Transcript Plants and Pollinators

Human Reproduction
and Development
Chapter 42
Modes of Reproduction
1. Sexual reproduction
– Meiosis (gamete formation) followed by
fertilization
– Offspring show genetic variation
2. Asexual reproduction
– Mitosis
– Single parent produces offspring
– Offspring are genetically identical
3. Hermaphrodites
-produce eggs and sperm, some can self-fertilize
Ex.-Tapeworms…why is this an advantage?
Cost of Sexual Reproduction
• Specialized cells and structures must be
formed (to deliver/receive sperm)
– Reproductive timing; pheromones,
• Visual signals, special courtship, and parental
behaviors can be costly
• Nurturing developing offspring, either in egg
or body, requires resources from mother
Costs of Sexual Reproduction
Gamete Formation
The Reproductive System
• Gonads – primary sex organs
– Testes in males
– Ovaries in females
• Gonads produce gametes (sex cells)
and secrete hormones
– Sperm – male gametes
– Ova (eggs) – female gametes
Male Reproductive System
PROSTATE
GLAND
EJECULATORY DUCT
SEMINAL
VESICLE
urinary bladder
URETHRA
urethra
anus
anterior
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
TESTIS
EPIDIDYMIS
• Accessory organs(Seminal vesicle, Prostate gland,
Bulbourethral gland)
• External genitalia (penis, Scrotum: testes, epididymis)
Testes
• Spermatogenesis
• Seminiferous tubules
– Tightly coiled structures
– Function as spermforming factories
• Sperm travels from testes
to epididymis
• Produce testosterone
Figure 16.1
Epididymis
• Comma-shaped,
tightly coiled tube
• Function: to mature and store sperm cells (at
least 20 days)
• Expels sperm with the contraction of muscles
in the epididymis walls to the vas deferens
Vas Deferens
• Carries sperm from epididymis to the ejaculatory
duct
• Vasectomy – cutting of the vas deferens at the
level of the testes to prevent transportation of
sperm
PROSTATE
GLAND
EJECULATORY DUCT
SEMINAL
VESICLE
urinary bladder
URETHRA
urethra
anus
anterior
BULBOURETHRAL
GLAND
posterior
VAS DEFERENS
PENIS
erectile tissue
TESTIS
EPIDIDYMIS
Urethra
• Extends from the base of the urinary
bladder to the tip of the penis
• Carries both urine and sperm
• Sperm enters from the ejaculatory duct
Semen
• Mixture of sperm and accessory gland
secretions
• Advantages of accessory gland secretions
– Seminal Vesicles: Fructose provides energy
for sperm cells
– Prostate Gland: raises pH of semen helps
neutralize the acidic environment of vagina
– Bulbourethral gland: lubricating mucus clears
urethra of urine
– Semen inhibits bacterial multiplication
– Elements of semen enhance sperm motility
External Genitalia
• Scrotum
– Divided sac of skin outside the abdomen
– Maintains testes at 3°C lower than normal
body temperature to protect sperm viability
• Penis
– Delivers sperm into the female reproductive
tract
– Internally, three areas of spongy erectile
tissue around the urethra
Sperm Formation: Seminiferous
Tubules
vas
deferens
seminal vesicle
prostate gland
bulbourethral
gland
urethra
penis
epididymis
semini ferous
tubule
testis
Spermatogenesis
• Production of sperm cells
• Begins at puberty and continues thru-out life
• In the seminiferous tubules (inside testes)
• Spermatogonium (2n) divides by mitosis to
form primary spermatocyte (2n)
• Meiosis produces haploid spermatids
• Spermatids mature to become sperm
• Spermatogenesis takes 64 to 72 days
Sperm Formation
(in seminferous tubule in testes)
part of the lumen of one seminiferous tubule
MITOSIS
MEIOSIS I
MEIOSIS II
lumen
Sertoli
cell
spermatogonium
(diploid)
primary
early
spermatocyte secondary spermatids
late
spermatocyte
spermatid
head
midpiece with
mitochondria
tail with core of
microtubules
immature
sperm
(haploid)
Anatomy of Mature Sperm
•
•
•
•
The only human flagellated cell
DNA is found in the head
Little cytoplasm
48-72 hour lifespan (up to 5 days)
Figure 16.5b
Testosterone Production
• Produced in Testes
• Functions of testosterone
– Stimulates reproductive organ development
– Underlies sex drive
– Causes secondary sex characteristics
• Deepening of voice
• Increased hair growth
• Enlargement of skeletal muscles
• Thickening of bones
Regulation of
Male Androgens
(Sex Hormones)
Female Reproductive System
• Ovaries
• Duct System
– Uterine tubes (fallopian tubes)
– Uterus
– Vagina
– Urethra is NOT part of reproductive system
in females
• External genitalia
Female Reproductive Organs
Female Reproductive Organs
UTERUS
OVIDUCT
MYOMETRIUM
OVARY
urinary
bladder
ENDOMETRIUM
urethra
opening
of cervix
CLITORIS
LABIUM
MINOR
LABIUM
MAJOR
anus
VAGINA
• Produces eggs
Ovaries
• Composed of ovarian follicles (sac-like
structures)
• Ovulation –
egg is mature and
the follicle ruptures
– Occurs every 28 days
• Ruptured follicle is transformed into a
corpus luteum
Figure 16.7
Fallopian Tubes
(Oviducts)
• Receive the ovulated oocyte
• Cilia move the oocyte towards the
uterus (takes 3–4 days)
• Provide a site for fertilization
• Attaches to the uterus
• Does not physically attach to the ovary
Uterus
• Hollow organ
• Cervix – narrow outlet that protrudes into the vagina
• Functions of the uterus
– Receives a fertilized egg
– Retains the fertilized egg
– Nourishes the fertilized egg
• Endometrium
– Inner layer
– Allows for implantation of a fertilized egg
– Sloughs off if no pregnancy occurs (menses)
Vagina
• Extends from cervix to exterior of body
• Serves as the birth canal
• Receives sperm during sexual
intercourse
Oogenesis
•
•
•
•
Making eggs
Total supply of eggs are present at birth
Ovulation begins at puberty
Many eggs “die off” in earlier stages of
development, before ovulation occurs
• Reproductive ability ends at menopause
• Oocytes are matured in developing
ovarian follicles
Oogenesis
• Girl is born with 2 million primary oocytes already
in ovaries
• Each oocyte has entered meiosis I and stopped
• Meiosis resumes, with the first menstrual cycle
• Meiosis completed only after fertilization
• Unfertilized egg: lifespan 24 hours
Ovarian Cycle
a Primary oocyte,
not yet released
from meiosis I. A
cell layer is forming
around it. A follicle
consists of the cell
layer and the
oocyte.
b A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
c A fluid-filled cavity
(antrum) starts forming in
the follicle’s cell layer.
ovary
primordial
follicle
d Mature follicle.
Meiosis I is over. The
secondary oocyte
and first polar body
are now formed.
first polar body
secondary oocyte
g The corpus
luteum breaks
down when the
woman doesn’t
get pregnant.
f A corpus luteum
forms from
remnants of the
ruptured follicle.
e Ovulation. Mature follicle ruptures and releases
the secondary oocyte and the first polar body.
Oogenesis
Figure 16.10
Menstrual Cycle
• Function: produce an environment that is
hospitable to the growing embryo
• Lining of uterus builds up cyclically
• Bleeding is a by-product resulting from no
pregnancy
• The fertile period for a human female occurs
on a cyclic basis
Menstrual Cycle
• Cyclic changes of the endometrium
– Regulated by cyclic production of estrogens and
progesterone
• Menstrual cycle lasts about 28 days
– Day 1: first day of bleeding
– Ovulation around day 14
• Stages of the menstrual cycle
– Menses: endometrium is sloughed
– Follicular phase: prior to ovulation
– Luteal phase: after ovulation
Hormonal Control of the Ovarian
and Uterine Cycles
Figure 16.12a, b
Hormonal Control of the Ovarian and
Uterine Cycles
Figure 16.12c, d
Menstrual Cycle Overview
hypothalamus
GnRH
anterior pituitary
LH
Blood levels of
FSH (purple) and
LH (lavender)
midcycle peak of LH
(triggers ovulation)
FSH
LH
growth of follicle
ovary
endometrium
of uterus
estrogens
Blood levels of estrogens
(light blue) and progesterone
(dark blue)
estrogens
LH
ovulation
corpus luteum
progesterone, estrogen
progesterone, estrogen
menstruation
Days of one menstrual cycle (using 28
days as the average duration)
FOLLICULAR PHASE
LUTEAL PHASE
Hormone Production by the
Ovaries
• Estrogens
– Produced by follicle cells
– Cause secondary sex characteristics
• Enlargement of accessory organs
• Development of breasts
• Appearance of pubic hair
• Increase in fat beneath the skin
• Widening and lightening of the pelvis
• Onset of menses
Hormone Production by the
Ovaries
• Progesterone
– Produced by the corpus luteum
– Production continues until LH diminishes in
the blood
– Helps maintain pregnancy
Female Hormonal Control
HYPOTHALAMUS
(+)
c Blood level
of estrogens
rises, will
stimulate a
surge in LH
secretion
(–)
(–)
(+)
PITUITARY
a GnRH prods
anterior lobe cells
to secrete FSH
and LH
f The rise in
progesterone,
estrogen in
blood will inhibit
FSH, LH
secretion during
last phase of
cycle
d Midcycle surge
of LH triggers
ovulation, then
formation of
corpus luteum
b In ovary, FSH and LH promote
follicle growth and oocyte
maturation, estrogen production,
priming of endometrium, other
reproductive events
e Progesterone, estrogen secreted
by corpus luteum will maintain the
endometrium if pregnancy occurs
Cycle Overview
• GnRH secretion affects LH and FSH
secretion by pituitary
• LH and FSH affect follicle maturation
• Estrogen and progesterone from ovary
affect uterus
Probability of Pregnancy
Wilcox, A. J et al. BMJ 2000;321:1259-1262
What day on a regular cycle is there the
highest probability of pregnancy?
Copyright ©2000 BMJ Publishing Group Ltd.
Fertilization
• Sperm penetrates
to egg cytoplasm
Fertilization
oviduct
• Secondary oocyte
ovary
ovulation
undergoes meiosis
II; forms mature
egg
• Egg nucleus and
sperm nucleus
fuse to form diploid
zygote
follicle cell
egg nucleus
zona pellucida
uterus
opening
of cervix
vagina
Birth Control
Options