Human Development, Gestation, Genetics, and Meiosis

Comprehensive practice flashcards covering gestation, embryonic and fetal development, hormones of pregnancy, heredity, genetics, and meiosis.

What is gestation?

The period of development that begins with the fertilization of an ovum and ends at childbirth.

What is Obstetrics (Ob)?

The care of women during pregnancy and during the $6\,\text{weeks}$ after birth.

How are the three trimesters of pregnancy divided?

The $1\text{st}$ trimester is the first $3\,\text{months}$, the $2\text{nd}$ trimester is months $4\text{--}6$, and the $3\text{rd}$ trimester is month $7$ to birth.

Where does fertilization occur, and what is formed when the sperm and egg combine?

Fertilization occurs in the uterine tube when the nuclei of the sperm and egg combine to form a zygote with $46$ chromosomes ($23$ from mom and $23$ from dad).

What is a morula and how does it develop into a blastocyst?

A morula is a rapidly dividing ball of identical cells formed while traveling to the uterine cavity; before reaching the uterus, it becomes a blastocyst, which is a partially hollow structure.

What occurs during implantation?

The blastocyst burrows into the thick uterine lining until it is completely covered.

What are the functions of the inner mass and trophoblasts of a blastocyst?

The inner mass is a group of cells within the blastocyst that becomes the embryo, while the trophoblasts are the remaining cells that become tissue supporting the developing offspring.

How are the terms embryo and fetus distinguished during development?

An embryo is the growing offspring in early gestation, while a fetus is the growing offspring after the $1\text{st}$ trimester.

What is the placenta and what functions does it perform during gestation?

The placenta consists of maternal and embryonic tissue and serves as the organ of nutrition, respiration, and excretion during gestation.

What blood vessels are contained within the umbilical cord?

The umbilical cord contains $2$ arteries and $1$ vein.

What is the purpose of fetal circulation?

It consists of specialized circulatory mechanisms that allow blood to be carried to and from the umbilical cord, bypassing the offspring's nonfunctioning lungs.

What produces human chorionic gonadotropin (hCG) and what does it do?

It is produced by the blastocyst soon after implantation to stimulate the growth of the corpus luteum.

Why is hCG used as an indicator of pregnancy in tests?

Because hCG only occurs in fetal tissues.

What are the main functions of progesterone during pregnancy?

It provides endometrial secretions to nourish the embryo, maintains the endometrium, reduces the uterine muscle's ability to contract, and prepares the breasts for milk secretion.

What is the role of relaxin during childbirth?

Relaxin is a placental hormone that softens the cervix and relaxes the sacral joints and pubic symphysis to help widen the birth canal.

How long does the corpus luteum function post-fertilization before the placenta takes over?

It continues to grow and produce increased amounts of progesterone and estrogen for $11\text{--}12\,\text{weeks}$ post-fertilization until the placenta is formed, functioning, and producing adequate amounts.

What is the timeline for embryonic nervous system and heart development?

Heart and blood vessels originate during the $2\text{nd}$ week, the primitive nervous system begins to form in the $3\text{rd}$ week, and the $1\text{st}$ heartbeat appears in week $4$.

When does the offspring enter the fetus stage, and what happens during this period?

The offspring becomes a fetus beginning in the $3\text{rd}$ month until birth, during which all organs grow and mature.

What are the functions of the amnion and vernix caseosa?

The amnion is a sac filled with amniotic fluid that acts as a protective cushion around the fetus, while vernix caseosa is a cheese-like substance that protects the fetus's skin.

What are genes and how do they govern cell function?

Genes are segments of DNA inside chromosomes located in the nucleus of every cell; they govern cells by controlling the manufacture of proteins, especially enzymes.

What is the difference between autosomes and sex chromosomes?

Autosomes are the $22$ chromosome pairs not involved in sex determination, whereas sex chromosomes are the $1$ pair ($23\text{rd}$ pair) that determines the sex of the offspring.

What is the difference between homozygous and heterozygous alleles?

Homozygous means both alleles for a specific gene are the same, while heterozygous means the alleles are different.

What is the difference between phenotype and genotype?

Phenotype is the observed characteristic or what is expressed, whereas genotype is what the allele actually is despite what is expressed.

What are the products of meiosis at the end of the process?

A single cell divides its chromosomes in half to produce $4$ cells, each containing $23$ chromosomes ($22$ autosomes and $1$ sex chromosome).

What is a Punnett square?

A grid used by geneticists to show all possible combinations of alleles that can result from one mating.

How is the sex of an offspring determined?

Males have $XY$ chromosomes ($X$ from mom, $Y$ from dad) and females have $XX$ chromosomes; the male determines the sex because of the $Y$ chromosome, which is smaller than the other chromosomes.

What is a gene mutation and how can it occur?

A gene mutation is any change in a gene or chromosome that may occur spontaneously or be induced by an agent called a mutagen.