The human body depends upon cooperation and communication between cells in order to function. Cells must receive signals from--and send signals to--distant body organs on a regular basis, and hormones are an important part of this communication network. The hormone hCG, for instance, communicates to the body cells that there's a fertilized egg--and later an embryo--in the uterus, and causes many of the changes of pregnancy.
Significance
An adult human doesn't produce hCG, regardless of gender or pregnancy status. Instead, fertilized eggs--and later embryos--make hCG as a mechanism of communicating with the mother's body and letting her cells know that she's pregnant. Dr. Lauralee Sherwood, in her book "Human Physiology," explains that many of the changes of pregnancy--especially early pregnancy--arise as direct results of the influence of hCG upon the rest of the body.
Features
HCG is short for human chorionic gonadotropin, which means it's a hormone produced by part of the placenta. Very early after fertilization, developing embryos don't have distinct placentas yet, but cells that will become the placenta begin secreting hCG to inform the mother's body that the embryo is there. Once an embryo implants in the uterine lining and begins to develop distinct tissue regions--including a region known as the chorion, of which the placenta is a part--hCG comes specifically from the chorion.
Function
Each month, a woman's uterine lining proliferates and she ovulates an egg. If the egg isn't fertilized, the uterine lining sloughs off--this is menstruation. If the egg is fertilized, however, it's important that her body not slough the uterine lining, since the fertilized egg needs a place to implant, explains Dr. Sherwood. This is the purpose of hCG--it communicates with a cell group in the ovary called the corpus luteum, and causes this cell group to keep producing progesterone and estrogen, which maintain the uterine lining.
Considerations
Since only fertilized eggs--and later, placentas--secrete hCG, physicians can use the hormone as a marker for pregnancy. In a physician's office or with the help of a home pregnancy test, it's possible to test the urine or blood of a pregnant woman for hCG. Generally, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting," women get positive results on a pregnancy test within a few days in either direction of their expected menstrual period.
Effects
Increasing levels of hCG in a woman's body lead to high levels of estrogen and progesterone, and cause many of the symptoms of early pregnancy, explains Dr. Miriam Stoppard in her book "Conception, Pregnancy and Birth." Morning sickness, tender breasts, headaches and early back pain or cramps are all symptoms of hormones produced as the result of hCG release. Many of these symptoms are similar to those of an impending period, however, which can make it difficult to spot an early pregnancy.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008
- "Conception, Pregnancy and Birth"; Miriam Stoppard, M.D.; 2008
