Search results
Results from the WOW.Com Content Network
A human fetus, attached to placenta, at three months gestational age. In humans, the fetal stage starts nine weeks after fertilization. [7] At this time the fetus is typically about 30 millimetres (1 + 1 ⁄ 4 in) in length from crown to rump, and weighs about 8 grams. [7] The head makes up nearly half of the size of the fetus. [8]
The fetus starts producing leukocytes at 2 months gestational age, mainly from the thymus and the spleen. Lymphocytes derived from the thymus are called T lymphocytes (T cells), whereas those derived from bone marrow are called B lymphocytes (B cells). Both of these populations of lymphocytes have short-lived and long-lived groups.
The fetus reaches a length of about 40–48 cm (16–19 in). The fetus weighs about 2.5 to 3 kg (6 lb 10 oz)to 6 lb 12 oz). Lanugo begins to disappear. Body fat increases. Fingernails reach the end of the fingertips. A baby born at 36 weeks has a high chance of survival, but may require medical interventions. Fetus at 38 weeks after fertilization.
At 5 weeks, the embryo is a mass of cells with a developing neural tube (pre-spinal cord and brain). The forming fetus is no larger than a grain of rice.” Pregnancy tissue after an abortion at 5 ...
In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or 36 weeks.
[4] [5] This is just over nine months. Counting by fertilization age, the length is about 38 weeks. [5] [13] Pregnancy is "the presence of an implanted human embryo or fetus in the uterus"; implantation occurs on average 8–9 days after fertilization. [15]
Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL. [5] Biologically, pregnancy starts at implantation of the fertilized egg. Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester.
One example of this is the gradual change in head size relative to body size during human growth. During prenatal growth, from conception to 5 months, the head grows more than the body. In humans, the head comprises almost 50% of total body length at approximately the third month of intrauterine development. By the time of birth the head has ...