Gestation
Gestation is embryo development inside viviparous animals.
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals. It is typical for mammals, but also occurs for some non-mammals. The time interval of a gestation is called the gestation period.
- definition
- Period of development of embryo/fetus inside viviparous animals
- typical for
- Mammals, also some non-mammals
- gestation period
- Time interval of gestation
- human birth range
- 37 to 42 weeks gestational age
- preterm labor
- Labor prior to 37 weeks gestation
- non-mammal examples
- Scorpions, some sharks, velvet worms, certain lizards
Lore & Background
In mammals, pregnancy begins when a zygote implants in the female's uterus and ends when the fetus leaves the uterus during labor or abortion. Human pregnancy can be defined clinically (from last menstrual period), biochemically (hCG above 25 mIU/mL), or biologically (at implantation). It is divided into three trimesters, each about three months long, with birth normally at about 40 weeks. In placental mammals, gestation involves a gradual increase in senescence in the maternal decidua and placental cells, associated with increased DNA damage. Non-mammals exhibit viviparity (live birth) or ovoviviparity (embryos develop in eggs inside mother, nourished by yolk). The fish family Syngnathidae (seahorses, pipefish, sea dragons) is unique in that females lay eggs in a male's brood pouch, a phenomenon termed 'male pregnancy'.
Reader's Guide
Gestation is a fundamental biological process in viviparous animals, encompassing the development of offspring within the parent's body. In mammals, it involves complex physiological changes, including implantation, placental formation, and eventual labor. The article notes that prenatal care is important for healthy pregnancy and that factors like diseases and care access influence gestation duration. In placental mammals, a link between gestation period and lifespan suggests evolutionary significance. Non-mammalian examples, such as ovoviviparous vipers and male pregnancy in Syngnathidae, illustrate diverse reproductive strategies. Understanding gestation is crucial for obstetrics, evolutionary biology, and comparative physiology, as it affects both maternal and offspring health across species.
Did You Know?
- In humans, gestational age is calculated from the last menstrual period, averaging fertilization age plus two weeks.
- The fish family Syngnathidae is the only family in the animal kingdom to which the term 'male pregnancy' has been applied.
- Ovoviviparous embryos are nourished by egg yolk, not the mother's body, though the mother provides gas exchange.
Frequently Asked Questions
What is Gestation in Reproduction and Development 1-24?
Gestation refers to the developmental phase in which an embryo, and subsequently a fetus, grows inside the body of a viviparous animal. It is the defining reproductive strategy for mammals, though a handful of non-mammalian lineages share this trait.
Which animals undergo Gestation besides mammals?
While mammals are the classic group, gestation also occurs in certain non-mammals such as scorpions, some shark species, velvet worms, and particular lizards.
What does the term 'gestation period' mean?
The gestation period is simply the time interval spanning from the start of internal development through to birth. It marks how long the embryo and fetus remain inside the mother before delivery.
How long is a full-term human gestation?
A normal human pregnancy runs from about 37 to 42 weeks of gestational age. If labor begins before the 37-week threshold, it is classified as preterm.
Why is Gestation significant in the Reproduction and Development chapter?
It represents the core mechanism by which viviparous species nurture their offspring in a protected internal environment before birth. Understanding it is essential to distinguishing viviparous reproduction from oviparous strategies.
More in Reproduction And Development 1-24
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