Chapter 17 Compendium Review

I. Fertilization
II. Pre-Embryonic and Embryonic Development
III. Fetal Development
IV. Pregnancy and Birth
V. Development After Birth

I. Fertilization
A. Fertilization is the union of a sperm and egg to form a zygote, the first cell of the new individual.
- Only the nucleus from the sperm head fuses with the nucleus of the egg.
- Zygote receives cytoplasm and organelles only from mother.
- Although several sperm penetrate the corona radiata ( few layers of adhering follicular cells), and several sperm attempt to penetrate the zona pellucida (the extracellular matrix surrounding the egg), only one sperm enters the egg.
- Sperm head binds tightly to zona pellucida, and acrosome releases digestive enzymes that create a pathway for the sperm through the zona pellucida.
- When the sperm binds to the egg, their plasma membranes fuse, and this sperm enters the egg entirely.
- Fusion of nucleus' occur.
- As soon as sperm touches egg, the egg's plasma membrane depolarizes to prevent the binding of any other sperm.
- Zona pellucida becomes impenetrable from any further fertilization.
(Insert Stages of Fertilization picture / http://www.fiu.edu/ / http://www.fiu.edu/~srose/femsexfiu/pregnancy.html)
II. Pre-Embryonic and Embryonic Development
A. Processes of Development:
1a. Cleavage: Immediately after fertilization, they zygote divides so that there are first 2, then 4, 8, 16, and 32 cells, etc.
- No increase in size.
-Mitotic: Each cell receives a full complement of chromosomes and genes.
(Insert Cleavage picture / dtc.pima.edu / http://dtc.pima.edu/~biology/202alpha/lesson13/lesson13c.htm)
2a. Growth: During embryonic development, cell division is accompanied by an increase in size of daughter cells.
3a. Morphogenesis: Shaping of embryo. First evident when cells move, or migrate, in relation to other cells.
4a. Differentiation: Cells take on specific structure and function. Nervous system is first.
B. Extraembryonic Membranes
1b. Not part of embryo and fetus; located outside of embryo.
2b. Chorion: Develops into fetal half of placenta, which gives embryo / fetus nourishment and oxygen and takes away its waste.
3b. Allantois: Extends away from embryo. Accumulates small amount of urine produced by fetal kidneys and gives rise to urinary bladder. Its blood vessels become umbilical blood vessels, to take blood to and from fetus.
4b. Yolk Sac: First embryonic membrane to appear. First site of blood cell formation.
5b. Amnion: Enlarges as embryo and then fetus enlarges. Contains fluid to cushion and protect embryo.
C. Stages of Development
1c. Fertilization to Birth
- 280 days = gestation period.
2c. Pre-embryonic development: Events of first week.
- Morula: Compact ball of embryonic cells that become a blastocyst.
- Inner Cell Mass: the cells of the blastocyst arrange themselves so that there is an inner cell mass surrounded by an outer layer of cells. Inner cell mass will become embryo, and the layer of cells will become the chorion.
(Insert Pre-embryonic Development picture / Frolich PowerPoint Slide 19)
3c. Embryonic Development: Begins with second week and lasts until end of second month of development.
- Second Week: Embryo begins process of implanting itself in the wall of uterus at end of first week.
- At this point, embryo is approx. the size of a period. ( . )
- As week progresses, the inner cell mass becomes the embryonic disk, and two more extraembryonic membranes form. (Yolk sac, and amniotic cavity.) (Mader 354-357)
- Gastrulation: turns inner cell mass into embryonic disk. Example of morphogenesis, when cells move or migrate, in this case to become tissue layers called the primary germ layers.
- By completion of gastrulation, embryonic disk has become an embryo with three germ layers: ectoderm, mesoderm, and endoderm. (Mader 358)
- Fetal “germ layers” destined to become specific adult structures. (Frolich PowerPoint Slide 21)
4c. Third Week: Appearance of two organ systems:
- Nervous System
- Heart
5c. Fourth and Fifth Week:
- Body stalk (future umbilical cord) connects embryo to the chorion which has projections called chorionic villi.
- Umbilical cord is formed.
- Limb buds appear.
- Head enlarges.
- Sense organs become more prominent.
- Can make out developing eyes, ears, and nose.
6c. Sixth through Eighth Weeks:
- Form becomes easily recognizable as human.
- Nervous system allows for reflex movement.
- Embryo is approx. 1.5 in long.
- All organ systems are established. (Mader 359)
(Insert Embryo at 8 Weeks Picture / epigee.org / http://epigee.org/pregnancy/methods.html)
4c. Ectopic pregnancy—fertilized egg implants but not in uterine wall. (Frolich PowerPoint Slide 19)
- This pregnancy cannot be successful, because oviduct is unable to support it.
III. Fetal Development
A. Carbon dioxide and other wastes move from the fetal side to the maternal side, and nutrients and wastes move from the maternal side to the fetal side of the placenta by diffusion.
B. Path of Fetal Blood: Umbilical vein carries blood rich in nutrients and O2 away from placenta and to fetus.
- Blood is returned to right atrium.
- Mixed blood enters heart.
- All blood entering right atrium by-passes the lungs.
(Mader 361)
(Insert Fetal Blood Circulation Picture / http://www.brainconnection.com/ / http://www.brainconnection.com/topics?main=gal/fetal-circulation)
C. Events of Fetal Development: Months 3-9
1c. Months 3-4
- Beginning of 3rd month, fetal head is still very big relative to the rest of the body.
- Head growth slows, rest of body increases in length.
- Epidermal refinements (fingernails, eyelashes, eyebrows, etc.) appear.
- Cartilage begins to be replaced by bone.
- Fontanels: Six large membranous areas in skull.
- Possible to distinguish sex sometime in 3rd month.
- During 4th month, fetal heartbeat can be heard through stethoscope.
- By the end of this month, fetus is approx. 6 inches long.
(Insert Fetus- 4 Months picture / epigee.org / http://epigee.org/fetal2.html)
2c. Months 5-7
- Mother begins to feel movement.
- Lanugo: Fine down that covers the translucent skin of fetus.
- Vernix Caseosa: Coats lanugo, to protect skin from amniotic fluid.
- Eyelids fully open.
- Approx. 12 inches long.
(Insert Fetus - 7 Months picture / http://answers.yahoo.com/question?qid=1006052905521)
3c. Months 8-9
- By end of 9th month, fetus is approx. 20.5 in.
- Accumulation of fat occurs.
- Breech birth: Baby comes "rump" first.
- C-Section: Birth through incision and extraction. (Mader 363)
D. Development of Male and Female Genitals
1d. Sex of individual is determined at the moment of fertilization: Males have X and Y chromosomes, females have two X chromosomes.
2d. Internal Genitals:
- Gonads develop during 7th week of development.
- At 14 weeks, sperm or tiny follicles in ovaries are already developing.
3d. External Genitals:
- Tissues are indifferent at first.
- By 14 weeks, the "groove" persists if female, disappears int scrotum if male.
4d. Abnormal Development of Genitals:
- Some XY individuals become females, because a piece of the Y chromosome is missing.
- Some XX individuals become males, because the same small piece is present on an X chromosome.
5d. Ambiguous Sex Determination: Individual has external appearance of a female, although the gonads of a female are absent.
- Androgen Insensitivity Syndrome: Testes produces hormones, but individual develops as a female because the plasma membrane receptors for testosterone are ineffective. External genitalia develop as female. (Mader 365)
IV. Pregnancy and Birth
A. Placental Hormones cause the changes in a mother's body during pregnancy.
1a. Energy level fluctuates.
- Nausea, vomiting.
- Loss of appetite.
- Fatigue.
- Weight gain results from all of the following: breast and uterine enlargement, weight of fetus, amount of amniotic fluid, size of placenta, her own increase in body fluids, increase in storage of proteins, fats, and minerals. Can lead to lower back pain.
2a. Uterus relaxes:
- Increase in blood volume.
- Blood flow rises significantly.
- Smooth muscle relaxation.
3a. Pulmonary Values Increase.
- Increased size of uterus.
- Occupies most of abdominal cavity.
- Pushes intestines, liver, stomach, and diaphragm from top, and widens thoracic cavity.
- Blood carbon dioxide levels fall.
4a. Other Effects:
- Compression of ureters and bladder causes frequent passage of urine.
- Stretch marks.
- Possibility of pregnancy-induced diabetes. (Mader 368)
–Bladder, rectum pushed superiorly, squeezed--change in urination, defecation patterns.
–Stomach compressed--eat more often, less at each meal.
–Immune response may change appetite to avoid possible poisons for fetus.
- Postural changes to compensate for anterior weight.
- Breasts enlarge--first milk production. (Frolich PowerPoint Slide 22)
(Insert Stages of Pregnancy picture / pregnancy.more4kids.info / http://pregnancy.more4kids.info/category/stages-of-pregnancy)
B. Birth:
- Uterus contracts throughout pregnancy.
- Braxton Hicks Contractions: False labor.
- Uterine contractions push fetus downwards, and cervix stretches.
- Parturition: Process of giving birth to an offspring.
- Loss of mucous plug, that during pregnancy, keeps out bacteria and other sperm.
1b. Stage 1: Contractions cause cervical canal to slowly disappear, and lower part of uterus is pulled up toward baby's head, = Effacement.
- Baby's head helps cervical dilation.
- Amniotic membrane ruptures.
2b. Stage 2: Contractions occur every 1-2 mins.
- Desire to push.
- Episiotomy: incision to enlarge opening of vagina, to allow for birth.
- Umbilical cord is cut and tied.
3b. Stage 3: Afterbirth: Placenta is delivered.
(Mader 369)
(Insert Process of Birth picture / Frolich PowerPoint Slide 23)
V. Development After Birth
A. Stages of life: Infancy, childhood, adolescence, and adulthood.
1a. Gerontology: Study of aging.
- Human life span maximum: 120-125 years.
2a. Hypotheses of Aging
- Genetic in Origin: Aging has genetic basis.
- Some genes decrease life span. When inactive, the mitochondria do not produce energy, and the cell uses alternative pathways. Defective mitochondria may produce more free radicals than usual. Caloric restriction can shut down the genes that decrease life span.
- Whole-Body Process: Decline in hormonal system can affect many different organs of body.
- Perhaps aging results from loss of hormonal activities and a decline in functions they control.
- Aging may be due to a specific type of tissue change that affects all organs and even the genes.
- Extrinsic Factors: Diet, exercise, cigarette smoking, heavy alcohol intake, inadequate calcium intake, etc.
B. Effect of Age on Body Systems:
1b. Skin: Skin becomes thinner and less elastic because the number of elastic fibers decreases and collagen fibers undergo cross-linking. = sagging and wrinkling.
2b. Processing and Transporting:
- Cardiovascular disorders are leading cause of death today.
- Arteries become more rigid with time.
- Heart shrinks due to reduction in cardiac muscle cell size.
- Blood flow to liver and kidneys is reduced.
- Respiratory disorders.
- Loss of teeth.
3b. Integration and Coordination:
- Reaction time slows.
- Hearing, taste, and smell receptors need more stimulation.
- Lens of eyes do not accommodate as well as before.
- Loss of skeletal muscle mass.
- Decline of bone density.
- Weight gain.
4b. Reproductive System
- Females undergo menopause.
- Males undergo andropause.
(Mader 370-372)