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If no fertilized egg is implanted into the uterus, the corpus luteum degenerates and the levels of estrogen and progesterone decrease. The endometrium begins to degenerate as the progesterone levels drop, initiating the next menstrual cycle. The decrease in progesterone also allows the hypothalamus to send GnRH to the anterior pituitary, releasing FSH and LH and starting the cycles again.

Career in action

Reproductive endocrinologist

A reproductive endocrinologist is a physician who treats a variety of hormonal disorders related to reproduction and infertility in both men and women. The disorders include menstrual problems, infertility, pregnancy loss, sexual dysfunction, and menopause. Doctors may use fertility drugs, surgery, or assisted reproductive techniques (ART) in their therapy. ART involves the use of procedures to manipulate the egg or sperm to facilitate reproduction, such as in vitro fertilization.

Reproductive endocrinologists undergo extensive medical training, first in a four-year residency in obstetrics and gynecology, then in a three-year fellowship in reproductive endocrinology. To be board certified in this area, the physician must pass written and oral exams in both areas.


Pregnancy begins with the fertilization of an egg and continues through to the birth of the individual. The length of time of gestation    , or the gestation period    , in humans is approximately 266 days.

Within 24 hours of fertilization, the egg nucleus has finished meiosis and the egg and sperm nuclei fuse. With fusion, the cell is known as a zygote. The zygote initiates cleavage and the developing embryo travels through the oviduct to the uterus. The developing embryo must implant into the wall of the uterus within seven days, or it will deteriorate and die. The outer layers of the developing embryo or blastocyst grow into the endometrium by digesting the endometrial cells, and healing of the endometrium closes up the blastocyst into the tissue. Another layer of the blastocyst, the chorion, begins releasing a hormone called human beta chorionic gonadotropin (β-HCG)    , which makes its way to the corpus luteum and keeps that structure active. This ensures adequate levels of progesterone that will maintain the endometrium of the uterus for the support of the developing embryo. Pregnancy tests determine the level of β-HCG in urine or serum. If the hormone is present, the test is positive.

The gestation period is divided into three equal periods or trimesters. During the first two-to-four weeks of the first trimester, nutrition and waste are handled by the endometrial lining through diffusion. As the trimester progresses, the outer layer of the embryo begins to merge with the endometrium, and the placenta forms. The placenta    takes over the nutrient and waste requirements of the embryo and fetus, with the mother’s blood passing nutrients to the placenta and removing waste from it. Chemicals from the fetus, such as bilirubin, are processed by the mother’s liver for elimination. Some of the mother’s immunoglobulins will pass through the placenta, providing passive immunity against some potential infections.

Questions & Answers

how does hormones produce in our body
Shubham Reply
what is an organelle
Shemia Reply
it is the membranious componet within a cell... eg mitochondrion
what is the Endothelial cell?
Jumana Reply
classification of heart
classification of heart 5 points
wym by classification?
differences between meiosis and mitosi
Daniel Reply
how much function it have
Kerlon Reply
what is a cell membrane
call membrane is outer most part of cell
cell membrane consists from phospholipids and proteins
what is elastic constant in muscle in human of body
which topic you at now
what is chromosome
jeff Reply
a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes
what are the medical application of hooks law experiment in human body
what is the physical reason that make people get fractured in bones or rupture of tissues
Hooke's Law is the Law of Elasticty. In scientific terms, Hooke's Law is the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load
what is DNA
deoxyribonucleic acid, a self-replicating material which is present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.
what is prokaryotic cell
am Modesta
what is deamination
what is defusion
Rashima Reply
diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration through a permeable membrane
and osmosis is the same thing ?
The spreading of something more widely
Osmosis is the movement of water molecules from a region of higher concentration to a region of lower concentration
What is a color of blood before it is exposed to oxygen?
hello there....I have a problem concerning an infection in my feet...so can any one help me?
Ngole Reply
what sort of infection?
is the blood pressure increase? why?
Jumana Reply
what is the reason for cardiac arrest
Oseni Reply
stop the heat suddenly
It's usually triggered when there's a malfunction in the heart which causes arrhythmia..hope u get more clarity online
what is cardiovascular system
cardiovascular system in a lame mans under
what y
the heart
cardiovascular system is a system that circulates blood and lymph through the body, consisting of the heart, blood vessels, blood, lymph, and the lymphatic vessels and glands
thanks dein-aboh perfect
your welcome bro
what is the difference between white blood cells and red blood cells?
Gecious Reply
what is the difference between white blood cell and red blood cells
idk enlightening me... the red is for oxygen the white is for the immune system
what are nephrons and their types
Note Reply
when is the actual time that woman can be pregnant?
Jackson Reply
What symptoms occur during menstruation?

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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