Lecture 4 (2b) - Male Reproductive Systems Flashcards
Aquatic invertebrates
- predominantly external fertilization
- eg echinoderms
- cephalopod molluscs - hectocotylus delivers the spermatophore into the female mantle
- octopus with specialized tentacle into female mantle
- more efficient/less sperm if internal fertlization
Cephalopod molluscs
…. delivers the spermatophore into the female mantle
hectocotylus
Aquatic invertebrates
hectocotylus delivers the spermatophore into the female
mantle
Aquatic vertebrates
“Fish” and Amphibians
- predominantly external fertilization
- eg most teleosts and amphibia
- elasmobranchs - claspers deliver spermatophore into female cloaca
Aquatic vertebrates
… deliver spermatophore into female cloaca
claspers
Aquatic vertebrates
claspers deliver spermatophore into female
cloaca
Terrestrial animals
invertebrates practice
-
indirect internal fertilizatoin
- eg arachnids
- or direct internal fertilizatoin
- eg insects
- vertebrates always have direct internal fertiliation - insemination
Terrestrial animals
Invertebrates practice
indirect internal fertilization
- eg arachnids
direct internal fertilizatoin
- eg insects
Terrestrial animals
vertebrates always have
direct internal fertilization
(insemination)
Scorpions
- indirect internal fertilization
- male paraxial organs deliver the spermatophore
- packages 2 halves of spermatophore
- “promenade a deux”
- female cloaca dragged over spermatophore
- deposit sperm on ground and drag female over it
- she resists as he pulls her → rocking motion takes up sperm
- must be quick so the sperm doesn’t dry out
Spiders
- indirect internal fertilization
- spermatophore depositied and then sperm picked up by pedipalp
- pedipalp produced at back (?)
- pedipalp delivers spermatophore into female cloaca
-
copulatory plug
- pedipalp breaks off
- only 2 so males mate twice then die
Insects
- direct internal fertilization
- several specialized structures for insemination
- aedeagus
- juxta
- “traumatic insemination” in Cimicidae
- male punctures female abdomen and sperm goes in “anywhere” and into paragenital system
Terrestrial vertebrates
reptiles and mammals
direct fertilization via a penis
Terrestrial vertebrates
birds
- 97% of birds (and tuatara) lack a penis
- direct fertilization via a “cloacal kiss”
- no intromissive organ
- tuatara really old/primitive so penises are a relatively new feature
- ostriched DO have penises - “runs” on lymphatics
Mammalian testis size
- highly variable
- allometric scaling - testis as a proportoin of body mass decreases with increasing size
- eg body mass doubles but structures don’t exactly double
Animals bigger
→
testis bigger
(but not necessarily proportional)
(testis mass vs body mass)
Testis mass vs body mass (%)
- average size of testis is ~1% body mass unless very small organism (>1%)
- animals with biggest testes proportionally - rodents
Rodents testes size
- most variation in very small
- proportionally largest testes in smallest animals
- biggest proportionally = gerbil
Internal testes
- TESTICONDIDS
- testes internal - don’t have to be scrotal
- for purposes of streamlining/aerodynamics
Where would you find mamalian testes?
- originate in abdomen
- anterio-rostral migration (in scrotum)
- contraction of gubernuculum
- caused by androgens
Why do testes desccend in scrotal mammals?
- **NOT **scrotal because of temperature
- can cool testes without requiring testicular descent
- ?galloping (in the way of gait)
- ?sexual display
Size of testes based on
whether or not there’s sperm competition
(no competition → smaller testes)
Testis structure
- comprised primarily of seminiferous tubules
- one tubule goe back and forth
- seminiferous tubules contain Sertoli cells and sperm
- Sertoli cells inside tubules look after maturing sperm
- packed in between the seminiferous tubules are interstitial Leydig cells
- Leydig cells outside tubules, make testosterone
Testis comprised primarily of
seminiferous tubules
Seminiferous tubules contain
Sertoli cells and maturing sperm
(Sertoli cells inside tubules looking after maturing sperm)
Packed in between the seminiferous tubules are interstitial
Leydig cells
(outside tubules, make testosterone)
Function of Sertoli cells
to mature the sperm
Sperm are germ cells but…
they are looked after by Sertoli cells which are somatic cells
- Sertoli cells are diplod
2 major cell types
Sertoli cells
- look after sperm
- inside the tubule
Leydig cells
- make testosterone
- outside the tubule
The tubule collects into the
epididymis
a single duct flows out for ejaculation
Direction of cell movement inside the tubule
basal → adluminal
2 main hormones
leuteinizing hormone (LH)
- Leydig cells respond to leuteinizing hormone
follicle-stimulating hormone (FSH)
- Sertoli cells respond to follicle-stimulating hormone
Leydig cells respond to
luteinizing hormone
Sertoli cells respond to
follicle-stimulating hormone
Sperm cells on the basal side of the tubule close to the junction between Leydig cells and the Sertoli cells have
spermatogonia
- diploid
- dividie by mitosis
- mitosis turns one spermatogonium into multiple spermatogonia
Spermatogonia
- diploid
- dividie by mitosis
- mitosis turns one spermatogonium into multiple spermatogonia
When spermatogonia enter meiosis, they become
spermatocytes
Spermatocytes become
spermatids
Spermatids will ultimately mature to become
spermatozoa
Sperm stages
spermatogonia
spermatocytes
spermatids
spermatozoa
Spermatogonia → spermatozoa
happens in
a single sertoli cell
- these cells all require very different microenvironments
- has an environment onthe basal side perfect for spermatogonia
- an environment in the middle for spermatocytes
- an environment at the apex for spermatids and spermatozoa
Endocrine products
- Leydig cells make testosterone (steroid) in response to LH
- Sertoli cells also produce some hormones
- inhibin (not a steroid) but is a growth factor
- androgen-binding protein (ABP) - with the ability to carry testosterone
Leydig cells make
testosterone
Leydig cells make testosterone in response to
LH
Sertoli cells produce
- inhibin (not a steroid but a growth factor)
- androgen-binding protein (ABP) with the ability to carry testosterone
Inhibin is a
growth factor
Androgen-binding proten (ABP) has the ability to
carry testosterone
Paracrine products
products that act on each other
(act on neighboring cells rather than elsewhere in the body)
We make LH and FSH in
the pituitary gland
LH and FSH are
heterodimeric glycoproteins
- have 2 subunits which are dissimilar
- heavily glycosylated that gives them the weight of 25-30kDa
Both LH and FSH have the same
α-subunit
α-subunit of LH and FSH
gonadotrophin α-subnit (GSU)
- paired with LHβ → luteinizing hormone
- LH will stimulate Leydig cells to synthesize testosterone
- paired with FSHβ → FSH
- FSH will stimulate Sertoli cells to make mature sperm
Sperm have no receptors for
gonadotrophins
- if the endocrine system wants to stimulate sperm division, it can’t do that on the sperm
- must stimulate Sertoli cells
- the Sertoli cells have to tell the sperm what to do
NO … on sperm
FSH or LH receptors
(no FSH or LH receptors on sperm)
FSH receptors are on
Sertoli cells
FSH also stimulates Sertoli cells to make
the growth factor inhibin
In the brain you have the
gonadotrophin releasing hormone (GnRH)
GnRH
- the hormone in the hypothalamus that drives reproduction
- important in puberty
- stimulates the anterior pituitary glad to produce LH and FSH gonadotrophins
GnRH stimulates the anterior pituitary gland to produce
LH and FSH gonadotrophins
LH stimulates the testis to make
testosterone
FSH stimulates Sertoli cells to make
inhibin
and closely related
activin
Inhibin and activin
together exert negative feedback
Testosterone exerts negative feedback on
both LH and FSH
Inhibin exerts negative feedback on
FSH
(inhibin produced in response to FSH and suppresses FSH)
Negative feedback…
keeps the testes small
- if the negative feedback is lost in a species that produces a lot of LH and FSH, the testes will grow larger and larger
→ testicular hypoplasia
In animals with sperm competition we see
a really strong endocrine drive and large testes
- want to produce lots of sperm
- semen from elsewhere, sperm comes from testis
Testosterone transport
- testosterone has limited solubility in blood
- can associate with serum albumin
- 54% in humans
- associates with hydrophobic core of hepatic sex hormone binding globulin (SHBG)
- 44% in humans
Meiosis in the testis
1 spermatogonium (2n)
→
2 primary spermatocytes (2n)
→
4 secondary spermatocytes (n)
Spermatogenesis
spermatogonium A
spermatogonium B
primary spermatocyte (leptoptene) primary spermatocyte (zygotene)
primary spermatocyte (pachytene)
primary spermatocyte (diplotene)
primary spermatocyte (diakinesis)
secodary spermatocyte
round spermatid
Spermiogenesis
round spermatid
elongate spermatid
spermatozoon
Endocrine control of spermatogenesis
Complete spermatogenesis + spermiogenesis dependeng on
FSH + testosterone/DTH
Endocrine control of spermatogenesis
FSH more important in
early stages of meiosis
(via Sertoli cells)
Endocrine control of spermatogenesis
Androgens more important in
latter stages (RS) plus spermiogenesis
Male pelvic anatomy
Male pelvic anatomy
(bullets)
- testis are a collection of supercoiled tubules
- also supercoiling in the epididymis
- looks like a simple tube but isn’t
- that’s a covering under which we see convoluted tubules
- vas deferens is a simple tube that runs out of the epididymis to the penal urethra
- on its way it passes seminal vesicles
Epididymis is composed of
supercoiled tubules until it runs into the vas deferens
Vas deferens
a simple tube that runs out of the epididymis to the penal urethra, passing seminal vesicles
Epididymis
2 and 3. caput epididymis (head)
- corpus epididymis (body)
- cauda epididymis (tail)
- called body and tail because of way sperm moves through them
- in humans oriented to earth this way
- in many eutherians not oriented this way
Spermiogenesis finishes off in the
epididymis
Normal spermatozoan
Spermatozoan
- when mature has acrosome
- membrane-bound enzymes
- spiral micochondrium
- wraps around flagellum
- very plastic
- tail
- flagellum that makes sperm depending where the sperm is
Acrosome
- mature spermatozoan
- enzymes that sit over the nucleus
Spiral mitochondrion
- wraps around the flagellum
- very plastic
- dividing and fushing, not as mean as there appears
Tail
- flagellum that makes sperm swim depending where sperm is
When sperm leave the testes they are
immotile
Epididymal sperm maturation
testicular spermatozoa still need to acquire
- motility
- ability to fertilizie oocyte
both acquired as sperm pass through caput and cauda epididymis
Testicular spermatozoa still need to acquire
- mobility
- ability to fertilize oocyte
both acquired as sperm pass through the caput and cauda epididymes
Don’t want sperm to be hyperactive in the
epididymis
Sperm are stored in the
cauda epididymis
(before going to the vas deferens)
Sperm acquire …. to prevent hyperactivation
decapacitation factors
(keeps them calm)
looks like just extra cholesterol
Decapacitation factors need to be removed
in female tract prior to fertilization
Decapacitation factors need to be remoed in the female tract prior to fertilization
- alkaline due to pH
- why epididymis can’t fertilize
- may involve progesterone to remove cholesterol
Secretions of the epididymis also include
- inositol
- man, stallion, ram
- sugar, carb
- preserves seminal osmolarity
-
glycerophosphorylcholine
- substrate for phospholipid metabolism
Species variations in accessory sex glands
- dogs don’t have bulbo-urethral glands
- humans have large prostrates as do dogs
- bull has sall prostrate, but huge seminal vesicles
- boar - culper gland is enormous but the prostrate is reduced
- because of different strategies to maximize fertilization different animals have evolved different structures
The prostrate gland
secretions of the prostrate gland include
- citric acid
- chelates Ca2+ to prevent semen coagulation
- the anticoagulant property of citric acid will be neutralized when entering the female tract
- the semen will coagulate and set (to form mating plug)
- acid phosphatase
- hydrolyses choline from glycerophosphorylcholine
- added in the epididymis
- prostaglandins cause female tract to convulse
Citric acid
- from prostrate gland
- chelates Ca2+ to prevent semen coagulation
- the anticoagulant property of citric acid will be neutralized when entering the female tract
- the semen will coagulate and set (to form mating plug)
Acid phosphatase
- produced by prostate gland
- hydrolyses choline from glycerophosphorylcholine
- added in the epididymis
Prostaglandins
- produced by prostate gland
- prostaglandins cause female tract to convulse
Secretions of the seminal vesicles
fructose
- anaerobic fructolysis in sperm
- for sperm propulsion
inositol
- bull and boar (convergent evolution)
- preserves seminal osmolarity
citric acid
- stallion, ram, boar, bull
- to stop semen from coagulating in the semen tract
Fructose
- secretion of the seminal vesicles
- anaerobic fructolysis in sper
- for sperm propulsion
Inositol
- secretion of seminal vesicles
- bull and boar (convergent evolution)
- preserves seminal osmolarity
Citric acid
- stallion, ram, boar, bull
- to stop semen from coagulating in the semen tract until in female
The bulbo-urethral (cowper’s) gland
- produces clear, viscous “pre-ejaculate” on sexual arousal
- lubricates penis
- alkaline secretion
- neutrlizes acidic urine in the penile urethera
- if too acidic then the sperm will die
- biggest acid must worry about is uric acid from urine in the urethra
- in mammals sperm move down the same tract as urine
- causes semen coagulation
- contributes to “gel fraction” in boar
- bull produces 1.5 liters of ejaculate - a large fraction of which is gel fraction which stops the ejaculate falling out
- this is made in the bulbo-urethral gland - hence why the bulbo-urethral gland is huge in boars
