Gynaecological Anatomy (Structure) and Physiology (Function) – Female Pelvic Anatomy-Chapter 2:

Q 2. 1 What is meant by the term anatomy?

• The study of the structure of the body is called anatomy. Surprisingly, this science has only developed in the last few centuries. Before then, even the basic structure of the human body remained shrouded in mystery as dissection of the human body was forbidden by most religions. As technology advances, we gain the tools to study the body in greater detail. The microscope, first described just three hundred years ago, opened up details of the structures of the body too small to be seen by the naked eye. The microscope allows us to look at the finer detail of the structure, called the histology, of the body. The smallest entities of life are called cells (Figure 21.2).

Q 2. 2 What is the anatomy of the external genital area?

• The anatomy of the external genital area, the vulva, of an adult woman is shown in Figure 2.2. There are two folds of skin (labia – lips) on each side. The labia majora contain fatty tissue and they are covered by hair. They help to keep the vaginal introitus (entrance) closed, which assists in the prevention of infection. The inner labia (labia minora) contain no fat and they are not covered by hair. The clitoris is a small structure seen at the top of the labia minorae. In addition to protection, the labia minorae, together with the clitoris, play a critical role in sexual activity. They have a rich nerve supply which makes them very sensitive and during sexual arousal they become engorged with blood.

• Inside the labia minorae and outside the hymen is the vestibule. There is a Bartholin’s (greater vestibular) gland on each side which provide some of the lubrication for sexual intercourse.
• The vagina has an epithelium (skin-like covering) which is surrounded by muscle. It is flat with the front and back walls in contact. The vagina extends upwards and backwards (Figure 2.1). It opens to become a tube during sexual intercourse and during childbirth. Before first intercourse, the hymen has a very small opening. Many teenagers use tampons which will stretch or tear it.

• One or two finger widths behind the vagina is the anus which is the opening from the lowest part of the bowel called the rectum. The perineum is the area between the vagina and the rectum.
• It may be surgically cut, an episiotomy, or torn during childbirth.

• The urethra is the tube leading out from the bladder. It opens between the labia above the vaginal opening.

Q 2. 3 What are the internal genital organs?

• The internal genital organs are the uterus, ovaries and Fallopian tubes. The uterus is the size and shape of a medium sized pear although it is flattened from front to back. The narrow end of the uterus is the cervix and the upper part is called the body. The cervix, the neck of the womb, protrudes into the top of the vagina (Figure 2.1). In a child, the cervix forms about two-thirds of the length of the uterus but as the uterus enlarges following puberty, the proportions are reversed. After the menopause the uterus becomes small again. During childbirth the cervix is stretched open. When fully open it becomes continuous with the vagina to form the birth-canal through which the baby descends into the world.

• You may be able to feel the cervix by introducing a finger inside the vagina. It is a firm structure that feels like the tip of the nose. The small central depression , the external os, is the entrance to the cavity of the uterus. The cervical canal is the inner tube of the cervix leading from the vagina to the cavity of the uterus. Cervical mucus is secreted by tiny glands lining the canal. During reproductive years this mucus is watery around the time of ovulation (egg release) – at other times it is thick and acts as a barrier to sperm and infection.

• The body of the uterus has a central cavity, the endometrial cavity, which is triangular with the front and back walls touching. The endometrial cavity has a very special covering – the endometrium. During menstruation most of the endometrium is shed leaving just a residual basal layer which regenerates the endometrium during each menstrual cycle (Figure 2.3). The endometrium has the ability to allow an early embryo to become implanted and to receive nourishment before the placenta (afterbirth) develops.

• The Fallopian tubes, or oviducts, extend for about 10 cm from each cornu (Latin, horn) of the body of the uterus, outwards to their openings near the ovaries (Figure 2.1). At their openings there are very fine finger-like fronds called fimbria. The inner surface of the tubes have fine hair-like structures called cilia which help to move eggs, released from the ovaries, along the tubes and into the cavity of the uterus.

• The ovaries release ova (eggs) and female sex hormones. Primordial follicles consist of a primary oocyte (egg) and pre-granulosa cells which surround the egg and when it matures it is these cells that will produce the sex hormones (oestrogens and progesterone – Q 2.9 and Q 2.13). Primordial follicles first appear in the female fetus 16 weeks after conception and it is believed that all the follicles are formed within six months of birth. A baby girl will have between two and three million primordial follicles but by puberty the number has fallen to about 250,000. These follicles lie dormant until they go into a phase of maturation. During reproductive years, one or two follicles will become ‘dominant’ each month and are released at ‘ovulation’. There may be about 300 episodes of ovulation during a woman’s reproductive years. If we were to assume ova were scheduled to start their active phase of development on a regular basis, this would equate to 20 each day or 600 each month. During a process called atresia, eggs are lost at some stage without maturing to ovulation.

• There remain many unanswered questions about reproductive physiology. Perhaps the most intriguing of these relates to the timing of individual egg maturation. Although the exact mechanism remains to be established, from a functional point of view, each primordial follicle behaves as if it has its own egg-timer so that it will start its maturation process at a pre-determined time (Figure 2.4). Some ova have relatively small egg-timers resulting in the egg maturing whilst the woman is in her teens and others may have larger egg-timers resulting in egg maturation perhaps in her thirties or forties.

Q 2. 4 What is the peritoneum?

• The peritoneum is a thin, transparent layer that covers the inner aspect of the abdominal wall and most of the organs within the abdomen. The uterus and the Fallopian tubes are covered by peritoneum but the ovaries are not.

Q 2. 5 Why did I develop into a girl?

• The reproductive organs of boys and girls are determined by chromosomes (genes). Human cells have twenty-three pairs of chromosomes. One of each pair comes from your mother and the other from your father. The chromosomes determine how the body develops and functions. The length of each pair of chromosomes is identical with the exception of the sex chromosomes of the male. The chromosomes are numbered 1- 23. The mother will provide an X chromosome to all her eggs but the father provides either an X-chromosome from his mother or a Y-chromosome from his father. The sex chromosomes (X and Y) are the chromosome pair number 23.

• Ordinary cells duplicate themselves completely, including the pairs of chromosomes, before dividing into two, by a process called mitosis. During production of egg cells and sperm cells, only one of each pair of chromosomes is replicated, this process being called meiosis. As a result, the gametes, the eggs and sperm, have twenty-three single chromosomes; they are not in pairs. The fertilised egg, which is now called the embryo, will have twenty-three pairs of chromosomes – the twenty-three from the egg and the twenty-three from the sperm. If the fertilised egg has two X-chromosomes, the resulting child will be a girl and if there is one X-chromosome and one Y-chromosome the child will be a boy.

• Until the eighth week after conception, there is no obvious difference between the external genital area of the two sexes. Over the next few weeks the differences become apparent.

• Q 2. 1 What is meant by the term anatomy?
• Q 2. 2 What is the anatomy of the external genital area?
• Q 2. 3 What are the internal genital organs?
• Q 2. 4 What is the peritoneum?
• Q 2. 5 Why did I develop into a girl?
• Q 2. 6 How do sperm development and egg development differ?
• Q 2. 7 What is meant by the term physiology?
• Q 2. 8 What is a hormone?
• Q 2. 9 What are steroid hormones?
• Q 2. 10 What is sex hormone binding globulin?
• Q 2. 11 What controls sex hormone release?
• Q 2. 12 How do oestrogens and androgens affect me?
• Q 2. 13 What are progesterone and progestogens?
• Q 2. 14 How do my menstrual cycles occur?
• Q 2. 15 Could I have some useful Web sites?

Q 2. 6 How do sperm development and egg development differ?

• All the eggs available to a woman have developed in her ovaries whilst she was a baby. They lie dormant until they go into an active phase (Q2.3). Sperm development (spermatogenesis) is an ongoing process throughout a man’s adult life. It takes approximately three months for a sperm to be produced and reach maturity. It has been estimated that each testicle is producing 1000 new sperm every second.

• Q 2. 1 What is meant by the term anatomy?
• Q 2. 2 What is the anatomy of the external genital area?
• Q 2. 3 What are the internal genital organs?
• Q 2. 4 What is the peritoneum?
• Q 2. 5 Why did I develop into a girl?
• Q 2. 6 How do sperm development and egg development differ?
• Q 2. 7 What is meant by the term physiology?
• Q 2. 8 What is a hormone?
• Q 2. 9 What are steroid hormones?
• Q 2. 10 What is sex hormone binding globulin?
• Q 2. 11 What controls sex hormone release?
• Q 2. 12 How do oestrogens and androgens affect me?
• Q 2. 13 What are progesterone and progestogens?
• Q 2. 14 How do my menstrual cycles occur?
• Q 2. 15 Could I have some useful Web sites?

Q 2. 7 What is meant by the term physiology?

• Physiology is the study of the way that the body functions.

• Q 2. 1 What is meant by the term anatomy?
• Q 2. 2 What is the anatomy of the external genital area?
• Q 2. 3 What are the internal genital organs?
• Q 2. 4 What is the peritoneum?
• Q 2. 5 Why did I develop into a girl?
• Q 2. 6 How do sperm development and egg development differ?
• Q 2. 7 What is meant by the term physiology?
• Q 2. 8 What is a hormone?
• Q 2. 9 What are steroid hormones?
• Q 2. 10 What is sex hormone binding globulin?
• Q 2. 11 What controls sex hormone release?
• Q 2. 12 How do oestrogens and androgens affect me?
• Q 2. 13 What are progesterone and progestogens?
• Q 2. 14 How do my menstrual cycles occur?
• Q 2. 15 Could I have some useful Web sites?

Q 2. 8 What is a hormone?

• A hormone is a chemical substance that is produced in a special tissue within a gland. Hormones are released into the bloodstream and then travel to distant responsive cells where they exhibit characteristic effects. A hormone acts like a key fitting into a lock and this produces a characteristic response. We call the ‘locks’ receptors. Hormones are essential chemical regulators of body functions. Well known examples include insulin, which prevents our blood sugar rising too high after a meal, and thyroxin, the thyroid hormones, which regulates the speed of body activities.

• Hormones are extremely potent. Although they are released in tiny amounts, their effects are profound. An oestradiol implant, which is introduced under the skin, usually when the ovaries are no longer functional after the menopause (Q28.6), is smaller than an airgun pellet and most of it is composed of inert material which slowly releases the hormone. A typical oestradiol implant will contain only one twentieth of a gram of oestradiol. This may be enough for one year to maintain generalised well-being, to relieve menopausal symptoms and, in the long-term, to reduce the risks of cardiac disease and osteoporosis significantly.

• Endocrinology is the medical discipline involving hormone investigation and treatment.

Q 2. 9 What are steroid hormones?

• Steroid hormones are a subgroup of lipids (‘fat’ chemicals), which share a chemical structure characterised by four fused rings (Figure2.5). Each ring has five carbon atoms (C). Cholesterol (chole – bile, and steros- solid) was the first of this group to be purified and gave us the group name ‘steroids’. There are complex chemical pathways from cholesterol through to the sex steroids – progesterone, testosterone and the oestrogens. A simplified pathway is shown in Figure 2. 6 . Testosterone is one of the male hormones, called androgens, and oestradiol is one of the female hormones called oestrogens. Men and women have both androgens and oestrogens although in women oestrogens predominate whereas in men there are more androgens. There is only one progesterone although synthetic ‘progestogens’ used in treatment regimens are similar in structure.

• What is ‘anatomy’?
• Describe the anatomy of the external female genitalia.
• Anatomy of the Female Pelvis
• What is the peritoneum?
• Why did I develop into a girl?
• How do sperm development and egg development differ?
• Physiology. What is meant by the term physiology?
• Female Physiology. What is a hormone?
• What are steroid hormones?
• What is sex hormone binding globulin (SHBG)?
• Reproductive Hormone Release
• Female Physiology. How do oestrogens and androgens affect me?
• Female Physiology. What are progesterone and progestogens?
• Female Physiology. How do my menstrual cycles occur?
• Female anatomy and physiology – Web Sites

Q 2. 10 What is sex hormone binding globulin?

• Hormone molecules are bound to proteins in the blood. Bound hormone molecules are inactive until they are released and become free. The main protein produced by the liver and released into the blood is albumin, which is similar to the egg white of a chicken egg. Sex hormone-binding globulin (SHBG) is one of the proteins produced by the liver. The binding capacity of this protein for testosterone is 30,000 times greater than that of albumin. During their reproductive years, women have double the concentration of SHBG when compared to men as oestrogens encourage SHBG production. Androgens, such as testosterone, suppress SHBG production. Women with hirsutism (excess body hair Q 8.6) associated with hyperandrogenism have relatively low SHBG levels resulting in increased levels of free, actively available, androgens.

• Q 2. 1 What is meant by the term anatomy?
• Q 2. 2 What is the anatomy of the external genital area?
• Q 2. 3 What are the internal genital organs?
• Q 2. 4 What is the peritoneum?
• Q 2. 5 Why did I develop into a girl?
• Q 2. 6 How do sperm development and egg development differ?
• Q 2. 7 What is meant by the term physiology?
• Q 2. 8 What is a hormone?
• Q 2. 9 What are steroid hormones?
• Q 2. 10 What is sex hormone binding globulin?
• Q 2. 11 What controls sex hormone release?
• Q 2. 12 How do oestrogens and androgens affect me?
• Q 2. 13 What are progesterone and progestogens?
• Q 2. 14 How do my menstrual cycles occur?
• Q 2. 15 Could I have some useful Web sites?

Q 2. 11 What controls reproductive hormone release?

• There are a number of biological rhythms controlled by a pacemaker near the hypothalamus. Releasing hormones are discharged episodically in pulses from the hypothalamus rather than as a continuous flow. External stimuli including darkness and light (circadian rhythm) and the sleep-wake cycles influence the releasing hormone pulse frequency. Abnormality of these biorhythms may be responsible for some types of abnormal reproductive function.
• There are usually negative feed back systems that reduce stimulating hormone release. As oestrogen levels rise, the gonadotrophin, the hormones that influence the production of the sex steroids ovaries, output falls (Figure 2.6).

Q 2. 12 How do oestrogens and androgens affect me?

• Oestrogens are fundamental in the development of your feminine characteristics including physical shape, breasts, uterus, external genitalia, skin texture and emotion.

• Oestrogens are characterised by their relationship to oestrus, or sexual heat, in many species. Libido, the sexual drive, is more complex in women than in men with emotion probably having a more significant role than hormones. The androgens play a major part in the libido of a man but they do not seem to be quite as important for a woman.

• An interesting variation of hormone action is the effect of oestrogens, which increase SHBG levels and this reduces the free, actively available, androgen level. This oestrogenic action is of benefit in the treatment of hirsutism (excess body hair).

Q 2. 13 What are progesterone and progestogens?

• Fourteen days before the next period is due, the dominant follicle releases its egg at ovulation. The follicle changes its structure and becomes a corpus luteum (Figure 2.3) in the ‘luteal’ phase of the menstrual cycle. It continues to function but now it not only releases oestrogens but also progesterone. The progestogen causes a change in the lining of the womb from a proliferative to a secretory pattern. In pregnancy, the lining of the uterus changes its structure to become the decidua which in turn develops into the placenta or afterbirth. Progesterone (pro -in favour and gestation – pregnancy) is essential for the development of the decidua. The decidua produces a hormone called HCG (human chorionic gonadotrophin). This HCG is essential to keep the corpus luteum functioning. A cycle is set up with the decidua producing HCG which results in the corpus luteum producing progesterone and this in turn maintains the decidua. From about the twelfth week of pregnancy, the placenta has formed and is self-sufficient in the production of progesterone.

• In non-conception cycles, there is no HCG to maintain the corpus luteum and it gets smaller and disappears. When the corpus luteum stops releasing oestrogen and progesterone, the endometrium is shed and a period is the result.

• Progesterone has effects on the endometrium and the breasts but only when they are primed by oestrogen.

Q 2. 14  How do my menstrual cycles occur?

• From your menarche, the first period, to your menopause (Greek: men- month; pausis – cessation) the endometrium (lining of the womb) changes its structure cyclically under the influence of the sex steroids hormones, oestrogen and progesterone with menstruation marking just one of these cyclical changes. The menstrual cycle is interrupted by pregnancy when specific endometrial changes occur (decidualisation). The menstrual cycle is controlled by hypothalamic and pituitary hormones (the hypothalamus and pituitary gland are situated at the base of the brain) and by ovarian hormones. (Figure 2.6)

• The hypothalamus provides the link between the brain and pituitary gland by producing ‘releasing’ and ‘inhibiting’ factors which control the pituitary gland’s secretion of hormones into the blood. There are five releasing hormones each composed of a chain of peptides, which are the basic unit for proteins. Gonadotrophin releasing hormones, which controls the sex hormone stimulating hormone output of the pituitary gland, is a decapeptide – a chain of 10 peptides. Thyrotrophin releasing hormones, which controls the thyroid gland through thyroid stimulating hormone of the pituitary, consists of just three peptides. Reproductive dysfunction, an abnormality of the control of the menstrual cycle and fertility, can result from functional abnormality of any of these releasing hormones.

• The pituitary gland functions as two separate areas – the anterior pituitary, which is at the front of the gland and the posterior pituitary which is the part at the back. The anterior pituitary produces the two gonadotrophic hormones known as follicle stimulating hormone (FSH) and luteinising hormone (LH).

• Ovarian control of pituitary function is principally through a negative feedback by oestradiol (Figure 2.6). A rise in LH level, the LH surge, triggers egg release (ovulation) 36 hours later. At the end of a menstrual cycle, oestradiol production falls with the demise of the corpus luteum (Figure  2.3) and FSH levels begin to rise. FSH release is inhibited by oestradiol. At themenopause, the ovaries run out of functional eggs and oestradiol levels fall. As a result, the pituitary releases high levels of FSH in an attempt to gain a response from the ovaries (Q 26.4).
• There are other regulators of pituitary gonadotrophin release. Current interest is focusing on one called inhibin.

• A third important pituitary hormone involved in reproduction is prolactin. This hormone derives its name from the fact that it encourages milk production. Levels of prolactin normally rise after childbirth.

 Q 2. 15 Could I have some useful Web sites?

• Evaluation of the quality of Web sites is discussed in Q4.27. You may find that several generalwomen’s health, sites may help you (Q4.28). The following are more specialised Web sites on topics found in this chapter.

Women’s Health – Home Page