Learning Objectives: Chapter 49 & 50 –
Reproduction and Development
1. Define and give examples of sexual and asexual reproduction.
Asexual Reproduction – a single parent gives rise to offspring that are genetically identical to the parent
(except in the case of mutations).
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Many invertebrates – sponges, cnidarians; some rotifers, flatworms, and annelids. Some
vertebrates can reproduce asexually under certain conditions
Budding – Sponges and cnidarians mostly – a small part of the parent’s body separates from the
rest and develops into a new individual. Can remain attached and become independent
members of a colony
Fragmentation – body of the parent breaks into several pieces; each piece regenerates the
missing parts and develops into a whole animal
o Flatworms, nemerteans, annelids
Parthenogenesis – “virgin development” – an unfertilized egg develops into an adult animal that
is typically haploid.
o Insects and crustaceans; some species of nematodes, gastropods, fishes, amphibians,
and reptiles.
o Periods of parthenogenesis typically alternate with periods of sexual reproduction
o Means of rapidly producing individuals when conditions are favorable.
Sexual Reproduction – involves the production and fusion of two types of gametes - sperm and egg
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Male parent gives sperm, female gives ovum
 Egg large and nonmotile with store of nutrients for developing embryo
 Sperm small and motile
 Sperm and egg unite to form a zygote – fertilized egg
o External fertilization – gametes meet outside the body; release eggs and sperm into the
water simultaneously
 Amphibians, fish
o Internal fertilization – male delivers sperm cells directly into the body of the female;
moist internal tissues provide the watery medium required for the movement of sperm
– gametes fuse inside body
 Terrestrial animals, sharks, and aquatic reptiles, birds and mammals
o Hermaphroditism – a single individual produces both sperm and eggs
 Some (tapeworm) capable of self fertilization
 Typically 2 animals come together and fertilize one another’s eggs; copulate and
mutual cross-fertilization occurs, with each inseminating the other.
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In some self fertilization is prevented by the development of testes and
ovaries at different.
2. List the advantages and disadvantages of sexual and asexual reproduction.
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Asexual Reproduction
o Advantages
 Fastest, most efficient
 Don’t need a mate
 Takes advantage of a good environment
o Disadvantages
 No (or little) genetic variability
 Difficult to evolve
Sexual Reproduction
o Advantages
 Increases genetic variability
 Better able to adapt and evolve
 Removes harmful mutations from a population
o Disadvantages
 Requires mating (2 gametes)
 Generally takes longer
 Cannot respond quickly to environment
 Requires more energy
3. Define and give examples of different methods of asexual reproduction.
See Objective #1
4. Name the external and internal components of the male reproductive
system and (Obj. 5) describe the function of each component of the system.
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Internal Components
o Accessory Structures – glands produce semen (provide nutrients and other components
of the fluid) and duct system stores and transports sperm and semen.
 Testes – paired male gonads; site of spermatogenesis – the process of sperm
cell production
 Spermatogenesis takes place in tangle of hollow tubules – seminiferus
tubules housed within the testis
 Spermatogenesis begins with the undifferentiated spermatogonia in the
walls of the seminiferous tubules.
 Epididymis – larger, coiled, tube where sperm finish maturing and are stored
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Vas deferens – during ejaculation, sperm pass from each epididymis into this
sperm duct.
 Extends from the scrotum to the inguinal canal and into the pelvic cavity
 Ejaculatory duct – vas deferens empties into this duct which passes through the
prostate gland and opens into the urethra
 urethra – conducts semen and urine to the outside of the body
 Seminal vesicles – paired vesicles that secrete a fluid rich in fructose and
prostaglandins into the vas deferentia
 Prostate gland – secretes alkaline fluid containing calcium, citric acid, and
enzymes to neutralize the acidic environment of the vagina and increases sperm
motility
 Bulbourethral glands – on either side of the urethra release a mucous section
during arousal; lubricates the penis making penetration easier
External Components
o Scrotum – a skin-covered sac suspended from the groin; maintains the sperm below
body temperature.
 an outpocketing of the pelvic cavity and connected to it by the inguinal canals.
o Penis – erectile copulatory organ that delivers sperm into the female reproductive tract
 Consists of 3 columns of erectile tissue
 2 cavernous bodies
 1 spongy body - surrounds portion of urethra that passes through the
penis.
o Glans – the expanded tip
o Prepuce - or foreskin; covers proximal portion of the glans
5. Describe the process of spermatogenesis, including meiosis and mitosis, the
site of sperm production, the hormones and cells involved in the process
and the blood testis barrier.
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Spermatogenesis occurs in the testes within the seminiferous tubules . The process begins with
undifferentiated cells (spermatogonia) in the walls of the tubules. The spermatogonia are
diploid cells and divide by mitosis to produce more spermatogoina. Some enlarge and become
primary spermatocytes which undergo meiosis and produce haploaid gametes. Each primary
spermatocyte undergoes a first meiotic division that produces two haploid secondary
spermatocytes. In the second meiotic division, each of the two secondary spermatocytes
produce two haploid spermatids. Four spermatids are produced from the original primary
spermatocyte. Each spermatid differentiates into a mture sperm. Developing sperm cells lie
between the large, nutritive Sertoli cells which ring the fluid-filled lumen of the seminiferous
tubule. Sertoli cells also secrete hormones and signaling molecules. Each cell extend from the
outer membrane of the seminiferous tuble into its lumen and are joined to one another by tight
junctions just within the outer membrane of the tubule. The sertoli cells form a blood-testis
barrier that prevents harmful substances from entering the tubule and interfering with
spermatogenesis and from sperm passing out of the tubule into the blood where it could
stimulate an immune response. The hypothalamus secretes gonadotropin-releasing hormone
(GnRH) which stimulates the anterior pituitary to secrete gonadotropic hormones folliclestimulating hormone (FSH) and luteinizing hormone (LH). Both are glycoproteins that use cyclic
AMP as a 2nd messenger. FSH stimulates the Sertoli cells to secrete androgen-binding protein
(ABP) and signaling molecules necessary for spermatogenesis. LH stimulates interstitial cells to
secrete testosterone. A high concentration of testosterone in the testes is necessary for
spermatogenesis to occur. Testosterone and FSH stimulate Sertoli cells to produce ABP which
binds to testosterone and concentrates it in the tubules.
6. Describe the composition of semen.
Semen consists of approximately 200 million sperm cells suspended in the secretions of the accessory
glands.
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Seminal vesicles secrete fructose that the sperm use for energy
Prostate gland secretes alkaline fluid that neutralizes the acidity of the vagina
7. Name the components of the female reproductiv e system and (obj. 8)
describe the function of each component.
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Internal Structures
o Vagina – an elastic, muscular tube that extends from the uterus to the exterior of the
body. Serves as a receptacle for sperm during intercourse and is part of the birth canal.
o Cervix – The lower portion of the uterus; extends slightly into the vagina.
o Uterus – pear shaped structure that oviducts open into; located in the central area of
the pelvic cavity. Made of thick walls of smooth muscle and epithelial lining. Made of
the fundus, body, and cervix.
 Perimetrium
 Myometrium (smooth muscle)
 Endometrium – thickens in preparation for pregnancy
 Endometriosis – painful disorder in which fragments of the
endometrium migrate to other areas
 Embryo implants in the endometrium and is sustained by nutrients and
oxygen delivered by surrounding maternal blood vessels
o If not fertilized the endometrium sloughs off and discharged
through menstruation
o Oviduct(s)/fallopian tubes – funnel shaped opening of the oviduct where secondary
oocytes migrate after ovulation.
 Fertilization takes place in the oviduct
 If secondary oocyte remains unfertilized it degenerates here
o Ovary(ies) – female gonads that produce both gametes and sex hormones
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Process of ovum production, oogenesis, begins here
Before birth, the ovaries contain hundreds of thousands of oogonia
 No new oogonia are produced after birth
9. Describe oogenesis including meiosis and mitosis, the site of ovum production,
the hormones, and cells involved in the process and the blood -ovarian barrier.
The female gonads, or ovaries, are the location of ovum production or oogenesis. Before birth, oogonia
are present in the ovaries and no more are formed after birth. During prenatal development, the
oogonia enlarge and become primary oocytes. At birth they are in prophase of the first meiotic division
and then enter a resting phase that lasts throughout childhood and into adult life. A primary oocyte and
the granulose cells surrounding it together make up a follicle. Granulosa cells are connected by tight
junctions that form a protective barrier around the oocyte. After puberty, a few follicles mature each
month in response to FSH secreted by the anterior pituitary gland. The follicle grows and the granulosa
proliferate and form several layers. Connective tissue cells surrounding the granulosa cells differentiate
and form a layer of theca cells. As the follical matures, the primaryoocyte completes its first meiotic
division, producing two haploid cells differing in size. The smaller one is the first polar body and may
later divide forming two polar bodies which eventually disintegrate. The larger secondary oocyte
proceeds to the second meiotic division but remains in metaphase II until it is fertilized. If meiosis
continues, the second division gives rise to a single enlarged ovum and a second polar body. The polar
bodies dispose of unneeded chromosomes. As the oocyte develops it becomes separated from its
surrounding follicle cells by glycoproteins called the zona pellucida. Follicle cells secrete fluid that
collecte in the antrum or space between them. The follicle cells also secrete estrogens or female sex
hormones. The principal estrogen is estradiol. As a follicle matures it moves closer to the surface of the
ovary. Follicle cells secrete proteolytic enzymes that break down a small area of the ovary wall through
which the secondary oocyte ejects into the pelvic cavity during ovulation. The portion of the follicle
remaining develops into the corpus luteum, a temporary endocrine gland that secretes estrogen and
progesterone.
10. Name and describe the events associated with the ovarian and the uterine
cycles.
Ovarian Cycles
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Follicular phase:
o Follicle – contains ovum or egg which will mature
o Primordial Follicle – enlarges and ovum develops into a primary oocyte
o As follicle matures, primary oocyte undergoes Meiosis I and first polar body forms
o Now have a secondary oocyte and ovulation is ready to occur
o Full size follicle, preceding ovulation ~1 inch in diameter
o More than one primordial follicle stimulated to develop, usually only one fully develop
Luteal phase
o Always 14 days after ovulation
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Variations in the cycle occur during first 14 days and changes total length of the cycle
Ruptured follicle takes on a secretory role, becomes an endocrine gland – corpus luteum
Corpus luteum secretes progesterone and some estrogen which sustain functionality
until it becomes apparent implantation has not occurred; it degenerates leaving a scar
Three phases to uterine cycle
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Menstrual Stage – time the functionalis layer is shed
o Gonadotropins from pituitary (FSH and LH) and ovarian hormones (estrogen and
progesterone) are at lowest levels.
o Functional layer detaches from the uterine wall; ovaries are beginning to produce more
estrogen, levels begin to rise
Proliferative Stage
o Rising estrogen levels stimulate proliferation of endometrium, basal layer, forming new
functionalis
o Functionalis becomes thick, vascularization increases, mucus production increases
o Mucus thins and channels appear, this facilitates sperm movement through uterus
o Ovulation occurs on day 14, the last day of the proliferative stage
Secretory stage
o Endometrium prepares for possible implantation of fertilization product
o Progesterone levels rise, stimulates increase in vascularization of endometrium and
enlargement of uterine glands and glycoprotein secretion (will nourish embryo)
o If no implantation occurs, LH no longer stimulates corpus luteum to produce
progesterone; thus progesterone levels fall dramatically
o Drop in progesterone causes arteries of functionalis to kink and spasm
o Functionalis deprived of oxygen and nutrients, cells die and lysosomes self destruct layer
o Arteries constrict a final time and then dilate, blood rushes into capillary beds causing
functionalis to fragment and slough off
o Occurs in parallel with the ovarian cycle
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11. Describe the process of fertilization including the site of fertilization, the
capacitation reaction, the acrosomal reaction, the fast block to polyspermy, and
the slow block to polyspermy.
Fertilization is the fusion of sperm and egg. After ejaculation into the female reproductive tract, wperm
remain live and are able to fertilize an ovum for 48-72 hours. When conditions in the vagina and cervix
are favorable, sperm arrive at the site of fertilization in the upper oviduct. At the time of ovulation
when estrogen is high, the cervical mucus has a consistency that permits passage of sperm from the
vagina into the uterus. After ovulation, when progesterone concentration rises, the cervical mucus
becomes thick and sticky, blocky the entrance of sperm (as well as harmful bacteria). Once sperm enter
the uterus, contractions of the uterine wall help transport them and are induced by the prostaglandins
in the semen. When a sperm encounters an egg , openings develop in the sperm acrosome and
becomes depleted in cholesterol and less rigid which causes the membrane to become fragile and
acrosomal enzymes are more easily released when sperm contacts the cell layers surrounding the ovum.
Sperm are not capable of fertilization until they undergo this capacitation reaction. This exposes
enzymes that digest a path through the zona pellucida surrounding the secondary oocyte. As soon as
one enters the oocyte, changes occur that prevent the entrance of other sperm or polyspermy. The
slow block to polyspermy, cortical reaction, requires up to several minutes to complete but it is a
complete block. Binding of the sperm to receptors on the viteline envelope activates one or more signal
transduction pathways in the egg which cause calcium ions stored in the egg endoplasmic reticulum to
be released into the cytosol. This causes thousands of cortical granules to release enzymes, various
proteins, and other substances by exocytosis into the space between the plasma membrane and the
vitelline envelope. The vitelline envelope becomes elevated away from the plasma membrane and
forms the fertilization envelope, a hardened covering that prevents entry of another sperm. Mammals
do not form a fertilization envelope, but the enzymes released during exocytosis of the cortical granules
alter the sperm receptors on the egg’s zona pellucida so that no additional sperm bind to them. As the
sperm enters, it loses its flagellum and its entrance stimulates the secondary oocyte to complete its
second meiotic division. The head of the haploid sperm swells to form the male pronucleus and fuses
with the female pronucleus to form the dipoloid nucleus of the zygote. DNA synthesis occurs in
preparation for the first cell division.
12. Describe the developmental differences between the zygote, blastocyst,
embryo, and fetus.
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Zygote
o Totipotent – gives rise to all the cell types of the new individual
o Bulk of the zygote cytoplasm and organelles come from the ovum
o After fertilization, the zygote undergoes cleavage – a series of rapid mitotic divisions
with no period of growth during each cycle.
 Cell number increases but the embryo does not increase in size.
 Initially divides to form a 2 celled embryo then it undergoes mitosis and divides
 4 cells.
 Repeated divisions increase the number of cells called blastomeres that make
up the embryo
 At 32 cell stage embryo is a solid ball of blastomeres called a morula
 64 to several hundred blastomeres form the blastula which is usually a hollow
ball with a fluid-filled cavity, the blastocoels.
Blastocyst
o The zygote continues to divide creating an inner group of cells with an outer shell
(trophoblast).
o The inner group of cells will become the embryo while the outer group of cells will
become the membranes that nourish and protect it. (inner cell mass
o Blastocyst implants in the endometrial lining.
Embryo
o Cells begin to multiply and take on specific functions – differentiation
o Rapid growth
Fetus
o After 2 months of development
o Growth and refinement of the organs
13. Define and describe what happens during gastrulation.
The process by which the blastula becomes a three layered embryo, or gastrula, is called gastrulation.
Zygote  early cleavage stages  morula  blastula  gastrula.
During gastrulation, the embryo begins to approximate its body plan as cells arrange themselves into
three distinct germ layers – ectoderm, endoderm, mesoderm. Ectoderm is the outermost layer, endo
derm is the innermost layer and mesoderm separates the two. Many cells establish new cell to cell
contacts and establish new ones.
14. Briefly describe the process of implantation and the establishment of the
placenta.
Implantation:
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Inner cell mass side of blastocyst is somewhat sticky which assists in the orientation and
attachment at this site
Blastocyst implants in uterine wall by digesting a hole in functionalis of endometrium
Implantation usually on posterior wall near fundus of the uterus;
Basalis proliferates and the imbedded blastocyst is covered and now contained within the
uterine wall
Now called an embryo (fetus end of second month of development)
Nutrients from maternal capillaries pool in sinuses of partially digested tissue
This and contents of the digested cells are source of nutrients for embryo
Process of implantation takes about a week; at end of implantation ~2 weeks have passed since
ovulation
Placenta:
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Placenta has a dual origin; fetal and maternal; fully functional about end of third month; only
organ with a functional life span of less than a year
Fetal contribution is from chorion which began as microvilli from the trophoblast cell layer of
blastocyst invading the endometrium (chorionic microvilli)
Maternal contribution from the endometrium [part of functionalis remaining after implantation,
the decidua shed after birth] that underlies the embryo
[separate areas to decidua ]
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basalis, under the embryo –between chorinic villi and basalis of endometrium
capsularis, surrounding the embryo on side of uterine cavity
parietalis, lines rest of uterine cavity]
Placenta is important in gas exchange, waste removal and nutrient source
Placenta acts as endocrine gland producing hormones to sustain pregnancy
Fetal side smooth and highly vascularized; maternal side lobed and rough
Placenta does not act as a barrier to drugs or to viruses, but most other microorganisms cannot
cross
Some maternal antibodies actively transported across placenta (antibodies to blood groups do
not cross, but anti-Rh factor antibodies do)
15. Name, give the source and function of the hormones associated with
pregnancy and development.
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Placental horomones
Endocrine structure life less than 1 yr
hCG – human chorionic gonadotropin
Pregnancy tests
Chorion produces (embryonic origin)
Stimulates corpus leteum (progesterone)
Stimulates testosterone production fetal testes
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Progesterone – secreted by the ovaries
Stimulate development, maintenance of endometrium
Stimulate mammary development
Inhibit uterine motility
Inhibit pituitary secretion of gonadotropin
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Estrogen – comes from the ovaries
Stimulate mass increase myometrium
Stimulate mammary gland development
Maintenance of endometrium
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hCS – human chorionic somatomammotropin
(placental lactogen)
Maintenance of corpus luteum
Growth effects on fetus
Stimulate prostaglandin release
Decrease maternal use of glucose
Increase maternal use of fatty acids
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Inhibin: inhibits secretion of FSH (secreted by ovaries)
Relaxin
Endometrial source identified
Corpus luteum
Transform pubic symphysis cartilage from rigid to more flexible
Relaxes myometrium (prevent expulsion)
Stimulates proliferation of blood vessels
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Corpus luteum
Estrogen
Progesterone
Inhibin
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Pancreas
Insulin production increases
response to decreased maternal sensitivity (glucose sparing)
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Adrenal glands
Maternal aldosterone levels rise
Sodium retained
Water retained (obligatory)
Fetal and maternal plasma volumes increase
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Thyroid hormones
Maternal levels increase
Increased metabolism
Increased resting pulse pressure
Increased oxygen delivery to fetus
16. Describe the processes of CVS and amniocentesis.
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CVS is performed by removing a small sample of the placenta (nourishment for the baby) from
the uterus. It is removed with either a catheter (a thin tube) or a needle. Local anesthesia is used
for this test to reduce pain and discomfort. The sample of placenta may be obtained through the
cervix. A catheter is inserted into the vagina and through the cervix and the sample is
withdrawn. The sample can also be obtained by inserting a needle into the abdomen and
withdrawing some of the placenta.
During amniocentesis, a sample of amniotic fluid (the fluid around the baby) is removed from
your uterus and sent to a laboratory for evaluation. Amniocentesis is performed by inserting a
thin needle through your abdomen into your uterus (womb) and withdrawing a small amount of
fluid. Your body will make more fluid to replace the fluid that is taken out. The baby will not be
hurt during the procedure. Some women feel mild cramping during or after the procedure. Your
doctor may tell you to rest on the day of the test, but usually you can resume normal activity the
next day.