Module 28: Development and Inheritance

Lesson 5: Childbirth

Sinh Con

Nội dung bài học:
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.
Childbirth, or parturition, typically occurs within a week of the due date, unless the pregnancy involves more than one fetus, which usually causes labor to begin early. As a pregnancy progresses into its final weeks, several physiological changes occur in response to hormones that trigger labor.

First, recall that progesterone inhibits uterine contractions throughout the first several months of pregnancy. As the pregnancy enters its seventh month, progesterone levels plateau and then drop. Estrogen levels, however, continue to rise in the maternal circulation (Figure 1). The increasing ratio of estrogen to progesterone makes the myometrium (the uterine smooth muscle) more sensitive to stimuli that promote contractions (because progesterone no longer inhibits them). Moreover, in the eighth month of pregnancy, fetal cortisol rises, which boosts estrogen secretion by the placenta and further overpowers the uterine-calming effects of progesterone. Some people may feel the result of the decreasing levels of progesterone in late pregnancy as weak and irregular peristaltic Braxton Hicks contractions, also called false labor. These contractions can often be relieved with rest or hydration.

A common sign that labor will be short is the so-called “bloody show.” During pregnancy, a plug of mucus accumulates in the cervical canal, blocking the entrance to the uterus. Approximately 1–2 days prior to the onset of true labor, this plug loosens and is expelled, along with a small amount of blood.

Meanwhile, the posterior pituitary has been boosting its secretion of oxytocin, a hormone that stimulates the contractions of labor. At the same time, the myometrium increases its sensitivity to oxytocin by expressing more receptors for this hormone. As labor nears, oxytocin begins to stimulate stronger, more painful uterine contractions, which—in a positive feedback loop—stimulate the secretion of prostaglandins from fetal membranes. Like oxytocin, prostaglandins also enhance uterine contractile strength. The fetal pituitary also secretes oxytocin, which increases prostaglandins even further. Given the importance of oxytocin and prostaglandins to the initiation and maintenance of labor, it is not surprising that, when a pregnancy is not progressing to labor and needs to be induced, a pharmaceutical version of these compounds (called pitocin) is administered by intravenous drip.

Finally, stretching of the myometrium and cervix by a full-term fetus in the vertex (head-down) position is regarded as a stimulant to uterine contractions. The sum of these changes initiates the regular contractions known as true labor, which become more powerful and more frequent with time. The pain of labor is attributed to myometrial hypoxia during uterine contractions.

The process of childbirth can be divided into three stages: cervical dilation, expulsion of the newborn, and afterbirth (Figure 2).
For vaginal birth to occur, the cervix must dilate fully to 10 cm in diameter—wide enough to deliver the newborn’s head. The dilation stage is the longest stage of labor and typically takes 6–12 hours. However, it varies widely and may take minutes, hours, or days, depending in part on whether the person has given birth before; in each subsequent labor, this stage tends to be shorter.

True labor progresses in a positive feedback loop in which uterine contractions stretch the cervix, causing it to dilate and efface, or become thinner. Cervical stretching induces reflexive uterine contractions that dilate and efface the cervix further. In addition, cervical dilation boosts oxytocin secretion from the pituitary, which in turn triggers more powerful uterine contractions. When labor begins, uterine contractions may occur only every 3–30 minutes and last only 20–40 seconds; however, by the end of this stage, contractions may occur as frequently as every 1.5–2 minutes and last for a full minute.

Each contraction sharply reduces oxygenated blood flow to the fetus. For this reason, it is critical that a period of relaxation occur after each contraction. Fetal distress, measured as a sustained decrease or increase in the fetal heart rate, can result from severe contractions that are too powerful or lengthy for oxygenated blood to be restored to the fetus. Such a situation can be cause for an emergency birth with vacuum, forceps, or surgically by Caesarian section.

The amniotic membranes rupture before the onset of labor in about 12 percent of people; they typically rupture at the end of the dilation stage in response to excessive pressure from the fetal head entering the birth canal.
The expulsion stage begins when the fetal head enters the birth canal and ends with birth of the newborn. It typically takes up to 2 hours, but it can last longer or be completed in minutes, depending in part on the orientation of the fetus. The vertex presentation known as the occiput anterior vertex is the most common presentation and is associated with the greatest ease of vaginal birth. The fetus faces the maternal spinal cord and the smallest part of the head (the posterior aspect called the occiput) exits the birth canal first.

In fewer than 5 percent of births, the infant is oriented in the breech presentation, or buttocks down. In a complete breech, both legs are crossed and oriented downward. In a frank breech presentation, the legs are oriented upward. Before the 1960s, it was common for breech presentations to be delivered vaginally. Today, most breech births are accomplished by Caesarian section.

Vaginal birth is associated with significant stretching of the vaginal canal, the cervix, and the perineum. Until recent decades, it was routine procedure for an obstetrician to numb the perineum and perform an episiotomy, an incision in the posterior vaginal wall and perineum. The perineum is now more commonly allowed to tear on its own during birth. Both an episiotomy and a perineal tear need to be sutured shortly after birth to ensure optimal healing. Although suturing the jagged edges of a perineal tear may be more difficult than suturing an episiotomy, tears heal more quickly, are less painful, and are associated with less damage to the muscles around the vagina and rectum.

Upon birth of the newborn’s head, an obstetrician will aspirate mucus from the mouth and nose before the newborn’s first breath. Once the head is birthed, the rest of the body usually follows quickly. The umbilical cord is then double-clamped, and a cut is made between the clamps. This completes the second stage of childbirth.
The delivery of the placenta and associated membranes, commonly referred to as the afterbirth, marks the final stage of childbirth. After expulsion of the newborn, the myometrium continues to contract. This movement shears the placenta from the back of the uterine wall. It is then easily delivered through the vagina. Continued uterine contractions then reduce blood loss from the site of the placenta. Delivery of the placenta marks the beginning of the postpartum period—the period of approximately 6 weeks immediately following childbirth during which the body gradually returns to a non-pregnant state. If the placenta does not birth spontaneously within approximately 30 minutes, it is considered retained, and the obstetrician may attempt manual removal. If this is not successful, surgery may be required.

It is important that the obstetrician examines the expelled placenta and fetal membranes to ensure that they are intact. If fragments of the placenta remain in the uterus, they can cause postpartum hemorrhage. Uterine contractions continue for several hours after birth to return the uterus to its pre-pregnancy size in a process called involution, which also allows the abdominal organs to return to their pre-pregnancy locations. Breastfeeding facilitates this process.

Although postpartum uterine contractions limit blood loss from the detachment of the placenta, the person who has recently given birth does experience a postpartum vaginal discharge called lochia. This is made up of uterine lining cells, erythrocytes, leukocytes, and other debris. Thick, dark, lochia rubra (red lochia) typically continues for 2–3 days, and is replaced by lochia serosa, a thinner, pinkish form that continues until about the tenth postpartum day. After this period, a scant, creamy, or watery discharge called lochia alba (white lochia) may continue for another 1–2 weeks.

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.

A positive feedback loop of hormones works to initiate labor.

The stages of childbirth include Stage 1, early cervical dilation; Stage 2, full dilation and expulsion of the newborn; and Stage 3, delivery of the placenta and associated fetal membranes. (The position of the newborn’s shoulder is described relative to the person giving birth.)

Nội dung này đang được cập nhật.
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. Childbirth unfolds through distinct stages, each marked by specific changes in the body.
  2. Initially, hormones in late pregnancy prepare the uterus for labor by making it more sensitive to contractions.
  3. This transition, often accompanied by irregular contractions known as Braxton Hicks, indicates the beginning of true labor.
  4. As labor continues, oxytocin and prostaglandins increase contractions, while the cervix dilates due to reflexive responses and hormonal changes.
  5. During the expulsion stage of childbirth, the baby emerges from the birth canal, a process that may vary depending on factors such as the baby’s position and size.
  6. In cases where the baby is in a breech position or there are other complications, alternative delivery methods such as cesarean section may be necessary to ensure the safety of both the baby and the mother.
  7. Following the birth of the baby, the placenta and membranes are expelled from the uterus, completing the birthing process.
  8. This initiates the postpartum period, during which the uterus undergoes involution, gradually returning to its pre-pregnancy size.
  9. Additionally, lochia, a vaginal discharge consisting of blood, mucus, and uterine tissue, is expelled as the uterus sheds its lining.
  10. It typically lasts for several weeks as the body recovers from childbirth.
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