Histology of the Testis Testes in the scrotal sac (→extension of abdominal cavity) Produce sperm and male sex hormones Have a constant temp "body temp - 5°C" maintained by) Heat exchange system in arteries and veins Semi-external position Muscles in scrotal sac → move testes up/down against warmer abdomen Sterility if testes do not descend during development Spermatogenesis occurs in walls of seminiferous tubules (→compartment of testes) Sperm are passively carried to the epididymis Network of seminiferous tubules → leads into vas deferens Sperm acquire ability to swim and are stored Urethra (joining of vas deferens) carries fluids from the urinary and reproductive system During interaction / pressure in erectile tissue rises / arteries supplying it dilate and veins draining it constrict Not discharged sperm are degenerated, absorbed, lost via urine Histology of the Ovary Ovaries in the abdominal cavity produce gametes + sex hormones Stroma within the ovary contains blood vessels Supply of oxygen and nutrients Removal of waste products → CO2 Transports hormones which control process of reproduction Follicle development occurs within the ovary Each follicle consists of follicle cells surrounding an oocyte (→developing egg) At birth ≈1 million primary follicles in each ovary Remain in suspension until puberty → at puberty, only ≈400k are present ≈400 will be released into the oviduct during reproductive life of a female At month intervals ≈20-25 follicles begin to develop further, from these only a single oocyte is released Gametogenesis (→Formation of Gametes) SAME in both sexes a) spermatogenesis, b) oogenesis Multiplication of diploid cells by MITOSIS Epithelium of seminiferous tubules multiplies Daughter cells are pushed towards lumen of tubule Epithelial cell inside ovary of female fetus multiplies GROWTH of daughter cells from mitotic divisions Products of the growth phase divide by MEIOSIS producing haploid cells (46→23) MATURATION of haploid daughter cells into gametes (eggs, sperm) Heads are embedded in Sertoil cells Prevent destruction of sperm by immune system Sperm and body cells are genetically different Provide nutrients Tails are projected into fluid-filled lumen How gametogenesis differs in females Unequal cell division in meiosis / 1 ovum and tiny polar bodies produced Primary oocytes form before birth / growth phase before birth Pause in meiosis at prophase I / further development suspended until puberty Pause in meiosis at metaphase II / meiosis not complete until fertilisation occurs"1 Follicle Development/Ovarian Cycle Follicular stage [days1-13] Anterior pituitary gland is secreting follicle-stimulating hormone FSH FSH travels in bloodstream to ovary Stimulates development (division) of follicle cells surrounding oocyte Developing follicle cells secrete oestrogen Stimulates proliferation of endometrium and its blood supply Inhibits further secretion of FSH by negative feedback Stimulates anterior pituitary gland to secrete luteinising hormone LH LH brings about ovulation Ovulation [day14] // Mature ovarian follicle ≈15mm in diameter Mature ovarian follicle bursts and releases secondary oocyte (now called ovum!) Corpus luteum forms from remaining follicle cells in ovary Ovum passes down fallopian tube/oviduct towards uterus; fertilization now possible Happens once a month, menstrual cycle ≈28days Each ovary alternatively releases an ovum every ≈56days (→56/2) Luteal phase [days15-28] Corpus luteum secretes sex hormones Progesterone continues to stimulate Profileration of endometrium and its blood supply Development of nutrient fluid glands in uterus lining High levels of sex hormones inhibit secretion of LSH and LH IF FERTILISATION DOES NOT OCCUR Corpus luteum degenerates \ levels of sex hormones fall Uterus lining breaks down; FSH is not inhibited anymore → cycle starts again Uterine Cycle Menstruation [days1-5] → Endometrium breaks down Low levels of female sex hormones causes uterus lining/endometrium to disintegrate its blood vessels to rupture Flow of blood (menses) passes out of the vagina Proliferative phase [days6-13] → Endometrium rebuilds Increased production of oestrogen by ovarian follicle Secretory phase [days15-28] → Endometrium thickens and glands are secretory Structure of a Mature Sperm Cell Head: acrosome (enlarged lysosome → digestive enzymes → penetrate egg), nucleus (n) Middle piece: mitochondria, ATP needed for tail movement Tail: flagellum, movement Movement of Sperm in the Female Reproductive Tract Sperm are ejaculated into the vagina / deposited outside the cervix Alkalinity of semen neutralises acidic pH in vagina Mucus allows sperm to swim through cervix / mucus is thin and watery during ovulation / glycoprotein chains run parallel Wall of uterus has two distinct layers Bulk of uterus wall consists of myometrium (→smooth muscle) / expels fetus at birth Active muscular contractions during intercourse support sperm Travel to oviduct in ≈5hours / survival rate of sperm ≈48hours Endometrium is concerned with anchorage and nourishment of embryo Sperm undergo capacitation while travelling Acquire ability to fertilise 2° oocyte by removal of acrosome membrane proteins Takes ≈6hours Fertilisation occurs in the fallopian tube Walls are lined with ciliated epithelia and contain smooth muscles Egg moves to uterus via cilia movement and peristaltic muscle contraction Contact between sperm and oocyte is by chance Structure of the Egg 0.1mm (100um) in diameter. Sperm's head is only 2.5um across Haploid nucleus is surrounded by cytoplasm / with enzymes and organelles Yolk droplets contain proteins and lipids Outside plasma membrane is a glycoprotein coat called a jelly coat Acrosome Reaction and Penetration of the Oocyte Membrane Acrosome reaction Contact of jelly coat and sperm Triggers Ca2+ to enter membrane of sperm Causes acrosome to burst / releases enzymes / digest jelly coat // enzymes: hyluronidase + acrosin Sperm filament attaches to receptor on vitelline membrane Sperm and egg plasma membranes fuse Sperm nucleus enters egg, tail and middle piece remain outside Depolarisation of membrane / blocks entry of more sperm 2° oocyte undergoes 2nd division of meiosis / produces ovum + second polar body Nuclei (ovum + sperm) fuse forming a zygote Female Infertility Pituitary gland fails to produce FSH and prevents ovulation TREATMENT: Injections of FSH SIDE EFFECTS: May produce several eggs at the same time (→twins) Too much oestrogen is secreted which inhibits FSH secretion TREATMENT: non-steroidal drugs (e.g. clomiphene) which oppose action of oestrogen Male Infertility Semen contain too few sperm TREATMENT: natural/synthetic androgens such as testosterone // Viagra (sildenafil) is an enzyme inhibitor → causes smooth muscle surrounding erectile tissue to relax → more blood can be pumped into them during erection process In Vitro Fertilisation (IVF) FSH is injected in woman Just before ovulation eggs are collected and matured Fertilisation → collected sperm sample is added to collected mature egg Nucleus of sperm is micro-injected into the egg Fertilisation outside the body in a plastic disc Advantage: possible to screen embryos for genetic defects Maximum of three are transferred into the uterus