List structures that make up urinary tract and broadly what they do
- Kidney
- Ureters - convey urine from the kidneys to the bladder
- Bladder - storage of urine prior to evacuation
- Urethra - convey urine from bladder to outside world
positioning of kidney
What can you palpate in dog
- Located DORSAL abdomen, just behind ribs
- L caudal to R.
- In dog may palpate left kidney (difficult if fat), R kidney under costal arch, relatively fixed; L more mobile, position variable. In cat both kidneys palpable and relatively mobile
How much blood supply to kidneys receive?
o Kidneys receive 20 – 25% of cardiac output via renal arteries
Function of ureters
- how do they course
enter bladder at waht
- what process moves urine
- Urine passes from collecting ducts into renal pelvis and then enters ureters – fibromuscular tubes, lined by transitional epithelium. Ureters course retroperitoneally and enter the bladder at the trigone. Urine is moved by peristalsis.
Function bladder
- Urine collects in the bladder and is stored before voiding. Lined by transitional epithelium, layers of smooth muscle and outer serosa. Innervation and control of micturition is complex - covered in incontinence seminar
Function urethra
- Conveys urine from neck of the bladder to the outside. 3 layers of smooth muscle, plus external sphincter of voluntary striated muscle. Transitional epithelium apart from terminal part in male – stratified squamous. Male has three parts – prostatic portion, pelvic or membranous portion and cavernous or penile portion
Functions of kidney
- Regulation of fluid volume and electrolyte homeostasis
- ECF and blood pressure
- Osmolarity
- Ion balance
- pH
- Nitrogenous waste excretion
- Metabolic waste e.g. urea
- Urea produced from metabolism of amino acids
- Got rid off through kidney and urine
- Formed in the liver
- Foreign substances e.g. medicines
- Production of hormones: modified and/ or produced
- Activation of vitamin D3
- Synthesis of erythropoietin – hormone responsible for driving production of RBC in bone marrow
- Synthesis and release of the enzyme renin – control of blood pressure
- Acid-base homeostasis
- Synthesis of calcitriol (active vitamin D3 / 1,25-dihydroxycholecaliferol)
- Erythropoietin production
- Renin production
- Blood pressure homeostasis
- Catabolism of peptide and protein hormones in renal tubules e.g. gastrin, insulin, glucagon, growth hormone
Nephron
functional unit of the kidney composed of tubules and blood vessels (v important for function) that collect the filtrate with will ultimately become urine
Renal anatomy broadly
- Two distinct regions of the internal anatomy:
- outer cortex = filtration to form urine
- Glomerulus sits in OC
- Inner medulla = collect and excrete urine
- Loop and collecting duct
One collecting duct has what entering
LOTS of DCT
Blood flow through kideny
- 20-25% cardiac output passes through renal arteries to be filtered by kidney
- REnal artery - segmental arteries - arcuate arteries - interlobular arteries - afferent arteries - glomerulus - efferent arteriole - peritubular capillaries - venules - interlobular veins - arcuate veins - interlobar veins - renal vein
What is unique about the kidney blood supply?
- Capillary portal system
2. Glomerulus (capillaries, sits between 2 arterioles, the afferent A and efferent A, not V)
Reabsorption in PCT
- extensive
- active and passive
- Around 70% of filtrate is reabsorbed in PCT
- Peritubular capillaries have v high oncotic pressure
Why is oncotic pressure so high in peritubular capillaries
a) Because those caps are derived from efferent arteriole and loads fo filtrate is taken out of system just upstream of efferent arteriole
When filtrate reaches the DCT it is:
- HyPO osmotic
- 90% filtered Na has been reabsorbed
- 80% filtered water has been reabsorbed
- 100% bicarbonate has been reabsorbed
Clinically what are important things to know what happens to, about kidney
what happens to water, Na and K+ ions, Ca and phosphate ions and Acid base
If obstruction stops urine output, what will build up?
urea, creatinine, K+ and phosphate will build up
• Phosphate is one of the best metrics for whether the animal will recover
- Explain the forces responsible for filtration
- Same forces as bulk flow just increased pressure – massive blood supply in afferent arteriole also hydrostatic BUT MUCH greater volume
BULK flow: - Difference in hydrostatic pressure between 2 sides of filter
- Difference in protein-osmotic pressure between 2 sides of filter
How does oncotic pressure change in glomerus?
V little protein forced out of g caps so oncotic pressure gets increasingly greater
How come filtration occurs across whole capillary bed?
In theory, across whole bed of glomerular capillaries, the hydrostatic pressure would keep forcing fluid out until balanced out by oncotic pressure
In practise SUCH big blood flow and pressure differential, pressures don’t abalnce out filter WHOLE length of glomerular caps until E arteriole
3 factors that mean filtration is so large
- large SA due to many capillaries
- Greater pressure than in cap beds
- Huge volume of blood going through this system
what is GFR and how does this vary?
- GFR is Vol of fluid filtered from glomerular capillaries into bowman’s space per minute
- Varies with metabolic mass of animal:
70% volume is reabsorbed.
Why design something that filters lots out and reabsorbs most back within a few seconds
- Anything filtered into nephron (20 mins) is destined for removal in the urine unless it is reabsorbed
- E.g. quick way of getting rid of poisons in blood!
Where does the bulk reabsorption occur and what is it described as being?
- PCT
- selective but unregulated:
s - most things aren’t so fat soluble won’t get through membranes (channels
U - no hormonal type control
