Urinary System & Kidney Anatomy

• Urinary organs include the kidney, ureter, urinary bladder, and urethra
• The kidneys are referred to as Ren s.nephros and exist as a paired organ in domestic mammals and poultry
• Ureters connect the kidneys to the urinary bladder and are also paired
• The urinary bladder is also known as Vesica urinaria
• The urethra serves as the terminal part of the urinary system

Kidney

• Also referred to as REN and nephros
• Kidneys are paired and have a firm consistency
• The kidneys are located in the abdominal cavity and lumbar region in a retroperitoneal position
• The right kidney is positioned more cranially than the left, except in pigs (su)
• In most mammals, the kidney is bean-shaped, however this varies among species with birds differing in morphology
• Tthe color is reddish-brown

Kidney Structure

• Kidneys have lateral and medial borders
• The Margo medialis features the Hilus renalis, where the renal artery enters and the renal vein and ureter exit
• The ventral and dorsal surfaces are called Facies ventralis and Facies dorsalis, respectively
• Kidneys exhibit cranial and caudal ends
• The Capsula fibrosa is a fibrous capsule intimately covering the external cortical surface that covers the kidney and extends inward at the hilus to the renal sinus
• The Capsula adiposa renis is an adipose capsule with a variable amount of perirenal fat, which is thicker dorsally
• The Fascia renalis consists of two layers enclosing the kidney and the Capsula adiposa
• The Peritoneum covers the ventral surface (facies ventralis) of the kidney

Internal Kidney Structure (Parenchyma)

• The kidney consists of STROMA and PARENCHIMA
• Nephrons serve as the structural and functional unit of the kidney
• Nephrons are made up of the corpuscula renis and tubulus renalis
• A glomerulus is a cluster of capillaries within a shell called Bowman's capsule
• Nephrons attach to collecting tubules located within the stroma which facilitate urine flow
• The medulla is where urine is concentrated through tubules with pyramids, and constitutes the inner-most part of the kidney
• The outer portion, called the cortex, is lighter in color and has a granular texture as this is where the blood is filtered through the glomeruli

Functional Anatomy

• Lobus renalis refers to a renal lobe, including a renal pyramid and its cortical cap
• Pyramides renales are renal pyramids with the base at the cortex and the apex forming the renal papilla;
• The number of renal pyramids varies by species
• Pigs (su): 10-12
• Sheep (ov): 10-16
• Cattle (ca:) 12-17
• Horse (eq): 40-64
• Columnae renalis are renal columns, composed of sections of cortical tissue between the pyramids
• Papilla renalis is the tip of the pyramid
• They are separate with their own calyx in ox (bo) and pigs (su)
• They are fused from the crest in dogs (car), sheep (ov), goats (cap), and horse (eq)

Internal Structure

• Calices renales are renal calices, cup-like expansions (calix) of the renal pelvis
• Calices minores are minor renal calices that receive papillae
• Calices majores are major renal calices forming the primary branches of the renal pelvis
• Pelvis renalis refers to a renal pelvis, a space which collects urine, extending at the ureter's beginning
• Sinus renalis is a cavity within the kidney at the hilus containing fat, connective tissue surrounding the renal pelvis, and vessels

Kidney Types

• Kidney types in domestic mammals vary based on the degree of fusion
• Smooth unilobar kidneys have a fused cortex+medulla
• They feature a smooth external surface and a single papilla internally/renal crest
• Found in dogs (car), horses (eq), sheep (ov), and goats (cap)
• REN of the dog:
• Found in the abdominal cavity, in the ventral position relative to VTh 12-13 ↔ VL 3 on the right
• It is located ventrally to VL 1-5 on the left
• Bean shaped, dark brownish to bluish red in color
• Weighs 40-60g in large dogs
• Features 12-17 renal pyramids leading to a single Papilla renalis
• Crista renalis then links to the Pelvis renalis
• REN of the cat:
• Found ventrally between VL 1-4 on the right and VL 2-5 on the left
• About 38-44 mm x 27-31 mm x 20-25 mm
• Weighs 7-15 g
• Distinct venous network on the surface
• Renal papilla → Crista renalis → Pelvis renalis
• Kidney of small ruminants:
• The right kidney is located ventrally to VTh13 ↔VL 2 with the left extending to VL 4-5
• They are bean-shaped and light brown
• Short with 5.5-7cm dimensions, almost circular on cross-section
• Weighs 100-160g
• Hilus renalis is shallow
• Significant amount of perirenal fat present
• The kidneys are surrounded by large masses of fat reducing the mobility of the left kidney
• REN of horse:
• Bean-shaped on the left
• Heart-shaped on the right
• Both are smooth-unilobar
• Smooth multilobar kidneys have a smooth external surface and multiple papillae internally
• Each papilla is surrounded by a calyx minor with several merging into a calyx majore
• The cortex and the zona externa of the medulla are fused
• REN of pig:
• The pig kidney is in the abdominal cavity, lumbar region
• Located ventrally to VL1-4
• Not touching the liver on the right side
• Smooth multilobar (multipyramidal) with 8-12 papillae
• Lobated multilobar kidneys are lobated externally with numerous internal papillae and have zona interna of CORTEX and zona externa of MEDULA
• Each lobe has a renal pyramid and cortical cap
• REN of ox (Bovine kidney ):
• The right kidney is 18-24 cm long
• Located at the level of VTh13 ↔VL 1-2
• Weighs 1.2-1.5 kg
• The left kidney is 19-25 cm long
• Located at the level of VL 2 ↔ 5
• It is caudoventrally to the right
• Connected to the rumen of the left side and the colon on the right

Ureter

• The ureter is a paired duct which transports urine from the kidney to the urinary bladder
• It comprises two parts
• The abdominal part (pars abdominalis) from the pelvis renalis through the hilus renalis towards the caudal direction
• The pelvic part (pars pelvina) extending from the pelvic cavity to the urinary bladder
• It has three layers of tissue
• Tunica adventitia (fibrous outer coat)
• Tunica muscularis (functional layer using peristalsis for urine movement)
• Tunica mucosa
• Ureters penetrate the dorsolateral wall of the urinary bladder very obliquely
• Extending intramuraly for 2 cm prior to entering the lumen through two slits or ureteric ostium

Urinary Bladder

• The urinary bladder is also known as VESICA URINARIA
• It consists of 3 defined regions
• Apex vesicae (the blind cranial end)
• Corpus vesicae (the body, located between the apex and the neck)
• Cervix vesicae (neck, funneled shaped caudal region that connects to the urethra)
• No constant place that depends on fillness
• When full, extends into peritoneal cavity (caudoventral abdomen)and cranial to the pubis
• When empty, on ventral floor of the pelvic cavity
• It is ventral to the uterus, rectum and descending colon
• When the bladder is empty it is smaller
• Contraction of the mucosa causes many irregular folds
• Folds and transitional epithelium stretching when filled with urine

Urinary Bladder Anatomy

• Columna ureterica refers to ureteral columna of elevated mucosa, produced by the ureter within the wall of the bladder
• Plica ureterica are uretral folds, that forms the urethral crest continuous with the urethra
• This forms the trigonum vesicae, a smooth area on the dorsal internal wall of the bladder between ureteral and urethral orifices
• Includes:
• Apex vesicae
• Corpus vesicae
• Ureter
• Ostium ureteris
• Trigonum vesicae
• Crista urethralis
• Urethra

Urinary Bladder Ligaments

• There are three ligaments associated with the urinary bladder
• Lig. vesicae laterale: Attaches dorsolaterally in males and via the broad ligament in females, includes Lig. teres vesicae)
• Lig. teres vesicae: the round ligament of the urinary bladder
• Lig. vesicae medianum: Attaches ventrally to the Symphysis pelvina and Linea alba

Urethra

• The urethra is the final passageway for urine out of the bladder
• Thin-walled tube from cervix of the urinary bladder
• Extends through internal urethral orifice (ostium urethrae internum) to the external urethral orifice (ostium urethrae externum).
• The female urethra (Urethra feminina) exclusively transports urine
• The Male urethra (Urethra masculina) serves as excretory passage for urine and semen

Female Urethra Details

• Length: -- Dogs (ca), horses (eq), and pigs (su): 6-8 cm -- Ox (Bo): 10-13 cm
• Extends from ostium urethrae internum to the external urethral orifice (external urethral orifice)
• Connects to the vestibulum vaginae
• Features diverticulum suburethrale, which a blind sac vetral to the urethra that that opens into the urethral orifice

Male Urethra Details

• The male urethra serves as a shared pathway for products of the urinary and reproductive systems
• The urethra includes:
• The Pelvic part (pars pelvina)
• The Penile part (pars penina)
• The terminal end at the osmium urethrae externum at the apex of the glands penis

Avian Urinary Organs

• Avian urinary organs include the Kidneys and Ureters which attach to the Cloaca-Urodeum
• Avian kidneys are paired, brown reddish, and extend toward both lungs
• They are located in the fossa renalis ventral to the synsacrum

Avian Kidney Anatomy

• Three renal divisions: cranial, middle, and caudal
• Avian kidneys do not include pelvis renalis
• Avian kidneys do not include papila renalis

Avian Ureters

• The ureter (paired) emerges from the ventral surface of the kidney's middle renal division
• Ureters enter the dorsolateral wall of the cloaca at an acute angle
• They will open into urodeum at the ureteric ostium (ostium cloacale ureteris)