Chapter 28: The Reproductive System

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Chapter 28 The Reproductive System
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• The reproductive system is the only body system
  not essential for life
• Ensures continuation of human species
• Functions
• Production, maintenance and distribution of
  gametes (sex cells)

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Components of Reproductive System

• Gonads
• Duct system
• Accessory glands and organs
• External genitalia

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Sex Determination in Humans

• Primarily determined by the presence or absence
  of a Y chromosome
• Somatic cells have 23 pairs of chromosomes
• 23rd pair are sex chromosomes - X and Y
• Females have two copies of the X
• Males have an X and a Y chromosome

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• Humans begin with both male and female
  reproductive tracts
• male tract is called the Wolffian system
• female tract is called the Mullerian system
• At 12 weeks gestation, sexual differentiation
  begins

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• If the Y chromsome is present
• TDF gene is expressed testes to develop
• testes secrete testosterone causes Wolffian duct
  system to develop
• secrete Mullerian Inhibiting Hormone which causes
  Mullerian duct system to degenerate
• dihydroxytestosterone causes male external
  genitalia to develop

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• If the Y chromosome is absent
• testes will not develop, so the Wolffian duct
  system degenerate
• In the absence of MIH, the Mullerian duct system
  develops
• In the absence of dihydroxytestosterone, the
  female external genitalia develops

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What are the components of the male reproductive
system?
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• Gonads
• Testis
• Duct System
• Epididymis
• Ductus deferens (vas deferens)
• Ejaculatory duct
• Urethra

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• Accessory glands
• Seminal vesicles
• Prostate gland
• Bulbourethral gland
• external genitalia
• Scrotum and penis

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Male Reproductive System
Figure 281
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Anterior View
Figure 283
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Testis

• Egg-shaped organ which hangs in scrotum
• Spermatic Cords
• Extend from abdominopelvic cavity to testes
• Enclose ductus deferens, blood vessels, nerves,
  and lymphatic vessels of testes

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• Dartos Muscle
• smooth muscle in dermis of scrotum
• Causes characteristic wrinkling of scrotal
  surface
• Cremaster Muscle
• skeletal muscle deep to dermis
• Tenses scrotum and pulls testes closer to body
  (temperature regulation)

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Structures of Testes

• Testies are divided into lobules
• Lobules contain seminiferous tubules
• Site of sperm production
• Connected to epididymis by rete testis

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Structure of the Testes
Figure 284
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• Seminiferous tubule is surrounded by a capsule
  that contains interstitial cells
• Produce androgens - male sex hormones
• Testosterone is the most important androgen

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• Tubule contains several cells types
• Spermatogonia, Spermatocytes, Spermatids and
  Spermatozoa
• Sustentacular cells
• important for sperm development

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• Sustentacular cells
• Maintenance of the blood-testis barrier
• Support of mitosis and meiosis
• Support spermiogenesis
• Secretion of inhibin
• Secretion of androgen-binding proteins
• Secretion of MIH

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Spermatogenesis

• Process of sperm production
• Begins at outermost cell layer of seminiferous
  tubules

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Steps of Spermatogenesis

• Stem cells (spermatogonia) divide by mitosis
• to produce 2 daughter cells
• 1 remains as spermatogonium
• second differentiates into primary spermatocyte

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• Primary spermatocytes
• begin meiosis
• form secondary spermatocytes
• Secondary spermatocytes
• divide into haploid spermatids (immature gametes)

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• Spermatids
• differentiate into spermatozoa
• Spermatozoa
• enter fluid in lumen

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Figure 285b
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Figure 285c
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Spermatogenesis
Figure 287
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Spermiogenesis

• last step of spermatogenesis
• Spermatid matures into a spermatozoon
• Sperm cell
• looses much of the cytoplasm and develops a
  flagellum

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Anatomy of a Spermatozoon

• Head
• Neck
• Middle piece
• Tail

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• Acrosomal Cap
• At tip of head
• membranous compartment which contains enzymes
  essential to fertilization

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Spermiogenesis
Figure 288a
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Spermatozoon Structure
Figure 288b
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Sperm Maturation

• Spermatozoa leaving testes are incapable of
  locomotion or fertilization
• Other parts of reproductive system are
  responsible for
• functional maturation, nourishment, storage, and
  transport

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Epididymis

• Is the start of male reproductive tract
• Head
• Receives spermatozoa
• Body
• Tail
• connection with ductus deferens

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The Epididymis
Figure 289
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Functions of the Epididymis

• Monitors and adjusts fluid produced by
  seminiferous tubules
• Recycles damaged spermatozoa
• Stores and protects spermatozoa
• facilitates maturation

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The Ductus Deferens

• vas deferens
• Begins at tail of the epididymis
• Ascends through spermatic cord
• Curves inferiorly along urinary bladder
• toward prostate gland and seminal vesicles

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• Capacitation
• when mixed with secretions of seminal vesicles
  sperm become motile
• sperm become capable of fertilization when
  exposed to conditions in female tract
• The epididymis secretes a substance to prevent
  premature capacitation

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The Ejaculatory Duct

• Continuous with the ductus deferens
• Site of seminal vesicle secretion
• Penetrates wall of prostate gland
• Empties into urethra

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The Ductus Deferens and Accessory Glands
Figure 2810a, b
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The Male Urethra

• Is used by urinary and reproductive systems
• Is divided into 3 regions
• prostatic
• membranous
• spongy

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Seminal Fluid

• Is a mixture of secretions from accessory glands
• each with distinctive biochemical characteristics
• Important glands include
• seminal vesicles
• prostate gland
• bulbourethral glands

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• Functions include
• activating spermatozoa
• providing nutrients spermatozoa need for motility
• propelling spermatozoa and fluids along
  reproductive tract
• producing buffers

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The Seminal Vesicles

• paired organ
• produce about 60 of semen volume
• secretions include
• fructose, prostaglandins and fibrinogen
• Secretions are slightly alkaline to neutralize
  acids in prostate and vagina

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The Prostate Gland

• Is a small, muscular organ
• Encircles portion of urethra
• Secretes 2030 of semen volume
• Secretions are slightly acidic
• Contains antibiotic seminalplasmin

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The Bulbourethral Glands

• Also called Cowpers glands
• Located at base of penis
• Secrete thick, alkaline mucus
• helps neutralize urinary acids in urethra
• lubricates the glans

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Male Reproductive System
Figure 281