The Urinary SystemThis system includes the organs
that produce and excrete the waste substance urine. These
organs are:*kidneys*ureters*bladder*urethra
The Kidneys (nephro or reno)These are bean shaped organs located on both sides of the vertebral column. Kidneys are retroperitoneal: situated
outside the peritoneal cavity.Renal fasciae surrounds the kidneys,
holding them in place. Each kidney has a concave depression (hilus) on it’s
medial margin. This provides entrance for blood vessels, nerves and the ureter
The kidneys are dark reddish brown (except feline which are yellowish red). A cross section shows the external cortex and
the internal medulla
The renal sinus contains the renal pelvis, blood vessels and fat. The renal pelvis is a funnel shaped reservoir that occupies
most of the sinus. Passing out of the sinus is the ureter, the outlet tube that extends to the bladder
Medullary pyramids make up the medulla, stud the walls of the renal sinus. Urine collects
through ducts
The nephron is the functional unit of the kidney, consisting of the renal corpuscle and the renal tubule. There are about 1 million
nephrons I the kidney
The renal corpuscle consists of a double walled cup shaped
structure called the glomerular or Bowman’s capsule, which
contains a twisted cluster of capillary channels called the
glomerulus
Kidney functions as a filter for waste products from the blood and excretes them in the urine. These
waste products include: *nitrogenous waste from the breakdown of proteins, toxic
substances, mineral salts, excess glucose and water.
Video the urinary systemVideo the anatomy of the kidney
The speed that the blood filters through the kidneys is affected
by the blood pressure. If systemic blood pressure drops, as in shock, it may cause blood filtration to slow to a point to
where the kidneys stop functioning. If the blood
pressure is too high, kidney damage may result
The kidneys affect the rate of secretion of some hormones,
synthesize other hormones and maintain the pH of the blood so
it remains neutral.
The UretersThese are muscular tubes
extending from the renal pelvis of the kidneys. The walls of the ureters are made up of an outer fibrous tissue layer, two central layers of smooth muscle and a
mucous membrane lining.
The ureters enter the neck of the bladder at the trigone. The
ureters enter the bladder obliquely, the flow of urine back
to the kidney is effectively controlled by a natural valve
Urine enters the bladder on average of every 10 to 30 seconds in spurts, rather than a continuous flow. These spurts are produced by peristaltic waves. At
the bladder entrance there is is a ureteral opening that opens every 2 – 3 seconds,
then it closes until another peristaltic wave open it again. This prevents urine
from flowing back into the ureters during bladder contraction
The Urinary BladderThis is an elastic sac lying in the
pelvis.. It is formed of three layers of smooth muscle lines with mucous membrane. The size and position depends on
how much urine it contains. It has two openings to receive urine from the ureters and
another opening into the urethra
The neck of the bladder, uniting with the urethra contains a
sphincter muscle that controls the amount of urine into the
urethra. The bladder has two main functions:*to store urine
*to excrete urine
The voiding of urine from the bladder is called micturition.
The act of preventing or concluding urination is a learned
and voluntary action in more intelligent forms of animal life
The urethra is a membranous tubular canal that carries urine from the bladder to the exterior of the body. In the female the
urethra length varies by species. The exterior opening of the urethra is called the urinary
meatus
In the female the urinary meatus is located between the vagina and the clitoris directly cranial to the vulva. The only function
of the urethra is urination.
The male urethra varies in length by species and penile structure.
It is narrower than the female and this makes the male more prone to blockages from urolithiasis. (stone formation) It extends from the neck of the bladder
through the accessory sex glands, between the fascia and through
the penis.
The male urethra is divided in to three sections.
*prostatic*membranous*cavernous.
The exterior opening is also clled the urinary meatus and serves a
dual function, carrying both urine and reproductive secretions
Normal Urine:Urine in most species is clear,
pale amber with a characteristic odor. Urine is approx 95% water containing dissolved substances
such as nitrogenous waste, electrolytes, toxins, pigments,
hormones, and abnormal substances like glucose, albumin
or blood
The average urine output in a 24 hour period varies by:
*species*temperature*water intake
*type of work animal is performing
Male Reproductive Organs:The basic male reproductive organs
(gonads) are the testes. The ducts are the epididymides, vas deferentia,
ejaculatory ducts and urethra.The accessory sex glands (not present in all species) include the seminal vesicles, prostate, bulbourethral and coagulating
glands. The penis, scotum and spermatic cord are the primary structures
The Testes:A pair of egg shaped glands
normally located in a sac like structure called the scotum. The
size shape and location vary depending on the species. Each testicle is enclosed in a fibrous, white capsule called the tunica
albuginea.
The interior of the testicle is divided into compartments each
containing a mass of coiled seminiferous tubules and
interstitial cells (cells of Leydig), which join into a cluster and enter
the head of the epididymis.
The testes have two functions:*producing spermatozoa
*secreting hormonesthe sperm cells are produced by the seminiferous tubules. The
primary hormone, testosterone, is secreted by the cells of Leydig.
Testosterone has several functions:
*induces and maintains male secondary sex characteristics
such as massive head and shoulders, crest of withers, tusks on boars and horns on rams. It
also influences muscle and bone growth
Male Female
Male animals generally have less subcutaneous fat and the meat is less tender and juicy. Castration
is performed on all animals intended for meat production to
eliminate accumulation of testosterone after maturity.
Testosterone also has an influence on fluid and electrolyte
metabolism as well as as an excitatory effect on the kidney tubule and suppresses anterior
pituitary secretions
Epididymus:a pair of tightly coiled tube like
structures. They act as a place for sperm to mature, store sperm before ejaculation and they
secrete a small portion of the seminal fluid
Vas Deferens:a pair of muscular tubes with diameters that
vary by species. They are the continuation of the tail of the epididymis and runs through
the inguinal canal. Each epididymis is encased in the spermatic cord. Then they travel to the bladder and connect with the
seminal vesicle and form the ejaculatory duct. The vas deferens moves sperm from the tail
of the epididymis to the ejaculatory duct
Ejaculatory ducts:two short tubes formed by the
joining of the vas deferens with the ducts of the seminal vesicles. They pass through the prostate gland and extend to the urethra
Vesicular glands (seminal vesicles, term used in stallions):two twisted pouches lying along the dorsal and caudle surface of
the bladder, ventral to the rectum. They are lacking in the dog and cat. They secrete the
mucid, liquid part of the semen
Prostate gland:smooth muscle and glandular tissue. It secretes a viscous,
alkaline substance that makes up most of the seminal fluid. The alkalinity protects the sperm.
Spermatic cords:White fibrous tissue encasing the
vas deferens, blood and lymph vessels and nerves
Scrotum:saclike structure that houses the
testicles. It is separated internally by the scrotal septum.
The scrotum regulates the temperature of the testicles
Penis:made up of three rounded masses
of erectile tissue encased in a fibrous capsule. The penis contains the urethra which carries both reproductive
secretions and urine
Female reproductive organs:The ovaries:
located caudle to the kidneys. Each ovary is connected to the uterus by a ligament. A single layer of cells
forms the ovarian surface. The interior consists of a network of
connective tissue where the follicles are embedded, and these
contain the ova.
The functions of the ovaries are ovulation and hormonal secretion (estrogen and
progesterone)Estrogen induces female
characteristics and uterine preparation.
Progesterone prepares the uterus to receive the fertilized ovum
Fallopian tubes (ovaducts):consist of an inner ciliated mucous membrane layer, a
middle smooth muscle layer and outer layer of serous tissue. This acts as ducts to the uterus for the ova. Fertilization usually takes
place in the fallopian tubes
Uterus (metro, hystero):This is thick walled hollow organ. It is
made up of the body (corpus), the cervix (neck), and two horns (cornus)
The walls are made of three layers * endometrium (inner)myometrium (middle)perimetrium (external)
The perimetrium is continuous with a band of the peritoneum known as the
broad ligament.
The uterus has several functions:* prepares for the acceptance of the
fetus* develops specialized structures
for attachment of placenta* produces uterine milk to nourish
the embryo before implantation* maintains and supports
developing fetus* contracts to move fetus into birth
canal
The Cervix:Composed of smooth muscle
arranged in a ring like structure called a sphincter.
It prevents foreign bodies from entering the uterus during gestation.
It is usually tighly closed exceot during estrus when it relaxes to allow sperm to enter. During
pregnancy the cervix is filled with a mucous plug.
The Vagina:an elastic tube lined with a mucous
membrane. Before sexual maturity the external vaginal orifice may be occluded by a fold of mucous membrane called the hymen.
The vagina acts as a sheath to accept the penis during copulation and
provides passage for uterine secretions and the neonate during pregnancy
The Vulva:The vulva consists of the vaginal
orifice, vestibular glands, clitoris, hymen, and the urethral
orifice.
Mammary Glands:These are milk producing glands
composed of connective and adipose tissue. The milk secreting cells
(alveoli), these form larger ducts called the udder cistern. This transports milk
to the base of the teat.Milk production is stimulated by the lactogenic hormone prolactin. The emptying of milk secreting tissue is caused by the hormone oxytocin.
The estrous cycle:The purpose of the estrous cycle is to
prepare the uterus to receive a fertilized ovum.
At the beginning of the cycle, ova within the follicles in the ovaries begin to
develop. They will continue to develop until they reach ripened follicle size
(graafian follicle). One or more of the graafian follicles rupture and the ovary is
expelled
Ovuation usually occurs during estrus. The ruptured follicle grows larger and fills with a yellow lipoid
material and becomes the corpus luteum. The corpus luteum secretes progesterone. If fertilization occurs,
the corpus luteum continues to secrete progesterone and prevent
future estrous cycles during pregnancy.
If fertilization does not take place the corpus luteum and its secretions deminish forming a
corpus albicans.
The Stages of Estrus:The estrus cycle is divided into four
phases*proestrus
*estrus*metestrus
*diestrus and in some species*anestrus
Proestrusthis is the building up phase. During
this phase, follicle stimulating hormone (FSH) is secreted by the
pituitary gland and causes the follicle to develop within the ovary. FSH stimulates the ovary to release
increased amounts of estrogen which causes changes to the vagina,
uterus, oviducts and ovaries.
EstrusThis is the period of sexual
receptivity. Ovulation occurs during this phase and in some
cases right after this phase. FSH levels decrease and luteinizing
hormone (LH) increases causing the ripened follicle to rupture
Metestrusthis is the postovulatory phase.
During this phase the corpus luteum forms and produces progesterone.
Amounts of estrus decrease. Progesterone is responsible for proper
implantation and maintaining pregnancy. If pregnancy does not occur the corpus
luteum decreases in size to a corpus albicans. The cycle continues metestrus
will be followed by pregnancy, false pregnancy, diestrus, anestrus.
Diestrus and AnestrusDiestrus is a short inactive phase
before the onset of the next proestrus in polyestrus animalsAnestrus is a period of sexual
inactivity. Canines are in estrus twice a year and have long periods of anestrus between
cycles
Pregnancy:This is the period between conception and parturition. After fertilization, the ova moves from the uterine tube to the
uterus. Until implantation the organism is called an embryo. After implantation
the organism is called a fetus. The placenta is the only connection between
the dam and the fetus.
Gestation periods vary:bovine: 280 daysequine: 336 days
caprine, ovine: 150 daysporcine: 114 days
canine and feline: 63 days