During the first trimester, the ovaries are responsible for controlling the production of hormones, while the cells that become the embryo are forming.
By week fourteen, the embryo has taken on human form, and now it is the job the placentaThe placenta is a large disk shaped membrane responsible for providing nourishment to the fetus during pregnancy. It consists of three parts, the fetal part made up from the chorion membrane surrounding the fetus, the maternal part, formed from the decidua basalis layer of the uterine lining, and the intervillous space between the two plates. It is connected to the fetus by the umbilical cord and consists of tissue from both the mother and the embryo.
Its function is complex. It has been described as a simple organ that combines the functions of a kidney-dialysis machine, heart and lung machine and intravenous drip. It consists of enormous numbers of blood vessel branches that permit the exchange of nutrition and oxygen, from the mother's bloodstream to the fetus and the removal of wastes to the mother to be excreted. The placenta's remarkable quality is that it does so without the blood of the mother mixing with that of the baby.
It also is responsible for the production of vital hormones including, estrogen, progesterone, and human chorionic gonadotropin. After birth, the placenta is delivered, and is sometimes referred to as the afterbirth.
Visit our comprehensive glossary for more pregnancy terms and definitions. to provide the hormonesA complex chemical substance created in a part or organ of the body. When released it initiates or regulates activity in an organ or group of cells in another part of the body.
Hormones secreted by endocrine glands are transported through the bloodstream to their target organ. The amount of hormone secreted is regulated either by other hormones, by neurotransmitters, or simply when an excess of the organ's activity indicates a need to reduce the amount of the hormone produced.
Other hormones are produced locally by the organs themselves and are common in the digestive tract.
Visit our comprehensive glossary for more pregnancy terms and definitions., nourishment and oxygen while the baby matures.
Last week your baby's eye lids closed so that the eyes could develop. This week that development has begun. Over the next four months many layers of cells will form the eye: a complex muscle that measures light, adjusting for brightness and converting what it sees into electrical impulses that are interpreted by the brain. To do this, the layers of cells that make up the eye will develop into the corneaA dense transparent structure that forms the outermost portion of the eye. It is nonvascular (does not contain blood), and projects like a dome beyond the sclera.
Visit our comprehensive glossary for more pregnancy terms and definitions., irisA part of the eye that separates the space between the lens and the cornea into an anterior and posterior chamber. It is a circular disk, capable of contracting and perforated by a circular pupil. It serves to limit or maximize the amount of light entering the eye.
Until the fetus reaches about week 28, the two chambers are separated by the membrana pupilaris. Subsequently and into all adult life the two chambers communicate through the pupil.
Dark pigment cells under the translucent tissue of the iris are arranged to produce different eye colors. In blue eyes, the pigment cells only appear on the posterior surface of the iris. In gray, brown and black eyes, the pigment cells appear in the anterior epithelium and the stroma.
Visit our comprehensive glossary for more pregnancy terms and definitions., lensThe crystalline lens of the eye which lies behind the cornea and iris, and is used to focus the light onto the retina permitting vision.
Visit our comprehensive glossary for more pregnancy terms and definitions. and retinaA membrane of the eye consisting of nervous tissue and comprising ten layers. It is contiguous with the optic nerve sending visual impulses to the brain.
The retina is soft and contains rhodopsin which gives it its purple tint. If exposed to direct sunlight it will become clouded.
Visit our comprehensive glossary for more pregnancy terms and definitions..
Your baby's internal organs have been largely laid down during trimester one. Now it needs structure. Your baby's skeleton is being formed, and some of these bones may be visible on ultrasound.
As you enter the second trimester you will begin to notice a need for maternity clothes. Maybe you can manage a bit longer without zipping your fly all the way closed, but soon larger clothing will be a must. But don't worry, you will enjoy your pregnancy more while wearing comfortable clothes and there are now many fashionable styles to choose from. Browse BabyPartner's store (in association with Amazon.com) for clothes from A Pea in the Pod, BabyStyle, Mimi Maternity, Motherhood Maternity and other great maternity designers.
If this is your first pregnancy you will grow more slowly. Previous pregnancies have already stretched skin and muscles to account for the growing uterus. If you have been pregnant before you will show sooner and feel bigger already.
As you will already have noticed, pregnancy is responsible for many changes in you, both emotionally and physically. You may start to notice skin tags and moles appearing or changing, both in size or color. If you notice such changes, you should discuss it with your doctor.
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