Chapter 60 - Testis part I Flashcards
What does the scrotum of a horse contain?
The testes, associated ducts, and distal spermatic cords.
What is the function of the tunica dartos?
It regulates testicular temperature by relaxing with heat and contracting with cold.
Which vessel provides vascular supply to the scrotum?
The external pudendal vessels.
What type of muscle is the tunica dartos?
Involuntary muscle. This muscle
relaxes with heat and contracts with cold to regulate testicular temperature, thus varying the size of the scrotum
Where is the epididymis located on the testis?
On the dorsolateral border of the testis.
Name the three parts of the epididymis.
Head (caput), body (corpus), and tail (cauda).
How does sperm travel during ejaculation?
Through peristaltic contractions of the epididymis into the ductus deferens.
What covers the testis externally?
The tunica albuginea.
What is the role of the Sertoli cells in the testis?
They provide mechanical and nutritive support for developing spermatozoa.
What hormone stimulates spermatogenesis?
Follicle-stimulating hormone (FSH).
What do Leydig cells produce?
Androgens and estrogen.
What structure do the seminiferous tubules form when they converge?
The rete testis.
Where do the efferent ductules unite to form a single coiled tube?
In the head of the epididymis.
What is the inguinal canal?
An oblique passage in the abdominal wall through which the spermatic cord and other structures pass.
What forms the internal opening of the inguinal canal?
The deep inguinal ring.
What structure lines the wall of the inguinal canal?
The peritoneum, forming the tunica vaginalis.
What two layers make up the tunica vaginalis?
The visceral tunic and the parietal tunic.
What is the purpose of serous fluid in the vaginal cavity?
It lubricates to facilitate movement of the testis.
What is the gubernaculum testis?
A fetal mesenchymal cord that guides testis descent.
What does the cranial part of the gubernaculum testis become?
The proper ligament of the testis.
Where is the vaginal ring located?
About 10-12 cm abaxial to the linea alba and 6-8 cm cranial to the iliopectineal eminence.
What ligament connects the tail of the epididymis to the parietal tunic?
The ligament of the tail of the epididymis.
What could result from abnormal gubernaculum function?
Abdominal or inguinal retention of a testis.
What separates the right and left pouches of the scrotum?
A sagittal septum formed by the tunica dartos.
Which nerve supplies the scrotum?
The genitofemoral nerve.
Which tunic forms the scrotal sac lining?
The parietal tunic of the tunica vaginalis.
What hormone produced by the hypophysis stimulates Leydig cells?
Luteinizing hormone (LH) or interstitial cell-stimulating hormone.
Which side of the horse’s body usually has a larger, more caudal testis?
The left side.
The tail projects beyond the
caudal border of the testis, wraps around to the medial side, and
continues proximally as the
ductus deferens
Figure 60-1. Left testis and epididymis of a stallion, lateral aspect. a,
Testis; b, head of epididymis; c, body of epididymis; d, tail of epididymis;
e, proper ligamentum testis; f, ligament of the tail of the epididymis; g,
spermatic cord; h, cremaster muscle; i, external inguinal ring; j, vaginal
ring; k, visceral tunic; l, vaginal cavity; m, parietal tunic.
Figure 60-2. Graphic representation of the reproductive tract of the stallion, left-sided view. a, Testicular artery and vein; b, spermatic cords with their inguinal canal; c, external lamina of the prepuce; d, testis within scrotum; e, external inguinal ring; f, internal inguinal (vaginal) ring.
Figure 60-3. Descent of the testis. G, Gubernaculum; K, kidney; T, testis; U, ureter; V, vaginal ring.
Figure 60-4. Transverse section of the spermatic cord. 1, Testicular artery; 2, ductus deferens; 3, pampiniform plexus; 4, testicular nerves and lymphatic vessels; 5, mesorchium; 6, mesoductus; 7, cremaster muscle; 8, vaginal cavity; 9, spermatic fascia; 10, visceral layer of vaginal tunic; 11, parietal layer of vaginal tunic.
At what day of gestation do the gonads begin differentiating into testes or ovaries?
Day 40.
What ligament suspends the testis cranially at gestational day 55?
The cephalic (suspensory) ligament.
How large is the testis at 5 months of gestation compared to a mature stallion?
Nearly as large as that of a mature stallion.
What is the concentration of which hormone elevated in the mare during testicular hypertrophy?
Estrogen.
What is the gubernaculum’s role in testicular descent?
It guides the fetal testis from the kidney region to the scrotum.
At what gestational day does the gubernaculum begin to shorten?
Between 8 to 12 months of gestation.
What does the gubernaculum become after testicular descent?
It forms various ligaments, including the proper ligament of the testis.
What change occurs to the testis in the last month of gestation?
It regresses to one-tenth of its size.
What comprises the spermatic cord?
The tunica vaginalis, testicular blood vessels, nerves, lymphatics, and ductus deferens.
Is the cremaster muscle part of the spermatic cord?
No, it lies external to the parietal tunic.
What membrane encloses the neurovascular components of the spermatic cord?
The mesorchium.
Where does the ampulla of the ductus deferens form in the stallion?
Dorsal to the bladder.
What supplies blood to the cremaster muscle?
The cremasteric artery.
What structures are in the mesoductus deferens?
The ductus deferens and deferential vessels.
What structure is the mesoductus deferens continuous with?
The mesorchium.
What allows the testis to pass into the inguinal canal close to birth?
Increased intra-abdominal pressure and gubernaculum expansion.
What is monorchidism?
The complete absence of one testis.
How can monorchidism be confirmed?
Through an hCG-stimulation test or measuring anti-Müllerian hormone levels.
Define cryptorchidism.
It is a developmental defect where one or both testes fail to descend into the scrotum.
Why are bilateral cryptorchids typically sterile?
Because the seminiferous tubules are rudimentary due to high abdominal temperatures.
Why might cryptorchidism be considered genetically unsound?
The condition can be inherited and is often linked to genetic abnormalities.
What is the approximate prevalence of cryptorchidism among young colts?
About 17%.
Which breeds have the highest prevalence of cryptorchidism?
Percherons, American Saddlebreds, American Quarter Horses, ponies, and crossbred horses.
What dysfunction is thought to contribute to cryptorchidism?
Improper function or failure of the gubernaculum to enlarge or regress.
What role do androgens play in testicular descent?
They influence the development of the vaginal process and gubernaculum differentiation indirectly through the genitofemoral nerve.
How does the cranial suspensory ligament affect testicular descent?
Failure to regress may result in the testis remaining near the kidney.
What genetic factor was initially proposed in cryptorchidism studies?
Cryptorchidism could be an autosomal dominant or recessive trait, though the inheritance mechanism is complex.
What percentage of cryptorchid horses exhibit bilateral retention?
Studies show between 9% and 14%, with most retained testes being abdominal.
A study with 350 crypto found that ____% of left undescended testes were located within the abdomen, whereas only ___% of right undescended testes were retained abdominally
75% of left undescended testes were located within the abdomen, whereas only 42% of right undescended testes were retained abdominally
What type of intestine usually protrudes in inguinal herniation in horses?
Ileum or distal jejunum.
What is another term used interchangeably with inguinal herniation?
Scrotal herniation.
What occurs in a ruptured inguinal hernia?
Intestine protrudes through the vaginal ring and a rent in the parietal tunic and scrotal fascia, lying subcutaneously.
What distinguishes inguinal rupture from a direct hernia in horses?
Inguinal rupture lacks a peritoneum-lined sac.
Which horses are almost exclusively affected by inguinal herniation and rupture?
Stallions.
Why do geldings rarely develop inguinal hernias?
The vaginal rings decrease in size post-castration.
What type of inguinal hernia is typically congenital in foals?
Reducible hernia.
What potential congenital cause leads to inguinal hernia in foals?
Excessive outgrowth of the extraabdominal part of the gubernaculum
By what age do congenital inguinal hernias in foals typically resolve?
3 to 6 months.
what complication may arise from longstanding congenital inguinal hernias?
Testicular atrophy.
What activities may contribute to inguinal herniation in adult horses?
Exercise or copulation.
Which breeds show a higher incidence of acquired inguinal herniation?
Standardbreds, draft breeds, and Andalusian horses.
What clinical signs indicate obstruction of the small intestine in acquired inguinal hernia?
Nasogastric reflux recovery and palpable distended small intestine.
What typically causes strangulation in inguinal hernias?
Constricted intestine by the vaginal ring.
