The Female Reproductive System PDF

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Summary

The Female Reproductive SystemFemale reproductive physiology Ovaries are the primary female reproductive organs - Produce ova (oogenesis) – develop within a follicle - Secrete female sex hormones  Oestrogen - Essential for ova maturation and release - Establishment of female secondary sexual chara...

Description

The Female Reproductive System Female reproductive physiology 

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Ovaries are the primary female reproductive organs - Produce ova (oogenesis) – develop within a follicle - Secrete female sex hormones Oestrogen - Essential for ova maturation and release - Establishment of female secondary sexual characteristics - Essential for transport of sperm from vagina to fertilisation site - Contribute to breast development in anticipation of lactation Progesterone - Important in preparing suitable environment for nourishing a developing embryo/foetus - Contributes to breasts’ ability to produce milk

Menstrual Cycle: Follicular Development     

At birth, primordial follicles are present in the ovary (1-2 million) Unlike males, mitosis complete by the end of the first trimester Every day, small numbers begin to develop and grow, but most die (atresia). At puberty – approx. 200,000 remain To grow through to ovulation a follicle must receive correct levels of LH and FSH Each cycle 15-20 follicles develop but only one continues to ovulation – the rest die

Female Sexual Development       

Just prior to puberty GnRH pulse generation begins Luteinizing Hormone (LH) and Follicle Stimulating hormone (FSH) are released from the anterior pituitary This ‘awakens’ the ovary – start of follicular development Developing follicles release oestrogens Development of female secondary characteristics (e.g. fat deposition, growth of reproductive tract) Growth of auxiliary hair, libido and pubertal growth spurt due to the rise in adrenal androgens When sufficient GnRH, LH and FSH are present = First period occurs (menarche)

Menstrual Cycle    

Average cycle lasts 28 days in humans Normally interrupted only by pregnancy Finally terminated by menopause Consists of two alternating phases

Follicular Phase   

First half of the 28 day cycle Dominated by presence of maturing follicles Follicle produces oestrogens

Luteal Phase   

Second half of the 28 day cycle Characterized by presence of corpus luteum Corpus luteum produces progesterone (& oestrogen)

Hormonal Changes during Follicular Phase      

FSH and LH rise at the beginning of the cycle due to GnRH release Rising FSH and LH stimulate oestrogen release from the developing follicle Oestrogen stimulates follicle development Moderate oestrogen levels inhibit FSH, but not tonic LH secretion, from the anterior pituitary Inhibin also inhibits FSH Moderate oestrogen stimulates positive feedback on the follicle causing further oestrogen release - Oestrogen levels significantly rise

Luteal Surge & Ovulation  

High oestrogen levels stimulate the anterior pituitary to produce large amounts of LH ( = LH surge) Ovulation occurs due to LH surge

Hormonal Changes during Luteal Phase    

Ovulation: Released oocyte enters oviduct where it may or may not be fertilized Corpus luteum produces progesterone Luteal surge causes follicle rupture and releases oocyte from thee ovary LH – when your oocyte is being released

Hormonal Changes during Luteal Phase       

Ruptured follicle forms the corpus luteum Corpus luteum produces large amounts of progesterone (and oestrogen) Progesterone (and oestrogen) inhibit LH and FSH release from the anterior pituitary After approximately 10 days the corpus luteum degenerates Progesterone and oestrogen levels significantly drop as corpus luteum degenerated FSH (and LH) rise as no longer inhibited by progesterone (and oestrogen) New cycle begins

Luteal Stage  

Ruptured follicle forms the corpus luteum  releases large amounts of Progesterone & Oestrogen Corpus luteum functions: - Oestrogens responsible for endometrium thickening - Progesterone responsible for endometrium development and maintenance - Progesterone inhibits LH and FSH secretion

Endometrium Development 

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First 4 days (menstrual phase) - Endometrium lining of the uterus is disintegrating - Bleeding occurs from ruptured blood vessels in endometrium - Blood and disintegrating outer layers of endometrium expelled as menstrual fluid Proliferative phase - Oestrogen secreted by developing follicle leads to growth and thickening of the endometrium - Uterine glands develop in endometrium but do not produce anything yet Secretory (progestational) phase - Corpus luteum formed (from day 14) secretes progesterone and oestradiol - Progesterone stimulates the uterine glands to secrete “uterine milk”, which is high in protein and glycogen - Provides correct environment should ovum fertilisation occur New menstrual phase - If fertilisation does not occur, CL regresses and progesterone and oestrogen not produced - Endometrium cannot be maintained and necrosis occurs - Expelled with blood as menstrual fluid - Menstruation usually lasts 3-5 days (20-200ml blood lost)

Fertilization    

Sperm deposited in vagina travel through cervical canal, uterus and up to the upper third of the oviduct Site of fertilization: oviduct (upper third) Must occur within 24-36 hours of ovulation Sperm usually survive about 48 hours but can survive up to 7 days in female reproductive tract

Implantation   

Fertilized ovum begins to divide and reaches uterus in 3-4 days  Gives time for the endometrium to develop for implantation of developing blastocyst By day 9, the blastocyst/developing placenta produces human chorionic gonadotrophin (hCG) at high levels for 8 weeks, before decreasing HCG prevents corpus luteum from regressing

When an Egg is Not Fertilized  

The corpus luteum stops secreting progesterone and decays – Degenerates into a corpus albicans Uterine lining sloughs (sheds) off without progesterone and is expelled

When an Egg is Fertilized  

HCG signals the corpus luteum to continue progesterone secretion, thereby maintaining endometrium HCG prevents corpus luteum degenerating into a corpus albicans

Development   

Corpus Luteum continues to produce progesterone and oestrogen for 8 weeks before its function declines (due to decreased hCG levels) This maintains the endometrium and survival of blastocyst until the placenta is developed Placenta takes over production of oestrogen and progesterone

The Placenta as an Endocrine Organ  

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hCG - Ensures continued secretion of progesterone in early pregnancy Progesterone - Maintains endometrium, reduces myometrial excitability and stimulates mammary development Oestrogens - Important for the buildup of uterine muscle and mammary development. Human placental lactogen (hPL, somatomammotropin) - Secreted about week 10 of gestation. Regulates and coordinates fetal growth and metabolism and maternal metabolism

Parturition (Childbirth)  

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Contraction of myometrium that are sufficiently strong to expel foetus Contractions stimulated by: - High oestrogen:progesterone ratio that occurs towards the end of pregnancy - Upregulates oxytocin receptors in myometrium so circulating oxytocin can bind - Muscle contraction Pressure of foetus against the cervix increases oxytocin secretion - Causes stronger contractions - Positive-feedback cycle progressively increases until cervical dilation and delivery are complete

Lactation 

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During gestation - Elevated placental oestrogen and progesterone promote development of ducts and alveoli in mammary glands Prolactin - Stimulates synthesis of enzymes essential for milk production by alveolar epithelial cells - Withdrawal of placental steroids at birth initiates lactation Sustained by suckling

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Triggers release of oxytocin and prolactin Oxytocin causes milk ejection Prolactin stimulates synthesis of more milk to replace milk ejected...