Reproductive System PDF

Reproductive System Sex vs. Reproduction Sex - process by which a genome is changed by rearrangement and combining of genes Reproduction - process by which individuals are added to a population  Asexual reproduction – the production of offspring whose genes all...

Reproductive System Sex vs. Reproduction Sex - process by which a genome is changed by rearrangement and combining of genes Reproduction - process by which individuals are added to a population  Asexual reproduction – the production of offspring whose genes all come from one parent without the fusion of egg and sperm. – Usually diploid eggs are produced by mitosis which then develop directly.  Asexual Reproduction Fragmentation occurs in some sponges, cnidarians, polychaete annelids, tunicates. – Sea stars can regenerate lost limbs, but only species in the genus Linckia can form new individuals from ?  Sexual Reproduction Why do so many animals reproduce sexually rather than asexually? Generally involves two parents. Special germ cells unite to form a zygote. Sexual reproduction recombines parental characters. – A richer, more diversified population results. In haploid asexual organisms mutations are expressed and selected quickly. In sexual reproduction a normal gene on the homologous chromosome may mask a gene mutation.  Sexual Reproduction The costs of sexual reproduction are greater than asexual methods: – More complicated. – Requires more time. – Uses more energy. – The cost of meiosis to the female is passage of only half of her genes to offspring. – Production of males reduces resources for females that could produce eggs.  Sexual Reproduction The mechanics of fertilization play an important part in sexual reproduction. Many aquatic animals – use external fertilization and – discharge their gametes into the water, where fertilization occurs. Nearly all terrestrial animals reproduce by internal fertilization, in which a male deposits sperm within a female’s body. © 2016 Pearson Education, I nc.  Sexual Reproduction In some species, each individual is a hermaphrodite, with male and female reproductive systems. Some hermaphrodites can fertilize their own eggs, while other species require a partner. © 2016 Pearson Education, I nc.  Sexual reproduction involves: Male Female Fertilization Embryo development Figure 26.5 Urinary bladder Seminal vesicle (behind Prostate gland Front bladder) view Erectile tissue of penis Urethra Vas deferens Side view Glans of penis Epididymis Rectum Testis Scrotum Seminal Testicle vesicle Vas Urinary bladder deferens Sperm Pubic bone duct Erectile Prostate tissue gland Urethra Vas deferens Penis Anus Epididymis Glan Testicle Testis Scrotum s Prepuce Figure 26.7-1 Epididymis Penis Testis Scrotum Testis Seminiferous Cross tubule section of seminiferous tubule Leydig cell ---produces testostosterone Sertoli cell-nourishes germ cells, releases chemicals Male Reproductive Anatomy Because sperm do not develop optimally at body temperature, the scrotum promotes sperm formation by keeping sperm-forming cells about 2C cooler. © 2016 Pearson Education, I nc. Male Reproductive Anatomy From puberty into old age, the testes produce hundreds of millions of sperm each day. From the testes, sperm pass into a coiled tube called the epididymis. – During ejaculation—expulsion of sperm-containing fluid from the penis— the sperm leave the epididymis and travel through a duct called the vas deferens. © 2016 Pearson Education, I nc. Male Reproductive Anatomy – The seminal vesicles and prostate gland add fluid that nourishes the sperm and provides protection from the natural acidity of the vagina. – Each vas deferens, one from each of the two testes, empties into the urethra. © 2016 Pearson Education, I nc.  Spermatogenesis Outermost layer of the seminiferous tubules contain spermatogonia, diploid cells that grow to become primary spermatocytes. After the first meiotic division, they are called secondary spermatocytes. When meiosis is complete the haploid cells are spermatids. Figure 26.7 Epididymis Cell division continuously Testis Penis produces new cells Scrotum 2n Diploid cell Differentiation and onset of meiosis I Testis Seminiferous Cross 2n Primary spermatocyte tubule section of (diploid) seminiferous Meiosis I completed tubule n n Secondary spermatocyte (haploid) Meiosis II n n n n Developing sperm cells Cellular differentiation (cells become specialized) Sperm cells n n n n (haploid) Mature sperm released into center of seminiferous tubule  The female reproductive system Ovaries [ gonads] Uterine tubes [ fallopian tubes] Uterus Vagina Accessory glands External genitalia Breasts  Ovaries Ovaries are where female gametes, egg cells, are produced. – A follicle contains one egg cell as well as follicle cells that nurture the developing egg. – Most/all of the follicles a woman will produce have formed before birth. Developing follicleEpithelial lining ovary Mature follicle Corpus luteum Atretic follicle  FEMALE REPRODUCTIVE SYSTEM The Ovarian Cycle  OVARY 3 to 5 million OOGONIA differentiate into PRIMARY OOCYTES during early development OOCYTES becomes surrounded by squamous (follicular) cells to become PRIMORDIAL FOLLICLES most PRIMORDIAL FOLLICLES undergo atresia leaving 400,000 at birth oocytes at birth arrested at Meiosis I (prophase) Figure 26.8-2-s4 Before birth Primary 2n oocyte Diploid cell within in embryo follicle Differentiation and onset of meiosis I Growing follicle 2n Primary oocyte (diploid) arrested at prophase Mature Completion of of meiosis I; present follicle meiosis I and at birth onset of n First meiosis II polar body n Secondary oocyte (haploid) Entry of sperm arrested at metaphase Ruptured triggers of meiosis II follicle completion of meiosis II Second n polar body Ovulated Mature egg (ovum) secondary n oocyte (haploid) Figure 26.8-3 Secondary oocyte Ovary Ruptured follicle Ovulated secondary oocyte LM A secondary oocyte being released during ovulation Corpus luteum  Female Reproductive Cycle The female reproductive cycle in humans contains two parts: – Uterine (menstrual) cycle – Ovarian cycle One integrated cycle involving the uterus & ovaries. The Menstrual Cycle: The Uterus Proliferative stage: increasing estradiol levels stimulate proliferation of the functional layer of the uterine endometrium. - Results in increased thickness of the endometrium. - Increased growth of uterine glands (secrete mucus) and uterine arteries. Secretory stage: progesterone acts on the endometrium. - uterine glands become coiled and secrete more mucus - uterine arteries become coiled (spiral arteries) The Menstrual Cycle: The Ovary Follicular phase: small antral follicles develop, a dominant follicle is selected and grows to the preovulatory stage. Midcycle: the gonadotropin surges cause ovulation of the dominant follicle. Luteal phase: the corpus luteum forms and becomes functional, secreting large amounts of progesterone, followed by estradiol (results in negative feedback, not positive feedback, because P increases before E2). If pregnancy does not take place, the corpus luteum regresses, and P and E2 levels decrease. Female Reproductive Cycle The ovarian and uterine cycles are regulated by changing hormone levels in the blood. The Uterine Cycle To be discussed below Figure 28.20 No fertilization – Days 24-28, Premenstrual phase Degeneration of endometrium Fertilization first polar body metaphase of second meiotic division Figure 26.12-1 2 The sperm’s acrosomal enzymes digest the jelly coat surrounding the egg. 3 1 The plasma The sperm membranes of the 4 The sperm nucleus squeezes through sperm and egg fuse. enters the egg cells left over from cytoplasm. the follicle. Acrosomal enzymes Sperm Nucleus Acrosome n n n 5 The sperm Follicle Sperm and egg cell nucleus chromosomes n Plasma intermingle. Jelly membrane coat n 2n Cytoplasm Egg Zygote nucleus nucleus Figure 26.15-s5 3 Cleavage of 4 The embryo 5 The blastocyst embryo starts. develops into implants in the a blastocyst. endometrium. Oviduct 2 Sperm fertilizes ovum, forming Ovary a zygote. 1 Ovulation releases Endometrium secondary Uterus oocyte. Cleavage Cleavage Changes in Uterus Dilation Stage  Contraception Three general strategies: – Prevent ovulation; – Prevent fertilization; Keep sperm & oocyte away from each other. – Prevent implantation. 15 April 2013 Contraception.ppt 43  Hormone-based contraceptives 5 types 1) Oral contraceptives (pills) 2) Vaginal ring 3) Transdermal patch 4) Injected hormones 5) Hormonal IUDs