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