1. Reproductive Physiology

2. What will be covered: Gametogenesis How gametes form Sexual differentiation Pituitary-gonadal axis Female reproductive physiology Ovarian cycle Uterine cycle Hormonal control and changes Male reproductive physiology

3. Gametogenesis This is the formation of gamete cells via meiosis Gametes are specialised as they contain only half of the genetic material required to reproduce; this is so they can bind with another gamete via sexual reproduction In meiosis 4 haploid gametes are formed from a diploid oogonium (female) or spematogonium (male) The process differs slightly between oocytes and spermatocytes

4. Spermatogenesis During development germ cells are produced, however these remain inactive until puberty Hormones act on germ cells, causing them to undergo mitosis and meiosis to form sperm cells Stages of sperm production: 1.Spermatocytogenesis 2.Spermatidogenesis 3.Spermiogenesis

5. Spermatogenesis Spermatogonium undergo mitosis to ‘double up’ DNA, ready for meiosis. The spermatocytes undergo meiosis twice to produce four spermatids each with one set of DNA, ready to mature into sperm and eventually bind with an ovum in sexual reproduction Mitosis Meiosis I Meiosis II Spermatogonium Primary spermatocyte Secondary spermatocyte Spermatid Sperm

6. Oogenesis Oogenesis produces a secondary oocyte which is released during the ovulatory stage of the menstrual cycle If no fertilisation occurs it will not undergo further meiotic division (i.e. will not undergo meiosis II on diagram) Stages of oocyte production: 1.Oocytogenesis – finished by birth 2.Ootidogenesis 3.Fertilisation of ovum

7. Oogenesis The primary oocyte divides by meiosis to produce a secondary oocyte and a polar body (these are non-functioning waste products). Meiosis II occurs after fertalisation. Mitosis Meiosis I Meiosis II Oogonium Primary oocyte Secondary oocyte Ootid Ovum Primary polar body Secondary polar body Sperm

8. Further differences in male vs female gamete production MaleFemale Continuous production of sperm from puberty indefinitely Stem cells are retained Sperm cells are mobile with little cytoplasm All oocytes are produced before birth Stem cells are used up Sperm cells are large, and are immobile Oocytes are surrounded by follicular cells, and together form a follicle

9. Gender Determination Chromosomes determine gender Humans have 23 chromosomes donated by the egg, and 23 donated by the sperm Two gametes fuse to form a zygote. This requires fusion of both the cytoplasm and the genetic material XXXY XXXYXXXY Zygotes

10. Non-disjunction Occasionally, zygotes form without ‘normal’ separation of X/Y chromosomes. This is non-disjunction in meiosis I or II This can result in monosomy (only one sex chromosome) or polyploidy (more than two sex chromosomes) Monosomy: XO = Turner Syndrome Polyploidy: XXY = Kleinfelter Syndrome XYY = Jacob Syndrome XXX = Trisomy X

11. Turner Syndrome (XO) Females have typical phenotype of short stature, neck skin folds, primitive sexual characteristics, no menstruation and typical facial features Kleinfelter Syndrome (XXY) Males with small testes, infertility, feminine sexual characteristics, normal IQ Jacob Syndrome (XYY) Males with above-average height and reduced IQ Trisomy X (XXX) Females who are normal, and are only identifiable by karyotype

12. Gender Determination At week 7 of embryonic development the SRY gene is activated (SRY = sex-determining region of Y chromosome) As the name suggests, it is only present in males The SRY gene determines the development of sexual characteristics Absence of SRY causes gonads to become ovaries Presence of SRY causes gonads to descend down the Wolffian duct and become testes. The testes produce anti-mullerian hormone which causes the mullerian duct to degenerate. The Wolffian duct becomes the vas deferens The ovaries then produce female hormones and there is an absence of testosterone, so the Wolffian duct degenerates. An absence of anti-mullerian hormone allows the Mullerian duct continue developoing to become fallopian tubes

14. Pituitary-Gonadal Axis The hypothalamus produces gonadotrophin-releasing hormone (GnRH) GnRH stimulates the release of follicle-stimulating hormone (FSH) and lutenising hormone (LH) from the anterior pituitary gland FSH acts on ovaries/testes to stimulate them to produce gametes LH acts on endocrine cells to stimulate them to secrete steroid and peptide hormones This is a negative feedback system

15. Female Reproduction The pituitary-gonadal axis controls menstruation in females What the hormones do Oestrogen: produced by developing follicle. Stimulates LH surge. Progesterone: maintains endometrium for implantation. LH: oocyte maturation and subsequent release from follicle. FSH: stimulates a few follicles to complete meiosis.

16. Menstrual Cycle Lasts 28days ( range is 24-35days) Starts with shedding of endometrium (period) and release of FSH Involves a ovarian cycle and a uterine cycle Ovarian cycle Development of ovarian follicle Production of hormones Ovum release Uterine cycle Shedding of endometrium prior to ovum release Preparation for implantation of potential embryo via hormones These cycles are linked by hormone production/release

17. The Cycles Ovarian cycle: follicular phase (follicle develops), ovulation phase (follicle released), luteal phase (unfertalised follicle degenerates) Uterine cycle: menses (endometrium sheds), proliferative phase (endometrium builds up), secretory phase (endometrium secretes progesterone for potential zygote)

18. If Fertalisation Occurs… The endometrium lining is maintained by: Progesterone from the corpus luteum Human chorionic gonadotrophin (hCG) until w7 Progesterone from the placenta from w7 The placenta also produces oestrogen (breast development) and human placental lactogen (milk production) Birth is stimulated by: Increased corticotrophin-releasing hormone from the placenta for 2weeks prior to birth Reduced progesterone, increased oxytocin (uterine contraction), increased inhibin (cervical relaxation)

19. Male Reproduction The aim of the male reproductive system is to produce, maintain and transport viable sperm It also produces hormones which: Develop secondary sexual characteristics Offer feedback for spermatogenesis Parts of the male reproductive system: Testes Accessory glands Prostate Seminal vesicles Bulbourethral glands

20. Testes Site of sperm production Divided into lobules, each with one seminferous tubule Seminferous tubule maintains a suitable environment for sperm to develop by… Blood-testis barrier Compartments, therefore low glucose/high hormone Hormone production

21. Testes cells Sertoli cellsAnti-mullerian hormoneSecreted in embryology, causes Mullerian duct degeneration InhibinRegulates FSH release Androgen-binding hormoneBinds to testosterone/DHT and reduces their loses, increasing testosterone activity Estradiols/AromataseSupport spermatogenesis Leydig cellsTestosteroneSpermatogenesis and secondary sexual characteristics (stimulated by LH to produce testosterone) FSH increases response to LH

22. Spermatogenesis Hormonal Control GnRH hypothalamus FSH ant. Pituitary Androgen-binding peptide release Sertoli cells Inhibin release Sertoli cells -ve feedback loop LH ant. pituitary Testosterone Leydig cells Spermatogenesis Secondary characteristics

23. Males and Reproduction The role of the male in reproduction is to deliver sperm to the vagina This requires an erection reflex Erotic stimuli stimulate the autonomic nervous system, which vasodilates penile arterioles This causes blood to flood the penile tissue, causing an erection Following the erection reflex an ejaculation reflex is required Emission (movement of sperm from vas deferens into urethra, along with seminal fluids) is stimulated by the sympathetic nervous system Strong muscle contractions (bulbospongiosus) due to a spinal reflex cause expulsion of semen - ejaculation

24. Problems Sometimes problems occur with this: Erectile dysfunction = unable to initiate an ejection or maintain it until ejaculation Premature ejaculation = male reaches orgasm and ejaculates too quickly for partner to achieve enjoyment Prolonged ejaculation = inability for male to orgasm and ejaculate