What is conception?
Conception is when two gametes (sperm and ovum), each containing 23 chromosomes, combine to create a new individual.
What are gametes?
Gametes are reproductive cells, specifically sperm and ova, and each contains 23 chromosomes.
What is a zygote?
A zygote is the initial cell formed at conception, which starts to duplicate and divide within hours.
What is the typical length of a woman’s reproductive cycle?
A woman’s cycle is typically 28-32 days long, with ovulation generally occurring between days 11 and 21. An egg is viable for 12-24 hours after its release.
How long does a full-term pregnancy last?
Full-term pregnancies last 266 days (38 weeks or 9 months) from conception, or 40 weeks if measured from the last menstrual period (LMP). It is important to note that only about 5% of babies are born on their exact due date.
What are the three main periods of prenatal growth?
The three main periods are the Germinal Period, the Embryonic Period, and the Fetal Period.
What key developments occur during the germinal period?
This period is characterized by rapid cell division and differentiation. The placenta develops, and implantation occurs around 10 days after conception. The organism grows rapidly during this time.
What is the vulnerability of the zygote during the germinal period?
Approximately 60% of zygotes do not grow or implant properly and therefore do not survive this period.
What are the major developments during the embryonic period?
During this period, the basic forms of all body structures develop. The primitive streak forms the neural tube, which becomes the brain and spine of the central nervous system. The head takes shape, and the eyes, ears, nose, and mouth begin to form. The heart starts to pulsate, and extremities develop, with webbed fingers and toes separating. The embryo begins to move spontaneously as nerves and muscles connect to the brain. External sex organs start to form, though sex is difficult to distinguish. Intestines move into the body cavity, and cartilage begins to turn into bone, making the body evenly rounded.
What is the vulnerability during the embryonic period?
About 20% of embryos are spontaneously aborted, typically due to chromosomal abnormality.
What characterizes the fetal period?
The fetus grows significantly in size and matures in functioning.
What key developments occur during the fetal period?
Genitals form, and sex hormones lead to brain organization differences. The heartbeat can be detected via a stethoscope. Although the brain is the biggest part of the baby, the cortex is not fully mature at birth. Growth follows cephalocaudal (head to feet) and proximodistal (center to extremities) patterns.
What happens during the middle three months (Trimester 2) of the fetal period?
The digestive and excretory systems develop, and fingernails, toenails, teeth buds, and hair form. The brain experiences rapid growth, neurogenesis, and synaptogenesis, and it begins to regulate basic bodily functions.
What happens during the final three months (Trimester 3) of the fetal period?
Lungs expand and contract, heart valves, arteries, and veins mature, and extensive growth and folding of the cortex occur.
What is the vulnerability during the fetal period?
Approximately 5% of fetuses are spontaneously aborted before viability (22 weeks) or are stillborn (born dead after 22 weeks).
What is the overall survival rate from zygote to newborn?
Only about 31% of all zygotes become newborns.
What are teratogens?
Teratogens are agents or conditions, such as viruses or drugs, that can cause birth defects or complications.
What are behavioral teratogens?
Behavioral teratogens specifically harm the prenatal brain, potentially leading to impaired intellectual and emotional functioning.
What factors influence the risk of teratogen effects?
The impact depends on several factors: Critical Time, Dose and/or Frequency (Threshold Effect), and Innate Vulnerability (Genetic Vulnerability).
Can you provide examples of specific teratogen effects?
Orofacial Clefts (Cleft Palate/Lip): Risk factors include mothers who smoke, have diabetes, or take certain medications. Fetal Alcohol Syndrome (FAS): This can develop from heavy alcohol consumption and is often more apparent when mothers are poorly nourished and smoke cigarettes.
How can prenatal diagnosis help?
Early care and recognition of complications can increase the chance of a healthy birth.
When are birth complications more likely?
Birth complications are more likely when a fetus is at risk.
What is Cerebral Palsy and what is it linked to?
Cerebral Palsy is a congenital disorder affecting movement, muscle tone, or posture, often linked to anoxia-related damage.
