A&P Chapter 29 Development

How long does pregnancy typically last?

9 months

What is the risk of retained afterbirth fragments?

can lead to extensive bleeding or other postpartum complications

What happens when this hormone regresses after three months?

corpus luteum degenerates because it is no longer needed due to placenta producing its own estrogen and progesterone to maintain pregnancy

How is this hormone clinically significant?

detected in urine by end of second week of development basis of most pregnancy test; levels high for first 3 months of pregnancy

When do the weeks of pregnancy start being counted?

from the first day of last menstrual period-approximately two weeks before fertilization and lasts approximately 40 weeks.

Define the term embryo

from the third-eighth weeks of development

Define the term fetus

from week nine of development up to birth

What hormone is released when a blastocyst burrows into the uterine wall?

human chorionic gonadotropin (hCG)

Define lactation. What hormone is responsible for milk production?

is the production and release of breast milk from mammary glands -prolactin

What hormones are involved in labor contractions?

maternal oxytocin, fetal oxytocin and prostaglandins

What tissues secrete high amounts of estrogen and progesterone during pregnancy?

produced by corpus luteum during first trimester mostly produced by placenta in second and third trimester

Define the process of cleavage

series of mitotic divisions of zygote

Define blastocyst

shortly after the morula enters the lumen of the uterus, fluid begins to leak through the degenerating zona pellucida into the morula. As a result, a fluid-filled cavity called the blastocyst cavity develops within the morula. The pre-embryo at this state of development is known as a blastocyst.

What are the physiological effects of this hormone?

signals corpus luteum that fertilization and implantation have occurred promotes maintenance of corpus luteum produces estrogen and progesterone to build uterine lining

Define zygote

single diploid cell formed from pronuclei essentially a fertilized egg

How is capacitation related to fertilization?

sperm are not capable of fertilizing the secondary oocyte when they are ejaculated, they must undergo this process before accomplishing fertilization

Define teratogens

substances causing birth defects or death, they include alcohol, tobacco, drugs and some viruses most dangerous during peak development of particular systems

Define pronucleus

the nucleus of sperm and ovum because they have a haploid number of chromosomes. they come together and fuse, forming a single nucleus that contains a diploid number of chromosomes

1. Define afterbirth.

the placenta and remaining fetal membranes (amnion)

Which trimester corresponds to the largest weight gain of the fetus?

third trimester

Describe the dilation, expulsion and placental stages of labor.

-dilation: cervix dilates and fetus moves toward cervical canal, the frequency of contractions increases and the amniochorionic membrane ruptures "water breaks" -expulsion: cervix is completely dilated and the mother experiences the maximum intensity of contractions, the contractions continue until the fetus emerges from the vagina (delivery/birth) -placental: uterine contractions tear the connection between the endometrium and the placenta, the placenta is ejected through the vagina, it is accompanied by a loss of blood, which is usually tolerated without difficulty.

Describe the main functions of the placenta.

-exchange of nutrients, waste products, and respiratory gases -transmits maternal antibodies to developing embryo/fetus -produces estrogen and progesterone to maintain and build the uterine lining

What are the effects of estrogen and progesterone during pregnancy?

-facilitate uterine enlargement, mammary gland enlargement, and fetal growth -facilitate faster growing nails and fuller hair -estrogen primarily responsible for relaxation of ligamentous joints -progesterone is responsible for growth of functional layer of uterus and prevention of menstruation

Define false and true labor contractions.

-false labor: uterine contractions not resulting in 3 stages of labor; contractions known as Braxton-Hicks contractions. Irregularly spaced and do not become more frequent, relatively weak and do not increase in intensity, pain limited to lower abdomen and pelvic region, pain sometimes stopping with movement, do not lead to cervical changes -true labor: uterine contractions that increase in intensity and regularity, result in changes to cervix, Mother's hypothalamus secreting increasing levels of oxytocin and fetus also secreting ooxytocin during true labor

List the 3 stages of pregnancy and briefly describe the major events associated with each.

-first trimester: first 3 months of pregnancy; zygote becoming embryo and then early fetus -second trimester: months 4-6 of pregnancy; growth of fetus and expansion of maternal tissues -third trimester: months 7-9; fetus growing most rapidly, mother's body preparing for labor and delivery

Explain the types of twins, identical, fraternal and conjoined.

-identical twins result from the fertilization of a single egg that split in two. share all of their genes and are always of the same sex -fraternal twins result from the fertilization of two separate eggs during the same pregnancy, separate amniotic sacs, placentas, and supporting structures, may be of the same or different sex -conjoined twins occur when in the early stages of development, an embryo only partially separates to form two babies.

1. Describe the positive feedback mechanism of labor.

-intense contractions pushing fetus's head against cervix stimulates stretching and dilation of the cervix, signals hypothalamus to secrete more oxytocin, stimulate placenta to secrete more prostaglandins, which also results in more intense uterine contractions -positive feedback mechanism continues to intensify until fetus expelled; with expulsion, major source of prostaglandins removed, uterus and cervix no longer fully stretched, drop of oxytocin levels, labor ceases.

1. Define colostrum. Why is colostrum important?

-is produced by the mammary glands during late pregnancy and first few days after birth. -watery, yellowish, milklike substance -lower concentrations of fat than true breast milk -it is rich in immunoglobulins, especially IgA, the infant acquires passive immunity from the mother and has a laxative effect, which facilitates an infant's first bowl movement

Describe the milk let-down reflex.

-is the release of breast milk -it involves a positive feedback mechanism -when the infant suckles at the breast, mechanoreceptors in the nipple and areola are stimulated, and they send nerve signals to the hypothalamus. the hypothalamus is stimulated to produce oxytocin, which is released into the bloodstream. the oxytocin targets myoepithelial cells in the mammary glands to contract, thereby releasing breast milk from acini. as milk is released, the infant continues to nurse. milk will continue to be released from the breast as long as the infant continues to nurse

Define premature labor. What are the risk factors of premature labor?

-labor prior to 38 weeks -undesirable since infant's body system not fully developed (especially lungs) -if very premature, at greater risk for morbidity and mortality due to underdeveloped organ systems

Define organogenesis. When does organogenesis occur?

-organ development -begins once the three primary germ layers have formed and the embryo has undergone cephalocaudal and transverse folding -peak development of different organ systems occurs at different times (limbs; 4-8 weeks, external genitalia;late embryonic/early fetal)

Define labor. What hormones facilitate labor?

-physical expulsion of fetus and placenta from uterus -typically at 38 weeks for full term -not all uterine contractions lead to true labor -estrogen and oxytocin

Describe the functions of relaxin, prolactin and oxytocin during pregnancy.

-relaxin: secreted by corpus luteum and placenta; promotes blood vessel growth in uterus -prolactin: increased levels produced by anterior pituitary; ensures lactation occurs after giving birth -oxytocin: increased levels produced by hypothalamus; involved in uterine contractions, milk expulsion from mammary glands, and increase in second and third trimesters in response to rising estrogen levels

Define breast milk. Why breast milk is considered an optimal source of nutrition?

-starts to be produced a few days postpartum -has a higher fat content than colostrum -it has essential fatty acids, enzymes for digestion, and immunoglobulins -more easily digestible than breast milk substitutes

Define capacitation of sperm.

-the physiological conditioning undergone by sperm before they can accomplish fertilization. -during this time, a glycoprotein coat and some proteins are removed from the sperm plasma membrane that overlies the acrosomal region of the sperm. -occurs in the female reproductive tract and lasts several hours

Where and when does fertilization typically occur?

-typically occurs in widest part of uterine tube known as ampulla -following ovulation, the secondary oocyte remains viable for 24 hours following ovulation, where as sperm remain viable for an average of 3-4 days after ejaculation from the male.

After the sperm and oocyte fuse, what events immediately take place?

when the sperm and oocyte plasma membranes come into contact, they immediately fuse. only the nucleus of the sperm enters the cytosol of the secondary oocyte. the midpiece and flagellum of the sperm degenerate shortly thereafter and typically never enter the fertilized cell. when the nucleus of the sperm enters the secondary oocyte, the secondary oocyte completes the second meiotic division and forms an ovum.