Chapter 18 Glossary, Summary, and Practice Questions

KEY TERMS

asexual reproduction a mechanism that produces offspring that are genetically identical to the parent

blastocyst the structure formed when cells in the mammalian blastula separate into an inner and outer layer

budding a form of asexual reproduction that results from the outgrowth of a part of an organism leading to a separation from the original animal into two individuals

bulbourethral gland

ejaculation

the paired glands in the human male that produce a secretion that cleanses the urethra prior to

clitoris a sensory and erectile structure in female mammals, homologous to the male penis, stimulated during sexual arousal

corpus luteum the endocrine tissue that develops from an ovarian follicle after ovulation; secretes progesterone and estrogen during pregnancy

estrogen a reproductive hormone in females that assists in endometrial regrowth, ovulation, and calcium absorption

external fertilization the fertilization of eggs by sperm outside an animal’s body, often during spawning

fission (also, binary fission) a form of asexual reproduction in which an organism splits into two separate organisms or two parts that regenerate the missing portions of the body

follicle stimulating hormone (FSH) a reproductive hormone that causes sperm production in men and follicle development in women

fragmentation the breaking of an organism into parts and the growth of a separate individual from each part

gastrulation the process in which the blastula folds over itself to form the three germ layers

gestation the development before birth of a viviparous animal

gestation period the length of time of development, from conception to birth, of the young of a viviparous animal

gonadotropin-releasing hormone (GnRH)

from the anterior pituitary

a hormone from the hypothalamus that causes the release of FSH and LH

hermaphroditism the state of having both male and female reproductive structures within the same individual

human beta chorionic gonadotropin (β-HCG) a hormone produced by the chorion of the zygote that helps to

maintain the corpus luteum and elevated levels of progesterone

inhibin a hormone made by Sertoli cells, provides negative feedback to hypothalamus in control of FSH and GnRH release

inner cell mass the inner layer of cells in the blastocyst, which becomes the embryo

internal fertilization the fertilization of eggs by sperm inside the body of the female

interstitial cell of Leydig a cell type found next to the seminiferous tubules that makes testosterone

labia majora the large folds of tissue covering inguinal area

labia minora the smaller folds of tissue within labia majora

luteinizing hormone (LH) a reproductive hormone in both men and women, causes testosterone production in men and

ovulation and lactation in women

menstrual cycle the cycle of the degradation and re-growth of the endometrium

oogenesis the process of producing haploid eggs

organogenesis the process of organ formation during development

ovarian cycle the cycle of preparation of egg for ovulation and the conversion of the follicle to the corpus luteum

oviduct (also, fallopian tube) the muscular tube connecting uterus with ovary area

oviparity a process by which fertilized eggs are laid outside the female’s body and develop there, receiving nourishment from the yolk that is a part of the egg

ovoviparity a process by which fertilized eggs are retained within the female; the embryo obtains its nourishment from the egg’s yolk, and the young are fully developed when they are hatched

ovulation the release of an oocyte from a mature follicle in the ovary of a vertebrate

parthenogenesis a form of asexual reproduction in which an egg develops into a complete individual without being fertilized

penis the male reproductive structure for urine elimination and copulation

placenta the organ that supports the transport of nutrients and waste between the mothers and fetus’ blood in eutherian mammals

progesterone a reproductive hormone in women; assists in endometrial regrowth and inhibition of FSH and LH release prostate gland a structure that is a mixture of smooth muscle and glandular material and that contributes to semen scrotum a sac containing testes, exterior to body

semen a fluid mixture of sperm and supporting materials

seminal vesicle a secretory accessory gland in male; contributes to semen

seminiferous tubule the structures within which sperm production occurs in the testes

Sertoli cell a cell in the walls of the seminiferous tubules that assists developing sperm and secretes inhibin

sex determination the mechanism by which the sex of individuals in sexually reproducing organisms is initially established

sexual reproduction a form of reproduction in which cells containing genetic material from two individuals combines to produce genetically unique offspring

spermatogenesis the process of producing haploid sperm

testes a pair of male reproductive organs

testosterone a reproductive hormone in men that assists in sperm production and promoting secondary sexual characteristics

trophoblast the outer layer of cells in the blastocyst, which gives rise to the embryo’s contribution to the placenta

uterus a female reproductive structure in which an embryo develops

vagina a muscular tube for the passage of menstrual flow, copulation, and birth of offspring

viviparity a process in which the young develop within the female and are born in a nonembryonic state

zona pellucida the protective layer around the mammalian egg

CHAPTER SUMMARY

How Animals Reproduce

Reproduction may be asexual when one individual produces genetically identical offspring, or sexual when the genetic material from two individuals is combined to produce genetically diverse offspring. Asexual reproduction in animals occurs through fission, budding, fragmentation, and parthenogenesis. Sexual reproduction may involve fertilization inside the body or in the external environment. A species may have separate sexes or combined sexes; when the sexes are combined they may be expressed at different times in the life cycle. The sex of an individual may be determined by various chromosomal systems or environmental factors such as temperature.

Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. This can occur either outside the bodies or inside the female. The method of fertilization varies among animals. Some species release the egg and sperm into the environment, some species retain the egg and receive the sperm into the female body and then expel the developing embryo covered with shell, while still other species retain the developing offspring throughout the gestation period.

Development and Organogenesis

The early stages of embryonic development begin with fertilization. The process of fertilization is tightly controlled to ensure that only one sperm fuses with one egg. After fertilization, the zygote undergoes cleavage to form the blastula. The blastula, which in some species is a hollow ball of cells, undergoes a process called gastrulation, during which the three germ layers form. The ectoderm gives rise to the nervous system and the epidermal skin cells, the mesoderm gives rise to the muscle cells and connective tissue in the body, and the endoderm gives rise to the digestive system and other internal organs. Organogenesis is the formation of organs from the germ layers. Each germ layer gives rise to specific tissue types.

Human Reproduction

The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring. Gametogenesis, the production of sperm (spermatogenesis) and eggs (oogenesis), takes place through the process of meiosis.

The male and female reproductive cycles are controlled by hormones released from the hypothalamus and anterior pituitary and hormones from reproductive tissues and organs. The hypothalamus monitors the need for FSH and LH production and release from the anterior pituitary. FSH and LH affect reproductive structures to cause the formation of sperm and the preparation of eggs for release and possible fertilization. In the male, FSH and LH stimulate Sertoli cells and interstitial cells of Leydig in the testes to facilitate sperm production. The Leydig cells produce testosterone, which also is responsible for the secondary sexual characteristics of males. In females, FSH and LH cause estrogen and progesterone to be produced. They regulate the female reproductive cycle, which is divided into the ovarian cycle and the menstrual cycle.

Human pregnancy begins with fertilization of an egg and proceeds through the three trimesters of gestation. The first trimester lays down the basic structures of the body, including the limb buds, heart, eyes, and the liver. The second trimester continues the development of all of the organs and systems. The third trimester exhibits the greatest growth of the fetus and culminates in labor and delivery. The labor process has three stages (contractions, delivery of the fetus, and expulsion of the placenta), each propelled by hormones.

ART CONNECTION QUESTIONS

• Figure 18.12 Which of the following statements about the male reproductive system is false?
• The vas deferens carries sperm from the testes to the seminal vesicles.
• The ejaculatory duct joins the urethra.
• Both the prostate and the bulbourethral glands produce components of the semen.
• The prostate gland is located in the testes.
• Figure 18.17 Which of the following statements about hormone regulation of the female reproductive cycle is false?
• 
  LH and FSH are produced in the pituitary, and estrogen and progesterone are produced in the ovaries.
• Estradiol and progesterone secreted from the corpus luteum cause the endometrium to thicken.
• Both progesterone and estrogen are produced by the follicles.
• Secretion of GnRH by the hypothalamus is inhibited by low levels of estrogen but stimulated by high levels of estrogen.

REVIEW QUESTIONS

• In which group is parthenogenesis a normal event?

• chickens
• bees
• rabbits
• sea stars
• Genetically unique individuals are produced through

.

• sexual reproduction
• parthenogenesis
• budding
• fragmentation
• External fertilization occurs in which type of environment?
• aquatic
• forested
• savanna
• steppe
• The process of gastrulation forms the .

• blastula
• zygote
• organs
• germ layers
• Which of the following gives rise to the skin cells?

• ectoderm
• endoderm
• mesoderm
• none of the above

CRITICAL THINKING QUESTIONS

• What might be a disadvantage to temperature- dependent sex determination?
• Compared to separate sexes and assuming self- fertilizing is not possible, what might be one advantage and one disadvantage to hermaphroditism?
• What do you think would happen if multiple sperm fused with one egg?

• Sperm are produced in the .
• scrotum
• seminal vesicles
• seminiferous tubules
• prostate gland
• Which female organ has an endometrial lining that will support a developing baby?
• labia minora
• breast
• ovaries
• uterus
• Which hormone causes FSH and LH to be released?

• testosterone
• estrogen
• GnRH
• progesterone
• Nutrient and waste requirements for the developing fetus are handled during the first few weeks by .

• the placenta
• diffusion through the endometrium
• the chorion
• the blastocyst
• Which hormone is primarily responsible for the contractions during labor?
• oxytocin
• estrogen
• β-HCG
• progesterone

• Compare spermatogenesis and oogenesis as to timing of the processes, and the number and type of cells finally produced.
• Describe the events in the ovarian cycle leading up to ovulation.
• Describe the stages of labor.