Thursday, October 4, 2012

Veterinary Anatomy Online - The urinary system

urinary system
consists of two kidneys, two ureters, the bladder, and the urethra

The kidneys are organs for nitration of plasma and plasma constituents from blood, and selective rebsorption of water and nutrients from the nitrate.
 With the exception of the lobulated kidneys of the cow and the heartshaped right kidney of the horse, most domestic animals have somewhat 

beanshaped kidneys
In the cow, sheep, and goat, particularly with a full rumen, the left kidney may be pushed to the right as far as the median plane or beyond. In these animals the left kidney may be much more loosely attached to the body wall than the right kidney and consequently the left renal artery and vein are longer than the right vessels. Like other abdominal organs, the kidneys are retro peritoneal  that is, they are located outside of the peritoneal cavity. However, the kidneys are more closely attached to the abdominal wall by fascia, vessels, and peritoneum than are other organs
The medial border of the kidney is usually concave and has a marked depression, the renal hilus, where blood vessels and nerves enter and the ureter and lymphatic vessels leave.
 The expanded origin of the ureter within the kidney is called the renal pelvis. It receives urine from the collecting tubules of the kidney. The cavity within the kidney which contains the pelvis is called the renal sinus. The renal pelvis has no relationship to the bony pelvis described as a part of the skeleton.
In the horse, sheep, and dog the collecting tubules empty onto a longitudinal ridge that projects into the renal pelvis. This ridge is called the renal crest. In the kidney of the cow and pig individual pyramids project into minor calyces, which in turn empty into major calyces. These major calyces in the pig kidney empty into the renal pelvis and thence into the ureter. The kidney of the cow has no pelvis, so the major calyces empty into the ureter directly.
The portion of the kidney immediately surrounding the renal pelvis is the medulla, which appears striated because of the radially arranged collecting tubules. These tubules form the basis for the renal pyramids, which have their apices at the renal pelvis and their bases covered by the cortex.
 In addition to collecting tubules, the medulla also contains some loops of Henle. The cortex, located between the medulla and the thin connective tissue capsule, presents a granular appearance because of the large number of (glomeruli). Proximal convoluted tubules and distal convoluted tubules are also located in the cortex in fairly close relation to the glomeruli and many loops of Henle.

urinary system-kidney

The blood supply to the kidney is much more extensive than the size of the organ would suggest.
 The two renal arteries may carry as much as one-fourth of the total circulating blood. The renal artery enters the hilus of the kidney and divides into a number of relatively large branches, the interloba arteries.
 These pass peripherally between pyramids almost to the cortex, where they bend abruptly and travel in an arched manner, suggesting the name arciform or arcuate arteries.
Each arciform artery gives off a number of interlobular arterioles of tbr glomeruli. Leaving the glomeruli, most of j the efferent arterioles break up into a capillaif j network that surrounds the rest of nephron. Those arterioles leaving glom< close to the medulla travel directly into medulla as arteriae rectae where they capillary networks around the collecting tubules.
Arcuate veins drain blood from both the cortex and medulla, pass through the medulla as interlobar veins, and enter the renal Lymph drains from the kidney to the lymph nodes.
 The kidneys of reptiles and amphibians receive a portion of blood from veins which drain the body wall or hind legs.
This system, the renal system, is not found as such in mammal, pampiniform plexus of veins which mammalian testicle is believed to be remnant of the more primitive renal tern.
The kidneys are supplied with symathetic nerves from the renal plexus, which. follow blood vessels and terminate glomerular arterioles. Branches of the vagus nerve may also supply the kidneys,The success of kidney transplantation suggest the nerves do not have much to do but may only control the blood vessels Both vasoconstrictor and vasodilator nerve in the kidney.

The ureter is amuscular tube which conveys urine from the pelvis of the kidney to the bladder.
 Each ureter passes caudally to empty into the bladder near its neck at an area known as the trigont. Which the ureter passes obliquely through the wall of the bladder forms an effective valve to return flow of urine to the kidneyThe urinary bladder is a hollow muscular organ that varies in size and position with the amount of urine it contains. The empty bladder is a thick-walled, pear-shaped structure located on the floor of the pelvis. As the bladder fills with urine, the wall become thinner, and most of the bladder is displaced cranially toward or into the abdominal cavity.
 Peritoneum covers a variable amount of the cranial portion of the bladder depending on its fullness. The caudal part of the bladder is covered with pelvic fasciaThe neck of the bladder is continuous with theurethra caudally, and the muscle of the bladder arranged in a circular manner at the neck of the bladder, forming a sphincter that controls passage of urine into the urethra.
The pelvis,ureter. Bladder and urethra all are lined with transitional epithelium. This epithelial lining is useful in these areas where considerable distention of the lumen may occur.
When these organs are empty the lumen is small, walls are thick, and the lining epithelial cells are piled deeply to form stratification. However, when the organ are distended, the lumen is enlarged, the wall are thinner,

 The kidneys are located in the dorsal part of the abdominal cavity on each side of the aorta and vena cava just ventral to the
first few lumbar vertebrae

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