Reproduction and Development PDF

5 **REPRODUCTION AND DEVELOPMENT** Reproduction is the process by which organisms make more organisms like themselves. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it\'s not essential to keeping an individual alive. In the human repro...

5 **REPRODUCTION AND DEVELOPMENT** Reproduction is the process by which organisms make more organisms like themselves. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it\'s not essential to keeping an individual alive. In the human reproductive process, two kinds of sex cells, or gametes, are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female\'s reproductive system. When sperm fertilizes (meets) an egg, this fertilized egg is called a zygote. The zygote goes through a process of becoming an **embryo** and developing into a **fetus**. The male reproductive system and the female reproductive system both are needed for reproduction. Humans, like other organisms, pass some characteristics of themselves to the next generation. We do this through our genes, the special carriers of human traits. The genes that parents pass along are what make their children similar to others in their family, but also what make each child unique. These genes come from the male\'s sperm and the female\'s egg. The external part of the female reproductive organs is called the vulva, which means covering. Located between the legs, the vulva covers the opening to the vagina and other reproductive organs inside the body. The fleshy area located just above the top of the vaginal opening is called the **mons pubis**. Two pairs of skin flaps called the labia (which means lips) surround the vaginal opening. The clitoris, a small sensory organ, is located toward the front of the vulva where the folds of the labia join. Between the labia are openings to the urethra (the canal that carries pee from the bladder to the outside of the body) and vagina. When girls become sexually mature, the outer labia and the mons pubis are covered by pubic hair. A female\'s internal reproductive organs are the vagina, uterus, fallopian tubes, and ovaries. The vagina is a muscular, hollow tube that extends from the vaginal opening to the uterus. Because it has muscular walls, the vagina can expand and contract. This ability to become wider or narrower allows the vagina to accommodate something as slim as a tampon and as wide as a baby. The vagina\'s muscular walls are lined with **mucous membranes**, which keep it protected and moist. At the upper corners of the uterus, the fallopian tubes connect the uterus to the ovaries. The ovaries are two oval-shaped organs that lie to the upper right and left of the uterus. They produce, store, and release eggs into the fallopian tubes in the process called **ovulation**. There are two fallopian tubes, each attached to a side of the uterus. Within each tube is a tiny passageway no wider than a sewing needle. At the other end of each fallopian tube is a fringed area that looks like a funnel. This fringed area wraps around the ovary but doesn\'t completely attach to it. When an egg pops out of an ovary, it enters the fallopian tube. Once the egg is in the fallopian tube, tiny hairs in the tube\'s lining help push it down the narrow passageway toward the uterus. The ovaries are also part of the endocrine system because they produce female sex hormones such as estrogen and progesterone. Sexual reproduction couldn\'t happen without the sexual organs called the gonads. Most people think of the gonads as the male testicles. But both sexes have gonads: In females the gonads are the ovaries, which make female gametes (eggs). The male gonads make male gametes (sperm). When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which remain inactive until puberty begins. At puberty, the pituitary gland (in the central part of the brain) starts making hormones that stimulate the ovaries to make female sex hormones, including estrogen. The secretion of these hormones causes a girl to develop into a sexually mature woman. Toward the end of puberty, girls begin to release eggs as part of a monthly period called the menstrual cycle. About once a month, during ovulation, an ovary sends a tiny egg into one of the fallopian tubes. Unless the egg is fertilized by a sperm while in the fallopian tube, the egg leaves the body about 2 weeks later through the uterus --- this is menstruation. Blood and tissues from the inner lining of the uterus combine to form the menstrual flow, which in most girls lasts from 3 to 5 days. A girl\'s first period is called menarche. It\'s common for women and girls to have some discomfort in the days leading to their periods. **Premenstrual syndrome (PMS) **includes both physical and emotional symptoms that many girls and women get right before their periods, such as: - acne - bloating - tiredness - backaches - sore breasts - headaches - constipation - diarrhea - food cravings - depression - irritability - trouble concentrating or handling stress PMS is usually at its worst during the 7 days before a girl\'s period starts and disappears after it begins. Many girls also have belly cramps during the first few days of their periods caused by **prostaglandins**, chemicals in the body that make the smooth muscle in the uterus contract. These involuntary contractions can be dull or sharp and intense. It can take up to 2 years from menarche for a girl\'s body to develop a regular menstrual cycle. During that time, her body is adjusting to the hormones puberty brings. On average, the monthly cycle for an adult woman is 28 days, but the range is from 23 to 35 days. If a female and male have sex within several days of the female\'s ovulation, fertilization can happen. When the male ejaculates (when semen leaves the penis), a small amount of semen is deposited into the vagina. Millions of sperm are in this small amount of semen, and they \"swim\" up from the vagina through the cervix and uterus to meet the egg in the fallopian tube. It takes only one sperm to fertilize the egg. About 5 to 6 days after the sperm fertilizes the egg, the fertilized egg (pronounced: zygote) has become a multicelled blastocyst. A blastocyst is about the size of a pinhead, and it\'s a hollow ball of cells with fluid inside. The blastocyst burrows itself into the lining of the uterus, called the endometrium. The hormone **estrogen** causes the endometrium to become thick and rich with blood. **Progesterone**, another hormone released by the ovaries, keeps the endometrium thick with blood so that the blastocyst can attach to the uterus and absorb nutrients from it. This process is called implantation. As cells from the blastocyst take in nourishment, another stage of development begins. In the embryonic stage, the inner cells form a flattened circular shape called the **embryonic disk**, which will develop into a baby. The outer cells become thin membranes that form around the baby. The cells multiply thousands of times and move to new positions to eventually become the embryo. After about 8 weeks, the embryo is about the size of a raspberry, but almost all of its parts --- the brain and nerves, the heart and blood, the stomach and intestines, and the muscles and skin --- have formed. During the fetal stage, which lasts from 9 weeks after fertilization to birth, development continues as cells multiply, move, and change. The fetus floats in amniotic (pronounced: am-nee-AH-tik) fluid inside the amniotic sac. The fetus gets oxygen and nourishment from the mother\'s blood via the placenta. This disk-like structure sticks to the inner lining of the uterus and connects to the fetus via the umbilical** **cord. The amniotic fluid and membrane cushion the fetus against bumps and jolts to the mother\'s body. Pregnancy lasts an average of 280 days --- about 9 months. When the baby is ready for birth, its head presses on the cervix, which begins to relax and widen to get ready for the baby to pass into and through the vagina. Mucus has formed a plug in the cervix, which now loosen. It and amniotic fluid come out through the vagina when the mother\'s water breaks. When the contractions of labor begin, the walls of the uterus contract as they are stimulated by the pituitary hormone oxytocin. The contractions cause the cervix to widen and begin to open. After several hours of this widening, the cervix is dilated (opened) enough for the baby to come through. The baby is pushed out of the uterus, through the cervix, and along the birth canal. The baby\'s head usually comes first. The umbilical cord comes out with the baby. It\'s clamped and cut close to the navel after the baby is delivered. The last stage of the birth process involves the delivery of the placenta, which at that point is called the afterbirth. After it has separated from the inner lining of the uterus, contractions of the uterus push it out, along with its membranes and fluids. **At the end of this Module, you should be able to:** 1. Define reproduction and development, and explain how they are related 2. Distinguish the male reproductive system and female reproductive system. 3. Describe the internal organs of male reproductive system 4. Describe the female external and internal structure 5. Identify the aging changes in the male reproductive system and female reproductive system 6. Define meiosis and its divisions The **reproductive system** of an organism, also known as the **genital system**, is the biological **system** made up of all the anatomical **organs** involved in sexual **reproduction**. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the **reproductive system**. A. **Reproductive System** Male Reproductive System Unlike a woman, most of a man's reproductive system is located outside of his body. These external structures include the penis, the scrotum, and the testicles. The organs of the male reproductive system are specialized for the following functions: - To produce, maintain and transport sperm (the male reproductive cells) and protective fluid (semen) - To discharge sperm within the female reproductive tract - To produce and secrete male sex hormones The male reproductive anatomy includes internal and external structures. Most of the male reproductive system is located outside of the man's abdominal cavity or pelvis. The external structures of the male reproductive system are the penis, the scrotum and the testicles. **Penis** --- The penis is the male organ for sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the **glans**, which is the cone-shaped end of the penis. The glans, which also is called the head of the penis, is covered with a loose layer of skin called **foreskin**. (This skin is sometimes removed in a procedure called [**circumcision**](https://my.clevelandclinic.org/health/articles/circumcision).) The opening of the **urethra**, the tube that transports semen and urine, is at the tip of the glans penis. The penis also contains a number of sensitive nerve endings. The body of the penis is cylindrical in shape and consists of three internal chambers. These chambers are made up of special, sponge-like erectile tissue. This tissue contains thousands of large spaces that fill with blood when the man is sexually aroused. As the penis fills with blood, it becomes rigid and erect, which allows for penetration during sexual intercourse. The skin of the penis is loose and elastic to allow for changes in penis size during an [erection](https://my.clevelandclinic.org/health/articles/how-an-erection-ejaculation-occurs). **Semen**, which contains sperm, is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm. **Scrotum** --- The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It contains the testicles (also called testes), as well as many nerves and blood vessels. The scrotum has a protective function and acts as a climate control system for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than the body temperature. Special muscles in the wall of the scrotum allow it to contract (tighten) and relax, moving the testicles closer to the body for warmth and protection or farther away from the body to cool the temperature. **Testicles (testes)** --- The testes are oval organs about the size of very large olives that lie in the scrotum, secured at either end by a structure called the **spermatic cord.** Most men have two testes. The testes are responsible for making **testosterone**, the primary male sex hormone, and for producing sperm. Within the testes are coiled masses of tubes called seminiferous tubules. These tubules are responsible for producing the sperm cells through a process called spermatogenesis. **Epididymis** --- The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the carrying and storage of the sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of [fertilization](https://my.clevelandclinic.org/health/articles/ovulation-and-conception). During sexual arousal, contractions force the sperm into the vas deferens. The internal organs of the male reproductive system, also called accessory organs, include the following: - **Vas deferens** --- The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation. - **Ejaculatory ducts** --- These are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra. - **Urethra** --- The urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of expelling (ejaculating) semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm. - **Seminal vesicles** --- The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms' motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man's ejaculatory fluid, or ejaculate. - **Prostate gland** --- The prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland. - **Bulbourethral glands** --- The bulbourethral glands, or Cowper's glands, are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra. **Male reproductive system function** The entire male reproductive system is dependent on **hormones**, which are chemicals that stimulate or regulate the activity of cells or organs. The primary hormones involved in the functioning of the male reproductive system are follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone. FSH and LH are produced by the pituitary gland located at the base of the brain. FSH is necessary for sperm production (spermatogenesis), and LH stimulates the production of testosterone, which is necessary to continue the process of spermatogenesis. Testosterone also is important in the development of male characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive. **Female Reproductive System** The female reproductive system provides several functions. The **ovaries** produce the egg cells, called the **ova** or **oocytes**. The oocytes are then transported to the **fallopian tube** where fertilization by a sperm may occur. The fertilized egg then moves to the uterus, where the uterine lining has thickened in response to the normal hormones of the reproductive cycle. Once in the uterus, the fertilized egg can implant into thickened uterine lining and continue to develop. If implantation does not take place, the uterine lining is shed as menstrual flow. In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle. During menopause, the female reproductive system gradually stops making the female hormones necessary for the reproductive cycle to work. At this point, [menstrual cycles](https://my.clevelandclinic.org/health/articles/10132-normal-menstruation) can become [irregular](https://my.clevelandclinic.org/health/diseases/14633-abnormal-menstruation-periods) and eventually stop. One year after menstrual cycles stop, the woman is considered to be [menopausal](https://my.clevelandclinic.org/health/diseases/15224-menopause-perimenopause-and-postmenopause). The female reproductive anatomy includes both external and internal structures. The function of the external female reproductive structures (the genital) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms. The main external structures of the female reproductive system include: - **Labia majora**: The labia majora ("large lips") enclose and protect the other external reproductive organs. During puberty, hair growth occurs on the skin of the labia majora, which also contain sweat and oil-secreting glands. - **Labia minora**: The labia minora ("small lips") can have a variety of sizes and shapes. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body). This skin is very delicate and can become easily irritated and swollen. - **Bartholin's glands**: These glands are located next to the vaginal opening on each side and produce a fluid (mucus) secretion. - **Clitoris**: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the **prepuce**, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect. The internal reproductive organs include: - **Vagina**: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal. - **Uterus (womb)**: The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the **cervix**, which is the lower part that opens into the vagina, and the main body of the uterus, called the **corpus**. The corpus can easily expand to hold a developing baby. A canal through the cervix allows sperm to enter and menstrual blood to exit. - **Ovaries**: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones. - **Fallopian tubes**: These are narrow tubes that are attached to the upper part of the uterus and serve as pathways for the ova (egg cells) to travel from the ovaries to the uterus. Fertilization of an egg by a sperm normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine lining. Meiosis and Reproduction Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. During reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring. **Meiosis** begins with a parent cell that is diploid, meaning it has two copies of each chromosome. The parent cell undergoes one round of DNA replication followed by two separate cycles of nuclear division. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell. Meiosis has both similarities to and differences from mitosis, which is a cell division process in which a parent cell produces two identical daughter cells. Meiosis begins following one round of DNA replication in cells in the male or female sex organs. The process is split into meiosis I and meiosis II, and both meiotic divisions have multiple phases. Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis. Meiosis I, the first meiotic division, begins with prophase I. During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The pairs of replicated chromosomes are known as sister chromatids, and they remain joined at a central point called the centromere. A large structure called the meiotic spindle also forms from long proteins called microtubules on each side, or pole, of the cell. Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination. Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes. In metaphase I, the homologous pairs of chromosomes align on either side of the equatorial plate. Then, in anaphase I, the spindle fibers contract and pull the homologous pairs, each with two chromatids, away from each other and toward each pole of the cell. During telophase I, the chromosomes are enclosed in nuclei. The cell now undergoes a process called cytokinesis that divides the cytoplasm of the original cell into two daughter cells. Each daughter cell is haploid and has only one set of chromosomes, or half the total number of chromosomes of the original cell. Meiosis II is a mitotic division of each of the haploid cells produced in meiosis I. During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells. Then in anaphase II, the chromosomes separate at the centromeres. The spindle fibers pull the separated chromosomes toward each pole of the cell. Finally, during telophase II, the chromosomes are enclosed in nuclear membranes. Cytokinesis follows, dividing the cytoplasm of the two cells. At the conclusion of meiosis, there are four haploid daughter cells that go on to develop into either sperm or egg cells. **Aging changes in the male reproductive system** Unlike women, men do not experience a major, rapid (over several months) change in fertility as they age (like menopause). Instead, changes occur gradually during a process that some people call andropause. Aging changes in the male reproductive system occur primarily in the [testes](https://medlineplus.gov/ency/article/002334.htm). Testicular tissue mass decreases. The level of the male sex hormone, [testosterone](https://medlineplus.gov/ency/article/003707.htm) decreases gradually. There may be problems getting an erection. This is a general slowing, instead of a complete lack of function. FERTILITY The tubes that carry sperm may become less elastic (a process called **sclerosis**). The testes continue to produce sperm, but the rate of sperm cell production slows. The epididymis, seminal vesicles, and prostate gland lose some of their surface cells. But they continue to produce the fluid that helps carry sperm. URINARY FUNCTION The prostate gland enlarges with age as some of the prostate tissue is replaced with a scar like tissue. This condition, called [benign prostatic hyperplasia](https://medlineplus.gov/ency/article/000381.htm) (BPH), affects about 50% of men. BPH may cause problems with slowed urination and ejaculation. In both men and women, reproductive system changes are closely related to changes in the urinary system. EFFECT OF CHANGES Fertility varies from man to man. Age does not predict male fertility. Prostate function does not affect fertility. A man can father children, even if his prostate gland has been removed. Some fairly old men can (and do) father children. The volume of fluid ejaculated usually remains the same, but there are fewer living sperm in the fluid. Some men may have a lower sex drive (libido). Sexual responses may become slower and less intense. This may be related to decreased testosterone level. It may also result from psychological or social changes due to aging (such as the lack of a willing partner), illness, long-term ([chronic](https://medlineplus.gov/ency/article/002312.htm)) conditions, or medicines. Aging by itself does not prevent a man from being able to enjoy sexual relationships. COMMON PROBLEMS [Erectile dysfunction (ED)](https://medlineplus.gov/ency/article/007617.htm) may be a concern for aging men. It is normal for erections to occur less often than when a man was younger. Aging men are often less able to have repeated ejaculations. ED is most often the result of a medical problem, rather than simple aging. Ninety percent of ED is believed to be caused by a medical problem instead of a psychological problem. Medicines (such as those used to treat [hypertension](https://medlineplus.gov/ency/article/000468.htm) and certain other conditions) can prevent a man from getting or keeping enough of an erection for intercourse. Disorders, such as [diabetes](https://medlineplus.gov/ency/article/001214.htm), can also cause ED. ED that is caused by medicines or illness is often successfully treated. Talk to your primary health care provider or a urologist if you are concerned about this condition. BPH may eventually interfere with urination. The enlarged prostate partially blocks the tube that drains the bladder (urethra). Changes in the prostate gland make older men more likely to have [urinary tract infections](https://medlineplus.gov/ency/article/000521.htm). Urine may back up into the kidneys (vesicoureteral reflux) if the bladder is not fully drained. If this is not treated, it can eventually lead to [kidney failure](https://medlineplus.gov/ency/article/000501.htm). Prostate gland infections or inflammation ([prostatitis](https://medlineplus.gov/ency/article/000519.htm)) may also occur. [Prostate cancer](https://medlineplus.gov/ency/article/000380.htm) becomes more likely as men age. It is one of the most common causes of cancer death in men. [Bladder cancer](https://medlineplus.gov/ency/article/000486.htm) also becomes more common with age. [Testicular cancers](https://medlineplus.gov/ency/article/001288.htm) are possible, but these occur more often in younger men. PREVENTION Many physical age-related changes, such as prostate enlargement or testicular atrophy, are not preventable. Getting treated for health disorders such as high blood pressure and diabetes may prevent problems with urinary and sexual function. Changes in sexual response are most often related to factors other than simple aging. Older men are more likely to have good sex if they continue to be sexually active during middle age. Aging changes in the female reproductive system =============================================== Aging changes in the female reproductive system result mainly from changing [hormone levels](https://medlineplus.gov/ency/article/003445.htm). One clear sign of aging occurs when your menstrual periods stop permanently. This is known as [menopause](https://medlineplus.gov/ency/article/000894.htm). The time before menopause is called perimenopause. It may begin several years before your last menstrual period. Signs of perimenopause include: - More frequent periods at first, and then occasional missed periods - Periods that are longer or shorter - Changes in the amount of menstrual flow Eventually your periods will become much less frequent, until they stop completely. Along with changes in your periods, physical changes in your reproductive tract occur as well. AGING CHANGES AND THEIR EFFECTS Menopause is a normal part of a woman\'s aging process. Most women experience menopause around age 50, though it can occur before that age. The usual age range is 45 to 55. With menopause: - The ovaries stop making the hormones estrogen and progesterone. - The ovaries also stop releasing eggs (ova, oocytes). After menopause, you can no longer become pregnant. - Your menstrual periods stop. You know you have gone through menopause after you have had no periods for 1 year. You should continue to use a birth control method until you have gone a whole year without a period. Any bleeding that occurs more than 1 year after your last period is not normal and should be checked by your health care provider. As hormone levels fall, other changes occur in the reproductive system, including: - Vaginal walls become thinner, dryer, less elastic, and possibly irritated. Sometimes sex becomes painful due to these vaginal changes. - Your risk of [vaginal yeast infections](https://medlineplus.gov/ency/article/001511.htm) increases. - The external genital tissue decreases and thins, and can become irritated. Other common changes include: - Menopause symptoms such as hot flashes, moodiness, headaches, and trouble sleeping - Problems with short-term memory - Decrease in breast tissue - Lower sex drive (libido) and sexual response - Increased risk of bone loss ([osteoporosis](https://medlineplus.gov/ency/article/000360.htm)) - Urinary system changes, such as frequency and urgency of urination and increased risk of urinary tract infection - Loss of tone in the pubic muscles, resulting in the vagina, [uterus](https://medlineplus.gov/ency/article/001508.htm), or urinary bladder falling out of position (prolapse) MANAGING CHANGES Hormone therapy with estrogen or progesterone, alone or in combination, may help menopause symptoms such as hot flashes or vaginal dryness and pain with intercourse. Hormone therapy has risks, so it is not for every woman. Discuss the risks and benefits of hormone therapy with your provider. To help manage problems such as painful sexual intercourse, use a lubricant during sexual intercourse. Vaginal moisturizers are available without a prescription. These can help with vaginal and vulvar discomfort due to the drying and thinning of tissues. Applying topical estrogen inside the vagina may help thicken the vaginal tissues and increase moisture and sensitivity. Your provider can tell you if any of these measures is right for you. Getting regular exercise, eating healthy foods, and staying involved in activities with friends and loved ones can help the aging process go more smoothly. OTHER CHANGES Other aging changes to expect: - [Hormone production](https://medlineplus.gov/ency/article/004000.htm) - [Organs, tissues, and cells](https://medlineplus.gov/ency/article/004012.htm) - [Breasts](https://medlineplus.gov/ency/article/003999.htm) - [Kidneys](https://medlineplus.gov/ency/article/004010.htm) **Key Medical Terms Associated with the Reproductive System** - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - **B. 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bryology/index.php/Week_7) | | | | | | | | | (https:/ | | | /embryology.med.unsw.edu.au/embry | | | ology/index.php/Week_8) | | | --------------------- --------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | ------- ------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | -------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | ----- --------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | ------------------------------ -- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------- ----- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | ------------------------ -------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------- ----------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | --------------------------------- | | | ------------- | | | **Carnegie stage:** (https | | | ://embryology.med.unsw.edu.au/emb | | | ryology/index.php/Carnegie_stage_ | | | 1) (https://embryology.med.uns | | | w.edu.au/embryology/index.php/Car | | | negie_stage_2) (https://embryo | | | logy.med.unsw.edu.au/embryology/i | | | ndex.php/Carnegie_stage_3) (ht | | | tps://embryology.med.unsw.edu.au/ | | | embryology/index.php/Carnegie_sta | | | ge_4) (https://embryology.me | | | d.unsw.edu.au/embryology/index.ph | | | p/Carnegie_stage_5) (https://e | | | mbryology.med.unsw.edu.au/embryol | | | ogy/index.php/Carnegie_stage_6) | | | (https://embryology.med.unsw. | | | edu.au/embryology/index.php/Carne | | | gie_stage_7) (https://embryolo | | | gy.med.unsw.edu.au/embryology/ind | | | ex.php/Carnegie_stage_8) (http | | | s://embryology.med.unsw.edu.au/em | | | bryology/index.php/Carnegie_stage | | | _9) (https://embryology.med | | |.unsw.edu.au/embryology/index.php | | | /Carnegie_stage_10) (https:// | | | embryology.med.unsw.edu.au/embryo | | | logy/index.php/Carnegie_stage_11) | | |  (https://embryology.med.unsw | | |.edu.au/embryology/index.php/Carn | | | egie_stage_12) (https://embry | | | ology.med.unsw.edu.au/embryology/ | | | index.php/Carnegie_stage_13) [1 | | | 4](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Carnegi | | | e_stage_14) (https://embryolo | | | gy.med.unsw.edu.au/embryology/ind | | | ex.php/Carnegie_stage_15) ( | | | https://embryology.med.unsw.edu.a | | | u/embryology/index.php/Carnegie_s | | | tage_16) (https://embryology. | | | med.unsw.edu.au/embryology/index. | | | php/Carnegie_stage_17) (htt | | | ps://embryology.med.unsw.edu.au/e | | | mbryology/index.php/Carnegie_stag | | | e_18) (https://embryology.med | | |.unsw.edu.au/embryology/index.php | | | /Carnegie_stage_19) (https: | | | //embryology.med.unsw.edu.au/embr | | | yology/index.php/Carnegie_stage_2 | | | 0) (https://embryology.med.un | | | sw.edu.au/embryology/index.php/Ca | | | rnegie_stage_21) (https://emb | | | ryology.med.unsw.edu.au/embryolog | | | y/index.php/Carnegie_stage_22) [2 | | | 3](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Carnegi | | | e_stage_23) | | +-----------------------------------+-----------------------------------+ **Kyoto Collection** **Carnegie Collection** ------------------------------------ -- --------------------------------------------------- Kyoto Collection Embryos  Human Embryo, Carnegie stages 1-23 Human Embryo, Carnegie stages 10-23 +-----------------------------------+-----------------------------------+ | | Use the stage number links to | | | images and information about each | | | specific stage of human | | | development over the first 8 | | | weeks. The links below give a | | | broad overview of developmental | | | events during each week. | | | | | | Stage14compare23.jpg | | | | | | Embryo sizes - stage 14 compared | | | to 23 | | | | | | --------------------- | | |  ‎‎**Human Embryo** | | | --------------------- | | | | | | **Embryo Week**: [Week | | | 1](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_1) | | |  \| [Week | | | 2](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_2) | | |  \| [Week | | | 3](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_3) | | |  \| [Week | | | 4](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_4) | | |  \| [Week | | | 5](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_5) | | |  \| [Week | | | 6](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_6) | | |  \| [Week | | | 7](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_7) | | |  \| [Week | | | 8](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_8) | | |  \| [Week | | | 9](https://embryology.med.unsw.ed | | | u.au/embryology/index.php/Week_9) | +-----------------------------------+-----------------------------------+ **Week 1** ----------  Week 1 - Early zygote - [Week 1](https://embryology.med.unsw.edu.au/embryology/index.php/Week_1) Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_1) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_2) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_3) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_4) - [oocyte](https://embryology.med.unsw.edu.au/embryology/index.php/Oocyte_Development) \| [spermatozoa](https://embryology.med.unsw.edu.au/embryology/index.php/Spermatozoa_Development) \| [fertilization](https://embryology.med.unsw.edu.au/embryology/index.php/Fertilization) - [zygote](https://embryology.med.unsw.edu.au/embryology/index.php/Zygote) - [morula](https://embryology.med.unsw.edu.au/embryology/index.php/Morula_Development) - [blastocyst](https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development) --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- [**Week 1 Links**](https://embryology.med.unsw.edu.au/embryology/index.php/Week_1): [stage 1](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_1) \| [stage 2](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_2) \| [stage 3](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_3) \| [menstrual cycle](https://embryology.med.unsw.edu.au/embryology/index.php/Menstrual_Cycle) \| [fertilization](https://embryology.med.unsw.edu.au/embryology/index.php/Fertilization) \| [zygote](https://embryology.med.unsw.edu.au/embryology/index.php/Zygote) \| morula \| [blastocyst](https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development) \| [Lecture - Fertilization](https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Fertilization) \| [meiosis](https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Meiosis) \| [mitosis](https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Mitosis) \| [Lecture - Week 1 and 2](https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Week_1_and_2_Development) \| [menstrual cycle](https://embryology.med.unsw.edu.au/embryology/index.php/Menstrual_Cycle) \| [oocyte](https://embryology.med.unsw.edu.au/embryology/index.php/Oocyte_Development) \| [spermatozoa](https://embryology.med.unsw.edu.au/embryology/index.php/Spermatozoa_Development) \| [twinning](https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Twinning) \| [Genetic risk maternal age](https://embryology.med.unsw.edu.au/embryology/index.php/Genetic_risk_maternal_age) \| [Trisomy 21](https://embryology.med.unsw.edu.au/embryology/index.php/Trisomy_21) \| [Trisomy 18](https://embryology.med.unsw.edu.au/embryology/index.php/Trisomy_18) \| [Trisomy 13](https://embryology.med.unsw.edu.au/embryology/index.php/Trisomy_13) \| hydatidiform mole \| [**GA**](https://embryology.med.unsw.edu.au/embryology/index.php/Gestational_Age) week 3 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Carnegie stages** ------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- Early zygote labelled.jpg  CSt3.jpg  [stage 1](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_1) [stage 2](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_2) [stage 3](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_3) [stage 4](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_4) **Week 2** ---------- https://embryology.med.unsw.edu.au/embryology/images/a/a9/Week2\_001\_icon.jpg Week 2 Implantation - [Week 2](https://embryology.med.unsw.edu.au/embryology/index.php/Week_2) Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_5) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_6) - [trophoblast](https://embryology.med.unsw.edu.au/embryology/index.php/Trophoblast) - ([trophectoderm](https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development#Trophectoderm)) outer cell layer - [Embryoblast](https://embryology.med.unsw.edu.au/embryology/index.php/Embryoblast) - inner cell mass - [implantation](https://embryology.med.unsw.edu.au/embryology/index.php/Implantation) - [Bilaminar embryo](https://embryology.med.unsw.edu.au/embryology/index.php/Bilaminar_embryo) -- -- **Carnegie stages** ------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------  Stage5 bf11L.jpg  [stage 4](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_4) [stage 5](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_5) [stage 6](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_6) **Week 3** ---------- https://embryology.med.unsw.edu.au/embryology/images/thumb/4/43/Stage7\_features.jpg/300px-Stage7\_features.jpg Week 3 - Embryonic disc - [Week 3](https://embryology.med.unsw.edu.au/embryology/index.php/Week_3) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_7) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_8) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_9) - [Gastrulation](https://embryology.med.unsw.edu.au/embryology/index.php/Gastrulation) - [Notochord](https://embryology.med.unsw.edu.au/embryology/index.php/Notochord) - [Trilaminar embryo](https://embryology.med.unsw.edu.au/embryology/index.php/Trilaminar_embryo) - [Mesoderm](https://embryology.med.unsw.edu.au/embryology/index.php/Mesoderm) - [Somitogenesis](https://embryology.med.unsw.edu.au/embryology/index.php/Somitogenesis) - [Neurogenesis](https://embryology.med.unsw.edu.au/embryology/index.php/Neurogenesis) -- -- Carnegie stages ------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------  Stage8 SEM1.jpg  [stage 7](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_7) [stage 8](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_8) [stage 9](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_9) **Week 4** ---------- https://embryology.med.unsw.edu.au/embryology/images/thumb/c/c4/Stage11\_bf3b.jpg/120px-Stage11\_bf3b.jpg Week 4 - The heart begins - [Week 4](https://embryology.med.unsw.edu.au/embryology/index.php/Week_4) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_10) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_11) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_12) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_13) - [Heart](https://embryology.med.unsw.edu.au/embryology/index.php/Cardiovascular_System_-_Heart_Development) - [Placodes](https://embryology.med.unsw.edu.au/embryology/index.php/Placodes) - [Pharyngeal arches](https://embryology.med.unsw.edu.au/embryology/index.php/Pharyngeal_arches) -- -- **Carnegie stages** --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------  Stage11 sem13c.jpg  Stage13 sem1c.jpg [stage 10](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_10) [stage 11](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_11) [stage 12](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_12) [stage 13](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_13) **Week 5** ----------  Week 5 embryo - [Week 5](https://embryology.med.unsw.edu.au/embryology/index.php/Week_5) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_14) to (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_15) **Carnegie stages** --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- Stage14 sem1c.jpg  [stage 14](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_10) [stage 15](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_11) **Week 6** ---------- https://embryology.med.unsw.edu.au/embryology/images/thumb/0/02/Stage16-18\_face.jpg/300px-Stage16-18\_face.jpg Week 6 - Early face deevelopment - [Week 6](https://embryology.med.unsw.edu.au/embryology/index.php/Week_6) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_16) to (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_17) **Carnegie stages** --------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------  Stage17 bf1c.jpg [stage 16](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_10) [stage 17](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_11) **Week 7** ----------  Week 7 - Head and limb development - [Week 7](https://embryology.med.unsw.edu.au/embryology/index.php/Week_7) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_18) to (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_19) **Carnegie stages** --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- Stage18 bf1c.jpg  [stage 18](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_18) [stage 19](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_19) **Week 8** ---------- https://embryology.med.unsw.edu.au/embryology/images/thumb/a/a1/Stage23\_bf1c.jpg/300px-Stage23\_bf1c.jpg Week 8 - Last embryonic stage 23 - [Week 8](https://embryology.med.unsw.edu.au/embryology/index.php/Week_8) - Carnegie stage - (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_20) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_21) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_22) \| (https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_23) - Last week of embryonic development. **Carnegie stages** --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------  Stage21 bf1c.jpg  Stage23 bf1c.jpg [stage 20](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_20) [stage 21](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_21) [stage 22](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_22) [stage 23](https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_23) **Carnegie Stage Table** ------------------------ Weeks shown in the table below are embryonic post ovulation age, for clinical Gestational Age ([**GA**](https://embryology.med.unsw.edu.au/embryology/index.php/Gestational_Age)) measured from last menstrual period, add 2 weeks. +-------------+-------------+-------------+-------------+-------------+ | **Stage** | **Days** (a | **Size** | **Images\ | **Events** | | | pprox) | | **(not to | | | | | (mm) | scale) | | +=============+=============+=============+=============+=============+ | [**1**](htt | 1 | 0.1 - 0.15 |  |.edu.au/emb | | rnegie_stag | edu.au/embr | | | ryology/ind | | e_1) | yology/inde | | | ex.php/Zygo | | | x.php/Week_ | | | te), | | | 1)) | | | pronuclei | +-------------+-------------+-------------+-------------+-------------+ | [**2**](htt | 2 - 3 | 0.1 - 0.2 | Human | [morula](ht | | ps://embryo | | | embryo day | tps://embry | | logy.med.un | | | 3.jpg | ology.med.u | | sw.edu.au/e | | | | nsw.edu.au/ | | mbryology/i | | | | embryology/ | | ndex.php/Ca | | | | index.php/M | | rnegie_stag | | | | orula) cell | | e_2) | | | | division | | | | | | with | | | | | | reduction | | | | | | in | | | | | | cytoplasmic | | | | | | volume, [bl | | | | | | astocyst](h | | | | | | ttps://embr | | | | | | yology.med. | | | | | | unsw.edu.au | | | | | | /embryology | | | | | | /index.php/ | | | | | | Blastocyst) | | | | | |  formation | | | | | | of inner | | | | | | and outer | | | | | | cell mass | +-------------+-------------+-------------+-------------+-------------+ | [**3**](htt | 4 - 5 | 0.1 - 0.2 |  | ocyst](http | | ndex.php/Ca | | | | s://embryol | | rnegie_stag | | | | ogy.med.uns | | e_3) | | | | w.edu.au/em | | | | | | bryology/in | | | | | | dex.php/Bla | | | | | | stocyst) | +-------------+-------------+-------------+-------------+-------------+ | [**4**](htt | 5 - 6 | 0.1 - 0.2 | Week2 001 | attaching [ | | ps://embryo | | | icon.jpg | blastocyst] | | logy.med.un | | | | (https://em | | sw.edu.au/e | | | | bryology.me | | mbryology/i | | | | d.unsw.edu. | | ndex.php/Ca | | | | au/embryolo | | rnegie_stag | | | | gy/index.ph | | e_4) | | | | p/Blastocys | | | | | | t) | +-------------+-------------+-------------+-------------+-------------+ | [**5**](htt | 7 - 12\ | 0.1 - 0.2 |  |.med.unsw.e | | mbryology/i | y.med.unsw. | | | du.au/embry | | ndex.php/Ca | edu.au/embr | | | ology/index | | rnegie_stag | yology/inde | | |.php/Implan | | e_5) | x.php/Week_ | | | tation) | | | 2)) | | | | +-------------+-------------+-------------+-------------+-------------+ | [**6**](htt | 13 - 15 | 0.2 | Stage6 | extraembryo | | ps://embryo | | | bf03.jpg | nic | | logy.med.un | | | | mesoderm, | | sw.edu.au/e | | | | primitive | | mbryology/i | | | | streak, [ga | | ndex.php/Ca | | | | strulation] | | rnegie_stag | | | | (https://em | | e_6) | | | | bryology.me | | | | | | d.unsw.edu. | | | | | | au/embryolo | | | | | | gy/index.ph | | | | | | p/Gastrulat | | | | | | ion) | +-------------+-------------+-------------+-------------+-------------+ | [**7**](htt | 15 - 17 | 0.4 |  |.med.unsw.e | | mbryology/i | //embryolog | | | du.au/embry | | ndex.php/Ca | y.med.unsw. | | | ology/index | | rnegie_stag | edu.au/embr | | |.php/Gastru | | e_7) | yology/inde | | | lation), no | | | x.php/Week_ | | | tochordal | | | 3)) | | | process | +-------------+-------------+-------------+-------------+-------------+ | [**8**](htt | 17 - 19 | 1.0 - 1.5 | Stage8 | primitive | | ps://embryo | | | bf4.jpg | pit, | | logy.med.un | | | | notochordal | | sw.edu.au/e | | | | canal | | mbryology/i | | | | | | ndex.php/Ca | | | | | | rnegie_stag | | | | | | e_8) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**9**](htt | 19 - 21 | 1.5 - 2.5 | ![Stage9 | [Somitogene | | ps://embryo | | | dorsal.jpg] | sis](https: | | logy.med.un | | | (media/imag | //embryolog | | sw.edu.au/e | | | e44.jpeg) | y.med.unsw. | | mbryology/i | | | | edu.au/embr | | ndex.php/Ca | | | | yology/inde | | rnegie_stag | | | | x.php/Somit | | e_9) | | | | ogenesis) * | | | | | | *Somite | | | | | | Number 1 - | | | | | | 3** neural | | | | | | folds, | | | | | | cardiac | | | | | | primordium, | | | | | | head fold | +-------------+-------------+-------------+-------------+-------------+ | [**10**](ht | 22 - 23 | 2 - 3.5 | Stage10 | **Somite | | tps://embry | | | bf4b.jpg | Number 4 - | | ology.med.u | ([**week | | | 12** neural | | nsw.edu.au/ | 4**](https: | | | fold fuses | | embryology/ | //embryolog | | | | | index.php/C | y.med.unsw. | | | | | arnegie_sta | edu.au/embr | | | | | ge_10) | yology/inde | | | | | | x.php/Week_ | | | | | | 4)) | | | | +-------------+-------------+-------------+-------------+-------------+ | [**11**](ht | 23 - 26 | 2.5 - 4.5 |  | l | | embryology/ | | | | neuropore | | index.php/C | | | | closes | | arnegie_sta | | | | | | ge_11) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**12**](ht | 26 - 30 | 3 - 5 | Stage12 | **Somite | | tps://embry | | | bf5b.jpg | Number 21 - | | ology.med.u | | | | 29** caudal | | nsw.edu.au/ | | | | neuropore | | embryology/ | | | | closes | | index.php/C | | | | | | arnegie_sta | | | | | | ge_12) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**13**](ht | 28 - 32 | 4 - 6 |  | buds](https | | embryology/ | //embryolog | | | ://embryolo | | index.php/C | y.med.unsw. | | | gy.med.unsw | | arnegie_sta | edu.au/embr | | |.edu.au/emb | | ge_13) | yology/inde | | | ryology/ind | | | x.php/Week_ | | | ex.php/Musc | | | 5)) | | | uloskeletal | | | | | | _System_-_L | | | | | | imb_Develop | | | | | | ment), | | | | | | lens | | | | | | placode, | | | | | | pharyngeal | | | | | | arches | +-------------+-------------+-------------+-------------+-------------+ | [Stage | | | | | | 13/14 shown | | | | | | in serial | | | | | | embryo | | | | | | sections](h | | | | | | ttps://embr | | | | | | yology.med. | | | | | | unsw.edu.au | | | | | | /embryology | | | | | | /index.php/ | | | | | | Carnegie_st | | | | | | age_13_-_se | | | | | | rial_sectio | | | | | | ns) series | | | | | | of | | | | | | Embryology | | | | | | Program | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**14**](ht | 31 - 35 | 5 - 7 | Stage14 | lens pit, | | tps://embry | | | bf2c.jpg | optic cup | | ology.med.u | | | | | | nsw.edu.au/ | | | | | | embryology/ | | | | | | index.php/C | | | | | | arnegie_sta | | | | | | ge_14) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**15**](ht | 35 - 38 | 7 - 9 |  | pit, [hand | | embryology/ | | | | plate](http | | index.php/C | | | | s://embryol | | arnegie_sta | | | | ogy.med.uns | | ge_15) | | | | w.edu.au/em | | | | | | bryology/in | | | | | | dex.php/Mus | | | | | | culoskeleta | | | | | | l_System_-_ | | | | | | Limb_Develo | | | | | | pment) | +-------------+-------------+-------------+-------------+-------------+ | [**16**](ht | 37 - 42 | 8 - 11 | Link=Carneg | nasal pits | | tps://embry | | | ie\_stage\_ | moved | | ology.med.u | ([**week | | 16 | ventrally, | | nsw.edu.au/ | 6**](https: | | | auricular | | embryology/ | //embryolog | | | hillocks, | | index.php/C | y.med.unsw. | | | foot plate | | arnegie_sta | edu.au/embr | | | | | ge_16) | yology/inde | | | | | | x.php/Week_ | | | | | | 6)) | | | | +-------------+-------------+-------------+-------------+-------------+ | [**17**](ht | 42 - 44 | 11 - 14 |  | | | embryology/ | | | | | | index.php/C | | | | | | arnegie_sta | | | | | | ge_17) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**18**](ht | 44 - 48 | 13 - 17 | Stage18 | ossificatio | | tps://embry | | | bf1c.jpg | n | | ology.med.u | ([**week | | | commences | | nsw.edu.au/ | 7**](https: | | | | | embryology/ | //embryolog | | | | | index.php/C | y.med.unsw. | | | | | arnegie_sta | edu.au/embr | | | | | ge_18) | yology/inde | | | | | | x.php/Week_ | | | | | | 7)) | | | | +-------------+-------------+-------------+-------------+-------------+ | [**19**](ht | 48 - 51 | 16 - 18 |  | | | embryology/ | | | | | | index.php/C | | | | | | arnegie_sta | | | | | | ge_19) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**20**](ht | 51 - 53 | 18 - 22 | Stage20 | [upper | | tps://embry | | | bf1c.jpg | limbs](http | | ology.med.u | ([**week | | | s://embryol | | nsw.edu.au/ | 8**](https: | | | ogy.med.uns | | embryology/ | //embryolog | | | w.edu.au/em | | index.php/C | y.med.unsw. | | | bryology/in | | arnegie_sta | edu.au/embr | | | dex.php/Mus | | ge_20) | yology/inde | | | culoskeleta | | | x.php/Week_ | | | l_System_-_ | | | 8)) | | | Limb_Develo | | | | | | pment) long | | | | | | er | | | | | | and bent at | | | | | | elbow | +-------------+-------------+-------------+-------------+-------------+ | [**21**](ht | 53 - 54 | 22 - 24 |  | | | embryology/ | | | | | | index.php/C | | | | | | arnegie_sta | | | | | | ge_21) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [Stage 22 | | | | | | shown in | | | | | | serial | | | | | | embryo | | | | | | sections | | | | | | series](htt | | | | | | ps://embryo | | | | | | logy.med.un | | | | | | sw.edu.au/e | | | | | | mbryology/i | | | | | | ndex.php/Ca | | | | | | rnegie_stag | | | | | | e_22_-_seri | | | | | | al_sections | | | | | | ) of | | | | | | Embryology | | | | | | Program | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**22**](ht | 54 - 56 | 23 - 28 | Stage22 | eyelids, | | tps://embry | | | bf1c.jpg | external | | ology.med.u | | | | ears | | nsw.edu.au/ | | | | | | embryology/ | | | | | | index.php/C | | | | | | arnegie_sta | | | | | | ge_22) | | | | | +-------------+-------------+-------------+-------------+-------------+ | [**23**](ht | 56 - 60 | 27 - 31 |  | (https://em | | embryology/ | | | | bryology.me | | index.php/C | | | | d.unsw.edu. | | arnegie_sta | | | | au/embryolo | | ge_23) | | | | gy/index.ph | | | | | | p/Musculosk | | | | | | eletal_Syst | | | | | | em_-_Limb_D | | | | | | evelopment) | +-------------+-------------+-------------+-------------+-------------+ | Following | | | | | | this | | | | | | stage [Feta | | | | | | l | | | | | | Development | | | | | | ](https://e | | | | | | mbryology.m | | | | | | ed.unsw.edu | | | | | |.au/embryol | | | | | | ogy/index.p | | | | | | hp/Fetal_De | | | | | | velopment)  | | | | | | occurs | | | | | | until birth | | | | | | (approx 37 | | | | | | weeks) | | | | | +-------------+-------------+-------------+-------------+-------------+ **Important Maternal Changes During Pregnancy** Pregnancy and its changes is a normal physiological process that happens in all mammalian in response to the development of the fetus. These changes happen in response to many factors; hormonal changes, increase in the total blood volume, weight gain, and increase in fetus size. All these factors have a physiological impact on all systems of the pregnant woman; musculoskeletal, endocrine, reproductive system, cardiovascular, respiratory, gastrointestinal system, and renal changes. The full pregnancy period is about 40 weeks, when the delivery happens before 37 weeks it is called a premature baby. **Endocrine System Changes** ---------------------------- **Pregnancy** is a normal physiological process and is associated with changes in hormone levels, one of these hormones called **steroid hormones** including progesterone and estrogen they are important during pregnancy to save fetus delivery and maintenance of pregnancy stable[^\[3\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-3). Its levels increase gradually with pregnancy progression, unlike relaxin reaches the highest level at first trimester then decrease at the end of pregnancy. All steroids/ sex hormones produced from the placenta during pregnancy but the progesterone is the chief one. **Progesterone** at the beginning is produced by corpus luteum and reaches its maximum at 10 weeks then declined gradually and the placenta starts to produce the progesterone reaching its maximum amount at 40 weeks, the placenta production of progesterone is decreased in the last month. It is important to prevent premature uterine contractions, reduces the tone of smooth muscles causing constipation due to the water retention in the colon, decrease the tone of uterine and detrusor muscles, participate in the development of mammary glands and increase the storage of fat due to its catabolic effect on metabolism. **Estrogen**, like progesterone, its production starts at corpus luteum then the placenta takes the function to produce estrogen, reaching its peak at the date of birth. Estrogen has a vasodilation effect, increases blood flow to uteroplacenta in preparing for uterine contraction. In addition to its catabolic effect and its role for the development of the mammary gland, estrogen increases water retention and maybe a receptor site for relaxin. **Relaxin** is produced in the corpus luteum and later in the decidua and placenta, increases in the first trimester. it has a strong vasodilator effect, an effect on hemodynamic and affects kidney function[^\[4\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-:3-4), and affects on pelvic floor muscle relaxation. **Reproductive System Changes** ------------------------------- File:Figure 5 1 Appproximate height of the fundus 640.jpg **Fundus levels during pregnancy** During pregnancy, [the internal genital tract/ reproductive systems](https://www.physio-pedia.com/Female_Genital_Tract) undergone anatomical and physiological changes to accommodate the changes and development of the fetus. These changes presented as below: **Uterus**, With pregnancy progression, the uterus leaves the pelvic and ascends to the abdominal cavity and the [abdominal](https://www.physio-pedia.com/Abdominal_Muscles) content displaced in response to the increased size of the uterus which is five times more than normal this increases in the size of uterus associated with an increase of blood supply to the uterus and uterine muscle activity, uterus increases in size till the 38 weeks after that the funds level starts to descend preparing for delivery. Its weight increases from 50mg to 1000mg after that it doesn\'t get heavier any more and only [stretches](https://www.physio-pedia.com/Stretching) to accommodate the fetus size, and associated with an increase in the thickness and length of the fundus. **Cervix,** The enlarged mucus glands of the cervix during pregnancy secretes a mucus plug called "operculum", act as a seal for the uterus and protect it from ascending infection, and act as a barrier between the vagina and cervix. Later in pregnancy before delivery, there is a softening of the cervix in response to the increasing uterine contractions. **Vagina,** during pregnancy there is an increase in the blood supply to the vagina, its color change from pink to purple, and becomes more elastic in the second trimester^[\[5\]](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-5)[\[6\]](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-6)^. **Musculoskeletal Changes** ---------------------------  ### **Postural Changes** The overall equilibrium of the spine and pelvis alters as the pregnancy progresses[^\[7\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-7) but there is still confusion as to the exact nature of any associated postural adaptation. With weight gain, increased blood volume, and ventral growth of the fetus, the center of gravity no longer falls over the feet, increase in anteroposterior and medial-lateral sway[^\[8\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-8), and women may need to lean backward to gain equilibrium resulting in disorganisation of spinal curves. Reported postures include a reduction in lumbar lordosis an increase in both [lumbar](https://www.physio-pedia.com/Lumbar_Anatomy) lordosis and [thoracic](https://www.physio-pedia.com/Thoracic_Anatomy) [kyphosis](https://www.physio-pedia.com/Thoracic_Hyperkyphosis) or a flattening of the thoracolumbar spinal curve. There will be compensatory changes to posture in the thoracic and cervical spines, and this combined with the extra weight of the breasts may result in posterior displacement of the shoulders and thoracic spine, increase anterior pelvic tilting, and increase of the cervical lordosis.[^\[2\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-:1-2)These changes may be still similar for 8 weeks after delivery. ### **Articular Changes** Altered levels of relaxin, oestrogen, and progesterone during pregnancy result in an alteration to collagen metabolism, this laxity is due to the break down of collagen in the targeted tissue and replaces it by a modified form that contains higher water content**.** That increases connective tissue pliability and extensibility. Therefore, [ligamentous](https://www.physio-pedia.com/Ligament) tissues are predisposed to laxity with resultant reduced passive [joint](https://www.physio-pedia.com/Joint_Classification) stability, ligament laxity reaches its maximum at the second trimester[^\[9\]^](https://www.physio-pedia.com/Physiological_changes_during_pregnancy#cite_note-9). The symphysis pubis and [sacroiliac joints](https://www.physio-pedia.com/Sacroiliac_Joint) are particularly affected to allow for the birth of the baby. Ligamentous laxity may continue for six months postpartum. Biomechanical changes of the spinal and pelvic joints may involve an increase in sacral promontory, an increase in lumbosacral angle, a forward rotatory movement of the innominate bones, and downward and forward rotation of the symphysis pubis. The normal pubic symphyseal gap of 4--5 mm shows an average increase of 3 mm during pregnancy Pelvic joint loosening begins around 10 weeks, with maximum loosening near term. Joints