THE URINARY SYSYEM

THE URINARY SYSTEM

Paired kidneys form the urine from the blood

Ureters that convey the urine from the kidneys to the

bladder The bladder

where urine is stored until it can be discharged The urethra

through which urine finally passes to the exterior.

The kidney functions

1- Maintenance of the internal environment. They do this by filtering the plasma initially extracting an enormous volume of fluid subjecting the ultra filtrate to further

processing in which• useful substances selectively reabsorbed

• waste substances are concentrated for elimination

the volume is adjusted by the conservation of sufficient water to maintain the composition of the plasma

The kidney functions

In large dogs and animals of similar size 1000 to 2000 L of blood perfuse the kidneys daily

the 200 to 300 L of fluid that are filtered from this volume are later reduced by reabsorption until only 1 or 2 L of urine remain to be discharged

The kidney functions

2- The endocrine function consists of the production and release

of two hormones:• Renin, which plays a vital role in the

regulation of systemic blood pressure

• Erythropoietin, which influences erythropoiesis.

The kidneys are firm, reddish-brown glands whose appearance varies:

The most familiar “kidney-shaped” to the common vocabulary, is encountered in the dog, cat, and small ruminants.

The kidneys of the pig are a much flattened version, whereas those of the horse are more heart-shaped .

In contrast, the bovine kidneys are deeply fissured to outline many lobes

General morphology

General morphology

The kidneys are usually found pressed against the abdominal roof

one to each side of the vertebral column, and mostly in the lumbar region

General morphology

They are rarely symmetrical

the right one is about half a kidney-length in advance of its fellow

The cranial extremity of the right kidney commonly fits into a fossa of the liver, which helps fix its position

The left one, lacking this lodgment, is more mobile and is more likely to sag within the abdomen (pendulous left kidney)

R L

General morphology

• The surface of a kidney is generally smoothly convex except for an indentation of the medial border

• This indentation leads to a concealed space occupied by the dilated origin of the ureter (renal pelvis)

• The vessels and nerves passing to and from the renal hilus

The internal organization of the kidney

Longitudinal section will divide the organ into dorsal and ventral “halves.

Such a section shows that the parenchyma is enclosed within a tough fibrous capsule.

The capsule restricts the kidney’s ability to expand

• the swelling that occurs in certain disease conditions

• tends to compress the tissue and narrow the internal passages.

The internal organization of the kidney

The parenchyma is visibly divided into an outer cortex and an inner medulla.

The cortex is distinguished by its reddish-brown color and finely granular appearance.

The medulla consists of: a dark, purplish outer zonea paler, grayish-red inner zone

In many species the medulla is arranged as several discrete masses, each roughly pyramidal in form.

The internal organization of the kidney

The functional units of the kidney The functional units are known as renal tubules or

nephrons. These epithelial tubules are supported by a

connective tissue interstitium

• estimated number several hundred thousand or even a million in canine kidneys.

Each nephron begins with a blind expansion that is invaginated by a cluster of capillaries known as a glomerulus

The glomerulus and its epithelial covering together constitute renal corpuscle.

Estimated number severalhundred thousand or even a million in canine kidneys.

Each nephron begins witha blind expansion that isinvaginated by acluster of capillaries known as a glomerulus

The functional units are known as renal tubules or nephrons.

The general organization of the kidney

The remaining part of the nephron forms a long tubules differentiated into several successive segments

1- Proximal convoluted tubule 2- A long hairpin loop 3- Distal convoluted part that. 4- Collecting tubule within the

medullary ray. Each collecting tubule, which

serves many nephrons, runs through the medulla before opening into a larger vessel,

5- A papillary duct

Blood supply

Each kidney is supplied by a renal artery

The renal artery divides into several interlobar arteries They give rise to

branches known as Arcuate arteries

Blood supply

Arcuate arteries in turn give origin to numerous interlobular arteries that supply the units or lobules (cortex)

Each interlobular artery gives rise to many branches that supply individual glomeruli

The glomerular capillaries rejoin in one emissary vessel at the distal pole of the glomerulus

Renal Pelvis and Ureter :

In most domestic species the ureter begins in a common expansion, the renal pelvis All the papillary ducts open

The ureter penetrates the bladder wall very obliquely.

The length of the intramural course guards against reflux of urine into the ureter when the pressure is raised within the bladder.

It does not prevent further filling of the bladder since the resistance is overcome by peristaltic contractions of the ureter wall.

The Urinary Bladder

The bladder is a distensible storage organ and thus can have no constant size, position, or relationships.

The contracted bladder rests on the pubic bonesin the larger species it is confined to the

pelvic cavity in carnivores extends into the abdomen

The Urinary Bladder

In the larger species the contracted bladder is largely retroperitoneal

but most of the surface becomes intraperitoneal when the organ is even moderately expanded.

The Urinary Bladder

Three folds continue from the serosal covering onto the abdominal and pelvic walls.

Paired lateral vesical folds convey the round ligaments of the bladder

• these vestiges of the umbilical arteries

The third, median vesical fold

• is empty in the adult, but in the fetus it supports the urachus,

The Female Urethra

The female urethra runs caudally on the pelvic floor below the reproductive tract. It passes obliquely

through the vaginal wall to open ventrally at the junction of vagina and vestibule.