GAMETES Clara

Learning Outcomes GMC: P8a : Integrate an understanding of the gross anatomical and microanatomical structure of the reproductive systems with their function Describe the process of spermatogenesis Describe the ovarian cycle Describe the process and control of ovulation Describe the roles of the hormones of the HPG axis in regulating gamete production

FIRST THINGS FIRST XY Germ cells induce the testis XX Germ cells induce the ovary 2 pairs of 22 chromosomes, plus two sex chromosomes = 46 chromosomes Female gamete = ovum Male gamete = sperm Haploid cell = a cell that contains a single set of chromosomes Diploid cell = a cell that contains two sets of chromosomes Overall picture : 1.Germ cells colonise the gonad 2.The germ cells proliferate : numbers increase, via mitosis 3.There is a genetic reshuffling within the cells 4.The cells reduce to haploid cells, via meiosis 5.The haploid cells then mature, this is called cytodifferentiation

MITOSIS AND MEIOSIS Mitosis = One single cell divides to give two daughter cells, each containing the same number of chromosomes and genetic content as the original cell Meiosis = one parent replicates and recombines, divides once to give two daughter cells, then divides again creating four daughter cells, each containing half the genetic content of the original parent cell

SPERMATOGENESIS XY Germ cell Mitosis Spermatogonia Mitosis Spermatocytes Meiosis Spermatids (HAPLOID CELLS) Maturation Sperm Green : Before puberty, Orange : at puberty Each spermatocyte forms 4 haploid spermatids SPERMATOGENESIS stimulated by testosterone SPERMIOGENESIS

POINT… SHOOT… SCORE! Semen =  Secretions of seminal vesicle (fructose rich, alkaline fluid & fibrinogen fluid)  Secretions of prostate (seminal fluid: bicarbonate, nutrient citric acid + fibrinolytic)  Sperm  Secretion of bulbo-urethral glands (lubrication) Semen gets into the vagina via ejaculation. 1.5 – 4 mL may contain > 300M sperm, and 50 lucky boyz will get to the site of fertilisation! Mixed by emission

LADIES’ TURN Oogonia (XX Germ Cells) Mitosis Primary Oocyte (2n) Meiosis I Secondary Oocyte (1n) + Polar Body (1n) Meiosis II Ovum (1n) Colonise the cortex (outer layers of the gonad) Surrounded by a single layer of Granulosa Cells, form the Primordia Follicle The primary oocyte stays in Prophase until Puberty Meiosis is induced at puberty, thanks to FSH