ch 27 male reproduction lecture presentation fall%2c 2011-1
TRANSCRIPT
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Chapter 27
The Reproductive System
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Reproductive System
Primary sex organs (gonads)testes in males,ovaries in females
Gonads produce sex cells called gametes andsecrete sex hormones
Accessory reproductive organsducts, glands,and external genitalia
Sex hormonesandrogens (males), and estrogenand progesterone (females)
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Reproductive System
Sex hormones play roles in:
The development and function of the reproductiveorgans
Sexual behavior and drives
The growth and development of many other organsand tissues
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Male Reproductive System
The male gonads (testes) produce testosterone and liewithin the scrotum
Sperm are delivered to the exterior through a system of
ducts: epididymis, ductus deferens, ejaculatory duct,and the urethra
Accessory sex glands:
Empty their secretions into the ducts during ejaculation
Include the ______ vesicles, _______ gland, and ________glands
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Male Reproductive System
Figure 27.1
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testis
Epididymis
Vas deferens
Ejaculatory duct
Testis and ducts
urethra
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Seminal vesicle
prostate
Bulbourethral gland
Accessory glands
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The Scrotum
Sac of skin and superficial fascia that hangsoutside the abdominopelvic cavity at the root ofthe penis
Contains paired testicles separated by a midlineseptum
Its external positioning keeps the testes 3C______ than core body temperature (needed forsperm production)
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Testes protection - Testicular Thermoregulation
Sperms are not produced at core body temperature
In the scrotum, the testes are kept 2-3
C cooler than in the pelvic cavity.This is essential for sperm production.
Cooling mechanisms
The cremaster muscle contains strips of the internal abdominal
oblique muscle (skeletal muscle) around the spermatic cord.
It can elevate or lower the testes.
The dartos muscle is a subcutaneous layer of smooth muscle thatwrinkles skin reducing surface area of scrotum. Can lifts testis upwards
The pampiniform plexus is an extensive network of veins thatsurround the testicular artery in the spermatic cord, keeping the testescooler countercurrent heat exchange that cools arterial blood enteringtestis
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The Scrotum
Figure 27.2
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Cremaster muscle
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Countercurrent Heat Exchanger
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Pampiniformplexus
C ti b t t ti d th
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Connection between testis and the
body The structures that connect
the testis with the body areenclosed within a connectivetissue sheath called thespermatic cord
Blood vessels Nerve fibers PNS and SNS
Vas deferens
Cremaster muscle
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The Testes
Each testis is surrounded by two tunics:
The tunica vaginalis, derived from peritoneum
The tunica albuginea, the fibrous capsule of thetestis
Septa divide the testis into 250-300 lobules, eachcontaining 1-4 seminiferous tubules
Seminiferous tubules- where ____ is produced
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The Testes
The sperm:
Leave the testis via efferent ductules
Enter the ______
Surrounding the seminiferous tubules areinterstitial cells that produce androgens liketestosterone
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The Testes
Figure 27.3a
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Testis histology - Seminiferous tubules
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Cells in the testes Seminiferous tubule
lumen lined with germinal epithelium consisting ofseveral layers ofgerm cells in the process of becomingsperm
Sustentacular (Sertoli)cells.
Between the seminiferous tubules are clusters ofinterstitial (Leydig) cells, the source oftestosterone.
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The Penis
Internal penisthe urethra and three cylindricalbodies of erectile tissue
Erectile tissuespongy network of connectivetissue and smooth muscle riddled with vascularspaces
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The Penis Erectionduring sexual excitement, the erectile
tissue fills with ______ causing the penis toenlarge and become rigid
Corpus spongiosumsurrounds the urethra andexpands to form the glans and bulb of the penis
Corpora cavernosapaired dorsal erectilebodies bound by fibrous tunica albuginea
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The Penis
Figure 27.4
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Figure 28.11
The Penis
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Corpus spongiosum
Corpuscavernous
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Spermatic Ducts 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)
Ductus deferens/vas deferens (peristalsis during orgasm)
muscular tube 45 cm long passing up from scrotum through
inguinal canal to posterior surface of bladder Ejaculatory duct
2 cm duct formed from ductus deferens and seminal vesicleand passing through prostate to empty into urethra
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Epididymis
Nonmotile sperm enter, pass through its tubesand become motile
Upon ejaculation the epididymis contracts,expelling sperm into the __________
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Epididymis
Vas deferens Ejaculatoryduct
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The Epididymus and vas deferense
Figure 28.9
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https://reader009.{domain}/reader009/html5/0513/5af84ee10a7d2/5af84ef6b2ada.j
The Epididymis
E idid i f ti
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Epididymis functions The epididymis functions:
The duct of the epididymis has stereocilia that:Absorb testicular fluid
Pass nutrients to the sperm
Recycling center for damaged spermatozoa
Storage place for spermatozoa
Facilitate functional maturation preparing them forfertilization:
Plasma membrane changes, alterations inacrosomal membrane
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Ductus Deferens and Ejaculatory
Duct Runs from epididymis through the inguinal canal
into the pelvic cavity
terminus expands= ampulla, then joins the duct
of the seminal vesicle to form the _________ Propels sperm from the epididymis to thevas
deferens
________cutting and ligating the ductusdeferens, which is a nearly 100% effective formof birth control
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Male Reproductive System Gross
AnatomyVasectomy
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Urethra
Conveys both _______ and ________ (atdifferent times)
Consists of three regions
_____portion surrounded by the prostate
______lies in the urogenital diaphragm
_______runs through the penis and opens to the
outside at the external urethral orifice
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Prostatic
Membranous
penile
A Gl d S i l
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Accessory Glands: Seminal
Vesicles Lie on the posterior wall of the bladder and
secrete 60% of the volume of semen Semenalkaline fluid containing fructose, ascorbic
acid, coagulating enzyme (vesiculase), andprostaglandins
Join the ductus deferens to form the ejaculatoryduct
Sperm and seminal fluid mix in the ejaculatoryduct and enter the prostatic urethra duringejaculation
Accessory Glands: Seminal Vesicles
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Accessory Glands: Seminal Vesicles
Lie on the posterior wall of the bladder and secrete 60% of the volume ofsemen
Join the ductus deferens to form the ejaculatory duct
The composition of the gland secretions include:
High concentration of fructose that is easily metabolized byspermatozoa
Prostaglandins that stimulate smooth muscle contractions in both male
and female reproductive tract Fibrinogen that forms temporary clot within the vagina after ejaculation
When the inactive sperms mix with the seminal fluid they undergo the firststep of activation and the flagella start moving (in some book this is doneby the help of the prostate)
The secretion of the seminal gland are discharged into the ejaculatory ductunder the control of the sympathetic system
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SeminalVesicle
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Accessory Glands: Prostate Gland
Doughnut-shaped gland that encircles part ofthe ______ inferior to the bladder
Milky, slightly acid fluid, accounts for one-thirdof the semen volume
Plays a role in the activation of sperm
Enters the prostatic urethra during ejaculation
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http://www.mastersmensclinic.com/prostate.htm
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prostate
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Accessory Glands: Bulbourethral Glands
(Cowpers Glands)
Pea-sized glands inferior to the prostate
Produce thick, clear mucus prior toejaculation that neutralizes traces of acidicurine in the urethra
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Bulbourethral Gland
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Bulbourethralgland
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Semen Milky white, sticky mixture of sperm and
accessory gland secretions Provides a transport medium and nutrients
(_____), protects and activates sperm, and
facilitates their movement Prostaglandins in semen:
Decrease the viscosity of mucus in the cervix
Stimulate reverse ________ in the uterus
Facilitate the movement of sperm through thefemale reproductive tract
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Semen The hormone relaxinenhances sperm motility
The relative alkalinity of semen neutralizes the acidenvironment found in the male urethra and female
vagina
Clotting factors coagulate semen immediately afterejaculation, then fibrinolysin liquefies the sticky mass
Only 2-5 ml of semen are ejaculated, but it contains 50-130 million sperm/ml
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Male Sexual Response: Erection
During sexual arousal, a PNS reflex promotes therelease of nitric oxide
Nitric oxide causes erectile tissue to fill with blood Expansion of the corpora cavernosa:
Compresses their drainage veins
Retards blood outflow and maintains engorgement
The corpus spongiosum functions in keeping theurethra open during ejaculation
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Ejaculation
At ejaculation, sympathetic nerves serving thegenital organs cause: Reproductive ducts and accessory organs to contract
and empty their contentsThe bladder sphincter muscle to close, preventing
the expulsion of urine
Bulbospongiosus muscles to undergo a rapid seriesof contractions
Propulsion of semen from the urethra
Human Life Cycle
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Human Life Cycle
Figure 27.5
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Spermatogenesis
The sequence of events that produces sperm in theseminiferous tubules of the testes
Each cell has two sets of chromosomes (one maternal,one paternal) and is said to be diploid (2nchromosomal
number)
Humans have 23 pairs of homologous chromosomes
Gametes only have 23 chromosomes and are said to be
haploid (nchromosomal number) Gamete formation is by meiosis, in which the number
of chromosomes is halved (from 2nto n)
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Figure 27.8b, c
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Figure 27.6
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MeiosisInterphase
Two nuclear divisionshalve the number ofchromosomes
Chromosomesreplicate prior tomeiosis I
Figure 27.7.1
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MeiosisProphase I
Homologouschromosomes undergosynapsis
Tetrads are formedwith homologouspartners
Crossing over takesplace during prophase I
Figure 27.7.2.1
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MeiosisMetaphase I
Tetrads line up at thespindle equator duringmetaphase I
Figure 27.7.2.2
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MeiosisAnaphase I
Homologouschromosomescomposed of joined
sister chromatids aredistributed to oppositeends of the cell
Figure 27.7.2.3
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MeiosisTelophase I
Nuclear membraneforms aroundchromosomal masses
Spindle break down
Chromatin reappears
With telophase andcytokinesis completed,
two haploid daughtercells are formed (with2namount of DNA)
Figure 27.7.2.4
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Meiosis II
Mirrors mitosis except that chromosomes are not_________ before it begins
Meiosis accomplishes two tasks: It reduces the chromosome number by ____ (2nto n)
It introduces genetic variability
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Meiotic Cell Division: Meiosis II
Figure 27.7.3
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Spermatogenesis
Cells making up the walls of seminiferoustubules are in various stages of cell division
These spermatogenic cells give rise to sperm in a
series of events Mitosis of spermatogonia, forming spermatocytes
Meiosis forms spermatids from spermatocytes
Spermiogenesisspermatids form sperm
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Mitosis of Spermatogonia
Spermatogoniaoutermost cells in contact withthe epithelial basal lamina
Spermatogenesis begins at puberty as each
mitotic division of spermatogonia results in typeA or type B daughter cells
Type A cells remain at the basement membraneand maintain the germ line (aka _____ cells)
Type B cells move toward the lumen andbecome primary spermatocytes
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Spermatocytes to Spermatids
Primary spermatocytes undergo meiosis I,forming two haploid cells called secondaryspermatocytes
Secondary spermatocytes undergo meiosis IIand their daughter cells are called spermatids
Spermatids are small round cells seen close to
the lumen of the tubule
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Figure 27.8b, c
Spermatogenesis
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p gSpermatogonium (2n)
Primary spermatocyte (2n)
Primary spermatocyteDivision1st meiosis
secondary spermatocyte (n)
Spermatid (n)
differentiation
2nd meiosis
Spermiogenesis: Spermatids to
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Spermiogenesis: Spermatids to
Sperm Late in spermatogenesis, spermatids are haploid
but nonmotile
Spermiogenesisspermatids lose excess
cytoplasm and form a tail, becoming sperm
Spermiogenesis: Spermatids to
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Spermiogenesis: Spermatids to
Sperm Sperm have 3 major regions:
Headcontains DNA and has a helmetlikeacrosome containing hydrolytic ______ that allow
the sperm to penetrate the egg Midpiececontains mitochondria spiraled around
the tail filaments-- What are the mitochondriafor?
Taila typical flagellum produced by a centriole--What are centrioles composed of?
Spermiogenesis: Spermatids to Sperm
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Spermiogenesis: Spermatids to Sperm
Figure 27.9a
Spermiogenesis
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p g
spermatozoa
Spermiogenesis spermatids lose excess cytoplasm and form a tail becoming sperm
Spermiogenesis: Spermatids to Sperm
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http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.ht
spermatogenesis
spermiogenesis
Spermiogenesisspermatids lose excess cytoplasm and form a tail, becoming sperm
Sustentacular Cells (Sertoli Cells)
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Sustentacular Cells (Sertoli Cells)
Extend from basal lamina to lumen- surroundsdeveloping cells
They are bound together with tight junctionsforming an unbroken layer with the
seminiferous tubule, dividing it into twocompartments:
Basal compartmentcontains spermatogonia and
primary spermatocytesAdluminal compartmentcontains meiotically
active cells and the tubule lumen
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Adluminal Compartment
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Adluminal Compartment
Activities Spermatocytes and spermatids are nearly
enclosed in sustentacular cells, which: Deliver nutrients to dividing cells
Move them along to the lumen Secrete testicular fluid that provides the transport
medium for sperm
Dispose of excess cytoplasm sloughed off during
maturation to sperm Produce chemical mediators that help regulate
spermatogenesis
The functions of Sertoli cells and BTB
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Sustentacular cells protect the germ cells and promote their
development. Tight junctions between adjacent sustentacular cellsform a blood-testis barrier (BTB)
The fluid inside the tubules contains high levels ofandrogens,potassium and amino acids
The BTB prevents the immune system from attacking thedeveloping spermatozoa (contain specific Ag that are notfound on any other cell)
Sertoli cell supply nutrients to the developing sperms
Phagocytize cytoplasm shed by spermatids
Secrete inhibin (we will talk about this hormone later)
Secrete androgen-binding-protein (ABP) binds testosteroneinside tubules to maintain high levels
Hormonal Regulation of
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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 to release androgen-
binding protein (ABP)
LH stimulates interstitial cells to release testosterone
ABP binding of testosterone enhancesspermatogenesis
Hormones and Brain-Testicular Axis
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Hormonal Regulation of Testicular Function
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Feedback inhibition onthe hypothalamus andpituitary results from:
Rising levels oftestosterone
Increased inhibin
Figure 27.10
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Testosterone
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estoste o e The principal androgen (male sex hormone) is
testosterone. This steroid is manufactured by the interstitial (Leydig) cells
of the testes.
Secretion of testosterone increases sharply at puberty and isresponsible for the development of the secondary sexualcharacteristics of men.
Testosterone is also essential for the production of sperm.
Male Secondary Sex
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y
Characteristics
Male hormones make their appearance at puberty andinduce changes in nonreproductive organs, including
Appearance of pubic, axillary, and facial hair
Enhanced growth of the chest and deepening of the voice
Skin thickens and becomes oily
Bones grow and increase in density
Skeletal muscles increase in size and mass Testosterone is the basis of libido in both males and
females