Module 28: Development and Inheritance

Lesson 3: Fetal Development

Phát Triển Thai

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module Development and Inheritance.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: Development and Inheritance

acrosomal reaction
release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization
acrosome
cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte
afterbirth
third stage of childbirth in which the placenta and associated fetal membranes are expelled
allantois
finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder
allele
alternative forms of a gene that occupy a specific locus on a specific gene
amnion
transparent membranous sac that encloses the developing fetus and fills with amniotic fluid
amniotic cavity
cavity that opens up between the inner cell mass and the trophoblast; develops into amnion
autosomal chromosome
in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)
autosomal dominant
pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
autosomal recessive
pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
blastocoel
fluid-filled cavity of the blastocyst
blastocyst
term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta
blastomere
daughter cell of a cleavage
Braxton Hicks contractions
weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent
brown adipose tissue
highly vascularized fat tissue that is packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat
capacitation
process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers
carrier
heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to their offspring
chorion
membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi
chorionic membrane
precursor to the chorion; forms from extra-embryonic mesoderm cells
chorionic villi
projections of the chorionic membrane that burrow into the endometrium and develop into the placenta
cleavage
form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells
codominance
pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles
colostrum
thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins
conceptus
pre-implantation stage of a fertilized egg and its associated membranes
corona radiata
in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur
cortical reaction
following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy
dilation
first stage of childbirth, involving an increase in cervical diameter
dominant
describes a trait that is expressed both in homozygous and heterozygous form
dominant lethal
inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span
ductus arteriosus
shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta
ductus venosus
shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
ectoderm
primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails
ectopic pregnancy
implantation of an embryo outside of the uterus
embryo
developing human during weeks 3–8
embryonic folding
process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder
endoderm
primary germ layer that goes on to form the gastrointestinal tract, liver, pancreas, and lungs
epiblast
upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers
episiotomy
incision made in the posterior vaginal wall and perineum that facilitates vaginal birth
expulsion
second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth
fertilization
unification of genetic material from male and female haploid gametes
fertilization membrane
impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy
fetus
developing human during the time from the end of the embryonic period (week 9) to birth
foramen ovale
shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit
foremilk
watery, translucent breast milk that is secreted first during a feeding and is rich in lactose and protein; quenches the infant’s thirst
gastrulation
process of cell migration and differentiation into three primary germ layers following cleavage and implantation
genotype
complete genetic makeup of an individual
gestation
in human development, the period required for embryonic and fetal development in utero; pregnancy
heterozygous
having two different alleles for a given gene
hindmilk
opaque, creamy breast milk delivered toward the end of a feeding; rich in fat; satisfies the infant’s appetite
homozygous
having two identical alleles for a given gene
human chorionic gonadotropin (hCG)
hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo
hypoblast
lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac
implantation
process by which a blastocyst embeds itself in the uterine endometrium
incomplete dominance
pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes
inner cell mass
cluster of cells within the blastocyst that is fated to become the embryo
involution
postpartum shrinkage of the uterus back to its pre-pregnancy volume
karyotype
systematic arrangement of images of chromosomes into homologous pairs
lactation
process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple
lanugo
silk-like hairs that coat the fetus; shed later in fetal development
let-down reflex
release of milk from the alveoli triggered by infant suckling
lightening
descent of the fetus lower into the pelvis in late pregnancy; also called “dropping”
lochia
postpartum vaginal discharge that begins as blood and ends as a whitish discharge; the end of lochia signals that the site of placental attachment has healed
meconium
fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile
mesoderm
primary germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys
morula
tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself
mutation
change in the nucleotide sequence of DNA
neural fold
elevated edge of the neural groove
neural plate
thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue
neural tube
precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium
neurulation
embryonic process that establishes the central nervous system
nonshivering thermogenesis
process of breaking down brown adipose tissue to produce heat in the absence of a shivering response
notochord
rod-shaped, mesoderm-derived structure that provides support for growing fetus
organogenesis
development of the rudimentary structures of all of an embryo’s organs from the germ layers
parturition
childbirth
phenotype
physical or biochemical manifestation of the genotype; expression of the alleles
placenta
organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus
placenta previa
low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows
placentation
formation of the placenta; complete by weeks 14–16 of pregnancy
polyspermy
penetration of an oocyte by more than one sperm
primitive streak
indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation
prolactin
pituitary hormone that establishes and maintains the supply of breast milk; also important for the mobilization of maternal micronutrients for breast milk
Punnett square
grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype
quickening
fetal movements that are strong enough to be felt by the mother
recessive
describes a trait that is only expressed in homozygous form and is masked in heterozygous form
recessive lethal
inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span
sex chromosomes
pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes
shunt
circulatory shortcut that diverts the flow of blood from one region to another
somite
one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo
syncytiotrophoblast
superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall
trait
variation of an expressed characteristic
trimester
division of the duration of a pregnancy into three 3-month terms
trophoblast
fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes
true labor
regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time
umbilical cord
connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother
vernix caseosa
waxy, cheese-like substance that protects the delicate fetal skin until birth
X-linked
pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair
X-linked dominant
pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair
X-linked recessive
pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair
yolk sac
membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure
zona pellucida
thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur
zygote
fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines
Nội dung này đang được cập nhật.
Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
As you will recall, a developing human is called a fetus from the ninth week of gestation until birth. This 30-week period of development is marked by continued cell growth and differentiation, which fully develop the structures and functions of the immature organ systems formed during the embryonic period. The completion of fetal development results in a newborn who, although still immature in many ways, is capable of survival outside the womb.
Sexual differentiation does not begin until the fetal period, during weeks 9–12. Embryonic males and females, though genetically distinguishable, are morphologically identical (Figure 1). Bipotential gonads, or gonads that can develop into male or female sexual organs, are connected to a central cavity called the cloaca via Müllerian ducts and Wolffian ducts. (The cloaca is an extension of the primitive gut.) Several events lead to sexual differentiation during this period.

During male fetal development, the bipotential gonads become the testes and associated epididymis. The Müllerian ducts degenerate. The Wolffian ducts become the vas deferens, and the cloaca becomes the urethra and rectum.

During female fetal development, the bipotential gonads develop into ovaries. The Wolffian ducts degenerate. The Müllerian ducts become the uterine tubes and uterus, and the cloaca divides and develops into a vagina, a urethra, and a rectum.
During prenatal development, the fetal circulatory system is integrated with the placenta via the umbilical cord so that the fetus receives both oxygen and nutrients from the placenta. However, after childbirth, the umbilical cord is severed, and the newborn’s circulatory system must be reconfigured. When the heart first forms in the embryo, it exists as two parallel tubes derived from mesoderm and lined with endothelium, which then fuse together. As the embryo develops into a fetus, the tube-shaped heart folds and further differentiates into the four chambers present in a mature heart. Unlike a mature cardiovascular system, however, the fetal cardiovascular system also includes circulatory shortcuts, or shunts. A shunt is an anatomical (or sometimes surgical) diversion that allows blood flow to bypass immature organs such as the lungs and liver until childbirth.

The placenta provides the fetus with necessary oxygen and nutrients via the umbilical vein. (Remember that veins carry blood toward the heart. In this case, the blood flowing to the fetal heart is oxygenated because it comes from the placenta. The respiratory system is immature and cannot yet oxygenate blood on its own.) From the umbilical vein, the oxygenated blood flows toward the inferior vena cava, all but bypassing the immature liver, via the ductus venosus shunt (Figure 2). The liver receives just a trickle of blood, which is all that it needs in its immature, semifunctional state. Blood flows from the inferior vena cava to the right atrium, mixing with fetal venous blood along the way.

Although the fetal liver is semifunctional, the fetal lungs are nonfunctional. The fetal circulation therefore bypasses the lungs by shifting some of the blood through the foramen ovale, a shunt that directly connects the right and left atria and avoids the pulmonary trunk altogether. Most of the rest of the blood is pumped to the right ventricle, and from there, into the pulmonary trunk, which splits into pulmonary arteries. However, a shunt within the pulmonary artery, the ductus arteriosus, diverts a portion of this blood into the aorta. This ensures that only a small volume of oxygenated blood passes through the immature pulmonary circuit, which has only minor metabolic requirements. Blood vessels of uninflated lungs have high resistance to flow, a condition that encourages blood to flow to the aorta, which presents much lower resistance. The oxygenated blood moves through the foramen ovale into the left atrium, where it mixes with the now deoxygenated blood returning from the pulmonary circuit. This blood then moves into the left ventricle, where it is pumped into the aorta. Some of this blood moves through the coronary arteries into the myocardium, and some moves through the carotid arteries to the brain.

The descending aorta carries partially oxygenated and partially deoxygenated blood into the lower regions of the body. It eventually passes into the umbilical arteries through branches of the internal iliac arteries. The deoxygenated blood collects waste as it circulates through the fetal body and returns to the umbilical cord. Thus, the two umbilical arteries carry blood low in oxygen and high in carbon dioxide and fetal wastes. This blood is filtered through the placenta, where wastes diffuse into the maternal circulation. Oxygen and nutrients from the pregnant person diffuse into the placenta and from there into the fetal blood, and the process repeats.
During weeks 9–12 of fetal development, the brain continues to expand, the body elongates, and ossification continues. Fetal movements are frequent during this period, but are jerky and not well-controlled. The bone marrow begins to take over the process of erythrocyte production—a task that the liver performed during the embryonic period. The liver now secretes bile. The fetus circulates amniotic fluid by swallowing it and producing urine. The eyes are well-developed by this stage, but the eyelids are fused shut. The fingers and toes begin to develop nails. By the end of week 12, the fetus measures approximately 9 cm (3.5 in) from crown to rump.

Weeks 13–16 are marked by sensory organ development. The eyes move closer together; blinking motions begin, although the eyes remain sealed shut. The lips exhibit sucking motions. The ears move upward and lie flatter against the head. The scalp begins to grow hair. The excretory system is also developing: the kidneys are well-formed, and meconium, or fetal feces, begins to accumulate in the intestines. Meconium consists of ingested amniotic fluid, cellular debris, mucus, and bile.

During approximately weeks 16–20, as the fetus grows and limb movements become more powerful, the pregnant person may begin to feel quickening, or fetal movements. However, space restrictions limit these movements and typically force the growing fetus into the “fetal position,” with the arms crossed and the legs bent at the knees. Sebaceous glands coat the skin with a waxy, protective substance called vernix caseosa that protects and moisturizes the skin and may provide lubrication during childbirth. A silky hair called lanugo also covers the skin during weeks 17–20, but it is shed as the fetus continues to grow. Extremely premature infants sometimes exhibit residual lanugo.

Developmental weeks 21–30 are characterized by rapid weight gain, which is important for maintaining a stable body temperature after birth. The bone marrow completely takes over erythrocyte synthesis, and the axons of the spinal cord begin to be myelinated, or coated in the electrically insulating glial cell sheaths that are necessary for efficient nervous system functioning. (The process of myelination is not completed until adolescence.) During this period, the fetus grows eyelashes. The eyelids are no longer fused and can be opened and closed. The lungs begin producing surfactant, a substance that reduces surface tension in the lungs and assists proper lung expansion after birth. Inadequate surfactant production in premature newborns may result in respiratory distress syndrome, and as a result, the newborn may require surfactant replacement therapy, supplemental oxygen, or maintenance in a continuous positive airway pressure (CPAP) chamber during their first days or weeks of life. In male fetuses, the testes descend into the scrotum near the end of this period. The fetus at 30 weeks measures 28 cm (11 in) from crown to rump and exhibits the approximate body proportions of a full-term newborn, but still is much leaner.

The fetus continues to lay down subcutaneous fat from week 31 until birth. The added fat fills out the hypodermis, and the skin transitions from red and wrinkled to soft and pink. Lanugo is shed, and the nails grow to the tips of the fingers and toes. Immediately before birth, the average crown-to-rump length is 35.5–40.5 cm (14–16 in), and the fetus weighs approximately 2.5–4 kg (5.5–8.8 lbs). Once born, the newborn is no longer confined to the fetal position, so subsequent measurements are made from head-to-toe instead of from crown-to-rump. At birth, the average length is approximately 51 cm (20 in).

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

Differentiation of the male and female reproductive systems does not occur until the fetal period of development.

The fetal circulatory system includes three shunts to divert blood from undeveloped and partially functioning organs, as well as blood supply to and from the placenta.

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. The fetal period lasts from the ninth week of development until birth.
  2. During this period, male and female gonads differentiate.
  3. The fetal circulatory system becomes much more specialized and efficient than its embryonic counterpart.
  4. It includes three shunts—the ductus venosus, the foramen ovale, and the ductus arteriosus.
  5. These shunts enable the circulation to bypass the semifunctional liver and pulmonary circuit until after childbirth.
  6. The brain continues to grow and its structures differentiate.
  7. Facial features develop, the body elongates, and the skeleton ossifies.
  8. In the womb, the developing fetus moves, blinks, practices sucking, and circulates amniotic fluid.
  9. The fetus grows from an embryo measuring approximately 3.3 centimeters and weighing 7 gram to an infant measuring approximately 51 centimeters and weighing an average of approximately 3.4 kilograms.
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