Chapter 43 Animal Reproduction

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Transcript Chapter 43 Animal Reproduction

Chapter 43 Animal Reproduction
Biology 102
Tri-County Technical College
Pendleton, SC
Let me answer that one, Doc!!!
Asexual reproduction DOES NOT involve
formation of any type (kind) of gametes
(sex cells)
Sexual reproduction DOES involve the
formation of gametes (sex cells)
How those gametes are gotten together is
another matter and can be a real hoot!!!!
Types of Asexual Reproduction
Fission involves separation of parent into
two or more individuals of approximately
same size (sea anemone)
Budding occurs when new individual splits
off from existing one (hydra and tunicates)
Release of specialized cells that grow into
new adults
Freshwater sponges produce gemmules which
form from aggregates of several types of cells
surround by protective coat
Asexual, cont.
Fragmentation is breaking of body into
several pieces, each of which develops into
complete animal
Must be accompanied by regeneration
(regrowth of lost body parts)
 Sponges, cnidarians, polychaete annelids, and
Regeneration allows many animals to
replace lost parts
Asexual Advantages???
Allows production of many offspring in
short time thereby exploiting favorable
environment with maximum offspring in
shortest possible time
Perpetuates successful genotypes precisely
In other words, makes clones
Sexual Advantages???
Offspring have combination of genes
inherited from both parents
***Increases genetic variability in the
Highly advantageous in a fluctuating
Sociobiology, anyone?
Daring to define…
Parthenogenesis is development of an egg
without fertilization
Daphnia; male honeybees (drones)
Hermaphroditism: each individual has
both functional male and female
reproductive parts
Some self-fertilize but most mate with another
individual (earthworms are classic example)
Daring to define, cont.
Sequential hermaphroditism describes
situation where individual reverses its sex
during its lifetime
Some species are protogynous (female
Others are protandrous (male first)
Reversal often associated with age and size
Male form and function…
External genitalia includes scrotum and
penis (copulatory organ)
Internal reproductive organs consist of
gonads (testes), accessory glands, and
associated ducts
Testes comprised of highly coiled tubules
(seminiferous tubules) surrounded by layers
of connective tissue
“Mountain oysters,” anyone???
Male F & F, cont.
Interstitial cells (Leydig cells) scattered among
tubules and produce testosterone and other
Sperm passes from seminiferous tubules into
tubules of epididymis
Sperm are stored and mature (gain motility and
fertilizing power)
At ejaculation, sperm forced through vas
deferens (muscular duct connecting epididymis to
ejaculatory duct)
Male F & F III
Ejaculatory duct forms by joining of two
vas deferens ducts with duct from seminal
Ejaculatory duct opens into urethra (tube
that runs through penis and drains both
excretory/reproductive systems)
There are 3 sets of accessory glands
associated with the male system
They add their secretions to semen
Male F & F IV
Pair of seminal vesicles located below and
behind urinary bladder and empty into
ejaculatory duct
Secrete fluid containing mucus, amino acids
(for coagulation), fructose, and prostaglandins
 Comprise about 60% of total semen volume
Prostate gland is large gland surrounding
upper portion and emptying directly into
Male F & F V
Prostate secretes thin, milky alkaline fluid
with enzymes
Balances acidity of residual urine in system
 Buffers acidity of vagina/activates sperm
Bulbourethral glands are pair of small
glands below prostate that empty into
urethra at base of penis
Secrete clear mucus before ejaculation
 Neutralize remaining acidic urine in urethra
Male F & F V
Head of penis (glans penis) covered with
foreskin called prepuce
Is it the “y” or is it just tough being born a
Some male mammals possess a baculum ( a
penis bone)
Male Visual
Female Form and Function
Internal reproductive organs are gonads
(ovaries) and associated ducts and chambers
Involved with gamete movement/embryo
External genitalia include clitoris/2 sets of
Ovaries located in abdominal cavity
enclosed in tough protective capsule
Female Form & Function, cont.
Mesentery flanks & attaches each ovary to uterus
Each ovary contains follicles (1 egg cell
surrounded by follicle cells which nourish and
protect egg cell)
Follicle cells also produce estrogens
During ovulation, egg expelled from follicle
Remaining tissue forms corpus luteum which
secretes progesterone (maintains uterine lining)
and additional estrogen
Female F & F III
Egg cell expelled into abdominal cavity
near opening of oviduct
Cilia lining oviduct draw egg cell in
(hopefully) uterus
Uterus (womb) is thick muscular organ that
can expand to accommodate a 4-kg fetus
Inner uterine lining (endometrium) is
richly supplied with blood vessels
Female F & F IV
Cervix is the neck of the uterus which opens into
Vagina is thin-walled chamber that is repository
for semen during copulation, forms birth canal,
and is exit for menstrual fluids
Hymen is vascularized membrane usually
covering vaginal opening from birth until ruptured
by vigorous physical activity or sexual intercourse
Female F & F V
Vestibule: chamberlike area formed by 2
pairs of skin folds covering vaginal
orifice/urethral opening
Libia minora: slender skin folds bordering
Libia majora: pair of thick, fatty ridges
enclosing and protecting libia minora &
Female F & F VI
Clitoris: bulb of erectile tissue at front edge of
vestibule which is covered by a prepuce (small
Bartholin’s glands: small glands located near
vaginal opening that secrete mucus into vestibule
during sexual arousal, facilitates intercourse by
lubricating vagina
Mammary glands: important to reproduction but
NOT part of reproductive system
Female Visual
Hormones are flowing…
Androgens directly responsible for
formation of primary sex characteristics
(reproductive organs) & secondary sex
characteristics (deepening of voice, hair
growth patterns, muscle growth)
Are steroid hormones produced primarily
by Leydig cells of testes
Testosterone most important androgen
Male hormones
Androgens are potent determinants of
sexual and aggressive behavior
It’s the testosterone that’s killing the
guys…but one can go to the front of the line
GnRH from hypothalamus stimulates
anterior pituitary to release LH (stimulates
androgen production) and FSH (acts on
seminiferous tubules to > sperm production)
Comparing cycles
Menstrual cycle characterized by
endometrium break down, sloughing off of
lining, and discharge from body via vagina
if fertilization has NOT occurred
From “menses” which is Latin for “months”
Uterine cycles of mammals other than
humans does NOT include menstruation
Uterine lining is reabsorbed into body
Cycles, cont.
Ovarian cycle characterized by state of
sexual receptivity called estrus (correlated
with ovulation)
Female solicits male attention and may be
aggressive to other females
Time for sociobiology
Female Hormones
Hormones coordinate menstrual and ovarian
Ovulation synchronized with uterine
preparation for possible implantation of
FIVE hormones participate in elaborate
positive and negative feedback scheme
Female Hormones, cont.
GnRH from hypothalamus
FHS (responsible for follicle maturation)
and LH (responsible for egg release) from
anterior pituitary
Estrogens (family of closely related
hormones) and progesterone (female sex
hormone secreted by ovaries)
Female Hormones Visual
Sync’ing the Cycles
Cycles coordinated and timed by same
hormones that initiate sexual maturation
In response to FSH and LH, ovarian tissue
grows and produces estrogen
Estrogen causes development of secondary
sexual characteristics
Menstruation marks beginning of
uterine/ovarian cycles
Cycles, cont.
Few days before menstruation begins,
anterior pituitary > secretion of FSH and
Some follicles begin to mature in ovaries
Generally only one follicle continues with
Developing follicle secretes > amounts of
estrogen which causes endometrium to
Cycles III
Estrogen exerts negative feedback control on
gonadotropin release by anterior pituitary (FHS &
LH) during first 12 days of cycle
On day 12, estrogen exerts positive feedback on
pituitary and there is surge of LH and slight surge
of FSH
LH triggers mature follicle to rupture and release
its egg
Also stimulates follicle to become corpus luteum
which secretes estrogen and progesterone
Cycles IV
Estrogen and progesterone CRITICAL to
continued growth and maintenance of
These sex steroids exert negative feedback
on pituitary inhibiting gonadotropin release
thereby preventing new follicles from
beginning to mature
Cycles V
Egg NOT fertilized, corpus luteum
degenerates on about day 26 of cycle
Without progesterone from corpus luteum,
endometrium sloughs off and menstruation
Decrease in circulating steriods allows
hypothalamus/anterior pituitary to release
GnRH, FSH, and LH and next cycle begins
Spermatogonia are diploid cells that are
precursors of sperm
Located near outer wall of seminiferous tubules,
spermatogonia undergo repeated mitoses which
produce large populations of potential sperm
In mature male, about 3 million spermatogonia per
day differentiate into primary spermatocytes
Primary spermatocytes undergo meiosis I to
produce two secondary spermatocytes which are
now haploid but still have duplicated
Spermatogenesis, cont.
Secondary spermatocytes undergo meiosis
Separates sister chromatids and produces four
Spermatids mature into mature spermatozoa
(sperm cells)
Involves association with Sertoli cells
which transfer nutrients to spermatids
Spermatogenesis III
During spermatogenesis, developing sperm
gradually pushed toward center of
seminiferous tubule
Make their way to epididymis where they
acquire motility
From spermatogonia to motile sperm = 65
to 75 days
Spermatogenesis Visual
Oogenesis is development of ova (mature,
unfertilized egg cells)
Begins in embryonic female when
primordial germ cells undergo mitotic
divisions to produce diploid oogonia
Each oogonium develops into primary
oocyte by time of birth
All potential ova present in ovaries at birth
Oogenesis, cont.
Primary oocytes (2N) proceed to Prophase I
between 3rd and 7th month of fetal development
Then enter state of suspended development until
female reaches puberty
After puberty, with each ovarian cycle, FSH
stimulates a follicle to enlarge & primary oocyte
within completes Meiosis I to produce haploid
secondary oocyte and first polar body
Oogenesis III
Meiosis STOPS again
LH triggers ovulation and secondary oocyte
released from follicle
IF fertilization occurs, Meiosis II will occur and
second polar body will separate from ovum
Female strategy appears to be QUALITY of
reproductive cell whereas male strategy appears to
be QUANTITY of reproductive cells
Oogenesis Visual
Comparing the Processes
In spermatogenesis all 4 products of
Meiosis I and II become mature
In oogenesis, only one daughter cell will
become single ovum, the other cells (polar
bodies) will degenerate
Spermatogenesis is continual process
throughout reproductive life of male
Comparing, cont.
All potential ova that can be produced by
oogenesis are present as primary oocytes in
ovaries at time of female’s birth
Spermatogenesis occurs as uninterrupted
sequence (subject to brain stem
influence…time for an Estesism…yeah!!!
Oogenesis has long resting periods between
formation of initial steps and final
production of ovum
What a Miracle….
Human gestation divided into 3 trimesters
(about 3 months each)
FIRST trimester is when most radical
changes occur for both mother and baby
Fertilization occurs in oviduct and cleavage
(cell division) begins in about 24 hours
Zygote develops into a ball of cells
Pregnancy, cont.
Embryo reaches uterus in 3-4 days and
develops into hollow ball of cells called
blastocyst (about 1 week after fertilization)
Blastocyst will implant in endometrium in
next 5 days (critical thinking time)
During implantation, blastocyst bores into
endometrium and endometrium begins to
grow over blastocyst
Pregnancy III
Embryonic tissues begin to mingle with
endometrium to form placenta which functions in
respiratory gas exchange, nutrient transfer, and
waste removal from embryo
Also main period of organogenesis (organ
After 8 weeks, embryo becomes a fetus
Fetus possesses ALL adult organs in rudimentary
Pregnancy IV
Fetus is about 5 cm in length by end of 1st
Embryo secretes hormones that signal its
presence and control’s mother reproductive
**Human chorionic gonadotropic (HCG)
maintains progesterone and estrogen
secretion by corpus luteum to prevent
Pregnancy V
High progesterone levels stimulate
formation of protective mucus plug in
cervix, growth of maternal part of placenta,
uterus enlargement, and cessation of
ovulation and menstrual cycling
SECOND TRIMESTER time of rapid
growth and fetal activity
Fetus grows to about 30 cm in length
Pregnancy VI
Mother will feel movement (quickening)
Hormone levels stablize as HCG declines
Corpus luteum degenerates
 Placenta secretes its own progesterone to
maintain pregnancy
Uterus grows sufficiently for pregnancy to
be obvious
THIRD TRIMESTER is time of rapid
growth but decreasing fetal activity
Pregnancy VII
Fetus grows to about 50 cm in length, and 3 to 3.5
kg in weight
Maternal abdominal organs become compressed
and displaced
Labor induced & regulated by interplay among
estrogen, oxytocin, and prostaglandins
High estrogen levels during last weeks of
pregnancy trigger formation of oxytocin receptors
on uterus
Pregnancy VIII
Oxytocin (from fetus/maternal posterior
pituitary) stimulate smooth muscles of
uterus to contract
Oxytocin stimulates prostaglandin secretion
by placenta (enhance muscle contractions)
Parturition (birth) occurs through series of
strong, rhythmic contractions of uterus
(called labor)
Pregnancy IX
Three stages to labor
1st stage: involves opening and thinning of
cervix until completely dilated
2nd stage: expulsion of baby from uterus
Contractions are strong and continuous
3rd stage: expulsion of placenta from the
Positive Feedback Visual
Hormonal Control of Pregnancy
Hormones secreted by embryo necessary to insure
pregnancy continues
HCG acts like pituitary LH to maintain secretion
of progesterone and estrogens by corpus luteum
through 1st trimester
In absence of hormonal override provided by
embryo, decline in maternal LH due to inhibition
of pituitary by progesterone would result in
menstruation and spontaneous abortion of embryo
EPT (and others) based on HCG hormone
Hormonal Control, cont.
Cervix mucus plug, growth of maternal part
of placenta, enlargement of uterus, cessation
of ovulation and menstruation all result of
high levels of progesterone
Three major ways to achieve contraception
(1) Prevent fertilization by keeping egg and
sperm apart
(2) Prevent implantation of embryo
(3) Prevent release of mature egg and/or
sperm from gonads
Contraception, cont.
Keeping egg and sperm from meeting in the
female reproductive tract prevents fertilization
Rhythm method
Condoms, diaphragms, cervical caps,
contraceptive sponges, and spermicides
Coitus interruptus
Tubal ligation and vasectomy
Contraception III
Preventing implantation can be
accomplished by using intrauterine device
Probably works by irritating endometrium
Chemical contraception prevents release of
mature gametes from gonads
Birth control pills, minipills, and male birth
control pill????