Chap 27 Male Reproductive System

1
Chap 27 - Male Reproductive System

• Sexual reproduction and development
• Male reproductive anatomy
• Puberty and climacteric
• Sperm and semen
• Male sexual response

2
Essence of Sex

• Reproduction
• one property of a living thing
• great variety of methods
• Sexual reproduction
• each offspring has 2 parents and receives genetic
  material from both
• provides genetic diversity
• foundation for survival and evolution of species

3
Two Sexes

• Male and female gametes (sex cells) combine their
  genes to form a fertilized egg (zygote)
• one gamete has motility (sperm)
• parent producing sperm considered male
• has Y chromosome
• other gamete (egg or ovum) contains nutrients for
  developing zygote
• parent producing eggs considered female
• in mammals female also provides shelter for
  developing fetus (uterus and placenta)

4
Overview of Reproductive System

• Primary sex organs
• produce gametes (testes or ovaries)
• Secondary sex organs
• male - ducts, glands, penis deliver sperm cells
• female - uterine tubes, uterus and vagina receive
  sperm and nourish developing fetus
• Secondary sex characteristics
• develop at puberty to attract a mate
• pubic, axillary and facial hair, scent glands,
  body morphology and low-pitched voice in males

5
Role of Sex Chromosomes

• Our cells contain 23 pairs of chromosomes
• 22 pairs of autosomes
• 1 pair of sex chromosomes (XY males XX females)
• males produce 50 Y carrying sperm and 50 X
  carrying
• all eggs carry the X chromosome
• Sex of child determined by type of sperm that
  fertilizes mothers egg

6
Hormones and Sex Differentiation

• Gonads begin to develop at 6 weeks
• 2 sets of ducts
• mesonephric ducts develop into male reproductive
  system or
• paramesonephric ducts (müllerian ducts) develop
  into female reproductive tract
• SRY gene (Sex-determining Region of Y gene)
• in males, codes for a protein that causes
  development of testes ?
• secrete testosterone
• secrete müllerian-inhibiting factor ? degenerates
  paramesonephric ducts
• Female development occurs in absence of hormones

7
Embryonic Development

• External genitals of both sexes begin as a
• genital tubercle
• becomes glans of penis or
• clitoris
• pair of urogenital folds
• enclose urethra of male or
• form labia minora
• a pair of labioscrotal folds
• scrotum or
• labia majora

8
Embryonic Development
9
Androgen-Insensitivity Syndrome

• Genetically male (XY)
• Testosterone secreted
• target cells lack receptors for hormone
• No masculizing effects occur

10
Development of External Genitalia
11
Development of External Genitalia

• All 8 week old fetuses have same 3 structures
• by end of week 9, begin to show sexual
  differentiation
• distinctly male or female by end of week 12

12
Descent of Testes

• Begin development near kidney
• gubernaculum (cordlike structure containing
  muscle) extends from gonad to abdominopelvic
  floor
• it shortens, guides testes to scrotum
• vaginal process
• peritoneum develops fold extends into scrotum
• create inguinal canal, pass through abdominal
  wall
• Descent begins in weeks 6-10, finished by 28
• 3 born with undescended testes (cryptorchidism)
• Location outside pelvic cavity essential for low
  temperatures needed for sperm production

13
Descent of Testis
14
Boundaries of Male Perineum
15
Male Reproductive System
16
Scrotum

• Pouch holding testes
• divided into 2 compartments by median septum
• Spermatic cord travels up from scrotum to pass
  through inguinal canal
• contains testicular artery, vein, nerve and
  lymphatics

17
Testicular Thermoregulation

• Sperm not produced at core body temperature
• cremaster muscle pulls testes close to body
• dartos muscle
• wrinkles skin reducing surface area of scrotum
• lifts it upwards
• pampiniform plexus veins ascending near
  testicular artery
• countercurrent heat exchanger cools arterial
  blood entering testis

18
Male Inguinal and Scrotal Region
19
Countercurrent Heat Exchanger
20
Testes

• Oval organ, 4 cm long x 2.5 cm in diameter
• covered anteriorly by tunica vaginalis
• Tunica albuginea
• white fibrous capsule on testes
• Septa divide testes into compartments containing
  seminiferous tubules
• each tubule lined with a thick germinal
  epithelium for sperm
• interstitial cells between tubules - testosterone
• Sustentacular cells
• promote sperm cell development

21
Blood-testis barrier

• Formed by tight junctions between sustentacular
  cells -- separating sperm from immune system

22
Testis and Associated Structures

• Seminiferous tubules drain into rete testis
• Low BP of testicular artery results in poor O2
  supply
• sperm develop very large mitochondria helping
  them survive hypoxic environment of female
  reproductive tract
• Testicular veins drain to inferior vena cava

23
Spermatic Ducts

• Efferent ductules
• 12 small ciliated ducts collecting sperm from
  rete testes and transporting it to epididymis
• Epididymis (head, body and tail)
• 6 m long coiled duct adhering to posterior of
  testis
• site of sperm maturation and storage (fertile for
  60 days)
• Ductus deferens (peristalsis during orgasm)
• muscular tube 45 cm long passing up from scrotum
  through inguinal canal to posterior surface of
  bladder
• Ejaculatory duct
• 2 cm duct formed from ductus deferens and seminal
  vesicle and passing through prostate to empty
  into urethra

24
Male Duct System
25
Male Urethra

• Regions prostatic, membranous and penile ---
  totals 20 cm long

26
Accessory Glands

• Seminal vesicles
• posterior to bladder
• empty into ejaculatory duct
• Prostate gland
• below bladder, surrounds urethra and ejaculatory
  duct
• 2 x 4 x 3 cm
• Bulbourethral glands
• near bulb of penis
• empty into penile urethra
• lubricating fluid

27
Penis

• Internal root, shaft, and glans
• external portion 4 in. long when flaccid
• skin over shaft loosely attached allows expansion
• extends over glans as prepuce (foreskin)
• 3 cylindrical bodies of erectile tissue
• corpus spongiosum along ventral side of penis
• encloses penile urethra
• ends as a dilated bulb ensheathed by
  bulbospongiosus muscle
• corpora cavernosa
• diverge like arms of a Y
• each crus attaches to pubic arch covered with
  ischiocavernosus muscle

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Anatomy of Penis
Fig. 27.12 a and b
29
Puberty and Climacteric

• Reproductive system remains dormant for years
  after birth
• surge of pituitary gonadotropins begins
  development
• 10-12 in most boys 8-10 in most girls
• Puberty
• period from onset of gonadotropin secretion until
  first menstrual period or first ejaculation of
  viable sperm
• Adolescence
• ends when person attains full adult height

30
Brain-Testicular Axis

• Hypothalamus produces GnRH
• Stimulates anterior pituitary (gonadotrope cells)
  to secrete
• LH
• stimulates interstitial cells to produce
  testosterone
• FSH
• stimulates sustentacular cells to secrete
  androgen-binding protein that interacts with
  testosterone to stimulate spermatogenesis

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Other Effects of Testosterone

• Enlargement of secondary sexual organs
• penis, testes, scrotum, ducts, glands and muscle
  mass enlarge
• hair, scent and sebaceous glands develop
• stimulates erythropoiesis and libido
• During adulthood, testosterone sustains libido,
  spermatogenesis and reproductive tract

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Hormones and Brain-Testicular Axis
33
Aging and Sexual Function

• Decline in testosterone secretion
• peak secretion at 7 mg/day at age 20
• declines to 1/5 of that by age 80
• Rise in FSH and LH secretion after age 50
  produces male climacteric (menopause)
• mood changes, hot flashes and illusions of
  suffocation
• Erectile dysfunction
• 20 of men in 60s 50 of those in 80s

34
Mitosis and Meiosis

• Mitosis produces two genetically identical
  daughter cells (for tissue repair, embryonic
  growth)
• Meiosis produces gametes
• for sexual reproduction
• keeps chromosome number constant from generation
  to generation after fertilization
• 2 cell divisions (only one replication of DNA)
• meiosis I separates homologous chromosome pairs
  into 2 haploid cells
• meiosis II separates duplicated sister chromatids
  into 4 haploid cells

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Meiosis
36
Spermatogenesis

• Spermatogonia produce 2 kinds of daughter cells
• type A remain outside blood-testis barrier and
  produce more daughter cells until death
• type B differentiate into primary spermatocytes
• cells must pass through BTB to move inward
  toward lumen - new tight junctions form behind
  these cells
• meiosis I ? 2 secondary spermatocytes
• meiosis II ? 4 spermatids

37
Spermatogenesis

• Blood-testis barrier is formed by tight junctions
  between and basement membrane under sustentacular
  cells.

38
Spermiogenesis

• Changes that transform spermatids into
  spermatozoa
• discarding excess cytoplasm and growing tails

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Spermatozoon

• Head is pear-shaped front end
• 4 to 5 microns long structure containing the
  nucleus, acrosome and basal body of the tail
  flagella
• nucleus contains haploid set of chromosomes
• acrosome contains enzymes that penetrate the egg
• basal body
• Tail is divided into 3 regions
• midpiece contains mitochondria around axoneme of
  the flagella (produce ATP for flagellar movement)
• principal piece is axoneme surrounded by fibers
• endpiece is very narrow tip of flagella

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Spermatozoon
41
Semen or Seminal Fluid

• 2-5 mL of fluid expelled during orgasm
• 60 seminal vesicle fluid, 30 prostatic, 10
  sperm
• normal sperm count 50-120 million/mL
• Other components of semen
• fructose - energy for sperm motility
• fibrinogen causes clotting
• enzymes convert fibrinogen to fibrin
• fibrinolysin liquefies semen within 30 minutes
• prostaglandins stimulate female peristaltic
  contractions
• spermine is a base stabilizing sperm pH at 7.2 to
  7.6

42
Male Sexual Response - Anatomy

• Arteries of penis
• dorsal and deep arteries(brs. of internal
  pudendal)
• deep artery supplies lacunae of corpora cavernosa
• dilation fills lacunae causing an erection
• normal penile blood supply comes from dorsal a.
• Nerves of penis
• abundance of tactile, pressure and temperature
  receptors
• dorsal nerve of penis and internal pudendal
  nerves lead to integrating center in sacral
  spinal cord
• both autonomic and somatic motor fibers carry
  impulses from integrating center to penis

43
Excitement and Plateau

• Excitement is characterized by vasocongestion of
  genitals, myotonia, and increases in heart rate,
  BP, and pulmonary ventilation
• Initiated by many different erotic stimuli
• Erection of penis is due to parasympathetic
  triggering of nitric oxide (NO) secretion
• dilation of deep arteries and filling of lacunae
  with blood
• Erection is maintained during plateau phase

44
Sexual Response

• Parasympathetic signals produce an erection with
  direct stimulation of penis or perineal organs

45
Orgasm and Ejaculation

• Climax (orgasm) is 15 second reaction that
  includes the discharge of semen (ejaculation)
• Ejaculation
• emission sympathetic nervous system propels
  sperm through ducts as glandular secretions are
  added
• expulsion semen in urethra activates muscular
  contractions that lead to expulsion
• Ejaculation and orgasm are not the same
• can occur separately

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Resolution

• Sympathetic signals constrict internal pudendal
  artery and reduce blood flow to penis
• penis becomes soft and flaccid (detumescence)
• Cardiovascular and respiratory responses return
  to normal
• Refractory period (10 minutes to few hours)

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How Viagra Prolongs Erection