Urinary System I Flashcards
Kidney macroscopic structure
- Cortex and medulla
o 1:2 or 1:3 (1:5 for animals who need to conserve water=camels)
Cortex structure
- Dark red or brown
- Radial streaks on cross section
Medulla structure
- Light red or grey
- Pyramids or lobes
- Apex of each lobe=renal papilla
What is the only animal with a unipyramidal kidney?
- Cats
o One lobe during embryo stage and after birth
What are the animals with a unipyramidal kidney?
- Dogs
- Cats
- Horses
- Sheep and goats
- *all but cats, are actually multipyramidal in the embryo stage
- *renal pyramids and papilla fuse together in late development=renal crest
What are the animals with a multipyramidal kidney?
- Bovine
- Porcine
Bovine kidney
- Multipyramidal
- External lobation
Pig kidney
- Multipyramidal
- NO external lobation
- Dorso-ventally flattened
Cat kidney
- Unipyramidal
- **Yellow cortex
o Lots of fat stored within renal tubules normally (ex. obese cat) - Prominent subscapular veins
Granulomatous inflammation=white nodules (DDx: neoplasia, likely lymphoma) on a cat kidney, LOCATION
- If nodules along capsular vesicles=FIP
- If not along=neoplastic
Dog, sheep and goat kidney
- Unipyramidal with renal crest
Horse kidney
- unipyramidal
- Right=heart shaped
- Left=bean shaped
- *urine of horses appears turbid due to lots of calcium carbonate=NORMAL
What are the 4 microscopic structures of the kidney?
- Vessels
- Glomeruli
- Tubules
- Interstitium
- **INTERDEPENDENT=if damage one part=damage ALL parts
o Why in chronic conditions kidney will grossly look the same no matter the primary cause
Vascular supply of the kidney
- Receive 20-25% of CO (weights less than 1% of the body)
o Good place to culture if suspecting septicaemia - *major regulator of systemic and renal blood pressure
- Supplied by end arterioles (ex. no anastomosis)
Where is the number place to culture if suspecting septicemia?
- Spleen
- Kidney is good second choice
What can happen to BP if kidney failure?
- Get hypertension
- But hypertension can also cause kidney failure
Why is the kidney prone to infraction (necrosis secondary to loss of blood supply)?
- End arterial blood supply with LIMITED collateral circulation=PRONE
What is the ‘pathway’ of the vascular supply to the kidney?
- Renal artery
- Interlobar artery
- Arcs and courses into cortico-medullary junction= arcuate artery
- Branches into multiple interlobular arteries
- Each branches to multiple afferent arterioles
- Each leads to a glomerulus
- Efferent arteriole leading to vascular plexus of small capillaries surrounding the tubules (vasa recta)
What kind of blood is the blood supply after the glomerulus?
- Still arterial
- *if damage glomerulus=decreasing blood supply to tubules causing tubular damage
What 2 receptors does the kidney have to regulate the flow of blood?
- BP
- Na
- *release 3 molecules ADH, Ang-II and aldosterone
- **2 receptors do 3 things
What is a part of the juxtaglomerular apparatus? (4)
- Juxtaglomerular cells (afferent arteriole)
- Efferent arteriole
- Macula densa (distal convoluted tubule)
- Mesangial cells
What does the kidney/juxtaglomerular apparatus respond to (3)?
- Depletion of ECF >ADH release
- Decrease in renal BP >Ang II
- Decrease in sodium concentration > aldosterone
What happens if there is a decrease in BP, ECF or Na concentration?
- Juxtaglomerular cells release renin
- Renin converts angiotensinogen to Ang-I
- Ang-I to Ang II via ACE
- Ang-II has 3 effects
What are the 3 effects of Ang II?
- Release ADH from pituitary: greater reabsorption and decrease water excretion
- Constriction of AA: less plasma filtered=conserve more water
- Release aldosterone from adrenal cortex=increase K excretion and Na retention (water follows Na)
What organ is affected the most with too much K?
- Heart!
o Need to pee it out!
Nephron
- Functional unit of kidney
- Fixed number throughout life time
- *all parts are interdependent=if damage one part=damage the whole nephron
o Collecting duct is NOT part of the nephron
Glomerulus function
- Production of ultrafiltrate
- Goes from vessels lined by endothelial cells to tubular structure lined by epithelial cells
Glomerulus structure
- Capillaries
o Many small ones to increase SA - Mesangial cells
o Hold together the capillaries - Podocytes (epithelial cells)
o Foot processes attached to basement membrane of capillaries
What is the glomerular filtration barrier composed of?
- Fenestrated endothelium
- Glomerular basement membrane
- Podocytes
What is between each 2 foot processes of podocytes?
- Filtration slit covered by a diaphragm
What is the selective permeability of the glomerular filtration barrier based on? (3)
- Size (<70,000 Da)
- Charge: negative=repelled (ex. albumin, some goes through ~70kDa)
- Capillary pressure: high=more filtration
Proximal convoluted tubules
- Reabsorb water solutes, glucose, AA
o BRUSHBORDER (microvillus border) - Excrete hydrogen
- *large number of mitochondria
- *NOT uncommon to see necrosis secondary to shock and toxin injury
What are the 2 key points to remember about the proximal convoluted tubule?
- Resorptive capacity is dictated by energy (oxidative phosphorylation form mitochondria)
o Very O2 dependent on function and survival
o *very prone to ischemic injury - First portion to receive what is in the ultrafiltrate=very susceptible to toxins and toxic injury
Loop of Henle
- Establishes hypertonicity within the medullary interstitium through the ‘counter current multiplier mechanism’
o U: multiplier - Creates a CORTICOPAPILLARY OSMOLARITY GRADIENT
- Descending loop: permeable to water only (water goes out)
- Ascending loop: permeable to solutes only (solutes go out)
How is urine concentrated? 2 requirements
- Cortico-papillary osmolarity gradient within interstitum (papilla=1200, cortical=300)
- Presence of ADH
What are the 4 points about urine concentration?
- Most water reabsorbed form PCTs and DLH and goes back to blood
- Mechanisms to keep interstitium very concentrated compared to urine flowing through DCTs and CD (ultrafiltrate is then hypotonic)
- If need to conserve water=ADH released
- ADH makes DCT and CD permeable to water=water is taken by the blood immediately
How is the cortico-papillary osmolarity gradient created? What maintains it?
- Countercurrent multiple (loop of Henle)
- Urea recycling in renal medulla
*maintain by countercurrent exchanger (vasa recta)
Urea recycling
- Only segment permeable to urea is medullary CD
o High concentration and some leaves to interstitium
o Then eventually goes back into loop of Henle and is recycled
Distal convoluted tubule
- Contains macula densa
o Sensor for Sodium - Susceptible to aldosterone hormone
Collecting duct
- Permeable to small amount of water but NOT urea (except in distal end)
- Susceptible to ADH
o Increases water reabsorption from 4-24%
Interstitium
- Contains peritubular capillaries and fibroblasts
- *expansion is ABNORMAL
o Due to edema, infiltrate or fibrosis
Gross examination of the kidney
- *autolyze quickly (due to being very metabolically active)
- Position and number
- Size (normally the size to 2 vertebra or 2 ribs)
- Connection with ureters
- Capsular adherence
- Colour
- Contours
- C:M ratio
- Papilla/crest
- Pelvic/calyces
**Capsular adherence
- In most (except horses), it should peal easily
- **If not easy=might be adhered to underlying parenchyma because of fibrosis
What are the 4 main functions of the kidney?
- Formation of urine elimination of waste and conservation of water
- Acid-base regulation(excretes H and reabsorbs bicarbonate)
- Maintenance of electrolyte balance: **pee K+
- Endocrine function
a. Renin-angiotensin system
b. Erythropoietin
c. Vitamin D
What are the 3 things needed for the kidney to function?
- Adequate blood flow
- Functioning nephrons
- Excretion of urine
