Questions and Answers
Where does fertilization occur in the female reproductive system?
What happens to the ovum after one sperm penetrates it?
What is the term for the mass of cells formed during the process of cleavage after fertilization?
How long can sperm remain functional after ejaculation?
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What role do trophoblast cells play in the early development of the embryo?
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What is the first placental hormone produced during pregnancy?
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What role does progesterone play during pregnancy?
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Which of the following hormones is responsible for mammary gland development and lactation?
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What effect does low progesterone have during pregnancy?
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Which substance crosses the placenta through pinocytosis?
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At the end of which week can sex be distinguished in fetal development?
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What significant development occurs at the end of the 4th week of fetal growth?
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Which developmental milestone occurs at the end of the 20th week?
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What is the function of passive antibody transfer from the mother?
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Which development is observed at the end of the 28th week?
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What is the process by which sperm move towards the ovum?
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What defines the term 'zygotic stage'?
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What happens during the apposition phase of implantation?
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Which structure is primarily responsible for the secretion of HCG?
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What is the main role of hyaluronidase released by sperm?
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At what point is the conceptus defined?
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What is a key physiological change during capacitation of sperm?
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Which factor does NOT contribute to the prevention of fertilization?
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What is the primary function of the chorionic villi?
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Which layer of the trophoblast is responsible for producing placental hormones?
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What role does the placenta serve during pregnancy?
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What is the significance of lying on the left side during pregnancy?
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What substance crosses the placenta via facilitated diffusion?
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How do nutrients like oxygen and carbon dioxide primarily cross the placenta?
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What is the approximate weight of a mature placenta at term?
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What does the cytotrophoblast primarily do?
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Study Notes
Human Conception
- Sperm enters the vagina and travels to the ampulla of the fallopian tube for fertilization.
- Only one sperm can penetrate the ovum; once successful, the ovum becomes impermeable to additional sperm.
- Sperm release hyaluronidase enzyme to facilitate penetration of the ovum's protective layer.
- Fertilization results in the formation of a zygote, with male (XY) or female (XX) genetic information.
- Zygote travels through the fallopian tube for 3-4 days before reaching the uterus.
- The zygote undergoes cleavage to form a morula, composed of 16-50 cells.
- Implantation occurs when the morula transforms into a blastocyst, attaching to the uterine endometrium.
- Trophoblast cells develop from the blastocyst, forming the placenta and surrounding membranes, while the inner cell mass develops into the embryo.
Fertilization
- Marks the beginning of pregnancy, also termed conception or fecundation.
- Occurs in the outer third of the fallopian tube.
- Sperm remains functional for about 72 hours, while the ovum can be fertilized within 48 hours post-ovulation.
- Ovulation releases the ovum from the Graafian follicle.
Ejaculation
- Semen averages 2.5 ml, containing 50 to 200 million sperm per milliliter; totals can reach 400 million sperm per ejaculation.
Sperm Characteristics
- Sperm travel from the vagina to the cervix within 90 seconds and reach the fallopian tube within 5 minutes.
- Movement is facilitated by flagella and uterine contractions.
- Hyaluronidase helps sperm penetrate the zona pellucida of the ovum.
Factors Affecting Fertilization
- Maturation of both sperm and ovum must be equal.
- Sperm must be able to reach and penetrate the zona pellucida and ovum cell membrane.
Terminology for Fetal Growth
- Ovum: from ovulation to fertilization.
- Zygote: from fertilization to implantation.
- Embryo: from implantation to 5-8 weeks.
- Fetus: from 5-8 weeks to term.
- Conceptus: includes the developing embryo/fetus and placental structures.
Implantation
- Occurs 8-10 days after fertilization, also known as "Nidation."
- The zygote becomes an embryo post-implantation, typically at 5-8 weeks.
- Implantation can cause spotting due to capillary rupture.
Phases of Implantation
- Apposition: blastocyst brushes against the uterine endometrium.
- Adhesion: blastocyst attaches with the help of enzymes.
- Invasion: blastocyst burrows into the endometrium.
Parts of Decidua
- Decidua basalis: underlies the embryo.
- Decidua capsularis: wraps around trophoblast.
- Decidua vera: remaining uterine lining.
Chorionic Villi
- By the 11th and 12th day, chorionic villi develop and begin forming the placenta.
- Chorionic villi contain connective tissues and capillaries, covered by a double layer of trophoblast cells.
Placenta
- Develops from trophoblast tissue; serves as fetal lungs, kidneys, and gastrointestinal tract.
- Measures approximately 10-15 centimeters and weighs 400-600 grams by term.
Placental Circulation
- Maternal blood collects in intervillous spaces by the 12th day.
- Nutrients are exchanged via osmosis; no direct blood exchange occurs.
- Optimal placental circulation occurs when the mother lies on her left side to prevent blood trapping.
Nutrient Transport Mechanisms Across the Placenta
- Diffusion: for gases and some ions.
- Facilitated diffusion: example includes glucose.
- Active transport: for essential amino acids and vitamins.
- Pinocytosis: also allows for some substances like viruses to enter.
Endocrine Functions of the Placenta
- Human Chorionic Gonadotropin (HCG): first placental hormone, maintains corpus luteum function.
- Estrogen: promotes mammary gland development and uterine growth.
- Progesterone: maintains endometrial lining and physical changes in the mother.
- Human Placenta Lactogen: regulates maternal nutrient levels for fetal growth.
Milestones of Fetal Growth Development
- End of 4th week: embryo measures 1 cm, developing spinal cord.
- End of 8th week: measures 2.5 cm, heart with valves beats.
- End of 12th week: reaches 8 cm, sex differentiation can be observed.
- End of 16th week: fetal heartbeat can be heard.
- End of 20th week: mother can feel spontaneous fetal movements.
- End of 24th week: passive antibody transfer occurs; survival rate increases.
- End of 28th week: lung alveoli mature; testes descend.
- End of 32nd week: active reflexes and continued growth.
- End of 36th week: subcutaneous fat accumulates.
- End of 40th week: average weight of 7-7.5 pounds and measures 37 cm at birth.
Additional Terminologies
- Age of Gestation: determined by the last menstrual period.
- Estimated Date of Birth (EDB) and Naegle’s Rule for calculating pregnancy duration.
- McDonald's Rule: used for symphysis-fundal height measurement.
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Description
This quiz explores the intricate process of human conception and fertilization, detailing the journey of sperm to egg and subsequent zygote development. Understand the stages from ovum penetration to implantation, as well as the formation of critical structures like the placenta and embryo. Perfect for students studying human biology and reproductive science.
