Endometrium
Overview
The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium
Myometrium
The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells , but also of supporting stromal and vascular tissue...

, thereby maintaining the patency
Patency
-Definition:The property of being open and unobstructed, with continuity of lumen .-Examples:* An obstructed coronary artery was treated by balloon angioplasty and patency was restored....

 of the uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...

 cavity. During the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

 or estrous cycle
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...

, the endometrium grows to a thick, blood vessel-rich, glandular tissue layer. This represents an optimal environment for the implantation of a blastocyst
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...

 upon its arrival in the uterus.
Encyclopedia

Function

The endometrium is the innermost glandular layer and functions as a lining for the uterus, preventing adhesions between the opposed walls of the myometrium
Myometrium
The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells , but also of supporting stromal and vascular tissue...

, thereby maintaining the patency
Patency
-Definition:The property of being open and unobstructed, with continuity of lumen .-Examples:* An obstructed coronary artery was treated by balloon angioplasty and patency was restored....

 of the uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...

 cavity. During the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

 or estrous cycle
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...

, the endometrium grows to a thick, blood vessel-rich, glandular tissue layer. This represents an optimal environment for the implantation of a blastocyst
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...

 upon its arrival in the uterus. The endometrium is central, echogenic (detectable using ultrasound scanners), and has an average thickness of 6.7mm.

During pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

, the glands and blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

, which supplies oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and nutrition to the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 and foetus.

Cycle

The endometrial lining undergoes cyclic regeneration. Humans and the great apes
Great Apes
Great Apes may refer to*Great apes, species in the biological family Hominidae, including humans, chimpanzees, gorillas, and orangutans*Great Apes , a 1997 novel by Will Self...

 display the menstrual cycle
Menstrual cycle
The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

, whereas most other mammals are subject to an estrous cycle
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...

. In both cases, the endometrium initially proliferates under the influence of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...

. However, once ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...

 occurs, in addition to estrogen, the ovary will also start to produce progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...

. This changes the proliferative pattern of the endometrium to a secretory lining. Eventually, the secretory lining provides a hospitable environment for one or more blastocysts. If a blastocyst implants, then the lining remains as decidua
Decidua
Decidua is the term for the uterine lining during a pregnancy, which forms the maternal part of the placenta. It is formed under the influence of progesterone and forms highly-characteristic cells.-Etymology:...

. The decidua becomes part of the placenta; it provides support and protection for the gestation.

If there is inadequate stimulation of the lining, due to lack of hormones, the endometrium remains thin and inactive. In humans, this will result in amenorrhea. After menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...

, the lining is often described as being atrophic. In contrast, endometrium that is chronically exposed to estrogens, but not to progesterone, may become hyperplastic. Long-term use of oral contraceptives with highly potent progesterone
Progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...

 can also induce endometrial atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

.

In humans, the cycle of building and shedding the endometrial lining lasts an average of 28 days. The endometrium develops at different rates in different mammals. Its formation is sometimes affected by seasons, climate, stress, and other factors. The endometrium itself produces certain hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s at different points along the cycle. This affects other portions of the reproductive system
Reproductive system
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...

.

Histology

The endometrium consists of a single layer of columnar epithelium resting on the stroma
Stroma (animal tissue)
In animal tissue, stroma refers to the connective, supportive framework of a biological cell, tissue, or organ.The stroma in animal tissue is contrasted with the parenchyma.Examples include:* Stroma of iris...

, a layer of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

 that varies in thickness according to hormonal influences. Simple tubular uterine glands reach from the endometrial surface through to the base of the stroma, which also carries a rich blood supply of spiral arteries
Spiral artery
Spiral arteries are small arteries which temporarily supply the endometrium of the uterus during the luteal phase of the menstrual cycle.In histology, identifying the presence of these arteries is one of the most useful techniques in identifying the phase of the cycle.The spiral arteries are...

. In a woman of reproductive age, two layers of endometrium can be distinguished. These two layers occur only in endometrium lining the cavity of the uterus, not in the lining of the Fallopian tubes:
  • The functional layer is adjacent to the uterine cavity. This layer is built up after the end of menstruation during the first part of the previous menstrual cycle
    Menstrual cycle
    The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

    . Proliferation is induced by estrogen
    Estrogen
    Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...

     (follicular phase of menstrual cycle), and later changes in this layer are engendered by progestrone from the corpus luteum
    Corpus luteum
    The corpus luteum is a temporary endocrine structure in mammals, involved in production of relatively high levels of progesterone and moderate levels of estradiol and inhibin A...

     (luteal phase). It is adapted to provide an optimum environment for the implantation and growth of the embryo
    Embryo
    An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

    . This layer is completely shed during menstruation
    Menstruation
    Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...

    .
  • The basal layer, adjacent to the myometrium
    Myometrium
    The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells , but also of supporting stromal and vascular tissue...

     and below the functional layer, is not shed at any time during the menstrual cycle, and from it the functional layer develops.

In the absence of progesterone, the arteries supplying blood to the functional layer constrict, so that cells in that layer become ischaemic and die, leading to menstruation
Menstruation
Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...

.

It is possible to identify the phase of the menstrual cycle by observing histological differences at each phase:
Phase Days Thickness Epithelium
>-
| menstrual phase
1-4 thin >-
| proliferative phase
Follicular phase
The follicular phase is the phase of the estrous cycle, during which follicles in the ovary mature. It ends with ovulation. The main hormone controlling this stage is estradiol....

 
4-14 intermediate >-
| secretory phase 
15-28 thick columnar. Also visible are helicine branches of uterine artery
Helicine branches of uterine artery
The arcuate vessels of the uterus are a component of the blood supply of the uterus. They are arteries and veins that branch from the uterine arteries and veins, respectively, with additional anastomoses from the ovarian arteries and veins, and penetrate and assume a circumferantial course in the...



Chorionic tissue can result in marked endometrial changes, known as an Arias-Stella reaction
Arias-Stella reaction
Arias-Stella reaction, also Arias-Stella phenomenon, is a benign change in the endometrium associated with the presence of chorionic tissue.Cytologically, it looks like a malignancy and, historically, it was diagnosed as endometrial cancer....

, that have an appearance similar to cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

. Historically, this change was diagnosed as endometrial cancer
Endometrial cancer
Endometrial cancer refers to several types of malignancies that arise from the endometrium, or lining, of the uterus. Endometrial cancers are the most common gynecologic cancers in the United States, with over 35,000 women diagnosed each year. The incidence is on a slow rise secondary to the...

 and it is important only in so far as it should not be misdiagnosed as cancer.

Pathological conditions

Adenomyosis
Adenomyosis
Adenomyosis is a medical condition characterized by the presence of ectopic glandular tissue found in muscle. The term adenomyosis is derived from the terms adeno- , myo- , and -osis...

 is the growth of the endometrium into the muscle layer of the uterus (the myometrium
Myometrium
The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells , but also of supporting stromal and vascular tissue...

).

Endometriosis
Endometriosis
Endometriosis is a gynecological medical condition in which cells from the lining of the uterus appear and flourish outside the uterine cavity, most commonly on the ovaries. The uterine cavity is lined by endometrial cells, which are under the influence of female hormones...

 is the growth of endometrial tissue outside the uterus.

Endometrial cancer
Endometrial cancer
Endometrial cancer refers to several types of malignancies that arise from the endometrium, or lining, of the uterus. Endometrial cancers are the most common gynecologic cancers in the United States, with over 35,000 women diagnosed each year. The incidence is on a slow rise secondary to the...

 is the most common cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 of the human female genital tract.

Asherman's syndrome
Asherman's syndrome
Asherman's syndrome , also called "uterine synechiae" or intrauterine adhesions , presents a condition characterized by the presence of adhesions and/or fibrosis within the uterine cavity due to scars...

, also known as intrauterine adhesions occurs when the basal layer of the endometrium is damaged by instrumention (e.g. D&C
Dilation and curettage
Dilation and curettage refers to the dilation of the cervix and surgical removal of part of the lining of the uterus and/or contents of the uterus by scraping and scooping . It is a diagnostic gynecological procedure.D&C normally is referred to a procedure involving a curette, also called sharp...

) or infection (e.g. endometrial tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

) resulting in endometrial sclerosis and adhesion formation partially or completely obliterating the uterine cavity.

Thin endometrium may be defined as an endometrial thickness of less than 8 mm. It usually occurs after menopause
Menopause
Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...

. Treatments that can improve endometrial thickness include Vitamin E
Vitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...

, L-arginine and sildenafil citrate.

Gene expression profiling using cDNA microarray can be used for the diagnosis of endometrial disorders.

External links

- "The uterus, uterine tubes and ovary with associated structures." - "Female Reproductive System uterus, endometrium"
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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