chapter 26

Place these steps of development in order: organ formation, fertilization, gastrulation, cleavage.

fertilization, cleavage, gastrulation, organ formation

define fission

fission, the separation of a parent into two or more offspring of about equal size. The sea anemone

define fragmentation with regeneration, what organism found in

fragmentation, the breaking of the body into several pieces, followed by regeneration, the regrowth of lost body parts. Some organisms have remarkable powers of regeneration. In certain species of sea stars, for example, an arm plus a bit of the central body that has split off can give rise to a new sea star

define asexual reproduction

(reproduction without sex) is the creation of genetically identical offspring by a lone parent.

What are the three stages of labor?

1. dilation (of the cervix) 2. delivery of the infant 3. delivery of the placenta (afterbirth)

name a 2 advantages of asexual reproduction

1. rapid, quick 2. without need to find a mate--can be done in isolation, 3. no need to expend energy to create gametes--- In nature, asexual reproduction has several potential advantages. Because it eliminates the need to find a mate, asexual reproduction allows the individual members of a species to perpetuate themselves even if they are isolated from one another. Asexual reproduction also allows organisms to multiply quickly, without spending time or energy producing sperm and eggs. If an individual is very well suited to its environment, asexual reproduction allows it to reproduce rapidly and exploit available resources.

How many follicles is a human female born with? How many release eggs? When are eggs released?

A female is born with over a million follicles, but only several hundred will release egg cells during her reproductive years. Starting at puberty and continuing until menopause (the end of fertility, which usually occurs during middle age), a woman undergoes ovulation about every 28 days. During ovulation, one follicle (or rarely two or more) matures and ejects an immature egg cell.

name a disadvantage of asexual reproduction

A potential disadvantage of asexual reproduction is that it produces genetically uniform populations. Genetically similar individuals may thrive in a particular environment. But if the environment changes and becomes less favorable to survival (as a result of some natural disaster, say, or a new predator or pathogen), then all individuals may be affected equally, and the entire population may die out.

Describe the process of IVF or in vitro fertilization.

A procedure performed in vitro ("in glass") happens under artificial laboratory conditions rather than within the living body (in vivo). In vitro fertilization (IVF)—sometimes called the creation of a "test-tube baby"—begins with the administration of drugs that promote the development of multiple eggs (instead of the one egg that typically occurs during each ovulation). The eggs are surgically removed and then fertilized with sperm in a petri dish, allowed to develop for several days, and then injected into a woman's uterus (Figure 26.20). There, one or more embryos may successfully implant and continue development. The sperm and eggs, as well as the embryos created, can be used immediately or frozen for later use.

What is AIDS, and what virus causes it? Is it often spread heterosexually?

AIDS, caused by HIV (discussed in Chapters 10 and 24), poses one of the greatest health challenges in the world today, particularly among the developing nations of Africa and Asia. But even within the United States, there are 56,000 new infections each year, one-third of which result from heterosexual contact.

What does the embryo look like early in the first trimester of pregnancy at about 5 weeks gestation? What structures does the embryo have that it will not be born with?

About 5 weeks after fertilization: In that brief time, a single cell has developed into a highly organized multicellular embryo about 7 mm (0.28 inch) long. Its brain and spinal cord have begun to take shape. It also has four stumpy limb buds, a short tail, and primitive gill-like structures.

What form is the embryo in when it reaches the uterus? What is the structure of this blastocyst? see book figure

About 6-7 days after fertilization, the embryo has reached the uterus as a fluid filled hollow ball of about 100 cells called a blastocyst. Protruding into the central cavity on one side of the human blastocyst is a small clump of cells called the inner cell mass, which will eventually form the fetus.

What methods of contraception are foolproof or nearly so?

Abstinence and sterilization (vasectomy or tubal ligation)

After ovulation what becomes of the left over follicle? What does it do?

After ovulation, what remains of the follicle grows to form a solid mass called the corpus luteum, which secretes hormones during the reproductive cycle (as you'll see later in the chapter).

What is an IUD

An intrauterine device (IUD) is a T-shaped device placed within the uterus by a healthcare provider. IUDs are safe and highly effective at preventing pregnancy for up to 12 years, but can be safely removed at any time.

What is HPV, can it be prevented?

Another sexually transmitted virus is the human papillomavirus (HPV). There are many known strains of HPV, some of which cause genital warts. Furthermore, HPV infection causes nearly all cases of cervical cancer. A vaccine against HPV is available, but it is only effective before infection. Therefore, it is recommended that preteen boys and girls (ages 11-12) be vaccinated via a series of three shots over 6 months before sexual activity begins.

How can one check for and prevent STDs?

Anyone who is sexually active should have regular medical exams, be tested for STDs, and seek immediate help if any suspicious symptoms appear—even if they are mild. STDs are most prevalent among teenagers and young adults; nearly two-thirds of infections occur among people under 25. The best way to avoid the spread of STDs is, of course, abstinence. Alternatively, latex condoms provide the best protection for "safe sex."

At the time of birth of a female, each ovary contains about how many follicles? What is the single dormant primary oocyte?

At birth, each ovary contains many thousands of follicles. Each follicle contains a single dormant primary oocyte, a diploid cell that has paused its cell cycle in prophase of meiosis I.

What is the most important difference between STDs caused by viruses and STDs caused by bacteria in terms of their treatment?

Bacterial STDs can be cured with antibiotics. Viral STDs are permanent

what is the purpose of the scrotum

Because sperm do not develop optimally at body temperature, the scrotum promotes sperm formation by keeping sperm-forming cells about 2°C cooler. In cold conditions, muscles around the scrotum contract, pulling the testes toward the body, thereby maintaining the proper temperature.

Name five differences between spermatogenesis and oogenesis.

Both oogenesis and spermatogenesis produce haploid gametes, but there are several important differences between the two processes. 1. One obvious difference is location: testes in the male and ovaries in the female. 2. Furthermore, human males create new sperm every day from puberty through old age. Human females, on the other hand, create primary oocytes only during their fetal development. 3. Another difference is that four gametes result from each diploid parent cell during spermatogenesis, whereas oogenesis results in only one gamete from each parent cell. 4. There are also significant differences in the cells produced by meiosis: Sperm are small, move by means of a whiplike flagellum, and contain relatively few nutrients; eggs are large, not self-propelled, and well stocked with nutrients and organelles. 5.Finally, spermatogenesis is completed before sperm leave the testis, whereas oogenesis cannot be completed without stimulation from a sperm cell.

define gonads

Both sexes have a pair of gonads, the organs that produce gametes.

What does the fetus look like by the end of the first trimester?

By the end of the first trimester, the fetus looks like a miniature human being, albeit one with an oversized head. By this time, the sex of the fetus can be determined by an ultrasound exam

What is the only totally effective method of contraception?

Complete abstinence (avoiding intercourse) is the only totally effective method of contraception, but other methods are effective to varying degrees. Study table in book to compare.

What hormonal changes trigger the start of menstruation?

Decreasing levels of estrogen and progesterone (due to degeneration of the corpus luteum)

What is the process of clevage or the first phase of development?

Development begins with cleavage, a series of rapid cell divisions that produces a multicellular ball. After the zygote divides for the first time, about 24 hours after fertilization, it is called an embryo.

As a human develops in the uterus, why are the first trimester changes considered the most dramatic?

Development proceeds from a single celled zygote to a miniature human during the first trimester. The second and third trimesters involve growth and refinement of structures formed in the first trimester.

What treatments exist for impotence?

Drug therapies (such as Viagra) and penile implants can treat impotence.

Why should a woman who is trying to get pregnant avoid drugs such as alcohol and nicotine?

Drugs can pass to the fetus from the mother's bloodstream before she even realizes she is pregnant.

What processes occur during clevage? Does the overall size of the embryo change during clevage? Where does clevage occur?

During cleavage, DNA replication, mitosis, and cytokinesis occur rapidly, but the total amount of cytoplasm remains unchanged. As a result, the overall size of the embryo does not change; instead, each cell division partitions the embryo into twice as many smaller cells (Figure 26.13). Cleavage continues as the embryo moves down the oviduct toward the uterus. A

describe path of sperm during ejaculation--where do they travel from and what structures do they path through what two glands contribute fluid to the semen, name two purposes of this fluid

During ejaculation—expulsion of sperm-containing fluid from the penis—the sperm leave the epididymis and travel through a duct called the vas deferens. Each vas deferens, one from each of the two testes, empties into the urethra. The urethra conveys, at different times, both sperm and urine out through the penis. Ejaculation, caused by the contraction of muscles along the sperm ducts, releases about 5 mL (1 teaspoonful) of semen. Only 5% of semen consists of sperm (typically 200-500 million of them); the remaining 95% of semen is fluid secreted by the various glands. The seminal vesicles and prostate gland add fluid that nourishes the sperm and provides protection from the natural acidity of the vagina.

What prevents fertilization of an egg by more than one sperm?

During fertilization, the union of sperm and egg to form a zygote, a sperm releases enzymes that pierce the egg's membrane; then the sperm and egg plasma membranes fuse, and the two nuclei unite. Changes in the egg membrane prevent entry of additional sperm, and the fertilized egg is stimulated to develop into an embryo.

What does a follicle consist of? What hormone does it secrete?

Each follicle consists of a single developing egg cell surrounded by cells that nourish and protect it. The follicles also produce estrogen, the female sex hormone (see Chapter 25).

What causes a primary oocyte to develop further? Every 28 days, how many of the dormant follicles develops?

FSH (follicle stimulating hormone) One. A primary oocyte can be triggered to develop further by the hormone FSH (follicle-stimulating hormone). After puberty and until menopause, about every 28 days, FSH from the pituitary gland stimulates one of the dormant follicles to develop. The follicle enlarges, and the primary oocyte within it completes meiosis I and begins meiosis II. The division of the cytoplasm in meiosis I is unequal, with a single secondary oocyte receiving almost all of it. The smaller of the two daughter cells, called the first polar body, receives almost no cytoplasm.

What are some causes of female infertility?

Female infertility can result from a lack of eggs, a failure to ovulate, or blocked oviducts (often due to scarring resulting from a sexually transmitted disease). Other women are able to conceive but cannot support a growing embryo in the uterus. The resulting multiple miscarriages can take a heavy emotional toll.

where are sperm stored

From puberty into old age, the testes produce hundreds of millions of sperm each day. From the testes, sperm pass into a coiled tube called the epididymis.

What causes the levels of estrogen and progesterone to begin to fall off later in the cycle? What effect does this have on the endometrium? How doe this lead to the beginning of the next cycle?

Further degeneration of the corpus luteum causes the levels of estrogen and progesterone to fall off. Once these hormones fall below a critical level, the endometrium begins to shed, starting menstruation again. Now that estrogen and progesterone are no longer there to inhibit it, the pituitary secretes FSH and LH, and a new cycle begins.

What are several causes of infertility in males?

In most cases, infertility can be traced to problems with the man. His testes may not produce enough sperm (a "low sperm count"), or the sperm may not be vigorous enough to reach an egg. In other cases, infertility is caused by impotence, also called erectile dysfunction, the inability to maintain an erection. To a certain degree, erectile dysfunction is a normal part of the male aging process. Temporary impotence can result from alcohol or drug use or from psychological problems. Permanent impotence can result from nervous system or circulatory problems.

What is the seconds stage of development called? See figure.

Gastrulation. For viable embryos, the second stage of development, gastrulation, begins about 9 days after conception (see the bottom of Figure 26.13).

What option exists if a woman cannot maintain or carry a pregnancy?

If a woman cannot maintain pregnancy, she and her partner may enter into a legal contract with a surrogate mother who agrees to carry the couple's child to birth. Ethical and legal problems can arise. A number of states have laws restricting surrogate motherhood.

What options exist for woman not releasing eggs or producing no eggs?

If a woman has normal eggs that are not being released properly, hormone injections can induce ovulation; such treatments frequently result in multiple pregnancies (twins, triplets, or more). If a woman has no eggs of her own, they can be obtained from a donor for fertilization and injection into the uterus. Although sperm can be collected without any danger to the donor, the collection of eggs is a surgical procedure that involves pain and risk for the donating woman. For this reason, egg "donors" are typically paid several thousand dollars for their time and discomfort.

What birth control methods physically block union of sperm and egg? What are they used with to enhance effectiveness?

If used correctly, methods that physically block the union of sperm and egg can be quite effective. Condoms are sheaths, usually made of latex, that fit over the penis or within the vagina. A diaphragm is a dome-shaped rubber cap that covers the cervix. It requires a doctor's visit for proper fitting. To be more effective, condoms and diaphragms can be used in combination with spermicides, sperm-killing chemicals in the form of a jelly, cream, or foam; spermicides used alone are not reliable contraceptives.

What is the function of a sperm's acrosome?

It releases enzymes that break down the jelly coat of the egg and allow the sperm to penetrate.

What triggers ovulation?

LH (lutenizing hormone) About the time the secondary oocyte forms, the pituitary gland secretes LH (luteinizing hormone), which triggers ovulation. The ripening follicle bursts, releasing its secondary oocyte from the ovary. The ruptured follicle then develops into a corpus luteum.

define external fertilization and spawning

Many aquatic animals use external fertilization, in which the parents discharge their gametes into the water, where fertilization occurs (Figure 26.4). The female and male don't necessarily have to touch to mate. Among some species with external fertilization, individuals clustered in the same area release their gametes into the water simultaneously, a process called spawning.

Why do some embryos not develop fully? What results? Is this relatively common?

Many other embryos spontaneously stop developing as a result of chromosomal or developmental abnormalities. The result, called a spontaneous abortion or miscarriage, occurs in as many as one-third of all pregnancies, often before the woman is even aware she is pregnant.

What compound do most home pregnancy test kits detect?

Most home pregnancy tests work by detecting HCG that passes from a pregnant woman's blood to her urine.

What is an ectopic pregnancy?

Occasionally, an embryo does not travel down the oviduct to the uterus. The result is an ectopic pregnancy, one in which the embryo develops in the wrong location. Ectopic pregnancies are invariably fatal to the embryo and can be dangerous to the mother, requiring immediate medical attention.

What is genital herpes and how common is it in Americans?

One in five Americans is infected with genital herpes, caused by the herpes simplex virus type 2, a variant of the virus that causes cold sores. Most outbreaks heal within a few weeks, but the virus lies dormant within nearby nerve cells. Months or years later, it can reemerge, causing fresh sores that allow the virus to be spread to sexual partners. Abstinence during outbreaks, the use of condoms, and the use of antiviral medications that minimize symptoms can reduce the spread of herpes. But there is no cure, so infection lasts a lifetime.

What do oral contraceptives or birth control pills contain?

Oral contraceptives, or birth control pills, come in several different forms that contain varying formulations of a synthetic estrogen and/ or a synthetic progesterone.

In which organ of the human female reproductive system does fertilization occur? In which organ does pregnancy occur?

Oviduct, uterus

What do the ectoderm, mesoderm and endoderm develop into?

The ectoderm eventually develops into the nervous system and outer layer of skin (epidermis). The endoderm becomes the innermost lining of the digestive system and organs such as the liver, pancreas, and thyroid. The mesoderm gives rise to most other organs and tissues, such as the heart, kidneys, and muscles.

What is the important hormone that brings about labor?

Oxytocin, a hormone produced by the fetus's cells and, late in pregnancy, the mother's pituitary gland. Oxytocin stimulates muscles in the uterus to contract. Uterine contractions stimulate the release of more oxytocin, which in turn increases the contractions—an example of positive-feedback control. The result is climactic—the intense muscle contractions that propel a baby from the womb. If a mother is overdue, or if labor has continued for a long time, a doctor may inject oxytocin to promote a more rapid birth.

How does programmed cell death help to shape the development of the hand?

Programmed cell death kills selected cells. For example, some genes encode proteins that kill certain cells in developing human hands and feet, creating spaces between the fingers and toes (Figure 26.14).

What is the mechanism for monozygotic (identical twins)? What is the mechanism for dizygotic (nonidentical twins)?

Rarely, and apparently at random, the two cells of the early embryo separate from each other. When this separation happens, each cell may "reset" and act as a zygote; the result is the development of identical (monozygotic) twins. (Nonidentical, or dizygotic, twins result from a completely different mechanism: Two separate eggs fuse with two separate sperm to produce two genetically unique zygotes that develop at the same time.)

estrogen and progesterone have what effects on the endometrium? What effects do the combination of estrogen and progesterone have on further FSH and LH production?

Rising levels of these two hormones promote thickening of the endometrium. The combination of estrogen and progesterone also inhibits further secretion of FSH and LH, ensuring that a second follicle does not mature during. (Note that the peaking of estrogen levels had caused the surge in FSH and LH--see prior slide, whereas the combination of estrogen and progesterone inhibit further secretion of FSH and LH)

How many sperm released during intercourse verses number causing fertilization?

Sexual intercourse releases hundreds of millions of sperm into the vagina, but only a few thousand sperm survive the several-hour trip to the egg in the oviduct. Of these sperm, only a single one can enter and fertilize the egg. All the other millions of sperm die.

Have many babies been born by IVF?

Since its introduction in 1978, over 5 million babies have been born after in vitro fertilization treatments.

why would some animals reproduce both sexually and asexually

Some animals reproduce asexually when food is ample and conditions are favorable. But when conditions change (becoming colder or drier, for example), these animals switch to sexual reproduction, producing a generation of genetically varied individuals that has a better potential to have some well-adapted individuals.

What hormone does an implanting embryo secrete? How does this hormone affect the corpus luteum? What effect does this have on the endometrium?

The embryo implants into the endometrium and secretes a hormone called HCG (human chorionic gonadotropin). HCG maintains the corpus luteum, which then continues to secrete progesterone and estrogen, keeping the endometrium intact..

How do birth control pills work?

Steady intake of these hormones simulates their constant levels during pregnancy. In response to being "fooled" that pregnancy has occurred, the hypothalamus fails to send the signals that start development of an ovarian follicle. Ovulation ceases, preventing pregnancy.

What is the rhythm method or natural family planning? Is it very effective?

Temporary abstinence, also called the rhythm method or natural family planning, depends on refraining from intercourse during the days around ovulation, when fertilization is most likely. In theory, the time of ovulation can be determined by monitoring changes in body temperature and the composition of cervical mucus, but careful monitoring and record keeping are required. Additionally, the length of the reproductive cycle can vary from month to month, and sperm can survive for 3-5 days within the female reproductive tract, making natural family planning among the most unreliable methods of contraception in actual practice.

What is labor?

The birth of a child is brought about by labor, a series of strong, rhythmic contractions of the uterus.

What is the structure of the gastrula? What are the 3 cell layers called?

The cells of the early embryo begin an organized migration that produces the gastrula, an embryo with three main layers. The three layers produced in gastrulation are embryonic tissues called ectoderm, endoderm, and mesoderm.

What is the clitoris and what is it analogous to?

The clitoris is an organ that engorges with blood and becomes erect during sexual arousal. Analogous to the male penis, the clitoris consists of a short shaft supporting a rounded glans, or head, covered by a small hood of skin called the prepuce. The clitoris has an enormous number of nerve endings and is very sensitive to touch.

define sexual reproduction

The creation of genetically distinct offspring by the fusion of two haploid sex cells (gametes: sperm and egg), forming a diploid zygote.

Follow these events through figure 26.9 in your book, and see other side of this card. The hypothalmaus secretes what? The anterior pituitary then secretes what? FSH stimulates what? The follicle secretes what? What causes a surge in FSH and LH? What results form the surge in FSH and LH? Ovulation takes place on what day of a 28 day cycle?

The hormones shown in parts (a), (b), and (d) of Figure 26.9 regulate the ovarian and menstrual cycles, synchronizing ovulation with preparation of the uterus for possible implantation of an embryo. At the start of the ovarian cycle, the hypothalamus secretes a releasing hormone that stimulates the anterior pituitary gland to increase its output of FSH (follicle-stimulating hormone) and LH (luteinizing hormone). True to its name, FSH stimulates the growth of an ovarian follicle. As the maturing follicle grows, it secretes estrogen in increasing amounts. After about 12 days, estrogen levels peak, which causes a sudden surge of FSH and LH. The surge in FSH and LH stimulates ovulation, and the developing follicle within the ovary bursts and releases its egg. Ovulation takes place on day 14 of the typical 28-day cycle.

What are the main developmental changes during the second and third trimesters?

The main developmental changes during the second and third trimesters involve an increase in size and general refinement of the human features—nothing as dramatic as the changes of the first trimester.

When does the menstrual cycle begin? What is menstruation? What can prevent menstruation from occurring? How long does menstruation last? How long for endometrium to reach maximal thickness?

The menstrual cycle begins on the first day of a woman's period. Menstruation is uterine bleeding caused by the breakdown of the endometrium, the blood-rich inner lining of the uterus. If an embryo implants in the uterine wall, it will obtain nutrients from the endometrium, and the thickened lining will not be discharged. Menstruation is thus a sign that pregnancy has not occurred during the previous cycle. Menstruation usually lasts 3-5 days. The menstrual discharge, which leaves the body through the vagina, consists of blood, clusters of cells, and mucus. After menstruation, the endometrium regrows, reaching its maximum thickness in 20-25 days.

What is the cervix, what does it do, what disease affects it?

The narrow neck at the bottom of the uterus is the cervix. It is recommended that a woman have a yearly Pap test in which cells are removed from around the cervix and examined under a microscope for signs of cervical cancer. Regular Pap smears greatly increase the chances of detecting cervical cancer early and treating it successfully. The cervix opens into the vagina. During intercourse, the vagina serves as a repository for sperm.

Define and describe function of: vulva vagina labia major labia minora hymen

The outer features of the female reproductive anatomy are collectively called the vulva. The vagina, or birth canal, opens to the outside just behind the opening of the urethra, the tube through which urine is excreted. An outer pair of thick, fatty ridges, the labia majora, protects the entire genital region, and a pair of inner skin folds, the labia minora, borders the openings. A thin membrane called the hymen partly covers the vaginal opening until sexual intercourse or other vigorous physical activity ruptures it.

What are the female gonads called?

The ovaries are the female gonads, the site of gamete production. Each ovary is about an inch long and has a bumpy surface. The bumps are follicles.

name the 3 principal parts of the penis

The penis consists of a shaft that supports a highly sensitive glans (head). A prepuce, or foreskin, covers the glans. The foreskin may be surgically removed, a procedure known as circumcision.

define penis and mechanism of erection

The penis is the structure that transfers sperm from the male to the female during sexual intercourse. It contains three cylinders of erectile tissue (shown in blue), which consists of modified veins and capillaries that can fill with blood and cause an erection during sexual arousal.

What hormone promotes milk production in the mother?

The pituitary hormone prolactin promotes milk production (called lactation) by the mammary glands. At first, a yellowish antibody-rich fluid called colostrum is secreted. After 2-3 days, normal milk production begins.

What are the chorionic villi of the placenta, what function do they serve? Does the blood supply of the fetus mix with the mothers or do substance diffuse between the two blood supplies? Why is chorionic villus tissue important for genetic testing?

The placenta develops chorionic villi, finger-like outgrowths containing embryonic blood vessels. These blood vessels are closely associated with blood vessels of the mother's endometrium. The chorionic villi absorb nutrients and oxygen from the mother's blood via diffusion and pass these substances to the embryo. The villi also diffuse wastes from the embryo to the mother's bloodstream. Although substances can pass back and forth via diffusion, the fetus has its own blood supply that does not mix with the mother's. A small sample of chorionic villus tissue can be removed for prenatal genetic testing

What protective factors can flow from the mother to the fetus through the placenta? What harmful factors can also flow?

The placenta provides for other needs of the embryo as well. For example, it allows protective antibodies to pass from the mother to the fetus. Unfortunately, harmful substances may also cross the placenta and harm the developing embyro. Most drugs—both prescription and nonprescription—can harm the developing embryo. Alcohol, the chemicals in tobacco smoke, and other drugs increase the risk of miscarriage and can cause developmental abnormalities. Additionally, viruses—the German measles virus and HIV, for example—can cross the placenta and cause disease. German measles can cause serious birth defects; if untreated, HIV-infected babies usually die of AIDS within a few years.

What are the symptoms of chlamydia? Why is chlamydia often not recognized?

The primary symptoms are genital discharge and a burning sensation during urination. But chlamydia is frequently "silent"— half of infected men and three-quarters of infected women do not notice any symptoms.

What happens to the egg after it is released from the follicle? What are its two possible fates?

The released egg enters an oviduct (also called a fallopian tube), where cilia sweep it toward the uterus, like a crowd surfer being carried hand-over-hand across a mosh pit. If sperm are present, fertilization may take place in the upper part of the oviduct. If the released egg is not fertilized, it is shed during menstruation, and a new follicle matures during the next cycle.

In what way is the reproductive cycle really two cycles, coordinated by hormones?

The reproductive cycle is actually two cycles in one. The ovarian cycle (Figure 26.9c) controls the growth and release of an egg. During the menstrual cycle (Figure 26.9e), the uterus is prepared for possible implantation of an embryo. Hormonal messages coordinate the two cycles, keeping them synchronized with each other.

Where inside the testes do sperm cells develop? About how many differentiate each day?

The seminiferous tubules. Cells near the outer walls of the tubules multiply constantly by mitosis. Each day, about 3 million of them differentiate into primary spermatocytes, the cells that undergo meiosis.

Define embryo and fetus?

The term embryo is used for the stage in development from the first division of the zygote until body structures begin to appear, about the 9th week. From the 9th week until birth, a developing human is called a fetus.

What treatments exist for underproduction of sperm?

Underproduction of sperm is frequently caused by a man's scrotum being too warm, so a switch of underwear from briefs (which hold the scrotum close to the body) to boxers may help. If that doesn't work, sperm can be collected, concentrated, and then injected into the woman's uterus via the vagina.

define testes, verses scrotum, verses testicle

The testes (singular, testis), the male gonads, are located outside the abdominal cavity in a sac called the scrotum. A testis and a scrotum together are called a testicle.

Where does the infant develop during pregnancy?

The uterus (also called the womb) is the actual site of pregnancy. The uterus is about the size and shape of an upside-down pear, but grows to several times that size during pregnancy.

What is the lining of the uterus called?

The uterus has a thick muscular wall lined with a blood-rich layer of tissue called the endometrium.

What are the complications of unrecognized chlamydia?

Up to 40% of infected women develop pelvic inflammatory disease (PID). The inflammation associated with PID may block the oviducts or scar the uterus, causing infertility. Fortunately, chlamydia can be easily treated with a single dose of an antibiotic. But early screening is required to catch the disease before any scarring occurs. Sexually active women are encouraged to be screened for chlamydia and other STDs annually.

What determines whether the secondary oocyte undergoes meiosis two?

Whether a sperm cell fuses with it. The secondary oocyte enters the oviduct, and if a sperm cell fuses with it, the secondary oocyte completes meiosis II. Meiosis II is also unequal, yielding a small polar body and a mature egg (ovum). The chromosomes of the egg can then fuse with the chromosomes of the sperm cell.

Why is withdrawal ineffective?

Withdrawal of the penis from the vagina before ejaculation is also ineffective, because sperm may exit the penis before climax.

Are there drugs that can be used after unprotected sex to prevent a pregnancy?

Yes. Certain drugs can prevent fertilization or implantation even after intercourse. Morning-after pills ("Plan B") are birth control pills that can be taken in high doses for emergency contraception. If taken within 3 days of intercourse, morning-after pills are about 75% effective at preventing pregnancy. Such treatments should only be used in emergency situations because they have significant side effects. If pregnancy has occurred, the drug RU-486 (mifepristone) can induce an abortion, the termination of a pregnancy in process. RU-486 must be taken within the first 7 weeks of pregnancy and requires a doctor's prescription and several visits to a medical facility.

what does vasectomy surgery entail?

a doctor cuts a section out of each vas deferens to prevent sperm from reaching the urethra.

What does tubal ligation surgery entail?

a doctor removes a short section from each oviduct, often tying (ligating) the remaining ends and thereby blocking the route of sperm to egg.

define egg

a female gamete

define sperm

a male gamete

What is the most important difference in the genetic makeup of the offspring resulting from sexual versus asexual reproduction?

asexual reproduction produces genetically identical offspring. Sexual reproduction produces genetically diverse offspring.

What are the four classes of organisms that can cause STDs?

bacteria, viruses, protists, funghi (Review table 26.2 on page 561 of book)

name 3 types of asexual reproduction

budding, fission, fragmentation with regeneration

define budding

budding, the outgrowth and eventual splitting off of a new individual from a parent. Hydras, freshwater relatives of jellies, reproduce this way.

The onset of labor is marked by the dilation of the ______________.

cervix

What is the most common sexually transmitted disease?

chlamydia The most common bacterial STD (with nearly a million new cases reported annually in the United States and over 90 million worldwide) is chlamydia.

The production of gametes is called what? Are gametes haploid or diploid? Are there significant differences between males and females?

gametogenesis. Human gametes—sperm and egg—are haploid cells with 23 chromosomes that develop by meiosis from diploid cells with 46 chromosomes. There are significant differences in gametogenesis between human males and females, so we'll examine the processes separately.

define hermaphrodite, name two ways they reproduce in different species

in some species, each individual is a hermaphrodite, meaning that it has both male and female reproductive systems. 1. Some hermaphrodites (such as tapeworms, which can live as parasites in the human intestine) can fertilize their own eggs. 2. Other species require a partner. For example, when earthworms mate, each individual donates and receives sperm, any two individuals can mate.

what type of animals fertilize internally, what advantage does it confer

nearly all terrestrial animals reproduce by internal fertilization, in which a male deposits sperm within a female's body. This adaptation enables sperm to reach eggs despite a dry environment.

During gametogenesis in a human female, how many ova are produced from one primary oocyte? In a male, how many sperm arise from one primary spermatocyte?

one, four

the development of mature egg cells is called what?

oogenesis

Need to review table 26.2 on page 561 of book-- name 3 bacterial STDS name 3 viral STDS name 1 protist STD name 1 fungal STD What are treatments?

see table in book

name an advantage of sexual reproduction

sexual reproduction increases genetic variability among offspring as a result of the huge variety of gametes produced by meiosis (see Chapter 8). Variation is the raw material of evolution by natural selection. When an environment changes, there is a better chance that some of the various offspring will survive and reproduce than if all the offspring were genetically identical.

The production of sperm cells is called what?

spermatogenesis (Figure 26.7).

Arrange the following organs of the male reproductive system in the correct sequence for the travel of sperm: epididymis, testis, urethra, vas deferens.

testis, epididymis, vas deferens, urethra

define zygote

the fertilized egg that results from the union of haploid gametes

what is the target of a vasectomy

the vas deferens (the target of a vasectomy).

What is sterilization surgery called in a male, in a female?

vasectomy, tubal ligation