Female Reproductive Physiology and Menstrual cycle Lecture 4 Dr. Zahoor 1

Objectives Oogenesis and the stages of follicle development Ovulation and formation of corpusluteum Ovarian cycle Secretion of FSH and LH through negative and positive feedback mechanisms during a menstrual cycle Uterine cycle Draw a diagram and show changes in FSH, LH, estradiol, progesterone, and correlate these with ovarian and uterine changes during the menstrual cycle 2

Female Reproductive Physiology Characterized by complex cycling Ovaries – Primary female reproductive organs Produce ova (oogenesis) Secrete female sex hormones – Estrogen (estradiol) – progesterone 3

Female Sex Hormones – These are steroid hormone – Estrogen- Functions » Maturation and maintenance of entire female reproductive system. » Essential for ova maturation and release » Establishment of female secondary sexual characteristics » Essential for transport of sperm from vagina to fertilization site in oviduct » Contributes to breast development in anticipation of lactation – In general action of estrogen is important in preconception events 4

Female Sex Hormones – Progesterone - Functions » Important in preparing suitable environment for nourishing a developing embryo/fetus » Contributes to breasts’ ability to produce milk – In general progesterone is important in post conception events 5

OOGENESIS [GAMETOGENENSIS] Formation of Primary oocytes from oogonium is completed before birth, 6-7 million oogonia by the fifth month of gestation. Soon Atresia starts and the number starts reducing. After birth the number is reduced to 2 million (No new oocyte appear after birth ) At puberty – 300, oogonia present. During reproductive age only ova mature and ovulate. 6

Oogenesis 7

OOGENESIS [GAMETOGENENSIS] The first meiotic division of primary oocyte begins during embryonic life but is arrested at prophase Primary oocyte remains in the state of meiotic arrest for years and first meiotic division is completed prior to the ovulation [Release of ovum from ovary] at puberty. 8

At ovulation it is Secondary Oocyte which is released and contains half the Chromosomes (22+x) and 1st polar body which undergoes degeneration. The secondary oocyte then undergoes the 2nd meiotic division but is arrested at metaphase, and completed during fertilization. It form the mature ovum (22+x) and the 2nd polar body. The second polar body too undergoes degeneration 9

Oogenesis Identical steps of chromosome replication and division during gamete production in both sexes – Timing and end result are very different SpermatogenesisOogenesis Accomplished within two months Take anywhere from 12 to 50 years to complete on cyclic basis from onset of puberty until menopause Postpubertal male can produce several hundred million sperm each day Female born with limited, largely nonrenewable supply of germ cells Each primary spermatocyte yields four equally viable spermatozoa Each primary oocyte yields only one cytoplasm-rich ovum and three cytoplasm-poor polar bodies that disintegrate

Female reproductive system We will discuss Menstrual cycle under the heading of : 1.Ovarian cycle 2.Hormonal effects (hypothalamus & ant. Pituitary) 3.Uterine cycle 11

1. Ovarian Cycle Average ovarian cycle lasts 28 days Normally interrupted only by pregnancy Finally terminated by menopause Ovarian cycle Consists of two alternating phases – Follicular phase(1-14 days ) Dominated by presence of maturing follicles – Luteal phase(15-28 days) Characterized by presence of corpus luteum 12

Ovarian Cycle-Follicular phase – Follicular phase is characterized by maturation of follicles. – Granulosa cells and Theca cell of some primary follicles proliferate —Theca cells and Granulosa cells are collectively known as follicular cells and secrete estrogen. – Under the effect of FSH of the follicles grow rapidly forming secondary follicle which are capable of secreting estrogen – Oocyte inside each follicle enlarges 13

Ovarian Cycle-Follicular phase – One follicle called Dominant follicle usually grows more rapidly and mature (graafian follicle) about 14 days after onset of follicular development. – Graafian follicle bulges on ovarian surface - ruptures to release secondary oocyte from ovary (ovulation)- facilitated by burst in LH secretion (LH SURGE ) – LH SURGE is due to increased Estrogen level. – Released oocyte enters oviduct where it may or may not be fertilized. – Other developing follicles which did not mature under go degeneration. 14

Development of the Follicle, Ovulation, and Formation and Degeneration of the Corpus Luteum 15

Ovarian Cycle-Luteal phase Last 14 days of ovarian cycle – The remnants of the ruptured graafian follicle develop into Corpus luteum under influence of LH (leuteinization) – The granulosa cells are filled with yellowish lipid- lutein. – Becomes highly vascularized 16

Ovarian Cycle-Luteal phase – Corpus Luteum has endocrine functions and it secretes progesterone & estrogen (more of progesterone). It remains for 14 days ( days ). – If fertilization does not occurs it degenerates into Corpus Albicans. – If fertilization takes place it persists until placenta is formed & secrete increase quantity of progesterone & estrogen (corpus luteum of pregnancy) 17

Ovarian Cycle 18

2. EFFECT OF PITUITARY HORMONES ON OVARIAN CYCLE 19

Regulation of Ovarian Cycle by hormonal interactions 1. During follicular phase, rise in FSH signals ovarian follicle to secrete more estrogen 2.Rise in estrogen feeds back to inhibit FHS secretion which declines as follicular phase proceeds 3.LH rises in follicular phase As it peaks in mid-cycle, it triggers ovulation 4.Estrogen output decreases and mature follicle is converted to a corpus luteum 20

Regulation of Ovarian Cycle by hormonal interactions 5.Corpus luteum secretes progesterone and estrogen during luteal phase – Progesterone output inhibits release of FSH and LH Low LH – corpus luteum degenerates Progesterone levels decline 6.FSH can start to rise again, initiating new cycle 21

Production of estrogen by ovarian follicle 22

Correlation Between Hormonal Levels and Cyclic Ovarian and Uterine Changes 23

24 Ovarian cycle

Feedback control of FSH & LH during follicular phase 25

Control of LH surge at ovulation 26

Feedback control during luteal phase 27

3. Uterine Cycle Reflects hormonal changes during ovarian cycle Averages 28 days Outward manifestation of cyclic changes in uterus is menstrual bleeding once during each cycle Consists of three phases – Menstrual phase (3-5days) – Proliferative phase (6-14 days) – Secretory or progestational phase (15-28 days) 28

29 Estrogen stimulates growth of both endometrium and myometrium. It also induces synthesis of progesterone receptors in endometrium. Progesterone: make endometrial connective tissue loose and edematous Growth of endometrial blood vessels and glands to secrete glycogen

Uterine Cycle-Menstrual phase – 3-5 days of cycle – Characterized by discharge of blood and endometrial debris from vagina – First day of menstruation is considered start of new cycle – Coincides with end of ovarian luteal phase and onset of follicular phase 30

Uterine Cycle-Menstrual phase – As corpus luteum degenerates the level of progesterone & estrogen drops that results in - Release of uterine prostaglandin Causes vasoconstriction of endometrial vessels – Disrupts blood supply – Causes death of endometrium Stimulates mild rhythmic contractions of uterine myometrium – Help expel blood and endometrial debris from uterine cavity out through vagina (menstrual flow) Bleeding lasts for 3-5 days, ml of blood is lost per cycle. Fibrinolysins are present which dissolves any clots. 31

Uterine Cycle Proliferative phase (6-14days) – Begins concurrent with last portion of ovarian follicular phase Endometrium starts to repair itself and proliferate under influence of estrogen from newly growing follicles Glands and arteries proliferate and there is increases thickness of endometrium – Estrogen-dominant proliferative phase lasts from end of menstruation to ovulation – Peak estrogen levels trigger LH surge responsible for ovulation 32

Uterine Cycle Secretory or progestational phase(15-28day) – Uterus enters this phase after ovulation when new corpus luteum is formed – Corpus luteum secretes large amounts of progesterone and estrogen Under effect of Progesterone – The endometrium grows further in thickness with increase in secretions of glands and arteries become more coiled – The secretion are rich in electrolytes, enzymes and glycogen which provide nourishment to the developing embryo before implantation, if fertilization has taken place. – If fertilization and implantation does not occur Corpus luteum degenerates New follicular phase and menstrual phase begin once again 33

Various factors can disrupt the menstrual cycle Weight loss/low body weight Disordered eating Vigorous physical activity Stress

Athletic Menstrual Irregularities (AMI ) Amenorrhea ( Cessation of Menstrual periods) Oligomenorrhea (Less flow, decreased frequency, irregular) Anovulatory cycle In general population menstrual cycle dysfunction occurs – 2-5% But survey done in Athlete(Daily 3.5 hours of moderate intensity sports) showed Menstrual cycle irregularity 2-51% 35

AMI (C0NT) MECHANISM RESPONSIBLE Rapid loss of weight, decreased body fat, dietary insufficiencies. Stress, intensity of training, age at onset of training. Hormonal changes responsible – FSH-LH environment totally unbalanced, – Decreased estrogen in follicular phase – Decreased progesterone in luteal phase IMPORTANT- All women athlete returned to normal within 6 months after training 36

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THANK YOU 38