Changes

*[[Nephron Microscopic Anatomy  #The Vasa Recta| Vasa recta]]

*[[Nephron Microscopic Anatomy  #The Vasa Recta| Vasa recta]]

===Renal Pelvis===

===Renal Pelvis===

The renal pelvis is located within the renal sinus. The '''renal sinus''' is located within an indentation on the medial side of the kidney.  The renal sinus is a potential space, which is occupied by the ureter, branches of the renal artery and vein, lymphatics and nerves that enter the kidney at the hilus. The '''renal''' crest opens into the renal pelvis. The renal pelvis then drains into the ureters. The renal pelvis is lined with transitional epithelium and contains mucous glands in the horse; giving urine a frothy appearence. The '''terminal recess''' is unique to the horse. This is a long tube-like structure that collects urine from the poles of the kidneys into the renal pelvis.

The '''renal''' crest opens into the renal pelvis. The renal pelvis is an expansion where the proximal ureter begins. The renal pelvis is located within the renal sinus. The '''renal sinus''' is located within an indentation on the medial side of the kidney.  The renal sinus is a potential space, which is occupied by the ureter, branches of the renal artery and vein, lymphatics and nerves that enter the kidney at the hilus. In the horse, the renal pelvis consists of a central cavity and two large '''terminal recesses'''. The '''terminal recess''' is a long tube-like structure that collects urine from the poles of the kidneys into the renal pelvis. Most of the papillary ducts open into the terminal recesses. The renal pelvis is lined with '''transitional epithelium''' and contains '''mucous glands''' in the horse; giving urine a frothy appearence.

===Vascularization===

 

===Vascular Supply===

The kidney receives approximately 25% of cardiac output. Each kidney is supplied by a '''renal artery''', which is a branch of the '''abdominal aorta'''. The renal artery subsequently divides at the hilus of each kidney into '''interlobar arteries''', which run to the '''corticomedullary junction'''. Here they branch into '''arcuate arteries'''. The arcuate arteries then give rise to '''interlobular arteries''' which radiate into the renal cortex. The interlobular arteries become the '''afferent arteriole''' and subsequently the capillary loops of the glomerulus.  These capillary loops then unite to become the '''efferent arteriole''', which supplies a capillary network around the nephrons. This capillary network drains blood from the renal cortex into the '''interlobular veins''', '''arcuate veins''', then '''interlobar veins'''. The interlobar veins drain into the '''renal veins''', which subsequently drain into the '''caudal vena cava'''.

The kidney receives approximately 25% of cardiac output. Each kidney is supplied by a '''renal artery''', which is a branch of the '''abdominal aorta'''. The renal artery subsequently divides at the hilus of each kidney into '''interlobar arteries''', which run to the '''corticomedullary junction'''. Here they branch into '''arcuate arteries'''. The arcuate arteries then give rise to '''interlobular arteries''' which radiate into the renal cortex. The interlobular arteries become the '''afferent arteriole''' and subsequently the capillary loops of the glomerulus.  These capillary loops then unite to become the '''efferent arteriole''', which supplies a capillary network around the nephrons. This capillary network drains blood from the renal cortex into the '''interlobular veins''', '''arcuate veins''', then '''interlobar veins'''. The interlobar veins drain into the '''renal veins''', which subsequently drain into the '''caudal vena cava'''.

[[Image:ureterhistoanat.jpg|right|thumb|300px|<small><center>Histology section of a normal ureter (© RVC 2008)</center></small>]]

[[Image:ureterhistoanat.jpg|right|thumb|300px|<small><center>Histology section of a normal ureter (© RVC 2008)</center></small>]]

[[Image:ureterhistoanat2.jpg|right|thumb|300px|<small><center>Histology section of a normal ureter (© RVC 2008)</center></small>]]

[[Image:ureterhistoanat2.jpg|right|thumb|300px|<small><center>Histology section of a normal ureter (© RVC 2008)</center></small>]]

The ureters convey urine from the renal pelvis to the bladder.  There are two of them, one for each kidney. The ureters run retroperitoneally along the roof of the abdominal cavity and then enters the pelvis.  Once entering the pelvis it moves medially in the broad ligament of the female or the genital fold of the male.  It ends at its junction on the dorsolateral surface of the bladder within the lateral ligament.

The ureters convey urine from the renal pelvis to the bladder.  There are two of them, one for each kidney. The ureters run retroperitoneally along the roof of the abdominal cavity and then enters the pelvis.  Once entering the pelvis it moves medially in the broad ligament of the female or the genital fold of the male.  It ends at its junction on the dorsolateral surface of the bladder within the lateral ligament. The ureter then runs intramurally (within the bladder wall) before opening into the bladder lumen at slit-like openings known as '''ostia'''.

===Wall===

===Wall===

The wall of the ureters has an internal mucosa layer formed from transitional epithelium.  This provides protection against the urine. The middle layer is a muscularis layer. This is well developed for peristalsis, though can enter into spasm on irritation. The outer layer is composed of adventitia.

The wall of the ureters has an internal mucosa layer formed from transitional epithelium.  This provides protection against the urine. The middle layer is a muscularis layer. This is well developed for peristalsis, though can enter into spasm on irritation. The outer layer is composed of adventitia. In the horse, the wall in the proximal urethra contains mucous-producing glands.

===Junction with the Bladder===

===Junction with the Bladder===

The ureter enters the bladder obliquely near the neck of the bladder and runs between the muscular layers and mucosa. They open through 2 slits on a raised '''hillock'''.

The ureter enters the bladder obliquely near the neck of the bladder and runs between the muscular layers and mucosa. They open through 2 slits on a raised '''hillock'''.

===Lymphatic Drainage===

===Lymphatic Drainage===

* Lumbar lymph nodes

* Lumbar lymph nodes

==Bladder==

==Bladder==

*Intermediate body

*Intermediate body

*Caudal neck

*Caudal neck

Its wall comprises a muscle layer covered in '''transitional epithelium'''. Its size and posistion are determined by how full it is. When empty the bladder wall is wrinkled and thicker.  It rests on the pubic bones, entirely within the pelvis and is largely retroperitoneal. When full and distended, the folds disappear and the wall appears thinner, it then becomes intraperitoneal.

Its wall comprises a muscle layer covered in '''transitional epithelium'''. Its size and posistion are determined by how full it is. When empty the mucosa of the bladder wall is wrinkled and thicker.  The bladder rests on the pubic bones, entirely within the pelvis and is largely retroperitoneal. When full and distended, the mucosal folds disappear and the wall appears thinner, it then becomes intraperitoneal. There are two folds ('''plicae uretericae''') that do not disappear, even when the bladder is distended; these extend from the ureteral opening to the neck of the bladder before folding to become the '''urethral crest'''.

The '''trigone''' of the bladder gets its name as it looks like a triangle without a base.  It is of clinical importance and is formed by the paired '''ureteric folds''', which are comprised of the orifice of the ureters. The trigone is visible even when the bladder is full. Ureteral folds extend from the urethral opening to the neck of the bladder, where they merge to form the '''urethral crest'''. It is believed to have increased sensitivty and is of different embryological origin to the rest of tissue.  More details can be found [[Kidney and Urinary Tract Development - Anatomy & Physiology#The Bladder|here]].

The '''trigone''' of the bladder gets its name as it looks like a triangle without a base. The trigone is bounded by the '''plicae uretericae'''. It is believed to have increased sensitivty and is of different embryological origin to the rest of tissue.  More details can be found [[Kidney and Urinary Tract Development - Anatomy & Physiology#The Bladder|here]].

===Muscles of the Bladder===

===Muscles of the Bladder===

====Detrusor Muscle====

====Detrusor Muscle====

This network of smooth muscle fibres lie in three sheets within the bladder wall and are supplied by both parasympathetic and sympathetic nerves. It is responsible for storage and expression of urine from the bladder.

This network of smooth muscle fibres lie in three sheets within the bladder wall and are supplied by both parasympathetic and sympathetic nerves. It is responsible for storage and expression of urine from the bladder.

*Parasympathetic supply: This comes from S1-S3, synapses within the pelvic plexus, continues as the pelvic nerves and is excitatory to the destrusor muscle. Parasympathetic dominance allows emptying of the bladder.

The combination of the pre-prostatic and prostatic portions are called the pelvic portion.

*Sympathetic Supply: This comes from L1-L4, synapses within the caudal mesenteric ganglion in the bladder wall, continues as the hypogastric nerve and ends on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.

The '''''urethralis''''' muscle runs the entire length of the urethra and forms the '''external urethral sphincter'''. Unlike the [[Urinary Bladder - Anatomy & Physiology#Internal Urethral Sphincter|internal sphincter]], the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system.  

===Innervation of the External Urethral Sphincter===

The ''urethralis'' muscle receives somatic innervation originating from S1-S3 and continuing via the '''pudendal nerve'''. This releases the neurotransmitter Acetylcholine, which binds to nicotinic Acetylcholine receptors and mediates skeletal muscle contraction of the external urethral sphincter. This is important in urine retention.

==Urethra==

===Vascular Supply===