Presentation on theme: "Reproductive System Getting Genes Into The Next Generation."— Presentation transcript:
Reproductive System Getting Genes Into The Next Generation
Fertilization brings together a haploid sperm and a haploid egg (ovum) to form a diploid zygote and embryo. Haploid Diploid
Overall Strategies of Reproduction Males Produce haploid gametes (sperm - testes) Produce lubricants and nutrients for sperm (seminal fluids) Deliver semen to female reproductive system (penis) Provide hormones to coordinate system Females Produce haploid gametes (ovaries) Produce lubricants for intercourse Receive semen from male (vagina) Provide for development of embryo (uterus and placenta) Provide nutrients for growth of enfant (breasts – lactation) Provide hormones to coordinate system
Basic Female Anatomy Ovary Oogenesis Endocrine tissue Oviduct (uterine tube) site of fertilization carries sperm to ovum carries embryo to uterus Uterus Site of embryological development Cervix separates the uterus and the vagina Vagina accommodates the penis Clitoris sensitive nerve endings Ureter Urinary Bladder Urethra
Development of Reproductive Organs 1.Undifferentiated gonad 2.Wolffian ducts 3.Mulerian Ducts 4.Ureter 5.Genital tubercle 6.Cloaca 7.and 8. Labioscrotal fold 9.Anus
Genetics of Sex Normally humans have two complete sets of chromosomes: pairs of 23 different chromosomes. Normally females have two “X” chromosomes and males have a mismatched pair: one “X” and one “Y”. The Y chromosome carries genes that will help to regulate the normal development of a male embryo/fetus.
At 10 weeks of development, visible differences in male and female embryos begin to occur. Genes from the Y chromosome (only present in males) activate the production of testosterone and Mullerian Inhibiting Substance (MIS). These Substances sustain the development of the Wolffian Ducts and inhibit the development of the Mullerian ducts. In the absence of testosterone and MIS, the reproductive tract will develop as a normal female phenotype.
Androgen Insensitivity Syndrome (Testicular Feminizing Syndrome) Normal XY genotype Have a mutated gene that codes for the testosterone receptor, and sometimes the MIS receptor as well. Produce normal levels of testosterone, but the target tissues are unable to respond. Wolffian ducts do not persist and Mullerian ducts may develop. If MIS is present, then no uterus will develop and the vagina is small. Normal female phenotype develops - except, testes are located where the ovaries belong. Often undetected prior to puberty. Externally puberty proceeds as normal, but no menstruation occurs.
Three Siblings with Androgen Insensitivity Syndrome
Male Reproduction Testis Seminiferous Tubules Epididymis Spermato- genesis DCBADCBA A and B = Spermatogonia C= Spermatocyte D = Spermatids Interstitial Cells Of Leydig
Interstitial Cells of Leydig = produce Testosterone. Sertoli Cells (Sustenacular Cells) Surround spermatocytes and spermatids. Produce Inhibin
What Effects Does Testosterone Have? Normal Embryological Development in Males Stimulates growth and development of the male reproductive tract at puberty Stimulates spermatogenesis Male secondary sex traits (Height, muscle mass, larger larynx, facial and body hair)
Role of the Accessory Glands Seminal Vesicles – fructose (energy source) and prostaglandins that stimulate contractions of female repro. Tract. Prostate Gland – High pH fluid that neutralizes the acidic environment of the vagina and increases the motility of the sperm. Bulbourethral gland (Cowper’s Gland) Role of the Scrotum Temperature regulation
Overview of the Menstrual Cycle Approximately 28 days (may be highly variable) Day one is counted as the first day after menstrual bleeding stops. Days 1-14 - Ovum enlargess inside a growing follicle and the endometrial lining of the uterus thickens in preparation to receive a fertilized egg Day 14 - Ovulation (release of egg from ovary) occurs and the ovum enters the uterine tube. Days 15-20 – Ovum (or fertilized egg) moves to uterus. Days 18-21 – If embryo exists, it begins to implant in endometrium Days 25-28 – If embryo does not implant, endometrial lining as lost in menstrual bleeding.
GnRH LH + FSH E E Positive Feedback Low levels of LH and FSH GnRH = gonadotropin Releasing hormone FSH = follicle stimulating hormone LH = luteinizing hormone Pre-ovulation
1. The positive feedback of Estrogen at the hypo- Thalamus causes a surge in GnRH release. 2.The GnRH release causes a surge in FSH and LH 3.The LH surge causes ovulation and the formation of the corpus luteum 4.The Corpus luteum continues to release E and high levels of P 5.The E and P provide negative feedback to the hypothalamus Rising levels of estrogen over several days. GnRH surge FSH and LH Surge E and P
Physiological Effects of Estrogen Estrogen - steroid produced by the ovary *growth of the female reproductive tract *stimulates growth of endometrial lining during each menstrual cycle *stimulates the production of a watery secretion at the cervix. *stimulates breast and hip development and subcutaneous fat layer (secondary sex traits)
Progesterone * Increases endometrial lining and maintains the endometrial lining. * Causes a thick mucous secretion from the cervix. * Increases the basal metabolic rate (increase in resting body temperature by about 1 degree) Physiological Effects of Progesterone
If Fertilization Does Not Occur Without additional LH or some other source of hormonal stimulation, the corpus luteum has a limited life; typically around 10 days. After 10 days the corpus luteum will degenerate and turn into scar tissue (corpus albicans). At this point the levels of estrogen and progesterone decline very rapidly. Without estrogen and progesterone, the endometrial lining is lost.
Chemical Contraception Birth control pills, Depoprovera (injected 2-4 times per year), and “patches” All contain relatively high levels of estrogen and lower amounts of progesterone. Provides negative feedback to hypothalamus. Interferes with normal secretions of cervix.
Signaling by the Embryo Blastocyst Trophoblast releases Human Chorionic Gonadotropin (HCG) HCG acts like LH and stimulates the ovary to maintain the corpus luteum Ovary continues to make progesterone and estrogen. Endometrial lining is retained - woman “misses her period.”