Transcript Male Repro

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Reproduction
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one property of a living thing
great variety of methods
Sexual reproduction
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each offspring has 2 parents and receives genetic
material from both
provides genetic diversity
foundation for survival and evolution of species
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Male and female gametes (sex cells) combine their
genes to form a fertilized egg (zygote)
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one gamete has motility (sperm)
 parent producing sperm considered male
 has Y chromosome in most mammals
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other gamete (egg or ovum) contains nutrients for
developing zygote
 parent producing eggs considered female
 in mammals the female also provides shelter for the
developing fetus (uterus and placenta)
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Primary sex organs
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Secondary sex organs
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produce gametes (testes or ovaries)
male - ducts, glands, penis deliver sperm cells
female - uterine tubes, uterus and vagina receive sperm
and nourish developing fetus
Secondary sex characteristics
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develop at puberty to attract a mate
 pubic, axillary and facial hair, scent glands, body morphology
and low-pitched voice in males
27-3
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Our cells contain 23 pairs of chromosomes
22 pairs of autosomes
 1 pair of sex chromosomes (XY males: XX females)
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 males produce 50% Y carrying sperm and 50% X carrying
 all eggs carry the X chromosome
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Sex of child
determined by type
of sperm that fertilizes
mother’s egg
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Gonads begin to develop
at 6 weeks
The male and female
reproductive systems
have different
embryological origins
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mesonephric ducts
develop into male
reproductive system
paramesonephric ducts
(müllerian ducts) develop
into female reproductive
tract
27-5
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SRY gene (Sex-determining Region of Y gene)
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in males, codes for a protein that causes development of
testes
testes secrete testosterone
testes secrete müllerian-inhibiting factor which
degenerates paramesonephric ducts
In absence of hormones, fetus becomes
phenotypically ‘female’
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External genitals of both
sexes begin as a
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genital tubercle
 becomes glans of penis or
 clitoris
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pair of urogenital folds
 enclose urethra of male or
 form labia minora
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a pair of labioscrotal folds
 scrotum or
 labia majora
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All 8 week old fetuses
have same 3 structures
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by end of week 9, begin to
show sexual differentiation
distinctly male or female by
end of week 12
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Begin development near kidney
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gubernaculum (cordlike structure containing muscle) extends
from gonad to abdominopelvic floor
 it shortens, guides testes to scrotum
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Descent begins in weeks 6-10, finished by 28
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3% born with undescended testes (cryptorchidism)
Location outside pelvic cavity essential for low
temperatures needed for sperm production
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27-10
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Impotence – Inability to sustain an erection sufficient
for sexual intercourse, or inability to ejaculate
Male Sterility – Infertility caused by disorders of the
male reproductive system
BPH – Benign Prostatic Hypertrophy
Cryptorchidism – Undescended testicle(s)
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Pouch holding testes
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divided into 2
compartments by
median septum
Spermatic cord
travels up from
scrotum to pass
through inguinal
canal
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contains testicular
artery, vein, nerve and
lymphatics
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Muscular control
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Cremaster muscle
Dartos muscle
Counter-current exchange
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Pampiniform plexus
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Oval organs, 4 cm long x 2.5 cm in
diameter
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Tunica albuginea
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white fibrous capsule on testes
Septa divide testes into
compartments containing
seminiferous tubules
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covered anteriorly by tunica vaginalis
each tubule lined with a thick
germinal epithelium for sperm
interstitial cells between tubules testosterone
Rete testis
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seminiferous tubules drain here
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Efferent ductules
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12 small ciliated ducts collecting sperm
from rete testes and transporting it to
epididymis
Epididymis (head, body and tail)
6 m long coiled duct adhering to
posterior of testis
 site of sperm maturation and storage
(fertile for 60 days)
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Ductus deferens (peristalsis during
orgasm)
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muscular tube 45 cm long passing up
from scrotum through inguinal canal to
posterior surface of bladder
Ejaculatory duct
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2 cm duct formed from ductus
deferens and seminal vesicle and
passing through prostate to empty into
urethra
Vasectomy
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Regions: prostatic, membranous and penile --totals 20 cm long
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Seminal vesicles - pair
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Prostate gland - single
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posterior to bladder
empty into ejaculatory duct
below bladder, surrounds urethra
and ejaculatory duct
2 x 4 x 3 cm
Bulbourethral glands - pair
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near bulb of penis
empty into penile urethra
lubricating fluid
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Internal root, shaft, and glans
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external portion 4 in. long when flaccid
The foreskin is termed the prepuce
3 cylindrical bodies of erectile tissue
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corpus spongiosum along ventral side of penis
 encloses penile urethra
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corpora cavernosa
 diverge like arms of a Y
 Erection
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Hypothalamus produces GnRH
Stimulates anterior pituitary (gonadotrope
cells) to secrete
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LH
 stimulates interstitial cells to produce testosterone
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FSH
 stimulates sustentacular cells (Sertoli cells) to secrete
androgen-binding protein (ABP) that interacts with
testosterone to stimulate spermatogenesis
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Reproductive system remains dormant for years after birth
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surge of pituitary gonadotropins begins development
 10-12 in most boys; 8-10 in most girls
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Puberty
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period from onset of
gonadotropin
secretion until first
menstrual period or
first ejaculation of
viable sperm
Adolescence
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ends when person
attains full adult
height
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Enlargement of secondary sexual organs
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penis, testes, scrotum, ducts, glands
Development of secondary sexual characteristics
hair, scent and sebaceous glands develop
 muscle mass, vocal quality
 stimulates erythropoiesis and libido
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During adulthood, testosterone sustains libido,
spermatogenesis and reproductive tract
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Enlargement of secondary sexual organs
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penis, testes, scrotum, ducts, glands
Development of secondary sexual characteristics
hair, scent and sebaceous glands develop
 muscle mass, vocal quality
 stimulates erythropoiesis and libido
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During adulthood, testosterone sustains libido,
spermatogenesis and reproductive tract
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Mitosis produces two
genetically identical
daughter cells (for tissue
repair, embryonic growth)
Meiosis produces gametes
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for sexual reproduction
2 cell divisions (only one
replication of DNA)
 meiosis I separates
homologous chromosome
pairs into 2 haploid cells
 meiosis II separates
duplicated sister chromatids
into 4 haploid cells
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Blood-testis barrier is
formed by tight
junctions between and
basement membrane
under sustentacular
cells (Sertoli cells)
1 basal lamina, 2 spermatogonia, 3
spermatocyte 1st order, 4
spermatocyte 2nd order, 5 spermatid,
6 mature spermatid, 7 Sertoli cell, 8
tight junction (blood testis barrier)
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Spermatogonia produce 2 kinds of daughter cells
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type A remain outside blood-testis
barrier and produce more
daughter cells until death
type B differentiate into
primary spermatocytes
 cells must pass through
BTB to move inward
toward lumen - new tight
junctions form behind
these cells
 meiosis I  2 secondary
spermatocytes
 meiosis II  4 spermatids
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Changes that transform spermatids into spermatozoa
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discarding excess cytoplasm and growing tails
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Head is pear-shaped front end
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4 to 5 microns long structure
containing the nucleus, acrosome
and basal body of the tail flagella
 nucleus contains haploid set of
chromosomes
 acrosome contains enzymes that
penetrate the egg
 basal body
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Tail is divided into 3 regions
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midpiece contains mitochondria
around axoneme of the flagella
(produce ATP for flagellar
movement)
principal piece is axoneme
surrounded by fibers
endpiece is very narrow tip of
flagella
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2-5 mL of fluid expelled during orgasm
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60% seminal vesicle fluid, 30% prostatic, 10% sperm
normal sperm count 50-120 million/mL
Other components of semen
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fructose - energy for sperm motility
fibrinogen causes clotting
 enzymes convert fibrinogen to fibrin
fibrinolysin liquefies semen within 30 minutes
 prostaglandins stimulate female peristaltic contractions
 spermine is a base stabilizing sperm pH at 7.2 to 7.6
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Arteries of penis
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dorsal and deep arteries (branches of internal pudendal)
deep artery supplies lacunae of corpora cavernosa
 dilation fills lacunae causing an erection
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normal penile blood supply comes from dorsal artery
Nerves of penis
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abundance of tactile, pressure and temperature receptors
dorsal nerve of penis and internal pudendal nerves lead to
integrating center in sacral spinal cord
both autonomic and somatic motor fibers carry impulses
from integrating center to penis
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Excitement is characterized by vasocongestion of
genitals, myotonia, and increases in heart rate, blood
pressure and pulmonary ventilation
Initiated by many different erotic stimuli
Erection of penis is due to parasympathetic triggering
of nitric oxide (NO) secretion
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dilation of deep arteries and filling of lacunae with blood
Erection is maintained during plateau phase
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Climax (orgasm) is 15 second reaction that typically
includes the discharge of semen (ejaculation)
Ejaculation has two stages
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emission = sympathetic nervous system propels sperm
through ducts as glandular secretions are added
expulsion = semen in urethra activates muscular
contractions that lead to expulsion
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Sympathetic signals constrict internal pudendal artery
and reduce blood flow to penis
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penis becomes soft and flaccid (detumescence)
Cardiovascular and respiratory responses return to
normal
Refractory period (10 minutes to few hours)
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