Title: MALE REPRODUCTIVE SYSTEM
1MALE REPRODUCTIVE SYSTEM
2Objectives
- At the end of the topic, the students should be
able to - Explain the functions of the testis
- Discuss spermatogenesis
- Describe the characteristics of a normal sperm
- Explain the role of FSH and inhibin on
spermatogenesis - Discuss the contents of semen and its
abnormalities - Explain the functions of testosterone
- Explain the control of secretion of
testosterone
3Main points in male reproductive physiology
- Importance of Leydig cells and testosterone in
puberty - Role of Sertoli cells,testosterone, DHT, and
estrogen in spermatogenesis - How testosterone and inhibin functions in the
adult feedback regulation of the Hypothalamic/
Pituitary/ Gonadal Axis
4INTRODUCTION
- A pair of testes
- A pair of accessory glands
- Ductal system
- Copulatory organ
5Male reproductive system (Lateral view)
6Male reproductive system (Anterior view)
7Structure of testis
8Seminiferous tubules
9FUNCTIONS
- Production of spermatozoa after puberty for
fertilization with the ovum from the female - Coitus process
- Produce androgens
10Testis
- Originates from indifferent gonads during the
embryonic phase - Contains lobules (200-300) separated by septum
- Each lobule has 4 seminiferous tubules
- Blood supply is from testicular artery and blood
drainage is through the Pampiniform plexus into
the testicular vein - Seminiferous epithelium contains Sertoli cells
(Sustentacular cells) and Germ cells - Leydig cells exist in between tubules
- Produce spermatozoa and androgens
- Divided into two compartments extratubular and
intratubular
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12Histology of the testis
ETC
ITC
Spermatogonia
Leydig cells
SCN
Lumen
13Compartments
- Extratubular vascular and interstitial
divisions (inclusive of lymphatic channels and
Leydig cells) - Intratubular basal and adluminal divisions
located in the seminiferous tubules
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16Spermatogenesis
17Spermatogenesis and spermatozoon structure
18Epididymis
19Blood Testis Barrier
- Formed before spermatogenesis commences
- Formed by Sertoli cells
- Functions
- Stop intratubular spermatozoa from entering
systemic and lymphatic circulation - The blood testes barrier is important since
sperm (with their unique surface antigens) elicit
an immune response if detected by the immune
cells in the mans blood, and the antibodies that
are formed against sperm are designed to
immobilize and destroy them
20- A number of events can disrupt the blood testes
barrier and allow the immune system to become
activated against the sperm. - These include
- trauma to the testes
- torsion (twisting) of the testes
- a history of a vasectomy and reversal
- any other surgery within the scrotum
- infection within the testes
21Allergic orchitis
Inflammation of the testis due to antisperm
antibodies
22- Ensure the intratubular chemical composition is
different from the intertubular chemical
composition (blood, interstitial fluid and lymph) - As spermatogenesis must occur in a controlled
microenvironment, any changes in the chemical
composition will affect normal spermatogenesis
23Functions of Sertoli cells
- Sertoli cells are joined by tight junctions that
provides barrier to chemicals (Blood testis
barrier) - Nourish developing sperm
- Secrete luminal fluid including androgen binding
proteins (ABP) - Phagocytize defective sperm
- Mediate testosterone and FSH effects on
spermatogenesis - Secrete inhibin which inhibits FSH secretion
- Influence Leydig cells via paracrine secretions
- Embryonic secretion of Mullerian Inhibiting
Substance (MIS) that ensures male phenotype
24Sertoli cells
25Spermatogenesis
- Process for formation of spermatozoa
- The seminiferous tubules produce haploid cells
(n) - Involves several steps including mitosis and
meiosis - Takes about 64 days in human
- Consists of three stages
- Spermacytogenesis formation of spermatid from
spermatogonia - Spermiogenesis formation from spermatid to
spermatozoa - Spermiation the release of spermatozoa into the
epididymis
26Spermacytogenesis
- Mitosis stage
- spermatogonia type Ad give rise to a pair of
spermatogonia type Ad or Ap - spermatogonia type Ap give rise to a pair of
spermatognia type Ap or B - mitosis of the germ cells occurs in the basal
compartment - incomplete cytokenesis of committed cells (type
Ap) results in the cells being linked by
cytoplasmic bridges until spermatozoa is form - this linkage results in a synchronous development
of the cells within a given region of the tubule
27Types of cells
- germ cells - - spermatogonia (types A and B)
- spermatogonia type A - for spermatogenic lineage
(type A dark (Ad) or A pale (Ap), type Ad are
true stem cells) - spermatogonia type B - progenitor cell for
primary spermatocyte - primary spermatocyte (46 chromosomes, 4N DNA)
- first meiotic division from these cells result in
secondary spermatocyte (23 chromosomes, 2N DNA) - second meiotic division from these cells results
in spermatids - spermatids (23 chromosomes, 1N DNA) undergoes
modifications in many parts and gives rise to
spermatozoa - spermatozoa, within the seminiferous tubules (and
distally) the flagella is not motile
28Spermiogenesis
- spermatid phase spermatids develop into
spermatozoa in 4 stages - Golgi phase
- - development of the acrosomal granule from the
Golgi complex forming the acrosomal vesicle at
the nascent apex (anterior) of cell - positioning of centrioles at the nascent base of
flagella - initiation of formation of axonemal complex from
one of the centrioles - Cap phase
- development of acrosomal cap over nucleus and
condensation of chromatin - development of flagellum from axonemal complex
- acrosome contains hydrolases (proteases,
hyaluronidase, neuramidase, acid phosphatase)
important in penetration of the oocyte membrane
during fertilization
29Spermiogenesis
- Acrosome phase - spermatid re-orients so tail
(flagellum) projects into the lumen of the tubule
and the acrosome towards the base of the
epithelium - further condensation of chromatin
- flattening and elongating of nucleus at the
anterior of the cell - movement of cytoplasm to the posterior of cell
- further development of flagellum
- linkage of flagellum to nucleus via the
connecting piece developed from a centriole - Maturation phase - residual body of cytoplasm
shed (cell linkages lost) and the cells released
by Sertoli cell into lumen of tubule
30Spermiation
- released spermatid moved with fluid via
- peristaltic action of myoid cells transporting
it to the straight tubule - sperm cannot move yet
- will develop motility in epididymis
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32- 1 germ cell produces 64 spermatozoa
- Process takes 2 months (56 64 days ) to
complete - 100 million sperm produced each day
- Not all are normal i.e., abnormal increases
with alcohol, heat, cigarettes, drugs
33- Temperature sensitivity
- Spermatogenesis is temperature sensitive, optimal
34o C - Achieved by the descent of the testes out of the
abdomen - Arteries and veins supplying the testes
intertwine, efficiently exchanging heat (from
artery to veins) to further cool testes
34Scrotum
- Originates from labioscrotal swellings and
urethral fold - Pouch that houses the testes
- Main function is to provide an environment which
is 1-80F lower than the body temperature and also
to control testicular temperature - Testicular temperature needs to be controlled for
spermatogenesis to occur normally
35Control and regulation of testicular temperature
(1)
- Two muscle system cremaster external and tunica
dartos - Cremaster external muscle passes along inguinal
canal and attaches to tunica vaginalis - Pulls tunica vaginalis as it contracts when the
environmental temperature drops - Tunica dartos muscle attaches to scrotal skin and
forms a septum separating the scrotum - - Pulls scrotal skin as it contracts when the
environmental temperature drops
36Control and Regulation of testicular temperature
(2)
- Pampiniform plexus
- consists of convoluted veins and arteries which
follow the spermatid cord into the inguinal
canal. Arterial branch comes from spermatid
artery and venous part enters the spermatid vein - - controls temperature by dissipating heat from
the aortal blood through the convolutions before
reaching the testis
37- The testes is located in the abdominal cavity
during the fetal stage - Only descents into scrotum at 7 months of
pregnancy - Sometimes do not descend and when born, two
conditions may occur i.e., cryptochidism or
monochidism - Crypotochidism cryptochids are males with both
testes in inguinal canal/abdominal cavity - usually sterile
- may either be hereditary or due to lack of
hormones - undescended testes are associated with reduced
fertility, increased risk of testicular cancer
and psychological problems when the boy is grown - undescended testes are also more susceptible to
testicular torsion, infarction and inguinal
hernias
38- Monochidism monochids are males with only one
testis descended into scrotum, the other remained
in inguinal canal/abdominal cavity - - usually fertile as one testis still functioning
normally therefore spermatogenesis is not
impaired - Approximately 3 of full-term and 30 of
premature infant boys are born with at least one
undescended testis, making monochidism/cryptorchid
ism the most common birth defect of male
genitalia - However, most testes descend by the first year of
life (the majority within three months), making
the true incidence of cryptorchidism around 1
overall.
39Ductal System
- Originates from Wolffian ducts (mesonephric
kidney) - Mullerian ducts rudiments in prostate gland
(prostatic utricle/uterus masculinus)
non-functional but can grow when there is
estrogen influence causing prostate cancer - Mesonephric tubules vasa efferentia
- Mesonephric ducts epididymis, vas deferens and
seminal vesicles - Urogenital sinus prostatic, cavernous and
membranous urethra, prostate glands and
Bulbo-urethral gland (Cowpers gland) - Rete testis in the testis efferentia ducts and
then becomes epididymis and vas deferens
40Epididymis
- Originates from mesonephric ducts
- Divided into caput (head), corpus (body) and
cauda (tail) - Extra fluid from sperm is reabsorbed to
concentrate spermatozoa 100X - Presence of high concentrations of testosterone/
DHT in the tubule causes epididymis to secrete a
motility- inducing protein that binds to the cell
membrane of sperm cells - Secrete mucoproteins/glycoproteins that coats the
head of the sperm - Also secretes carnitine, glycerolphosphorycholine,
fructose and glycoproteins - Transit time for spermatozoa to attain maturation
and the ability to move/motility is about 6 12
days - Spermatozoa can move forward and has the ability
to fertilize ovum once has entered cauda
epididymis - Morphological and biochemical changes also occur
41Caput
Corpus
Cauda
42Vas deferens
- Developed from Wolffian ducts
- Vas deferens have a lot of muscle layers (inner
and outer longitudinal muscle layer with circular
layers in between this muscles layers are
important for sperm motility - Vas deferens form the ampulla near the bladder
- Sperm enters vas deferens from epididymis
- Acts as a reservoir to store spermatozoa
- Also acts as a conduit between testes and urethra
- Mature sperm stored in the Vas Deferens and can
remain viable for up to 3 months - If no ejaculation occurs, sperm will dribble into
terminal ampulla into urethra
43Copulatory organ - penis
- Originates from genital tubercle
- Provides an outlet for both urine and the
copulatory ejaculate (spermatozoa and seminal
plasma) - Histology/anatomy of penis varies from species to
species and from region to region within the same
species - Body of the penis consists of
- the urethra
- erectile tissue (corpora cavernosa penis and
corpora cavernosum urethra), cavernous bodies act
as erectile tissues where it can be engorged with
blood to erect the penis - touch and pressure receptors (Pacinian
corpuscles) - a dense connective tissue capsule (tunica
albuginea - tip of penis is called glans penis and in humans
it is mushroom-shaped
44Penis
45Accessory glands
- A pair of seminal vesicles, prostate glands and
bulbo-urethral glands (Cowpers glands) - Originates from urogenital sinus and mesonephric
ducts - Produces seminal plasma which is the fluid
component of semen
46- seminal vesicle empties contents into ampulla
- tubuloalveolar gland
- yellowish secretory product and contains
fructose, citrate, ascorbic acid, inositol,
prostaglandins and proteins - fructose is an important energy source for
spermatozoa - 70 of ejaculate (semen) derives from the seminal
vesicles - secretory activity stimulated by testosterone
- prostrate gland empties contents into the
prostatic urethra - prostrate is a branched tubuloalveolar gland
- secretions include acid phosphatase, amylase, and
fibrinolysin - gland wraps around prostatic urethra and empties
into it - glycoprotein deposits develop and can become
calcified, these are called prostatic concretions
or corpora amylacea and are a characteristic
feature of the adult prostrate - secretory activity stimulated by testosterone
- hyperplasia occurs within the gland with
increasing age, gradually decreasing the
diameter of the urethra and slowing urine voiding
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48- bulbourethral (Cowpers) gland empty into the
post-prostatic urethra - tubuloalveolar glands that secrete a lubricating
mucous that contains galactose, galactosamine,
galacturonic acid, sialic acid, and methylpentose - secretions precede other ejaculatory products and
release involves the oxytocin axis - secretory activity of epithelia stimulated by
testosterone
49Seminal plasma
- Three functions
- as a media that provides the suspension/vehicle
and also activation to spermatozoa - provides electrolytes, nitrogen, citric acid,
fructose etc for nutrition - provides an alkaline pH to semen to combat
acidity of vagina
50Spermatozoa
- A very simple cell but highly adapted for
reaching and penetrating the ovum - Basically have head, midpiece and tail
- Different sizes in different species
- Head shape may be paddle (human, rabbit, bull,
ram), cylindrical (cockerel) or hooked (rodent
species) - Acrosome in the head contains hydrolytic enzymes
for digesting cells around ovum can also digests
sperm upon death - Carries the necessary package for fertilization
(enzymes and chromosomes) Needs to travel light
as main function is for fertilization - Tail contains mitochondria that provides ATP for
energy for increased motility to reach ovum
before sperm dies - Tail have 9 2 doublets arrangement called
axoneme - Has no energy reserves, hence has a limited life
span once released (48 72 hrs) - Dies by degeneration (hydrolytic enzymes in
acrosome destroy sperm upon death)
51Spermatozoa
Rat sperm
Rabbit sperm
Human sperm
Chicken sperm
52Sperm motility
53Semen
- Ejaculate - spermatozoa and seminal plasma
- By volume lt10 sperm
- Accessory Glands 60 seminal vesicle,
- 10 bulbourethral, 30 prostate
- Usually ph 7 to 7.4
- Coagulate after ejaculation in human
- Coagulation is important so that sperm
- number that enters vagina is maintained
- Liquefaction of semen occurs usually before 30
mins - Liquefaction is due to enzyme-substrate
interaction - The liquefaction time denotes semen quality the
longer the liquefaction time, the lower is the
quality. WHY? As the life span of sperm is only
about 72 hours, the sperm will need to break free
from the gel ASAP to enable it to swim up to meet
the ovum
54Normal semen values (WHO,1999)
- Volume 2 3 ml
- Liquefaction time ideally 30 mins)
- Colour Milky
- Viscosity Fairly watery
- pH 7 7.2
- Motility 50 60
- Count gt 20 million/ml
- Viability gt 50
- Normal morphology variable 30
55Terms
- Normospermia/normozoospermia (normal semen
values) - Azoospermia no sperm found in sample
- Oligospermia less than 20 million/ml sperm
- Asthenozoospermia sperm present but non-motile
- Necrozoospermia high number of dead sperm
- Teratozoospermia high number of abnormal sperm
56Regulation of spermatogenesis
- Prepubertal LH and FSH are low, thus testes
activity is low - Between the ages of 13 and 20 the hypothalamic/
pituitary/ gonadal axis is reactivated (puberty) - The precise trigger is not known
- could be percentage body adipose tissue
- could be pineal gland/ melatonin involvement
57Regulation of testicular function
- GnRH released every 2- 3 hours
- Results in a pulsatile release of LH and FSH
- Testosterone from Leydig cells inhibits both the
release of LH and GnRH - Inhibin from Sertoli cells inhibits the release
of FSH (but not LH or GnRH).
58Hormonal influence
- GnRH from hypothalamus goes to anterior
pituitary FSH and LH are released - LH (Interstitial Cell Stimulating Hormone/ICSH)
goes to Leydig cells to initiate production of
testosterone - FSH and testosterone stimulates Sertoli cell
(Sustentacular cells) to increase enzyme activity
(5?-reductase, aromatase) and synthesis Androgen
Binding Proteins (ABP) - ADP will bind to testosterone causing level of
testosterone in lumen of seminiferous tubules to
rise - Sustentacular cells also produce inhibin (a
peptide hormone) - FSH and LH only acts on testis but testosterone
influences testis and initiate development of
sexual organs and male secondary sexual
characteristics
59Control of testosterone secretion
- When testosterone and inhibin levels in the blood
are high, two negative feedback mechanisms are
initiated to regulate the spermatogenic process - When levels of circulating testosterone are high
in the blood, this high testosterone will send a
negative feedback mechanism to hypothalamus to
inhibit LH release
60Control of sperm production
- When there are gt20 million spermatozoa in the
testicles, inhibin will send a negative feedback
mechanism to the hypothalamus to inhibit the
release of FSH - This two negative feedback mechanisms are
terminated when level of testicular spermatozoa
falls below 20 million and testosterone level
falls below required level for normal
spermatogenesis
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63Functions of testosterone
- Produced by the Interstitial cells of Leydig
under influence of LH and GnRH - Testosterone has a number of functions
- Promotes maturation of sperm cells
- Maintains male 2nd sex organs
- Determines secondary male characteristics (wide
shoulders, narrow hips, body hair patterns,
enlargement of thyroid cart of larynx, deepens
voice) - Stimulates bone and muscle growth, epiphysial
closure, protein metabolism