Chapter 31: Male Reproductive System

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Chapter 31 Male Reproductive System

• Dr. Kim Wilson

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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

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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

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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

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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

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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

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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

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Testosterone Secretion
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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

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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

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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

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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

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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)

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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)

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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

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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

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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

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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

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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