1. Male Reproductive Anatomy

8/13/2019 1. Male Reproductive Anatomy

http://slidepdf.com/reader/full/1-male-reproductive-anatomy 1/25

MALE REPRODUCTIVE ANATOMY

Summary

Male reproductive anatomy includes:

Paired testes → Produce spermatozoa and hormones

Paired duct system (epididymis and deferent ducts) →

Transport spermatozoa

Accessory glands → Secretion Urethra → Transport seminal plasma

Penis and associated muscles → Delivery of semen

Skin adaptations (prepuce and scrotum)

Hormones result in sexual dimorphism, e.g. testosterone in males.

Describe the structure of the testis, epididymis, scrotum and

spermatic cord

Testes

The testis is a solid, smooth, ellipsoid organ and is orientateddorsocaudally in the dog. The epididymis is the coiled portion of the

external duct system and adheres to the dorsolateral surface of each

testis. Each testis is separately suspended in the scrotum by the

spermatic cord, which consists of the deferent duct, vessels and

nerves covered by the peritoneum.

Testicular Parenchyma

The testicular parenchyma is soft and yellow-brown. It consists of

contorted canals called seminiferous tubules in a connective tissue

matrix. The cells lining the tubules produce spermatozoa.Testis Structure

The testicular support structure is a dense CT framework.

There are 3 main components:

Tunica albuginea → surrounds the testis and holds the

spherical shape (white tunic)

Mediastinum testis → median rod of CT (can be more lateral in

some species)

Testicular septa → separates the lobes of the testis by coursing

between the tunica albuginea and the mediastinum testis



Describe the arrangement of the duct system that transports

spermatozoa through the male reproductive tract

Convoluted seminiferous tubule

(spermatozoa created here)

↓

Straight seminiferous tubule

↓ Rete testis

↓

Cranial direction

↓

Efferent ductules

↓

Out of testis

↓

Epididymal duct

↓

Ductus deferens

Epididymis

Consists of:

Head (caput) → cranial region

Body (corpus) → dorsal longitudinal surface

Tail (cauda) → caudal region

In the head and body, spermatozoa undergo changes that allow

them to become fertile. In the tail, spermatozoa is

diluted in a buffer solution and stored ready for

ejaculation.

The epididymis must be firmly attached to the testis.

The head is attached by ductules. The medial side of

the body has a peritoneal reflection for attachment.

The tail is attached by the proper ligament of the

testis. The lateral side also houses the testicular bursa.

Ductus deferens

The epididymis becomes the ductus deferens at the

testicle and moves craniodorsal in the body. Just past

the bladder, the ducts turn caudally and merge

towards each other as they near the prostate. They

never fuse to form a single duct but lie next to each

other, connected by peritoneal folds.

Ampulla

At the distal end of the ductus deferens, there is a

slight swelling of glandular tissue. This is the

ampulla.

Lobule

Mediastinum



Understand the process of testicular descent and the resultant positional arrangement of the testes and

testicular attachments

Testicular Descent

Testicular descent begins during embryological development. Initially the testes are located dorsally in the

abdominal cavity near the kidneys.

The gubernaculum is a mass of undifferentiated CT that is attached to a testis.

1.

The testes are initially retroperitoneal in the dorsal abdominal cavity2. During embryological development, the peritoneum wraps around the gubernaculum and testis

3. The gubernaculum grows through the inguinal canal, taking parietal and visceral peritoneum with

it

4. When it reaches the skin, the gubernaculum grows pulling the testis to sit in/near the inguinal canal

5. The gubernaculum regresses and forms a skin pocket. The combination of two skin pouches is the

scrotum.

6. Around birth, as the gubernaculum shrinks it pulls the testis through the inguinal canal until it sits in

the scrotum.

Remnants of the gubernaculum attach the testis to the scrotal wall

Failure of Descent

When a testicle (or both) fails to descent, it is termed cryptorchidism. It can be uni- or bi-lateral. It can be

caused by genetic predisposition, and is more prevalent in certain breeds, e.g. greyhound. Cryptorchid

animals should not be bred from and undescended testes should be removed surgically as they can

form/become tumours. At 35-40 days the testes should be completely descended, but give until 6 months

to descend. If bilateral cryptorchidism is present, the testes still produce testosterone but spermatozoa

need a lower body temperature, and so these animals are infertile.

Testicular Attachments

Visceral vaginal tunic is the peritoneum directly

surrounding the testis; adheres to the tunica

albuginea

Parietal vaginal tunic is the peritoneum of the wall of

the scrotum

Cavity of vaginal tunic is the space between the

vaginal tunics

Internal spermatic fascia arises from the m. transverses abdominus

External spermatic fascia arises from the m. external abdominal oblique



Skin and Associated Sub-Cutaneous Tissues

The skin of the testes is thin with sparse hair. It houses well developed

sebaceous glands.

Dartos m. → layer of smooth muscle sub-cutaneously

Sometimes called tunica dartos

When contracts it pulls the testes in

Cremaster m. → skeletal muscle in spermatic cord; arises from internalabdominal oblique m.

Pulls testes up/retracts

Scrotal septum → divides the

scrotum into two separate cavities

housing one testis in each

Spermatic Cord

Testicular artery (direct branch from

aorta) → path through abdominalcavity is straight, then after inguinal

canal is contorted

Testicular vein (Right v. drains into caudal vena cava; Left v. into Left renal v.)

Lymphatic drainage

Sympathetic nerve fibres

Cremaster muscle

Ductus deferens

CT

Surrounding peritoneumPampiniform Plexus

Counter-current heat exchange

from testicular a. (warm blood

from body) to testicular v.

(cooler blood from testes). Ensures that blood going to the testes is cool

and blood returning to the body is warm.



Describe the arrangement and structure of the prostate and pelvic urethra of the dog

Urethra

Pelvic Urethra

Preprostatic → before the prostate, has a purely

urinary function

Prostatic → passes through the prostate

The prostatic part of the pelvic urethra has mucosalfolds. When the urethra is distended, these spread

out and disappear. There is one fold that does not

disappear during distention, the dorsal urethral crest.

Additionally, the colliculus seminalis is where the urethra, ductus deferens,

seminal vesicles and the body of prostate empty into; it is a ridge that does not

disappear during distention.

Spongiose Urethra

The part of the urethra enclosed in the penis. After entering the bulb of the

penis, the urethra is always surrounded by corpus spongiosum.

Prostate

Accessory sex gland that secretes seminal plasma that allows sperm to swim

(also secreted by epididymis). It creates a rectogenital pouch with the colon and a vesicogenital pouch

with the bladder.

The prostate is divided into left and right lobes internally by a median septum, apparent externally by a

dorsal sulcus. Connective tissue lamellae further divide lobes into lobules, each consisting of several

compound glands that drain independently into the urethra. The prostate is also present as a disseminate

portion of scattered glands in the submucosa of the pelvic urethra. The prostate is dependent ontestosterone.

The deferent ducts do not have any direct communication with the prostate as they only pass through.

They enter the prostate on either side of the colliculus seminalis. Both the urethra and the deferent ducts

pass through the dorsal half of the prostate.

In uncastrated dogs, prostatic hyperplasia can occur → can treat with drugs or by castration.



Describe the components of the penis and prepuce of the dog and their functional significance

Penis

The copulatory organ that houses the extrapelvic part of the urethra and functions to insert semen into the

female vagina. Has 3 parts:

Root → crura

Body → corpus

Apex → glansThe penis is attached caudally to

the ischiatic tuberosities

at the root of the penis.

Erectile Tissue

The corpora cavernosa penis is a

pair of erectile tissue rods. Caudally, at the root of

the penis, the rods are separate and form a pair of

crura (feet). Each crus attaches to its respective

ischiatic tuberosity. In the body of the penis, the corpora

cavernosa are joined. The rods are covered externally by a

thick dense connective tissue tunic, the tunica albuginea.

The interior is a honeycomb arrangement of connective tissue

trabeculae filled with vascular spaces. This tissue is filled with blood

to become rigid during erection. Ventrally, a deep

longitudinal groove exists between the corpora

cavernosa.

The corpus spongiosum is the third rod of erectiletissue in the penis. It has a thinner tunica

albuginea and thus is capable of greater expansion

during erection. At the root of the penis, the

corpus spongiosum lies between and caudal to the

corpora cavernosa; this forms the bulb of the

penis. In the body of the penis, the corpus

spongiosum penis lies within the ventral

longitudinal groove. In the glans of the penis, the

corpus spongiosum glandis forms two erectile structures that fully surround the os penis. The more caudalof the structures is the bulbus glandis, the more cranial is the longa glandis. The bulbus glandis is the more

distensible of the two, and forms a bulbus swelling that serves to lock the penis into the vagina of the bitch

during copulation.

Os Penis

Within the glans penis, the corpora cavernosa fuse and are replaced by the os penis, that continues to the

tip of the penis. The caudal part bears a deep ventral groove, the urethral groove, while the cranial part

ends in a cartilaginous tip.





Muscles

Bulbospongiosus→ transversely oriented skeletal muscle covering the bulb of the penis, extending

cranially along the ventral surface of the caudal half of the penis. It partly encloses the caudal part of the

corpus spongiosum. Sits deep to the retractor penis m.

Ischiocavernosus→ paired skeletal muscles enclosing the crura of the penis, from the ischiatic tuberosity

to the corpus cavernosum. Sits laterally.

Ischiourethralis → small paired skeletal muscles arising from the ischiatic tuberosity to insert on a smallmedian fibrous ring surrounding the penile veins. When this muscle contracts, it constricts the fibrous ring

and hence venous drainage. This occurs during erection.

Retractor penis → paired smooth muscle from the first 2 caudal vertebrae, passing caudal to the bulb of

the penis and ventral to the body to insert on the ventral surface of the penis at the junction of the body

and the glans. Sits superficial to the bulbospongiosus m.

Blood VesselsInternal pudendal a. gives rise to:

A. of bulb of penis → corpus spongiosum, penile urethra

Deep a. of penis → corpus cavernosum

Dorsal a. of penis → glans

Superficial v. of glans (drains longa glans) → external pudendal v.

Dorsal v. of penis (drains bulbus glans) → internal pudendal vv.

Erection

Stage 1

Increase arterial flow → corpora cavernosa fills

- Intromission -

Stage 2

Restricted drainage → bulbus glandis and longa

glandis fill

1. Contraction of ischiourethralis mm.

2. Contraction of bulbospongiosus and

ischiocavernosus mm.

3. Pressure from female vaginal tract



Prepuce

The fold of skin covering the penis when in a flaccid state. Consists of an internal lamina

and external lamina (hairy outer skin). A fornix is present where the laminae meet.

Describe the histological structure of the testis and the process of

spermatogenesis (in sequence)

Testicular Histology

Visceral Vaginal Tunic → Single layer mesothelial cells

→ Adheres to the t. albuginea

beneath it

Tunica Albuginea → Consists of dense connective tissue, has a

large number of collagen and some elastic fibres; is vascular

Septula and Mediastinum Testis → consist of CT

→ the septula are continuous with

the t. albuginea

→ the mediastinum testis contains

rete testis and vessels.

Rete Testes Channels → Simple squamous -

cuboidal epithelium

Interstitial Tissue

Interstitial tissue is part of the testicular parenchyma. Present

between seminiferous tubules and consists of loose, vascular CT. Non

vascular cells include fibrocytes, free mononuclear cells and leydig

cells.

Leydig cells (interstitial endocrine cells) are large polymorphous cells

with spherical nuclei. They are often found in clusters. They

produce androgens, such as testosterone, which diffuse into

seminiferous tubules due to close association with blood

vessels.

Seminiferous Tubules

Seminiferous tubules are part of the testicular parenchyma and

are lined by stratified germinal epithelium surrounded by a

lamina propria. It contains 2 cell lines:

Sertoli cells (sustentacular cells) are supportive cells – do not

undergo meiosis. Their function is to provide nutrition,

protection and support to spermatogenic cells. Sertoli cells are

tall, extending the full thickness of the germinal epithelium.

They are pale staining with an oval/pear shaped nucleus and a

prominent nucleolus. Their cytoplasm is not visible except with special stains, and they have lateral and

apical cytoplasmic processes.

Spermatogenic cells are cells that replicate and differentiate into mature sperm.

Spermiation is the process of spermatozoa being released into the lumen of the convoluted seminiferous

tubules. Peritubular cells of the basal lamina participate in transport and spermiation.

Straight seminiferous tubules are lined by simple squamous to columnar epithelium.



Spermatogenesis

Spermatogonia

↓

Primary spermatocytes

↓

Secondary spermatocytes

↓ Spherical spermatids

↓

Elongate spermatids

↓

Spermatozoa

Spermatogonia

Spermatogonia are rounded to slightly flattened cells with a central dark

staining nucleus. They undergo mitotic division, where some daughter cells

remain as stem cells and others continue mitosis. After several divisions, the

daughter cells become primary spermatocytes and migrate through theblood-testis barrier. All descendants of one proliferating spermatogonia

remain connected by cytoplasmic bridges during maturation, resulting in

synchronised maturation.

Spermatocytes

Primary spermatocytes replicate DNA. They are large cells with large nuclei. They undergo meiosis 1 to

create 2 secondary spermatocytes.

Secondary spermatocytes undergo meiosis 2 and create 2 spermatids.

I.e. Two meiotic divisions; 1 primary spermatocyte → 2 secondary spermatocytes → 4 spermatids

Spermatocytogenesis

Spermiogenesis

Meiosis



Spermatids

Spermatids retain cytoplasmic bridges between cells of the same generation. Spermatids are initially

spherical spermatids. They then mature and develop tails, becoming elongate spermatids. They migrate

apically whilst remaining attached to a sertoli cell. The elongate spermatids mature into spermatozoa.

Spermiogenesis

Spermatid → spermatozoa

Spermatids must form an acrosomal cap and tail (flagellum),

condense nuclear chromatin and expel unnecessary material.

Spermiogenesis has 4 phases that occur while attached to sertoli cell:

Golgi phaseCap phase

Acrosomal phase

Maturation phase

Spherical spermatids

Elongated spermatids



1. Golgi Phase

This phase involves spherical spermatids. Proacrosomal granules appear in the vesicles of the Golgi

complex. They fuse into a single acrosomal vesicle, which lies near the dimple of the nucleus. Centrioles

initiate the development of flagellum.

2. Cap Phase

Involves spherical spermatids. The acrosomal vesicle grows to form a cap, called the acrosome that covers

over half of the nucleus. The nucleus shifts eccentrically. The centrioles polarise at the opposite end. Themore distal centriole gives rise to the developing flagellum.

3. Acrosomal Phase

The cell body and nucleus elongate. The spermatid rotates so the flagellum faces the lumen and the head

faces the periphery of the seminiferous tubules. The nucleus condenses and the centrioles move back

towards the nucleus. Elongate spermatids become deeply embedded in recesses of sustentacular cells.

4. Maturation Phase

Nuclear condensation is complete and the flagellum matures. Excess cytoplasm forms a residual body and

is pinched off. Spermatids are no longer attached to sertoli cells.

Describe the structure of the mature spermatozoon

Spermatozoa Structure

Head

Tail

Neck

Middle piece

Principal piece

End piece

Spermatids which have almost completed

spermiogenesis. Note all the tails orientated

adluminally and the cast off cytoplasmic

droplets below. Another wave of spermatids is

commencing the process of differentiation.



Head

The head consists of a dense nucleus covered apically by an acrosomal cap. The cap has inner and outer

acrosomal membranes and contains enzymes important in fertilisation for penetration of the egg. The

base of the acrosome is surrounded by a postacrosomal sheath that consists of fibrous proteins rich in

sulphur.

Neck

The neck is short and narrow. It has a centrally located centriole and nine peripheral longitudinallyorientated fibres. These fibres are continuous with the outer dense fibres of the middle piece.

Middle Piece

The middle piece has an axoneme at its core that has a typical flagellum

structure of 2 central microtubules and 9 microtubule doublets. This is

surrounded by 9 dense fibres (continuous with the neck) which are then

surrounded by spirally arranged mitochondria. The middle piece

terminates with a thickened ring of plasmalemma.

Principal Piece

The principal piece is the longest section of the tail. It consists of theaxoneme and the surrounding 9 dense fibres present in the middle piece.

These are then surrounded by semicircular protein molecules, creating a

fibrous sheath. This gradually tapers and terminates with the loss of the

fibrous sheath and the dense fibres.

End Piece

The end piece only consists of the axoneme; this gradually tapers, reducing the

doublets to singlets and then terminating.

Describe the histological structure of the duct system, accessory glands, urethra and penis, and how thisrelates to their function

Rete Testis

Simple squamous to cuboidal epithelium

Elastic fibres and contractile tissue are found under the epithelium to

help with movement of the spermatozoa. Movement is also aided by a

high concentration of spermatozoa.

Efferent Ductules

Efferent ductules are short, highly coiled ducts. They are lined by

pseudostratified (simple in some areas) columnar epithelium with bothciliated (apical row of nuclei) and non-ciliated cells (basal row of nuclei). Lymphocytes are often seen

basally and it is surrounded by loose CT. The epithelium often varies in height giving the duct a scalloped

appearance. Cilia help propel the spermatozoa along and increase in number along the duct.



Epididymis

Spermatozoa are present in the lumen. The epithelium is

pseudostratified columnar with microvilli that absorbs excess fluid.

The epithelium also contains columnar principal cells with microvilli

(stereocilia) and small polygonal basal cells. The principal cells are

taller and the microvilli are longer in the head of the

epididymis. The duct is surrounded by a small amountof loose CT and circular smooth muscle fibres. The epididymis has a golgi

apparatus in its cells (between the free surface and nucleus) that produces

glycoprotein that coats sperm and enables capacitation (penetration of the

egg). The distal epididymis is used for storage.

As you move distally from head → tail:

Overall diameter ↑

Wall becomes thicker and more muscular

Microvilli become shorter

Contraction of muscular walls and pressure move sperm throughepididymis

Ductus Deferens

The ductus deferens has pseudostratified columnar epithelium with more basal cells. The microvilli are

gradually lost. Distally, the epithelium becomes simple. The lamina propria is very vascular and it has a well

developed muscularis with fibres orientated longitundinal – circular – longitudinal. The muscularis

constricts the lumen into a stellate shape.

The ampulla contains many branched tubuloalveolar glands in the submucosa which have columnar to

cuboidal epithelium.



Urethra

The walls of the urethra consist of mucosa, submucosa, tunica

muscularis and tunica adventitia. It is predominantly

transitional mucosa with patches of simple to stratified

cuboidal to columnar epithelium. The lumen is compressed due

to longitudinal mucosal folds when not transporting fluids. One

fold that does not disappear is the urethral crest. Thesubmucosa is thick with many smooth muscle cells and elastic

fibres and erectile tissue. The tunica muscularis consists of

smooth muscle proximally and skeletal muscle distally.

Prostate

The urethra forms a smile-shaped lumen in the prostate. Glandular components form radial secretory

regions around the urethra. The prostate is surrounded by a dense CT capsule. Internally, the glandular

tissue is divided into 2 main lobes which are separated by a median septum. It contains many branched

tubuloalveolar glands (serous in the dog) with simple cuboidal to columnar epithelium. The ducts have

stratified columnar to transitional epithelium which may have saccular dilations of ducts where secretionsare stored.

Penis

The corpus cavernosum has large cavernous spaces, separated by trabeculae of fibrous CT and smooth

muscle and lined by endothelium. T. albuginea is thick and made of dense

fibrous CT. Numerous coiled terminal arteries, helicine arteries, are

present, which have a layer of smooth muscle in their t. interna, allowing

occlusion of the lumen. The corpus spongiosum is similar to the corpora

cavernosa, but the cavernous spaces are large. The CT and t. albuginea

have a greater elastic fibre component.



Prepuce

The external lamina consists of unmodified hair skin; the

internal lamina is a thinner skin with very few hairs but many

sebaceous and sweat glands and solitary lymphatic nodules.

Describe the variation in the structure, position and

orientation of the testis, epididymis and scrotum between

domestic mammals

The testis are structurally similar between species, however, there are differences

Position of Testes and Scrotum

Bull – as the testis descends, it falls straight down into scrotum, sits vertically under inguinal canal

Dog/Horse – pulled caudally when descending

Cat/Boar – positioned obliquely, tail is located dorsocaudally

Marsupials – scrotum located cranial to penis

Elephant – internally. The elephant embryo has no gubernaculum, no vaginal

process, no pampiniform plexus and no means of effecting testicular descent

Possible reasons for external testes:

Lower temp needed for spermatogenesis

Adaptation to a jumping/leaping/running lifestyle, intra-abdominal testes may be compressed

leading to ejaculation

Scrotal Hair Coat

Cat – very hairy

Dog/Ruminants – sparse hair

Location of the Mediastinum Testis

Displaced to the side, adjacent to the epididymal margin and

smaller in some species

Relative Abundance of Different Cells

Testis contains mostly seminiferous tubules, with little interstitial

tissueBoar – 30% interstitial cells

Ram – 1% interstitial cells



Relative Size (Relative to Body Size)

Inter-species variation in testis:body size is large

There is no correlation between the relative size of testes and location,

body form or type of locomotion.

There is a relationship between the relative testis size and the incidence

of sperm competition (and mating system) in mammals.

Sperm competition – the competition between sperm of two ormore males for the fertilisation of an ovum

Testes are relatively small in a single male mating species

Intra-species variation

In humans, the testis volume positively correlated with the number of

sperm ejaculated.

In bulls, the scrotal circumference is used as an indicator of sperm quantity and quality

Duct System

The epididymal duct has a varied length between species → 2cm (cat) – 75cm (horse)

The relationship between the testis, epididymis, ductus deferens and supporting peritoneum is basicallythe same → apart from orientational changes due to testis migration

Describe the gross and histological structure of male accessory glands and differences between dog, cat,

horse, pig, sheep and ox (e.g. presence, appearance and proportions of these glands)

Accessory Sex Glands

- Ampullary glands A

- Vesicular glands Very

- Prostate Proud

- Bulbourethral glands Boy All paired except for the prostate. All large glands have a thick capsule with septa. There is species

variation of different combinations, different proportions, however they have the same relative positions.

Ampullary Glands

The ampullary glands are found in the

submucosa of the distal ductus deferens.

Branched tubuloalveolar glands with

pseudostratified, columnar epithelium.

Not seen in the cat or boar.



Vesicular Glands

The vesicular gland is a lateral outgrowth of the distal ductus deferens. It is a compound tubuloalveolar

gland which lies within the submucosa. The glandular epithelium is pseudostratified columnar and the

epithelium in the secretory ducts is simple cuboidal (pseudostratified columnar in horse). The glands are

arranged in lobules, separated by connective tissue trabeculae and tunica muscularis and serosa surrounds

the gland.

Stallion – forms the common ejaculatory duct with the ductus deferens which passes through the

prostate. It has a smooth surface and a large central cavity

Bull – forms the common ejaculatory duct with the ductus deferens which passes through the prostate. It

has a lobulated surface and a more compact structure

Boar – No common ejaculatory duct, instead separate ducts for the ductus deferens and the vesicular

glands, however they still pass through the prostate. The glands are very large and obscure the sight of the

ductus deferens. It has a lobulated surface and a more compact structure.

Dog – Not present

Prostate

The prostate consists of either a compact

body and/or internal diffuse portion (disseminate). The disseminate portion consists of individual glands in

the submucosa of the urethra. The body is a pair of variably fused lobes with a thick CT capsule and

trabeculae dividing the gland into smaller lobules.

It has tubuloalveolar glands. The

glandular mucosa consists of

pseudostratified cuboidal –

columnar (serous in dog, seromucous

in others) and the epithelium of the

ducts is stratified columnar –

transitional.



Stallion – well defined body with two lobes connected by a dorsal isthmus. There is an absent/reduced

disseminate portion.

Bull/Boar – a small, caudodorsally located body (ring-shaped in the bull) and an extensive disseminate

portion

Small ruminants – lack a prostatic body but have an extensive disseminate portion

Carnivores – large, well defined body, divided into 2 lobes. The degree of fusion of the lobes varies. Has a

reduced disseminate portion. Its duct drains secretions into the urethra.

Bulbourethral Glands

Bulbourethral glands are generally small (except in the pig) and when present, they always lie caudal to the

prostate and laterodorsal to the urethra. The size of the gland relates to seminal volume.

Their glands are compound tubular (boar, cat, goat)/tubuloalveolar (stallion, bull, ram) mucous glands. It

has an outer thick capsule, surrounded by m. bulboglandularis. Its secretory portions have simple –

pseudostratified columnar epithelium. The glandular units are surrounded by loose CT and denser

trabeculae with some smooth muscle. It has a duct system:

Collecting duct

(simple cuboidal)

↓

Intraglandular duct

(pseudostratified columnar)

↓

Bulbourethral duct

(transitional epithelium)





Describe anatomical differences between the penis of the dog, cat, ox, sheep, horse and pig, and relate

some of these to differences in penile development and the erection mechanism

All eutherian mammals (mammals that have a placenta) have:

A pair of corpora cavernosa penis attached to the ischiatic tuberosities; adjacent cranially,

diverging to crura caudally Corpus spongiosum lying in the ventral groove between corpora cavernosa; extends as a bulb

caudally, and beyond the corpora cavernosa cranially; enlarges to varying degrees as the glans penis and

surrounds the penile part of the urethra

Musculocavernous/Fibroelastic Penis

Musculocavernous (Vascular) Fibroelastic

Stallion Pigs and ruminants

Corpora cavernosa:

Extensive cavernous spaces

T. albuginea contains smoothmuscle

Corpora cavernosa:

Limited cavernous spaces

Thick t. albuginea with no smooth muscle

↑ diameter and length on erection ↑ in rigidity but not in length or diameter

The sigmoid flexure in the penis is stretched by the relaxation of the

m. retractor penis muscle causing an increase in the penis length



The dog and cat are halfway between musculocavernous and fibroelastic, i.e. they do not have a sigmoid

flexure but there is less expansion of the penis than with a musculocavernous penis.

Extent of Glans

Only the dog has the pars longa and the pars bulbus. In all other species, the glans forms a single erectile

body that is continuous with the corpus spongiosum. The relative size of the glans varies and other

features such as the raphe and keratinised spines may be present.



Dog – pars longa and bulbus glandis present

Stallion – well developed glans that is mushroom shaped

Bull – less developed glans which is present as a small asymmetrical pad. It is a plexus of veins, rather than

true erectile tissue.

Boar – The glands is even more reduced than in the

bull. Also has a raphe which is a non-elastictendinous cord. It will not expand and during

erection it causes the penis to form a twisted

shape. The penis twists in a clockwise direction.

Cat – the glans is very small and is covered in

spines. The spines are oriented proximally; when

entering female, causes no problem, when exiting

the spines rub along the female vagina which is

thought to induce ovulation. The spines are

testosterone dependent, so if cats are castrated

before puberty, the spines will not form.

Termination of Urethra

Horse – the urethra opens at the tip of a short

urethral process, which sits in the fossa glandis.

The urethral process does not extend beyond the

glans.



Bull – the glans does not cover the end of the penis,

hence the urethra is not contained within the glans

and projects as a urethral process

Small Ruminants – a long, thread-like urethral

process extends beyond the apex of the penis and

contains erectile tissue.

Dog – the urethral opens just below the tip of theglans on the ventral surface.

Pig – the urethra is not covered by the glans, and it

sits ventral and caudal to the tip.

Os Penis

The os penis is present only in the domestic carnivores, but

is also present in many non-domestic animals. It replaces

the distal end of the corpora cavernosa. There is dispute as

to whether the cat has an os penis.

The Cat Penis

The cat penis is quite small and seemingly upside down; the urethra and corpus spongiosum are dorsal to

the corpora cavernosa. The penis faces almost caudally.

Muscles of the Penis

The retractor penis, ischiocavernosus and bulbospongiosus mm. are consistently present. In the

fibroelastic penis, the retractor penis m. inserts cranial to the sigmoid flexure.



Describe anatomical peculiarities of the prepuce of the horse and pig

Horse

The horse prepuce has an additional inner fold

Pig

The pig has a preputial diverticulum which is a subcutaneoussac opening dorsally into the prepuce. It can

contain stale urine, decomposing cellular

debris and pheromones – smells.

Documents

1. Male Reproductive Anatomy