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Bull Reproductive Anatomy


Hi, my name is Heather Schlesser with the Marathon County Extension Office. Today we are talking about the first part in
our series on bull health and fertility. Our first part is on male anatomy.
To truly understand bull health and fertility, you need to know the different
components of the male reproductive system, and what their function is. There
are 6 major components to the male reproductive system: the spermatic cord,
scrotum, testis, excurrent ducts, accessory sex glands, penis, and muscles for
protrusion and erection or ejaculation. The first part of the system is the
spermatic cord. The spermatic cord’s main function is to connect the body to
the testis, or the testis to the body. The spermatic cord is also responsible
for holding the cremaster muscle, and the pampiniform plexus. Each of which we will talk about in more detail. The cremaster muscle is the
primary muscle supporting the testis. The cremaster muscle creates a pumping
action that facilitates blood flow and cooling efficiency within the testis. It
is not responsible for elevating the testis during cold temperatures; it
cannot maintain contractions for long periods of time, therefore, it is not part
of our cooling mechanism. The pampiniform plexus, the other item that is housed within the spermatic cord, is responsible for cooling the blood as it
enters into the testis. The blood that is within the testis is 4 to 6
degrees cooler than body temperature. This heat transfer is necessary for
proper spermatogenesis. The transferring of heat goes from the arteries to the
venous blood, and out through the walls of the scrotum. The pictures shown here
shows the interconnectedness of the arteries and the veins within the testis.
There are many veins that circulate around the arteries that help dissipate
that heat, and allow the cooling effect that we see. The scrotum is a thermo-sensor, and is responsible for sensing the temperatures that are affecting the
testis. When the males experience elevated body temperatures, or elevated
scrotal temperatures, the hypothalamus detects this change and sends nerve impulses to the sweat glands. The sweating then allows the scrotum to be cooled by evaporative
heat transfer. Therefore, the scrotum is also known
as a swamp cooler because it is heavily populated with sweat glands, and it is
effective at conducting heat away from the testis by evaporative heat transfer.
The last function of the scrotum is to act as a protective sac; this sac keeps
the testes safe from injury. It also raises and lowers the testis depending
on body temperature. So, when the animal is hot, the scrotum is lowered, allowing
the testes to move farther from the body. During periods of cold temperature when
the testicles are cold, the scrotum holds the testis up close to the body, making
sure that they can efficiently be warmed by the body temperature. This infrared
thermogram shown in the picture is of a bull scrotum; it shows that there are
elevated testicular temperatures closer to the body, and as
we get to the base of the testis, we see that there are lower temperatures. This
is an indication of the function of the panpimiform plexus, and the cooling
effect that we see. The testis is the main reproductive organ. It’s a paired
organ, meaning that there are two of them within the male species. Within the
testis, we have production of spermatozoa, or sperm cells, hormones and proteins, and various fluids. The fluids that are produced within the testis serve as
a vehicle in which spermatozoa are suspended, and facilitates the removal
from the testis. It is not the fluid that we see in the ejaculate; the seminal
fluid is produced by accessory sex glands, not by the testis itself. Within the testis, the Sertoli cells are known as the governors of spermatogenesis. Each Sertoli cell hosts a maximum number of developing germ cells. Germ cells are
what become our sperm, so if the more Sertoli cells we have, the more sperm
cells we will ultimately have. The excurrent duct system is the final stage for maturation, storage, and delivery of the sperm. The excurrent duct
system consists of the efferent ducts, the epididymal duct, and the ductus
deferens. The efferent duct is a tube that connects the testis to the
epididymal ducts, and it conveys newly-formed spermatozoa and fluid into
the epididymal duct. The epididymal ducts, or the epididymis, is responsible for
final maturation of the sperm and ultimately storage of the sperm. The
ductus deferens is the tube that carries the mature sperm from the epididymal
ducts, out through the urethra for insemination. So, the epididymal duct is
broken into three parts: the head, the body, and the tail. Within the head and the
body, final maturation of the sperm occurs, and within the tail, we have
storage of that matured sperm. Sperm located in the head is not motile, not
fertile, and there is a cytoplasmic droplet located right below the
head on the start of the tail piece. The reason there is a cytoplasmic droplet is
because the sperm wants to decrease its size. So, during the final maturation
stages, we lose part of the cytoplasm, decrease the sperm, so that it is smaller
in size. Within the body of the epididymis, sperm has some expression of motility, it has some fertility, and that cytoplasmic droplet has moved farther
down the tail. At this point, sperm can be bound to oocytes, or will bind oocytes if
it is removed from the epididymis. Within the tail of the epididymis, we have fully
mature sperm. It has full expression of motility, it has full fertilizing
potential, and that distal droplet has moved even further down the tail; and the sperm in the tail can also bind an oocyte. Epididymal Transmit Time
is the time required to transport spermatozoa from the head to the tail of
the epididymis. Sperm stays 2 days within the head, 2 days within the body,
and sperm is stored in the tail for 10 days. Sperm is ejaculated out of the tail
on a continual basis, so that we can keep fresh stores of sperm within that tail
epididymis. The ductus deferens is the last part of our afferent duct system,
and it transports spermatozoa to the pelvic urethra. As the sperm goes through
the pelvic urethra, it meets up with fluids that are produced by accessory
sex glands, so the accessory sex glands are responsible for production of the
liquid portion of the semen. It is not required for fertility, but it is
important for natural insemination. The fluid acts as the vehicle for sperm
delivery. The penis is the copulatory organ of the male, and it is composed of
three parts: the base, the shaft, and the glans penis. The base is the attachment
point, or the point where the penis attaches to the animal’s body; the shaft
is the main portion, it is the long stem portion of the penis; the glans is the
specialized end, or the tip of the penis that is responsible for excitation and
ejaculation. It is the stimulation of the glans penis that is the primary factor
initiating the mechanism of ejaculation. The penis in the bull is a fiber elastic
penis, meaning that there is limited erectile tissue, and it has a sigmoid
flexure, or an s-shaped curve within the penis. This sigmoid flexure allows the
penis to be retracted inside the body until erection occurs. When the male is
excited, the smooth muscle of the retractor penis muscle is released, and
the penis is allowed to extend outside the sheath of the animal. The penis has
several erectile tissues within it, and it is stiffening of these erectile
tissues that cause an erection. However, in the fiber elastic penis, stiffening
occurs without significant change in diameter, so erection occurs when there
is relaxation of the retractor penis muscle, and that sigmoid flexure is
allowed to expand. There is also rushing of blood into the corpus cavernosum, and
the corpus spongiosum, the two erectile tissues within the penis. Thank you for
watching this video, and we hope you learn something!

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