Transcript No Slide Title

•
•
•
•
•
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
–
•
•
•
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
-testis: develop internally near the kidneys and descend through the inguinal canal during the latter half of
the seventh month gestation
-covered by several protection 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
• 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
– produces numerous chemicals involved in
spermatogenesis
– some of these chemicals result in a blood-testis
barrier
– this barrier prevents an immune response against
the spermatogenic cells’ surface antigens which
are recognized as they develop as being foreign
– other chemicals - cytokines and growth factors
that mediate 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 - faciliate
spermatogenesis and sperm maturation
• between adjacent seminiferous tubules are the interstitial cells or Leydig cells
– for the production of testosterone (androgen)
– can be a site for the development of testicular cancer - along with Sertoli cells
– androgen = hormone for the development of masculine characteristics
Spermatogenesis
•
•
•
•
•
•
sperm development – from sperm stem cells
called spermatogonia
the maturing sperm can be found toward the
lumen of the seminiferous tubule, the
spermatogonia in the
most mature = sperm cells or spermatozoa
1. some spermatogonium break away from the
basement membrane of the seminiferous tubule
2. each spermatogonium forms two primary
spermatocytes (2n = 46)
3. primary spermatocyte starts meiosis I - the
formation of secondary spermatocytes (n = 23)
–
•
however despite having 23 chromosomes, these
chromosomes are still comprise of two chromatids
4. completion of meiosis II and formation of 4
spermatids (n) – 23 chromosomes each made up
of one chromatid
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
Mitosis
Meiosis I
Meiosis II
Spermiogenesis
interstitial cell
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
• specialized organelle
• 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
1.
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)
2.
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
•
testosterone and DHT both bind to same receptors
–
•
•
receptors are found within the nuclei of the target cells
targets – bone, muscle
effects
– 1. prenatal development
• stimulates the male pattern of the reproductive system
–
gonads develop during the 5th week of gestation from two sets of ducts: 1) Wolffian ducts (males) and 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 stimulates development of the epididymus, vas deferens, ejaculatory duct and seminal vesicle
• DHT stimulates development of external genitalia
–
–
–
–
development around the 8th week
from the genital tubercle (both males and females) – comprised of a urethral groove and two labiosacral swellings
elongation of part of the genital tubercle into the penis
labiosacral swellings - scrotum
• testosterone is converted in the brain to estrogens – development of certain brain regions in males
– 2. development of male sexual characteristics
– 3. development of sexual function
• male sexual behavior
• spermatogenesis
• libido in both males and females
–
females – androgen release by the adrenal cortex
– 4. stimulation of anabolism
• stimulate protein synthesis
Testosterone
-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
Reproductive Ducts
-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:
•
A. prostatic - runs through the prostate
• connects to ducts from the prostate and to the ejaculatory duct
•
B. membranous - between prostate and penis
• -through the muscles of the perineum – urogenital diaphragm
•
C. spongy - through the erectile tissue of the penis
Male reproductive
glands
•
•
•
•
•
•
•
•
•
•
-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
-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
•
•
•
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)
–
•
•
undergo mitosis to produce millions of germ cells
most of the germ cells degenerate by atresia
a few develop further into primary oocytes – entered prophase I of
meiosis
–
–
–
–
–
surrounded by a layer of follicular cells = primordial follicle
continue to develop into primary follicles
at birth – 200,000 to 2,000,000 follicles within the ovary
at puberty 40,000 are still present
400 will develop further (rest undergo atresia)
-release of FSH and LH each month causes the development of one primary oocyte into a secondary oocyte
-development of a few primordial follicles into primary follicles (only one will continue until ovulation)
-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 contact a basement membrane which begins to develop into two layers (theca layers)
-now known as the secondary follicle
-secondary follicle begins to accumulate fluid in the center of the follicle (antrum)
-innermost granulosa cells firmly attaches to the zona pellucida = corona radiata
-becomes larger and turns into the tertiary or mature Graafian follicle
-completes meiosis I – two haploid cells
-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
-stops at metaphase II
-ovulated
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
• uterus: receives and nourishes the embryo
•
-comprised of a body, a curved portion (fundus) and the cervix
•
•
•
-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): conduction of egg from ovary to
uterus
•
-expands at end near the ovary = infundibulum with fimbrae (fingers) for the
•
“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
-3 major types of estrogens:
1.
beta-estradiol
2.
estrone
3.
estriol
4.
other smaller quantities
-follicular estrogens:
a.
promote the development of the
female reproductive structures,
secondary sex characteristics and
the mammary glands
b. increase protein anabolism, including
bone synthesis
c. lower blood cholesterol
d. inhibit the release of GnRH, FSH
and LH
-GnRH causes release of FSH and LH from anterior pituitary
-FSH initiates follicular growth
-LH stimulates the maturation of follicles
-both LH and FSH stimulate the secretion of estrogens from the follicle
-LH stimulates the theca layers of the follicle to make androgens
-FSH stimulates the uptake of these androgens and converts them to estrogens
-LH triggers ovulation and results in development of corpus luteum
-corpus luteum produces and releases progesterone and some estrogen plus relaxin and inhibin
-estrogen and progesterone regulate pregnancy, menstruation, secondary sex char’s
& development of sex organs at puberty
-relaxin – relaxes the uterus by inhibiting contractions of the myometrium
-important to the implantation of the embryo – produced by the placenta during pregnancy
-also increases the flexibility of the pubic symphysis
-inhibin - inhibits secretion of FSH and LH
1.
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
-forms a blister-like bulge due to
an increase in fluid within the antrum of the
follicle
-the GF continues to increase its
estrogen production
B. Uterine events – E stimulates
the repair of the SF – growth from the
stratum basalis
-increase in arteriole size and
blood supply
• 3. Ovulation
•
A. Ovarian events – rupture
of the GF usually around day 14
• ovulated secondary follicle
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 preovulatory 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
• basis for the at-home ovulatory
tests – detect rises in LH
•
B. Uterine events - none
• signs of ovulation
–
–
–
–
Increase in basal body temperature
Changes in cervical mucus
Cervix softens
Mittelschmerz---pain
• 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
• granulosa and thecal cells come into direct contact – 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 –ve feedback signals for inhibition of GnRH – together with inhibin
• if the ovum is NOT fertilized, the CL degenerates into the corpus albicans – 2
weeks
• 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 chorion that surrounds
the embryo (8 days post-fertilization)
GnRH release
Stratum functionalis
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
•
•
•
•
•
Surgical
Hormonal
Mechanical barriers
Periodic abstinence
Coitus interruptus
Reproductive disorders
•
Males
–
–
–
–
•
Females
–
–
–
–
–
–
•
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
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
1. sperm penetrates corona radiata
2. several sperm enter 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
3. ONE sperm penetrates the plasma
membrane of the egg
4. immediate change in the oocyte cell
membrane (depolarizes)
-also binding results in release of intracellular
calcium which stimulates exocytosis of
secretory vesicles whose contents inactivate
ZP3 and harden the zona pellucida
- impervious to more sperm
5. oocyte releases the 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 pronuclei
-union of sperm and egg pronuclei 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)
Implantation
• 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
-day 4 – formation of morula and passage into the uterine cavity
-endometrial glands release a glycogen-rich fluid = uterine milk
-enters the morula through the zona pellucida and provides nourishment
-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. placenta,
yolk sac)
-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
-second week of development - the inner cell mass flattens = embryonic disk (hypoblast and epiblast)
-hypoblast = primitive endoderm
-epiblast = primitive ectoderm
-amniotic cavity forms between the inner cell mass 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 (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 two layers within the region where the blastocyst and
the endometrium make contact – become part of the chorion
-these trophoblast cells will secrete digestive enzymes that allow the embryo to
burrow into the decidua
-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
–
–
–
–
–
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