Test Yourself - Chapter 17

Front 1

How does the reproductive system differfrom other body systems?

Back 1

ANS: The rest of the body's systems workto ensure the survival of the individual animal they are part of, whereas thereproductive system works to ensure the survival of the species of animal. Itinteracts with other body systems, but purely reproductive structures are notessential to the life of an animal. Another difference from other body systemsis that the reproductive system requires a second animal (of the opposite sex)to fully carry out its function, which is to produce a brand new animal (theoffspring).

Front 2

Why is the reproductive system of anindividual animal considered only half a system?

Back 2

ANS: It is considered only half a systembecause it requires a second animal (of the opposite sex) to fully carry outits function.

Front 3

What is the difference between the diploidchromosome number and the haploid chromosome number? In which body cells iseach found?

Back 3

ANS: The total number of chromosomes in the nucleusof each of the body’s cells (except for the reproductive cells) is the same forall members of a species. This number is called the diploid chromosomenumber, which is always an even number because the chromosomes occur inpairs. The diploid chromosome number is sometimes expressed generically withthe abbreviation 2n. The n is a mathematical expression that representsa number, and the 2 indicates that the number is doubled (diploid). Thenumber of chromosomes in the reproductive cells is half the number in all othercells in the body. This is called haploid chromosome number. It has tobe reduced to half the diploid number so that when the spermatozoon and theovum come together, the total number of chromosomes in the fertilized ovum getsback to the diploid number.

Front 4

Which reproductive cell, the ovum or thespermatozoon, determines the genetic sex of the offspring when fertilizationoccurs?

Back 4

ANS: Spermatozoon

Front 5

How does cell division by meiosis differ from celldivision by mitosis?

Back 5

ANS:Most of the body’s cells divide through a process called mitosis. When acell divides by mitosis, each of its chromosomes first produces a duplicatecopy of itself. When the two daughter cells pull apart, half the chromosomes goto one cell and half go to the other. Each of them ends up with an identicalfull diploid set of chromosomes. The genetic makeup of the two daughter cellsis exactly the same as each other and as the parent cell. This ensures that thegenetic information in all of the body's cells (except for the reproductivecells) stays exactly the same. Reproductive cells are produced by meiosis, inwhich the chromosomes do not produce duplicate copies of themselves before thedaughter cells pull apart. Half of the total chromosomes (one from each diploidchromosome pair), including one sex chromosome, go to each daughter cell. Whichchromosomes go to which daughter cell is entirely random. The chromosomesmerely pull apart into their new cells. In this way the genetic material of thereproductive cells gets shuffled, resulting in genetically unique offspring.

Front 6

How does spermatogenesis differ from oogenesis? Whyare the basic processes so different?

Back 6

ANS: Spermatozoa are produced continuouslyand in very large numbers in an effort to ensure that one spermatozoon willsuccessfully reach and fertilize the ovum when breeding occurs, so the processof spermatogenesis is designed to produce huge numbers of spermatozoa.Alternatively, ova are not produced continuously like spermatozoa. At or soonafter birth, a female has a fixed number of primary oocytes (the precursor cellto ova) formed in her ovaries. That will be the total number available in herlifetime. They remain in a quiet immature state until the ovarian cycles begin.Each ovarian cycle produces one or more mature ova, depending on the species.Because spermatozoa come to the ovum to fertilize it, large numbers of ova arenot needed. Therefore the process of oogenesis is designed to produce smallnumbers of ova at a time.

Front 7

What are the two main functions of thetestes? Where in the organ does each take place?

Back 7

ANS: Spermatogenesis takes place in seminiferoustubules, and hormone production occurs in interstitial cells between theseminiferous tubules

Front 8

What are the three main parts of a spermatozoon?What is the main purpose or function of each?

Back 8

ANS: The three main parts of a spermatozoonare an enlarged head, a midpiece, and a long, narrow tail. The head containsthe nucleus of the cell and is covered by a caplike structure called the acrosome.The acrosome contains digestive enzymes that are released once the spermatozoonis inside the female reproductive tract, helping the spermatozoon reach theovum and penetrate through the layers surrounding it to accomplishfertilization. The midpiece is the power plant of the cell. It contains a largeconcentration of energy-producing mitochondria arranged in a spiral pattern.The long, thin tail resembles the flagellum that many single-celled organismsuse for propulsion. It contains musclelike contractile fibrils that produce awhiplike movement of the tail and propel the cell forward once it is activated.

Front 9

Why is a bilaterally cryptorchid animalusually sterile?

Back 9

ANS: A bilaterally cryptorchid (undescendedtestes) animal is usually sterile because spermatogenesis requires atemperature slightly lower than body temperature. The interior of the abdomenis too hot for spermatozoa to be produced. Testosterone continues to beproduced, however. So a bilaterally cryptorchid animal has all thecharacteristics of a male animal but cannot reproduce.

Front 10

Would a bilaterally cryptorchid animal exhibit normal male behavior? Why or why not?

Back 10

ANS: Yes, because testosterone, which isresponsible for the male libido, continues to be produced. Therefore abilaterally cryptorchid animal has all the characteristics of a male animal butcannot reproduce.

Front 11

What is important about the scrotum’sability to adjust the position of the testes relative to the body?

Back 11

ANS: The testes have to be kept slightly coolerthan body temperature to produce spermatozoa. A bandlike muscle, the cremastermuscle, passes down through the inguinal ring and attaches to the scrotum. Itcan adjust the position of the testes relative to the body. In warm conditions,the cremaster muscle relaxes, and the testes hang down away from the warm body.This position helps to reduce their temperature. In cold conditions, however,the cremaster muscle pulls the testes up tight against the body wall, whichhelps to warm them.

Front 12

What are the main components of the spermatic cord?

Back 12

ANS: Spermatic cords are tubelikeconnective tissue structures that contain blood vessels, nerves, lymphaticvessels, and the vas deferens. Surrounding the artery is a structure called thepampiniform plexus, which is an intricate meshwork of tiny veins derivedfrom the testicular veins.

Front 13

From what are the visceral and parietal vaginaltunics that cover the testes derived?

Back 13

ANS: They are derived from layers ofperitoneum that were pushed ahead of the testes as they descended through theinguinal rings. The very thin inner layer, the visceral vaginal tunic (alsoknown as the proper vaginal tunic), is derived from the visceral layerof peritoneum that coated the testes as they developed in the abdomen. Thethick outer layer, the parietal vaginal tunic (also known as the commonvaginal tunic), is derived from the parietal layer of peritoneum that linesthe abdominal cavity. It forms a fibrous sac around each testis and spermaticcord.

Front 14

Where are spermatozoa stored before ejaculation?

Back 14

ANS:Epididymis

Front 15

Will the volume or gross appearance ofthe semen of an animal that has had a vasectomy be significantly different fromthat of a normal animal? Why or why not?

Back 15

ANS:Because sperm typically account for less than 1% of seminal fluid, theirabsence after a vasectomy is negligible in terms of both the amount and gross appearanceof the seminal fluid.

Front 16

How does the function of the bulbourethralglands differ from that of the other accessory reproductive glands?

Back 16

ANS: They secrete a mucinous(mucus-containing) fluid just before ejaculation that clears and lubricates theurethra for the passage of semen. The fluid from the bulbourethral glands issecreted in advance of the ejaculate and does not contribute greatly to itsvolume, composition, or function.

Front 17

What are the three main parts of thepenis?

Back 17

ANS: Roots, body, and glans

Front 18

How does the mechanism of erection inanimals with a sigmoid flexure in their penis differ from that of otheranimals?

Back 18

ANS:Erection occurs when more blood enters the penis via the arteries than leavesit via the veins. The connective-tissue-enclosed erectile tissue becomesengorged with blood causing the penis to become enlarged and rigid.Mechanically what happens is that the arteries supplying blood to the penisdilate, increasing the blood flow into the organ. At the same time, the veinscarrying blood away from the penis are compressed against the brim of thepelvis by contractions of the ischiocavernosus muscles (part of the roots ofthe penis). This acts like a tourniquet and decreases the flow of blood out ofthe penis. The net effect is that more blood enters the penis than leaves it.This generates hydraulic pressure in the erectile tissue, producing theenlargement and stiffening of the penis that we call erection. Animalsthat have a sigmoid flexure have a higher proportion of connective tissue toerectile tissue than other species, and so the penis does not enlarge much whenerection occurs. Rather, the main mechanism of erection in these species isstraightening of the sigmoid flexure from internal hydraulic pressure. When bloodtries to enter the penis, it causes the penis to protrude from the prepuce forbreeding. A long thin cordlike muscle, the retractor penis muscle, originatesup near the base of the tail and attaches to the bend of the sigmoid flexure.It functions like a small bungee cord. When erection straightens out thesigmoid flexure, the retractor penis muscle stretches. When the erectionsubsides, the retractor penis muscle pulls the penis back into its non-erectS-shape.

Front 19

What structures do spermatozoa pass throughfrom their site of production to their eventual deposition in the femalereproductive tract?

Back 19

ANS: Spermatozoa pass through theseminiferous tubules, tube lumen, duct system of the rete testis, epididymis,vas deferens (including the ampulla in some species), and urethra.

Front 20

What two main types of hormones areproduced in the ovary? Where is each produced? some

Back 20

ANS: The hormones produced in the ovariesare estrogens and progestins. Estrogens are produced by the cells of thedeveloping ovarian follicles. Progestins, principally progesterone, areproduced by the corpus luteum that develops from the empty follicle afterovulation.

Front 21

What changes does an ovarian follicle undergo as itdevelops from a primordial follicle to a mature follicle?

Back 21

ANS:The beginning stage of follicle development in the ovary is the primordial(sometimes called the primary) follicle. After FSH is released from theanterior pituitary, the follicle undergoes follicular recruitment or follicularactivation, and is now called a growing follicle. The follicular cellsbecome thickened into cuboidal shapes and begin to multiply. Multiple layers offollicular cells form around the developing oocyte. At this stage thefollicular cells are called granulosa cells. As the granulosa cellsmultiply, the follicle starts to grow rapidly in size. The granulosa cells domore than just physically surround the developing oocyte. They also produceestrogen hormones that begin preparing the animal for breeding and pregnancy.The larger the follicle or follicles become, the greater the amount ofestrogens produced. As the follicle continues to grow, fluid-filled spacesbegin to form between the granulosa cells. The spaces gradually becomeconfluent (join together), forming one large fluid-filled space called the antrum. Whenthe follicle has reached its maximum size, it looks like a large, blisterlikestructure on the surface of the ovary. At this stage it is called a maturefollicle. Alternative names for the mature follicle include "graafianfollicle" and "vesicular ovarian follicle." At this stage,estrogen production from the follicle or follicles is at maximum level, and theanimal is ready for breeding to take place.

Front 22

After ovulation has occurred, what cells in theovary multiply to form the corpus luteum?

Back 22

ANS: Granulosa cells

Front 23

When ovulation occurs, what causes theovum to enter the oviduct?

Back 23

ANS: When ovulation takes place, the ovumis “caught” by the fimbriae of the infundibulum. The infundibulum is theenlarged opening at the ovarian end of each oviduct. At the time of ovulation,it more or less surrounds the area of the ovary where follicles have formed.The fimbriae are muscular, fingerlike projections that form the margin of theinfundibulum. They “feel” along the surface of the ovary and position theinfundibulum where the follicle or follicles are located. This helps ensurethat the infundibulum is properly positioned to catch the ovum or ova whenovulation occurs. If ova miss the opening of the oviduct, they fall into the abdominalcavity, where they usually just disintegrate after a time.

Front 24

Describe the functions of the uterusrelating to pregnancy and parturition.

Back 24

ANS: The uterus is the womb, where thefertilized ovum implants and lives while it grows and develops into a newanimal. When fully developed, the uterus helps push the newborn out through thebirth canal into the outside world. It forms part of the placenta, which is thelife-support system that keeps the fetus alive while it develops duringpregnancy. The uterus has to remain quiet during the pregnancy and contractpowerfully at the time of birth. After it has delivered the newborn and theplacenta (the afterbirth), it has to contract quickly to stop bleeding from thesite where the placenta was attached to its lining. The uterus is vital to thesuccess of reproduction. Thefertilized ovum implants in the uterus and begins development. As the offspringdevelops, the placenta forms around it and attaches to the lining of the uterusso that nutrients, wastes, and respiratory gases can be exchanged between thefetal bloodstream and the maternal bloodstream. When the time comes for theoffspring to be delivered, the muscular uterus provides most of the forcenecessary to open (dilate) the cervix so that the fetus can pass through it onits way to the outside world.

Front 25

Where is the urethral opening located inthe female?

Back 25

ANS: In females, the urethra opens on thefloor (ventral portion) of the vestibule, which is part of the vulva (the partthat is considered the entrance to the vagina).

Front 26

What is the difference in the estrouscycle intervals of polyestrous animals, seasonally polyestrous animals,diestrous animals, and monoestrous animals?

Back 26

ANS: Polyestrous animals, such as cattleand swine, cycle continuously throughout the year if they are not pregnant. Assoon as one cycle ends, another begins. Some polyestrous animals show seasonalvariations in their estrous cycles. They cycle continuously at certain times ofthe year and not at all at others. These animals are called seasonallypolyestrous animals. Diestrous animals have two cycles per year, usually inthe spring and fall. Monoestrous animals usually have only one cycle each year.

Front 27

How do the stages of the estrous cyclerelate to the events of the ovarian cycle?

Back 27

ANS: The estrous cycle stages areproestrus, estrus, metestrus, and diestrus. Anestrus occurs in some animalsbetween breeding seasons. Proestrus is the period of follicular development inthe ovary. During this stage, follicles begin developing and growing. As theyincrease in size, the follicles’ output of estrogen increases accordingly,causing many physical changes that prepare the rest of the reproductive tractfor ovulation and breeding. These changes include thickening and development ofthe linings of the oviduct, uterus, and vagina. The epithelial lining of thevagina also begins cornifying, that is, forming a layer of tough keratin on itssurface to help protect against the physical trauma of breeding that is aboutto come. Estrusis the "heat" period, or the period of sexual receptivity in thefemale. It occurs when the estrogen level from the mature follicles reaches itspeak. This high estrogen level causes physical and behavioral changes thatsignal the female’s willingness to breed to the male. Metestrusis the period after ovulation when the corpus luteum develops. The granulosacells left in the now empty follicle begin to multiply under continuedstimulation from LH. They soon produce a solid structure, the corpus luteum(yellow body), which is about the same size as the former mature follicle. Thehormone progesterone produced by the corpus luteum temporarily inhibitsfollicular development in the ovary, causes the lining of the uterus to getvery thick in preparation for implantation of a fertilized ovum, and causesloss of the cornified epithelial lining that developed in the vagina duringproestrus and estrus. Diestrusis the active luteal stage when the corpus luteum has reached maximum size andexerts its maximum effect. If the animal is bred and becomes pregnant, thecorpus luteum receives an endocrine signal from the developing embryo and isretained well into the pregnancy. If the animal is not pregnant, the corpusluteum degenerates at the end of diestrus. The animal either goes back intoproestrus or the ovary shuts down and the animal goes into anestrus. Anestrusis a period of temporary ovarian inactivity seen in seasonally polyestrus,diestrous, and monoestrous animals. It is the period between breeding cycles whenthe ovary essentially shuts down temporarily.