The

menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...

is on average 28 days in length. It begins with

menses Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and Mucous membrane, mucosal tissue from the endometrium, inner lining of the uterus through the vagina. The menstrual cycle is characterized ...

(day 1–7) during the follicular phase (day 1–14), followed by

ovulation Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and ...

(day 14) and ending with the luteal phase (day 14–28). While historically, medical experts believed the luteal phase to be relatively fixed at approximately 14 days (i.e. days 14–28), recent research suggests that there can be wide variability in luteal phase lengths not just from person to person, but from cycle to cycle within one person. The luteal phase is characterized by changes to hormone levels, such as an increase in

progesterone Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

and

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

levels, decrease in gonadotropins such as

follicle-stimulating hormone Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, puberty, pubertal maturat ...

(FSH) and

luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (G ...

(LH), changes to the endometrial lining to promote implantation of the fertilized egg, and development of the

corpus luteum The corpus luteum (Latin for "yellow body"; : corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is the ...

. In the absence of fertilization by sperm, the corpus luteum degenerates leading to a decrease in progesterone and estrogen, an increase in FSH and LH, and shedding of the endometrial lining (menses) to begin the menstrual cycle again.

Hormonal events

After

and release of the

oocyte An oocyte (, oöcyte, or ovocyte) 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 a female fetus in the ovary during female gametogenesis. The female ger ...

, the anterior pituitary hormones–

(FSH) and

(LH) are released and cause the remaining parts of the dominant follicle to transform into the

. It continues to grow during the luteal phase after ovulation and produces significant amounts of hormones, particularly progesterone, and, to a lesser extent,

and inhibin. Progesterone plays a vital role in making the

endometrium The endometrium is the inner epithelium, epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The funct ...

receptive to implantation of the

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

and supportive of early pregnancy. High levels of progesterone inhibit the follicular growth. The increase in estrogen and progesterone also lead to increased basal body temperature during the luteal phase. The LH surge that occurs during ovulation triggers the release of the oocyte and its cumulus oophorus from the ovary and into the fallopian tube and triggers the oocyte to divide and enter metaphase of meiosis II (46 or 2n chromosome) and extrude its first polar body. The oocyte will only continue through meiosis and extrude its second polar body once it is fertilized. Ovulation occurs ~35 hours after the beginning of the LH surge or ~10 hours following the LH surge. Several days after

, the increasing amount of estrogen produced by the corpus luteum may cause one or two days of fertile

cervical mucus The cervix (: cervices) or cervix uteri is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity. The human female cervix has been documented anatomically since at least the tim ...

, lower basal body temperatures, or both. This is known as a "secondary estrogen surge". The hormones released by the corpus luteum suppress production of the FSH and LH from the anterior pituitary gland. The corpus luteum relies on LH activation on its receptors in order to survive. The loss of the corpus luteum can be prevented by implantation of an

: after implantation, human embryos produce human chorionic gonadotropin (hCG), which is structurally similar to LH and can preserve the corpus luteum. If implantation occurs, the corpus luteum will continue to produce progesterone for eight to twelve weeks, after which the

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

takes over this function. In the absence of fertilization, hCG is not produced and the corpus luteum will atrophy in 10–12 days (Luteolysis or luteal regression). The death of the corpus luteum results in falling levels of progesterone and estrogen. The drop in ovarian hormones releases negative feedback on LH and FSH, thereby increasing LH and FSH concentrations and leading to shedding of the endometrium and another round of ovarian follicle selection.

Uterine events

During the follicular phase in the menstrual cycle, the uterine endometrium is in the proliferative phase which is characterized by an increase in circulating estrogen produced by the developing follicle. Increased estradiol alters the endometrial lining and promotes proliferation of epithelial cells, thickening of the tissue, and elongation of the spiral arteries that provide nutrients to the growing tissue. Estrogen also makes the endometrium more sensitive to progesterone in preparation for the luteal phase. After ovulation and during the luteal phase, the uterine endometrium is in the secretory phase which is characterized by the production of progesterone from the growing corpus luteum. Progesterone inhibits endometrial proliferation, and preserves uterine tissue in preparation for fertilized egg implantation. At the end of the luteal phase, progesterone levels fall and the corpus luteum atrophies. The drop in progesterone leads to endometrial ischemia which will subsequently shed in the beginning of the next cycle at the start of menses. This last stage in the luteal or secretory phase may be called the ischemic phase and lasts just for one or two days.

Symptoms

Changes in the level of progesterone during this phase may cause typical symptoms of pre-menstrual syndrome (PMS), such as: * Anxiety * Headaches * Mood swings * Irritability * Tender breasts * Weight gain * Trouble sleeping * Changes in sexual desire * Bloating * Emotional stresses

References

{{DEFAULTSORT:Luteal Phase Menstrual cycle Human female endocrine system ru:Менструальный цикл