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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
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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
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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
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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.
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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.
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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)
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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
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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.
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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.
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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.
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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.