3.4 mindtap assignment the female reproductive system exercise ii

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157 18.6 Structures of the Female Reproductive System

Created by CK-12 Foundation/Adapted by Christine Miller

Fertility Symbol

The geometric design on the ancient stone carving in Figure 18.6.1 represents a powerful symbol of female fertility: the vagina . The symbol is called yoni in Hindu, and it reflects the value placed by Hindu culture on the ability of females to give birth. The vagina is one of several organs in the female reproductive system.

Female Reproductive Organs

The female reproductive system is made up of internal and external organs that function to produce haploid female gametes called ova (or oocytes), secrete female sex hormones (such as estrogen ), and carry and give birth to a fetus . The internal female reproductive organs include the vagina, uterus , oviduct s , and ovaries . The external organs — collectively called the vulva — include the clitoris and labia .

The  vagina is an elastic, muscular canal leading from its opening in the vulva to the neck of the uterus, called the cervix . It is about 7.5 cm (about 3 in) long at the front, and about 9 cm (3.5 in) long at the back. The vagina accommodates the penis and is the site where sperm are usually ejaculated during sexual intercourse. In the context of pregnancy and natural (vaginal) childbirth, the vagina is referred to as the birth canal. In addition, it channels the flow of menstrual blood from the uterus .

Structure of the Vagina

Muscles and ligaments support the vagina within the pelvic cavity . The vagina itself is made up of several layers of fibrous and muscular tissues and lined with mucous membrane s . Folds in the mucosa provide the vagina with extra surface area so it can stretch in both length and width during intercourse or childbirth. The elasticity of the vagina and the extra mucosa allow it to stretch to many times its normal diameter in order to deliver a baby.

Bacteria and pH in the Vagina

A healthy vagina is home to many symbiotic   bacteria that help prevent pathogens (such as yeast) from colonizing the vagina. The pH in the vagina is normally between 3.8 and 4.5, and this acidity also helps keep pathogenic microorganisms from colonizing it. The vagina constantly sheds its epithelium, so it is considered self-cleaning. As a consequence, there is no need for douching to clean it. Physicians actually discourage the practice, as it may upset the normal bacterial and pH balance in the vagina, although washing the vulva with a mild soap is good practice.

The  uterus (commonly called the womb) is a pear-shaped, muscular organ that is about 7.6 cm (about 3 in) long. It is located above the vagina and behind the bladder in the centre of the pelvis. The position of the uterus in the pelvis is stabilized by several ligaments and bands of supportive tissue. The uterus is where a fetus develops during gestation, and the organ provides mechanical protection and support for the developing offspring. Contractions of the muscular wall of the uterus are responsible for pushing the fetus out of the uterus during childbirth.

Parts of the Uterus

As shown in Figure 18.6.2, the lower end of the uterus forms the cervix , which is also called the neck of the uterus. The cervix is about 2.5 cm (almost 1 in) long and protrudes downward into the vagina. A small canal runs the length of the cervix, connecting the uterine cavity with the lumen of the vagina. This allows semen deposited in the vagina to enter the uterus, and a baby to pass from the uterus into the vagina during birth. Glands in the cervix secrete mucus that varies in water content and thickness, so it can function either as a barrier to keep microorganism s  out of the uterus during pregnancy, or as a transport medium to help sperm enter the uterus around the time of ovulation . The rest of the uterus above the cervix is called the body of the uterus. The upper end of the uterus is connected with the two oviduct s .

Tissues of the Uterus

As indicated in Figure 18.6.3, the uterus consists of three tissue layers, called the endometrium, myometrium, and perimetrium.

• The  endometrium is the innermost tissue layer of the uterus. It consists of epithelial tissue, including mucous membranes. This layer thickens during each menstrual cycle and, unless an egg is fertilized, sloughs off during the following menstrual period. If an ovum is fertilized, the thickened endometrium is maintained by hormones and provides nourishment to the embryo. As gestation progresses, the endometrium develops into the maternal portion of the placenta.
• The placenta  is a temporary organ that consists of a mass of maternal and fetal blood vessels through which the mother’s and fetus’s blood exchange substances.
• The  myometrium  is the middle layer of the uterus. It consists mostly of a thick layer of smooth muscle tissue. Powerful contractions of the smooth muscle allow the uterus to contract and expel an infant during childbirth.
• The  perimetrium  is the outermost layer of the uterus. It covers the outer surface of the uterus. This layer actually consists of two layers of epithelium that secrete fluid into the space between them. The fluid allows for small movements of the uterus within the pelvis, without causing it to rub against other organs.

The  oviduct s (often referred to as Fallopian tubes) are two thin tubes that lie between the ovaries and the uterus . The oviducts are not attached to the ovaries, but their broad upper ends — called infundibula — lie very close to the ovaries. The infundibula also have fringe-like extensions called fimbriae that move in a waving motion to help guide eggs from the ovaries into the oviducts. The lower ends of the oviducts are attached to the upper part of the body of the uterus on either side of the body. They open into the uterus.

The oviducts are made up of multiple tissue layers. The innermost layer consists of mucosal epithelium. The epithelium is covered with cilia , which can move in a sweeping motion to help ova move through the tube from the ovary to the uterus. In between the ciliated cells of the epithelium are cells that secrete a fluid called tubular fluid. This fluid contains nutrients for sperm, ova, and zygotes. The secretions in tubular fluid also remove certain molecules from the plasma membrane of sperm so they are better able to penetrate an egg. Other layers of the oviducts consist of connective tissue and smooth muscle. Contractions of the smooth muscle allow peristalsis to help move eggs through the tubes.

Like the testes in males, the  ovaries  in females are gonad s  that produce gamete s and secrete sex hormones . The gametes produced by the ovaries are called ova , or oocytes. The main sex hormone secreted by the ovaries is estrogen . The position of the paired ovaries relative to the other reproductive system organs is shown in Figure 18.6.4. Each ovary lies along one side of the uterus and is about 4 cm (a little more than 1.5 in) long. Fibrous ligaments attach one end of each ovary to its nearby oviduct and the other and to its side of the uterus. These ligaments keep the ovaries in place within the pelvis.

Ovarian Follicles

The ovary consists of two main layers, called the ovarian medulla (the inner layer) and the ovarian cortex (the outer layer). The ovary also contains  blood  and lymphatic vessels. The ovarian cortex consists primarily of the functional units of the ovaries, which are called  ovarian follicle s . The follicles are nests of epithelial cells, within each of which is an ovum. The photomicrograph in Figure 18.6.5 shows an ovarian follicle and the developing ovum inside it. If an ovum and follicle complete maturation, the follicle ruptures and the ovum is released from the ovary. This event is called ovulation .

Ova in the Ovaries

Whereas the male testes produce sperm continuously after  puberty , the female ovary already contains all the ova it will ever produce by the time a female is born. At birth, a baby girl’s ovaries contain at least a million eggs, each of which is contained within a follicle . Only about 500 of these eggs will eventually mature and be ovulated. This process starts at puberty and typically continues at monthly intervals until menopause occurs around age 52. The remaining eggs never mature, and their number declines as the woman ages. By menopause, a woman’s reserve of eggs is nearly depleted, and ovulation no longer occurs.

The  vulva is a general term for all of the external female reproductive organs. The vulva includes the clitoris, labia, and external openings for the urethra and vagina.

The  labia (singular, labium) refer to the “lips” of the vulva, which are folds of tissue that contain and protect the other, more delicate structures of the vulva (as shown in Figure 18.6.6). There are two pairs of labia: the outer and larger labia majora, and the inner and smaller labia minora. The labia minora contain numerous sebaceous glands. These glands release secretions that help lubricate the labia and vulvar area.

The  clitoris ,  is located at the front of the vulva where the labia minora meet. The visible portion of the clitoris is called the glans clitoris. It is roughly the size and shape of a pea. It is highly sensitive, because it contains many nerve endings. A hood of tissue called the clitoral hood (shown in Figure 18.6.5 above), or prepuce, normally covers and protects the clitoris. The clitoris is the homologue to the male penis, and they both contain spongy tissue.   Stimulation of the glans clitoris during sexual activity generally results in sexual arousal in females, and may lead to orgasm. The glans clitoris is the only part of the overall clitoris visible externally, but this spongy tissue extends down either side of the openings to the urethra and vagina, as seen in Figure 18.6.7.

Other Vulvar Structures

The area between the two labia minora is called the vestibule of the vulva. Both the urethra and vagina have openings to the outside of the body in the vestibule. As you can see in Figure 18.6.7 above, the urethral opening (or meatus) is located just in front of, and is much smaller than, the vaginal opening. Both openings are protected by the labia. Two glands — called Bartholin’s glands — open on either side of the vaginal opening. These glands secrete mucus and a vaginal and vulvar lubricant.

The breasts are not directly involved in reproduction, but because they contain  mammary gland s , they can provide nourishment to an infant after birth. The breasts overlay major muscles in the chest from which they project outward in a conical shape. The two main types of tissues in the breast are adipose (fat) tissue and glandular tissue that produces milk. As shown in Figure 18.6.8, each mature breast contains many lobules, where milk is produced and stored during pregnancy. During breastfeeding (or lactation), the milk drains into ducts and sacs, which in turn converge at the nipple. Milk exits the breast through the nipple in response to the suckling action of an infant and is regulated by a positive feedback loop . The nipple is surrounded by a more darkly pigmented area called the areola. The areola contains glands that secrete an oily fluid, which lubricates and protects the nipple during breastfeeding.

18.6 Summary

• The female reproductive system is made up of internal and external organs that function to produce haploid female gametes called ova, secrete female sex hormones (such as estrogen ), and carry and give birth to a fetus .
• The vagina is an elastic, muscular canal that can accommodate the penis . It is also where sperm are usually ejaculated during sexual intercourse . The vagina is the birth canal, and it channels the flow of menstrual blood from the uterus . A healthy vagina has a balance of symbiotic bacteria and an acidic pH .
• The uterus is a muscular organ above the vagina where a fetus develops. Its muscular walls contract to push out the fetus during childbirth. The cervix is the neck of the uterus that extends down into the vagina. It contains a canal connecting the vagina and uterus for sperm, or for an infant to pass through. The innermost layer of the uterus — the endometrium — thickens each month in preparation for an embryo , but is shed in the following menstrual period if fertilization does not occur.
• The oviducts  extend from the uterus to the ovaries. Waving fimbriae at the ovary ends of the oviducts guide ovulated eggs into the tubes where fertilization may occur as the ova travel to the uterus. Cilia and peristalsis help ova move through the tubes. Tubular fluid helps nourish sperm as they swim up the tubes toward ova.
• The ovaries are gonads that produce ova and secrete sex hormones, including estrogen . Nests of cells called follicles in the ovarian cortex are the functional units of ovaries. Each follicle surrounds an immature ovum. At birth, a baby girl’s ovaries contain at least a million ova, and they will not produce any more during her lifetime. During a woman’s reproductive years, one ova typically matures and is ovulated each month.
• The vulva is a general term for external female reproductive organs. The vulva includes the clitoris , two pairs of labia , and openings for the urethra and vagina . Secretions from mucosal glands near the vaginal opening lubricate the vulva.
• The breasts are not technically reproductive organs, but their mammary glands produce milk to feed an infant after birth. Milk drains through ducts and sacs, and out through the nipple when a  baby sucks during breastfeeding.

18.6 Review Questions

• State the general functions of the female reproductive system.
• Describe the vagina and its reproductive functions.
• Outline the structure and basic functions of the uterus.
• What is the endometrium? How does it change during the monthly cycle?
• Why are breasts included in discussions of reproduction, if they are not organs of the female reproductive system?
• What is the function of the folds in the mucous membrane lining of the vagina?
• What are two ways in which the female reproductive system protects itself from pathogens?

18.6 Explore More

The uncomplicated truth about women’s sexuality | Sarah Barmak, TED, 2019.

Human Physiology – Functional Anatomy of the Female Reproductive System, Janux, 2015.

Figure 18.6.1

1024px-Cattien_stone_yoni by Binh Giang on Wikimedia Commons is in the   public domain (https://en.wikipedia.org/wiki/en:public_domain).

Figure 18.6.2

1000px-Gray1167.svg by Henry Vandyke Carter  (1831-1897) on Wikimedia Commons is in the   public domain  (https://en.wikipedia.org/wiki/public_domain). ( Bartleby.com :  Gray’s Anatomy , Plate 1167 ).

Figure 18.6.3

Uterine_anatomy. from Uterine Stem cells by The Stem Cell Research Community, StemBook on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 18.6.4

Sites_of_tubo_ovarian_abscess by Bfpage on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 18.6.5

Ovarian_follicle by TiagoLubiana on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 18.6.6

HumanVulva-NewText-PhiloViv by Amphis (edited) on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. ( Original   en:Image:HumanVulva-NoText-PhiloVivero.jpg by en:user:PhiloVivero )

Figure 18.6.7

Vulva  by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 18.6.8

Breast-Diagram by Women’s Health (NCI/ NIH) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/en:Public_domain).

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure  27.10   The vulva [digital image].  In Anatomy and Physiology (Section 27.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/27-2-anatomy-and-physiology-of-the-female-reproductive-system

Janux. (2015, January 10). Human physiology – Functional anatomy of the female reproductive system. YouTube. https://www.youtube.com/watch?v=9rs2gNchQig&feature=youtu.be

TED. (2019, March 22). The uncomplicated truth about women’s sexuality | Sarah Barmak. YouTube.  https://www.youtube.com/watch?v=SkB4gG8ke7Q&feature=youtu.be

Teixeira, J., Rueda, B.R., and Pru, J.K. (September 30, 2008). Figure 1 Uterine anatomy. In Uterine Stem Cells (StemBook, ed.). The Stem Cell Research Community, StemBook, doi/10.3824/stembook.1.16.1, http://www.stembook.org

The female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth.

The female sex hormone secreted mainly by the ovaries.

An unborn offspring of a mammal, in particular an unborn human baby more than eight weeks after conception.

The female reproductive organ in which first an embryo and then a fetus grows and develops until birth.

One of two female reproductive organs that carry eggs from an ovary to the uterus and are the site where fertilization usually takes place.

A pair of female reproductive organs that produces eggs and secretes estrogen.

External female reproductive structures, including the clitoris, labia, and vaginal and urethral openings.

The small, sensitive external female organ that is part of the vulva and may lead to sexual arousal and/or orgasm when stimulated.

The “lips” of the vulva, consisting of folds of tissue that protect the urethral and vaginal openings.

The neck of the uterus that protrudes down into the vagina and through which a canal connects the vagina and uterus.

The male reproductive cell.

A body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains reproductive organs, the urinary bladder, the pelvic colon, and the rectum.

Epithelial tissue that lines inner body surfaces and body openings and produces mucus.

Any type of a close and long-term biological interaction between two different biological organisms.

Any member of a large group of unicellular microorganisms which have cell walls but lack organelles and an organized nucleus, including some which can cause disease.

A measure of the acidity or basicity of aqueous or other liquid solutions. The term translates the values of the concentration of the hydrogen ion in a scale ranging from 0 and 14. In pure water, which is neutral (neither acidic nor alkaline), the concentration of the hydrogen ion corresponds to a pH of 7. A solution with a pH less than 7 is considered acidic; a solution with a pH greater than 7 is considered basic, or alkaline.

A sac-like organ that stores urine until it is excreted from the body.

An organisms that is so small it is invisible to the human eye.

The release of a secondary oocyte from an ovary about half way through the menstrual cycle.

The innermost layer of the uterus that builds up during each menstrual cycle and helps nourish the embryo if fertilization occurs or is shed from the uterus as menstrual flow if fertilization does not occur.

A temporary organ that consists of a large mass of maternal and fetal blood vessels through which the mother’s and embryo’s or fetus’s blood exchange substances.

The middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells (also called uterine myocytes) but also of supporting stromal and vascular tissue. Its main function is to induce uterine contractions.

The outer serous layer of the uterus. The serous layer secretes a lubricating fluid that helps to reduce friction.

Small, fingerlike projections at the end of the oviducts, through which eggs move from the ovaries to the uterus. The fimbriae are connected to the ovary.

Tiny hairlike organelles, identical in structure to flagella, that line the surfaces of certain cells and beat in rhythmic waves, providing locomotion to ciliate protozoans and moving liquids along internal epithelial tissue in animals.

A semi-permeable lipid bilayer that separates the interior of all cells from their surroundings.

An involuntary, nonstriated muscle that is found in the walls of internal organs such as the stomach.

A distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines.

Two male reproductive organs that produce sperm and secrete testosterone; male gonad.

One of a pair of organs that secrete sex hormones and produce gametes; testis in males and ovary in females.

A mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.

A hormone is a signaling molecule produced by glands in multicellular organisms that target distant organs to regulate physiology and behavior.

The gamete produced by a female.

A hollow, tube-like structure through which blood flows in the cardiovascular system; vein, artery, or capillary.

The functional unit of an ovary that consists of a nest of epithelial cells surrounding an egg.

A period during which humans become sexually mature.

The cessation of a woman’s menstrual cycles, usually by age 52.

A tube-like organ of the urinary system that carries urine out of the body from the bladder and, in males, also carries semen out of the body.

An exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma, "breast".

A control mechanism that serves to intensify a response until an endpoint is reached.

The term used when a cell has half the usual number of chromosomes.

The male reproductive organ containing the urethra, through which semen and urine pass out of the body.

The physical activity of sex between two people.

Having a higher proportion of hydronium ions than hydroxide ions; having the properties of an acid; having a pH below 7.

A stage of growth and development that occurs from implantation in the uterus through the eighth week after fertilization.

The fusion of haploid gametes, egg and sperm, to form the diploid zygote.

Human Biology Copyright © 2020 by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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18.7 Functions of the Female Reproductive System

Created by CK-12 Foundation/Adapted by Christine Miller

Waiting Expectantly

A mother-to-be waits patiently for her baby to grow as her belly gradually swells. Reproduction is all about making babies, and the female reproductive system is specialized for this purpose. Its functions include producing female gamete s called ova, secreting female sex hormones (such as estrogen ), providing a site for fertilization , gestating a fetus if fertilization occurs, giving birth to a baby, and breastfeeding a baby after birth. The only thing missing is sperm .

Ova Production

At birth, a female’s ovaries contain all the ova she will ever produce, which may include a million or more ova. The ova don’t start to mature, however, until she enters puberty and attains sexual maturity. After that, one ovum typically matures each month, and is released from an ovary. This continues until a woman reaches menopause (cessation of monthly periods), typically by age 52. By then, viable eggs may be almost depleted, and hormone levels can no longer support the monthly cycle. During the reproductive years, which of the two ovaries releases an egg in a given month seems to be a matter of chance. Occasionally, both ovaries will release an egg at the same time. If both eggs are fertilized, the offspring are fraternal twins (dizygotic, or “two-zygote,” twins), and they are no more alike genetically than non-twin siblings.

The process of producing ova in the ovaries of a female fetus is called oogenesis . Ova are haploid gametes, and their production occurs in several steps that involve different types of cells, as summarized in Figure 18.7.2. Oogenesis is completed long before birth. It occurs when diploid germ cells called oogonia  (singular, oogonium) undergo  mitosis . Each such cell division produces two diploid daughter cells. One is called the primary oocyte, and the other is retained to help maintain a reserve of oogonia. The primary oocyte , in turn, starts to go through the first cell division of meiosis (meiosis I). However, it does not complete meiosis I until much later. Instead, it remains in a resting state, nestled within a tiny, immature follicle in the ovary until the female goes through puberty.

Maturation of a Follicle

Beginning in puberty, about once a month, one of the follicles in an ovary undergoes maturation, and an egg is released. As the follicle matures, it goes through changes in the numbers and types of its cells, as shown in Figure 18.7.2. The primary oocyte within the follicle also resumes meiosis. It completes meiosis I, which began long before birth, to form a secondary oocyte and a smaller cell, called the first polar body. Both the secondary oocyte and the first polar body are haploid cells. The secondary oocyte has most of the cytoplasm from the primary oocyte and is much larger than the first polar body, which soon disintegrates and disappears. The secondary oocyte begins meiosis II, but only completes it if the egg is fertilized.

Release of an Egg

It typically takes 12 to 14 days for a follicle to mature in an ovary, and for the secondary oocyte to form. Then, the follicle bursts open and the ovary ruptures, releasing the secondary oocyte from the ovary. This event is called  ovulation .  The now-empty follicle starts to change into a structure called a  corpus luteum . The expelled secondary oocyte is usually swept into the nearby oviduct by its waving, fringe-like fimbriae .

Uterine Changes

While the follicle is maturing in the ovary, the uterus is also undergoing changes to prepare it for an embryo if fertilization occurs. For example, the endometrium gets thicker and becomes more vascular. Around the time of ovulation , the cervix undergoes changes that help sperm reach the ovum to fertilize it. The cervical canal widens, and cervical mucus becomes thinner and more alkaline. These changes help promote the passage of sperm from the vagina into the uterus and make the environment more hospitable to sperm.

Fertilization — or Not

Fertilization of an ovum by a sperm normally occurs in an oviduct, most often in the part of the tube that passes above the ovary (see Figure 18.7.3). In order for fertilization to occur, sperm must “swim” from the vagina where they are deposited, through the cervical canal to the uterus, and then through the body of the uterus to one of the oviducts. Once sperm enter a oviduct, tubular fluids help carry them through the tube toward the secondary oocyte at the other end. The secondary oocyte also functions to promote fertilization. It releases molecules that guide the sperm and allow the surface of the ovum to attach to the surface of the sperm. The ovum can then absorb the sperm, allowing fertilization to occur.

If Fertilization Occurs

If the secondary oocyte is fertilized by a sperm as it passes through the oviduct, the secondary oocyte quickly completes meiosis II, forming a diploid zygote and another polar body. This second polar body, like the first, normally breaks down and disappears. The zygote then continues the journey through the oviduct to the uterus , during which it undergoes several mitotic cell divisions. By the time it reaches the uterus up to five days after fertilization, it consists of a ball of cells called a blastocyst . Within another day or two, the blastocyst implants itself in the endometrium lining the uterus, and gestation begins.

If Fertilization Does Not Occur

What happens if the secondary oocyte is not fertilized by a sperm as it passes through the oviduct? It continues on its way to the uterus without ever completing meiosis II. It is likely to disintegrate within a few days while still in the oviduct. Any remaining material will be shed from the woman’s body during the next menstrual period.

Pregnancy and Childbirth

Pregnancy is the carrying of one or more offspring from fertilization until birth. This is one of the major functions of the female reproductive system. It involves virtually every other body system including the cardiovascular, urinary, and respiratory systems, to name just three. The maternal organism plays a critical role in the development of the offspring. She must provide all the nutrients and other substances needed for normal growth and development of the offspring, and she must also remove the wastes excreted by the offspring. Most nutrients are needed in greater amounts by a pregnant woman to meet fetal needs, but some are especially important, including folic acid, calcium, iron, and omega-3 fatty acids. A healthy diet (see photo in Figure 18.7.4 ) , along with prenatal vitamin supplements, is recommended for the best pregnancy outcome. A pregnant woman should also avoid ingesting substances (such as alcohol) that can damage the developing offspring, especially early in the pregnancy when all of the major organs and organ systems are forming.

Trimesters of Pregnancy

When counted from the first day of the last menstrual period, the average duration of pregnancy is about 40 weeks (38 weeks when counted from the time of fertilization), but a pregnancy that lasts between 37 and 42 weeks is still considered within the normal range. From the point of view of the maternal organism, the total duration of pregnancy is typically divided into three periods, called  trimesters ,  each of which lasts about three months. This division of the total period of gestation is useful for summarizing the typical changes a woman can expect during pregnancy. From the point of view of the developing offspring, however, the major divisions are different. They are the embryonic and fetal stages. The offspring is called an embryo from the time it implants in the uterus through the first eight weeks of life. After that, it is called a fetus for the duration of the pregnancy.

First Trimester

The first trimester begins at the time of fertilization and lasts for the next 12 weeks. Even before she knows she is pregnant, a woman in the first trimester is likely to experience signs and symptoms of pregnancy. She may notice a missed menstrual period, and she may also experience tender breasts, increased appetite, and more frequent urination. Many women also experience nausea and vomiting in the first trimester. This is often called “morning sickness,” because it commonly occurs in the morning, but it may occur at any time of day. Some women may lose weight during the first trimester because of morning sickness.

Second Trimester

The second trimester occurs during weeks 13 to 28 of pregnancy. A pregnant woman may feel more energized during this trimester. If she experienced nausea and vomiting during the first trimester, these symptoms often subside during the second trimester. Weight gain starts occurring during this trimester, as well. By about week 20, the fetus is getting large enough that the mother can feel its movements. The photo in Figure 18.7.5 shows a pregnant woman at week 26, toward the end of the second trimester. (For comparison, the same woman is shown on the right at the end of the third trimester.)

Third Trimester

The third trimester occurs during weeks 29 through birth (at about 40 weeks). During this trimester, the uterus expands rapidly, making up a larger and larger portion of the woman’s abdomen. Weight gain is also more rapid. During the third trimester, the movements of the fetus become stronger and more frequent, and they may become disruptive to the mother. As the fetus grows larger, its weight and the space it takes up may lead to symptoms in the mother such as back pain, swelling of the lower extremities, more frequent urination, varicose veins, and heartburn. By the end of the third trimester, the woman’s abdomen often will transform in shape as it drops, due to the fetus turning to a downward position before birth so its head rests on the cervix . This relieves pressure on the upper abdomen, but reduces bladder capacity and increases pressure on the pelvic floor and rectum.

Near the time of birth, the amniotic sac — a fluid-filled membrane that encloses the fetus within the uterus — breaks in a gush of fluid. This is commonly called “breaking water.” Labour usually begins within a day of this event, although it may begin prior to it.  Labour is the general term for the process of childbirth in which regular uterine contractions push the fetus and placenta out of the body. Labour can be divided into three stages, which are illustrated in Figure 18.7.6: dilation, birth, and afterbirth.

• During the dilation stage of labour, uterine contractions begin and become increasingly frequent and intense. The contractions push the baby’s head (most often) against the cervix, causing the cervical canal to dilate, or become wider. This lasts until the cervical canal has dilated to about 10 cm (almost 4 in.) in width, which may take 12 to 20 hours — or even longer. The cervical canal must be dilated to this extent in order for the baby’s head to fit through it.
• During birth, the baby descends (usually headfirst) through the cervical canal and vagina, and into the world outside. This is the stage when the mother generally starts bearing down during the contractions to help push out the fetus. This stage may last from about 20 minutes to two hours or more. Usually, within a minute or less of birth, the umbilical cord is cut, so the baby is no longer connected to the placenta.
• During the afterbirth stage, the placenta is delivered. This stage may last from a few minutes to a half hour.

Breastfeeding

Although the breas t s  are not classified as organs of the reproductive system, they nonetheless may play an important role in reproduction. The physiological function of the female breast is  lactation , or the production of breast milk to feed an infant. This function is illustrated in Figure 18.7.7. Besides nutrients, breast milk provides hormones, antibodies, and other substances that help ensure a healthy start after birth.

The Figure 18.7.7 (above) shows the correct way for an infant to suck the breast to stimulate the letdown of milk from the mammary glands (lips flanged, baby’s mouth on the nipple symmetrically). The letdown of milk when an infant sucks at the breast is one of the few examples of a positive feedback loop in the human organism. Sucking causes a release from the posterior pituitary gland of the hypothalamic hormone oxytocin . Oxytocin, in turn, causes milk to flow from the alveoli in the breasts where milk is produced, through the milk ducts, and into the milk sacs behind the areola. You can trace this route of milk through the breast in Figure 18.7.8. The baby can suck the milk out of the sacs through the nipple, where they converge. The release of milk stimulates the baby to continue sucking, which in turn keeps the milk flowing.  Oxytocin is also an important hormone for maternal-child attachment.

Female Sex Hormones

Female reproduction could not occur without sex hormones released by the ovaries. These hormones include estrogen and progesterone.

Before birth, estrogen is released by the gonads in female fetus es  and leads to the development of female reproductive organs. At puberty , estrogen levels rise and are responsible for sexual maturation, and for the development of female secondary sex characteristics (such as breasts). Estrogen is also needed to help regulate the  menstrual cycle  and ovulation throughout a woman’s reproductive years. Estrogen is produced primarily by follicular cells in the ovaries. During pregnancy, estrogen is also produced by the placenta . There are actually three forms of estrogen in the human female: estradiol, estriol, and estrone.

• Estradiol  is the predominant form of estrogen during the reproductive years. It is also the most potent form of estrogen.
• Estriol  is the predominant form of estrogen during pregnancy. It is also the weakest form of estrogen.
• Estrone  is the predominant form of estrogen in post-menopausal women. It is intermediate in strength between the other two forms of estrogen.

Progesterone

Progesterone  stands for “pro-gestational hormone.” It is synthesized and secreted primarily by the corpus luteum in the ovary. Progesterone plays many physiological roles, but is best known for its role during pregnancy. In fact, it is sometimes called the “hormone of pregnancy.” Among other functions, progesterone prepares the uterus for pregnancy each month by building up the uterine lining. If a pregnancy occurs, progesterone helps maintain the pregnancy in a number of ways, such as decreasing the maternal immune response to the genetically different embryo, and decreasing the ability of uterine muscle tissue to contract. Progesterone also prepares the mammary gland s  for lactation during pregnancy, and withdrawal of progesterone after birth is one of the triggers of milk production.

Feature: Myth vs. Reality

There are many myths associated with pregnancy. Most are harmless, but some may put the pregnant woman or fetus at risk. As always, knowledge is power.

18.7 Summary

• Oogenesis is the process of producing ova in the ovaries of a female fetus . Oogenesis begins when a diploid oogonium divides by mitosis to produce a diploid primary oocyte . The primary oocyte begins meiosis I and then remains at this stage in an immature ovarian follicle until after birth. By birth, a female’s ovaries contain all the eggs she will ever produce, numbering at least a million.
• After puberty , one follicle a month matures, and its primary oocyte completes meiosis I to produce a secondary oocyte, which begins meiosis II. During ovulation , the mature follicle bursts open, and the secondary oocyte leaves the ovary and enters an oviduct .
• While a follicle is maturing in an ovary each month, the endometrium in the uterus is building up to prepare for an embryo . Around the time of ovulation, cervical mucus becomes thinner and more alkaline to help sperm reach the secondary oocyte.
• If the secondary oocyte is fertilized by a sperm, it quickly completes meiosis II and forms a diploid zygote , which will continue through the oviduct. The zygote will go through multiple cell divisions before reaching and implanting in the uterus . If the secondary oocyte is not fertilized, it will not complete meiosis II, and it will soon disintegrate.
• Pregnancy is the carrying of one or more offspring from fertilization until birth. The maternal organism must provide all the nutrients and other substances needed by the developing offspring, and also remove its wastes. She should also avoid exposures that could potentially damage the offspring, especially early in the pregnancy when organ systems are developing.
• The average duration of pregnancy is 40 weeks (from the first day of the last menstrual period) and is divided into three trimesters of about three months each. Each trimester is associated with certain events and conditions that a pregnant woman may expect, such as morning sickness during the first trimester, feeling fetal movements for the first time during the second trimester, and rapid weight gain in both fetus and mother during the third trimester.
• Labour , which is the general term for the birth process, usually begins around the time the amniotic sac breaks and its fluid leaks out. Labour occurs in three stages: dilation of the cervix , birth of the baby, and delivery of the placenta (afterbirth).
• The physiological function of female breasts is lactation , or the production of breast milk to feed an infant. Sucking on the breast by the infant stimulates the release of the hypothalamic hormone oxytocin from the posterior pituitary, which causes the flow of milk. The release of milk stimulates the baby to continue sucking, which in turn keeps the milk flowing. This is one of the few examples of positive feedback in the human organism.
• The ovaries produce female sex hormones, including estrogen and progesterone . Estrogen is responsible for sexual differentiation before birth, as well as for sexual maturation and the development of secondary sex characteristics  at puberty . It is also needed to help regulate the  menstrual cycle  and ovulation after puberty and until menopause . Progesterone prepares the uterus for pregnancy each month during the menstrual cycle, and helps maintain the pregnancy if fertilization occurs.

18.7 Review Questions

• What is pregnancy, and what is the role of the maternal organism in pregnancy?
• What is the average duration of pregnancy? Identify the trimesters of pregnancy.
• Define labour. What event is often a sign that labour will soon begin?
• Identify the stages of labour.
• Describe the physiological function of female breasts. How is this function controlled?
• Identify the functions of the female sex hormones estrogen and progesterone.
• Describe the roles of the cervix in fertilization and childbirth.

18.7 Explore More

Pregnancy 101 | National Geographic, 2018.

How do pregnancy tests work? – Tien Nguyen, TED-Ed, 2015.

Fertilization, Nucleus Medical Media, 2013.

The science of milk – Jonathan J. O’Sullivan, TED-Ed, 2017.

Attributions

Figure 18.7.1

Pregnant by Mustafa Omar on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 18.7.2

Oogenesis by Acedatrey2 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 18.7.3

Blausen_0404_Fertilization by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.

Figure 18.7.4

Prenatal Diet/ Milch-Jogurt-Früchte by Peggy Greb, Agricultural Research Service (USDA) on Wikimedia Commons is in the public domain  (https://commons.wikimedia.org/wiki/Public_domain).

Figure 18.7.5

Pregnancy_comparison by Maustrauser  at  English Wikipedia on Wikimedia Commons is in the public domain  (https://commons.wikimedia.org/wiki/Public_domain).

Figure 18.7.6

Stages_of_Childbirth-02 by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.

Figure 18.7.7

Childhood: breast feeding [photo] by Jan Kopřiva on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 18.7.8

Breast-Diagram by Women’s Health (NCI/ NIH) on Wikimedia Commons is in the public domain  (https://commons.wikimedia.org/wiki/Public_domain).

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure  28.21   Stages of childbirth [digital image]. In Anatomy and Physiology (Section 28.4). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/28-4-maternal-changes-during-pregnancy-labor-and-birth

Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436

National Geographic. (2018, December 20). Pregnancy 101 | National Geographic. YouTube.  https://www.youtube.com/watch?v=XEfnq4Q4bfk&feature=youtu.be

Nucleus Medical Media. (2013, January 31). Fertilization. YouTube. https://www.youtube.com/watch?v=_5OvgQW6FG4&feature=youtu.be

TED-Ed, (2015, July 7). How do pregnancy tests work? – Tien Nguyen. YouTube. https://www.youtube.com/watch?v=aOfWTscU8YM&feature=youtu.be

TED-Ed. (2017, January 31). The science of milk – Jonathan J. O’Sullivan. YouTube. https://www.youtube.com/watch?v=xmNzUEmFZMg&feature=youtu.be

A mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.

The female sex hormone secreted mainly by the ovaries.

The fusion of haploid gametes, egg and sperm, to form the diploid zygote.

An unborn offspring of a mammal, in particular an unborn human baby more than eight weeks after conception.

The male reproductive cell.

A pair of female reproductive organs that produces eggs and secretes estrogen.

The gamete produced by a female.

A period during which humans become sexually mature.

The cessation of a woman’s menstrual cycles, usually by age 52.

The production or development of an ovum.

The term used when a cell has half the usual number of chromosomes.

A diploid stem cell in an ovary that undergoes mitosis to begin the process of oogenesis.

A part of the cell cycle when replicated chromosomes are separated into two new nuclei and then subsequent cell division gives rise to genetically identical cells in which the number of chromosomes is maintained.

Describes a cell that contain two copies of each chromosome.

A cell in an ovary which may undergo meiotic division to form an ovum.

A special type of cell division in sexually-reproducing organisms used to produce the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome.

The functional unit of an ovary that consists of a nest of epithelial cells surrounding an egg.

The release of a secondary oocyte from an ovary about half way through the menstrual cycle.

An ovarian structure that forms from a follicle after it matures and ovulates an egg.

Small, fingerlike projections at the end of the oviducts, through which eggs move from the ovaries to the uterus. The fimbriae are connected to the ovary.

The female reproductive organ in which first an embryo and then a fetus grows and develops until birth.

The innermost layer of the uterus that builds up during each menstrual cycle and helps nourish the embryo if fertilization occurs or is shed from the uterus as menstrual flow if fertilization does not occur.

The neck of the uterus that protrudes down into the vagina and through which a canal connects the vagina and uterus.

The female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth.

The union of the sperm cell and the egg cell. Also known as a fertilized ovum, the zygote begins as a single cell but divides rapidly in the days following fertilization. After this two-week period of cell division, the zygote eventually becomes an embryo.

A fluid-filled ball of cells that develops a few days after fertilization in the process of blastulation.

The carrying of one or more offspring from fertilization until birth.

One of three, approximately three-month periods into which a pregnancy is divided.

A stage of growth and development that occurs from implantation in the uterus through the eighth week after fertilization.

The fluid-filled sac that contains and protects a fetus in the womb.

A general term for the process of childbirth, which includes three stages: dilation of the cervical canal, birth of the child, and delivery of the placenta (afterbirth).

Refers to the front of the chest or, more specifically, to the mammary gland. The mammary gland is a milk producing gland. It is composed largely of fat.

The production of breastmilk to feed an infant.

A control mechanism that serves to intensify a response until an endpoint is reached.

The master gland of the endocrine system that secretes many hormones, the majority of which regulate other endocrine glands.

An endocrine hormone secreted by the pituitary gland that controls a variety of functions, including during childbirth to stimulate uterine contractions and during lactation to trigger milk letdown.

The monthly cycle of processes and events in the ovaries and uterus of a sexually mature human female until menopause.

A temporary organ that consists of a large mass of maternal and fetal blood vessels through which the mother’s and embryo’s or fetus’s blood exchange substances.

The female sex hormone secreted mainly by the ovaries that helps maintain a successful pregnancy.

An exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma, "breast".

One of two female reproductive organs that carry eggs from an ovary to the uterus and are the site where fertilization usually takes place.

A trait that is different in males and females but is not directly involved in reproduction, such as male facial hair and female breasts.

Human Biology Copyright © 2020 by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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• Antenatal Care Module: Ethiopian Federal Ministry of Health
• Antenatal Care Module: Acknowledgements
• Antenatal Care Module: Introduction
• Antenatal Care Module: 1. Planning Antenatal Care
• Antenatal Care Module: 2. Promoting Antenatal Care
• Introduction
• Learning Outcomes for Study Session 3
• 3.1  Some common terms in anatomy and physiology
• 3.2  Anatomy and physiology of the female reproductive organs
• 3.3.1  Mons pubis
• 3.3.2  Labia majora and labia minora
• 3.3.3  Vestibule
• 3.3.4  Perineum and hymen
• 3.4.1  Fallopian tubes and ovaries
• 3.4.2  The uterus
• 3.4.3  The cervix and the vagina

Summary of Study Session 3

Self-Assessment Questions (SAQs) for Study Session 3

• Antenatal Care Module: 4. Hormonal Regulation of the Female Reproductive System
• Antenatal Care Module: 5. Fertilisation, Implantation and the Fetal and Placental Circulation
• Antenatal Care Module: 6. Anatomy of the Female Pelvis and Fetal Skull
• Antenatal Care Module: 7. Physiological Changes During Pregnancy
• Antenatal Care Module: 8. Diagnosing Pregnancy and Learning a Pregnant Woman’s History
• Antenatal Care Module: 9. General Assessment of the Pregnant Woman
• Antenatal Care Module: 10. Estimating Gestational Age from Fundal Height Measurement
• Antenatal Care Module: 11. Assessing the Fetus
• Antenatal Care Module: 12. Minor Disorders of Pregnancy
• Antenatal Care Module: 13. Providing Focused Antenatal Care
• Antenatal Care Module: 14. Health Promotion Issues During Pregnancy
• Antenatal Care Module: 15. Counselling Pregnant Women on Danger Symptoms
• Antenatal Care Module: 16. Antenatal Interventions to Reduce Mother to Child Transmission of HIV
• Antenatal Care Module: 17. Premature Rupture of Membranes (PROM)
• Antenatal Care Module: 18. Common Medical Disorders in Pregnancy
• Antenatal Care Module: 19. Hypertensive Disorders of Pregnancy
• Antenatal Care Module: 20. Abortion and other Causes of Early Pregnancy Bleeding
• Antenatal Care Module: 21. Late Pregnancy Bleeding
• Antenatal Care Module: 22. Starting IV Fluid Therapy and Catheterising the Pregnant Woman
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• Antenatal Care Part 1 PDF (3.7MB)
• Antenatal Care Part 2 PDF (3.1MB)

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About this course

• 44 hours study
• 1 Level 1: Introductory
• Course description

Antenatal Care

If you create an account, you can set up a personal learning profile on the site.

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.

SAQ 3.1 (tests Learning Outcomes 3.1 and 3.2)

Look at Figure 3.5. Label the anatomical features marked from ‘a’ to ‘i’.

The correct labels for Figure 3.5 are as follows:

a  is the vagina

b  is the cervix

c  is the uterus

d  is the ovary

e  is the fundus

f  is the ovarian suspensory ligament

g  is the fallopian tube

h  is the fimbriae

i  is the ovarian ligament.

SAQ 3.2 (tests Learning Outcome 3.1)

Choose the correct directional terms from Box 3.1 to describe the relative positions of the uterus and the rectum in Figure 3.1.

The uterus is anterior to (in front of) and superior to (above) the rectum. An alternative way of expressing the same positions is to say that the rectum is posterior to (behind) and inferior to (below) the uterus.

SAQ 3.3 (tests Learning Outcomes 3.2 and 3.3)

Which structures are removed in female genital mutilation, and what harm can come to a woman during labour and delivery as a result?

The structures removed in female genital mutilation are usually the clitoris and the labia minora. The scarring that results as the cuts heal interferes with the normal ability of the vulva to stretch during childbirth to allow the baby to pass through the birth canal. As a result, the birth can be obstructed and the vagina can tear, causing severe pain and loss of blood. In some cases, a fistula (hole in the vaginal wall) can tear open, and blood loss can put the woman’s life at risk.

SAQ 3.4 (tests Learning Outcomes 3.2 and 3.3)

Which of the following statements is false ? In each case, state why it is incorrect.

A  Infection in the uterus can get into the pelvic cavity through the vagina.

B  The perineum is a muscular area between the vaginal opening and the anus.

C  The maturation of an ovum is controlled by the female reproductive hormones.

D  Glands in the cervix produce secretions which lubricate the vagina.

E  The fundus is the narrow ‘neck’ at the bottom of the uterus.

A is false . Infection in the uterus can get into the pelvic cavity by passing outwards through the fallopian tubes, which are open at the ends. Infection in the uterus can pass down the vagina, and usually appears as a bad-smelling discharge from the vaginal opening in the vulva.

B is true. The perineum is a muscular area between the vaginal opening and the anus.

C is true. The maturation of an ovum is controlled by the female reproductive hormones.

D is true. Glands in the cervix produce secretions which lubricate the vagina.

E is false . The fundus is the name for the domed top of the uterus. The narrow neck at the bottom of the uterus is called the cervix.

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• Female reproductive system
• Assignment Topics

Reproduction is one process which is very important for the living beings. It is the process by which the living organisms procreate to form new organisms and thus leads to the continuation of life on Earth. Every organism undergoes reproduction. Non-livings things do not divide and thus forms the basic difference with the living organisms. There can be different ways that are broadly divided into two terms-

• Asexual Reproduction
• Sexual Reproduction

Humans reproduce by using the sexual methods of reproduction. There are two sexes of Homo sapiens and they are the male sex and the female sex. Both have their own set of reproductive organ. The male gamete is transferred to the female reproductive system through copulation and thus leads to formation of a new organism. The male gamete fertilizes the female gamete and the process is commenced further to formation of embryo.

The males carry sperm as the male gamete and the females carry egg as the female gamete. The female needs male gamete to fertilize the egg. Eggs are formed inside the female reproductive system through the various steps and the help of hormones.

FUNCTIONS OF FEMALE REPRODUCTIVE SYSTEM

There are many functions that need to be performed by a female reproductive system. Therefore the function are-

• The production of the female egg cells which is necessary for the reproduction to occur, called the ova or oocyte. They are formed through various steps.
• The reproductive system also has to transport the ova to the site of fertilization where the sperm can fertilize the egg.
• The fertilization of an egg by a sperm occurs in a specific part of the fallopian tubes. If fertilization takes place at any other part of the reproductive system it is known as ectopic pregnancy.
• The fertilized egg is to implant into the walls of the uterus, this step is the beginning the initial stages of pregnancy. The maintenance of pregnancy is also by the reproductive system.
• If fertilization does not occur due to the absence of male gamete or any other reason, the system has to undergo menstruation, to get rid of the upper lining of the endometrial layer.
• The female reproductive system also produces the female sex hormones which are responsible for all the functions of the reproductive cycle.

PARTS OF FEMALE REPRODUCTIVE SYSTEM

The female reproductive anatomy has some parts inside and some parts outside the body. Hence, it is divided into two parts- the external reproductive parts and the internal reproductive parts.

EXTERNAL REPRODUCTIVE SYSTEM

The function of external reproductive system is-

• It is the passage through which the sperm enters the female body and later on leads to fertilization.
• It also protects the internal genital organs from infectious organisms that can harm the internal reproductive system.

PARTS OF EXTERNAL REPRODUCTIVE SYSTEM

• Vagina: The vagina is also known as the birth canal and joins the cervix which is the lower part of uterus, to the outside of the body. It is the part of the reproductive system which receives the male gamete, sperms. They travel up the vaginal canal and meet the egg which is produced.
• Uterus: The uterus is a pear-shaped organ which is hollow from inside so that is the home to a developing fetus after the fertilization. The uterus can be mainly divided into two parts: the cervix that is the lower part that opens into the vagina. The man part of the body is the uterus which is known as the corpus. The function of corpus is that it can easily expand to hold a developing baby. Cervix allows the sperm to enter and the menstrual blood to exit through the opening. Uterus is termed as the womb in layman terms.
• Ovaries: The oval-shaped glands are known as the ovaries. They are two in number and that are located on either side of the uterus. The function of the ovaries is to produce eggs and hormones. One of the ovaries produces an egg each month and if the egg is not fertilized then the menstruation cycle takes place.
• Fallopian tubes: The fallopian tube is a narrow tube that is connected to the upper part of the uterus. They serve as the tunnel for the ova so that it can travel from the ovaries to the uterus. The fertilization process takes place in the fallopian tube only. The sperm enter the cervix and travel up to the fallopian tube where it meets the egg and the fertilization takes place. The fertilized egg then moves to the uterus. This is the site where it gets implanted into the lining of the uterine wall and the zygote is formed.

EGGS PRODUCED BY A FEMALE BODY

At the birth, there are around 1 million to 2 million eggs. When the time of puberty arrives, there are only 300,000 remaining. But all of these are not matured. Only 500 will be ovulated during the reproductive lifetime. Any remaining eggs will gradually accept their fate and die at menopausal age. One egg is matured every month and is available for the fertilization. The menstrual cycle continues up till 45-47 years of age. After this menopause occurs, and the menstrual cycle does not occur anymore and hence, no fertilization can take place.

MENSTRUAL CYCLE

The females that have reached puberty start experiencing the hormonal change in their bodies and undergo the menstrual cycle every month. Every month, a woman's body prepares for a potential pregnancy, whether it receives a male gamete or not. “Menstru” refers to monthly and the “menstruation” is termed as shedding of the uterine wall.

The menstrual cycle takes about 28 days on an average. The PHASES OF THE CYCLE-

• The follicular phase,
• The ovulatory phase
• The luteal phase.

There are four hormones which are responsible for the formation of egg from the ovaries and the menstrual cycle.

There are four major HORMONES involved in the menstrual cycle:

• Follicle-stimulating hormone
• Luteinizing hormone
• Progesterone

Follicular Phase-

This phase commences on the first day of your period cycle. During this phase of the menstrual cycle, these events occur:

• Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are the two hormones released from the brain and travel through the blood to the ovaries.
• The stimulation of the growth of about 15 to 20 eggs in the ovaries. The eggs are present in its own "shell," called a follicle. They are released after the action of the hormone on the ovaries.
• These hormones (FSH and LH) also cause an increase in female hormone estrogen. These hormones are directly related to each other.
• Slowly the estrogen levels rises in the body, like a switch, follicle-stimulating hormone is turned off. Due to this mechanism there is a limit to the number of follicles that will reach maturity age.
• Due to progression in follicular phase, one follicle continues to mature and thus becomes dominant. All the follicles are suppressed by this dominant follicle in the group.
• Therefore, all the other follicles die and only the dominant one is producing the estrogen.

Ovulatory Phase-

The ovulatory phase is when the ovulation takes place. Ovulation occurs around 14 days after the follicular phase has started. The ovulatory phase is the midpoint, as the cycle is of 28 days. The next menstrual period begins after two weeks. The following events occurring during this stage:

• There is a decrease in the LSH which is released from the brain as soon as there is a rise in estrogen from the dominant follicle.
• Dominant follicle hence, releases an egg from the ovary which will be available for fertilization.
• Finger-like projections on the end of the fallopian tubes which are known as fimbriae collect the egg once it is ready to be released from the ovary. The fimbriae keep the egg into the tube and thus await fertilization.
• The thickness of mucus produced by the cervix, the lower part of the uterus. If the sperm enters the female body during this phase then it can be nourished by the thick mucus. They also help in the movement of the sperm inside the reproductive system.

Luteal Phase-

After the ovulation the luteal phase of the menstrual cycle begins. The cycle occurs in the last two weeks of the menstrual cycle. The following processes occur in this phase:

• The empty follicle develops into a new structure called the corpus luteum after the egg has been released from the ovary.
• The corpus luteum secretes the hormone - progesterone. Progesterone helps in the preparation of the uterus for a fertilized egg. It prepares the uterus for the implantation.
• If the fertilization takes place after the entry of the male sperm in the female’s body, it leads to conception. The fertilized egg will travel from the fallopian tube to the uterus and prepares for the implantation. This is how the women become pregnant.
• But if there is no male sperm to fertilize the egg, then there is no pregnancy. Therefore, the uterus lining breaks down and leads to shedding. The wall is shed off from the body through the opening-cervix. This is the last stage of the menstrual cycle where the bleeding occurs.
• After his phase the follicular phase starts all over again and thus the same cycle is repeated every month until the pregnancy takes place.

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• 1.0. MODULE 1: CARDIOVASCULAR SYSTEM
• 1.1. FUNCTIONAL ANATOMY OF THE HEART
• 1.1.1. Chambers and Circulation
• 1.1.2. The Layers of the Heart Wall
• 1.1.3. Cardiac Muscle Histology and Organization
• 1.2. CARDIAC CELL ACTION POTENTIALS
• 1.2.1. Action Potentials in Cardiac Contractile Muscle Cells
• 1.2.2. Action Potentials in Cardiac Autorhythmic Cells
• 1.3. ELECTROPHYSIOLOGY OF HEART MUSCLE
• 1.3.1. Heart Conduction System
• 1.3.2. Cardiac Excitation Coupling
• 1.3.3. Electrocardiogram (EKG)
• 1.4. THE CARDIAC CYCLE
• 1.4.1. Cardiac Cycle
• 1.4.2. Cardiac Measurements
• 1.5. REGULATION OF CARDIAC FUNCTION
• 1.5.1. Intrinsic Regulation
• 1.5.2. Extrinsic Regulation
• 1.5.3. Mean Arterial Pressure
• 1.5.4. Baroreceptor and Chemoreceptor Reflexes
• 2.0. MODULE 2: BLOOD
• 2.1. INTRODUCTION TO BLOOD, STRUCTURE AND FUNCTION AND BREAKDOWN
• 2.1.1. Functions of Blood
• 2.1.2. Composition of Blood
• 2.1.3. Hematopoiesis
• 2.1.4. Red Blood Cells
• 2.1.5. Hemoglobin
• 2.1.6. Erythropoiesis
• 2.1.7. Breaking Down Red Blood Cells
• 2.1.8. White Blood Cells and Platelets
• 2.2. HEMOSTASIS
• 2.2.1. Vascular Spasm
• 2.2.2. Platelet Plug
• 2.2.3. Clotting (Coagulation) Cascade
• 2.2.4. Clot Retraction and Fibrinolysis
• 2.2.5. Blood Clot Regulation
• 2.3. BLOOD TYPING
• 2.3.1. Blood Antigens and Antibodies
• 2.3.2. ABO Blood Group System
• 2.3.3. Rh Blood Group System
• 2.3.4. Hemolytic Disease of the Newborn
• 2.4. BLOOD VESSEL STRUCTURE AND ATHEROSCLEROSIS
• 2.4.1. Arteries and Veins
• 2.4.2. Portal System
• 2.4.3. Capillaries
• 2.4.4. Atherosclerosis
• 2.5. CAPILLARY EXCHANGE
• 2.5.1. Edema
• 2.6. BLOOD PRESSURE REGULATION AND SHOCK
• 2.6.1. Blood Pressure Explained
• 2.6.2. Short-Term Regulation
• 2.6.3. 2.6.3 - Long-Term Regulation
• 2.6.4. Shock
• 3.0. MODULE 3: IMMUNE SYSTEM
• 3.1. OVERVIEW OF THE LYMPHATIC AND NON-SPECIFIC INNATE RESPONSE OF THE IMMUNE SYSTEM
• 3.1.1. Structure and Function of the Lymphatic System
• 3.1.2. Physical Barriers: First Wall of Defense
• 3.1.3. Internal Non-Specific Defense Mechanisms
• 3.2. SPECIFIC ADAPTIVE IMMUNE RESPONSE, ANTIBODIES, IMMUNITY & VACCINES
• 3.2.1. Specific Defenses of the Immune Response
• 3.2.2. Antibodies
• 3.2.3. Immunological Memory
• 3.2.4. Vaccines, Autoimmunity and Allergies
• 4.0. MODULE 4: THE INTEGUMENTARY SYSTEM
• 4.1. STRUCTURE AND FUNCTION OF THE INTEGUMENTARY SYSTEM
• 4.1.1. Functions of the Integumentary System
• 4.1.2. Composition of the Skin
• 4.1.3. Skin Color
• 4.1.4. Skin Cancer
• 4.2.1. Types of Hair
• 4.2.2. Structure of Hair
• 4.2.3. Hair Growth
• 4.2.4. Hair Loss
• 5.0. MODULE 5: THE RESPIRATORY SYSTEM
• 5.1. RESPIRATORY SYSTEM STRUCTURE, FUNCTION AND VENTILATION
• 5.1.1. Respiratory System Function
• 5.1.2. Respiratory Structure
• 5.1.3. Respiratory Membrane
• 5.1.4. Alveoli and Surfactant
• 5.2. RESPIRATORY PRESSURES
• 5.2.1. Ventilation: Inspiration and Expiration
• 5.2.2. Pressure Differences in the Thoracic Cavity
• 5.2.3. Pneumothorax and Pleuritis
• 5.2.4. Respiratory Volumes and Capacity
• 5.3. GAS EXCHANGE AND TRANSPORT
• 5.3.1. Rate of Diffusion
• 5.3.2. Gas Laws Important in Gas Exchange
• 5.3.3. Partial Pressure Gradients
• 5.3.4. Oxygen and Carbon Dioxide Transport in the Blood
• 5.4. RESPIRATORY CONTROL
• 5.4.1. Respiratory Control by the Medulla Oblongata
• 5.4.2. Chemicals that Regulate Ventilation
• 5.4.3. COPD and Asthma
• 6.0. MODULE 6: THE SKELETAL SYSTEM
• 6.1. FUNCTION AND STRUCTURE OF THE SKELETAL SYSTEM
• 6.1.1. Hyaline Cartilage
• 6.1.2. Bone Characteristics
• 6.1.3. Bone Classification and Anatomy
• 6.1.4. Bone Cells
• 6.1.5. Formation of Woven and Lamellar Bone
• 6.1.6. Bone and Blood Calcium Levels
• 6.2. FORMATION, GROWTH & REPAIR OF BONE
• 6.2.1. Fetal Development of Bone: Intramembranous and Endochondral Ossification
• 6.2.2. Bone Growth in Children and Repair of Bones
• 6.2.3. Factors that Influence Bone Growth
• 6.2.4. Bone Repair
• 7.0. MODULE 7: URINARY SYSTEM
• 7.1. THE KIDNEY: FUNCTION, ANATOMY, THE NEPHRON AND GLOMERULUS
• 7.1.1. Urinary System Function
• 7.1.2. Functional Anatomy of the Urinary System
• 7.1.3. The Nephron: Functional Unit of the Kidney
• 7.1.4. The Renal Corpuscle: Bowman’s Capsule and the Glomerulus
• 7.2. FILTRATION, REABSORPTION, AND SECRETION
• 7.2.1. Filtration
• 7.2.2. Tubular Reabsorption
• 7.2.3. Secretion
• 7.2.4. Excretion
• 7.3. PHYSIOLOGY OF URINE PRODUCTION
• 7.3.1. Renal Clearance
• 7.3.2. Urine Concentration and Dilution
• 7.3.3. Hormonal Regulation of Urine Production
• 7.4. ACID/BASE BALANCE
• 7.4.1. Buffers
• 7.4.2. Respiratory System
• 7.4.3. Kidneys
• 7.4.4. Acid Base Disturbances
• 8.0. MODULE 8: DIGESTIVE SYSTEM
• 8.1. FUNCTIONAL ANATOMY OF THE DIGESTIVE SYSTEM
• 8.1.1. Layers of Alimentary Canal of the Digestive System
• 8.1.2. Enteric Nervous System
• 8.1.3. Organs of the Digestive System
• 8.2. DIGESTION
• 8.2.1. Carbohydrate Digestion and Absorption
• 8.2.2. Protein Digestion and Absorption
• 8.2.3. Lipid Digestion
• 8.3. REGULATION OF DIGESTIVE SECRETIONS
• 9.0. MODULE 9: ENDOCRINE SYSTEM
• 9.1. THE ENDOCRINE SYSTEM AND HORMONES OF THE BODY
• 9.1.1. Overview of the Endocrine System
• 9.1.2. Hormone Receptors
• 9.1.3. Hormones of the Body
• 9.1.4. Other Hormones: Melatonin and Pheromones
• 9.2. THE HYPOTHALAMUS AND PITUITARY GLAND
• 9.2.1. Posterior Pituitary
• 9.2.2. Anterior Pituitary
• 9.3. THYROID AND ADRENAL GLANDS
• 9.3.1. Thyroid Hormone Synthesis
• 9.3.2. Regulation of Thyroid Hormone Secretion
• 9.3.3. Thyroid Hormone Actions
• 9.3.4. Thyroid Disorders
• 9.3.5. Adrenal Gland
• 9.4. PANCREAS
• 9.4.1. Insulin
• 9.4.2. Regulation of Secretion of Insulin
• 9.4.3. Glucagon
• 9.4.4. Diabetes Mellitus
• 10.0. MODULE 10: REPRODUCTIVE SYSTEM
• 10.1. REPRODUCTIVE SYSTEM ANATOMY AND GERM CELLS
• 10.1.1. Anatomy of the Male Reproductive System
• 10.1.2. Anatomy of the Female Reproductive System
• 10.1.3. Mitosis and Meiosis
• 10.2. THE MALE REPRODUCTIVE SYSTEM
• 10.2.1. Male Reproductive Endocrine Axis
• 10.2.2. Spermatogenesis
• 10.2.3. Physiology of the Male Erection and Ejaculation
• 10.3. FEMALE REPRODUCTIVE SYSTEM
• 10.3.1. Oogenesis
• 10.3.2. Folliculogenesis
• 10.3.3. Ovulation and Fertilization
• 10.3.4. The Menstrual Cycle: Ovarian and Uterine
• 10.3.5. Ovarian Cycle
• 10.3.6. Uterine Cycle
• 10.3.7. Getting Pregnant
• Translations

FEMALE REPRODUCTIVE SYSTEM

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