Lecture 4 (2b) - Male Reproductive Systems Flashcards
1
Q
Aquatic invertebrates
A
- 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
2
Q
Cephalopod molluscs
…. delivers the spermatophore into the female mantle
A
hectocotylus
3
Q
Aquatic invertebrates
hectocotylus delivers the spermatophore into the female
A
mantle
4
Q
Aquatic vertebrates
“Fish” and Amphibians
A
- predominantly external fertilization
- eg most teleosts and amphibia
- elasmobranchs - claspers deliver spermatophore into female cloaca
5
Q
Aquatic vertebrates
… deliver spermatophore into female cloaca
A
claspers
6
Q
Aquatic vertebrates
claspers deliver spermatophore into female
A
cloaca
7
Q
Terrestrial animals
A
invertebrates practice
-
indirect internal fertilizatoin
- eg arachnids
- or direct internal fertilizatoin
- eg insects
- vertebrates always have direct internal fertiliation - insemination
8
Q
Terrestrial animals
Invertebrates practice
A
indirect internal fertilization
- eg arachnids
direct internal fertilizatoin
- eg insects
9
Q
Terrestrial animals
vertebrates always have
A
direct internal fertilization
(insemination)
10
Q
Scorpions
A
- 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
11
Q
Spiders
A
- 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
12
Q
Insects
A
- 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
13
Q
Terrestrial vertebrates
reptiles and mammals
A
direct fertilization via a penis
14
Q
Terrestrial vertebrates
birds
A
- 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
15
Q
Mammalian testis size
A
- 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
16
Q
Animals bigger
→
A
testis bigger
(but not necessarily proportional)
(testis mass vs body mass)
17
Q
Testis mass vs body mass (%)
A
- average size of testis is ~1% body mass unless very small organism (>1%)
- animals with biggest testes proportionally - rodents
18
Q
Rodents testes size
A
- most variation in very small
- proportionally largest testes in smallest animals
- biggest proportionally = gerbil
19
Q
Internal testes
A
- TESTICONDIDS
- testes internal - don’t have to be scrotal
- for purposes of streamlining/aerodynamics
20
Q
Where would you find mamalian testes?
A
- originate in abdomen
- anterio-rostral migration (in scrotum)
- contraction of gubernuculum
- caused by androgens
21
Q
Why do testes desccend in scrotal mammals?
A
- **NOT **scrotal because of temperature
- can cool testes without requiring testicular descent
- ?galloping (in the way of gait)
- ?sexual display
22
Q
Size of testes based on
A
whether or not there’s sperm competition
(no competition → smaller testes)
23
Q
Testis structure
A
- 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
24
Q
Testis comprised primarily of
A
seminiferous tubules
25
Seminiferous tubules contain
Sertoli cells and maturing sperm
(Sertoli cells inside tubules looking after maturing sperm)
26
Packed in between the seminiferous tubules are interstitial
Leydig cells
| (outside tubules, make testosterone)
27
Function of Sertoli cells
to mature the sperm
28
Sperm are germ cells but...
they are looked after by Sertoli cells which are somatic cells
* Sertoli cells are diplod
29
2 major cell types
Sertoli cells
* look after sperm
* inside the tubule
Leydig cells
* make testosterone
* outside the tubule
30
The tubule collects into the
epididymis
a single duct flows out for ejaculation
31
32
Direction of cell movement inside the tubule
basal → adluminal
33
2 main hormones
**leuteinizing hormone (LH)**
* Leydig cells respond to leuteinizing hormone
**follicle-stimulating hormone (FSH)**
* Sertoli cells respond to follicle-stimulating hormone
34
Leydig cells respond to
luteinizing hormone
35
Sertoli cells respond to
follicle-stimulating hormone
36
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
37
Spermatogonia
* diploid
* dividie by mitosis
* mitosis turns one spermatogonium into multiple spermatogonia
38
When spermatogonia enter meiosis, they become
spermatocytes
39
Spermatocytes become
spermatids
40
Spermatids will ultimately mature to become
spermatozoa
41
Sperm stages
spermatogonia
spermatocytes
spermatids
spermatozoa
42
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
43
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
44
Leydig cells make
testosterone
45
Leydig cells make testosterone in response to
LH
46
Sertoli cells produce
* inhibin (not a steroid but a growth factor)
* androgen-binding protein (ABP) with the ability to carry testosterone
47
Inhibin is a
growth factor
48
Androgen-binding proten (ABP) has the ability to
carry testosterone
49
Paracrine products
products that act on each other
(act on neighboring cells rather than elsewhere in the body)
50
We make LH and FSH in
the pituitary gland
51
LH and FSH are
heterodimeric glycoproteins
* have 2 subunits which are dissimilar
* heavily glycosylated that gives them the weight of 25-30kDa
52
Both LH and FSH have the same
α-subunit
53
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
54
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
55
NO ... on sperm
FSH or LH receptors
(no FSH or LH receptors on sperm)
56
FSH receptors are on
Sertoli cells
57
FSH also stimulates Sertoli cells to make
the growth factor inhibin
58
In the brain you have the
gonadotrophin releasing hormone (GnRH)
59
GnRH
* the hormone in the hypothalamus that drives reproduction
* important in puberty
* stimulates the anterior pituitary glad to produce LH and FSH gonadotrophins
60
GnRH stimulates the anterior pituitary gland to produce
LH and FSH gonadotrophins
61
LH stimulates the testis to make
testosterone
62
FSH stimulates Sertoli cells to make
**inhibin**
and closely related
**activin**
63
Inhibin and activin
together exert negative feedback
64
Testosterone exerts negative feedback on
both LH and FSH
65
Inhibin exerts negative feedback on
FSH
(inhibin produced in response to FSH and suppresses FSH)
66
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
67
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
68
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
69
Meiosis in the testis
1 spermatogonium (2n)
→
2 primary spermatocytes (2n)
→
4 secondary spermatocytes (n)
70
Spermatogenesis
spermatogonium A
spermatogonium B
```
primary spermatocyte (leptoptene)
primary spermatocyte (zygotene)
```
primary spermatocyte (pachytene)
primary spermatocyte (diplotene)
primary spermatocyte (**diakinesis**)
secodary spermatocyte
**round spermatid**
71
Spermiogenesis
round spermatid
elongate spermatid
spermatozoon
72
Endocrine control of spermatogenesis
Complete spermatogenesis + spermiogenesis dependeng on
FSH + testosterone/DTH
73
Endocrine control of spermatogenesis
FSH more important in
early stages of meiosis
| (via Sertoli cells)
74
Endocrine control of spermatogenesis
Androgens more important in
latter stages (RS) plus spermiogenesis
75
Male pelvic anatomy
76
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
77
Epididymis is composed of
supercoiled tubules until it runs into the vas deferens
78
Vas deferens
a simple tube that runs out of the epididymis to the penal urethra, passing seminal vesicles
79
Epididymis
2 and 3. caput epididymis (head)
4. corpus epididymis (body)
5. 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
80
Spermiogenesis finishes off in the
epididymis
81
Normal spermatozoan
82
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
83
Acrosome
* mature spermatozoan
* enzymes that sit over the nucleus
84
Spiral mitochondrion
* wraps around the flagellum
* very plastic
* dividing and fushing, not as mean as there appears
85
Tail
* flagellum that makes sperm swim depending where sperm is
86
When sperm leave the testes they are
immotile
87
Epididymal sperm maturation
testicular spermatozoa still need to acquire
* motility
* ability to fertilizie oocyte
both acquired as sperm pass through caput and cauda epididymis
88
Testicular spermatozoa still need to acquire
* mobility
* ability to fertilize oocyte
both acquired as sperm pass through the **caput** and **cauda** epididymes
89
Don't want sperm to be hyperactive in the
epididymis
90
Sperm are stored in the
cauda epididymis
| (before going to the vas deferens)
91
Sperm acquire .... to prevent hyperactivation
decapacitation factors
(keeps them calm)
looks like just extra cholesterol
92
Decapacitation factors need to be removed
in female tract prior to fertilization
93
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
94
Secretions of the epididymis also include
* inositol
* man, stallion, ram
* sugar, carb
* preserves seminal osmolarity
* **glycerophosphorylcholine**
* substrate for phospholipid metabolism
95
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
96
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
97
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)
98
Acid phosphatase
* produced by prostate gland
* hydrolyses choline from glycerophosphorylcholine
* added in the epididymis
99
Prostaglandins
* produced by prostate gland
* prostaglandins cause female tract to convulse
100
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
101
Fructose
* secretion of the seminal vesicles
* anaerobic fructolysis in sper
* for sperm propulsion
102
Inositol
* secretion of seminal vesicles
* bull and boar (convergent evolution)
* preserves seminal osmolarity
103
Citric acid
* stallion, ram, boar, bull
* to stop semen from coagulating in the semen tract until in female
104
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
