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Questions and Answers
What is the main event that marks the beginning of the pre-embryonic stage?
During which week does the morula form after fertilization?
Which of the following structures develops finger-like projections during implantation?
What key process occurs during the embryonic stage of development?
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What structures are formed during the fetal stage of development?
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At what point in pregnancy are all major organ systems present in human form?
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What chromosome combination indicates that the fertilized egg will develop into a male?
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Which of the following functions does amniotic fluid NOT perform?
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What is the primary role of the placenta during pregnancy?
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Which of the following is a probable sign of pregnancy?
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What causes Chadwick's sign during pregnancy?
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At what week does the cervical mucus plug usually form during pregnancy?
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Which of the following changes is associated with Goodell's sign?
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What is not a presumptive sign of pregnancy?
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What is a common cause of hemoconcentration during pregnancy?
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Which statement accurately captures the changes in the respiratory system during the last trimester of pregnancy?
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How many blood vessels are present in the umbilical cord?
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What is the primary reason for increased coagulability of blood during pregnancy?
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What physiological change occurs to breast tissue during pregnancy?
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What might cause constipation in pregnant women?
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Which of the following skin changes are associated with pregnancy?
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Which condition is characterized by a burning sensation behind the sternum during pregnancy?
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Which factor contributes to frequent urination in pregnant women?
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What is the average weight gain for a normally pregnant woman?
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Study Notes
Developmental Stages
- Pregnancy is divided into three stages: pre-embryonic, embryonic, and fetal.
- The pre-embryonic stage lasts from fertilization until the end of the second week.
- The embryonic stage lasts from the end of the second week until the end of the eighth week.
- The fetal stage starts from the beginning of the ninth week until birth.
Pre-embryonic Stage
- The zygote undergoes mitotic division, transitioning from one cell to two, four, eight, and so on.
- This process results in the formation of a solid cell mass called a morula around the third day after fertilization.
- By the fifth day, the cell mass develops a hollow, fluid-filled core, becoming a blastocyst.
- Around the seventh day, the blastocyst implants into the endometrium, which is now called the decidua.
Embryonic Stage
- During this stage, the cells and tissues of the embryo multiply to form organs.
- Three germ layers, the ectoderm, mesoderm, and endoderm, develop in the embryo during the third week.
Fetal Stage
- Sex determination occurs in the fetal stage. If the egg is fertilized by a sperm containing an X chromosome, the baby will be a girl (XX). If the sperm contains a Y chromosome, the baby will be a boy (XY).
- During this stage, supportive structures, including fetal membranes, amniotic fluid, the placenta, and the umbilical cord, develop.
- The amnion and chorion are the two fetal membranes.
- Amniotic fluid protects the fetus from injury, acts as a temperature control mechanism, and allows for free movement and growth.
- The placenta transfers nutrients, including oxygen and glucose, to the fetus while removing waste products. It acts as a barrier to some harmful substances from passing to the fetus.
- The umbilical cord, containing two arteries and one vein, extends from the fetus's umbilicus to the placenta.
Signs and Symptoms of Pregnancy
- Presumptive signs: These are subjective changes that can be experienced by the pregnant woman. Examples include absent menstrual periods, nausea and vomiting, fatigue, frequent urination, breast tenderness, and skin changes.
- Probable signs: These are objective changes that are observed by an examiner. Examples include a softening of the cervical isthmus (Hegar's sign), abdominal ballotment, and a positive pregnancy test.
- Positive signs: These are definitive signs of pregnancy related to the presence of the fetus. Examples include hearing fetal heart sounds, visualizing the fetus by ultrasound, and feeling fetal movement.
Physiological Changes During Pregnancy
- Weight of the uterus: The uterus increases from 50-70 grams to 1000 grams during pregnancy.
- Changes in the cervix: The cervix becomes softer (Goodell's sign), and a mucus plug is formed by the eighth week from secretions of the cervical glands.
- Changes in the vagina: The vagina turns blue due to venous dilatation caused by progesterone, known as Chadwick's sign.
- Changes in the breasts: The breasts increase in size and weight, surface veins become visible, nipples become larger and darker, and Montgomery's tubercles appear around the areolae.
- Changes in the urinary system: Frequent urination occurs due to hormonal or mechanical causes.
- Changes in the digestive system: Nausea, vomiting, and heartburn may occur due to mechanical pressure from the enlarged uterus. Constipation can also occur due to reduced intestinal motility.
- Weight gain: The average weight gain during pregnancy is between 9 and 12 kilograms.
- Changes in the respiratory system: Dyspnea may occur in the last trimester due to elevation of the diaphragm.
- Skin changes: Pigmentation changes occur, leading to darker nipples, areolae, and abdomen. Chloasma (pregnancy mask), linea nigra, and stretch marks (striae gravidarum) may appear.
- Changes in the cardiovascular system: Blood volume increases significantly, increasing blood pressure and heart rate. The increased blood volume is called haemodilution and leads to physiological anemia of pregnancy. This makes the blood more coagulable, increasing the risk of venous thrombosis.
Minor Discomfort During Pregnancy
- Nausea and vomiting: About half of pregnant women experience nausea and vomiting in the first trimester.
- Varicose veins: Swollen, purple veins can develop in the legs and around the vaginal opening.
- Heartburn: A burning sensation behind the sternum can be reduced by eating smaller meals and avoiding lying down after meals.
- Bleeding gums: Spongy gums can lead to easy bleeding due to increased blood flow.
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