The Reproductive System

1
The Reproductive System

• Male and Female

2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5

• General Reproduction Principles
• sexual reproduction involves two types of
  gametes
• motile sperm cells (male)
• immotile (stationary) eggs (ova) (female)
• Both were produced through the process of meiosis
  in the male and female, respectively.
• The sperm cell contributes 23 chromosomes and the
  egg cell (ovum) contributes 23 chromosomes
• The ovum is much larger than the sperm cell the
  ovum contributes all of the cytoplasm to the
  fertilized egg (aka zygote).
• The zygote possesses 23 23 46 chromosomes and
  develops into an embryo, and eventually a fetus.

6
(No Transcript)
7

• The reproductive systems of males and females are
  generally described as two organ sets
• - the internal reproductive organs (testes,
  ovaries, (glands that produce hormones and
  gametes), uterus, fluid-producing structures, and
  a set of ducts connecting everything).
• - the external genitalia (scrotum, penis,
  vagina, clitoris).
• Male fig. 21.1 p. 420.
• Female fig. 21.5 p. 424.

8
Male Reproductive System

• Refer to fig. 21.1 p. 420 and table 21.1 p. 423.
• The male gonads are paired testes (sing. testis),
  which are suspended outside of the body cavity
  within the scrotum (this, to keep them cooler).
• The testes are a pair of tightly-coiled tubes
  surrounded by several layers of connective
  tissue.
• The testes actually develop inside the abdominal
  cavity and descend into the scrotum during the
  last two months of fetal development.
• Later, well examine the process by which the
  testes produce sperm, but for now, well mention
  that sperm production is most efficient, and
  sperm health (viability) is more prominent when
  the temperature of the testes is lower than body
  temperature ( 20C lower).

9

• Parts of the Testes (fig. 21.3 p. 422)
• Seminiferous Tubules make up the tubular
  portion of the testes (uncoiled 250 m)
  responsible for producing sperm cells (process
  known as spermatogenesis) packed with cells
  called spermatogonia at their outer tubule walls
  these spermatogonia eventually mature to become
  sperm cells (discussed later).
• Sertoli Cells support, nourish, and regulate
  cells destined to become sperm cells also
  produce and release the hormone inhibin as sperm
  cells are produced in order to regulate their
  numbers (form of negative feedback).
• Interstitial Cells scattered between the
  seminiferous tubules ? produce testosterone (the
  male sex hormone).

10
(No Transcript)
11

• The sperm that are produced by the seminiferous
  tubules (of the testes) are stored in the
  epididymis (pl. epididymides) here, they
  actually complete their maturation and gain their
  ability to swim (ie. each of their flagella
  complete their developments).
• Each epididymis lies just outside each testis,
  and each is a tightly-coiled tubule.
• Each epididymis connects to a vas deferens (pl.
  vasa deferentia), a tube where sperm may be
  stored (once they have matured).
• The vasa deferentia are lined with smooth muscle.

12

• Upon ejaculation, the sperm are propelled through
  the vas deferens by peristaltic contractions.
• Each of these tubes ascends into the abdominal
  cavity, loops around and behind the urinary
  bladder, and drain into the urethra via the
  ejaculatory duct (urinary and reproductive
  systems merge in males not in females).
• During orgasm/ejaculation, the bladders
  connection to the urethra is closed off to
  disallow urine from entering the semen (sperm
  fluid).
• The penis is the male organ of sexual
  intercourse it has erectile tissue with blood
  spaces. During arousal, these spaces fill with
  blood this squeezes off the veins that carry
  blood away from the penis creates an erection
  that is necessary for intercourse. An erection
  changes the penis angle in order to allow
  semen/sperm to actually enter the urethra (fig.
  21.2 p. 421).

13
(No Transcript)
14
Spermatogenesis (begins at Puberty)

• Occurs within seminiferous tubules of testes.
• Spermatogonia (46 chromosomes) exist near outer
  wall of seminiferous tubules undergo mitosis
  often in order to maintain numbers for future
  sperm prodn.
• FYI, within a mature male, 3 million
  spermatogonia mature per day into primary
  spermatocytes (spermatogonia replicate their
  chromosomes to get 92).
• Primary spermatocytes move away from wall of
  tubules and undergo meiosis I, which produces two
  secondary spermatocytes (46 chromosomes each) per
  one primary.
• Secondary spermatocytes undergo meiosis II to
  produce four spermatids (23 chromosomes each)
  (sperm without ability to swim).
• Sertoli cells nourish spermatids, which gradually
  move to center of seminiferous tubules for
  transference to epididymis for final maturation
  ability to move.

15
(No Transcript)
16

• Spermatids, upon growing a flagellum, become
  known as motile sperm cells (spermatozoa).
• Each ejaculation contains 400 million sperm
  cells.
• Spermatogenesis, as a whole, takes 65-75 days
  that said, the process is continuous and
  prolific.
• Males can ejaculate daily with no loss of
  fertilizing capacity.
• Structure of Sperm Cells
• Comprised of a head, midpiece, and tail.
• The tail is a flagellum, the midpiece consists of
  a concentration of mitochondria, which provide
  ATP energy to the flagellum for swimming.

17

• The head contains the nucleus (remember, 23
  chromosomes), which is behind (protected by) the
  acrosome a specialized lysosome containing
  enzymes required to penetrate the ovum (egg) so
  that DNA may be injected into the egg
  (fertilization).
• Only one sperm normally penetrates and injects
  its DNA into an egg.

18
(No Transcript)
19
(No Transcript)
20
Seminal Fluid

• Upon ejaculation, sperm cells exit the penis in a
  fluid known as semen (or seminal fluid).
• Three sets of glands add secretions to the semen
• i. Seminal Vesicles paired glands that lie
  below and behind the bladder and empty into the
  ejaculatory duct (which connects to the vas
  deferens) contribute 60 of seminal fluid
  fluid is thick and clear, contains mucus, amino
  acids, and large amounts of fructose, which
  provides the sperm with simple sugar energy for
  their mitochondria in their midpieces the
  seminal vesicles also secrete prostaglandins (a
  steroid) that promotes uterine contractions in
  the female in order to help propel semen up the
  uterus to the oviducts the amino acids act to
  help coagulate semen once it enters the female so
  that it is more easily conducted by the uterine
  contractions.

21

• ii. Prostate Gland the largest accessory
  gland (it is singular) surrounds the initial
  segment of the urethra and secretes its stuff
  directly into the urethra through several small
  ducts fluid secreted is thin, milky, and basic
  (HCO3-) the alkalinity of the fluid acts to
  balance the acidity of any urine still existing
  in the urethra, and to balance the acidity of the
  vagina as well, sperm cells are more viable
  (active) in fluid possessing a basic pH.
• iii. Bulbourethral (Cowpers) Glands paired,
  small glands along the urethra and below the
  prostate secrete a viscous fluid as
  pre-ejaculate to serve as lubrication for the
  penis in the vagina pre-ejaculate can carry some
  sperm (withdrawal method of contraception has low
  success rate).

22
(No Transcript)
23
(No Transcript)
24
Hormonal Control (Male Sex Hormones)

• See fig. 21.4 p. 423.
• Hypothalamus possesses the ultimate control over
  the testes with respect to their sexual
  functioning (ie. spermatogenesis and testosterone
  production) by secreting gonadotropin-releasing
  hormone (GnRH), which stimulates the anterior
  pituitary gland to release the gonadotropic
  hormones follicle-stimulating hormone (FSH) and
  luteinizing hormone (LH) (this actually occurs in
  females as well).
• FSH has two effects
• Promotes spermatogenesis in the seminiferous
  tubules of the testes
• Promotes production of hormone inhibin in the
  Sertoli cells of the testes.

25

• FSH stimulates spermatogonia to become primary
  spermatocytes, whereas inhibin feeds back
  (negatively) on the hypothalamus and the ant.
  pituitary to slow/stop GnRH/FSH release so that
  epididymis is not overloaded with sperm.
• LH targets the interstitial cells of the testes
  and stimulates them to produce testosterone, the
  main sex hormone in males (aka an androgen).
• Testosterone is directly responsible for the
  primary and secondary sexual characteristics of
  males.
• The primary characteristics include those
  associated with the reproductive system
  development of the vasa deferentia and other
  ducts, the penis, scrotum, and testes (associated
  with pre-puberty testosterone).

26

• Testosterone is also responsible for sex drives
  and erections both associated with the
  reproductive system.
• At puberty, GnRH secretions increase, which leads
  to increased FSH, LH, spermatogenesis, and
  testosterone.
• In an interesting hormonal cross-over,
  testosterone plays a role in spermatogenesis ?
  FSH actually stimulates developing sperm cells to
  take up testosterone, which promotes further
  maturation and activity (ie. Without
  testosterone, sperm would not be mature or
  viable).

27

• Puberty testosterone promotes secondary sexual
  characteristics, including
• - increased facial/body hair
• - growth of larynx (deeper voice, larger Adams
  Apple)
• - greater muscular development
• - increased oil/sweat gland secretions (acne)
• - receding hairline
• - increased height, broader shoulders, longer
  legs relative to trunk length.
• Increased testosterone at puberty also
  contributes to further maturation of the primary
  characteristics (ie. leads to final maturation of
  penis and testes).
• Testosterone levels in blood feed back
  (negatively) upon hypothalamus and anterior
  pituitary to slow/stop GnRH/LH release so as to
  regulate testosterone.

28

• Thus, GnRH, FSH, LH, and testosterone are all
  regulated by negative feedback loops.
• Regulation performed by inhibin (FSH) and
  testosterone (LH).

29
(No Transcript)