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UNIT OVERVIEW


This unit is about the birds and the bees, so to speak. A basic understanding of the reproductive organs and sex organs in both the male and female anatomy is critical to the understanding of the reproductive systems as a whole. Reproduction is the production of eggs and sperm and the processes leading to fertilization. The reproductive system consists of the primary sex organs, or gonads, (testes in males and ovaries in females), which secrete hormones and produce gametes (sperm and eggs). Accessory reproductive organs include ducts, glands, and the external genitalia.


3 MAJOR CONCEPTS


Spermatogenesis


The cells that line the walls of the seminiferous tubules are collectively called spermatogenic cells. Those cells nearest the basement membrane are called spermatogenic. These cells are stem cells. They are capable of continuous division and remain undifferentiated, never maturing into specialized cells. Extending from the spermatogenic toward the lumen of the tubule are cells at various levels of maturity, with the most mature cells-the sperm-facing the lumen.

Spermatogenesis begins at puberty within the seminiferous tubules of the testes. The spermatogenic, each of which contains 46 chromosomes, divide by mitosis repeatedly to produce primary spermatocytes (still diploid cells with 46 chromosomes each). The primary spermatocytes begin meiosis. During the first meiotic division (meiosis I, or the reduction division), each primary spermatocyte divides into two secondary spermatocytes, each with 23 chromosomes (haploid cells). During the second meiotic division (meiosis II, or the equatorial division), each secondary spermatocyte divides again, producing a total of four spermatids. Each spermatic still contains 23 chromosomes, but these chromosomes consist of only one chromatid (rather than the normal two chromatids).
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Spermiogenesis describes the development of spermatids into mature sperm (sperm cells, or spermatozoa). At the end of this process, each sperm cell bears the following structures:

The head of the sperm contains the haploid nucleus with 23 chromosomes. At the tip of the sperm head is the acrosome, a lysosome containing enzymes which are used to penetrate the egg. The acrosome originates from Golgi body vesicles that fuse to form a single lysosome.

The midpiece is the first part of the tail. Mitochondria spiral around the midpiece and produce energy (ATP) used to generate the whip like movements of the tail that propel the sperm.

The tail is a flagellum that consists of the typical 9 + 2 microtubule array.


Oogenesis


Oogenesis consists of the meiotic cell divisions that lead to the production of ova (eggs) in females. The process begins during fetal development with the fetal ovary. Diploid cells called oogonia divide by mitosis to produce primary oocytes (still diploid with 46 chromosomes). Each primary oocyte is encircled by one or more layers of cells. The oocyte and encircling cells together are called an ovarian follicle. The primary oocytes (within their follicles) begin meiosis, but division progresses only to prophase I. They remain at this stage until puberty.

The following stages in the development of an ovarian follicle are observed:

The primordial follicle, the initial fetal state of the follicle, encircles the oocyte with a single layer of cells called follicular cells.

The primary follicle, the next stage of follicular development, possesses two or more layers of encircling cells now called granulosa cells.
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The secondary follicle is distinguished by the presence of the antrum, a fluid-filled, central cavity.

In a mature (vesicular) follicle, the primary oocyte has completed meiosis I. It is the stage of follicular development that precedes ejection of the oocyte from the ovary (ovulation). The following features are observed:

The zona pellucida, a clear layer of glycoprotein, surrounds the oocyte.

The corona radiata, a ring of granulosa cells, encircles the zona pellucida.

The theca folliculi, the ovarian cells immediately surrounding the outer layers of granulosa cells, differentiate into an internal layer (facing the follicle) of secretory cells, the theca interna, and an external layer of cells, the theca interna, and an external layer of connective tissue, the theca externa.

The corpus luteum is the remains of the follicle following ovulation. It remains functional, producing estrogen, progesterone, and inhibin, until it finally degenerates.

During each menstrual cycle, one primary oocyte, enclosed in its follicle, resumes meiosis I to produce two daughter cells (each haploid with 23 chromosomes). One daughter cell, the secondary oocyte, contains most of the cytoplasm, ensuring that adequate amounts of stored food, as well as mitochondria, ribosomes, and other cytoplasmic organelles, will be available for the developing embryo. The other daughter cell, the first polar body, is much smaller, and contains little cytoplasm and few, if any, organelles. The secondary oocyte then begins meiosis II (equatorial division) but again stops at prophase (this time prophase II). The first polar body may also begin meiosis II, but it will eventually degenerate.

Ovulation occurs when a secondary oocyte and its first polar body, surrounded by the zona pellucida and corona radiata, rupture from their mature follicle and are expelled from the surface of the ovary. The oocyte is then swept up into the uterine (fallopian) tube and advances toward the uterus. If a sperm cell penetrates the corona radiata and zona pellucida and enters the secondary oocytes, meiosis II resumes in the secondary oocytes, producing an ovum and a second polar body. If a first polar body is present, it too may resume meiosis II, producing daughter polar bodies. Fertilization occurs when the nuclei of the sperm cell and ovum unite, forming a zygote (fertilized egg). Any polar bodies present ultimately degenerate.


Mammary Glands


The mammary glands are sweat glands specialized for the production of milk. The milk-producing secretory cells form walls of bulb-shaped chambers called alveoli that join together with ducts, in grapelike fashion, to form clusters called lobules. Numerous lobules assemble to form a lobe. Each breast contains a single mammary gland consisting of 15 to 20 of these lobes. Lactiferous ducts leading away from the lobes widen into lactiferous sinuses that serve as temporary reservoirs for milk. The ducts narrow again as they lead through a protruding nipple. The nipple, whose texture is made coarse by the presence of sebaceous glands, is surrounded by a ring of pigmented skin called the areola. Contraction of my epithelial cells surrounding the alveoli force milk toward the nipples.
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The breasts begin to enlarge in females at the onset of puberty. Proliferating adipose tissue expands the breast, while suspensory ligaments attached to the underlying fascia provide support. In non-pregnant females and males, the glands and ducts are not fully developed.

During pregnancy, estrogen and progesterone stimulate extensive development of the mammary glands and associated ducts. After childbirth, various hormones, especially prolactin from the anterior pituitary, initiate lactation, or mild production. When neurons are stimulated by the sucking of an infant, nerve impulses activate the posterior pituitary to secrete Oxytocin, which in turn stimulates contraction of the epithelial cells surrounding the alveoli. Milk is then forced toward the nipple (the letdown reflex).



PERSONAL APPLICATION

Endometriosis is a common problem for women. It is one that has caused significant pain in my life. It is a condition that I was not educated on, and because of that, has likely forever affected my life as well as my husband’s and family’s. I feel it is very important for young women to know what endometriosis is as well as the signs and symptoms, so that they are able to get treatment for it as soon as possible.

Endometriosis is a condition in which the tissue that lines the uterus or womb is found growing outside of the uterus on other organs of the body. Most often, endometriosis is found on the ovaries, fallopian tubes, tissues that hold the uterus in place, outer surface of the uterus, and the lining of the pelvic cavity. Other sites for growth can include the vagina, cervix, vulva, bowel, bladder or rectum. In rare cases, it has been found in other parts of the body, such as the lungs, brain, and skin.

Growths of endometriosis are benign, but they still cause many problems. Each month a woman’s ovaries produce hormones that stimulate the cells of the endometrium to multiply and prepare for a fertilized egg. The lining swells and gets thicker. If these endometrial cells grow outside the uterus, endometriosis results. Unlike cells normally found in the uterus that are shed during menstruation, the ones outside the uterus stay in place. They sometimes bleed a little bit, but they heal and are stimulated again during the next cycle. Tissue and blood that is shed into the body can cause inflammation, scar tissue, and pain. As endometrial tissue grows, it can cover or grow into the ovaries and block the fallopian tubes. Trapped blood in the ovaries can form cysts, or closed sacs. It can also cause the body to form scar tissue and adhesions, tissue that sometimes binds organs together.

The cause of endometriosis is unknown, but one theory is that the endometrial cells loosened during menstruation may “back up” through the fallopian tubes into the pelvis. Once there, they implant and grow in the pelvic or abdominal cavities. This is called retrograde menstruation. This happens in many women, but there may be something different about the immune system in women who develop endometriosis compared to those who do not get the condition.

To find out if you suffer from endometriosis, see your doctor. He/she will do a pelvic exam, ultrasound, and possibly a minor surgery called laparoscopy. During the pelvic exam, your doctor will feel for large cysts or scars behind your uterus. Smaller areas of endometriosis are hard to feel though. Your doctor could also perform an ultrasound, an imaging test to see if there are ovarian cysts from endometriosis. During a vaginal ultrasound, the doctor will insert a wand-shaped scanner into your vagina. During an ultrasound of your pelvis, a scanner is moved across your abdomen. Both tests use sound waves to make pictures of your reproductive organs. Magnetic resonance imaging (MRI) is another common imaging test that can produce a picture of the inside of your body.

A laparoscopy is the only true way your doctor can be sure that you have endometriosis. You will receive general anesthesia before the surgery. Then, your abdomen is expanded with a gas to make it easy to see your organs. A tiny cut is made in your abdomen and a thin tube with a light is placed inside to see growths from endometriosis. Sometimes doctors can diagnose endometriosis just by seeing the growths. Other times, they need to take a small sample of tissue and study it under a microscope. The video on the left shows part of a laparoscopy procedure on a patient with endometriosis.

If your doctor does not find signs of an ovarian cyst during an ultrasound, before doing a laparoscopy, your doctor may prescribe birth control pills to control your menstrual cycle. Sometimes this treatment helps lessen pelvic pain during your period. Some doctors may offer another treatment that blocks the menstrual cycle and lowers the amount of estrogen your body makes before doing a laparoscopy. This treatment is a medicine called a gonadotropin releasing hormone (GnRH) agonist, which also may help pelvic pain. If your pain improves on this medicine, the doctor will likely think that you have endometriosis. Laparoscopy is often recommended for diagnosis and treatment if the pelvic pain persists, even after taking birth control pills and pain medicine.

It is so important to see your doctor is you suspect that you may have endometriosis. The pain of endometriosis can interfere with your life. Many treatments can control the symptoms. Medicine can relieve your pain, but when endometriosis causes fertility problems, surgery can boost your chances of getting pregnant. In my case, my fertility doctor discovered my severe endometriosis. He said that because I unknowingly suffered with it for so long, I will likely never be able to have children. I had it on my ovaries, fallopian tubes, and outer surface of my uterus. He said that I am now left with such severe scar tissue that pregnancy is going to be highly unlikely.

CASE STUDY


Amber's Secret Case Study

What are the hormonal and physical changes that occurred in Amber’s normal menstrual cycle before she became pregnant?
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Cyclic changes in the secretion of gonadotropin hormones from the anterior pituitary cause the ovarian changes during a monthly cycle. The ovarian cycle is accompanied by cyclic changes in the secretion of estradiol and progesterone, which cause changes in the endometrium of the uterus during a menstrual cycle.

Apparently Amber did not use a birth control method. If she had, what options did she have and how do the various methods work?

There are many, many birth control options, but a few of them are birth control pills, patches, shots, sponges, implants, condoms, diaphragms, and IUDs. Birth control pills are made of hormones. Some pills contain two hormones - estrogen and progestin. These are combination pills. They work by keeping a woman’s ovaries from releasing eggs (ovulation). The birth control shot and implant work in the same way. Another option is the birth control sponge. The sponge covers the cervix and blocks sperm from entering the uterus. The sponge also continuously releases a spermicide that keeps sperm from moving.

What are the normal stages of development in a fetus during the first weeks after conception?

In the first weeks after conception, neural tubes are forming, heart and primitive circulatory system is rapidly forming, the heartbeats begin, the umbilical cord develops, blood starts pumping, most other organs are beginning to develop, and arm and leg buds appear.

What are the hormonal and physical changes going on in Amber during her pregnancy? What is keeping her from menstruating as normal?

Human chorionic gonadotropin, or hCG, is a hormone secreted by the placenta that maintains pregnancy during the early development of the embryo. Many of the symptoms that women experience in early pregnancy, such as morning sickness and fatigue, are caused by rising levels of hCG within the body.

Estrogen, a hormone that is produced by the ovaries and placenta, also increases during pregnancy. The hormone regulates progesterone levels during pregnancy, which is critical to a healthy pregnancy. Estrogen is responsible for continued growth of fetal lungs, kidneys and reproductive organs as well as the placenta. Estrogen also aids in the development of prolactin, which enables lactation after delivery.

Progesterone, a hormone that is produced by the ovaries and placenta, prepares the uterus for the implantation of a fertilized ovum. Because this hormone restricts the uterus from contracting during pregnancy, fights off hazardous cells that could harm the fetus and aids in maintaining the pregnancy, progesterone is crucial to a healthy pregnancy. Just like hCG, progesterone levels will increase as pregnancy progresses. Progesterone is the hormone that causes breast tenderness in the early weeks of pregnancy, as well as constipation, headaches, food cravings and mood swings throughout pregnancy.

Physical changes during pregnancy can also be brought on by increasing hormones. Many women will notice skin changes as pregnancy progresses. Darkening of the skin, red patches, pregnancy glow and oily skin can all be caused by rising hormone levels.
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How does a pregnancy test work?

Pregnancy tests work by detecting hCG. hCG is a hormone found only in pregnant woman. Both urine and blood tests can detect hCG.

How can we account for Amber’s symptoms?

Amber’s symptoms can be attributed to the hormones of pregnancy…hCG, estrogen, and progesterone.

Can we consider the embryo a parasite in Amber’s body? What prevents Amber’s body from rejecting the new tissue developing in her body that is genetically different from her tissues?

An immunosuppressant protein called Early Pregnancy Factor (EPF) is what kept her body from considering the embryo an antigen or foreign body.

How much control does the embryo/fetus have over its own development?

The embryo has no control over its own development. It is completely dependant on the mother’s body.

How is the sex of an embryo determined, and what happens during the developmental process when the sex organs finally become apparent?

Sex is determined by the presence or absence of the Y chromosome. By the end of the 11th week, the baby’s external genitalia will start developing into a penis or clitoris and labia majora.
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What is the degree of fetal development that has occurred by the end of the first trimester?

By the end of the first trimester, the vocal chords are completely formed, the brain is fully formed, and the child can feel pain. The thalamus, third ventricle, midbrain, brain stem, and cerebellar hemispheres are developed. Also, the hands are clearly formed and visible.

What are the regulations regarding abortion in your state and what are the medical, religious, and political reasons behind the legislation?

A law signed by Governor Dennis Daugaard made South Dakota the first state to require women who are seeking abortions to first attend a consultation at a “pregnancy help center” to learn what assistance is available to help the mother keep and care for her child. This law established the nation’s longest waiting period (3 days) after an initial visit with an abortion provider before the procedure can be done. It makes exceptions for medical emergencies, but not for rape or incest. The mandated counseling will come from people whose central qualification is that they are opposed to abortion.

Is it appropriate for the physician to raise the issue of abortion?

In my opinion, a physician should only raise the option of abortion if the mother’s life is at risk, or if the patient specifically asks. Offering it as a form of birth control for irresponsible women is wrong. Again, this is just my opinion (Jackie’s)…I do not necessarily speak for my WIKI partner on this issue.

Should the father have any say in the question of abortion?

I think the father absolutely should have a say in the question of abortion. Just because the mother may not be willing to raise the child, doesn’t mean the father wouldn’t be. The mother didn’t make the child on her own, and I believe the father should have a say as to whether or not his child’s life is terminated. Again, this is just my opinion (Jackie’s)…I do not necessarily speak for my WIKI partner on this issue.

References
All information was obtained from Human Physiology; Stuart Ira Fox; 12th Edition, Burton’s Microbiology For The Health Sciences; Paul G. Engelkirk and Janet Duben-Engelkirk; 9th Edition, http://www.wikipedia.org/_, http://www.howstuffworks.com/,_ http://www.physioweb.org/, and http://www.webmd.com/.
All sources for photos can be accessed directly by clicking on the photos.baby.jpgbaby2.jpg