Corpus luteum
Encyclopedia
The corpus luteum (plural corpora lutea) is a temporary endocrine structure in mammals, involved in production of relatively high levels of progesterone
and moderate levels of estradiol
and inhibin A. It is colored as a result of concentrating carotenoid
s from the diet.
The corpus luteum develops from an ovarian follicle
during the luteal phase
of the menstrual cycle
or estrous cycle
, following the release of a secondary oocyte from the follicle during ovulation
. The follicle first forms a corpus hemorrhagicum
before it becomes a corpus luteum, but the term refers to the visible collection of blood left after rupture of the follicle that secretes progesterone. While the oocyte
(later the zygote
if fertilization occurs) traverses the Fallopian tube
into the uterus
, the corpus luteum remains in the ovary
.
The corpus luteum is typically very large relative to the size of the ovary; in humans, the size of the structure ranges from under 2 cm to 5 cm in diameter.
Its cells develop from the follicular cells surrounding the ovarian follicle
.
Like the previous theca cells, the theca lutein cells lack the aromatase
enzyme that is necessary to produce estrogen, so they can only perform steroidogenesis until formation of androgen
s. The granulosa lutein cells do have aromatase, and use it to produce estrogens, using the androgens previously synthesized by the theca lutein cells, as the granulosa lutein cells in themselves do not have the 17α-hydroxylase or 17,20 lyase to produce androgens.
Once the corpus luteum regressed the remnant is known as corpus albicans
.
, which is a steroid hormone
responsible for the decidualization
of the endometrium
(its development) and maintenance, respectively.
, which is a mass of fibrous scar
tissue.
The uterine lining sloughs off without progesterone and is expelled through the vagina (in humans and some great apes, which go through a menstrual cycle
). In an estrus cycle, the lining degenerates back to normal size.
) cells of the blastocyst
secrete the hormone human chorionic gonadotropin
(hCG, or a similar hormone in other species) by day 9 post-fertilization.
Human chorionic gonadotropin signals the corpus luteum to continue progesterone secretion, thereby maintaining the thick lining (endometrium) of the uterus and providing an area rich in blood vessel
s in which the zygote
(s) can develop. From this point on, the corpus luteum is called the corpus luteum graviditatis.
The introduction of prostaglandin
s at this point causes the degeneration of the corpus luteum and the abortion
of the fetus
. However, in placental animals such as humans, the placenta
eventually takes over progesterone production and the corpus luteum degrades into a corpus albicans
without embryo/fetus loss.
s, especially lutein
. In 1968, a report indicated that beta-carotene was synthesized in laboratory conditions in slices of corpus luteum from cows. However, attempts have been made to replicate these findings, but have not succeeded. The idea is not presently accepted by the scientific community. Rather, the corpus luteum concentrates carotenoids from the diet of the mammal.
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...
and moderate levels of estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
and inhibin A. It is colored as a result of concentrating carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s from the diet.
Development and structure
The corpus luteum develops from an ovarian follicle
Ovarian follicle
Ovarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
during the luteal phase
Luteal phase
The luteal phase is the latter phase of the menstrual cycle or the estrous cycle . It begins with the formation of the corpus luteum and ends in either pregnancy or luteolysis...
of 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...
, following the release of a secondary oocyte from the follicle during 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...
. The follicle first forms a corpus hemorrhagicum
Corpus hemorrhagicum
The corpus hemorrhagicum is a temporary structure formed immediately after ovulation from the ovarian follicle. After the trauma heals, the subsequent structure is called the corpus luteum -External links:* *...
before it becomes a corpus luteum, but the term refers to the visible collection of blood left after rupture of the follicle that secretes progesterone. While the oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
(later the zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
if fertilization occurs) traverses the Fallopian tube
Fallopian tube
The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction...
into the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, the corpus luteum remains in the ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
.
The corpus luteum is typically very large relative to the size of the ovary; in humans, the size of the structure ranges from under 2 cm to 5 cm in diameter.
Its cells develop from the follicular cells surrounding the ovarian follicle
Ovarian follicle
Ovarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
.
| Follicular structure | Luteal structure | Secretion >- | Theca cells Theca of follicle The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become tertiary follicles.The theca are divided into two layers, the theca interna and the theca externa.... |
Theca lutein cells | androgen Androgen Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors... s and 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... >- | Granulosa cell Granulosa cell A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete in the ovary of mammals.-Anatomy and function:... s |
Granulosa lutein cells | progesterone, 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... , and inhibin A |
Aromatase
Aromatase is an enzyme responsible for a key step in the biosynthesis of estrogens. It is a member of the cytochrome P450 superfamily , which are monooxygenases that catalyze many reactions involved in steroidogenesis. In particular, aromatase is responsible for the aromatization of androgens into...
enzyme that is necessary to produce estrogen, so they can only perform steroidogenesis until formation of androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
s. The granulosa lutein cells do have aromatase, and use it to produce estrogens, using the androgens previously synthesized by the theca lutein cells, as the granulosa lutein cells in themselves do not have the 17α-hydroxylase or 17,20 lyase to produce androgens.
Once the corpus luteum regressed the remnant is known as corpus albicans
Corpus albicans
The corpus albicans is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans. This process is called "luteolysis". The remains of the corpus albicans may persist as a scar on the surface...
.
Function
The corpus luteum is essential for establishing and maintaining pregnancy in females. The corpus luteum secretes progesteroneProgesterone
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...
, which is a steroid hormone
Steroid hormone
A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens...
responsible for the decidualization
Decidualization
Decidualization is a characteristic of the endometrium of the pregnant uterus. It is a response of maternal cells to progesterone. Decidualization may be used to describe any change due to progesterone...
of the endometrium
Endometrium
-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, thereby maintaining the patency of the uterine cavity. During the menstrual cycle or estrous cycle, the endometrium grows to a...
(its development) and maintenance, respectively.
When egg is not fertilized
If the egg is not fertilized, the corpus luteum stops secreting progesterone and decays (after approximately 14 days in humans). It then degenerates into a corpus albicansCorpus albicans
The corpus albicans is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans. This process is called "luteolysis". The remains of the corpus albicans may persist as a scar on the surface...
, which is a mass of fibrous scar
Scar
Scars are areas of fibrous tissue that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound results in...
tissue.
The uterine lining sloughs off without progesterone and is expelled through the vagina (in humans and some great apes, which go through a 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....
). In an estrus cycle, the lining degenerates back to normal size.
When egg is fertilized
If the egg is fertilized and implantation occurs, the syncytiotrophoblast (derived from trophoblastTrophoblast
Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg...
) cells of the 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,...
secrete the hormone human chorionic gonadotropin
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...
(hCG, or a similar hormone in other species) by day 9 post-fertilization.
Human chorionic gonadotropin signals the corpus luteum to continue progesterone secretion, thereby maintaining the thick lining (endometrium) of the uterus and providing an area rich in 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 which the zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
(s) can develop. From this point on, the corpus luteum is called the corpus luteum graviditatis.
The introduction of prostaglandin
Prostaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....
s at this point causes the degeneration of the corpus luteum and the abortion
Abortion
Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
of the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
. However, in placental animals such as humans, 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...
eventually takes over progesterone production and the corpus luteum degrades into a corpus albicans
Corpus albicans
The corpus albicans is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans. This process is called "luteolysis". The remains of the corpus albicans may persist as a scar on the surface...
without embryo/fetus loss.
Content of carotenoids
The yellow color and name of the corpus luteum, like that of the macula lutea of the retina, is due to its concentration of certain carotenoidCarotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s, especially lutein
Lutein
Lutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach and kale...
. In 1968, a report indicated that beta-carotene was synthesized in laboratory conditions in slices of corpus luteum from cows. However, attempts have been made to replicate these findings, but have not succeeded. The idea is not presently accepted by the scientific community. Rather, the corpus luteum concentrates carotenoids from the diet of the mammal.