sexual excitement. It is extremely sensitive, and when stimulated its spongy tissue fills with blood and becomes erect. Friction on the erect clitoris either by movement of the penis during intercourse or by some other means will usually lead to orgasm. Other parts of the vulva also respond to sexual stimulation: the labia contain erectile tissue and often become enlarged during lovemaking; and the Bartholin’s glands become active. There are two pairs of glands associated with the vulva. The first are Skene’s glands which lie just below the clitoris and secrete an alkaline fluid which reduces the natural acidity of the vagina. The other, larger pair lies in the bottom of the vestibule. These are Bartholin’s glands and they secrete fluid when a woman is sexually aroused, so that the entrance to the vagina becomes moist and can more easily accommodate the penis. These glands are normally about the size of a pea and not prominent. They are liable, however, to venereal and other infections, becoming swollen, red and tender. This condition (Bartholinitis) requires treatment with antibiotics. In some cases, an abcess forms in one of the glands a Bartholin’s abcess - and this may need to be incised to release the pus. The Vagina The vagina is the channel which leads from the vulva to the uterus. During a won1an’s life the vagina undergoes` several changes. The vagina of a child is obviously smaller than that of a mature woman. The lining of the wall of the vagina is thinner in a child or post-menopausal woman than that of a woman in the reproductive years of her life. These changes are largely influenced by a group of hormones released by the ovary; these are called oestrogens. The vagina plays an important role during intercourse and childbirth. The role during childbirth is relatively passive when the vagina forms the lower portion of the birth canal and is capable of opening sufficiently to allow the birth of the baby. We have only relatively recently begun to understand some of the changes which occur in the vagina during intercourse. Structure The vagina is a canal 7 cm (2% in) to 9 cm (3% in) long, surrounded by fibrous and muscular tissue, but lined with a layer of cells called squamous epithelium. The walls of the canal are normally collapsed onto one another and thrown into many folds. These properties make it easy for the vagina to be distended during intercourse or childbirth. The urethra lies on the front wall of the vagina and the rectum lies on the upper third of the back of the vagina. The anus is separated from the vagina by a fibro-muscular tissue called the perineal body. During the reproductive years of a woman’s life the vaginal secretions are slightly acidic. This tends to inhibit the growth of harmful bacteria in the vagina, but during the pre-pubertal and post-menopausal years, the vagina becomes mildly alkaline. Under these circumstances the bacteria can thrive and occasionally make the vagina rather sore and uncomfortable a condition called atrophic vaginitis. The walls of the vagina are well lubricated with secretions from the cervical canal and Bartholin's glands. During intercourse, secretions also seep through the vaginal epithelium into the vaginal canal. A certain amount of discharge from the vagina is normal in all women. The amount increases during ovulation and sexual arousal. The hymen, also known as the maidenhead, is named after the Greek god of marriage, Hymen. The hymen has no known physiological function but has achieved great importance in nearly all cultures as an insignia of virginity. However, hymens come in all shapes and sizes, and there is no way in which a hymen can be a reliable indication of virginity. It is usually thin, punctured by holes and can easily be broken by strenuous physical exercise such as running and horse riding. Heavy petting, masturbation or the insertion of tampons can also cause a rupture. Although the condition of the hymen is no proof of virginity, very often the hymen is first broken during sexual intercourse. Contrary to popular belief, an intact hymen does not prevent pregnancy. A sperm that comes into contact with the genital area, perhaps as a result of heavy petting, can travel through a hole in the hymen and up into the vaginal canal. Function Of The Vagina During sexual arousal the genital organs, especially the labia minora and lower vagina, become engorged with blood and the amount of vaginal secretion increases. During an orgasm the muscles of the pelvis including those surrounding the vagina contract involuntarily. If a woman is particularly tense or anxious during intercourse, the muscles surrounding the vagina will go into spasm. This makes the vagina narrower and also makes sex painful. This condition is called vaginismus. It can be cured by help from a psycho-sexual counsellor, but if often takes many months before the woman can fully enjoy sex. The Uterus The uterus is composed of two main parts the corpus or body of the organ, and its cervix or neck and it is capable of undergoing major changes during a woman’s reproductive life. From puberty to the menopause, the endometrium develops each month to provide nutrition for a fertilized egg. If the egg is not fertilized the endometrium is shed during menstruation, and is slowly replaced in the course of the next menstrual cycle. The cervix is shaped like a cylinder and its lower part projects into the vagina. The cervix is about 2.5cm (in) long, and has a fine canal running through it which opens into the cavity of the uterus above, and the vagina below. If a finger is inserted into the vagina, the cervix can be felt as a small dimple. In a woman who has not had children, this opening into the vagina is circular and quite small. During child birth this stretches to allow the passage of the baby, and after childbirth it reshapes into a cross-wise slit. During pregnancy, the uterus expands to allow the foetus to grow, and provides it with protection and nutrition. At the same time, the large muscle fibres are prevented from contracting. The uterus suddenly changes its role when the foetus is mature and begins to contract in order to open the cervix and allow the baby and placenta to pass through. The uterus then contracts tightly to close off the large blood vessels which have been supplying the placenta. After the birth it rapidly returns to its pre-pregnant state, ready to accept another fertilized egg. Rarely, this has been reported as happening as early as 36 days after the birth. The uterus seems to have almost no function before puberty and after the menopause when it would obviously be unsuitable, mentally and physically, for a woman to have a baby. All these changes in the functioning of the uterus are orchestrated by hormones released from the pituitary gland and from the ovaries, and by similar substances called prostaglandins which are released by the uterine tissue. The way in which these substances interact is still not fully understood. Position In an adult woman the uterus is a hollow organ approximately the size and shape of a small pear, and lies inside the girdle of pelvic bones. The narrow end of the pear is equivalent to the cervix which protrudes into the vagina the remainder forms the body of the uterus. This is connected to the two Fallopian tubes which carry the monthly egg released from one of the pair of ovaries. In this way the uterus forms part of a channel between the abdominal cavity and the world outside the body. Special mechanisms exist to prevent the spread of infection via this route into the abdominal cavity. Thus the lining of the uterus is shed when a woman menstruates, the cervix secretes protective antibodies and the natural acidity of the vagina inhibits the growth of harmful bacteria. The front of the uterus sits on the bladder and the back lies near the rectum. The uterus is normally supported inside the pelvis by muscles called the pelvic floor muscles and by bands of connective tissue and blood vessels from the side wall of the pelvis which are attached to the cervix. During pregnancy the uterus enlarges so that by the 12th week it can just be felt inside the abdominal cavity above the pubic bone. At about 38 weeks it usually reaches the lower end of the rib-cage, and about two weeks after the baby is born, the uterus can normally no longer be felt in the abdomen. After the menopause, the uterus shrinks in size. The variations in size are controlled by the secretions of sex hormones, which also govern the nature of the endometrium. During the first half of a woman’s menstrual cycle, the endometrium increases in thickness until the egg is released. It then stops growing but begins to secrete substances rich in nutrients to allow further growth of the egg if it is fertilized. If the egg is not fertilized, the endometrium is shed during menstruation. The Ovaries The ovaries are the parts of the female reproductive system which are designed to make and release mature ova, or eggs. When the ovum is fertilized by a sperm from a man it marks the start of a new human life. From the first period to the menopause, normal ovaries release one egg each month. They are also essential parts of the body’s hormonal, or endocrine, system. The ovaries are two grey-pink, almond-shaped structures each about 3 cm (1.2 in) long and about 1 cm (0.4in) thick. They are found in the pelvis, the body cavity bounded by the hip or pelvic bones, and lie one on each side of the uterus. Each ovary is held in place by strong, elastic ligaments. Just above each ovary is the feathery opening of the Fallopian tube which leads to the womb, or uterus. Although they are very close to each other there is no direct connection between the ovary and the tube opening. n In a mature woman the ovaries have a rather lumpy appearance. The reason for this can be seen by looking at the internal structure under a microscope. Covering the ovary is a layer of cells called the germinal epithelium. lt is from the cells in this border layer that the eggs or ova form; thousands of immature eggs, each in a round casing or follicle (the egg sac) can be seen clustered near the ovary edge. Much more noticeable, however, are the follicles containing eggs in various stages of maturation. As these follicles enlarge, and after their eggs have been released, they produce the characteristic bumps on the ovary surface. The centre of the ovary is filled with elastic fibrous tissue which acts as a support for the follicle containing outer layer. Ovulation Under a microscope, maturing follicles of the ovary can be seen as tiny balls enclosing a small mound of cells. In the centre of the mound is the egg cell in its final stages of maturation. When the follicle is ripe and the ovum matures, the cells at the follicle edge allow the ovum to leave. Exactly how this happens is still a mystery. The ovum is then wafted by the feathery ends, or fimbria, of the Fallopian tubes into the tube openings. In their role as egg producers the ovaries also act as hormonal or endocrine glands. The ovaries function under the control of the pituitary gland at the base of the brain. The pituitary first makes a hormone, called follicle stimulating hormone (FSH), which travels in the bloodstream to the ovaries. FSH stimulates follicles and ovum development but it also brings about the secretion of the hormone oestrogen. Under oestrogen influence the lining of the uterus thickens in preparation for receiving a fertilized egg. Oestrogen also stimulates the build up of body proteins and leads to fluid retention. After a follicle has ripened and burst, another pituitary hormone, luteinizing hormone, or LH, goes into action and brings about the development of the corpus luteum (yellow body) in the empty follicle. (The job of corpus luteum is to help establish a pregnancy.) In turn, the corpus luteum makes and releases its own hormone, progesterone. If the egg is not fertilized within a fortnight the corpus luteum shrinks, progesterone production is turned off, and the lining of the uterus is shed as the monthly menstrual period. Now FSH production begins again and the whole cycle is repeated. lf, however, the egg has been fertilized then the corpus luteum goes on working until the placenta is established and there is no bleeding. Menstruation Ovary development is largely complete by the time the female foetus is in the third month of life in the womb, and few major changes will take place until puberty. By the time a baby girl is born her ovaries contain, between them, from 40,000 to 300,000 primary follicles, each containing an immature egg. At most only 500 or so of these eggs will ever be released, and probably no more than half a dozen - if that - will develop into new human beings. When the ovaries first start to make the hormone oestrogen, they are not yet capable of releasing mature eggs. These early oestrogens bring about the physical changes of puberty such as growth of breasts, pubic hair, and widening of hips. These changes begin at least a year before a girl has her first period, and are a sign that the oestrogens have begun to stimulate the release of mature eggs.
Conception is the union of a sperm and egg. It is a complex process in which a variety of conditions have to be right to ensure that it is successful. lf intercourse takes place around the time of ovulation, conception is very likely. A man produces around 400 million sperm in each ejaculation. These are surrounded by seminal fluid, which protects the sperm from the acidity of the vagina. Once deposited in the vagina, the sperm immediately start their journey up the vagina through the cervix and into the uterus. They move by vigorously lashing their tiny ‘tails’. Some of the sperm do not make this journey successfully, and will wither and die in the acid conditions of the vagina. This is nature’s way of ensuring that damaged or unhealthy sperm do not manage to fertilize the egg. Fertilization The millions of sperm that have reached the uterus are nourished by the alkaline mucus of the cervical canal. They then travel up into the Fallopian tubes. This journey of about 20 cm (8 in) takes approximately 45 minutes - only about 2000 sperm may actually survive. The sperm will stay alive within the Fallopian tubes for up to three days, ready to fuse with an egg if ovulation takes place. If an egg is already present within the tube, fertilisation will take place immediately. Fertilization is accomplished when a sperm penetrates the surface of the egg. Each sperm carries an enzyme (a substance responsible for causing life-supporting chemical processes) which helps liquefy the outer surface of the egg to make penetration of a single sperm easier. Once the egg is fertilized, the rest of the sperm die. The egg and sperm (which has now discarded its tail) then fuse together to form a single nucleus (centre), which then begins to divide into two cells. Within 72 hours the cells continue to divide until a 64- celled egg is produced. The fertilized egg then travels down to the uterus within approximately seven days (day 21 of a 28-day cycle). During this time it grows tiny projections which help it to burrow into the lining of the uterus, where it can be nurtured and a pregnancy can start. Once. this process, called nidation, has occurred conception is complete. The egg can now be nourished by the rich blood supply present in the uterine lining. From the moment of fertilization, the egg produces a hormone called human chorionic gonadatrophin (HCG), which informs the ovary that fertilization has taken place, and which maintains the blood flow to the lining of the. uterus so that the egg can continue its development. The placenta The placenta forms when a specialized part of the fertilized egg, called the trophoblast, embeds in the wall of the mother’s uterus. By the 12th week of pregnancy the placenta is a separate organ; at the time of the baby’s birth it weighs approximately 500 gm (a little over a pound) and is dark red, spongy and disc-shaped. Two layers of cells keep the circulation of the foetal blood in the placenta separate from the mother’s blood, but many substances can pass from mother to baby. Function All the food and oxygen the foetus needs it receives from the mother, and it is able to eliminate any waste products back into her. This vital exchange function is carried out by the placenta, to which the foetus is attached by the umbilical cord. Carbon dioxide, waste products and hormones pass from the foetus to the mother; oxygen, nutrients (simple carbohydrates, fats and amino acids) and hormones from mother to foetus. The placenta also acts as a barrier to protect the foetus from potentially harmful substances, although many drugs can cross the placenta and harm the foetus. Some of the mother’s antibodies, too, cross the placenta. Finally, the placenta produces several hormones, some of which prevent the woman from releasing more eggs or having more periods while she is pregnant. They also encourage breast development in preparation for breast feeding, and the laying down of fat on the thighs, abdomen and buttocks as a future energy store. Other hormones also stimulate the growth of the womb and probably inhibit it from contracting before labour starts. There is also evidence to suggest that the amounts of these hormones released by the placenta may be an important factor in determining when labour starts. Foetal development The foetus is the name given to the unborn child from the time it is recognizable as a developing human being (from about two months after the egg has been fertilized). Prior to this the developing fertilized egg is known as the embryo. A doctor will date the start of pregnancy from the first day of the last menstrual period, adding on nine calendar months and seven days to arrive at an estimate of the delivery date. Pregnancy is divided into trimesters (periods of three months in the life of the embryo or foetus), but in fact conception will probably take place between the tenth and fourteenth day of the menstrual cycle, when a woman is most likely to be ovulating and at her most fertile; therefore, pregnancy may actually begin during the second week of the first trimester. At this stage, the pregnancy consists of a single fertilised cell or egg. For three days or so after fertilization, this cell moves along the Fallopian tube towards the uterus, dividing and re-dividing to form a small group of cells called the morula. The First Trimester For about another three days the morula floats in the uterus. It divides and re-divides to form a hollow clump of cells called the blastocyst, just visible to the naked eye. Week 2: The blastocyst embeds itself in the endometrium: this is called implantation. Chorionic villi, projections from its covering, burrow into the lining of the uterus, to secure nourishment for the embryo. The outer lining of the blastocyst called the trophoblast, begins to develop into the placenta. Blood cells start to form and the first heart cells are laid down. Week 3: Hormonal changes cause the endometrium to thicken, and the blood from it nourishes the blastocyst. Week 4: The amniotic sac is well developed. The embryo and later the foetus will stay in it throughout the pregnancy, comfortably suspended in the amniotic fluid, at a constant temperature and buffered against shocks. The heart is already beating, irregularly at first, but soon quite steadily and faster than the mother’s. The spine and the beginning of the nervous system are starting to form in the embryo, which is now about 7mm (0.28in) in length. Week 5: The first organs form. The head is growing, enclosing the developing brain, which is linked to a rudimentary spinal cord. The arms and legs show as little buds, and the heart and blood circulatory systems are well established. Blood vessels from the embryo join with others in the developing placenta to form the umbilical cord. The chorionic villi continue to increase in number and to branch, attaching the embryo firmly to the wall of the uterus. In the embryo itself, now about 10mm (0.3in) long, the digestive sys- tem has begun to form, starting with the stomach and parts of the intestines. Although there is as yet no recognizable face, there are little depressions where the eyes and ears will be. The mouth and jaws also are starting to form, and the brain and spine continue to develop. Week 6: The development of the head gets quicker. The internal parts of the ear and the eyes continue to form (the latter covered with the skin that will become the eyelids). The little holes that later become the nostrils start to develop. The brain and the spinal cord are nearly formed. The development of the digestive and urinary systems continues, although the liver and kidneys are not yet able to function. The arm and leg buds have grown and it is now just possible to see the rudiments of hands and feet. By the end of week 6 the embryo is about 1.3cm (0.5in) long. Week 7: The placenta through which the embryo takes nourishment from its mother’s circulation into its own and passes back its waste products to be excreted is now well developed. This is an important time for the growth of the eyes and parts of the inner ear, and the heart beats more powerfully. The formation of the digestive system continues, and many of the internal organs, although still in a very simple state, now exist. The lungs are growing, but they are solid at this point. There are small spinal movements and the face continues to form, to the point where it is possible to see the beginnings of the mouth. The arms and legs are growing and have developed hip, knee, shoulder and elbow joints. Week 8: The eyes are almost fully developed, but are still covered with half-formed eyelid skin. The face continues to form and now has the beginnings of a nose. It is now possible to see separate toes and fingers and the limbs are able to move a little. The head, large in comparison with the rest of the body, leans downward over the chest. The foetus is now approximately 4cm (1.6in) long. Week 9: The umbilical cord is completely formed and nourishes the foetus’s circulatory system with blood. The inner part of the ear is complete; the outer part is starting to form. All the major inner organs of the body continue to develop, and the uterus has increased in size. By this point, the foetus is approximately 4.5cm (1.9in) long. Week 10: The circulatory system is now pumping blood round the body of the foetus. The reproductive system has begun to form, but only inside the body: the external genitals are not yet visible. The face continues to develop and the arms and legs are now very clearly formed, with tiny webbed fingers and toes. Movement of hands and feet is more vigorous, but still cannot be felt by the mother. By the end of week 10, the foetus measures 5.5cm (2.1in). Week 11: The face is almost completely formed and the eyelids have developed. Muscles are starting to form and the development of the external sexual organs has begun. The placenta is by now a separate organ, a soft pad of tissue. The volume of fluid in the amniotic sac continually increases between the eleventh and the fortieth weeks of pregnancy. Weeks 12-14: Nearly all the internal organs are now formed, but they can- not yet function independently of the mother. The uterus can now just be felt, rising above the pelvic bones, but the mother does not yet show her pregnancy. The Second Trimester Weeks 14-16: The limbs go on forming and the joints are able to move. Finger and toe nails develop, and a soft, fine hair, called langou, covers the whole foetus. After week 14 the placenta is fully formed. Growth in size begins to be rapid: the foetus now weighs about 135g (4%oz) and is approximately 12cm (5in) long. After week 16 or thereabouts, the kidneys begin to produce dilute urine. Week 20: By now, the foetus is able to make vigorous kicking movements, which the mother will be able to feel. The muscles are developing fast, and hair has begun to grow on the head. The foetus will now be about 21cm (8.4in) long. Week 24: The muscles ere almost completely formed. The placenta is growing continually: all necessary nutrients, including oxygen, pass through it from the mother to the foetus, end waste products go back through it into the mother’s circulation end she excretes them. The circulation end blood of the mother and baby remain quite separate. The foetus is still not able to exist independently of the mother, although, in very rare instances, babies born prematurely at this point and nursed with expert care have survived. The weight of the foetus is about 570gm (20oz) and the length about 33cm (12.7in). Week 28: This is the point at which the foetus is said to become viable, because it would have a 5 per cent chance of survival if it were born prematurely. Covered with a grease called vernix, to protect it from the fluid in the amniotic sac, it is now approximately 37cm (14.5in) long. The Third Trimester The growth of the foetal body has now caught up with that of the head, and the foetus has the physical proportions of a baby. It is much thinner, however, because the subcutaneous (under the skin) fat has not yet developed. The amount of vernix has in- creased. The length of the body is now about 45cm (1'7.7in), and the baby born prematurely at this stage has a 15 per cent chance of survival. Week 36: By this point, the chance of survival would be increased to 90 per cent, as the lungs are fully formed. In many cases, the baby has turned to rest head downwards in the womb, but in women who have already had a child, this may not happen until later. The testicles of the male baby have come down into the scrotal sac, and the vernix has increased. The baby’s. Weight goes up by about 28gm (loz) per day. Some babies are born with the fine lanugo hair still on the arms, legs or shoulders, but it usually disappears in the final weeks of pregnancy. Birth will take place at about the fortieth week, although some women go into labour later or earlier than this. When the baby is born, there will still be patches of vernix on the body, but not on the eyes and mouth. The child will be about 50cm (20in) long and have an average weight of about 3.4kg (7.7lb). The Mother Since the first trimester is the three- month period in which the basic formation of the foetus takes place, it is important for the mother to avoid anything which could cause foetal malformation. The doctor should be consulted before any drugs are taken, and all women are advised to give up smoking and drinking alcohol as soon as they become pregnant. Before starting a pregnancy, a woman should make sure that she is immune from rubella (German measles) and if she is not, should be vaccinated against it. Contracting it during pregnancy might cause the baby to be born with a number of grave abnormalities. It is important for the mother to see a doctor at the beginning of the pregnancy for a thorough physical check-up and to arrange for antenatal care. Checking on the progress of the foetus is an important part of this. Methods of doing this range from simply measuring the size of the mother’s abdomen to the use of ultra- sound. About a week before the normal menstrual period would start, there may be a little bleeding as new blood vessels are forming to nourish the growing embryo. The doctor should be told of this and of any other symptoms, and he will also give advice on diet and the extra vitamins and iron which may be needed throughout the pregnancy. Regular blood pressure and urine tests should be made to check that the mother is fit and healthy. During the second trimester, the mother will feel the foetus moving inside her, particularly just before she falls asleep. Her own blood circulatory system has changed, with a continual increase in the production of blood cells. Many women find that they drink a great deal more liquid than usual in this period, and some may need iron supplements to help in the increased production of blood. By week 20 the breasts are ready for breast feeding: some women find that the nipples produce a yellow fluid, called colostrum, but not all pregnant women experience this, and those who don’t should not worry that their ability to breast feed will be affected in any way. At this stage of the pregnancy, some mothers have indigestion, heart-burn and constipation, and they need to take these things into account when they are planning their diet. As the pregnancy advances, the increase of weight and pressure on the internal organs can cause haemorrhoids (piles) in the rectum and varicose veins in the legs. The haemorrhoids can partly be prevented by avoiding constipation, and the irritation they cause can be relieved by ointment or suppositories, obtained from the doctor. The wearing of elastic support stockings or tights can help to prevent the formation of varicose veins. But it is essential that these be put on before getting out of bed in the morning. The Third Trimester By the third trimester the uterus has expanded a great deal, and many women find that it is difficult to walk without leaning back a little, which can cause backache. There will be occasional painless contractions of the womb, which are normal and help with circulation through the placenta. Lying on the stomach will become uncomfortable. However, once the baby’s head has ‘engaged’ - descended into the pelvis - many women feel a great deal more comfortable, because the pressure on the stomach and diaphragm is much reduced. Some time in or about the fortieth week, labour will begin. The mother’s pelvic bones have already become more separated in readiness for the delivery of the baby. Powerful contractions, rupture of the amniotic sac, or the passing of a little blood from the uterus, are among the first signs that the baby is about to be born. The cervix starts to dilate and the baby begins its journey. At birth, the average baby weighs about 3.4kg (7.'/lb), but a birth weight of anything between 2.8kg (6.2lb) and 4.0kg (8.8lb) is regarded as normal. The hair on the newborn baby’s head varies in length from scarcely visible to about 4cm (1.5in), the nails reach to the ends of the fingers and toes, or even a little beyond them, and the eyes are almost always blue in colour, because the eye colouring is not yet fully formed.
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