Male Reproductive Tract

Question 1

What are androgens?

Answer 1

The major class of C-19 sex steroid hormones in males, with distinct structural and functional features:

• Beta-hydroxylated C-17
• Ketone structure at C-3

Question 2

What are SRY genes?

Answer 2

Sex determining genes region Y.

Can cause expression of testis determining factor, TDF.

If TDF is expressed = embryonic development of testes
If TDF is not expressed = development of ovaries

Question 3

Describe embryonic male development.

Answer 3

2 hormones produces by the developing testes change the developmental pathway of the internal genitalia from the default female to the male phenotype.

1. The developing testes maintains the Wolffian duct system, which develops into the epididymis and male reproductive tract.
2. Anti-Mullerian hormone (AMH) is produced by Sertoli cell type, causing regression of the Mullerian duct system and prevents development of the female internal genitalia.
3. Prenatal testosterone from the Leydig cells of the testes masculinise the external genitalia to becomes penis and scrotum.

Question 4

How can androgens be synthesised?

Answer 4

From cholesterol by progesterone.

Question 5

How can oestrogen be synthesised?

Answer 5

Testosterone converted into oestrogen by aromatase enzymes.

Androstenedione converted into oestrogen by aromatase enzymes.

Question 6

What is DHT and its function?

Answer 6

Peripheral conversion of testosterone to 5 alpha-dihydrotestosterone (DHT), which is much more biologically active.

This is vital for the maturation of the male external genitalia during development and for maintenance of reproductive function in the adult.

Question 7

What is adrostenone?

Answer 7

Testosterone is inactivated by the liver and one of the products produced is adrostenone, which has no hormonal activity, but has an important role in pigs as a sexual attractant produced by boars to attract sows for mating.

Boars that produce too much of these is responsible for boar taint, an unpleasant taste from the meat of sexually active boars.

Question 8

Describe the organisational mode of andorgens.

Answer 8

Organisational/determinative effects of steroids are totally or only partially irreversible. For example:

Mammals other than primates exposure to androgens during the perinatal period is important for having an organisational effect to matching areas of the brain involved in control for reproduction and behaviour.

Question 9

Describe the activational effects of androgens.

Answer 9

Activational/regulatory effects of steroids are reversible. Such as:

• Maintenance of spermatogenesis
• Maintenance of activity of accessory sex glands
• Anabolic effects
• Erectile capacity
• Secondary sexual characteristics, such as antler growth ]male-specific behaviour and aggression and increased physical activity

Means that energy does not need to be wasted in seasonal breeders for maintaining reproductive capacity outside breeding period when androgen levels fall.

Question 10

What is the link between castration and androgens?

Answer 10

Used to control reproduction and behaviours in domestic species. DUe to lack of adnrogens, there is:

• Decreased sexual motivation and sexual behaviour
• Decrease in ‘undesirable’ behaviours – fighting, roaming and urine spraying in cats

But castration after puberty often does not eliminate these behaviours completely.

Question 11

Give a brief overview of spermatogenesis.

Answer 11

• Spermatogenesis occurs in seminiferous tubules.
• Spermatozoa collected into rete testis.
• Efferent ducts reabsorb fluid and concentrate sperm.
• Epididymis matures and stores sperm.
• Deferent duct transports sperm to pelvic urethra at ejaculation.

Question 12

Describe and name scrotal species.

Answer 12

Androgen hormones, such as testosterone, cause descent. These have effect on the gubernaculum and suspensory ligament:

Pigs, cattle, goats, sheep, felids, canines, primates, rodents, etc.

• Cattle, horse, pig and sheep prenatal descent normally completed by a few weeks postnatally.
• Cat and dog postnatal descent completed in first few months.

Question 13

Define cryptorchidism.

Answer 13

A failure one or both testes to descend and causes sterility if bilateral and has increased risk of neoplasia.

Question 14

Name some non-scrotal species.

Answer 14

Birds
Elephants
Dolphins
Hedgehog

Question 15

What is the importance of the pampiniform plexus?

Answer 15

Pampiniform venous plexus surrounds testicular artery and functions as a counter current heat exchanger, and the exchange of other things, like testosterone.

Question 16

Describe the first stage of spermatogenesis - spermatocytogenesis.

Answer 16

1. First stage is known as spermatocytogenesis – spermatogonia develop into spermatocytes. It is initiated by asymmetric divisions of spermatogonia stem cell to generate a replacement stem cell and a spermatogonium.
2. Spermatogonium undergoes several rounds of mitotic proliferative division, helping to generate the large numbers of spermatogonia that are required to meet the normal sperm production rate.
3. After a species specific number of mitotic divisions, spermatogonia become spermatocytes in meiosis.
4. After the 2nd mitotic division, the spermatocytes becomes haploid spermatids and enter a process of differentiation known as spermiogenesis.
5. Spermiation causes them to be placed into the seminiferous tubular lumen.

Question 17

Define and the describe the process of the 2nd stage of spermatogenesis - spermiogenesis.

Answer 17

Converts a non-motile round cell into a highly efficient DNA vehicle.

1. Begins in golgi phase by alignment of centrioles and golgi apparatus on opposite sides of the nucleus, which determines the cell’s polarity. Golgi apparatus dramatically increases in synthetic activity during this phase, and the nuclear DNA undergoes packaging and becomes highly condensed.
2. During the cap phase, the golgi apparatus expands to form a cap IV anterior part of the nucleus. One of the centrioles elongates to start forming the tail.
3. In the acrosomal phase, the cap expands to form the acrosome, which becomes the anterior half of the chromosome. While mitochondria migrate to the midpiece region when residual cytoplasm is removed.
4. In the last phase, the unnecessary cytoplasm is removed and condensed following residual bodies. Tail continues to elongate. Mitochondria wrap tightly along the proximal region of the tail, forming the helical mitochondrial sheath.

Question 18

Describe the role of Sertoli cells in spermatogenesis.

Answer 18

Engulf the developing spermatogeneic cells, controlling and coordinating spermatogenesis.

• Sertoli cells mediate the effect of testosterone on follicle stimulating hormone on spermatogenesis, as there are no hormone receptors on developing spermatogenic cells themselves.
• Sertoli cells also involved in remodelling the cytoplasm of spermatids by phagocytosising the residual cytoplasm.
• The stem cells, a mitotically dividing spermatogonia, are found in the basal compartment between the basement membrane that surrounds the seminiferous tubule and the tight junctions between the Sertoli cells.
• As they become spermatocytes and enter meiosis, they move past junctions and into the ad luminal compartment.
• Spermatids differentiate into spermatozoa and released into Sertoli cells and tubule in spermiation.

Question 19

What is the blood-testis barrier?

Answer 19

Junctional complexes between Sertoli cells from blood-testis barrier.

• Mitosis occurs in basal compartment near basal lamina.
• Meiosis occurs in the adluminar compartment, on the other side of the tight junctions to protect from immune system and cytotoxins.
• Also allows a different seminiferous tubular fluid microenvironment for the late stages of spermatogenesis.

Infection can hide behind this barrier.

Question 20

Describe spermatogenic cycle and spermatogenic wave in the continuous production of spermatozoa.

Answer 20

The duration of the spermatic cycle is the interval between cohorts of spermatogonia entering spermatogenesis. Is a quarter of the time taken to complete spermatogenesis.

Stage of spermatogenic cycle is staggered in neighbouring regions of seminiferous tubule.

Question 21

Describe the morphology of mammalian spermatozoa.

Answer 21

• Head contains nucleus with highly condensed chromatin covered by acrosomal cap – hyaluronidase and acrosin.
• Middle contains packed spiral of mitochondria.
• 9 outer dense fibres
• Axoneme – 9 and 2 flagella arrangement which extends into tail.

Question 22

Describe the motility of spermatozoa.

Answer 22

• Dynein arms attach to adjacent microtubules.
• Dynein has calcium ions, which are dependent on ATPase activity.
• ATP hydrolysis results in microtubules sliding past one another.
• As the axoneme is fixed to the sperm head, this results in flagellar bending.
• Sequential activation of dynein arms generates a wave of bending which is propagated down and around the tail.

Question 23

How do spermatozoa do metabolism?

Answer 23

High ATP requirement for motility.

• Oxidative phosphorylation is restricted to the midpiece
• Glycolytic ATP production appears to be necessary for hyperactivated sperm motility in vicinity of egg, which is required for fertilisation.

Species differences in metabolic activity:

• Oxidative phosphorylation more important for bull sperm
• Glycolytic pathway more important in mice

Question 24

What are the 2 reasons to collect semen from animals?

Answer 24

• For fertility assessment and diagnosis

* Artificial insemination and assisted reproductive technology

Question 25

How is semen collected from bulls?

Answer 25

1. A teaser animal induces arousal
2. The bull has been trained to mount a steer as a teaser animal
3. An artificial vagina is used to collect semen

Question 26

How is semen collected from a stallion?

Answer 26

1. A teaser mare induces arousal
2. The stallion has been trained to mount phantom mare
3. An artificial vagina is used to collect semen
4. Post-ejaculatory refractory period

Question 27

What is a rectal probe?

Answer 27

A rectal probe delivers low voltage electrical impulses to the pelvic nerves involves in ejaculation.

• Can be used for almost any mammal but not stallions
• It does not require a mount animal to initiate arousal
• It may be painful and requires a skilled and experienced handler

Question 27

What is a rectal probe?

Answer 27

A rectal probe delivers low voltage electrical impulses to the pelvic nerves involves in ejaculation.

• Can be used for almost any mammal but not stallions
• It does not require a mount animal to initiate arousal
• It may be painful and requires a skilled and experienced handler

Question 28

How are sperm susceptible to environmental damage?

Answer 28

• Exposure to toxic chemicals including many detergents and disinfectants
• Thermal stress
• Rapid cooling affects motility and morphology
• Short exposure to even a few degrees above body temperature kills sperm

Question 29

How can semen be preserved using a sperm extender?

Answer 29

Sperm are diluted to adjust semen concentration and combat adverse constituents of ejaculate.

A sperm extender contains the following:
• Energy source
• Buffer
• Protein, such as egg yolk

Question 30

What are the advantages and disadvantages of cryopreservation of semen?

Answer 30

+ Controlled cooling will extend life of sperm for days and can be used for shipping semen for AI.

+ Can be used for all domestic species and is increasingly being used as a genetic bank to store samples from endangered animals.

• Free-thaw produces capacitation-like reaction and reduces viable lifespan in female reproductive tract.

Question 31

How can a visual assessment using the gross appearance of spermatozoa?

Answer 31

Clear semen = low concentration of sperm

Thick creamy semen = high concentration of sperm

No blood, pus or urine

Question 32

Describe progressive and non-progressive motility.

Answer 32

Progressive motility – assess the percentage of sperm that travel in a roughly straight line.
Satisfactory raw semen has a progressive motility of 30% in cattle AI.

Non-progressively motile sperm - move on the spot or swim with curved paths.

Question 33

How is spermatozoa morphology examined?

Answer 33

1. Examine individual sperm stained with nigrosine-oesin
2. Count spern heads in the 15 fields and fill in the report
3. Examine for normal and abnormal dead sperm, which will be pink.
4. Examine for normal and abnormal live sperm, which will be white

Question 34

List 7 possible abnormalities in sperm.

Answer 34

Coiled tail 
Double head 
Mis-shaped head 
Bent midpiece 
Coiled midpiece 
Proximal droplet 
Distal droplet

Question 35

How is sperm density counted and calculated?

Answer 35

Sperm density – count using haemocytometer, counting the sperm at the top left corner of squares.

Density = 10,000 x (total counted/total squares counted) x dilution (10)

Question 36

Which hormones do Sertoli and Leydig cells produce?

Answer 36

Sertoli:

• Oestrogen (minor product in boars and stallions)
• Cytokines, predominantly inhibin and activin/Mullerian hormone

Leydig:

• Androgens, predominantly testosterone
• Oxytocin with species differences

Question 37

What does testosterone act on?

Answer 37

Testosterone diffuses freely across cell membranes and affects several targets within the testes. It has an autocrine short loop negative feedback to the Leydig cells, to inhibit excessive testosterone production.

Also acts on myeloid cells that surround seminiferous tubules, maintaining their contractile function. Without testosterone, contractility decreases and spermiation is impaired.

Question 38

Describe the the role of FSH in the male reproductive tract.

Answer 38

Administering LH, luteinising hormone, restores testosterone production but not spermatogenesis. So there must be an additional factor from the anterior pituitary gland that controls spermatogenesis.

• This is FSH, follicle stimulating hormone, which with LH and gonadotropins, due to their stimulatory effect on the gonads.
• FSH acts on receptors on the basal lateral membrane of the Sertoli cells.
• Together with androgenic stimulation from testosterone as DHT has a permissive effect on spermatogenesis, meaning FSH and testosterone are both required for spermatogenesis to proceed.
• FSH also stimulates the Sertoli cells to produce androgen binding protein, ABP, which increases testosterone levels in seminiferous tubular fluid.
• FSH stimulates Sertoli cells to produce inhibin, activin and oestrogen, as well as trasnferrin.

Question 39

What determines pulsatile LH and FSH release?

Answer 39

Gonadal releasing hormone is released by neurones in the medial preoptic area of the hypothalamus. Released in a pulsatile fashion and drives pulsatile release of LH and FSH at 1 pulse per hour.

• Irregular, low amplitude GnRH = FSH release
• High frequency GnRH = LH release

Question 40

Explain how androgen exposure in the perinatal period masculinities the brain.

Answer 40

It Is not testosterone that causes the masculinisation of the brain circuits directly, but oestradiol, normally thought as a female sex steroid.

1. In the brain, aromatase enzymes locally convert the highest circulating levels of testosterone.
2. Results in high local levels of oestradiol, which deactivates the hypothalamic surge centre, as well as masculinising the brain circuits.
3. In females, oestradiol is bound by alpha fetoprotein in the blood which stops it crossing the blood brain barrier. The surge centre in the hypothalamus is maintained, enabling the LH surge in females.

Question 41

Describe the different routes of testosterone output from the testes.

Answer 41

• Major route via the venous blood. Though some testosterone can due to countercurrent be carried in arterial blood and back to the testes. Most of it enters the systemic circulation.
• The rate of blood flow far exceeds that of lymph so total output vis the blood is far greater. But lymph is still an important route to carry testosterone to the accessory glands of the reproductive tract.
• Via seminiferous tubular fluid itself. Androgen binding protein produced by Sertoli cells is important for transport of testosterone to the epididymis.

Question 42

What are the extra-sustentacular targets for androgens?

Answer 42

• Determination of primary male characteristics
• Epiphyseal close during development
• Accessory gland function
• Establishment of secondary male characteristics
• Anabolic effects on somatic tissue, which is important for meat production and carcass quality
• Establishment and maintenance of male behaviour – libido, aggression, increased physical activity levels

Question 43

Define puberty in males.

Answer 43

Puberty in male sis associated with a rise in gonadotropins, FSH and LH, which initiate spermatogenesis and testosterone production.

Puberty – the point at which a male is able to produce sufficient numbers of sperm to impregnate a female.

Question 44

How does the hypothalamus control puberty?

Answer 44

1. Puberty is initiated by an increase in sensitivity of GnRH neurones in the medial preoptic area of the hypothalamus to the neurotransmitter kisspeptin.
2. The lack of kisspeptin production or the lack of function of its receptors on the GnRH neurones leads to a failure of puberty.
3. This is a condition celled hypogonadotropic hypogonadism.
4. It is characterised by the lack of LH and FSH production and no testicular spermatogenic activity.

Question 45

Give the species differences in timings of puberty.

Answer 45

• Dogs and cats = 6-12 months
• Sheep and goats = 6-8 months
• Cattle = 8-12 months
• Horses = 12-18 months

Question 46

How is does the hypothalamus control seasonal breeding?

Answer 46

Many species that inhabit temperate climates undergo seasonal changes in reproductive activity, which ensures that offspring are born when environmental conditions are most likely to be favourable.

For instance, sheep are short day breeders and the ram reproductive activity increases as daylength decreases in the autumn and reproductive activity ceases as the rate of decrease in daylength slows in winter.

It’s the hypothalamus that responds to the rate of change of day length and controls the hypothalamic-pituitary-testicular axis by initiating or terminating GnRH production and FSH and LH release.

Question 47

Describe the process of copulation.

Answer 47

1. Male sexual behaviour starts with the arousal phase that assesses sensory information regarding the receptive state of females.
2. In the presence of a receptive female, a range of physiological processes in the preparatory phase ready the male reproductive tract for the delivery of semen. This leads on to mounting behaviour and intromission.
3. Sensory stimuli provide information that intromission has been successful and trigger ejaculation.
4. Finally, there is the post-copulatory sequel phase in which all males have a refractory period in which the threshold for sexual arousal is elevated and sexual behaviour is inhibited.

Question 48

List the sensory signals that initiate arousal phase.

Answer 48

• Olfactory – chemosensory sues are sensed by the main olfactory and vomeronasal system.
• Visual – sight of opposite sex conspecific, sexual swellings in primates.
• Auditory – calling or singing
• Behavioural cues
• Flehmen behaviour is used for pheromonal sampling via the vomeronasal system. Is obvious in many species as a curling of the upper lip and baring of the teeth suck, which sucks non-volatile pheromonal stimuli, such as steroid derivatives, into the vomeronasal organ.

Question 48

How do arousal signals then cause erection?

Answer 48

1. Sensory signals that activate the preparatory phase of sexual behaviour are sent from the hypothalamus, via brainstem centres, to the erection centre in the lumbar region of the spinal cord.
2. The erection centre also receives direct sensory input from tactile receptors in the genitalia, which can initiate erection directly.
3. The increased inflow of blood is due to a parasympathetic mediated vasodilation of arterioles supplying the erectile tissue, via endothelial nitric oxide production.
4. The decreased outflow of blood is due to compression of the venous outflow due to contraction of the ischiocavernosus muscle.
5. Parasympathetic activity also plays a role in relaxing the retractor penis muscle in those species that have one, which allowing the penis to extend from its sheath.

Question 49

How does hypothalamic control lead to mounting behaviour?

Answer 49

Hypothalamic circuits drive sex-specific behavioural patterns via brainstem motor centres. Male mounting behaviour is controlled the medial preoptic nucleus of the hypothalamus.

Importantly neurons in the medial preoptic area, along with neurons upstream in the amygdala, have steroid receptors, so high circulating testosterone levels are required in addition to sensory input from receptive females for male sexual behaviour to be displayed.

Question 50

Define and describe intromission.

Answer 50

Intromission - the successful insertion of the penis into the vagina of the female.

Occurs without any form of visual feedback, so requires sensory feedback from the glans penis. The glans penis is highly innervated by both tactile and temperature sensitive afferent nerve fibres.

Only when sensory feedback signals that the glans penis is in a sufficiently warm environment and receiving appropriate tactile stimulation will the spinal mechanisms underlying emission and ejaculation be initiated.

Question 51

Describe the process of ejaculation.

Answer 51

1. Emission, is initiated once successful intromission has occurred and once a sufficient level of stimulation of the glans penis has been reached. Emission is the coordinated series of contraction of smooth muscle in the male reproductive tract that deliver spermatozoa and accessory gland secretions into the pelvic urethra.
2. Sympathetic mediated contraction of smooth muscle in the tail of the epididymis and the ductus deferens propels spermatozoa and fluid from the extragonadal sperm reserve into the urethra.
3. Simultaneously, sympathetic mediated contraction of the smooth muscle in the accessory sex glands adds their contribution to the seminal fluid and sympathetic mediated closure of the bladder sphincter muscle seals off the urinary tract.
4. This prevents the pressure increase during ejaculation from forcing semen back into the bladder, which is a dysfunction known as retrograde ejaculation.