Unit 7, Quiz 3: Reproduction & Life Cycle of the Body

After meiosis in the male primary spermatocyte, the resultant secondary spermatocytes are genetically different than the body's somatic cells. The immune system is inclined to attack this 'foreign' cell. Which of the following contributes to the prevention of auto-immune responses to one's own spermatocytes?

The blood-testis-barrier.

Explanation: Since the primary spermatocyte is about to undergo meiosis and become genetically different from other cells of the body, it must be protected from the immune system. Ahead of the primary spermatocyte, the tight junction between two nurse cells is dismantled while a new tight junction forms behind the spermatocyte. The spermatocyte moves toward the lumen, like an astronaut passing through the double-door airlock of a spaceship, and is now protected by the blood-testis-barrier (BTB) closing behind it.

The decrease in reproductive function, resulting in a decrease in testosterone and inhibin secretion, is called _________

male climacteric

Explanation: From the 40s to old age, testosterone level declines, but at a slow rate of 1% or less per year. In old age, lower testosterone level is associated in many men with reduced interest in sex (libido) and ease of sexual arousal, loss of muscle mass and bone density, rising risk of osteoporosis, slower beard growth, and shrinkage of the external genitalia and seminal vesicles. Semen volume, sperm count, and sperm motility decline, but some men remain fertile and able to father children in very old age. Sperm quality is another issue, however. The sperm of older men carry an increasing load of new mutations. Some authorities refer to these changes as andropause or male climacteric, while others dislike these expressions because they invite a misleading comparison to menopause. 

Match each hormone with the description of what would happen if it was absent in a pubescent male.

FSH and LH would not be secreted by the anterior pituitary: GnRH

Testosterone secretion would not occur: LH

Spermatogenesis would not occur due to the absence of androgen-binding protein: FSH

A person would experience a loss of sex drive: Testosterone

Spermatogenesis would occur in excess: Inhibin

Explanation: As the hypothalamus matures, it begins producing gonadotropin-releasing hormone (GnRH), which travels by way of the hypophyseal portal system to the anterior lobe of the pituitary. Here, it stimulates cells called gonadotropic cells to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH), two gonadotropins that stimulate different cells in the testis.  LH stimulates the interstitial endocrine cells of the testes to secrete androgens, mainly testosterone. In the male, LH is sometimes called interstitial cell-stimulating hormone (ICSH). FSH stimulates the sustentacular cells to secrete a protein called androgen-binding protein (ABP) into the lumen of the seminiferous tubules. ABP raises the testosterone level in the tubules and epididymis by binding and accumulating the hormone. Without FSH and ABP, testosterone has no effect on the testes. Germ cells have no androgen receptors and do not respond to it.

Complete each sentence describing the prenatal hormones using one of the choices provided.

1. The sex-determing Y (SRY) gene stimulates the synthesis of testis-determining factor.

2. The protein called TDF interacts with genes on the X chromosome for genes that initiate male development.

3. The male gonadal ridge becomes a rudimentary testis and begins secreting testosterone

4. Testosterone stimulates the formation of the male reproductive ducts Correct.

5. Finally, the testis also secrete mullerian-inhibiting factor, which causes atrophy of the paramesonephric duct, which would have developed into the female reproductive system.

Explanation: The Y chromosome has a gene called SRY (sex-determining region of the Y) that codes for a protein called testis-determining factor (TDF). TDF then interacts with genes on some of the other chromosomes, including a gene on the X chromosome for androgen receptors and genes that initiate the development of male anatomy. By 8 to 9 weeks, the male gonadal ridge has become a rudimentary testis that begins to secrete testosterone. Testosterone stimulates the mesonephric duct on its own side to develop into the system of male reproductive ducts. By this time, the testis also secretes a hormone called müllerian-inhibiting factor (MIF) that causes atrophy of the paramesonephric duct on that side. Even an adult male, however, retains a tiny Y-shaped vestige of the paramesonephric ducts, like a vestigial uterus and uterine tubes, in the area of the prostatic urethra.

In humans, when do the secondary sexual characteristics first appear?

At puberty

What do interstitial endocrine cells produce?

Testosterone

A young female going through puberty comes to see you because they are concerned they haven't had their period yet.  An ultrasound reveals the absence of a uterus but the presence of abdominal testes.  What do you conclude?

This individual has XY chromosomes but has androgen insensitivity syndrome.

Explanation: Occasionally, a child who was always assumed to be a girl shows the usual changes of puberty except that she fails to menstruate. Medical examination reveals testes in the abdomen and the XY karyotype of a male. The testes produce a normal male level of testosterone, but the target cells lack receptors for it, and the testosterone therefore has no effect. This condition is called androgen insensitivity syndrome (AIS), or testicular feminization. 

Complete each sentence describing the male reproductive secretions using one of the choices provided.

1. The secretions of the male reproductive tract originate in the testes, where sperm cells are produced.

2. The fluid from the seminal vesicles joins the sperm from the ductus deferens at the ejaculatory duct.

3. The second largest producer of seminal volume, the prostate gland, surrounds the urethra and the ejaculatory duct.

4. Contributing about 5% of the overall seminal volume, the bulbourethral glands are involved with pre-ejaculatory secretions for lubrication and preparation of the urethra for the passage of semen.

Explanation: Semen consists of the combined secretions of four male reproductive glands. They are, in order of volume, contribution: seminal vesicles (60%), prostate (30%), and then the bulbourethral glands (5%) and testes (5%).

Which of the following might be a result of a breakdown of the tight junctions of nurse cells?

• An auto-immune response to secondary spermatocytesAn auto-immune response to secondary spermatocytes Correct

• A breakdown of the blood-testis-barrierA breakdown of the blood-testis-barrier Correct

• A lower sperm count

  Explanation: Since the primary spermatocyte is about to undergo meiosis and become genetically different from other cells of the body, it must be protected from the immune system. Ahead of the primary spermatocyte, the tight junction between two nurse cells is dismantled while a new tight junction forms behind the spermatocyte. The spermatocyte moves toward the lumen, like an astronaut passing through the double-door airlock of a spaceship, and is now protected by the blood-testis-barrier (BTB) closing behind it.  If there is an immune response targeting secondary spermatocytes, there will be a decrease in the number of mature sperm cells.

A 65-year-old male comes into your office complaining of difficulty urinating.  However, a urinalysis does not reveal a UTI, and they have normal PSA levels.  What do you conclude?

They have benign prostatic hyperplasia.

Explanation: By age 70, over 80% of men show some degree of benign prostatic hyperplasia (BPH)—noncancerous enlargement of the gland. The major complication of this is that it compresses the urethra, obstructs the flow of urine, makes it harder to completely empty the bladder, and sometimes promotes bladder and kidney infections.

What is the term for a mature sperm cell?

Spermatozoon

The _________ contributes a clotting component to semen that activates a protein that causes semen to stick to the inside of the female reproductive system rather than flowing back out after ejaculation.

prostate

Explanation: Each seminal vesicle has a secretory portion that is a very convoluted duct with numerous branches that form a complex labyrinth. The duct empties into the ejaculatory duct. The yellowish secretion of the seminal vesicles constitutes about 60% of the semen. The prostate surrounds the urethra and ejaculatory ducts immediately inferior to the urinary bladder. It measures about 2 by 4 by 3 cm and is an aggregate of 30 to 50 compound tubuloacinar glands enclosed in a single fibrous capsule. These glands empty through about 20 pores in the urethral wall. The thin, milky secretion of the prostate constitutes about 30% of the semen. The bulbourethral glands are named for their position near a dilated bulb at the inner end of the penis and their association with the urethra. During sexual arousal, they produce a clear, slippery fluid that lubricates the head of the penis in preparation for intercourse. Perhaps more important, though, it protects the sperm by neutralizing the acidity of residual urine in the urethra.

The _________ cell carries the chromosome that determines the sex of the zygote.

sperm

Explanation: Every egg contains an X chromosome, but half of the sperm carry an X and the other half carry a Y. If an egg is fertilized with an X-bearing sperm, it produces an XX zygote that usually becomes a female. If it is fertilized with a Y-bearing sperm, it produces an XY zygote that usually becomes a male. Thus, the sex of a child is normally determined at conception (fertilization), and not by the egg but by the sperm that fertilizes it.

Which of the following is a change in the male body during puberty?

• Increase in teste and scrotum size

• Hair growth in the axillary region, pubic region, and face

• Increased rate of spermatogenesis

• Increased testosterone levels resulting in increased libido (sex drive)

Explanation: Several changes in the male body occur as a result of the hormones associated with puberty. During puberty, males are maturing to a point of producing viable gametes capable of fertilizing an oocyte and producing offspring.

Complete each sentence describing the hormonal control of puberty using one of the choices provided.

1. GnRH from the hypothalamus stimulates the secretion of FSH and LH.

2. FSH stimulates the secretion of androgen-binding protein.

3. LH stimulates testosterone secretion.

4. Testosterone , in the presence of ABP, stimulates spermatogenesis.

5. Testosterone stimulates the development of a beard and chest hair.

6. Inhibin prevents FSH from stimulating further spermatogenesis.

Explanation: As the hypothalamus matures, it begins producing gonadotropin-releasing hormone (GnRH), which travels by way of the hypophyseal portal system to the anterior lobe of the pituitary. Here, it stimulates cells called gonadotropic cells to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH), two gonadotropins that stimulate different cells in the testis.  LH stimulates the interstitial cells of the testes to secrete androgens, mainly testosterone. In the male, LH is sometimes called interstitial cell-stimulating hormone (ICSH). FSH stimulates the sustentacular cells to secrete a protein called androgen-binding protein (ABP) into the lumen of the seminiferous tubules. ABP raises the testosterone level in the tubules and epididymis by binding and accumulating the hormone. Without FSH and ABP, testosterone has no effect on the testes. Germ cells have no androgen receptors and do not respond to it.

Which phase of the menstrual cycle is indicated in this picture?

Proliferative phase

 

Based on the graph above, which of the following occurs from weeks 7 to 17?

The corpus luteum degenerates.

Complete each of the following statements about labor contractions by selecting one of the words provided.

1. After true labor begins, contractions become more intense and increase in frequency.

2. As the fetus's head moves into the cervix, the walls begin to stretch and trigger stretch receptors.

3. Nerve impulses travel along sensory neurons to the hypothalamus and posterior pituitary

4. In response, the posterior pituitary gland releases the hormone oxytocin, which targets the myometrium.

5. This hormone then stimulates more contractions of the uterine muscle, therefore moving the fetus distally and further stretching the walls of the cervix.

6. This whole process is defined as a positive feedback loop because the initial stimulus is enhanced by the resultant action.

Explanation: Labor contractions begin about 30 minutes apart. As labor progresses, they become more intense and eventually occur every 1 to 3 minutes. It is important that they be intermittent rather than one long, continual contraction. Each contraction sharply reduces maternal blood flow to the placenta, so the uterus must periodically relax to restore flow and oxygen delivery to the fetus. Contractions are strongest in the fundus and body of the uterus and weaker near the cervix, thus pushing the fetus downward. According to the positive feedback theory of labor, labor contractions are induced by stretching of the cervix. This triggers a reflex contraction of the uterine body that pushes the fetus downward and stretches the cervix still more. Thus there is a self-amplifying cycle of stretch and contraction. In addition, cervical stretching induces a neuroendocrine reflex through the spinal cord, hypothalamus, and posterior pituitary. The posterior pituitary releases oxytocin, which is carried in the blood and stimulates the uterine muscle both directly and through the action of prostaglandins. This, too, is a positive feedback cycle: cervical stretching → oxytocin secretion → uterine contraction → cervical stretching.

Complete each of the following statements about the hormones of lactation by selecting one of the words provided.

1. Milk synthesis is promoted by prolactin secreted by the anterior pituitary gland.

2. Estrogen and progesterone suppress milk synthesis by acting as prolactin antagonists.

3. Once the placenta is expelled, progesterone levels drop sharply, allowing prolactin to stimulate milk synthesis.

4. After birth, baseline prolactin levels return to the pre-pregnancy state. When an infant nurses, prolactin surges to stimulate milk synthesis.

5. If the mother is not nursing the infant, prolactin levels decrease decline, and the mother stops synthesizing milk in about a week.

Complete each of the following statements about female reproductive secretions by selecting one of the words provided.

1. Secretions of the female reproductive system mostly serve to lubricate the reproductive organs involved with intercourse.

2. The mucosa located on the wall of the vagina produces a serous fluid called vaginal transudate .

3. The greater vestibular glands are similar to the bulbourethral glands of the male and deposit fluids into the vestibule and the labia minus.

4. Additional paraurethral glands are located more anteriorly and secrete fluids onto the vestibule near the clitoris.

Which of the following statements is true regarding the male and female sexual responses?

• Unlike the male, the female sexual response does not include a refractory period, making multiple orgasms possible.Unlike the male, the female sexual response does not include a refractory period, making multiple orgasms possible. Correct

• The male reproductive system has erectile tissue, and the female does not.The male reproductive system has erectile tissue, and the female does not. Correct

• Vasocongestion is a component of both the male and female sexual response.Vasocongestion is a component of both the male and female sexual response. Correct

• The female has an orgasmic platform while the male does not.The female has an orgasmic platform while the male does not. Correct

• Both the male and female have the capacity for ejaculation.

Explanation: There are many similarities in the male and female sexual response. However, there are also many differences. Although vasocongestion works by the same mechanism in both sexes, its effects are quite different in females. The lower end of the vagina constricts to form a narrow passage called the orgasmic platform, owing partly to vasocongestion of the vestibular bulbs (not present in males). Recall that the penis and clitoris are homologous structures. Both have a pair of corpora cavernosa with deep arteries and become engorged by the same mechanism. The glans and shaft of the clitoris swell to two or three times their unstimulated size. During female orgasm, the paraurethral glands, homologous to the prostate, sometimes expel copious fluid similar to prostatic fluid (“female ejaculation”). Unlike men, women do not have a refractory period and may quickly experience additional orgasms.

Which of the following is a reason why breast milk is more nutritionally beneficial than cow's milk?

• The excess protein in cow's milk makes it more difficult for the infant to digest.The excess protein in cow's milk makes it more difficult for the infant to digest. Correct

• Cow's milk can increase the likelihood of diaper rash.Cow's milk can increase the likelihood of diaper rash. Correct

• Human breast milk helps clear the meconium out of the newborn's intestines.Human breast milk helps clear the meconium out of the newborn's intestines. Correct

• Human breast milk helps populate the newborn's intestines with bacteria.Human breast milk helps populate the newborn's intestines with bacteria. Correct

• Human breast milk supplies antibodies to the newborn to help defend against infection.

Explanation

Cow's milk is not a good substitute for human milk. It has one-third less lactose but three to five times as much protein and minerals. The excess protein forms a harder curd in the infant's stomach, so cow's milk is not digested and absorbed as efficiently as mother's milk. It also increases the infant's nitrogenous waste excretion, which increases the incidence and severity of diaper rash, particularly as bacteria in the diaper break urea down to ammonia, a skin irritant. Colostrum and milk have a laxative effect that helps to clear the neonatal intestine of meconium, a greenish black, sticky fecal matter composed of bile, epithelial cells and other wastes that accumulated during fetal development. By clearing bile and bilirubin from the body, breast-feeding also reduces the incidence and degree of jaundice in neonates. Breast milk promotes colonization of the neonatal intestine with beneficial bacteria and continues to supply antibodies that lend protection against infection by pathogenic bacteria. Breast-feeding also tends to promote a closer bond between mother and infant.

If a woman has gone a year or more without having had her period, she is said to have gone through _________

menopause

Which phase of the ovarian cycle corresponds to the time period indicated?

Luteal phase

Complete each of the following statements about female reproductive development by selecting one of the words provided.

1. The earliest noticeable sign of puberty is thelarche, the onset of breast development.

2. This is soon followed by pubarche, the appearance of pubic and axillary hair, sebaceous glands, and axillary glands.

3. The very first menstrual bleeding is termed menarche .

4. A midlife change when hormone secretion begins to wane is called the climacteric

5. This leads to the permanent cessation of menstrual cycles called menopause

Explanation: Puberty is triggered by the same hypothalamic and pituitary hormones in girls as it is in boys. Rising levels of gonadotropin-releasing hormone (GnRH) stimulate the anterior lobe of the pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH, especially, stimulates development of the ovarian follicles, which, in turn, secrete estrogens, progesterone, inhibin, and a small amount of androgen. The earliest noticeable sign of puberty is thelarche, the onset of breast development. This is soon followed by pubarche, the appearance of pubic and axillary hair, sebaceous glands, and axillary glands. Next comes menarche, the first menstrual period. Estradiol stimulates growth of the ovaries and secondary sex organs. It causes a rapid increase in height and widening of the pelvis and is largely responsible for the feminine physique because it stimulates fat deposition in the mons pubis, labia majora, hips, thighs, buttocks, and breasts. Women, like men, go through a midlife change in hormone secretion called the climacteric. In women, it is accompanied by menopause, the cessation of menstruation.

The development of the breasts during pregnancy is due to the growth and extensive branching of mammary glands and ducts.

True

Explanation

When the mammary gland develops during pregnancy, it exhibits 15 to 20 lobes arranged radially around the nipple, separated from each other by stroma. Each lobe is drained by a lactiferous duct, which dilates to form a lactiferous sinus opening onto the nipple. Distally, each duct branches repeatedly with the finest branches ending in sacs called acini.

Which of the following are present in puberty in females?

• The onset of breast developmentThe onset of breast development

• Appearance of facial hair

• Appearance of axillary hair

• Menarche

• Menopause

Explanation

The earliest noticeable sign of puberty is thelarche, the onset of breast development. Estrogen, progesterone, and prolactin initially induce the formation of lobules and ducts in the breast. Duct development is completed under the influence of glucocorticoids and growth hormone while adipose and fibrous tissue enlarge the breast. Thelarche is soon followed by pubarche, the appearance of pubic and axillary hair, sebaceous glands, and axillary glands. Next comes menarche, the first menstrual period.

Which of the following endocrine glands or organs contribute to the development of the mammary glands during pregnancy?

• Anterior pituitary

• Pancreas

• Adrenal

• Ovaries

Explanation

The high estrogen level in pregnancy causes the ducts of the mammary glands to grow and branch extensively. Growth hormone, insulin, glucocorticoids, and prolactin also contribute to this development. Once the ducts are complete, progesterone stimulates the budding and development of acini at the ends of the ducts. The fully developed mammary gland is of the compound tubuloacinar type. The acini are organized into grapelike clusters (lobules) within each lobe of the breast.

Which of the following statements is true regarding the letdown reflex?

• The infant typically gets no milk for the first 30 to 60 seconds of suckling.The infant typically gets no milk for the first 30 to 60 seconds of suckling. Correct

• Damage to the posterior pituitary gland could result in a diminished ability to eject milk.

• In this process, epithelial cells contract like smooth muscle.

Explanation

Milk is continually secreted into the mammary acini, but it does not easily flow into the ducts. Its flow, called milk ejection (letdown), is controlled by a neuroendocrine reflex. The infant's suckling stimulates nerve endings of the nipple and areola, which in turn signal the hypothalamus and posterior pituitary to release oxytocin. Oxytocin stimulates myoepithelial cells, which form a basketlike mesh around each gland acinus. These cells are of epithelial origin but are packed with actin and contract like smooth muscle to squeeze milk from the acinus into the duct. The infant does not get any milk for the first 30 to 60 seconds of suckling, but milk soon fills the ducts and lactiferous sinuses and is then easily sucked out.

Complete each of the following statements about the perineum by selecting one of the words provided.

1. When a sperm encounters an egg it undergoes an  acrosomal reaction.

2. This reaction releases  enzymes Correct from the acrosome of the sperm, which then digest a path through the granulosa cells and the  zona pellucida

3. After the sperm contacts the egg, the sperm head Correct and midpiece enter the egg.

4. At this point, the  haploid Correct set of chromosomes from each gamete combine to produce a full  diploid Correct set.

5. Finally the egg  blocks all other sperm from entering, in order to prevent a triploid cell.

   Explanation

   When the sperm encounters an egg, it undergoes an acrosomal reaction—exocytosis of the acrosome, releasing the enzymes needed to penetrate the egg. However, the first sperm to reach an egg is not the one to fertilize it. Sperm must first penetrate the granulosa cells and zona pellucida that surround it. It may require hundreds of sperm to clear a path for the one that penetrates the egg proper. Two of the acrosomal enzymes are hyaluronidase, which digests the hyaluronic acid that binds granulosa cells together, and acrosin, a protease similar to the trypsin of pancreatic juice. When a path has been cleared through the granulosa cells, a sperm binds to the zona pellucida and releases its enzymes, digesting a pathway through the zona until it contacts the egg itself. The sperm head and midpiece enter the egg, but the egg destroys the sperm mitochondria and passes only maternal mitochondria on to the offspring.
   

What is the cell division that occurs in the earliest stages of zygote development called?

Cleavage

Which of the following results from the fertilization of an egg by more than one sperm?

Polyspermy

Explanation: Penetration by multiple sperm is called polyspermy.

A premature infant has an accelerated respiratory and heart rate, fatigue, and blood shows low-oxygen levels. From which of the following conditions might the infant be suffering?

Only the first and second choices are possible explanations

Explanation

When the lungs expand with air, resistance and blood pressure in the pulmonary circuit drop rapidly, and pressure in the right heart falls below that in the left. Blood flows briefly from the left atrium to the right through the foramen ovale (opposite from its prenatal flow) and pushes two flaps of tissue into place to close this shunt. In most people, these flaps fuse and permanently seal the foramen during the first year, leaving a depression, the fossa ovalis, in the interatrial septum. In about 25% of people, however, the foramen ovale remains unsealed, and the flaps are held in place only by the relatively high blood pressure in the left atrium. Pressure changes in the pulmonary trunk and aorta also cause the ductus arteriosus to collapse. It closes permanently around 3 months of age and leaves a permanent cord, the ligamentum arteriosum, between the two vessels. Failure of either of these to close could result in symptomatic mixing of oxygenated and deoxygenated blood.

What is senescence?

Degeneration in an organ system that occurs with aging

Complete each of the following statements about the placental development by selecting one of the words provided.

1. At implantation , extensions of the syncytiotrophoblast penetrate deep into the nourishing endometrium. These extensions are known as the  chorionic villi .

2. The placenta begins to develop approximately  11  days after conception.

3. The placenta becomes a dominant mode of nutrition at the begninning of week  9 .

4. By the end of week  12 , the placenta is the sole mode of nutrition until birth.

5. Blood flows between the fetus and the mother by way of  umbilical  arteries and veins attached to the placenta.

Explanation

The placenta is the fetus' life-support system—a disc-shaped organ attached to the uterine wall on one side, and on the other, attached to the fetus by way of the umbilical cord. It is the fetus' source of oxygen and nutrients and its means of waste disposal. The diffusion of nutrients from the mother's blood through the placenta into the fetal blood is called placental nutrition. The placenta begins to develop about 11 days after conception, becomes the dominant mode of nutrition around the beginning of week 9, and is the sole mode of nutrition from the end of week 12 until birth. The period from week 9 until birth is called the placental phase of the pregnancy.

What is an infant up to 6 weeks old called?

Neonate

Which of the following is an existing scientific theory regarding the mechanism of senescence?

• Cells lose their capacity for mitosis.Cells lose their capacity for mitosis. Correct

• Proteins fold differently in older tissues.

• The body's immune system begins to attack normal body cells.

  Explanation

  Numerous hypotheses have been proposed and discarded to explain why organ function degenerates with age. Some authorities maintain that senescence is an intrinsic process governed by inevitable or even preprogrammed changes in cellular function. Others attribute senescence to extrinsic (environmental) factors that progressively damage our cells over the course of a lifetime.

Which of the following is a function of the placenta?

• The placenta helps the fetus dispose of metabolic waste that would normally be excreted by its own kidneys.The placenta helps the fetus dispose of metabolic waste that would normally be excreted by its own kidneys. Correct

• The placenta allows for gas exchange.

• The placenta allows the building blocks of proteins to diffuse from maternal to fetal blood.The placenta allows the building blocks of proteins to diffuse from maternal to fetal blood. Correct

Explanation

The placenta is the fetus' life-support system—a disc-shaped organ attached to the uterine wall on one side, and on the other, attached to the fetus by way of the umbilical cord. It is the fetus' source of oxygen and nutrients and its means of waste disposal. The diffusion of nutrients from the mother's blood through the placenta into the fetal blood is called placental nutrition. The placenta begins to develop about 11 days after conception, becomes the dominant mode of nutrition around the beginning of week 9, and is the sole mode of nutrition from the end of week 12 until birth. The period from week 9 until birth is called the placental phase of the pregnancy.

Which of the following can cause birth defects?

• Radiation exposureRadiation exposure Correct

• Drinking one alcoholic beverage per day while pregnantDrinking one alcoholic beverage per day while pregnant Correct

• Cigarette smokingCigarette smoking Correct

• Infectious diseaseInfectious disease Correct

• Prescription medications

  Explanation

  Teratogens are agents that cause anatomical deformities in the fetus. They fall into three major classes: drugs and other chemicals, infectious diseases, and radiation such as X-rays.

Match each of the following physiological challenges faced by a premature infant with the under-developed organ or organ system to which it pertains.

1. Bilirubin deposits in the epidermis and sclera

   Liver

2. Inability to tolerate milk

   Digestive system

3. Inability to regulate body temperature

   Hypothalamus

4. Decrease in surfactant causes chronically collapsing alveoli, resulting in massive fatigue

   Respiratory system

Explanation

Neonates weighing under 2.5 kg (5.5 lb) are generally considered premature. They have multiple difficulties in respiration, thermoregulation, excretion, digestion, and liver function. Most neonates weighing 1.5 to 2.5 kg are viable but with difficulty. Those weighing under 0.5 kg rarely survive.

A friend tells you that she and her brother are twins, but he has green eyes, she has brown eyes, and they look nothing alike. How is this possible?

They are dizygotic.

Explanation

About two-thirds of twins are dizygotic (DZ)—produced when two eggs are ovulated and fertilized by separate sperm. They are no more or less genetically similar than any other siblings and may be of different sexes.

Which of the following is a legitimate reason why a neonate's first few breaths are relatively difficult?

Upon birth, the alveoli are collapsed, and the initial inflating requires a relatively large amount of force to generate the required pressure.

Explanation

It is an old misconception that a neonate must be spanked to stimulate it to breathe. During birth, CO2 accumulates in the infant's blood and strongly stimulates the respiratory chemoreceptors. Unless the infant is depressed by oversedation of the mother, it normally begins breathing spontaneously. It requires a great effort, however, to take the first few breaths and inflate the collapsed alveoli. For the first 2 weeks, an infant takes about 45 breaths per minute but subsequently stabilizes at about 12 breaths per minute.

Where does a sperm generally fertilize an egg?

Between the isthmus and ampulla of the uterine tube

Explanation

Fertilization occurs at the junction between the isthmus and ampulla of the uterine tube.

Which developmental stage is complete once the blastomeres arrange to form the three primary germ layers?

Embryogenesis