The Reproductive System
Male Reproductive System
Male Reproductive System
• The male gonads (testes) produce sperm and lie
within the scrotum
• Sperm are delivered to the exterior through a
system of ducts: epididymis  ductus deferens
 ejaculatory duct urethra
• Accessory sex glands:
– Empty their secretions into the ducts during
ejaculation
– Include the seminal vesicles, prostate gland, and
bulbourethral glands
The Scrotum
Figure 27.2
The Scrotum
•
Sac of skin and superficial fascia that hangs
outside the abdominopelvic cavity containing
paired testicles.
• Spermatic Cord: enclose nerves and blood
vessels
• The Testes are kept 3C lower than core body
temperature (needed for sperm production)
controlled by:
• Cremaster muscle
– When it is cold it contracts pulling
the testes up toward the core of the
body.
– When it is warm these muscles
relax allowing the testes to descend
away from the body.
The Testes
Seminiferous Tubules
– Produce the sperm
– Surrounding the
seminiferous tubules
are interstitial cells that
produce Testosterone
The Epididymis
– Sperm enter the epididymis were excess testicular
fluid is absorbed and nutrients are provided to the
sperm to enable them become motile
– Upon ejaculation the epididymis contracts, expelling
sperm into the ductus (VAS) deferens.
Spermatids to Sperm
• Sperm have three major regions
– Head – contains DNA and has a helmet like acrosome containing
hydrolytic enzymes that allow the sperm to penetrate and enter
the egg
– Midpiece – contains mitochondria spiraled around the tail
filaments
– Tail – a typical flagellum produced by a centriole
The Penis
Male Sexual Response
Erection: Mediated by parasympathetic
nervous system during sexual stimulation.
Penile arteries dilate which causes the erectile
tissue corpora cavernosa to compress the
penile veins draining the penis.
Ejaculation: Mediated by the sympathetic
nervous system. Muscles of the pelvic floor
and accessory glands(seminal vesicles,
prostate gland, bulbourethral glands) contract
secreting the contents out the urethra as
semen.
Ductus Deferens and Seminal Vesicles
• Ductus Deferens : runs from the epididymis to its an
enlarged section (ampulla) where it merges with the
seminal vesicle
• Sperm and seminal fluid mix in the ejaculatory duct and
enter the prostatic urethra during ejaculation
• Vasectomy – cutting and ligating the ductus deferens,
which is a nearly 100% effective form of birth control
• Seminal vesicle lies on the posterior wall of the bladder.
They functions to:
– and secrete 60% of the volume of semen
– Semen – viscous alkaline fluid containing:
• fructose: fuel for the road trip
• prostaglandins which stimulate reverse peristalsis
in the uterus
• ascorbic acid
Accessory Glands
• Prostate Gland
– Doughnut-shaped gland that encircles part of the
urethra inferior to the bladder
– Plays a major role in the activation of sperm
– accounts for one-third of the semen volume
– Its milky, slightly acid fluid, which contains citrate,
enzymes, and prostate-specific antigen (PSA),
• Acts as a anticoagulant for sperm. Elevated blood levels
suggest damage to the prostate which allows PSA to enter
the blood. The following are associated with elevated levels:
– Prostate cancer, prostatitis and BPH
• Bulbourethral Glands (Cowper’s Glands)
– Pea-sized glands inferior to the prostate
– Produce thick, clear mucus prior to ejaculation that neutralizes
traces of acidic urine in the urethra
Hormonal Regulation of
Testicular Function
• The hypothalamus releases gonadotropin-releasing
hormone (GnRH)
• GnRH stimulates the anterior pituitary to secrete FSH and
LH
– FSH causes sustentacular cells ( Nurse) to release androgenbinding protein (ABP) and inhibin.
– LH stimulates interstitial cells to release testosterone
• Testosterone
– ABP binding of testosterone enhances spermatogenesis
– secondary sex characteristics.
Additional Effects of Testosterone
• Prostate – converts Testosterone into dihydrotestosterone (DHT) before it
can bind within the nucleus.
– High levels of DHT may increase prostate size and cause male
pattern baldness.
• Symptoms of testosterone deficiency:
• Increased risk of insulin resistance and DM:
• Increased visceral obesity: increases activity of the enzyme
aromatase which can convert testosterone into estrogen .
– gynecomastia : female breast development in males
• Xenoestrogens : compounds found in pesticides, plastic bottles
(Bisphenol A) also increase estrogen levels
• Decreased muscle mass and bone strength
• Sleep apnea
• Low Libido
Female Reproductive Anatomy
• Ovaries are the primary female reproductive
organs
– Make female gametes (ova)
– Secrete female sex hormones (estrogen and
progesterone)
• Accessory ducts include uterine tubes, uterus,
and vagina
• Internal genitalia – ovaries and the internal ducts
• External genitalia – external sex organs
Female Reproductive Anatomy
External Genitalia: Vulva
• Perineum- space between
vagina and anus
• Lies external to the vagina and
includes the mons pubis, labia,
clitoris
–
Mons pubis – round, fatty area overlying
the pubic symphysis
– Labia majora – elongated, haircovered, fatty skin folds
covering the labia minora
– Labia minora – hair-free skin
folds covers the urethral and
vaginal openings
– Clitoris (erectile tissue)
• Primary center for sexual
stimulation
Vagina
• Thin-walled tube lying
between the bladder
and the rectum.
• Extending from the
cervix to the exterior of
the body.
• Provides a passageway
for birth, menstrual flow,
and is the organ for
sexual intercourse.
Uterus
• Hollow, thick-walled
organ located in the
pelvis anterior to the
rectum and
posterosuperior to the
bladder
• Body – major portion of
the uterus
• Fundus – rounded
region superior to the
entrance of the uterine
tubes
• Cervix- distal tip
contacts the vagina.
Fallopian Tubes
• Receive the ovulated
oocyte and provide a site
for fertilization at the
distal quarter of the tube.
• Expand distally around
the ovary forming the
ampulla
• The ampulla ends in the
funnel-shaped, ciliated
infundibulum containing
fingerlike projections
called fimbriae.
Uterine Wall
• Uterine Wall is composed
of three layers
– Perimetrium –
outermost serous
layer; the visceral
peritoneum
– Myometrium – middle
layer; interlacing
layers of smooth
muscle
– Endometrium –
mucosal lining of the
uterine cavity changes
in thickness during the
menstrual cycle
Ovaries
• Paired organs that function as both endocrine and reproductive
organs .
• Located within the pelvic cavity on either side of the uterus
• Each ovary contains primordial follicles consisting of an oocyte
and follicular cells.
• The ovary is stimulated by pituitary secretions of FSH and LH.
These hormones collectively stimulate the growth and
maturation of the oocyte within the follicle.
• The mature follicle secretes estrogen
• Estrogen-induced secondary sex characteristics include:
– Increased deposition of subcutaneous fat, especially in the
hips and breasts
– Widening and lightening of the pelvis
– Growth of axillary and pubic hair
Ovaries
•
•
Hormones and Ovarian Development
Follicular phase – period of follicle growth (days 1–14)
Day 1 – GnRH stimulates the release of FSH and LH
– FSH stimulates mitosis of the primordial follicle into a primary follicle.
– LH stimulates estrogen secretion promoting the growth of the
endometrium and development of the fluid filled antrum characteristic in
a mature graafian follicle.
Luteal phase of the Ovarian Cycle
•
•
•
•
•
Luteal phase – period of corpus luteum activity (days 14–28)
(Ovulation ) at Day14 a large surge in LH triggers causes follicle to the
rupture ejecting the ovum into the fallopian tube
LH transforms the ruptured follicle into a corpus luteum which produces
several hormones:
Inhibin: inhibits further production FSH and LH
progesterone and estrogen which maintain endometrium
Luteal phase of the Ovarian Cycle
Human chorionic gonadotropin (hCG) stimulates the continuous secretion of
LH preventing the degeneration of the corpus luteum.
If pregnancy does occur, the corpus luteum will continue to produce these
hormones until the placenta takes over at about 3 months.
If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving
a white scar (corpus albicans)
Endometrium
• Has numerous uterine glands
that change in length as the
endometrial thickness changes
• Uterine glands supply fertilized
egg with nourishment
– glycogen-rich uterine
fluid.
• Will increase in size during the
first half of the menstrual cycle.
• Reduction in estrogen levels
cause the endometrium to shed
Acrosomal Reaction and Sperm
Penetration
• An ovulated oocyte is encapsulated by:
– The corona radiata and zona pellucida
– Extracellular matrix
• Sperm binds to the zona pellucida and undergoes the
acrosomal reaction
– Enzymes are released near the oocyte
– Hundreds of acrosomes release their enzymes
(hyaluronidase) to digest the zona pellucida
• Once a sperm makes contact with the oocyte’s
membrane:
• A calcium mediated reaction blocks other sperm from
entering
Acrosomal Reaction and Sperm Penetration
From Zygote to Blastocyst
Degenerating
zona pellucida
Inner cell mass
Blastocyst cavity
Blastocyst
cavity
(a) Zygote
(fertilized egg)
Fertilization
(sperm meets
egg)
(b) 4-cell stage
2 days
(a)
(c) Morula
3 days
(d) Early blastocyst
4 days
Trophoblast
(e) Implanting
blastocyst
6 days
(b)
(c)
Ovary
Uterine tube
(d)
Oocyte
(egg)
Ovulation
(e)
Uterus
Endometrium
Cavity of
uterus
From Zygote to Blastocyst
• Fertilization occurs between the sperm and ovum in the distal ¼
segment of the fallopian tube.
• Cleavage – a series of mitotic divisions occur for 3 days after
fertilization forming a morula stage (solid ball of cells)
• Zona pellucida disintegrates to release a fluid-filled hollow sphere
called a Blastocyst
– outer cells (trophoblast) helps to form placenta
– inner cell mass develops into embryo
• Ectoderm – forms structures of the nervous system and
skin epidermis.
• Endoderm – forms epithelial linings of the digestive,
respiratory, and urogenital systems.
• Mesoderm – forms muscles and various connective tissues
• Implantation of Blastocyst occurs around day 6.
The Female Breast
• Modified sweat glands
consisting of 15-25 lobes
that radiate around and
open at the nipple
• Areola – pigmented skin
surrounding the nipple
• Suspensory ligaments
attach the breast to
underlying muscle fascia
• Lobes contain glandular
alveoli that produce milk
in lactating women
• Compound alveolar
glands pass milk to
lactiferous ducts, which
open to the outside
Figure 27.17
Lactation
• During pregnancy estrogen and progesterone high levels
stimulate the hypothalamus to secrete prolactinreleasing hormone (PRH) which targets the anterior
pituitary. This results in the secretion of prolactin
• Prolactin stimulates the production of milk in the
breasts
Lactation
• Suckling stimulates both prolactin and oxytocin :
– Prolactin secretion allows for continuous milk production
– Oxytocin secretion causes the smooth muscle around the
alveolar ducts in the breast to eject the milk for the nipple
Chromosomes and Heredity
• Heredity = transmission of genetic characteristics
from parent to offspring
– karyotype = chart of chromosomes at metaphase
• The body cells have 23 pairs homologous for a total
of 46 chromosomes 2n (diploid number of
chromosomes) 22 of the 23 pairs guide genetic
expression of most other traits. (autosomes)
• Sex cells (gametes) from the ova and the sperm
each has 1 chromosome that determine the sex
• Sperm and egg contain only 23 chromosomes n (
haploid)
– fertilized egg has diploid number of
chromosomes
Sex Determination of Offspring
Karyotype of What Sex ?
Questions???