The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer; the functional layer thickens and then is shed during menstruation in humans and some other mammals, including apes, Old World monkeys, some species of bat, and the elephant shrew. In most other mammals, the endometrium is reabsorbed in the estrous cycle. During pregnancy, the glands and blood vessels in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta, which supplies oxygen and nutrition to the embryo and fetus. The speculated presence of an endometrial microbiota has been argued against.
The uterus or womb is a major female hormone-responsive secondary sex organ of the reproductive system in humans and most other mammals. In the human, the lower end of the uterus, the cervix, opens into the vagina, while the upper end, the fundus, is connected to the fallopian tubes. It is within the uterus that the fetus develops during gestation. In the human embryo, the uterus develops from the paramesonephric ducts which fuse into the single organ known as a simplex uterus. The uterus has different forms in many other animals and in some it exists as two separate uteri known as a duplex uterus.
Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynaecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgical field.
The placenta is a temporary organ that connects the developing fetus via the umbilical cord to the uterine wall to allow nutrient uptake, thermo-regulation, waste elimination, and gas exchange via the mother's blood supply; to fight against internal infection; and to produce hormones which support pregnancy. Placentas are a defining characteristic of placental mammals, but are also found in marsupials and some non-mammals with varying levels of development.
The amnion is a membrane that closely covers the embryo when first formed. It fills with the amniotic fluid which causes the amnion to expand and become the amniotic sac which serves to provide a protective environment for the developing embryo or fetus. The amnion, along with the chorion, the yolk sac and the allantois form a protective sac around the embryo. In birds, reptiles and monotremes, the protective sac is enclosed in a shell. In marsupials and placental mammals, it is enclosed in a uterus.
The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida, known as the vitelline membrane in other animals. In insects it is developed by the follicle cells while the egg is in the ovary.
The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoel. The trophoblast gives rise to the placenta. The name "blastocyst" arises from the Greek βλαστός blastos and κύστις kystis. In other animals this is called a blastula.
The female reproductive system is made up of the internal and external sex organs that function in reproduction of new offspring. In humans, the female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes, and to carry a foetus to full term. The internal sex organs are the uterus, Fallopian tubes, and ovaries. The uterus or womb accommodates the embryo which develops into the foetus. The uterus also produces vaginal and uterine secretions which help the transit of sperm to the Fallopian tubes. The ovaries produce the ova. The external sex organs are also known as the genitals and these are the organs of the vulva including the labia, clitoris, and vaginal opening. The vagina is connected to the uterus at the cervix.
Trophoblasts are cells that form the outer layer of a blastocyst and are present four days post fertilization in humans. They provide nutrients to the embryo and develop into a large part of the placenta. They form during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures and do not directly contribute to the embryo. After gastrulation, the trophoblast is contiguous with the ectoderm of the embryo, and is referred to as the trophectoderm. After the first differentiation, the cells in the human embryo lose their totipotency and are no longer totipotent stem cells because they cannot form a trophoblast. They are now pluripotent stem cells.
Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but can occur through assisted reproductive technology procedures. A pregnancy may end in a live birth, a spontaneous miscarriage, an induced abortion, or a stillbirth. Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP). This is just over nine months – where each month averages 31 days. When using fertilization age it is about 38 weeks. An embryo is the developing offspring during the first eight weeks following fertilization, after which, the term fetus is used until birth. Signs and symptoms of early pregnancy may include missed periods, tender breasts, nausea and vomiting, hunger, and frequent urination. Pregnancy may be confirmed with a pregnancy test.
Prenatal development includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal development until birth.
The decidua is the modified mucosal lining of the uterus that forms in preparation for pregnancy. It is formed in a process called decidualization under the influence of progesterone. Endometrial cells become highly characteristic. The decidua forms the maternal part of the placenta and remains for the duration of the pregnancy. It is shed off during childbirth — hence why the term is used, "decidua" having the meaning of falling away, as in the word deciduous.
The cytotrophoblast is the inner layer of the trophoblast. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo.
Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood.
In humans, implantation is the stage of pregnancy at which the embryo adheres to the wall of the uterus. At this stage of prenatal development, the conceptus is called a blastocyst. It is by this adhesion that the embryo receives oxygen and nutrients from the mother to be able to grow.
Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. This includes morphological and functional changes to endometrial stromal cells (ESCs), the presence of decidual white blood cells (leukocytes), and vascular changes to maternal arteries. The sum of these changes results in the endometrium changing into a structure called the decidua. In humans, the decidua is shed during the third phase of birth.
Uterine glands or endometrial glands are tubular glands, lined by ciliated columnar epithelium, found in the functional layer of the endometrium that lines the uterus. Their appearance varies during the menstrual cycle. During the proliferative phase, uterine glands appear long due to estrogen secretion by the ovaries. During the secretory phase, the uterine glands become very coiled with wide lumens and produce a glycogen-rich secretion. This change corresponds with an increase in blood flow to spiral arteries due to increased progesterone secretion from the corpus luteum. During the pre-menstrual phase, progesterone secretion decreases as the corpus luteum degenerates, which results in decreased blood flow to the spiral arteries. The functional layer of the uterus containing the glands becomes necrotic, and eventually sloughs off during the menstrual phase of the cycle.
Fetal-maternal haemorrhage is the loss of fetal blood cells into the maternal circulation. It takes place in normal pregnancies as well as when there are obstetric or trauma related complications to pregnancy.
Prenatal nutrition addresses nutrient recommendations before and during pregnancy. Nutrition and weight management before and during pregnancy has a profound effect on the development of infants. This is a rather critical time for healthy development since infants rely heavily on maternal stores and nutrient for optimal growth and health outcome later in life.
Endometrial cups form during pregnancy in mares and are the source of equine chorionic gonadotropin (eCG) and a placenta-associated structure, which is derived from the fetus. Their purpose is to increase the immunological tolerance of the mare in order to protect the developing foal.
