Exercise 45 Physiology of Reproduction 1

Meiosis Gametes Haploid complement (n) Gametogenesis Process of gamete formation with the reduction by half of the chromosome number Homologous chromosome Carries genes for the same traits 2

Meiosis Meiosis I Prophase 23 tetrads Homologues chromosomes synapse Chiasmata or crossover 3

Meiosis Metaphase Anaphase Homologues separates Dyads stays together Telophase 2 cells with diploid number of chromosomes 4

Meiosis Meiosis II Prophase No chromosome replication Cells are diploid Metaphase 5

Meiosis Anaphase Breaks of the centromeres will result each cell having one chromatid 4 daughter cells Crossover and the way in which the homologues align on the spindle equator during the first maturation division introduces a great variability in the resulting gametes 6

Spermatogenesis It is the male gamete formation Starts at puberty and continues throughout life 7

Spermatogenesis 8

Steps of sperm formation: Spermatogonia (2n) Stem cell Found in the seminiferous tubules It undergoes mitosis and forms one primary spermatocyte and one spermatogonium Phase regulated by FSH 9

Spermatogenesis Primary spermatocyte (2n) It undergoes to a growth phase It undergoes to meiosis I after the growth phase and forms the secondary spermatocyte Secondary spermatocyte (n) It undergoes meiosis II and produces 4 spermatids 10

Spermatogenesis Spermatids (n) Nonfunctional gametes No motile They undergo spermiogenesis and form the sperm 11

Spermatogenesis Sperm Motile Smaller than the spermatid Head of the sperm Contain the genetic material Acrosome 12

Spermiogenesis 13

Spermatogenesis Midpiece Centriole that gives rise to the filaments that forms the tail Mitochondria present Tail flagellum 14

Spermatogenesis Sertoli cells Support cells responsible for sperm nourishment 15

Oogenesis and ovarian cycle It is the female gamete formation Steps of the oogenesis: Before birth Oogonia Primitive stem cell it undergoes mitosis many times It grows in size and becomes a primary oocyte 16

Oogenesis and ovarian cycle Primordial follicles Capsule formed by a single layer of squamouslike cells that surround the primary oocyte At birth Oogonias no longer exists All cells are oocytes encapsulated by a primordial follicle No more oocytes will be produced 17

Oogenesis and ovarian cycle From birth to puberty Primary oocytes are quiescent From puberty and on Increase of FSH levels cause: Follicle One or more primordial follicles to undergo maturation (every 28 days) 18

Follicle 19

Oogenesis and ovarian cycle Formation of primary follicle From the maturation of the primordial follicle Follicle cells The epithelium changes from squamous to simple cuboidal Many layers of cuboidal cells Granulosa It secrets estrogen It contains the primary oocyte 20

Oogenesis and ovarian cycle Secondary follicle Follicle with several layers of granulosa cells Presence of antrum Tertiary follicle (Graafian) Presence of granulosa cells Corona radiata 21

Oogenesis and ovarian cycle It is a mature follicle that continues secreting increasing amounts of estrogen It contains the secondary oocyte It expels the secondary oocyte accompanied by the corona radiata at the middle of the 28-day cycle 22

Oogenesis and ovarian cycle Corpus luteum It comes from the rupture Graafian follicle It produces mainly progesterone If pregnancy does not occur it will degenerate and will be replaced by scar tissue 23

Oogenesis and ovarian cycle Corpus albicans Scar tissue resulted from the disintegration of the corpus luteum Oocyte Primary oocyte Meiosis I is completed forming one secondary oocyte and one first polar body 24

Follicle 25

Oogenesis 26

Oogenesis and ovarian cycle Secondary oocyte Large cell (contains most of the cytoplasm of the primary oocyte) Haploid Arrested in metaphase of meiosis II It is expelled by the Graafian follicle (ovulation) It is captured by the uterine tube 27

Oogenesis and ovarian cycle If penetrated by the sperm, it will complete meiosis II and will produce a large ovum and one small secondary polar body Ovum Chromosomes of the ovum and sperm will combine to form a diploid cell 28

Oogenesis and ovarian cycle First polar body Small cell (almost no cytoplasm) Produced by the division of the primary oocyte It will disintegrate Secondary polar body Produced by the division of the secondary oocyte It will also disintegrate 29

Oogenesis and ovarian cycle Hormonal cycle Beginning of the menstrual cycle FSH is the dominant hormone Low levels of LH Low levels of estrogen and progesterone 30

Oogenesis and ovarian cycle Before ovulation Estrogen levels increase Progesterone level remain low Ovulation Caused mainly by a peak of LH After ovulation Estrogen levels decrease Progesterone levels increase FSH and LH levels decrease 31

Menstrual cycle Controlled by ovarian hormones Menstrual phase Lasts 1-5 days Sloughing off of the functional layer of the endometrium with bleeding 32

Oogenesis and ovarian cycle Proliferative phase From day 6-14 Estrogen is the main hormone Ovarian follicle grows Endometrium thickens with proliferation of its glands and blood vessels Ovulation occur at day 14 33

Oogenesis and ovarian cycle Secretory phase From day Progesterone produced by the corpus luteum is the main hormone Endometrium thickens even more with further proliferation and coiling of the glands Uterus is getting ready for the embryo implantation 34

Oogenesis and ovarian cycle If no implantation occurs the corpus luteum will deteriorate causing lack of ovarian hormones that will cause deterioration of the functional layer of the endometrium 35

Menstrual cycle 36