Introduction Reproductive System Dr. Shaikh Mujeeb Ahmed The power point is prepared by Dr. Amel Eassawi

Objectives Know the functional anatomy of male & female reproductive system. Describe how the chromosomal content determines the sex of an embryo and how this relates to the development of testes or ovaries. Explain how the sexual differentiation along male & female lines depends on the presence or absence of masculinizing determinants. Discuss the abnormalities on sexual differentiation.

Functional Anatomy of the Reproductive System

Reproductive System Depends on union of male and female gametes to form new individual. Male and female reproductive systems designed to enable union of genetic material.

Reproductive System Components of Reproductive System: 1. Primary reproductive organ (Gonads) 2. Reproductive tract 3. Accessory sex glands 4. External genitelia

Reproductive System 1. Primary Reproductive Organs (gonads) Pair of testes in male. Pair of ovaries in female. Functions of Mature Gonads Producing gametes (gametogenesis) Spermatozoa (sperm) in male. Ova (eggs) in female. Secreting sex hormones Testosterone in males. Estrogen and progesterone in females.

Reproductive System 2. Reproductive Tract: 3. Accessory Sex Glands: System of specialized ducts that transport or house gametes after they are produced. 3. Accessory Sex Glands: Empty supportive secretions into reproductive tract. 4. External Genitalia: Externally visible portions of reproductive system.

Reproductive System Secondary Sexual Characteristics: External characteristics not directly involved in reproduction that distinguish males and females Body configuration and hair distribution Governs by testosterone and estrogen Males have broader shoulders and beards Females have curve hips and no beards Progesterone has no influence on secondary sexual characteristic.

Male Reproductive System Functions and Organs: Testes Function: Production of sperm (spermatogenesis). Secretion of testosterone. Accessory Sex Glands Seminal vesicles, prostate gland, bulbourethral gland Function: Secretions provide bulk of semen (liquid substance that is conducive to sperm viability) Penis Function: Organ used to deposit semen in female Male Reproductive Tract Epididymis, ductus (vas) deferens Function: Sperm maturation Ejaculatory duct Function: Empty into urethra (canal running length of penis that empties into exterior)

Male Reproductive System

Female Reproductive System Functions and Organs Ovaries Function: Production of ova (oogenesis). Secretion of estrogen & progesterone. Female Reproductive Tract Oviducts (uterine or Fallopian tubes) Function: Pick up ova on ovulation, Serve as site for fertilization Uterus Function: Responsible for maintenance of fetus during development Responsible for expelling fetus at end of pregnancy The lower portion of the uterus is the cervix (projects in the vagina and contain single, small opening the cervical canal Serves as pathway for sperm through the uterus to the site of fertilization Serves as passageway for delivery of baby from uterus

Female Reproductive System Vagina Function: Connects uterus to external environment Vaginal opening Located in perineal region between urethral opening and anal opening Partially covered by thin mucous membrane, hymen Labia minora and labia majora Skin folds that surround vaginal and urethral openings Clitoris Small erotic structure located at anterior end of folds of labia minora Vulva Collective term for female external genitalia

Female Reproductive System

Reproductive Cells Body (somatic) cells Contain 46 chromosomes (diploid number) Can be sorted into 23 homologous pairs Gametes (sperm and egg) Have 23 chromosomes (haploid number) Contains only one member of each homologous pair of chromosomes Gametogenesis is accomplished by meiosis

Chromosomal Distribution in Sexual Reproduction

Reproductive Cells Autosomes 22 pairs which code for general human characteristics and specific traits. (example eye color) Sex chromosomes Remaining pair of chromosomes Two genetically different types Larger X chromosome Smaller Y chromosome

Sexual Differentiation

Sex Determination Depends on combination of sex chromosomes Genetic female Has two X chromosomes Genetic male Has an X and a Y chromosome Y chromosome Responsible for all the anatomical and functional distinctions between males and females Genetic sex Determined at time of conception Depends on which type of sex chromosome is contained within the fertilizing sperm

Sex Determination Three levels of differences between males and females Genetic Depends on combination of sex chromosomes at time of conception Gonadal Whether testes or ovaries develop Presence or absence of Y chromosome determines gonadal differentiation Phenotypic Apparent anatomic sex of individual Determined by gonadal sex

TIME SEQUENCE OF HUMAN SEXUAL DIFFERENTIATION IN MALES & FEMALES

Time Sequence of Human Sexual Differentiation in Males & Females The gonads (both XY and XX genotypes) are bipotential at seven weeks of gestation. In males, testicular differentiation begins after the seventh week of gestation. Primitive sertoli-like cells in the developing testis secrete AMH and regression of the Mullerian ducts begins at around 60 days of gestation. Differentiation of the Wolfian ducts in response to testosterone begins at 63-70 days of gestation in males and meoisis signals the beginning (60-70 days) of ovarian differentiation in females. Differentiation of the male external genitalia occurs during the 9-13 weeks of gestation in response to DHT. Androgen induced brain differentiation may occur via its conversion to estrogen in the target tissue.

Male Sexual Differentiation The first step toward sexual differentiation is action of the SRY gene product on primordial germ cells (PGC) to start testicular differentiation. The SRY gene is found distal to the ZFY gene on the Y chromosome of males. Subsequently, the PGC and associated cells start organizing into testicular-like structures Sertoli cells (or Sertoli precursor cells) secrete AMH which causes regression of the adjacent Müllerian duct. Leydig (or Leydig precursor cells) secrete testosterone which induces differentiation of the Wolffian ducts into the internal secondary sex organs. The external secondary sex structure differentiation occurs in response to DHT (dependent on the presence of 5DHT reductase in the target tissues).

UROGENITAL 5 REDUCTASE ACTIVITY DURING DIFFERENTIATION 5  DHT reductase must be present at adequate levels in cells of precursor structures during the critical 9 – 13 week period of gestation in order for differentiation into male external secondary sex organs to occur. An absence of this enzyme in male fetuses during that period (5  reductase deficiency) leads to female appearing external genitalia

DIFFERENTIATION OF MALE & FEMALE EXTERNAL GENITALIA

Fetal Plasma Gonadotropins, Androgen & Testis Development The decline in fetal gonadotropin levels after the first trimester leads to a decrease in numbers of Leydig cells and a reduction of seminiferous tubule growth Proliferation of Leydig cells and tubule development is associated with elevated fetal gonadotropin levels.

Male Sexual Differentiation Summary Testicular differentiation is mediated by TDF (TIF). The first endocrine function of the fetal testis is secretion of AMH (MIS). Dihydrotestosterone stimulates (mediates) differentiation of the urethra (?), prostate, and external genitalia. Testosterone mediates differentiation of the Wolffian ducts and associated internal secondary sex structures. Fetal testosterone reaches peak plasma levels at 16 weeks of gestation. hCG and fetal LH are important for continued growth of the penis and testis during the second and third trimesters.

Female Sexual Differentiation Summary In the absence of TDF, gonadal cells have an inherent tendency to form ovarian-like structures. In the absence of androgens an inherent tendency for formation of female secondary structure exists. Interstitial steroidogenic cells appear at 12 weeks of gestation. Oogonia formation is complete at 7 months of gestation. Approximately two million follicles are present in the new-born ovary. Primordial follicle development is completed at six months post-partrum.

OVARIAN DEVELOPMENT DURING FETAL GROWTH The first primordial follicles appear near the fourth month of gestation. The last oogonia enter meiosis at seven months of gestation. Around 2M follicles are present at birth and folliculogenesis is completed at six months post-partum

Errors in Sexual Differentiation

Errors in Sexual Differentiation Discrepancies occur between genetic and anatomic sexes Pseudo hermaphrodite: Gonad of one sex and genitalia of other 1. Male Pseudo Hermaphrodite: Genetic males whose target cells lack receptors for testosterone are feminized ( testicular feminizing syndrome) Defective testicular development 5α reductsae deficiency ( enzyme, coverts testosteron to DHT) Female phenotype & XY male genotype

Errors in Sexual Differentiation 2. Female Pseudo Hermaphrodite: Congenital virilizing adrenal hyperplasia Administration of androgen to mother Male phenotype and XX female genotype

(Turner’s syndrome) (Klinefelter’s syndrome) Four possible defects produced by maternal non-disjunction of the sex chromosomes at the time of meiosis

References Human physiology, Lauralee Sherwood, seventh edition. Text book physiology by Guyton &Hall,11th edition. Text book of physiology by Linda .s Contanzo, third edition. Physiology by Berne and Levy, sixth edition.