9. Urinary System Flashcards
What are the 3 functions of the kidney?
- Filters metabolic products & toxins from blood, excreting them as urine
- Regulated the bodies fluid status, electrolytes, & acid-base balance (Na+, K+, Ca2+, H+, Cl-)
- Humoral regulation of blood pressure & flow (as well as erythrogenesis, Ca2+ metabolism)
Slides 2-4 Nov 4
Why is the structure of the kidney?
Paired, bean shaped structures
Lie behind peritoneum on each side of vertebral column
Extend from 12th thoracic vertebra to 3rd lumbar vertebra
2 kidneys < 0.5% body weight
Receive 20% cardiac output
Covered by fibrous, non-distensible capsule
2 basic layers- cortex and medulla
Slide 5-6 Nov 4
What is the hilus of the kidney?
What is the renal sinus?
Hilus is a slit in the capsule around the kidney that serves as a port of entry for the renal artery and the site of exit for the renal vein, lymphatics, and ureter
Renal sinus is a shallow space the hilus opens up into that is surrounded by renal parenchyma except where it connects with the upper end of the ureter
Renal sinus includes the urine filled spaces: renal pelvis proper and it’s extensions the major and minor calyces
Slide 6 Nov 4
What is the cortex of the kidney?
What is the medulla of the kidney?
Cortex- granular outer region results from presence of glomeruli and highly convoluted epithelial structures in form of tubules
Medulla- darker inner region from presence of parallel arranged tubules and small blood vessels
Divided into 8-18 conical renal pyramids whose bases face cortical medullary border and tip contains perforations that urine flows through
Slide 7 Nov 4
What is the renal vasculature of the kidneys?
Blood flow
Kidneys have very high blood flow and glomerular capillaries flanked by afferent and efferent arterioles
Blood flows from: Afferent arterioles (high resistance) Glomerulus (high pressure) Efferent arterioles (high resistance) Peritubular capillaries (low hydrostatic pressure/high colloid osmotic pressure)
Slide 8 Nov 4
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What is the nephron?
What are the 2 types?
Basic structural and functional unit of kidney
Each kidneys consists of 800000-1200000 nephrons
Nephron consists of a glomerulus and a tubule
Urine formation by ultrafiltration (primary fluid) and reabsorbing and secretion by the tubules (form urine)
2 types: superficial & juxtamedullary
Depend on location and size of hoops
Slides 9-10 Nov 4
What are the 5 steps of plasma volume entering nephron and being excreted out?
- Plasma volume entering afferent arteriole = 100%
- 20% of volume filters in glomerulus
- > 19% of fluid is reabsorbed in remainder of nephron
- > 99% of plasma entering kidney returns to systematic circulation
- <1% of volume is excreted to external environment
Slide 9 Nov 4
What is the renal corpuscle?
Comprised of a glomerulus, Bowman’s space, and Bowman’s capsule
Fluid flows from glomerulus into Bowman’s space & continues down nephrons (glomerular ultrafiltrate)
Renal corpuscle is the site of formation of the glomerular filtrate
Slide 11 Nov 4
What is the glomerular filtration barrier?
Located between glomerular capillary lumen and Bowman’s space
Made up of 4 elements:
Glycocalyx- covers luminal surface of endothelial cells
Endothelial cells- contain large fenestrations (70nm holes) that provide no restriction to movement of water and small solutes out of lumen capillary
Basement membrane
Podocytes- contain filtration slits
Slides 13-15 Nov 4
What are the 2 tubular components of the nephron?
- Proximal tubule- convoluted, straight
Job is to reabsorb the bulk of filtered fluid back into circulation (cell membrane amplification) - Loop of Henle
Descending thin limb, ascending thin limb, thick ascending limb
Continue absorbing fluid back to circulation
Slide 16 Nov 4
What is the order of all the fundamental tubular components in nephron?
Page 728
Slides 16-19 Nov 4
Proximal convoluted tubule Proximal straight tubule Descending thin limb Ascending thin limb Thick ascending limb Distal convoluted tubule Connecting tubule Initial collecting tubule Cortical collecting tubule Outer medullary collecting duct Inner medullary collecting duct
What is the proximal tubules jobs?
Retrieves largest portion of glomerular filtrate
Most leaky epithelial junctions
NaCl, NaHCO3, filtered nutrients, etc leaves proximal tubule and enters back into blood stream
NH4 and other solutes leave capillary and enter tubule at this point
Slide 20 Nov 4
What is the main function of the loop of Henle?
Assist in forming concentrated or dilute urine by pumping NaCl into the interstitial space of the medulla
Increases osmolality in interstitial space
Collecting duct exploits the hypertonicity
Distal tubule and collecting duct perform fine control of electrolyte & H2O excretion
Slide 21 Nov 4
What is the juxtaglomerular apparatus (JGA)?
What are it’s 2 functions?
Region where glomerulus makes contact with the thick ascending limb of loop of Henle
Consists of 2 juxta-glomerular cells, macula densa & mesangial cells
2 functions:
- JGA senses fluid & NaCl arching the macula densa of loop of Henle & adjusts glomerular filtration
- When JGA is stimulated by a decrease stretch of afferent arterioles, juxtaglomerular cells release renin to affect arterial blood pressure
Slide 22 Nov 4
What 3 effects occur when norepinephrine and dopamine are released into loose connective tissue near smooth muscle of vasculature & near proximal tubules
(Sympathetic stimulation)
- Vasoconstriction
- Catecholamines (norepinephrine and dopamine) strongly enhance Na reabsorption by proximal tubules
- There is a lot of sympathetic innervation near the JGA dramatically stimulates secretion of renin from the juxtaglomerular cells
What are the 2 afferent (sensory) fibers?
Renal baroreceptors- around interlobular & afferent arterioles sense pressure changes
Renal chemoreceptors- near the renal pelvis sense extracellular H+ & K+, triggering alterations to capillary flow
What are the 5 things kidneys produce as endocrine organs?
Renin- released from JGA granule cells
25-dihydroxyvitamin D- proximal tubule converts to active form 1, 25-dihydroxyvitamin D (controls Ca and phosphorus metabolism by acting on intestine, kidney and bone)
Erythropoietin- releases by cell in the cortex and medulla in response to low PO2->stimulate development of red blood cells by stem cells in bone marrow
Prostaglandins- paracrine agent control circulation within kidney
Kinins (bradykinin)- same as prostaglandins
What is renal clearance?
The virtual volume of plasma that would be totally cleared of a solute in a given time
Kidney has 3 processes: glomerular filtration, tubule reabsorption, and secretion
Measure the difference between the substance filtered and excreted -> can estimate secretion and reabsorption
Slide 25 Nov 4
What is the clearance equation?
Cx= (Ux)(V)/(Px)
Ux is conc of X in urine
V is volume of urine formed in given time
Px is conc of X in systemic blood plasma (same as Pxa)
Arterial input = venous output + urine output
(Pxa)(RPFa) = (Pxv)(RPFv) + (Ux)(V)
Slide 26-27 Nov 4
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What is the clearance equation for solutes that are freely filtered and not secreted or absorbed?
Ex: insulin or creatinine
Cx = GFR
Glomerular filtration rate
High GFR is essential for maintaining stable and optimal extracellular levels of solutes (including toxins) & water
If not high; there is an inability to deal with sudden increases in toxic material and high steady state levels of waste materials
What is a solutes urinary excretion?
(Equation)
What about if solute is only reabsorbed, not secreted?
What about if solute is only secreted, not reabsorbed
Amount filtered - amount reabsorbed + amount secreted = amount excreted in the urine
Ex = Fx - Rx + Sx
If only reabsorbed, not secreted:
Rx= (GFR)(Px) - (Ux)(V)
If only secreted, not reabsorbed:
Sx= (Ux)(V) - (GFR)(Px)
Slide 29 Nov 4
Page 732
What are the 4 microscopic techniques that make it possible to measure single nephron rates of filtration, absorption, and secretion?
Free-flow micropuncture
Stopped-flow microperfusion
Continuous microperfusion
Isolated perfused tubule
Slide 30 Nov 4
What is glomerular filtration?
What is ultrafiltration?
Filtration of blood plasma by the renal glomeruli
Same as blood filtration across capillaries (driven by hydrostatic pressure and osmotic pressure)
Ultrafiltration happens when the hydrostatic pressure difference exceeds the colloid osmotic pressure difference, this results in movement of H2O out of the capillary and creates a glomerular filtrate
What are the 2 reasons the filtration rate in the glomerulus exceeds compared to other regions of body?
- Greater starling forces (hydrostatic & colloid osmotic)
- Higher capillary permeability (large fenestrations that provide no restriction to movement of water and small solutes out of the lumen of capillary)
What do the hydrostatic and oncotic pressures of the Bowman’s space or the glomerular capillary favour?
(Favour ultrafiltration or oppose ultrafiltration)
Hydrostatic pressure in the glomerular capillary (Pgc) favours ultrafiltration
Oncotic (colloid osmotic) pressure of the filtrate in Bowman’s space (πbs) favours ultrafiltration
Hydrostatic pressure in the Bowman’s space (Pbs) opposes ultrafiltration
Oncotic (colloid osmotic) pressure in the glomeruli (πgc) opposes ultrafiltration
Slide 36 Nov 4
Why is the GFR equation containing the hydrostatic and oncotic pressures?
GFR= Kf • [(Pgc-Pbs)-(πgc-πbs)]/Puf
Kf is ultrafiltration coefficient
Puf is net driving force
Normal GFR value is 125mL/min in 70kg man
Slide 37 Nov 4
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Slide 43 Nov 4
What is renal blood flow (RBF)?
It is 1L/min out of the total cardiac output of 5L/min
~350mL/min for each 100g of tissue
Renal plasma flow (RPF)=(1-hematocrit content) x RBF
Increased glomerular blood flow increases filtration
Low flow means filtration equilibrium occurs halfway down the capillary (filt exceeds flow)
High flow doesn’t allow filtration equilibrium to be reached since flow exceeds rate of filtration (filtration disequilibrium)
Slide 38 Nov 4
What is the pathway of glomerular plasma flow?
Afferent arterioles->glomeruli capillaries->efferent arterioles->peritubular capillary bed
Changes in resistance at the afferent and efferent arterioles control glomerular pressure and filtration (afferent and efferent arterioles resistance is effected simultaneously)
Plasma flow and total arteriolar resistance stay constant
Slide 39 Nov 4
What are the 3 determinants of filterability of solutes across glomerular filtration barrier?
Molecular size- molecular weight and radius determines how it’s filtrate across glomeruli (podocytes and junctions between them)
Electrical charge- glomerular basement membrane & podocyte end-feet are covered in negative charges (this restricts movements of anions (-) and enhances movement of cations (+))
Shape- rigid or globular molecules have lower clearance rations than molecules of similar size that are highly deformable
What are peritubular capillaries?
2 functions
Have 2 functions:
- deliver oxygen & nutrients to epithelial cells of tubules
- take up fluid from interstitial space that the renal tubules reabsorb
PC have very high oncotic pressure since glomerular capillaries precede then and fluid is removed from the blood at glomeruli
Resistance at efferent arterioles greatly decreases hydrostatic pressure in PC
Slide 42 Nov 4
What are the signs and symptoms of glomerular disease?
Reduced glomerular filtration rate- inefficient filtering of wastes from the blood
Hypoproteinemia- low blood protein
Proteinuria- large amounts of protein in the urine
Hematuria- blood in the urine
Edema- swelling in parts of the body
Slides 44-46 Nov 4
What is chronic kidney disease?
Decreased kidney function shown by a GFR of less than 60mL/min or makers of kidney damage of atleast 3 months duration
Renal fibrosis due to unsuccessful wound healing of kidney tissue after chronic sustained injury
Diabetes and hyper tension are main causes of CKD
Slides 1-17 Nov 19 Nov 19
How can chronic disease be related to climate change?
Evidence that daily heat exposure can cause daily acute kidney injury
Heat induced dehydration causes renal injury in rats
Systolic and diastolic BP falls, pulse rises
Ur one becomes progressively concentrated and acidic since renin-angiotensin-aldosterone system activated
Slides 4-17 nov 19
