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Reproduction > Male Reproductive System > Flashcards

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
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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
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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
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4
Q

Stallion Penis

A

muscular penis

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5
Q

Bull/Ram Penis

A
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6
Q

SPecies Penis Diff.

A
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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
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8
Q

2 Functions of the Testis

A
  1. Production & transmission of male genes (spermatozoa)
  2. 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.
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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

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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
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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

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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
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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
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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
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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
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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
Q

2 phases of Sperm movement

A
  • 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
Q

Sperm Structure

A

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
Q

Capacitation

A
  • 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
Q

Hyperactivation

A
  • 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
Q

Acrosome Reaction

A
  • 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
Q

Fertilization

A
  • 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

Reproduction (8 decks)

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