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Chapter 31: Male Reproductive System

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Title: Chapter 31: Male Reproductive System


1
Chapter 31 Male Reproductive System
  • Dr. Kim Wilson

2
SEXUAL REPRODUCTION
  • Functioning of the reproductive system ensures
    the survival of the genetic characteristics of a
    species
  • Male reproductive system consists of organs whose
    functions are to produce, transfer, and introduce
    mature sperm into the female reproductive tract,
    where fertilization can occur

3
MALE REPRODUCTIVE ORGANS
  • Classified as essential organs for production of
    gametes or accessory organs that support the
    reproductive process
  • Accessory glands produce secretions that nourish,
    transport, and mature sperm
  • Essential organs gonads (testes)
  • Accessory organs
  • Genital ducts convey sperm outside the body
  • pair of epididymides,
  • paired vasa deferentia
  • pair of ejaculatory ducts
  • urethra
  • pair of seminal vesicles
  • the prostate
  • bulbourethral glands
  • Supporting structures scrotum, penis, and pair
    of spermatic cords

4
Perineum
  • Structure roughly diamond-shaped area between
    thighs
  • Location extends anteriorly from pubic symphysis
    to coccyx posteriorly
  • Lateral boundary is the ischial tuberosity on
    either side
  • Divided into the urogenital triangle and the anal
    triangle

5
TESTES
  • Structure and location
  • Several lobules composed of seminiferous tubules
    and interstitial cells (Leydig cells), separated
    by septa and encased in fibrous capsule called
    the tunica albuginea (Figure 31-3)
  • Seminiferous tubules in testis open into a plexus
    called rete testis, which is drained by a series
    of efferent ductules that emerge from the top of
    the organ and enter the head of epididymis
  • Located in scrotum, one testis in each of two
    scrotal compartments

6
Microscopic Anatomy of the Testes
  • Interstitial (Leydig) cells endocrine cells
    between the seminiferous tubules
  • Seminiferous tubules
  • Spermatogenic cells produce sperm
  • Sustentacular cells also called nurse or Sertoli
    cells
  • Support and regulate sperm-producing functions of
    the testis
  • Produce androgen-binding protein that binds to
    testosterone to make it more soluble and thus
    increase its concentration, supporting sperm
    production
  • Tight junctions between sustentacular cells form
    the blood-testis barrier, which protects
    developing sperm from the immune system

7
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8
Functions of the Testes
  • Spermatogenesis formation of mature male gametes
    (spermatozoa) by seminiferous tubules
  • Stimulated by follicle-stimulating hormone from
    the anterior pituitary (and also
    gonadotropin-releasing hormone from hypothalamus)
  • Secretion of hormones by interstitial cells
  • Testosterone
  • Type of androgen maleness hormone
  • Functions include promoting primary and secondary
    male sexual characteristics and anabolism,
    affecting fluid and electrolyte balance
  • Regulated by luteinizing hormone from anterior
    pituitary
  • Inhibin inhibits release of follicle-stimulating
    hormone by anterior pituitary, allowing the
    testis some control over spermatogenesis
  • Estrogen small amounts secreted by interstitial
    cells, liver, and other organs role in males
    uncertain but may influence spermatogenesis and
    other functions

9
Testosterone Secretion
10
Spermatozoa
  • Structure consists of a head (covered by
    acrosome), neck, midpiece, and tail tail is
    divided into a principal piece and a short end
    piece

11
Reproductive Ducts - Epididymis
  • Epididymis
  • Structure and location
  • Single tightly coiled tube enclosed in fibrous
    casing
  • Lies along top and side of each testis
  • Anatomical divisions include head, body, and tail
  • Functions
  • Duct for seminal fluid
  • Also secretes part of seminal fluid
  • Sperm become capable of motility while they are
    passing through the epididymis

12
Reproductive Ducts Vas Deferens
  • Vas deferens (ductus deferens)
  • Structure and location
  • Tube, extension of epididymis
  • Extends through inguinal canal, into abdominal
    cavity, over top and down posterior surface of
    bladder
  • Enlarged terminal portion called ampulla joins
    duct of seminal vesicle
  • Function
  • Excretory duct for seminal fluid
  • Connects epididymis with ejaculatory duct

13
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14
Reproductive Ducts Ejaculatory Duct Urethra
  • Ejaculatory duct
  • Formed by union of vas deferens with duct from
    seminal vesicle
  • Passes through prostate gland, terminating in
    urethra
  • Urethra

15
Accessory Reproductive Glands
  • Seminal vesicles
  • Structure and location convoluted pouches 5 to 7
    cm long on posterior surface of bladder
  • Function secrete the viscous, nutrient-rich part
    of seminal fluid (60 of semen volume)
  • Prostate gland
  • Structure and location
  • Doughnut shaped
  • Encircles urethra just below bladder
  • Function adds slightly acidic, watery,
    milky-looking secretion to seminal fluid (30 of
    semen volume)

16
Accessory Reproductive Glands
  • Bulbourethral glands
  • Structure and location
  • Small, pea-shaped structures with approximately
    2.5-cm long (1 inch) ducts leading into urethra
  • Lie below prostate gland
  • Function secrete alkaline fluid that is part of
    semen (5 of semen volume)

17
Supporting Structures - Scrotum
  • Skin-covered pouch suspended from perineal region
    into which the testes descend near the time of
    birth
  • Divided into two compartments
  • Contains testis, epididymis, and lower part of a
    spermatic cord
  • Dartos and cremaster muscles elevate the scrotal
    pouch

18
Supporting Structures - Penis
  • Structure composed of three cylindrical masses
    of erectile tissue, one of which contains urethra
  • Functions penis contains the urethra, the
    terminal duct for both urinary and reproductive
    tracts during sexual arousal, penis becomes
    erect, serving as a penetrating copulatory organ
    during sexual intercourse
  • Spermatic cords (internal)
  • Fibrous cylinders located in inguinal canals
  • Enclose seminal ducts, blood vessels, lymphatics,
    and nerves

19
Seminal Fluid
  • Composition
  • Consists of secretions from testes, epididymides,
    seminal vesicles, prostate, and bulbourethral
    glands
  • Each milliliter contains millions of sperm
  • Flow
  • Passes from testes through epididymis, vas
    deferens, ejaculatory duct, and urethra

20
Male Fertility
  • Relates to many factors number, size, shape, and
    motility of sperm
  • Infertility may be caused by antibodies some men
    make against their own sperm
  • Male fertility begins at puberty and extends into
    old age

21
Reproduction Cycle
  • Reproductive functions begin at time of puberty
  • Development of organs begins before birth
    immature testes descend into scrotum before or
    shortly after birth
  • Puberty high levels of hormones stimulate final
    stages of development
  • System operates to permit reproduction until
    advanced old age
  • Late adulthood gradual decline in hormone
    production may decrease sexual appetite and
    fertility
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