Ref: Guyton, 12th edition. Page 993: Ganong's Review of Medical Physiology, 24th edition and Textbook of Medical Physiology By Khurana, Page 863Explanation:"Progesterone is a C21 steroid secreted by the corpus lute urn, the placenta, and (in small amounts) the follicle. About 2% of the circulating progesterone is free, whereas 80% is bound to albumin and 18% is bound to corticosteroid-binding globulin. Progesterone has a short half-life and is convened in the liver to pregnanediol, which is conjugated to glucuronic acid and excreted in the urine.' ' Ref: GanongQ. No. 5 Proliferative PhaseSecretorv PhaseMenstrual PhaseExtent* 6 - 14 days* Follow s of Phase of menstruation, following which only a thin basal layer of original endometrium is left* 15-28 days* Aka Postovulatory phase* First five days* Average duration 3-5 days* Aka Bleeding phaseHormones* Estrogen secreted from developing graafian follicle in the ovary* This phase coincides with follicular phase of ovarian cycle* Progesterone secreted by corpus luteum formed after ovulation* Estrogen* About 24 hours before this phase, there is sharp decline in plasma levels of estrogen and progesterone which causes bleedingChanges inEndometr-ium* Thickness of endometrium is increased (From <1 mm to 3-4 mm)* Angiogenesis in Stratum functionate leads to proliferation of vessels and spiral arterioles formation* Growth of endometrial glands* B contain glycogen but are non- secretory* Elongation and coiling of endometrial mucous glands.* The glands become secretory, secrete thick viscous fluid containing glycogen* Further increase on blood supply and spiraling of blood vessels due to progesterone effect* Prominent corkscrew shaped glands* Thickness of endometrium increases to 5-6 mm* if fertilization does not occur and there is no pregnancy, the corpus luteum in the ovary involute to form corpus albicans on Day 26 of cycle* The levels of estrogen and progesterone fall suddenly* Endometrial debris contains necrosed sloughed off tissue, blood, serous fluid containing prost-aglandins and fibrolysins* Average blood loss is 30 ml* Menstrual blood clots immediately in uterine cavity but gets liquefied by fibrolysins present in endometrial debris* Around 2/3rd of the superficial endometrium is sloughed off and only a thin basal layer isleft behind (1-2 mm)Cervix* The secretions of mucosal cells of endocervix become thin, watery and alkaline* During ovulation, cervical mucous is thinnest and has maximum elasticity* Mucous can he stretched like a long, thin elastic thread up to 8 - 12 cm(Spinnharkeit effect)* Produces characteristic Fern-like pattern on drying on glass slide (Fern Test)* Cervical mucous makes conditions favourable for transport of sperms and fertilization* Cervical secretions decrease in quantity and becomes thick, tenacious and cellular* Fern pattern NOT seen* These changes make a plug and prevent entry of sperms through cerv ical canal* Persistence of Fern pattern throughout the cycle indicates Anovulatory cycle'* Does NOT undergo desquamation like endometrial mucosaVagina* Epithelium becomes thickened and corntfied {estrogen effect)* Epithelium proliferated and gets infiltrated with leucocytes* Vaginal secretions become thiek and viscid "Progesterone is rapidly metabolized by liver and has a half life of 5 min. It is converted to Pregnanediol and conjugated to glucuronic acid in the liver. Pregnanediol glucuronide is excreted in the urine. Preganetriol is the main urinary metabolite of 17-OH- progesterone." Ref: ClinicalReproductive Medicine and Surgery: A Practical Guide By Tommaso Falcone. 2nd edition. Page 6PROGESTERONESecreted from luteinized theca granulosa cells of corpus lute uni.A trace amount is secreted from theca granulosa cell of the follicle and ovarian stroma.FUNCTIONSReproductive Actions(A) Actions on UterusProliferation of endometrial cells by decreasing mitotic activity.Decreases thickness of endometrium.Endometrial glands become tortuous and contain glycogen, glycoproteins and glyoclipids which provide nutrition to blastula if fertilization occurs.Glandular cells show vacuolation near their bases.The spiral arteries become more coiled.Stroma of endometrium becomes edematous.Responsible for secretory phase of endometrial cycle and prepares endometrium to receive zygote.Progesterone decreases uterine motility by:o Decreasing synthesis of voltage dependant Ca2+ channel proteins.o Decreases the number of oestrogen receptors on myometrium.(B). EndocervixCervical secretions become thick and viscid.Ferning pattern disappears.(C). VaginaVaginal epithelium becomes thickened, cornified and infiltrated by leukocytes.(D). Fallopian TubesIncreases the heating rate of cilia of fallopian tubes towards uterus.Increased epithelial cell secretion.Secretions are rich in nutritive materials to provide nutrition to shedded ovum and zygote.(E). BreastCauses lobular and alveolar growth.(F). During PregnancyMaintains pregnancy.Non-Reproductive Actions(A). Thermogenic EffectProgesterone is thermogenic steroid.Increases basal body temperature by 0.5 deg in postovulatory phase.(B). CMSAlters secretion and release of various NT in Hypothalamus.Decreases appetite and produces somnolence.(C). RespirationIncreases sensitivity of the respiratory centre to C02 stimulation.PACO 2 is slightly less in women during luteal phase.Progesterone is tried in Pickwickian syndrome.(D). MetabolismDecreases serum HDL-Pro-atherogenic. Mechanism of ActionThe receptors are present in cytoplasm of target cells.Receptors contain protein called heat shock protein (HSP).