Chapter 22 The Reproductive System (I) An Overview of Reproductive Physiology o The Male Reproductive System o The Female Reproductive System 22.1 Reproductive System Overview Reproductive system = all organs involved in mating, gametogenesis, or other functions involved in sexual producing offspring Components of the Reproductive System Gonads o Gonads: Produce gametes through gametogenesis (Figure 22.1) and secrete sex hormones o Accessary organs: Organs of the reproductive tract which transport of gametes and provide nutrients for gametes Glands: Secrete fluids into reproductive tract Fertilization (Figure 22.1) Sex Hormones o Testes: androgens o Ovaries: estrogens and progesterone o Although males have more androgens and females have more estrogens and progesterone, all of these hormones are found in both sexes o Adrenal cortex also produces sex hormones Events Following Fertilization o Copulation = act of mating o Sperm deposited into female to fertilize ovum o After fertilization = pregnancy or gestation First two months: embryo After two months: fetus About nine months: parturition or birth o Sex determination is the role of in gender determination Gender of the zygote is determined at the moment of fertilization by the fertilizing sperm Human somatic cells are diploid and have 23 pairs of homologous chromosomes. Autosomal chromosomes: 22 pairs. Sex chromosomes: XX female, XY male X chromosome has about 1,098 genes Y chromosome has about 80 genes. The most important gene: sex determining region on Y ( ). sry gene codes for a protein testes determining factor (TDF) If the sry gene is present testes form If the SRY is absent ovaries form Only one of two Xs in females becomes active. Other forms clump of 1
inactive heterochromatin called a Barr body. It is used as a test for chromosomal sex. The inactivated X chromosome may still express itself and become activated during meiosis to undergo crossing over o Sex differentiation is the control of sexual characteristics of an individual Development of Reproductive Organs (Figure 22.4) Figure 22.5 Sex Determination and Differentiation o Precursor to male tract is called. The development of this precursor is stimulated by the presence of this hormone and inhibits the development of the precursor to female reproductive tract. o Precursor to female tract is called. The development of this precursor is inhibited by these hormones and. Patterns of Reproductive Activity over the Human Life Span o Adolescence (up to 10 14 years): Inability to reproduce o Puberty (starts at 10 14 years, later in boys) Sexual maturation Reproductive organs mature (can produce gametes) Secondary sexual characteristics develop o During sexual maturation (from late teens onward) Female reproductive system cycles Female lose ability to reproduce around 45 50 Menopause: loss of female reproductive capacity Male retains ability to produce sperm Andropause is accompanied by decreased sexual desire o Early maturation 22.2 Male Reproductive System Male Reproductive Organs (Figure 22.6) o Testes o Reproductive tract o Accessory glands o External genitalia Testes and Functions of Testes o Testes produce in seminiferous tubules and. o cells (interstitial cells): Synthesize and secrete testosterone o cells (epithelial cells): Support sperm development o Functions of Sertoli Cells (Table 22.1) o Smooth muscle propels sperm movement by peristalsis 2
o Blood testis barrier (BTB) Contains tight junctions that limit the materials exchange between cells Prevents the male s immune system from destroying his own sperm. o Reproductive Tract transport sperm from tests to the penis Seminiferous tubules Rete testis efferent ductules epididymis vas deferens ejaculatory duct urethra Accessory Glands Structures Function a. Seminal vesicles 1. secretes viscous fluid with mucus for lubrication b. Prostate gland 2. Secrete alkaline fluid with fructose, proteins, and prostaglandins c. Bulbourethral glands 3. secrete citrate, zinc and enzymes such as acid phosphatase, and prostate specific antigen (PSA) External Genitalia o Penis is the ale copulatory organ that penetrates vagina and delivers sperm to the female reproductive tract o Scrotum suspended beneath penis houses testes Sperm cannot develop at body temperature Allows a cooler environment for sperm development Male Hormonal Regulation (Figure 22.8) o Hypothalamus secretes o From anterior pituitary gland stimulate sertoli cells to make which provde negative back signal to anterior pitutary gland to supress the release of FSH. LH reaches the targeted cells to increase secretion. provides negative feedback function to inhibit the production of tropic hormones released by hypothalamus and anterior pituitary gland.. FSH and work together promote spermatogenesis. Blood Levels of Sex Hormones in Males o Fairly constant on short term basis o Prepubescent: Low blood levels o Puberty and adulthood: High blood levels, its level declines after 30s Action of androgen or testosterone in males (Table 22.2). Sperm o Head: Nucleus: chromosomes Acrosome: Enzymes necessary for fertilization o Midpiece: Mitochondria generate ATP o Tail: Whip like movements propel sperm 3
Spermatogenesis (Figure 22.10) is the production of. Sperm Maturation and Storage o Spermatozoa released into lumen of seminiferous tubules remain there immotile for 20 days o Move to to reach maturation by peristaltic contractions and flow of lumenal fluid. The sperm are stored in the epididymis for up to 2 weeks where they mature, develop motility and become capable of fertilization. o The entire process of sperm maturation, from their primitive beginnings in the seminiferous tubules to their fully mature form in the vas deferens, takes about 74 days o Sperm are moved to vas deferens by peristalsis and remain in vas deferens until ejaculation 22.3 Female Reproductive System Functions: o Production of estrogen and progesterone. o Production of eggs and it receives the sperm, o It provides the optimal conditions for the development of the fetus. Characteristics of the Female Reproductive System o Cyclic changes in activity: Menstrual cycle o Restricted periods of fertility: Ovulation o Limited gamete production: Pool established at birth Female Reproductive Organs (Figure 22.12) o Gonads = ovaries o Reproductive tract = uterus, uterine tubes, vagina o External genitalia = vulva Ovaries and Reproductive Tract Functions of Ovaries o The ovaries produce eggs (oogenesis) as well as the hormones estrogen and progesterone. Follicles of Ovaries o Start as primordial follicle containing a developing oocyte (= ovum) o Granulosa cells: Target cells of estrogen and FSH o Later in development, some granulosa cells become theca cells o A mature follicle called Graafian follicle Table 22.1 Functions of Granulosa Cells Reproductive Tract: o Uterine Tubes Fallopian tubes or oviducts They contain cilia that pass the egg from the fimbria to the uterus Ova transported from ovaries to uterus Site of Infundibulum and fimbriae pick up released ovum 4
o Movement of ovum through uterine tube Initially peristaltic contractions Mostly ciliary actions Duration 4 days to uterus o Uterus Is the site of of the fertilized egg o Is where the developing embryo is nourished and maintained. Cervix Cervix = canal leading to vagina Cervix + vagina = birth canal The cervix secretes mucus that varies during the menstrual cycle from thin (to facilitate sperm entry) to thick (to prevent sperm entry). o Vagina Receives the penis and the sperm during copulation Allows for the discharge of fluid during menstruation, and the birth of the baby. Secretes acid fluid secreted from uterus or glands in cervix to protect against bacterial infections o External Genitalia: Vulva surrounds the entrance of reproductive system Oogenesis: Ova and Their Development (Figure 22.14) o is the production of ova o Females: number of oogonia is fixed prior to birth Males continually produce spermatogonia o Meiosis Begins in fetal life Is completed after fertilization 5