Podcast
Questions and Answers
What is uterine milk primarily composed of?
What is uterine milk primarily composed of?
Which nutrient source is dominant for the conceptus during the first week after implantation?
Which nutrient source is dominant for the conceptus during the first week after implantation?
When does placental nutrition become the primary mode of nutrition?
When does placental nutrition become the primary mode of nutrition?
By the end of 8 weeks, which of the following statements is true about the fetal development?
By the end of 8 weeks, which of the following statements is true about the fetal development?
Signup and view all the answers
What significant change occurs in fetal circulation starting from week 9?
What significant change occurs in fetal circulation starting from week 9?
Signup and view all the answers
During the placental phase of nutrition, how do nutrients reach the fetal blood?
During the placental phase of nutrition, how do nutrients reach the fetal blood?
Signup and view all the answers
What is the primary function of progesterone during the early stages of pregnancy?
What is the primary function of progesterone during the early stages of pregnancy?
Signup and view all the answers
What is the study of structure in biological terms referred to?
What is the study of structure in biological terms referred to?
Signup and view all the answers
At what stage does an individual typically become known as an embryo?
At what stage does an individual typically become known as an embryo?
Signup and view all the answers
What is the main process that occurs during the preembryonic stage?
What is the main process that occurs during the preembryonic stage?
Signup and view all the answers
How long can sperm survive after ejaculation?
How long can sperm survive after ejaculation?
Signup and view all the answers
What is the significance of human chorionic gonadotropin (HCG) during early pregnancy?
What is the significance of human chorionic gonadotropin (HCG) during early pregnancy?
Signup and view all the answers
What occurs during the cleavage phase of the preembryonic stage?
What occurs during the cleavage phase of the preembryonic stage?
Signup and view all the answers
Which of the following structures is formed from the trophoblast?
Which of the following structures is formed from the trophoblast?
Signup and view all the answers
During which trimester is the embryo most sensitive to environmental factors?
During which trimester is the embryo most sensitive to environmental factors?
Signup and view all the answers
What process is initiated when a blastocyst attaches to the uterine wall?
What process is initiated when a blastocyst attaches to the uterine wall?
Signup and view all the answers
What protective role does the amniotic fluid serve during pregnancy?
What protective role does the amniotic fluid serve during pregnancy?
Signup and view all the answers
Which layer of the embryo is responsible for forming the integumentary system?
Which layer of the embryo is responsible for forming the integumentary system?
Signup and view all the answers
What structure forms the primary source of nutrition for the fetus during development?
What structure forms the primary source of nutrition for the fetus during development?
Signup and view all the answers
How many germ layers are established by the process of embryogenesis?
How many germ layers are established by the process of embryogenesis?
Signup and view all the answers
What happens to the egg during meiosis II if it is not fertilized?
What happens to the egg during meiosis II if it is not fertilized?
Signup and view all the answers
Study Notes
Fetal Development
- Fertilization and Preembryonic Stage
- The term "embryo" has varying definitions.
- Some sources define it as the fertilized egg or two-cell stage.
- Others define it as an individual being 16 days old, consisting of three primary germ layers (ectoderm, mesoderm, and endoderm).
- The preembryonic stage lasts for the first 16 days after fertilization.
Sperm Migration
- Eggs must be fertilized within 12 to 24 hours of ovulation to survive.
- Sperm must encounter the egg in the distal one-third of the uterine tube.
- The vast majority of sperm make it to the egg.
- Sperm are destroyed by vaginal acid or exit the vagina.
- Sperm fail to penetrate the cervical mucus.
- Sperm are destroyed by leukocytes in the uterus.
- Half of the sperm go up the wrong uterine tube.
- Of 300 million ejaculated sperm, about 200 reach the vicinity of the egg.
Fertilization 1
- Sperm are viable for up to 6-7 days after ejaculation.
- Optimal fertilization occurs when sperm are deposited a few days before ovulation to 14 hours after ovulation.
- When sperm encounters an egg, it releases enzymes to penetrate the egg.
- Sperm penetrate granulosa cells, then the zona pellucida.
Fertilization 2
- Fertilization combines the haploid (n) set of sperm chromosomes with the haploid set of egg chromosomes to create a diploid (2n) set.
- Two mechanisms prevent polyspermy (multiple sperm fertilizing one egg):
- Fast block: Sperm binding opens Na+ channels in the egg membrane.
- Slow block: Involves secretory vesicles and cortical granules just beneath the egg membrane.
Meiosis II
- The secondary oocyte begins meiosis II before ovulation but completes it only if fertilized.
- Through the formation of the second polar body, the egg discards one chromatid from each chromosome.
- Sperm and egg nuclei swell and become pronuclei.
- Each pronucleus ruptures, and the chromosomes of the two gametes mix into one single diploid set.
- The fertilized egg, now called a zygote, is ready for its first mitotic division.
Major Stages of Prenatal Development 1
- Pregnancy is divided into three-month intervals (trimesters).
- First trimester: From fertilization through 12 weeks.
- Over half of embryos die during the first trimester due to natural causes.
- The conceptus is susceptible to various factors like stress, drugs, and nutritional deficiencies during this time.
Major Stages of Prenatal Development 2
- Second trimester (weeks 13-24): Organs complete most of their development.
- The fetus takes on a more human appearance.
- Survival chance increases near the end of the trimester (if born early, with intensive care).
- Third trimester (weeks 25-birth): Rapid fetal growth, organ maturation for life outside the womb.
- Maturity is considered at 35 weeks and 5.5 lbs.
The Preembryonic Stage 1
- The preembryonic stage is the first stage of development, culminating in the existence of an embryo.
- It involves three major processes: cleavage, implantation, and embryogenesis.
The Preembryonic Stage 2
- Mitotic divisions occur in the first three days as the conceptus migrates through the uterine tube.
- First cleavage within 30 hours after fertilization.
- Zygote divides into two daughter cells (blastomeres).
- By the time the conceptus reaches the uterus, about 72 hours after ovulation, it has formed a morula (solid ball of 16 cells resembling a mulberry).
- Morula remains smaller than the original zygote.
- Cleavage produces smaller and smaller blastomeres.
The Preembryonic Stage 3
- The preembryo lies free in the uterine cavity for 4-5 days.
- The preembryo divides into about 100 cells.
- The zona pellucida disintegrates, releasing the conceptus, which becomes a blastocyst.
- Blastocyst is a hollow sphere.
- Trophoblast: Outer layer of squamous cells, destined to form the placenta.
- Embryoblast: Inner cell mass, destined to become the embryo.
The Preembryonic Stage 4
- Ovulation: Egg releases from the ovary.
- Fertilization: Sperm unites with egg.
- Implantation: Process of attaching blastocyst to uterine wall; begins when blastocyst adheres to the endometrium.
- Embryogenesis: Arrangement of blastomeres into three primary germ layers (ectoderm, mesoderm, endoderm) in the embryoblast.
The Preembryonic Stage 5
- Trophoblast secretes human chorionic gonadotropin (hCG), which stimulates the corpus luteum to sustain estrogen and progesterone secretion.
- Progesterone suppresses menstruation.
- hCG levels rise in the mother's blood.
- Trophoblast develops into the membrane called the chorion.
- Chorion takes over the corpus luteum's function, and the ovaries become inactive for the rest of the pregnancy.
- Estrogen and progesterone levels rise from the chorion.
The Embryonic and Fetal Stages
- Embryonic stage: Begins when all three primary germ layers are present (usually around day 16).
- Placenta: Forms over the next 6 weeks, becomes the embryo's primary source of nutrition.
- Germ layers differentiate into organs and organ systems.
- Organs are present (but not fully functional) at 8 weeks, when the embryo becomes a fetus.
Embryonic Folding and Organogenesis 1
- Flat embryonic disc transforms into a cylindrical form.
- Embryo rapidly grows and folds around a membrane known as a yolk sac.
- Embryo has a C-shape; its head and tail almost touch.
- Lateral margins of the disc fold around the yolk sac's sides, forming the ventral surface of the embryo.
Embryonic Folding and Organogenesis 2
- Embryonic folding results in the entire surface being covered in ectoderm, which develops into epidermis.
- Mesoderm splits into two layers: One layer adheres to the ectoderm and the other to the endoderm; a body cavity forms between the layers.
Embryonic Folding and Organogenesis 3
- Formation of organs from primary germ layers.
- At eight weeks, all organs are present in the fetus (3 cm long).
- Derivatives of ectoderm: epidermis, nervous system, lens, cornea, integumentary glands, internal ear.
- Derivatives of mesoderm: skeleton, muscle, cartilage, blood, dermis, lymphatic tissue, gonads, and ducts (kidneys, ureters).
- Derivatives of endoderm: gut and respiratory epithelium, glands, bladder, urethra.
Embryonic Membranes 1
- Accessory organs develop with the embryo: placenta, umbilical cord, amnion, yolk sac, allantois, chorion.
- Amnion: Encloses the embryo, filled with amniotic fluid to protect the embryo from trauma, infections, and temperature fluctuations.
- Amniotic fluid also supports muscle development by allowing the embryo leeway for movement.
Embryonic Membranes 2
- Amniotic fluid enables symmetrical development, prevents body parts from adhering to each other, promotes lung development.
- Amniotic fluid originates from the mother's blood plasma.
- Fetus contributes to amniotic fluid volume by swallowing it and by filling the amniotic cavity.
- At full term, the fetus has about 700 to 1,000 ml of amniotic fluid.
Prenatal Nutrition 1
- During gestation, the conceptus is nourished in three ways: uterine milk, trophoblastic nutrition, and placental nutrition.
- Uterine milk: Glycogen-rich secretion from uterine tubes and endometrial glands, absorbed by the conceptus as it travels down the tube and lies free in the uterine cavity.
Prenatal Nutrition 2
- Endometrium: Progesterone from the corpus luteum stimulates decidual cells to proliferate; they accumulate glycogen, proteins, and lipids.
- Conceptus burrows into the endometrium; decidual cells are digested.
- Uterine milk, as dominant nutrition source during the first week post-implantation.
- Dominant source of nutrition for the first 8 weeks; wanes as placental nutrition increases.
Prenatal Nutrition 3
- Placental nutrition: Nutrients diffuse from the mother's blood through the placenta into the fetal blood.
- Placenta: Disc-shaped organ attached to the uterine wall on one side and the umbilical cord on the other.
- Placental phase: Mode of nutrition beginning at week 9 until birth.
Fetal Development 1
- By eight weeks, the fetus is about 3 cm long.
- Bones have started calcification.
- Skeletal muscles show spontaneous contractions.
- Heart, beating since week four, now circulates blood.
- The heart and liver are significant, forming the ventral bulge.
- The head is nearly half the total body length.
Fetal Development 2
- Images of a fetus at various developmental stages, labeled with Carnegie stages.
Fetal Development 3
- Fetus is the final stage of prenatal development (from week 9 until birth).
- Organs mature to support life outside of the mother.
- Unique aspects of fetal circulation: presence of three circulatory shortcuts (shunts).
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on fetal development and the fertilization process with this quiz. Understand key stages such as the preembryonic stage and the migration of sperm. Explore definitions and facts related to successful fertilization and the journey of sperm to the egg.
