The Reproductive System

1. The Reproductive System

2. Similarities and differences between males and females, but same goal: new life • Primary sex organs: gonads • Testes in males • Ovaries in females • These produce the gametes (sex cells) • Sperm in males • Ovum (egg) in females • Endocrine function also: secretion of hormones • Accessory sex organs • Internal glands and ducts • External genitalia

3. Meiosis is the first step in gametogenesis: separation of homologous chromosomes into haploid daughter cells Spermatogonia and oogonia are the germ cells that will eventually develop into the mature sperm or egg Primary spermatocyte or oocyte: the first step in this development is the duplication of homologous chromosomes to get ready for meiosis Secondary spermatocyte or oocyte: the first meiotic division separates the homologous chromosomes from each parent Spermatids or eggs: the second meiotic division separates the 2 chromatids and creates 4 haploid cells In males, this eventually produces 4 sperm cells by the process of spermiogenesis. In females, it produces 1 egg and 3 polar bodies. This allows the egg to retain more cytoplasm to support early stages of development

4. Meiosis generates tremendous genetic diversity. How many different types of gametes can be generated by an individual (male or female) with 23 different chromosomes?

5. More than 223 or 8,000,000 different gametes

6. The timing of meiosis differs in females and males In males, the spermatogonia enter meiosis and produce sperm from puberty until death. The process of sperm production takes only a few weeks. Each ejaculation has 100 to 500 million sperm. In females, this process is more complex. The first meiotic division starts before birth but fails to proceed. It is eventually completed about one month before ovulation in humans. In humans, the second meiotic division occurs just before the actual process of fertilization occurs. Thus, in females, the completion of meiosis can be delayed for over 50 years. This is not always good. Only I egg produced In addition, all meiosis is ended in females at menopause.

7. Male reproductive system Don’t panic! You don’t need to know all these names! • Testes (singular testis) or testicles: the gonads • Temp cooler in the scrotum because it’s outside the body.

8. Each lobule contains 1-4 coiled seminiferous tubules*: make sperm • Converge to form straight tube (tubulus rectus), then conveys sperm into rete testis • Sperm leave testis through efferent ductules which enter epididymis* * *

9. Spermatogenesis:sperm formation The mammalian testes are divided into many lobules, and each lobule contains many tiny seminiferous tubules. Sperm develop in an ordered fashion in these tubules. Cells start to mature on the outside and move inward (towards the lumen) as the become mature sperm. • Begins at puberty • 400 million sperm/day For baby not to end up with twice as many chromosomes as the parents, the sperm (as well as the egg) needs to have only half (1n) the # of chromosomes (1 of each of the 23) (2n means 2 of each chromosome, one from each parent, totaling 23 pairs = 46 chromosomes) • Three stages: • Formation of spermatocytes • Meiosis • Spermiogenesis

10. Cross section of seminiferous tubule • 1st stage: formation of spermatocytes • Spermatogonia are stem cells • Least differentiated (earliest in the process) • Divide continuously by mitosis (result 2n or diploid): daughter cells A (remains a stem cell) or B (goes on) • When start to undergo meiosis are by definition called spermatocytes • 2nd stage: meiosis I • Each primary spermatocytes (2n) undergoes meiosis I to become 2 secondary spermatocytes: • Each secondary spermatocyte undergoes meiosis II to become 2 spermatids • Therefore 4 total spermatids from each spermatogonium • 3rd stage: spermiogenesis • Spermatids differentiate into sperm

11. Stage 3: Spermiogenesis: spermatid streamlined to sperm • Head contains • Nucleus with chromatid (genetic material) • Acrosome with enzymes for penetrating egg • Midpiece: mitochondria spiraled around the core of the tail • Tail is an elaborate flagellum (allows sperm to swim) know these parts

12. Sperm leave testis though efferent ductules • Lined by simple columnar epithelium • Cilia and smooth muscle in wall help move sperm along • Sperm mature in epididymus (20 days) • Head of epididymus contains the efferent ductules which empty into duct of the epididymus • Sperm gain ability to swim • Sperm can be stored in epididymus for several months Duct of epididymis: highly coiled 6m long duct (pic left is multiple coils of same duct) *Note pseudostratified columnar epithelium (reabsorbs fluid) * Ductus (vas) deferens: note thick layers of smooth muscle

13. The Female Reproductive System • Production of gametes (ova, or eggs) • Preparation for support of developing embryo during pregnancy • Cyclic changes: menstrual cycle • Averages 28 days • Complex interplay between hormones and organs: at level of brain, ovaries and uterus

14. Gonads: the ovaries • Paired, almond-shaped, flanking the uterus in lateral wall of true pelvis • 3 x 1.5 x 1 cm in size Posterior view

15. Anterior view • Ovaries are retroperitoneal, but surrounded by peritoneal cavity • Held in place by mesentery and ligaments: • Broad ligament • Suspensory ligament of the ovary • Ovarian ligament • Innervation: • Sympathetic and parasympathetic

16. Structure of ovary • Fibrous capsule is called tunica albuginea • Outer cortex houses developing gametes the oocytes, within follicles • Inner medulla is loose connective tissue with largest vessels and nerves

17. The Ovarian Cycle • Follicular phase • 1st approx 14 days but variable • Egg develops in a follicle • Stimulated by FSH (see next slide) • Estrogen produced • Ovulation • Egg released from follicle (LH surge) • Egg in abdominal cavity • Picked up by fimbria of fallopian tube • Not necessarily halfway point • Luteal phase • Postovulatory phase 14 days (more constant) • Corpus luteum develops from exploded follicle • Produces progesterone as well as estrogen • Progesterone stimulates uterus to be ready for baby • If no pregnancy, corpus luteum degenerates into corpus albicans

18. Nearly mature follicle • Oocyte develops the zona pellucida • Glycoprotein coat • Protective shell (egg shell) • Sperm must penetrate to fertilize the oocyte • Thecal cells stimulated by LH to secrete androgens • Granulosa cells (with FSH influence) convert androgens to estrogen (follicular cells called granulosa cells now) • Clear liquid gathers to form fluid-filled antrum: now a secondary follicle • Surrounding coat of granulosa cells: corona radiata • Fully mature, ready to ovulate, called: ”Graafian follicle”

19. Ovulation • Signal for ovulation is LH surge • Ovarian wall ruptures and egg released, surrounded by its corona radiata

20. OogenesisGeneration of eggs • Starts in fetal period • No more oocytes made after about 7th month • Developed only to early stage of meiosis I by birth and stops (called primary oocyte) • 6-12 primordial oocytes each cycle selected to develop for ovulation (most die) • Only then is meiosis I completed • Secondary oocyte is then arrested in meiosis II • Meiosis II not completed (now an ovum) unless sperm penetrates its plasma membrane • Of the 4 daughter cells, only one becomes ovum (needs a lot of cytoplasm) • The other 3 become “polar bodies”

21. Fallopian (uterine) tubes, AKA oviducts ____Fallopian tubes__ * Fimbriae Fimbriae (fingers) pick up egg Beating cilia and muscular peristalsis propel egg to uterus Empties into superior part of uterus* Enlargement of mucosa layer showing ciliated columnar epithelium Cross section through entire tube PID

22. The Uterus (womb) • In pelvis anterior to rectum and posterosuperior to bladder • Hollow, thick-walled organ • Receives • Retains • Nourishes fertilized egg=embryo Uterus is pear-shaped (before babies) Usually anteverted, can be retroverted

23. Parts of uterus: Body (major part) Fundus Isthmus Cervix • Cavity of uterus small (except in pregnancy) • Cervical canal • Internal os • External os • Vagina • Cervix • Tough, fibrous ring • Inferior tip projects into vagina • Produces mucus

24. The Uterine Wall* • Three basic layers • Perimetrium: outer serous membrane • Myometrium: middle muscle • Endometrium: inner mucosal lining • Uterine supports: • Mesometrium (largest division of broad lig) – main support • Cardinal ligament • Round ligament • (Prolapse) *

25. Endometrium(inner mucosal lining of uterine cavity) • Simple columnar epithelium containing secretory and ciliated cells • Lamina propria of connective tissue Note: Uterine glands Uterine arteries • 2 main layers (Strata) • Functionalis (functional layer) • Basalis (basal layer) (shed if no implantation of baby) (not shed)

26. Time: one cycle (approx 28 d.) ovulation * • Pituitary hormones • FSH: follicle stimulating hormone • LH: luteinizing hormone • Ovarian hormones • Estrogen • Progesterone Follicular phase Luteal phase

27. The cyclic changes of uterine wall and follicle(hormone graphs should be above) If no baby, decreasing progesterone - slough Proliferative phase: rebuilds itself after slough Secretory phase: vascular rich glands enlarge: will sustain baby (needs progesterone: corpus luteum initially then placenta)

28. (inhibin: inhibits pituitary secretion of FSH)

29. The Vagina • Thin-walled tube • Inferior to uterus • Anterior to rectum • Posterior to urethra & bladder • “Birth canal” • Highly distensible wall: 3 layers • Adventitia • Muscularis • mucosa

30. External female genitalia aka vulva or pudendum • Mons pubis: fatty pad over pubic symphysis, with hair after puberty • Labia (lips) majora: long fatty hair-covered skin folds • Labia minora: thin, hairless, folds enclosing vestibule • Vestibule: houses external openings of urethra and vagina • Urethra is anterior (drains urine from bladder) • Baby comes out through vagina (vaginal orifice in pic) • Clitoris: anterior, homolog of penis (sensitive erectile tissue) • Perineum: diamond shaped region

31. Mammary glands (breasts) • Modified sweat glands • Both sexes but function (normally) only in lactating female • Produce milk to nourish baby • Respond to hormonal stimulation • Lymph drains into parasternal and axillalry lymph nodes • Nipple surrounded by pigmented ring of skin, the areola • Muscles underneath: pectoralis major and minor, parts of serratus anterior and external oblique

32. Mammary glands consist of 15-25 lobes • Each a distinct compound alveolar gland opening at the nipple • Separated by adipose and suspensory ligaments • Smaller lobules composed of tiny alveoli or acini • Like bunches of grapes • Walls: simple cuboidal epithelium of milk-secreting cells • Don’t develop until half-way through pregnancy (ducts grow during puberty) • Milk passes from alveoli through progressively larger ducts • Largest: lactiferous ducts, collect milk into sinuses

33. Conception • After ejaculation into the vagina, sperm swim to meet an egg • Sperm live 5-7 days (need cervical mucus) • Eggs live about 12-24 hours, so conception only occurs during this short window • Fertilization occurs in the fallopian tube • Events leading to fertilization: • Sperm binds to receptors on zona pellucida • Acrosomal reaction – enzymes digest a slit • Sperm passes through zona • Fusion of a single sperm’s plasma membrane with oocyte’s plasma membrane • Cortical reaction: sperm receptors destroyed in zona so no more enter; sperm nucleus engulfed by egg’s cytoplasm Fertilization occurs at the moment the chromosomes from the male and female gametes unite

34. Initial days • Cleavage (cell division) • Blastocyst stage by day 4: now in uterus

35. Implantation Blastocyst floats for 2 days: “hatches” by digesting zona enough to squeeze out 6-9 days post conception - burrows into endometrium

36. Formation of Placenta • Both contribute: • Trophoblast from embryo • Endometrial tissue from mother • Not called placenta until 4th month • Embryonic blood circulates within chorionic villi, close to but not mixing with mother’s blood • Nutrients to baby • Wastes to mom

37. The “Placental Barrier” • Sugars, fats and oxygen diffuse from mother’s blood to fetus • Urea and CO2 diffuse from fetus to mother • Maternal antibodies actively transported across placenta • Some resistance to disease (passive immunity) • Most bacteria are blocked • Many viruses can pass including rubella, chickenpox, mono, sometimes HIV • Many drugs and toxins pass including alcohol, heroin, mercury • Placental secretion of hormones • Progesterone and HCG (human chorionic gonadotropin, the hormone tested for pregnancy): maintain the uterus • Estrogens and CRH (corticotropin releasing hormone): promote labor

38. Childbirth • Gestational period: averages 266 days (this is time post conception; 280 days post LMP) • Parturition: the act of giving birth: 3 stages of labor • Dilation: 6-12h (or more in first child); begins with regular uterine contractions and ends with full dilation of cervix (10cm) • Expulsion: full dilation to delivery – minutes up to 2 hours • Placental delivery: 15 minutes Dilation of cervis; head enters true pelvis Expulsion: head first safest as is largest part Delivery of the placenta Late dilation with head rotation to AP position

39. Stages of Life • Embryologically, males and females start out “sexually indifferent” • Gonads, ducts and externally identical structures • At 5 weeks gestation changes start to take place • Puberty: reproductive organs grow to adult size and reproduction becomes possible • Between 10 and 15 • Influence of rising levels of gonadal hormones • Testosterone in males • Estrogen in females • Female menopause (between 46 and 54): • Loss of ovulation and fertility