Chapter 27 Study Guide

What is meant by "oocyte activation"?

A single spermatozoon makes contact with the oocyte membrane and membrane fusion occurs. This is the completion of meiosis 2. The secondary oocyte is now an ova.

What are some substances found in mother's milk. Describe the "milk let-down" reflex.

milk let-down reflex = milk ejection reflex. At the end of the 6th month of pregnancy the memory glands are fully developed and the gland cells begin to produce a secretion known as Colostrum. Colostrum: Container antibodies that may help the infant ward off infections until the infants own immune system becomes fully functional. After the first fews days of nursing the memory glands produce break milk which has a much higher fat content than colostrum but still contains antibodies. It also contains Lysozyme and enzyme with antibiotic properties.

Describe the main function/features of the following placental hormones. Relaxin

- increases flexibility of pubic symphysis: permitting the pelvis to expand during pregnancy -secreted by the placenta and corpus luteum -causes dilation of the cervix: making it easier for the fetus to enter vagina canal. -delays he onset of labor contractions until late in the pregnancy.

Describe the main function/features of the following placental hormones. Progesterone & Estrogen

-Placenta produces enough amount of progesterone to maintain the endometrial lining and continue pregnancy. -End of third trimester estrogen production by the placenta accelerates. Rising estrogen levels play a role in stimulating labor and delivery.

Describe the main function/features of the following placental hormones. Human Placental Lactogen (hPL)

-Prepares mammary glands for milk production. Simulates by placental hormones hPL,estrogen, progesterone.

Describe the main function/features of the following placental hormones. Human Chorionic Gonadotropin (hCG)

-Sustains corpus luteum (resembles LH) b/c it maintains the integrity go the corpus lute and promotes the continued secretion of progesterone. -Detected by a pregnancy test making it positive. -The corpus lute persists for 3-4 months before gradually decreasing in size and secretary function.

Approximately at what point in development could a fetus survive if born premature?

28-34 weeks, toward end of third trimester. 1 or 2 months early is survivable.

What are the two phases of gestation? How long does each last?

1.Embryonic development: Two months after fertilization. 8 Weeks 2.Fetal development: Starts the 9th week-birth. Both of these are called prenatal development.

Expulsion Stage

Begins as the cervix pushed open by the approaching fetus completes dilation about 10 cm. contraction reach maximum intensity occurring at perhaps 2 to 3 mins intervals and lasting a pull minute. Expulsion continues until the fetus has emerged from the vagina in most cases the expulsion stage last less than 2 hours. The arrival of the newborn infant into outside world is delivery or birth.

Dilation Stage

Beings with the onset of true labor as the cervix dilates the fetus shifts toward the cervical canal moved by gravity and uterine contractions. Typically last 8 or more hours. At the start of dilation stage labor contractions last up to half a minutes and occur once every 10-30 mins. Their frequency increases steadily. Late in the stage the amnion ruptured an event some's water break"

What kind of divisions occur after amphimixis? How do these divisions differ from the general mechanism by which cells normally divide?

Cleavage divison: producing two daughter cells and each 1/2 the size of the original zygote. These cells are called blastomeres. Last about 7 days.

Where and when (days post ovulation) must fertilization occur in order for a zygote to successfully implant into the endometrium.

Day 0 in the ampulla of the uterine tube.

Describe the process of gastrulation? What three important structures are produced from this process?

Day 12 Superficial cells of the blastodisc are migrating toward a central line known as the primitive streak. The migrating cells leave the surface and move between the two existing layers. Gastrulation: produces an oval, three layered sheet known as embryonic disc.Embryonic disc: forms the body of the embryo whereas all other cells of the blastocyst will be part of the extra embryonic membranes. 1. Ectoderm: consisting of superficial cell that do not migrate into interior of the blastodisc. 2. Endoderm: consisting of the cells that ace the yolk sac 3. Mesoderm: consisting of the poorly organized layer of migrating cells between the ectoderm and endoderm. (migration process process is called gastrulation)

Describe the structure of a developing embryo from Day 1 to Day 4.

Day 1: 2 cell stage Day 2: 4 cell stage Day 3: early morula Day 4: advanced morula

What must occur before a blastocyst can implant?

Day 5: loss of the zone pellucida. 5 days after amphimixus

Describe the structure/action of the syncytial trophoblast. Which important development organ does it become?

Day 8 Syncytial trophoblast:At the Endometrial wall the plasma membranes separating the trophoblast cells disappearing and creating a layer of cytoplasm contain multiple nuclei. Its becomes the placenta Secrets enzymes and absorbs nutrients. Now has access to moms blood supply

Differentiate between dizygotic and monozygotic twins

Dizygotic twins: (fraternal) not identical. 2 separate oocytes were ovulated and fertilized. Monozygotic twins: (identical) Separation of blastomeres early in cleavage, or from splitting of the inner cell mass before gastrulation.

Briefly describe the main feature of each trimester.

GESTATION First trimester:embryonic and early fetal development. Rudiments (beginning structures) of all organ being to appear. Second Trimester:development of organ and organ system. Body shape and proportions change and by the end of this trimester the fetus looks human. Third Trimester:majority of weight gain/ Largest gain in fetal weight. Early in this trimeter the organ systems become fully functional. An infant born 1-2 months premature can survive with medical care.

Briefly describe the state of an embryo/fetus at the following points in development 12th week/3 months

Human featured better defined. The axial and appendicular muscles are forming. Fetal movement will soon begin.

Placenta Stage

Muscle tension builds in the walls of the partially empty uterus, which gradually decreases in size. The uterine contraction tears the connection between the endometrium and the placenta. The placenta or afterbirth is ejected. The disruption of the placenta is accompanied by a loss of blood but associated uterine contraction compress the uterine vessels and usually restrict this flow.

What is a "placenta" and how does it work?

Placenta: an organ that develops in your uterus during pregnancy. This structure provides oxygen and nutrients to your growing baby and removes waste products from your baby's blood. Oxygen supplies are replenished, organic nutrients are added and carbon dioxide and other organic waste are removed. Oxygenated blood returns to the fetus within a single umbilical vein.

Briefly describe the state of an embryo/fetus at the following points in development 16th week/4 months

The face and palate have their proper form. The cerebral hemisphere are rapidly enlarging. Hair follicles are present and hair growth beings. Peripheral nerves have formed, sensory respecters are developing and the fetus move frequently. Weight about 1.4 lbs

What is meant by partuition. Describe the three phases involved.

The goal of labor or childbirth is parturition. The forcible explosion of the fetus followed by the placenta. 1. Dilation Stage 2. Expulsion Stage 3. Placenta Stage

Briefly describe the state of an embryo/fetus at the following points in development 4th week

The heart is bumping blood to and from the placenta. You can recognize the heart, medulla oblongata, ear, eye, forebrain, body stalk, arm bud, leg bud, and tail

What is "amphimixis"?

The male pronucleus migrate toward the center of the ova where the spine fibers are forming. The female and male pronucleus met and fuse. Fertilization is now complete.

Briefly describe the state of an embryo/fetus at the following points in development 6th week

The placenta has formed and the embryo floats within the amniotic cavity. Body portion changing, limbs are growing longer, and skull bones are beginning to organize around the already formed brain and eye.