tubule will make final adjustments to the filtrate , which will be dependent on several factors . Sodium reabsorption ( and potassium excretion ) is controlled by aldosterone to help maintain blood pressure , and hydrogen is excreted to maintain the acid – base balance .
The urine will then pass into the collecting ducts , with a number of nephrons emptying into the same collecting duct . Here there is a chance for water to be reabsorbed through the release of ADH , if required . The urine then moves into the renal pelvis to drain into the ureter .
Lower urinary tract
The lower urinary tract ( LUT ) collects and stores the urine until there is enough volume to be expelled . The organs that form the LUT are the ureters , bladder and urethra [ 5 ] .
Ureters
Each kidney has a ureter , which transports the urine to the bladder by peristaltic waves . The ureters enter the bladder close to the neck , through the trigone on the dorsal surface . The angle of the ureters entering the bladder prevents reflux of urine back into the ureters . The neck of the bladder ends at the sphincter , which consists of two parts : the internal sphincter ( smooth muscle , involuntary control ) and the external sphincter ( striated muscle with voluntary control ).
Assessment of learning
1 . Where in the kidney does filtration occur ? ( a ) In nephrons ( b ) In neurons ( c ) In a newton ( d ) In a nebula
2 . The activity of which vitamin is regulated by the kidneys ?
( a ) A ( b ) B ( c ) C ( d ) D
3 . Which organs form the lower urinary tract ? ( a ) Kidney , ureters , bladder ( b ) Ureters , kidney , urethra ( c ) Ureters , bladder , urethra ( d ) Bladder , kidney , urethra
4 . By the time the filtrate reaches the distal convoluted tubule , it is approximately what percentage of its original volume ?
( a ) 10 ( b ) 15 ( c ) 20 ( d ) 25
Bladder
The bladder is a pear-shaped organ that sits within the retroperitoneum but can be felt in the caudal abdomen when full . The main role of the bladder is to store urine . This is controlled by sympathetic nerves acting on the detrusor muscle to relax it and allow the bladder to fill . The bladder sphincter contracts to prevent urine leakage . Once the bladder is full , stretch receptors in the smooth muscle in the bladder wall are stimulated and send nerve impulses to the spinal cord . Parasympathetic nerves act on the detrusor muscle to cause contraction and the bladder sphincter relaxes . Urine is expelled only when both the internal and external sphincters are relaxed . If it is not appropriate to expel urine , the brain can exert voluntary control on the external sphincter to keep it closed .
Urethra
The urethra is the tube that carries the urine from the bladder to the outside of the body . In males , it has an additional role to carry sperm and spermatic fluid from the prostate gland to the penis as part of the reproductive system . The urethra is shorter in females , which reduces the risk of blockage . There is a difference between male dogs and male cats in the placement and anatomy of the urethra ( Figures 2 and 4 ). The male cat has additional bulbourethral glands ( not shown ), which open into the lumen of the urethra in the bulb of the penis .
REFERENCES
4 . ( a ) 20
3 . ( c ) Ureters , bladder , urethra
2 . ( d ) D
1 . ( a ) In nephrons
Answers
1 VetNurse . The Urinary System . In : The Revision Guide for Student Nurses ( Part 1 ). Available from : https :// www . vetnurse . co . uk / nursing / w / vet-nurse-revision _ 1 / 512 / the-urinary-system [ Accessed 4 January 2024 ].
2 Sanderson SL . Overview of the urinary system . MSD Manual . 2022 . Available from : https :// www . msdvetmanual . com / urinary-system / urinary-system-introduction / overview-of-the-urinary-system [ Accessed 4 January 2024 ].
3 Wikivet . Urinary System Overview – Anatomy & Physiology . 2023 . Available from : https :// en . wikivet . net / Urinary _ System _ Overview _ - _ Anatomy _% 26 _ Physiology [ Accessed 4 January 2024 ].
4 Dallas S . Canine and feline anatomy and physiology . In : Aspinall V . ( ed .) The Complete Textbook of Veterinary Nursing . Oxford : Butterworth-Heinemann ; 2006 . p . 49 – 108 .
5 Fraser M , Girling S . Anatomy and physiology . In : Cooper B , Mullineaux E , Turner L . ( eds .) BSAVA Textbook of Veterinary Nursing . 6th ed . Gloucester : BSAVA Publications ; 2020 . p . 110 – 111 .
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