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

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• 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

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• Erythropoietin: which influences erythropoiesis.

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

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• 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,
• 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

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

They are rarely symmetrical

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

General morphology

R

L

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

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

General morphology

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

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

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

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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.

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• The capsule restricts the kidneys ability to expand

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• 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.

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• The cortex is distinguished by its reddish-brown color and finely granular appearance.
• The medulla consists of:
• a dark, purplish outer zone
• a paler, grayish-red inner zone

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

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The internal organization of the kidney

Estimated number several

hundred thousand or even

a million in canine kidneys.

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Each nephron begins with

a blind expansion that is

invaginated by a

cluster 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

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• 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

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

Renal Pelvis and Ureter: �

Renal Pelvis and Ureter: �

• The ureter penetrates the bladder wall very obliquely.

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

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• 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 bones
• in 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

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

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The Urinary Bladder

• Three folds continue from the serosal covering onto the abdominal and pelvic walls.
1. Paired lateral vesical folds convey the round ligaments of the bladder
• these vestiges of the umbilical arteries
2. The third, median vesical fold
• is empty in the adult, but in the fetus it supports the urachus,

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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.