Download lecture #12

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scrotum = supportive structure for the testes
consists of loose skin and superficial fascia that hangs from the root of the penis
externally- single pouch separated at the midline by a raphe
internally – divided by a scrotal septum into two sacs each containing 1 testis
the septum = dartos muscle (smooth muscle) + superficial fascia
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dartos is also found in the subcutaneous portion of the scrotal skin
each testis is associated with a cremaster muscle – skeletal muscle that is a continuation of
the internal oblique
exterior location of the testis ensures its internal temperature is at least 2 to 3C lower than the
body core
contraction of the muscles lifts the
scrotal sac closer to the trunk of the
body and warms it
Male Anatomy
Review
Reproductive Ducts – Anatomy Review
-pressure generated by the Sertoli cells pushes the sperm into a series of ducts within the testes that end up
as the epididymis
-within the epididymis is the ductus epididymis
-also made up of a head, body and tail portion
-site of sperm maturation – acquire mobility (14 days)
-helps propel sperm into the:
-vas (ductus) deferens: conducting tube from testis to urethra
-connects to the tail of the epididymis
-connects the testes to the urethra
-made up of a pseudostratified columnar epithelium with a lamina propria connective tissue
plus three layers of smooth muscle
-contractions of these muscular layers propel the sperm
-spermatic cord supports the
vas deferens + blood vessels
(testicular artery and the
pampiniform venous plexus),
lymphatic vessels, the cremaster
muscle and autonomic nerves
-passes through the inguinal canal
• ejaculatory duct – forms from the union of the seminal vesicle and
the end of the vas deferens
– pass through the prostate gland and terminate in the urethra
• urethra: 3 sections:
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A. prostatic - runs through the prostate
• connects to ducts from the prostate and to the ejaculatory duct
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B. membranous - between prostate and penis
• through the muscles of the perineum – urogenital diaphragm
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C. spongy - through the erectile tissue of the penis
Male reproductive
glands
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glands: seminal vesicles, prostate, bulbourethral glands
-produce fluid that combine with sperm to make semen
-semen: alkaline, activates sperm cells
1. prostate: surrounds the urethra
-forms as an outgrowth of the urethra along with the
bulbourethral glands
-secretes a thin, milky fluid that enhances sperm motility
and neutralizes vaginal fluid
2. seminal vesicles: connect to urethra via the ejaculatory ducts
-secretes an alkaline fluid that contains sugars and
prostaglandins (stimulates uterine contractions)
3. bulbourethral glands: 2 glands behind
the prostate
-secrete a fluid that lubricates the penis
-conveys urine and semen
-body is found externally
-body is comprised of two tissue types of erectile tissue
surrounded by connective tissue
A. corpus cavernosum - large spaces
B. corpus spongiosum - smaller spaces
-surrounds the urethra
-root of the penis is attached to the pelvis
-corpus spongiosum enlargens at the tip - glans penis (sensory receptors)
-glans penis covered with a loose fold of skin = prepuce
Testes
-testis: covered by several protective membranes
1. tunica vaginalis – serous membrane derived from the peritoneum, forms during the descent
of the testes
2. tunica albuginea – internal to the TV
-extends inward to divide the testes into lobules (200-300)
-each lobule contains 1 to 3 coiled seminiferous tubules for sperm production
- each seminiferous tubule is lined with epithelium that produce sperm
- contained within that epithelium are germ cells for sperm production – known as spermatogenic cells or
spermatogonia
Seminiferous
tubules
- each seminiferous tubule is lined with an
epithelium that produces sperm
- contained within that epithelium are germ
cells for sperm production – known as
spermatogenic cells or spermatogonia
- each spermatogonium will form 4
spermatids at the end of meiosis
• embedded among the spermatogenic cells of the seminiferous tubules are large
cells called Sertoli cells
– sustenacular cells
– surround the spermatogenic cells and the developing spermatocytes and
spermatids
– phagocytosis of unused spermatids
– produces a blood-testis barrier
– this barrier prevents an immune response against the spermatogenic cell surface
antigens which may be recognized as foreign
• Sertoli cells
– produce numerous chemicals involved in spermatogenesis
• anti-Müllerian hormone (AMH) - secreted during the early stages of fetal life
• inhibin and activins - secreted after puberty, and work together to regulate FSH
secretion
• androgen binding protein/ABP - facilitate spermatogenesis and sperm
maturation
• between adjacent
seminiferous tubules are the
interstitial cells or Leydig
cells
– for the production of
testosterone (androgen)
– androgen = hormone for the
development of masculine
characteristics
Spermatogenesis
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sperm development – from sperm stem cells
called spermatogonia
each spermatogonium develops in the embryonic
testes from primordial germ cells that arise from
the yolk sac
the spermatogonium remain dormant in the
testes until puberty
the maturing sperm can be found toward the
lumen of the seminiferous tubule
most mature = sperm cells or spermatozoa
takes 60-75 days to complete
Spermatogenesis
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1. some spermatogonium break
away from the basement
membrane of the seminiferous
tubule
2. one spermatogonium forms two
primary spermatocytes by mitosis
(2n = 46)
3. ONE primary spermatocyte
starts meiosis I – forms two
secondary spermatocytes (n = 23)
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4. each secondary spermatocyte
completes meiosis II and forms 2
spermatids (n)
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however despite having 23
chromosomes, these chromosomes are
still comprise of two chromatids
23 chromosomes each made up of one
chromatid
at the end of meiosis each
primary spermatocyte has formed
4 spermatids
Spermatogenesis
• spermiogenesis – last stage of
spermatogenesis
• development of spermatids
into a sperm cell
– spherical spermatids
transform into elongated
sperm containing an
acrosome and bearing a
flagellum
Sperm
• three functions
– 1. reach the oocyte
– 2. penetrate the oocyte
– 3. donate its chromosomes to the oocyte
• major parts
– 1. head: contains the nucleus with 23 highly condensed
chromosomes (one chromatid)
– 2. acrosome: covers the anterior 2/3 of the head
• contains digestive enzymes to dissolve the protective barriers
surrounding the oocyte
– 3. midpiece
• contains mitochondria arranged in a spiral
• also contains a pair of centrioles for the production of the
microtubules for the tail
– 4. tail or flagellum
• made up of microtubules
• principal piece – longest portion of the tail
• end piece – terminal portion of the tail
• 300 million made each day
• 60 um long
-release of gonadotropic releasing hormone (GnRH) from the neurosecretory cells of the
hypothalamus
-GnRH travels to the anterior pituitary via the hypophyseal portal system
-in response - the gonadotrophs of the anterior pituitary gland produce and release the 2
gonadotropins
1. Follicle Stimulating Hormone - FSH
2. Leutenizing Hormone - LH
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Follicle stimulating hormone – works with
testosterone to stimulate spermatogenesis
-synergistic action by FSH and testosterone
on the Sertoli cells
-FSH binds to the surface of the Sertoli cell
-testosterone and its receptor is internalized
by the Sertoli cell
- together FSH + testosterone results in
secretion of androgen-binding protein by
Sertoli cells
-ABP binds to testosterone and promotes
better spermatogenesis
-GnRH and FSH release are both inhibited by
the release of inhibin (by the Sertoli
cells)
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Leutinizing hormone - stimulates male hormone production by the Leydig cells
-testosterone synthesized from cholesterol in the testes
-testosterone stimulates the final stages of spermatogenesis
-suppresses GnRH and LH synthesis by negative feedback
Testosterone
• two major forms: testosterone and 5-dihydrotestosterone (5-DHT)
• testosterone and DHT both bind to same receptors
– receptors are found within the nuclei of the target cells
Testosterone
• effects
– 1. prenatal development
• testosterone stimulates development of the epididymus, vas deferens,
ejaculatory ducts and seminal vesicles
– gonads develop during the 5th week of gestation from two sets of ducts:
1) Wolffian ducts (males)
2) Mullerian ducts (females)
– therefore the embryo has the potential to develop into either sex
– BUT “maleness” determined by a gene called SRY – sex determining
region of the Y chromosome
– SRY protein expression induces differentiation of Sertoli cells
– Sertoli cells secrete anti-Mullerian Hormone– apoptosis within the
Mullerian ducts which inhibits the development of female structures
-in response to hCG – Leydig cells begin to synthesize testosterone
Testosterone
– 2. development of male sexual characteristics
– 3. development of sexual function
• male sexual behavior
• spermatogenesis
• libido in both males and females
– 4. stimulation of anabolism
• stimulate protein synthesis in both bone and muscle tissue
Testosterone
• synthesis and secretion is controlled by a
negative feedback system
• increased testosterone promotes the
production of inhibin from the Sertoli cell
• decreased testosterone promotes the
production of activin from the Sertoli cell
-ovary: production of egg
-surface is covered with a germinal epithelium (simple epithelium) – does NOT give rise
to the ova!
-next layer is = tunica albuginea – dense irregular connective tissue capsule
-outer cortex- granular tissue due to the presence of tiny ovarian follicles
- inner medulla - connective tissue with blood & lymphatic vessels and nerves
Oogenesis and Follicular
Development
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begins before birth
early fetal development – primordial germ cells from the yolk sac migrate into the
developing ovaries
differentiate to form oogonia (diploid stem cells)
most of these cells degenerate by atresia
several oogonia split into primary oocytes (via mitosis)
before birth primary oocytes enter and stop at prophase I of meiosis
– primary oocyte is surrounded by a layer of follicular cells = primordial follicle
– continue to develop into primary follicles
Oogenesis and Follicular
Development
-release of FSH and LH each month causes the
development of several follicles and their
oocytes
-one will continue on to develop and being
ovulated
-primary follicle – primary oocyte surrounded
by several layers of epithelial cells called
granulosa cells
-develops a clear glycoprotein layer between the
oocyte and the granulosa cells – zona pellucida
-the outermost granulosa cells develop into two
layers (theca layers) – follicle is now known as
the secondary follicle
-secondary follicle begins to accumulate fluid in
the center of the follicle (antrum – mature
secondary follicle)
(immature
secondary
follicle
Oogenesis and Follicular
Development
-secondary follicle begins to accumulate fluid in
the center of the follicle (antrum)
-innermost granulosa cells firmly attach to the
zona pellucida = corona radiata
-oocyte is still considered a primary oocyte since
it hasn’t finished meiosis I
Oogenesis and Follicular
Development
-secondary follicle becomes larger and is called the tertiary or mature Graafian follicle
-inside the tertiary follicle is the secondary oocyte which has completed meiosis I and
has stopped at metaphase II
– two haploid cells are actually found within the tertiary follicle
-these haploid cells are uneven in size but each have 23 chromosomes (two
chromatids each - 46)
-smaller cell – first polar body (discarded nuclear material)
-larger cell – secondary oocyte
-receives most of the cytoplasm and has 23 chromosomes
-ovulated as the tertiary follicle ruptures
Oogenesis and Follicular
Development
• ovulation – expulsion of the secondary
oocyte into the pelvic cavity with the
first polar body and corona radiata
• fertilization – union of egg and sperm
– penetration of the sperm into the
secondary oocyte results in the
resumption of meiosis II
– the secondary oocyte splits again into
two cells of unequal size (n)
– larger one is called the ovum and the
smaller one is the second polar body
– combination of the ovum and the
sperm results in the formation of the
zygote
– the first polar body splits also into two
haploid cells
– therefore meiosis of the primary oocyte
produces one haploid ovum and three
haploid polar bodies that degenerate
secondary
tertiary
• uterus: receives and nourishes the embryo
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-comprised of a body, a curved portion (fundus) and the cervix
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-uterine wall outer perimetrium, muscular myometrium and
inner endometrium
-endometrium: mucosal layer covered with epithelium
-rich blood supply, sloughed off during menstruation
• uterine tubes (Fallopian tubes): fertilization of ovum & conduction
of ovum or zygote from ovary to uterus
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-expands at end near the ovary = infundibulum with fimbrae (fingers) for the
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“catching” of the released egg
-lined with a mucosal layer and columnar epithelium with cilia
-are also cells with microvilli rather than cilia – produce a nutritive fluid for the
egg
• cervix: projects into the vaginal canal
Female Reproductive Cycle
• two cycles
– 1. ovarian: during and after the maturation of
the oocyte
– 2. uterine: concurrent series of changes in the
endometrium of the uterus to prepare it for
embryo implantation
-GnRH causes release of FSH and LH from anterior pituitary
-FSH initiates follicular growth – primary  secondary
-LH stimulates the maturation of follicles into tertiary
-both LH and FSH stimulate the secretion of estrogens from the follicle
-called follicular estrogens
-3 major types of estrogens:
1. beta-estradiol
2. estrone
3. estriol
4. other smaller quantities
-follicular estrogens = estrogens made by the follicle:
a. promote the development of the female reproductive structures,
secondary sex characteristics and the mammary glands, increase
protein anabolism, including bone synthesis
c. lower blood cholesterol
d. inhibit the release of GnRH, FSH and LH
-LH triggers ovulation and results in development of corpus luteum
-corpus luteum produces and releases progesterone and some estrogen plus relaxin and
inhibin
-estrogens from the corpus luteum are called luteal estrogens
-estrogens and progesterone regulate pregnancy, menstruation, secondary sex characteristics
& development of sex organs at puberty
-relaxin – relaxes the uterus by inhibiting contractions of the myometrium
-inhibin - inhibits secretion of FSH and LH
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Menstrual Phase
A. Ovarian events – FSH
increase causes development
of primary follicles and
primary oocytes
B. Uterine events – 50-150 mL
of blood, tissue fluid, mucus
and epithelial cells
-shed from the stratum
functionalis
-occurs because of declining levels
of E and P – loss of stratum
functionalis
- leaving the stratum basalis intact
2. Preovulatory Phase – most variable in
length
A. Ovarian events – secretion of
E and inhibin from the secondary
follicles
-one secondary follicle outgrows
the rest to become the dominant follicle
-the dominant follicle secretes E
and I which causes an inhibition of FSH
and a decrease in the stimulation of other
follicles
-the dominant follicle develops
into the Graafian follicle
-the GF continues to increase its
estrogen production
B. Uterine events – E stimulates
the repair of the stratum functionalis
-increase in arteriole size and
blood supply to the SF
post-menstrual
phase
pre-menstrual
phase
• 3. Ovulation
• A. Ovarian events – rupture of the
GF usually around day 14
• ovulated secondary oocyte
remains surrounded by its
corona radiata and its zone
pellucida
• triggered by a positive feedback
system – high levels of E at the
end of the pre-ovulatory phase
increases the secretion of GnRH,
which then increases the release
of LH
• increased LH induces rupture of
the GF about 9 hours after the LH
peak
• B. Uterine events - none
• 4. Postovulatory Phase – most consistent part of the cycle (14
days)
– A. Ovarian events – the mature graafian follicle collapses and bleeds
- the development of a blood clot results as the follicle induces bleeding – follicle is
now called the corpus hemorrhagicum
• follicle is transformed into corpus luteum cells under the influence of LH
• luteal cells produce hormones - progesterone, estrogen, relaxin and inhibin
– progesterone and estrogen are now negative feedback signals for
inhibition of GnRH – together with inhibin
GnRH release
Stratum functionalis
• 4. Postovulatory Phase – most consistent part of the cycle (14
days)
– A. Ovarian events
• if the ovum is NOT fertilized, the CL degenerates into the corpus albicans
• resulting decrease in P, E and Inhibin results in the release of GnRH, FSH and
LH (loss of negative feedback) - new follicular growth begins
• if fertilized – the CL persists beyond 2 weeks by the secretion of human chorionic
gonadotropin (hCG) hormone produced by the developing embryo (8 days postfertilization)
corpus luteum
corpus albicans
post-menstrual phase
pre-menstrual phase
B. Uterine events – P and
E produced by the
corpus luteum promotes
the growth and
vascularization of the
endometrium and its
thickening to about 12-18
mm
-endometrial glands
within the endometrium
begin to secrete
glycogen – energy for
the fertilized egg
Summary
Birth Control Methods
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Surgical
Hormonal
Mechanical barriers
Periodic abstinence
Coitus interruptus
Reproductive disorders
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Males
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Females
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testicular cancer
prostate concer
erectile dysfunction (ED)
benign prostatic hyperplasia
PMS
PMDD
Endometriosis
Ovarian, uterine cysts
Ovarian, uterine, cervical cancer
vulvovaginal candidiasis
Both
– UTI
– STDs – gonorrhea, syphillis, chlamydia, genital herpes, genital warts
Fertilization & Pregnancy
-fertilization in the upper third of the oviduct/fallopian tube
-fertilization = union of egg and sperm
-plasma membrane of the egg is surrounded by an extracellular matrix = zona pellucida
and a ring of follicular cells = corona radiata (nourishment in the follicle)
-after fertilization = zygote
Fertilization
1. sperm penetrates corona radiata
2. several sperm contact the zona
pellucida
-one of the glycoproteins within the ZP
(ZP3) acts as a receptor for the sperm
-binding causes dissolution of the acrosome
and release of digestive enzymes (acrosomal
reaction)
3. ONE sperm penetrates the plasma
membrane of the egg
4. immediate change in the oocyte cell
membrane (depolarizes)
- binding results in release of intracellular
calcium which stimulates exocytosis of
secretory vesicles whose contents inactivate
ZP3 and harden the zona pellucida to make
it impervious to more sperm
5. oocyte releases the hardened zona
pellucida away from the egg surface
6. fusion of the sperm with nucleus of
the egg
-before fusion the secondary oocyte must
complete meiosis II and form the ovum
embryonic stage:
week 2 to week 8
-after sperm penetration and ovum development the nuclei of the egg and sperm
undergo changes to become pro-nuclei
-union of sperm and egg pro-nuclei nuclei forms the zygote
-first cell division = embryo
-first division takes place 24 hours post-fertilization – takes 6 hours to complete
-each succeeding division takes less time
-72 hr stage = 16 cells
-96 hr stage = morula (embryo is the size of the original ovum, filled with cells (blastomeres)
-day 4 – formation of morula and passage into the uterine cavity
-endometrial glands release a glycogen-rich fluid = uterine milk
-enters into the morula
-day 5 -the fluid begins to collect in the morula and reorganizes them around a fluid-filled cavity =
blastocoel
-embryo is now called a blastula or blastocyst (50-150 cells)
-outer layer = trophoblast - forms extraembryonic tissues (e.g. chorion, amnion)
-inner cell mass at one end - totipotent embryonic stem cells
-by the end of day 5, the blastocyst digests a hole in the ZP and squeezes through it
to undergo implantation
Implantation
• embryo attaches after
about 6 days
• usually in the fundus or
the body of the uterus
• orients its inner cell
mass toward the uterus
• 7 day – the endometrium
becomes more
vascularized
• 9 days – completely
embedded
• following implantation,
the endometrium is
called the decidua
– several layers with
defined functions
-second week of development - the inner cell mass flattens into an embryonic disk (hypoblast and epiblast)
-hypoblast = primitive endoderm
-epiblast = primitive ectoderm
-amniotic cavity forms between the embryonic disc and the trophoblast
-surrounded by an amniotic membrane – develops from the epiblast
-fills with amniotic fluid – filtrate from maternal blood at initial stages
-formation of the yolk sac below the disc - from the hypoblast
-forms blood cells, gives rise to sex cells and the stem cells of the immune system
-also forms part of the embryonic digestive tube
-portion will also become part of the umbilical cord
-the outer trophoblast cells develops into part of the chorion (to connect to the mother)
-these trophoblast cells will secrete digestive enzymes that allow the embryo to
burrow into the endometrium
-also secrete hCG – rescues the corpus luteum from degeneration
• day 15: embryonic disk undergoes gastrulation to form the gastrula embryonic
stage
– formation of the three embryonic germ layers by differentiation of the ES cells within
the embryonic disc
• epiblast form a specialized region = primitive streak
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clearly establishes a head and tail orientation
head end the streak enlargens to form the primitive node
cells from the epiblast move inward through the primitive streak
some cells displace the hypoblast and form the endoderm
other cells are retained in the area and form the mesoderm
• mesoderma forms a loose connective tissue = mesenchyme
– cells remaining in the epiblast form the ectoderm
-portions of the mesoderm that
do not form the notochord
segment into sections called
somites -> specific body
regions and structures
-in front of the primitive streak forms the primitive node – head and associated structures
-mesodermal cells from the primitive node form a hollow tube near the future head of the
embryo - become the notochord (day 22-24)
(progenitor to the vertebral column)
-four weeks of development - embryo forms a tubular structure
-embryo begins to form definitive structures:
-neural folds of ectoderm -> nervous system (brain and spinal cord)
** neurulation occurs by induction (one tissue influences the development of another)
-e.g. nervous system requires the mesodermal cells of the notochord