Animal Reproductive Systems. Chapter 42

Transcription

1 Animal Reproductive Systems Chapter 42

2 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

3 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

4 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)

5 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

6 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)

7 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

8 Examples of Animal Reproduction

9 Invertebrate and Vertebrate Parenting

10 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

11 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

12 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

13 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

14 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

15 Human Male Reproductive System

16 Human Male Reproductive System

17 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

18 Sperm Formation

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

20 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)

21 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

22 Signaling Pathways in Sperm Formation: Inhibin and Negative Feedback Control

23 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

24 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

25 Location of the Female Reproductive System

26 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

27 Female Reproductive Organs

28 Components of the Female Reproductive System

29 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

30 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

31 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

32 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

33 An Ovarian Cycle

34 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

35 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

36 Changes in Hormones, Ovary, and Uterus

37 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

38 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

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

40 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

41 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

42 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

43 Human Fertilization

44 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)

45 Common Methods of Contraception

46 Effectiveness of Contraceptive Methods

47 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

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

49 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

50 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

51 Consequences of Infection

52 New STD Cases Annually

53 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

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

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

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

57 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