Animal Reproductive Systems. Chapter 42

Animal Reproductive Systems Chapter 42

Impacts, Issues Male or Female? Body or Genes? Body and genes don t always match male or female characteristics also depend on hormones mutations can result in intersex conditions

42.1 Modes of Animal Reproduction Sexual reproduction dominates the life cycle of most animals Many invertebrates and some vertebrates can reproduce asexually or sexually

Asexual Reproduction in Animals Asexual reproduction A single individual makes offspring that are genetically identical to the parent Advantageous in a stable environment where a parent passes on successful gene combinations Methods of asexual reproduction Fragmentation (in many invertebrates) Parthenogenesis (from unfertilized eggs)

Costs and Benefits of Sexual Reproduction Sexual reproduction Two parents make gametes that combine at fertilization to produce offspring with gene combinations unlike either parent Genetic diversity increases chances of offspring survival in changing environments Genetic and energetic costs are higher than in asexual reproducers

Variations on Sexual Reproduction Most vertebrates have separate sexes that are fixed for life; an individual is either male or female Some animals produce eggs and sperm at the same time (simultaneous hermaphrodites), or produce both at different times in their life (sequential hermaphrodites)

Eggs: Fertilization and Development Most aquatic animals have external fertilization; most land animals have internal fertilization Internally fertilized eggs may be laid in the environment or develop in a mother s body Egg yolk nourishes developing offspring Amount varies with species Human eggs are nearly yolkless

Examples of Animal Reproduction

Invertebrate and Vertebrate Parenting

Fig. 42-3a, p. 741

Fig. 42-3b, p. 741

Fig. 42-3c, p. 741

Fig. 42-3d, p. 741

Fig. 42-3e, p. 741

Fig. 42-3f, p. 741

Fig. 42-3g, p. 741

42.1 Key Concepts Modes of Animal Reproduction Some animals reproduce asexually, but sexual reproduction predominates in most animals Some sexual reproducers make both eggs and sperm, but most are either male or female Living on land favored fertilization of eggs inside the female body

42.2 Reproductive System of Human Males The male reproductive system produces hormones and sperm, which it delivers to a female reproductive tract Male gonads (testes) Primary reproductive organs in human males Produce the male hormone testosterone Sperm production begins at puberty

The Path of Sperm Reproductive ducts Seminal tubules produce immature sperm Epididymis stores and matures sperm Vas deferens carries sperm to ejaculatory duct Ejaculatory duct connects to urethra in the penis The penis contains spongy tissue which fills with blood during sexual excitement

Semen and Accessory Glands Semen Sperm and secretions from accessory glands (proteins, nutrients, ions, signaling molecules) Accessory glands Seminal vesicles secrete fructose-rich fluid (an energy source) and prostaglandins Prostate gland produces alkaline secretions and prostaglandins Bulbourethral glands secret lubricating mucus

Prostate and Testicular Problems Prostate enlargement Can be caused by inflammation, age, or prostate cancer a leading cause of death Constricts urethra, causing difficulty in urination Diagnosed by blood tests, physical examination Testicular cancer is relatively rare Detected by self-examination

Human Male Reproductive System

Prostate Gland An exocrine gland that contributes some fluid to the semen urinary bladder Urethra Duct with dual functions; channel for ejaculation of sperm during sexual arousal and for excretion of urine at other times urethra cylinders of spongy tissue that swell with blood during an erection Penis Male organ of sexual intercourse scrotum anus Testis One of a pair of gonads, packed with small, sperm-producing tubes (seminiferous tubules) and cells that secrete testosterone and other sex hormones Ejaculatory Duct One pair of ducts that carry sperm to the penis Seminal Vesicle One of a pair of exocrine glands that contributes fructoserich fluid to semen Bulbourethral gland One of a pair of exocrine glands that secrete mucus Vas deferens One of a pair of ducts that carry sperm to the penis Epydidymis One of a pair of ducts in which sperm mature and are stored Fig. 42-4, p. 742

Animation: Male reproductive system

Human Male Reproductive System

42.3 Sperm Formation Seminiferous tubules in male testes continually produce new diploid germ cells (spermatogonia), which undergo meiosis to produce haploid male gametes (sperm) Spermatogonium Primary spermatocyte Secondary spermatocyte Spermatid Immature sperm

Sperm Formation

Fig. 42-5a, p. 744

vas deferens seminal vesicle prostate gland bulbourethral gland urethra penis seminiferous tubule epididymis testis Fig. 42-5a, p. 744

Fig. 42-5c, p. 744

mitosis meiosis I meiosis II lumen Sertoli cell secondary spermatocyte early spermatids immature sperm (haploid) spermatogonium (diploid) primary spermatocyte late spermatid Fig. 42-5c, p. 744

Animation: Route sperm travel

Animation: Spermatogenesis

A Spermatozoan Spermatozoan: a mature sperm Head with DNA and an enzyme cap Midpiece with mitochondria Flagellum for movement

head, with DNA and a cap of enzymes midpiece with mitochondria tail, with its core of microtubules Fig. 42-6, p. 745

Hormonal Control of Sperm Formation The hypothalamus produces gonadotropin releasing hormone (GnRH) GnRH causes the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Hormonal Control of Sperm Formation LH causes Leydig cells between seminiferous tubules to produce testosterone FSH causes Sertoli cells inside seminiferous tubules to produce growth factors and other molecular signals

Signaling Pathways in Sperm Formation: Inhibin and Negative Feedback Control

a Level of testosterone in blood decreases; the hypothalamus secretes GnRH, a releasing hormone. Hypothalamus f Elevated level of testosterone in blood inhibits secretion of GnRH. Anterior Pituitary b GnRH stimulates secretion of LH, FSH from anterior lobe of pituitary. g High sperm count induces Sertoli cells to secrete inhibin, which inhibits secretion of GnRH and LH. Testes c LH prompts Leydig cells in testes to produce and release testosterone. d Sertoli cells bind FSH and testosterone, and function in spermatogenesis at puberty. e Testosterone and secretions from Sertoli cells encourage sperm production. Fig. 42-7, p. 745

42.2-42.3 Key Concepts Male Reproductive Function A human male has a pair of testes that make sperm and secrete the sex hormone testosterone Sperm mixes with secretions from other glands and leaves the body through ducts

42.4 Reproductive System of Human Females The female reproductive system functions in the production of gametes and sex hormones The system receives sperm, and has a chamber in which developing offspring are protected and nourished until birth

Location of the Female Reproductive System

pelvic girdle urinary bladder uterus ovary vagina Fig. 42-8, p. 746

Components of the Female Reproductive System Female gonads (ovaries) secrete sex hormones and produce immature eggs (oocytes) on a cyclic basis Oocytes are released into an oviduct, where fertilization occurs, before entering the uterus, where the embryo develops The vagina functions in intercourse and as the birth canal

Female Reproductive Organs

Components of the Female Reproductive System

Ovary One of a pair of gonads that makes oocytes and sex hormones; during the course of a monthly cycle, releases hormones that stimulate maturation of an oocyte and prepares the lining of the uterus for a potential pregnancy Urinary bladder Urethra Clitoris Small organ responsive to sexual stimulation Labium Minora One of a pair of innermost thin, skin folds; part of the genitals Labium Majora One of a pair of outermost, fatpadded skin folds; part of the genitals Oviduct One of a pair of ciliated channels through which oocytes are propelled from an ovary to the uterus; usual site of fertilization anus Vagina Organ of sexual intercourse; also the birth canal opening of cervix Uterus Chamber in which embryo develops; its narrowed portion, the cervix, secretes mucus that helps sperm travel into the uterus and defends the embryo against many bacteria Myometrium Thick muscle layers of uterus; stretch greatly during pregnancy Endometrium Inner lining of the uterus into which a blastocyst implants itself; gets thicker and has increased blood supply during pregnancy; gives rise to maternal portion of placenta, an organ that metabolically supports embryonic and fetal development Fig. 42-9, p. 746

Animation: Female reproductive system

Overview of the Menstrual Cycle Menstrual cycle A hormone-controlled estrous cycle in which a female is fertile only at certain times Every 28 days, an oocyte matures and is released The uterus prepares for pregnancy If pregnancy does not occur, the endometrial lining of the uterus is shed (menstrual flow) Menopause Decline of hormone production and menstrual cycle

42.5 Hormones and Female Troubles Premenstrual syndrome (PMS) Changes in aldosterone secretion cause water retention also depression, irritability, headaches Menstrual pain Prostaglandins stimulate uterine contractions Fibroid tumors cause pain and bleeding Hot flashes and night sweats Side effects of hormonal changes of menopause

42.6 Preparations for Pregnancy At birth, a girl has about 2 million immature eggs (primary oocytes) arrested in meiosis I At puberty, oocytes begin to mature, one at a time, in a 28-day ovarian cycle

The Follicular Phase Ovarian follicle A primary oocyte and the cells that surround it Follicular phase First part of the ovarian cycle Cells around the oocyte divide Oocyte enlarges and secretes glycoproteins Zona pellucida Noncellular layer of secreted glycoproteins

An Ovarian Cycle

B The zona pellucida, a transparent, slightly elastic layer, starts to form around primary oocyte. A A primary oocyte, not yet released from meiosis I. A layer of cells is forming around it. A mature follicle consists of this cell layer and the oocyte inside it. primordial follicle C A fluid-filled cavity starts to form in the follicle s cell layer. first polar body ovary secondary oocyte D Mature follicle. Meiosis I is over. A secondary oocyte and the first polar body have formed. G If no pregnancy occurs, the corpus luteum breaks down. F A corpus luteum forms from remains of ruptured follicle. E Ovulation. Mature follicle ruptures, releasing the secondary oocyte and first polar body. Fig. 42-10, p. 748

Animation: Ovarian function

Hormonal Controls Hypothalamus secretes GnRH; the anterior pituitary increases FSH and LH secretion FSH and LH stimulate maturation of an ovarian follicle; the follicle secretes estrogens, which cause endometrium to thicken Rising estrogen levels cause a spike in LH, which stimulates a primary oocyte to complete meiosis I

Hormonal Controls The midcycle spike of LH triggers the release of a secondary oocyte, surrounded by the zona pellucida, into an oviduct (ovulation) After ovulation (luteal phase), progesterone secreted by the ruptured follicle (corpus luteum) reduces LH and FSH secretion, and promotes secretion by endometrial glands

Changes in Hormones, Ovary, and Uterus

Fig. 42-11, p. 749

A FSH and LH levels in blood FSH LH FSH and LH stimulate Follicle maturation LH surge Triggers ovulation Fig. 42-11, p. 749

Fig. 42-11, p. 749

B Follicle changes in an ovary follicle matures ovulation corpus luteum forms corpus luteum breaks down follicle secretes estrogens corpus luteum secretes estrogens, progesterone Fig. 42-11, p. 749

Fig. 42-11, p. 749

C Estrogen and progesterone levels in blood Progesterone Estrogen low estrogen estrogens, progesterone, cause uterine lining to thicken Fig. 42-11, p. 749

Fig. 42-11, p. 749

D Changes in uterine lining menstrual flow 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Days of cycle Follicular phase Luteal phase Fig. 42-11, p. 749

Animation: Menstrual cycle summary

If Pregnancy Does Not Occur The corpus luteum breaks down Drop in hormone levels causes the endometrial lining to break down (menstruation) New follicular phase begins

42.7 FSH and Twins Typically, only a single egg matures and is released during each menstrual cycle Abundant FSH can cause two eggs to mature and possibly lead to fraternal twins FSH levels are highest among women of African descent, and in older women

FSH and Twins FSH levels and frequency of fraternal twins vary among ethnic groups unrelated to chance formation of identical twins

42.4-42.7 Key Concepts Female Reproductive Function A human female has a pair of ovaries that produce eggs and sex hormones An approximately monthly hormonal cycle causes release of eggs Ducts carry eggs toward the uterus, where offspring develop The vagina receives sperm and is the birth canal

42.8 When Gametes Meet Sexual intercourse (coitus) Sexual arousal involves nervous and hormonal signals; ejaculation releases millions of sperm into the vagina Sperm travel through the uterus toward the oviducts, where fertilization typically occurs

Fertilization Sperm bind to the oocyte s zona pellucida, triggering release of acrosomal enzymes Penetration by a single sperm causes the secondary oocyte to complete meiosis II, and prevents penetration of additional sperm Sperm organelles disintegrate; sperm and egg DNA become the genetic material of the zygote

Human Fertilization

Fig. 42-13a, p. 751

oviduct Fertilization ovary uterus Ovulation opening of cervix vagina A Fertilization most often occurs in the oviduct. Many human sperm travel swiftly through the vaginal canal into oviducts (blue arrows). Inside an oviduct, the sperm surround a secondary oocyte that was released by ovulation. Fig. 42-13a, p. 751

Fig. 42-13b, p. 751

B Enzymes released from the cap of each sperm clear a path through the zona pellucida. Penetration of the secondary oocyte by a sperm causes the oocyte to releases substances that harden the zona pellucida and prevent other sperm from binding. oocyte nucleus zona pellucida follicle cell Fig. 42-13b, p. 751

Fig. 42-13c, p. 751

zona pellucida haploid egg and sperm nuclei C The oocyte nucleus completes meiosis II, forming a nucleus with a haploid maternal genome. The sperm s tail and other organelles degenerate. Its DNA is enclosed by a membrane, forming a haploid nucleus with paternal genes. Later, the two nuclear membranes will break down and paternal and maternal chromosomes will become arranged on a bipolar spindle in preparation for the first mitotic division. Fig. 42-13c, p. 751

Animation: Fertilization

42.9 Preventing or Seeking Pregnancy Birth control options Abstinence (the most effective method) Surgical methods (tubal ligation or vasectomy) Physical and chemical barriers block sperm (spermicides, diaphragms, condoms) IUDs prevent implantation Hormones prevent ovulation (pill, implant)

Common Methods of Contraception

Effectiveness of Contraceptive Methods

Most Effective Total abstinence Tubal ligation or vasectomy Hormonal implant (Norplant) Highly Effective IUD + slow-release hormones IUD + spermicide Depo-Provera injection IUD alone High-quality latex condom + spermicide with nonoxynol 9 The Pill or birth control patch Effective Cervical cap Latex condom alone Diaphragm + spermicide Billings or Sympto-Thermal Rhythm Method Vaginal sponge + spermicide Foam spermicide Moderately Effective Spermicide cream, jelly, suppository Rhythm method (daily temperature) Withdrawal Condom (cheap brand) Unreliable Douching Chance (no method) 100% 99.6% 99% 98% 98% 96% 95% 95% 94% 99% 86% 84% 84% 83% 82% 75% 74% 74% 70% 40% 10% Fig. 42-14, p. 752

After the Fact Spontaneous or induced abortion terminates a pregnancy About 10% of detected pregnancies end in spontaneous abortion (miscarriage) Morning-after pills prevent ovulation Abortion may be chemically or surgically induced

Assisted Reproductive Technology In vitro fertilization Eggs and sperm are combined outside the body Embryo is implanted into the mother

42.8-42.9 Key Concepts Intercourse and Fertilization Sexual intercourse requires coordinating nervous and hormonal signals It can lead to pregnancy, which humans use a variety of methods to prevent, promote, or terminate

42.10 Sexually Transmitted Diseases Sexually transmitted diseases (STDs) Result of transfer of pathogens in sexually transmitted body fluids from one host to another Consequences of infection 65 million in US infected with incurable STDs Increased risk of infertility or tubal pregnancy Transmission from mother to child

Consequences of Infection

New STD Cases Annually

Major STDs Human papillomavirus (HPV) Genital warts, cervical cancer Trichomoniasis (protist infection) Urinary tract damage, infertility, HIV risk Chlamydia (bacterial infection) Pelvic inflammatory disease, infertility

Major STDs Genital herpes (viral infection) Pain and blistering Gonorrhea (bacterial infection) Sterility Syphilis (spirochete bacterial infection) Multiple organ damage

Major STDs AIDS (Human immunodeficiency virus) Destruction of immune system Multiple opportunistic infections Living with HIV: Magic Johnson

Some Agents of Bacterial STDs Causes of chlamydia, gonorrhea, and syphilis

42.10 Key Concepts Sexually Transmitted Diseases A variety of pathogens make their home in the human reproductive tract; they are passed between partners by sexual interactions and may be transmitted to offspring during childbirth Effects of sexually transmitted diseases range from discomfort to death

Animation: Follicular phase

Animation: Hormonal control of sperm production

Animation: Hormones and the menstrual cycle

Animation: Ovulation and luteal phase

Animation: Where embryos develop