Male Reproductive System Flashcards
1
Q
Male Repro. Anatomy
A
- Testes or male gonads: Secrete male sex hormones (androgens) & Produce male gametes (sperm)
- Testes pass through the inguinal ring
- Contraction of Dartos & Cremaster muscles= important for testicular thermoregulation
- Ducts: Testis, Epididymis, Ductus deferens (vas deferens), Ejaculatory duct, Urethra
- Accessory Organs: Ampulla, Seminal vesicles, Prostate gland, Bulbourethral glands
- External genitalia: Penis, Scrotum
2
Q
Comparative Pelvic Anatomy
A
- Bull & ram- testis lies in vertical plane, side by side in a pendulous manner & penis has sigmoid flexure
- Boar- testis is located at an oblique angle, posterior to hams
- Stallion- testis is located in horizontal plane, side by side, pendulous between rear legs
- Cat- penis points backwards & testis located dorsally
- Dog- bone present (os penis), unique to dogs
3
Q
Accessory Organs
A
- Seminal vesicles – Active secretory gland, contributes ~60% total volume of semen,
- Secretions contain fructose, prostaglandins, fibrinogen
- Prostate gland – Secretes slightly acidic prostate fluid
- Bulbourethral glands – Secrete alkaline mucus (as vagina is acidic) with lubricating properties ( neutral pH)
- The size of the glands and the volume of their secretion are regulated by testosterone
4
Q
Stallion Penis
A
muscular penis
5
Q
Bull/Ram Penis
A
6
Q
SPecies Penis Diff.
A
7
Q
The Testis
A
- Seminiferous tubules: sertoli cells contain FSH receptors, FSH stimulates spermatogenesis
- Leydig cells: Contain receptor proteins for LH, LH stimulates secretion of testosterone
- Epididymis: Contains cilia which aid movement of immature sperm, which aren’t yet motile
8
Q
2 Functions of the Testis
A
- Production & transmission of male genes (spermatozoa)
- Production of reproductive hormones (androgens)
Blood supply: Vessels arranged as Pampiniform plexus- artery runs down the testis and the veins coil upwards around the testis forms a counter current system for temperature regulation
- Testicular artery –branches from aorta (below renal artery)
- Right Testicular vein – inferior vena cava
- Left Testicular Vein- left renal vein
Testis consists of 2 discrete compartments:
- Within seminiferous tubules: sperm develop & sertoli cells act as their nurse cells
- Between seminiferous tubules: leydig cells (responsive to LH) present which synthesize androgens- appear foamy under microscope due to cholesterol present.
9
Q
3 phases of Spermatogenesis
A
1. Mitotic proliferation- Spermatogonia (gonocytes/germ cells) undergo several rounds of mitosis–> large numbers of primary spermatocytes which are diploid & genetically identical
2. Meiotic division- undergo 2 rounds of meiosis: Primary spermatocytes –>(2n) Secondary spermatocytes–>(n) spermatids- this generates genetic diversity (chromatids exchange genetic material) & halves the chromosome number (haploid)
**1 and 2 are stages of spermatocytogenesis**
3. Cytodifferentiation (spermiogenesis)- Packages genes for delivery to oocyte, spermatids become elongated & offload excess cytoplasm –> Spermatozoa
10
Q
Sertoli Cells
A
- SCs are anchored to basement membrane & attach to neighbouring SCs via gap junctions–> a coordinated wave of spermatogenesis
- They control spermatogenesis by:
- Transferring developmental proteins to spermatocytes
- Removing material from elongating spermatids (cytoplasmic material)
- Mediating androgen hormone (testosterone) action
11
Q
Testis Hormones- Androgens
A
- Cholesterol from blood–> leydig cells, where its converted –> progesterone–> testosterone
- Testosterone passes from Leydig cells into:
- ->Blood (negative feedback on anterior pituitary & hypothalamus)
- ->Seminiferous tubules where sertoli cells convert testosterone –>dihydrotestosterone
-Which passes into testicular fluid to stimulate male reproductive tract & spermatogenesis
Both leydig cells & sertoli cells can produce oestrogen
12
Q
Hypothalamic- Pituitary-Gonadal Axis
(HPG)
A
- GnRH from hypothalamus–> A. pituitary via hypophyseal portal vessels –>release of LH & FSH
- Removal of pituitary gland–> testes shrink, no spermatogenesis, Leydig cells deteriorate, ↓ testosteroneoutput- Administration of LH returns function to normal
- LH stimulates leydig cells to produce ↑ testosterone & supports spermatogenesis
- FSH stimulates ↑ amount of androgen receptors in sertoli cells so they can respond
13
Q
Epididymis
A
Transport to the Epididymis
- Sperm released from associated sertoli cells–> lumen of seminiferous tubules–> rete testis (collecting duct)–> epididymis
Epididymal Structure
Caput (head)- Fluid from SCs resorbed concentrates sperm 100-fold
Corpus (body) – Modification of environment and sperm maturation
Cauda (tail) – Sperm storage
- Passage through epididymis takes 6-12 days
Epididymal Maturation- stabilises the sperm for its journey through the female tract
- Sperm structure – Loss of surplus cytoplasm (removal of cytoplasmic droplet) & Condensation of nuclear chromatin by ↑ the number of disulphide bridges
- Sperm membranes- Addition of surface glycoproteins (decapcitation factors) protect the oocyte binding proteins
- ↓ Membrane fluidity by selectively removing cholesterol
- Metabolism- ↓ metabolic activity to prolong life & ↑ dependence on external fructose for energy production
- Motility – cAMP content of tail ↑ allowing acquisition of motility
14
Q
Seminal Plasma
A
- Sperm are ejaculated in seminal plasma, which is derived from the accessory glands: - Prostate gland, Seminal vesicle, Ampulla & Bulbourethral gland
- Seminal plasma determines ejaculate volume (not testis)
- Contribution of each gland varies between species (+ indicates relative volume contributed)
- Prostate is large & double-lobed in dogs
15
Q
Composition of Seminal Plasma
A
- Glycoproteins (decapacitation factors)
- Fructose & Sorbitol – energy substrate (glusoce for E)
- Citric acid – stops sperm coagulating & forming ‘stones’
- Acid phosphotase – phospholipid metabolism
- Buffers – neutralise acid pH of vaginal fluids
- Ascorbic acid – reducing agent to protect against sperm oxidation at ejaculation
- Prostaglandins – stimulate muscle contractions in female tract, which will draw the sperm up the tract
16
Q
Penis Anatomy
A
- Fibroelastic Penis- in Ram , bull, boar
- Erectile tissue: Corpus cavernosum & Corpus spongiosum become engorged with blood
- But the erection is mainly due to the straightening of the sigmoid flexure via the relaxation of themretractor penis muscles which allows the penis to protrude
Musculovascular Penis- in Stallion, Human
- Erection is primarily due to blood engorgement of the large corpus cavernosum & spongisum- causing the penis to elongate & thicken
- Retractor penis muscle runs along the base of the penis, but there’s no sigmoid flexure
17
Q
Glans Penis
A
Glans Penis- Highly specialised!
- Tom cat- penis is covered in backwards facing barbs- important as cats are induced ovulators
- Boar corkscrew- goes cervix ejaculates directly into uterus (prevents retrograde movement of semen)
- Ram urethral process (bird thing)- thrashes & sprays a thin layer over the bottom of the cervix where it sticks
- Echidna- Penis has 4 branches, ejaculates from 2 at a time, as a way of maintaining quality of ejaculate as it ejaculates from one testis at a time- similar to what reptiles do
18
Q
Erection- Psychogenic Stimuli
A
- Visual cues: watching others mating, lordosis position
- Olfactory cues: Sniffing of vulva, Female urination (e.g. in guinea pigs), Pheromones
19
Q
Semen Collection
A
- Artificial vagina- works well in rams, bulls & elephants, doesn’t work for pigs due to corkscrew penis
- Use gloved hand method for pigs as pressure receptors must be depressed to ejaculate
- Electroejaculation probe- insert rectally so tip is behind the prostate gland - pulse low voltage supply prostate contraction which gives you an ejaculation
20
Q
Erection and Ejaculation
A
- Erection- Stimulation of pelvic nerve–> Arterial dilation & ↑ blood flow
- Relaxation of retractor penis muscle- Straightens sigmoid flexure (in some species)
- Muscles of vas deferens, seminal vesicles & prostate contract–> Spermatozoa & seminal plasma expelled (semen)
- Can be very forceful in some species (Stallion, as penis can’t get past cervix)
- Single spurt (bull 1-3sec) or extended (camel 6-20min)
21
Q
Copulation in the Dog
A
First stage coitus- Male mounts female- 1st & 2nd fractions of semen ejaculated (1-2min)
The Turn – Dog turns by lifting one leg over bitch- 2 adaptions allow this to occur:
- Os penis (penis bone) allows the penis to be inserted when only semi-erect
- Bulbus glandis- when inserted, muscles of vulva contract on back of penis, preventing venous outflow causing this erectile tissue to swell & locking the penis in place
Second stage coitus – 3rd fraction of semen ejaculated (30ml)- lasts 5-45min- dog penis cannot pass cervix but the high vaginal pressure created forces the semen –> uterus
22
Q
Challenges of Female Tract
A
- Avoid retrograde transport
- Transverse the cervix
- Travel through the uterus & oviduct
- Attain capacity to fertilise by undergoing 3 key stages
23
Q
Avoiding Retrograde Transport
A
- Intra uterine semen deposition (pig)
- Semen squirted through cervix at copulation (horse, dog)
- Maintain mating position, high pressure (dog)
- Viscous/gel fraction of seminal plasma acts to ‘plug’ tract (horse, pig, rodent)
24
Q
Sperm Motility
A
- Sperm move through the tract due to: Motility of sperm, Viscous fluid currents caused by uterine cilia & uterine contractions
- Sperm tail: midpiece contains mitochondrial sheath- supplies ATP & propulsive apparatus (axoneme)
25
2 phases of Sperm movement
* **Rapid transport phase** – Sperm reach oviducts within minutes- Unable to fertilise the oocyte as hasn’t undergone the 3 stages of maturation
* **Sustained transport phase**- Sperm undergo: **Capacitation, Hyperactivation & Acrosome reaction**
26
Sperm Structure
**_Variation Between Species_**
* Boar & bull sperm has a paddle shape,
* humans is more like a ball,
* starling sperm is like a corkscrew,
* drosophila have a few sperm which are very large & have a long elongated head
* **_Sperm cooperation_**- mouse sperm has a hook shape on its head- these sperm don’t attack rival sperm as first thought, but actually co-operate, hook deploys in the presence of rival males & seeks out sperms from the same male to form a **sperm train which can swim 2x quicker than normal sperm,** occurs where there’s **inter-male sperm competition.**
* Echidna sperms form bundles
**_Sperm Abnormalities_**
* **Head abnormalities:** Nuclear vacuoles, tapered heads, ruffled acrosome, knobbed acrosome
* **Tail abnormalities:** Coiled tail **(caused by fever)**, double midpiece, folded tail, detached head
**Morphological abnormalities reflect genetic problems**- Implications for fertility treatment:
- **IVF**- still allows some selection to occur
- ICSI (intra cytoplasmic sperm injection)- there’s no natural selection- **abnormal sperm may be used** and this could lead to an increased risk of genetic defects in offspring
27
Capacitation
* Progressive **destabilisation** of plasma membrane (reverses the epididymal changes), initiated when sperm enters the uterus
* Glycoprotein molecules coating sperm head removed --\>Exposure of **zona pellucida binding proteins--\>** Allows sperm to bind to the oocyte at fertilisation
* Surface charge altered – may attract sperm to oocyte?
* Membrane **fluidity increased to aid breakdown of acrosome**
28
Hyperactivation
* At the **uterotubal junction**, capacitation is completed & the sperm now **exhibit hyperactivated motility**
* ↑ intracellular calcium--\> ↑ cAMP--\> Strong, wide amplitude, whiplashing tail beats
-Necessary as ↑ force required to swim through the viscous environment within the oviduct
29
Acrosome Reaction
* Capacitation exposes **zona pellucida** binding proteins on sperm plasma membrane **(ZP3)**
* Sperm **binds** to zona pellucida via **ZP3 (requires \>50,000 of these)**
* **Binding initiates sperm acrosome reaction**
- Fusion of sperm plasma membrane & outer acrosomal membrane
- Release of enzymes (hyaluronidase & acrosin) to **digest the zona**
**pellucida**
- Exposure of inner acrosomal membrane & equatorial segment for
oocyte fusion
30
Fertilization
* Acrosomal enzymes digest small hole in **zona pellucida**- penetration is rapid & sperm moves--\> **perivitelline space** between zona & oocyte plasma membrane
* Oocyte plasma membrane fuses with **sperm equatorial segment & sperm is engulfed**
* Cortical granules from the oocyte--\> coat the plasma membrane- **preventing polyspermy**
**_Fertilisation- genetic content_**
**Gametes= haploid (1N)**- have a single copy of each chromosome
Following fertilisation the male and female pronuclei **fuse to produce a diploid (2N) zygote**
