Learn About Human Embryology Quiz Questions

Lanugo refers to fine, downy hair. This type of hair is commonly found on the bodies of fetuses and newborn babies. It serves as insulation to help regulate their body temperature. Lanugo typically sheds and is replaced by coarser hair as the baby grows and develops.

During the fetal period, which occurs between weeks 26 and 38 of pregnancy, one of the important features is the presence of lanugo. Lanugo refers to the fine, downy hair that covers the fetus's body during this stage of development. This hair serves as insulation and helps to regulate the fetus's body temperature. It also helps to protect the delicate skin. Lanugo is usually shed before birth, but its presence during the fetal period is a normal and necessary part of development.

The correct answer is "fingertips to elbow." During the third trimester of pregnancy, the fetus grows significantly in size. By the end of this trimester, the fetus is approximately the length from the fingertips to the elbow of the mother. This measurement gives an estimate of the size of the fetus and is commonly used to track fetal growth and development.

The term "fetus" refers to the stage of development in the womb when the organs, including the lungs, become functional. Therefore, the fetus becomes "viable" when the lungs are able to support breathing and other necessary functions outside of the womb.

The given answer "Embryo" is correct because during weeks 3-8 of development, the major organs and systems of the body start to form. This includes the development of the cardiovascular system, respiratory system, digestive system, urinary system, and reproductive system. However, the nervous system develops later, starting around week 8. Therefore, the correct answer is "Embryo" as it accurately represents the stage of development during weeks 3-8, where organs and systems are developing except for the nervous system.

The embryoblast evolved into the bilaminar disc during embryonic development. The bilaminar disc is a structure that forms during the second week of development and consists of two layers - the epiblast and the hypoblast. The epiblast gives rise to the three germ layers, which eventually differentiate into various tissues and organs in the body. The hypoblast, on the other hand, contributes to the formation of extraembryonic tissues. This transformation from embryoblast to bilaminar disc is a crucial step in the early development of an embryo.

The first differentiated tissue is the endoderm, which originates from the epiblast. During embryonic development, the epiblast undergoes differentiation and gives rise to the three primary germ layers, one of which is the endoderm. The endoderm is responsible for forming the innermost layer of various organs, such as the digestive tract, respiratory system, and glands. This process is crucial for the proper development and functioning of these organs.

The primitive streak is a structure that forms during embryonic development and is responsible for the establishment of the body axis. It is formed by the thickening of the ectoderm, which is one of the three primary germ layers in the developing embryo. The ectoderm gives rise to various structures, including the nervous system, skin, and sensory organs. The thickening of the ectoderm to form the primitive streak marks the beginning of gastrulation, a crucial process in which the three germ layers are established.

The three longitudinal bands referred to in the question are paraxial, intermediate, and lateral. These bands are used to describe the different regions or zones of the body. The paraxial band is the central region, located closest to the midline of the body. The intermediate band is the region between the paraxial and lateral bands, while the lateral band is the outermost region, farthest from the midline. These bands help in categorizing and understanding the different parts or sections of the body based on their position and proximity to the midline.

The lateral mesoderm is divided into somatic and splanchnic plates. The somatic plate is located closer to the ectoderm, while the splanchnic plate is closer to the endoderm. These plates play important roles in the development of various structures in the body. The somatic plate gives rise to the dermis, connective tissues, and the musculoskeletal system of the body wall, while the splanchnic plate forms the connective tissues and smooth muscles of the viscera. This division allows for the differentiation and specialization of these tissues during embryonic development.

The neural tube is highly susceptible to teratogens. Teratogens are substances or factors that can cause abnormalities or malformations in the developing fetus. These can include drugs, alcohol, certain infections, and environmental factors. The neural tube is the embryonic structure that eventually develops into the brain and spinal cord, making it particularly vulnerable to the harmful effects of teratogens. Exposure to teratogens during the critical period of neural tube development can lead to serious birth defects and neurological disorders.

During the embryonic period, which occurs during the first 8 weeks of pregnancy, the lungs begin to develop. The process starts with the formation of the respiratory diverticulum, a small outgrowth from the foregut. This diverticulum then elongates and branches, forming the bronchial tree. By the end of the embryonic period, the basic structure of the lungs, including the bronchi, bronchioles, and alveoli, has been established. However, it is important to note that lung development continues throughout the fetal period and even after birth.

The date of ovulation occurs around 14 days after the start of menses. Ovulation is the release of an egg from the ovary, and it typically occurs in the middle of a woman's menstrual cycle. The average menstrual cycle is about 28 days long, with ovulation occurring on day 14. However, it is important to note that every woman's cycle is different, and the timing of ovulation can vary.

The given sequence of events, fertilization, cleavage, migration and implantation, and formation of the bilaminar disc, describes the early stages of embryonic development. Fertilization occurs when the sperm and egg fuse to form a zygote. Cleavage is the rapid division of the zygote into multiple cells. Migration and implantation refer to the movement of the embryo to the uterus and its attachment to the uterine wall. Finally, the formation of the bilaminar disc marks the development of two distinct layers in the embryo. Therefore, the term "pre-embryo" is an appropriate description for this stage of development before the formation of a fully developed embryo.

Embryonic tissue refers to the cells and structures that form during the early stages of development. The bilaminar disc is a specific structure that forms during embryogenesis. It consists of two layers, the epiblast and the hypoblast, which are essential for the formation of the embryo and its subsequent development. Therefore, the bilaminar disc is the only component of embryonic tissue mentioned in the question.

The notochord process "induces" the formation of the neural plate. The notochord is a flexible rod-like structure that develops in the early embryo and plays a crucial role in the formation of the nervous system. It secretes signaling molecules that instruct the overlying ectoderm to differentiate into the neural plate. The neural plate is the precursor to the central nervous system, which eventually develops into the brain and spinal cord. Therefore, the notochord process induces the formation of the neural plate, initiating the development of the nervous system.

The neural tube is a structure that develops during embryonic development and gives rise to the brain and spinal cord. It is formed through a process called neurulation, where the ectoderm layer of the embryo folds and fuses together to create a hollow tube. This tube then differentiates into the brain at one end and the spinal cord at the other. Therefore, the correct answer is that the brain and spinal cord are formed from the neural tube.

The intraembryonic coelom develops within the lateral mesoderm. The lateral mesoderm is one of the three primary germ layers that forms during embryonic development. It gives rise to various structures in the body, including the coelomic cavities. The intraembryonic coelom is a fluid-filled cavity that forms within the lateral mesoderm and eventually gives rise to the body cavities, such as the pericardial, pleural, and peritoneal cavities. Therefore, the correct answer is lateral mesoderm.

The correct answer is "spaces within the lateral mesoderm." Intraembryonic coelom refers to the cavities that form within the lateral mesoderm during embryonic development. These spaces eventually give rise to various body cavities, such as the pericardial, pleural, and peritoneal cavities. The formation of these spaces is an early indication of the development of the coelomic cavities in the embryo.

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The correct answer is "Embryo" because during the development of an organism, all of its organs and systems start forming from the embryo stage, except for the nervous system. The nervous system develops later in the process. This is a crucial stage in the development of an organism as it lays the foundation for the formation of various organs and systems that are essential for its survival and functioning.

The syncytiotrophoblast is the outer layer of the implanting blastocyst. It is formed by the fusion of multiple cells, creating a syncytium. This layer plays a crucial role in implantation and early pregnancy by facilitating the attachment of the blastocyst to the uterine wall and promoting the exchange of nutrients and waste between the embryo and the mother.

The Syncytiotrophoblast is the outer layer of the implanting blastocyst.

The neural crest is a group of cells that form during embryonic development and give rise to various structures in the body. These structures include the peripheral nervous system (PNS), which consists of nerves and ganglia. The neural crest cells also differentiate into Schwann cells, which are responsible for supporting and insulating nerve fibers in the PNS. Additionally, some neural crest cells give rise to pigment cells, which are responsible for producing melanin and giving color to the skin, hair, and eyes.

Parturition refers to the process of giving birth to offspring. The given answer, "parturition," is correct because it provides different units of time (266 days, 38 weeks, 9 months) that are commonly associated with the duration of pregnancy in humans. This suggests that the question is asking for a term related to childbirth or the act of giving birth, which is accurately represented by the term "parturition."

The paraxial mesoderm is a layer of mesoderm that is located adjacent to the notochord. During embryonic development, the notochord secretes signaling molecules that induce the formation of the paraxial mesoderm. The paraxial mesoderm then gives rise to somites, which are segmented structures that give rise to various tissues and structures in the body, including the muscles, bones, and connective tissues. Therefore, the paraxial mesoderm is closely associated with the notochord and plays a crucial role in the development of the musculoskeletal system.

There are four classes of teratogens. Teratogens are substances or agents that can cause birth defects or developmental abnormalities in an embryo or fetus. These four classes include physical agents (such as radiation or temperature extremes), infectious agents (such as viruses or bacteria), chemical agents (such as drugs or chemicals), and maternal conditions (such as poorly controlled diabetes or certain autoimmune diseases). Each class of teratogens has its own specific effects on fetal development and can pose risks at different stages of pregnancy.

During pregnancy in the US, it is common for women to be prescribed an average of 6 medications. This could be due to various factors such as pre-existing medical conditions, pregnancy-related complications, or the need for prenatal vitamins and supplements. It is important for pregnant women to follow their healthcare provider's instructions and only take medications that are deemed safe during pregnancy to ensure the well-being of both the mother and the baby.

The pre-embryonic period refers to the first two weeks of development after fertilization. During this time, the fertilized egg undergoes multiple cell divisions and forms a blastocyst. The blastocyst then implants into the uterine wall. This period is crucial for the formation of the embryo and the establishment of the placenta. Therefore, the correct answer is week 1 and week 2.

The inner cell mass is a group of cells in the blastocyst stage of embryonic development. It contains the embryoblast, which is the cluster of cells that will eventually give rise to the embryo. Therefore, the correct sequence is embryoblast first, followed by the formation of the embryo.

The outer cell mass contains the trophoblast, which is the outer layer of cells that forms the placenta. The trophoblast is responsible for implantation of the embryo into the uterine wall and the formation of the placenta, which is a vital organ during pregnancy. It facilitates the exchange of nutrients, oxygen, and waste products between the mother and the developing fetus.

The syncytiotrophoblast is proteolytic because it secretes enzymes that break down proteins. This is important for various functions during pregnancy, such as implantation of the embryo into the uterine wall and the formation of the placenta. The syncytiotrophoblast also plays a role in the exchange of nutrients and waste between the mother and the developing fetus. By being proteolytic, the syncytiotrophoblast helps to ensure proper development and support for the growing embryo.

Proteolytic refers to the process of directed degradation of proteins. This means that proteins are broken down or degraded in a controlled and specific manner. Proteolytic processes play a crucial role in various biological processes such as protein turnover, regulation of cellular functions, and elimination of damaged or misfolded proteins. Through proteolysis, proteins can be modified, activated, or inactivated, allowing for the regulation of various cellular processes.

Endometrial glands are responsible for secreting nutrients to support the developing embryo during pregnancy. These nutrients include sugars and amino acids. Sugars provide energy for the growing embryo, while amino acids are the building blocks for proteins, which are essential for the development of tissues and organs. The secretion of these nutrients by the endometrial glands ensures that the embryo has the necessary resources for proper growth and development.

Nutrients diffuse from the glands and capillaries to the developing blastocyst. This means that as the blastocyst grows and develops, it receives necessary nutrients from the glands and capillaries in its surrounding environment. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration, and in this case, it allows the blastocyst to obtain the nutrients it needs for further development.

The correct answer explains that embryonic tissue refers specifically to the bilaminar disc, which is a specific structure within the developing embryo. On the other hand, extra-embryonic tissue refers to all other tissues that are not part of the bilaminar disc. This helps to differentiate between the two types of tissue and clarifies their respective roles in embryonic development.

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During week 2 of pregnancy, the trophoblast, which is the outer layer of cells of the blastocyst, implants itself fully within the endometrium, the lining of the uterus. This process is known as implantation. As the trophoblast embeds itself, lacunae, or small spaces, are formed from the maternal glands and endometrial capillaries. These lacunae will eventually become the spaces where blood vessels will develop to support the growing embryo.

The chorionic cavity forms within the extra-embryonic tissue of the cytotrophoblast. The cytotrophoblast is a layer of cells that surrounds the embryo and gives rise to the placenta. As the embryo develops, the cytotrophoblast divides and forms a cavity called the chorionic cavity. This cavity is filled with fluid and provides a protective environment for the developing embryo.

The chorion or chorionic membrane is formed from the cytophoblast. The cytophoblast is a layer of cells that develops during embryonic development. It is responsible for the formation of the outermost layer of the embryonic membrane, known as the chorion. The chorion plays a crucial role in the development of the placenta and is involved in the exchange of nutrients and waste between the mother and the developing fetus. Therefore, the correct answer is cytophoblast.

The bilaminar disc of the pre-embryo is attached to the trophoblast by the connecting stalk. The connecting stalk is a structure that forms during embryonic development and connects the developing embryo to the trophoblast, which eventually becomes the placenta. It provides a pathway for the exchange of nutrients and waste between the embryo and the mother.

Chorionic villi are small finger-like projections that grow from the chorion, a fetal membrane, into the uterine wall. These villi increase the surface area of contact between the fetal and maternal blood vessels, allowing for efficient exchange of nutrients, oxygen, and waste products. This helps in the transfer of essential substances from the mother to the developing fetus and the removal of waste products from the fetus.

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Gastrulation is a crucial process during embryonic development where the single-layered blastula transforms into a three-layered structure. The three primary germ layers formed during gastrulation are the endoderm, ectoderm, and mesoderm. The endoderm gives rise to the lining of the digestive tract, respiratory system, and associated organs. The ectoderm develops into the nervous system, skin, and other external structures. The mesoderm forms the muscles, bones, circulatory system, and reproductive organs. These three germ layers are essential for the formation of all the tissues and organs in the developing embryo.

The primitive streak is a key structure in embryonic development. It is formed during gastrulation and serves as the site where cells migrate and differentiate to form the three germ layers. In this case, the correct answer suggests that the primitive streak grows forward from the caudal end of the embryonic disc. This means that it extends in the direction opposite to the head end of the embryo. This information is important in understanding the orientation and positioning of the primitive streak during early embryogenesis.

The prochordal plate and cloacal membrane are both structures that lack mesoderm. The prochordal plate is located at the anterior end of the embryo, and it eventually gives rise to the mouth. The cloacal membrane, on the other hand, is located at the posterior end of the embryo, and it eventually forms the anus. These structures play crucial roles in the development of the digestive system and the establishment of the body's anterior-posterior axis.

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The cardiogenic area refers to the region in the developing embryo where the heart will form. In this context, "cephalic" means towards the head end of the embryo, and "prochondral plate" refers to a structure involved in the formation of cartilage. Therefore, the correct answer suggests that the cardiogenic area is located in the mesoderm (one of the germ layers) towards the head end of the embryo, specifically in a region anterior to the prochondral plate. This indicates the specific location where the heart will begin to develop during embryogenesis.

The notochord is a defining feature of chordates and it develops from the primitive pit of the primitive knot of the primitive streak. The primitive streak is a structure that forms during early embryonic development and gives rise to the three germ layers of the embryo. The primitive knot is a thickening in the middle of the primitive streak, and the primitive pit is a depression at the anterior end of the primitive knot. The notochord plays a crucial role in the formation of the vertebrate body plan, serving as a precursor to the spinal column.

The notochordal process extends between the ectoderm and endoderm to reach the nucleus pulposus of the intervertebral disc (IVD). The notochord is an embryonic structure that serves as a precursor to the spine. During development, the notochordal process extends from the notochord to the developing IVD, where it contributes to the formation of the nucleus pulposus. The nucleus pulposus is the gel-like center of the intervertebral disc that provides cushioning and shock absorption between the vertebrae. Therefore, the notochordal process plays a crucial role in the development and structure of the nucleus pulposus of the IVD.

Neurulation is the process by which the neural plate forms, folds, and eventually closes to form the neural tube. It starts with the formation of the neural plate, which then invaginates to form the neural groove. The neural folds then elevate and fuse together, creating the neural tube. The neural crest cells, which are located at the edges of the neural folds, give rise to various cell types in the body. The neuropores are the openings at the ends of the neural tube, and they eventually close to complete the formation of the central nervous system. The rostral (head) and caudal (tail) ends of the neural tube also close during this process.

Neural plate formation refers to the process of differentiating the neuroectoderm from the ectoderm. During embryonic development, the ectoderm gives rise to various tissues, including the neuroectoderm, which eventually forms the neural plate. The neural plate is a crucial structure that eventually develops into the central nervous system. Therefore, the correct answer is the differentiation of neuroectoderm from ectoderm.

The neural tube is the structure that eventually develops into the brain and spinal cord. It is formed from three primary segments, namely the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). These segments give rise to different regions of the brain, with the prosencephalon forming the cerebrum, the mesencephalon forming the midbrain, and the rhombencephalon forming the hindbrain structures such as the cerebellum and brainstem. Therefore, the correct answer is 3 cephalic segments, referring to the three segments that form the brain from the neural tube.

During week 3 of embryonic development, the mesodermal layers, which are located on the right and left sides of the embryo, form three longitudinal bands. These bands are likely to play a crucial role in the development and organization of various structures within the embryo. The formation of these bands is a significant milestone during this stage of development, as it contributes to the overall patterning and differentiation of the embryo's tissues and organs.

The intermediate mesoderm is located between the paraxial and lateral bands. This means that it is positioned in the middle of these two structures. The paraxial and lateral bands refer to specific regions or groups of cells in the developing embryo. The intermediate mesoderm plays a crucial role in the formation of the urogenital system, including the kidneys and reproductive organs. Its positioning between the paraxial and lateral bands suggests its involvement in the coordination and development of these adjacent structures.

The formation of the intraembryonic coelom involves the splitting of the lateral mesoderm. This splitting creates two layers of lateral mesoderm, and chorionic fluid flows between these layers. This process occurs around the cephalic ends of the embryo, resulting in the formation of a horseshoe or U-shaped cavity known as the intraembryonic coelom.

During the 4th week of development, the head and tail folds, as well as the lateral folds, play a crucial role in the enclosure of the intraembryonic coelom. These folds "pinch off" the coelom, which is a fluid-filled cavity, and enclose it within the tubular body of the embryo. This process is essential for the formation and development of various organ systems within the embryo.

During the formation of the Intraembryonic Coelum, the yolk sac is separated and enclosed to form the primitive gut. Additionally, the lateral mesoderm is split into two layers.

The 5 cavities that eventually form from the intraembryonic coelom are the pericardial cavity, which surrounds the heart, and two pleural cavities and two peritoneal cavities. The pleural cavities are located in the thoracic region and house the lungs, while the peritoneal cavities are located in the abdominal region and contain the abdominal organs.

During embryonic development, the head and tail regions of the embryo undergo folding, which causes the gut to separate from the yolk sac. At the same time, the lateral folds of the embryo also fold inwards, resulting in the formation of the intraembryonic coeloms from the chorionic cavity. This process of folding and pinching off allows for the formation and separation of these structures, essential for the development of the digestive system and body cavities in the embryo.

cardiogenic area = heart
septum transversum = diaphragm
oropharyngeal membrane = mouth

cloacal membrane = anus and urethra openings
allantois = urathus
connective stark = umbilical cord

The umbilical cord is composed of various structures including extraembryonic trophoblastic tissue, remnants of the yolk sac, allantois, umbilical vessels, and a gel-like matrix. These components are essential for the transfer of nutrients, oxygen, and waste between the developing fetus and the mother. The extraembryonic trophoblastic tissue helps in the attachment of the embryo to the uterine wall, while the remnants of the yolk sac provide nourishment to the developing fetus. The allantois is involved in the formation of blood vessels, and the umbilical vessels carry blood to and from the placenta. The gel-like matrix provides protection and support to the structures within the umbilical cord.

Conception is assumed to occur at the Last Menstrual Period plus 14 days because it is based on the average length of a woman's menstrual cycle, which is typically 28 days. The assumption is that ovulation, when the egg is released and can be fertilized, occurs around day 14 of the cycle. Therefore, conception is believed to occur around this time, adding 14 days to the start of the last menstrual period.

The correct answer is "menses" because it refers to the first day of bleeding as day 1 of the menstrual cycle. This term is commonly used to describe the monthly shedding of the uterine lining in women, which typically lasts for a few days. By considering the first day of bleeding as day 1, healthcare professionals can track and monitor the duration and regularity of a woman's menstrual cycle.

Fertilization occurs on day 14 of the menstrual cycle because this is typically when ovulation occurs. Ovulation is the release of a mature egg from the ovary, and it usually happens around day 14 in a 28-day menstrual cycle. Fertilization occurs when sperm meets the released egg in the fallopian tube, and it is during this process that pregnancy can occur. Therefore, day 14 of the menstrual cycle is the most likely time for fertilization to occur.

During the Embryonic Period, the formation of various structures occurs. The trilaminar disc refers to the three germ layers (ectoderm, mesoderm, and endoderm) that develop during this stage. Somites are segments that form along the neural tube and give rise to the vertebrae and muscles. Branchial arches are structures that develop in the head region and eventually form the jaw and face. Limbs also begin to form during this period. Additionally, the resorption of the tail takes place, as the embryo transitions from having a tail to developing a more human-like form.

The correct answer is "crosses the placental blood barrier, and development abnormalities." This answer accurately describes a teratogen. A teratogen is any substance that can pass through the placental blood barrier, which is the protective barrier between the mother's blood and the fetus, and cause abnormalities in fetal development. This means that teratogens have the potential to negatively affect the growth and formation of the baby, leading to birth defects or other developmental issues.

The correct answer includes four classes of teratogens: chemicals, drugs, infectious bacteria and viruses, and radiation. Teratogens are substances or factors that can cause abnormalities or birth defects in developing embryos or fetuses. Chemicals such as alcohol, tobacco, and certain medications can have teratogenic effects. Drugs, both legal and illegal, can also be teratogens. Infectious bacteria and viruses, such as rubella or Zika virus, can harm the developing fetus. Lastly, exposure to radiation, such as X-rays or nuclear radiation, can also be teratogenic. These teratogens can have detrimental effects on the developing embryo or fetus, leading to various birth defects or developmental disorders.

The correct answer is alcohol and nicotine. Alcohol and nicotine are both known teratogens, substances that can cause birth defects or developmental abnormalities in a fetus. Alcohol consumption during pregnancy can lead to fetal alcohol syndrome, which can result in physical, behavioral, and cognitive impairments. Nicotine, found in tobacco products, can also have harmful effects on fetal development, including an increased risk of low birth weight, preterm birth, and developmental issues. It is important for pregnant individuals to avoid alcohol and nicotine to ensure the health and well-being of their unborn child.

The correct answer includes tranquilizers, antidepressants, and antibiotics. These drug classes are known to have teratogenic effects, meaning they can cause harm to a developing fetus if taken during pregnancy. Tranquilizers are used to treat anxiety and can potentially lead to birth defects. Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), have been associated with an increased risk of certain birth defects. Antibiotics, particularly those in the tetracycline and fluoroquinolone classes, can interfere with fetal bone and teeth development. It is important for pregnant women to consult with their healthcare provider before taking any medications to ensure the safety of their unborn child.

Neural tube defects are the second most common development abnormality. This refers to a group of birth defects that occur when the neural tube, which forms the baby's brain, spinal cord, and spinal column, does not close properly during early pregnancy. These defects can vary in severity, with the most common types being spina bifida and anencephaly. Spina bifida occurs when the spinal column does not close completely, while anencephaly is a condition where a major part of the brain and skull is missing. These defects can have significant implications for the baby's health and development.

Turner's Syndrome is a genetic disorder that affects females, where one of the X chromosomes is either partially or completely missing. This condition leads to various developmental abnormalities, making it the most common one. Symptoms may include short stature, infertility, heart defects, and learning disabilities. Early diagnosis and appropriate medical intervention can help manage the associated health issues and provide support for affected individuals.

The U.S. Public Health Service recommends that women of child-bearing age supplement their diet with B Vitamin, Folate, at twice the recommended daily allowance (RDA) in order to prevent Neural Tube defects. This is because Folate plays a crucial role in the development of the neural tube in a fetus, which eventually becomes the baby's brain and spinal cord. By increasing the intake of Folate, the risk of these birth defects can be significantly reduced.

During the fetal period in weeks 12-13, one of the important features is the differentiation of external genitalia. This means that the reproductive organs of the fetus start to develop and take on male or female characteristics. This is a crucial stage in the development of the baby's sexual organs and is an indicator of their biological sex.

During the fetal period, which occurs between week 14 and 16 (month 4) of pregnancy, one of the important features is that the bony skeleton becomes visible on radiography. This means that the bones of the developing fetus can be seen using imaging techniques such as X-rays. This is a significant milestone in fetal development as it indicates the growth and ossification of the skeletal system. It allows healthcare professionals to assess the progress and health of the fetus, ensuring that everything is developing as expected.

During the fetal period in weeks 21-38, important features include the presence of vernix caseosa, which is a protective substance covering the baby's skin, weight gain as the baby continues to grow and develop, and the deposition of fat in the superficial fascia, which helps to insulate and protect the baby. These features are significant for the baby's development and preparation for life outside the womb.

Vernix caseosa refers to the waxy or cheese-like white substance that covers the skin of newborn humans. This substance serves as a protective layer, providing moisture and insulation to the baby's delicate skin. It also helps in regulating the baby's body temperature and preventing dehydration. Vernix caseosa is typically present at birth but gradually diminishes over time.

The most important event during the Fetal Period is the development of viability. Viability refers to the stage of fetal development when the fetus has the potential to survive outside the womb. This typically occurs around 24-28 weeks of gestation. It is a crucial milestone as it signifies that the fetus has developed enough to have a chance of survival if born prematurely. During this period, the organs and systems continue to mature, preparing the fetus for life outside the womb.

The size of the fetus at the end of the first trimester is typically described as being approximately one hand-width or 1 hand width. This measurement is often used as a general estimate to give an idea of the size of the fetus during this stage of pregnancy. It helps to visualize the size and development of the fetus, as the hand-width measurement is something that most people can easily understand and relate to.

The correct answer is "one hand-length" or "1 hand length". This refers to the average size of a fetus at the end of the second trimester, which is typically around 10-12 inches in length. The measurement is commonly used as a reference point to estimate the size of the fetus during this stage of pregnancy.

Viability, in the context of pregnancy, refers to the point at which a fetus has the potential to survive outside of the womb. Generally, this occurs around the 26th week of pregnancy. At this stage, the fetus has developed enough that its organs and systems are capable of functioning independently. This is why the correct answer is the 26th week.

Viability refers to the ability of a fetus to survive outside the womb. The given answer of 250 nm suggests that viability typically develops when the fetus reaches a length of 250 nanometers. This length is likely a reference to a specific stage of fetal development, such as the end of the embryonic period when the fetus is transitioning into the fetal stage. However, without additional context or information, it is difficult to provide a more detailed explanation.

Each lung lobe is partitioned into independent "bronchopulmonary" segments. The term "bronchopulmonary" refers to the combination of the bronchi (the main air passages in the lungs) and the pulmonary (related to the lungs) segments. These segments are distinct and separate from each other within the lung lobes, allowing for independent functioning and distribution of air and blood supply. This partitioning helps to ensure efficient ventilation and oxygenation of the lungs.

Surfactant is a bipolar molecule that reduces the surface tension of water. Surface tension is the force that holds the surface of a liquid together and makes it behave like a stretched elastic sheet. Surfactants have a hydrophilic (water-loving) head and a hydrophobic (water-repelling) tail. When added to water, the hydrophobic tails of surfactant molecules align with each other and the hydrophilic heads face outward, reducing the surface tension. This allows the surfactant to spread across the surface of the water and interact with other substances, making it useful in various applications such as cleaning agents, emulsifiers, and foaming agents.

Surfactant is a substance that reduces the surface tension in the alveoli of the lungs, preventing them from collapsing. Without surfactant, the surface tension would be too high, causing the alveoli to collapse. This collapse would lead to a decrease in the surface area available for gas exchange, making it difficult for oxygen to enter the bloodstream and carbon dioxide to be expelled. As a result, respiration cannot occur effectively, leading to respiratory distress and potentially respiratory failure.

The yolk sac is responsible for the formation of eggs or oocytes. It is an extraembryonic membrane that is present in the early stages of embryonic development. The yolk sac provides nutrients to the developing embryo and plays a crucial role in the formation and maturation of eggs. Therefore, it is the correct answer to the given question.

At birth, females have all the eggs they will ever have already formed. However, these eggs are arrested in the prophase stage of meiosis I, not metaphase I. During prophase I, the chromosomes pair up and exchange genetic material through a process called crossing over. This ensures genetic diversity in the offspring. The eggs remain arrested in this stage until a female reaches sexual maturity and starts ovulating. Only then does meiosis I resume, and the eggs progress to metaphase I, where they are arrested until fertilization occurs.

During puberty, a female's ovaries contain approximately 5,000 immature eggs, also known as ova. These eggs are stored in fluid-filled sacs called follicles. As a girl reaches puberty, some of these eggs will start to mature and be released during her menstrual cycles, while the rest will remain dormant and gradually decrease in number over time. Therefore, the statement that "At puberty only 5,000 eggs remained" implies that all the eggs that were present in the ovaries at the onset of puberty are still present, as no eggs have been released yet.

Fimbriae refers to a fringe-like structure made of tissue located near the ovary. These fimbriae are responsible for guiding the released egg from the ovary into the Fallopian tube, where fertilization can occur.

Fertilization occurs in the ampulla of the uterine tube. The ampulla is the widest part of the uterine tube, located between the isthmus and infundibulum. It is the site where the sperm and egg meet and fuse to form a zygote. The ampulla provides an optimal environment for fertilization to occur, as it contains secretions that nourish and protect the sperm and egg. Once fertilization occurs, the zygote then travels down the uterine tube towards the uterus for implantation.

In fertilization, capacitation refers to the process in which the sperm undergoes changes that enable it to penetrate through the protective layers surrounding the egg. The acrosome, a structure located at the head of the sperm, contains enzymes that help in breaking down these protective layers. Therefore, the correct answer is that capacitation involves the acrosome penetrating through the protection layers.

The term "acrosome" refers to an organelle that forms over the front half of the head in sperm cells. This structure plays a crucial role in fertilization as it contains enzymes that are necessary for the sperm to penetrate and fertilize the egg. The acrosome allows the sperm to break down the protective layer surrounding the egg, enabling fertilization to occur.

Corona radiata refers to a layer of cells that surround the oocyte (egg) in the ovary. These cells are derived from the follicular cells of the ovary and play a crucial role in supporting and nourishing the developing oocyte. They provide essential nutrients and growth factors to the oocyte during its maturation process. Therefore, the correct answer is "follicular cells from ovary."

The zona pellucida is a structure that surrounds the oocyte (egg) in mammals. It acts as a protective layer, similar to an eggshell, providing physical support and preventing the entry of multiple sperm cells. The zona pellucida also plays a crucial role in the fertilization process, as it allows only one sperm to penetrate and fuse with the oocyte, leading to the formation of an embryo.

The pronuclei refer to the nucleus of a sperm or an egg cell. During fertilization, when the sperm and egg fuse together, each brings its own pronucleus, which eventually merge to form the zygote's nucleus. This process allows for the combination of genetic material from both parents, leading to the development of a new individual.

During the first week of development, the embryo goes through several stages. The first stage is the 2 cell stage, where the fertilized egg divides into two cells. This is followed by the 4 cell stage, where the cells continue to divide and form a four-cell structure. The next stage is the Morula, where the cells continue to divide and form a solid ball of cells. Finally, the blastocyst stage is reached, where the cells differentiate into an outer layer called the trophoblast and an inner cell mass. The blastocyst is the stage at which the embryo implants into the uterus.

Morula refers to an early stage of embryonic development. It occurs after the zygote undergoes multiple rounds of cell division, resulting in a solid ball of cells. At this stage, the embryo is not yet differentiated into specific cell types. The morula will eventually develop into a blastocyst, which consists of an outer layer of cells called the trophoblast and an inner cell mass that will give rise to the embryo proper. Therefore, the correct answer is "embryo at an early stage of embryonic development."

The blastocyst is an early stage of embryonic development in mammals. It consists of two main parts: the inner cell mass and the outer cell mass. The inner cell mass is a cluster of cells located inside the blastocyst, which will eventually develop into the embryo. The outer cell mass, also known as the trophoblast, surrounds the inner cell mass and gives rise to the placenta and other supporting structures.