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Questions and Answers
What structure is formed by the complex of cotyledons and caruncles?
Which type of placenta retains all six layers intact?
Which type of placenta is specifically found in carnivores such as cats and dogs?
In which type of placenta does only one maternal layer remain intact?
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Which of the following species typically have a diffuse placenta?
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Which type of placenta is characterized by a band of tissue surrounding the fetus?
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What term describes the contact sites formed by the maternal tissue in placentary anatomy?
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Which of the following layers would be absent in a hemochorial placenta?
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What distinguishes viviparous animals from oviparous animals?
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Which extraembryonic membrane functions primarily in gas exchange and liquid waste collection?
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What is a primary function of the amniotic sac?
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What is the role of the chorion in embryonic development?
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Which statement accurately describes the yolk sac?
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What is the significance of the decidua in placentation?
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Which extraembryonic membrane is involved in maintaining the fetus's body temperature?
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How does the umbilical cord function in fetal development?
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What occurs during the implantation phase of mammalian embryonic development?
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What is the main characteristic of ovoviviparous animals?
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What type of implantation involves the blastocyst becoming completely cut off from the uterine lumen?
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Which type of implantation is commonly observed in rodents?
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What is histotroph commonly referred to as?
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Which of the following mammals lack a placenta?
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What term describes the vascular organ that develops inside the uterus of most pregnant mammals?
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Which of the following structures is part of fetal membranes?
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What type of placentation involves the entire surface of the allantochorion participating in the formation of the placenta?
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Which type of nutrient absorption occurs through the allantochorion?
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Study Notes
Animal Reproductive Strategies
- Oviparous: Animals that lay eggs; development occurs outside the mother's body.
- Viviparous: Animals give birth to live young; embryos develop inside the mother, typically through a placenta.
- Oviviparous: Eggs hatch inside the mother's body, resulting in live births.
Extraembryonic Membranes
- Yolk Sac: Provides nutrients early in development, disappears later.
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Allantois:
- Ventral outgrowth in reptiles, birds, and mammals.
- Vestigial in humans; contains umbilical arteries and veins.
- Functions in waste collection and gas exchange.
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Amnion/Amniotic Sac:
- Surrounds the fetus, containing amniotic fluid.
- Protects the fetus, allows movement, prevents adherence, and maintains temperature.
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Chorion:
- Outer trophoblast layer that forms the fetal part of the placenta.
- Involved in nutrient absorption, gas exchange, and hormone production.
Placenta Anatomy
- Decidua: Maternal portion rich in blood vessels, expelled at birth.
- Umbilical Cord/Urachus: Connects fetus to placenta; delivers oxygenated, nutrient-rich blood.
Embryonic Development and Implantation
- Implantation: Phase where the blastocyst embeds into the endometrium of the uterus.
- Endometrium: Inner uterine lining where implantation occurs.
Types of Implantation
- Interstitial Implantation: Blastocyst implants within the uterine wall (e.g., primates, guinea pigs).
- Centric/Superficial Implantation: Blastocyst enlarges to fill most of the uterine cavity (e.g., ungulates, carnivores).
- Eccentric Implantation: Blastocyst lodges in a fold of the uterine lumen (e.g., rodents).
Early Nutrition
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Embryotroph: Early nourishment comprising:
- Histotroph: Uterine milk for early nutrition before placenta is established.
- Hemotroph: Nutrition derived from maternal blood through allantochorion or vitellochorion.
Comparative Placentation
- Placentation: The formation, type, and structure of placentas.
- Most mammals have a placenta except monotremes (e.g., platypus) and marsupials (e.g., kangaroos).
- Placenta Functions: Supplies oxygen/nutrients, removes waste, expelled after birth.
Types of Placenta Based on Appearance
- Diffuse: Involves almost the entire placenta surface (e.g., pig, horse).
- Cotyledonary: Features discrete attachment areas called cotyledons (e.g., ruminants).
- Zonary: Forms a band of tissue around the fetus (e.g., cats, dogs).
- Discoid: A single, disc-shaped placenta (e.g., humans, mice).
Types of Placenta Based on Morphology
- Epitheliochorial: All six layers intact; no maternal tissue loss (e.g., horse, pig, cow).
- Synepitheliochorial: Five layers intact; some maternal tissue loss (e.g., sheep, goat).
- Endotheliochorial: Four layers intact; includes maternal endothelial cells (e.g., carnivores).
- Hemochorial: Only three fetal layers intact; uterine blood vessels are exposed (e.g., rodents, primates, humans).
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Description
This quiz covers extraembryonic membranes and comparative placentation in animal reproductive strategies. Explore the differences between oviparous, viviparous, and oviviparous animals. Test your understanding of these concepts and their significance in developmental anatomy.
