Renal Physiology - Glomerular Filtration Flashcards
where are the kidneys found?
found in cranio-dorsal abdomen - the right is typically more cranial than left but left is more mobile
meaning of retroperitoneal?
means sitting behind the peritoneum - or dorsal in domestic animals
What three areas is the kidney composed of?
cortex, medulla and pelvis
what does the cortex of the kidney contain?
contains glomerulus (glomeruli), proximal convoluted tubule and distal convoluted tubule
what does the medulla of the kidney contain?
loop of Henle and collecting duct
where does the pelvis of the kidney feed into?
feeds into ureters
what shapes is the renal medulla formed from?
formed of pyramid shaped areas - called renal pyramids
functional unit of the kidney is?
the nephron
how many nephrons does each renal pyramid contain?
contains approx 100,000 nephrons
A nephron can be divided into?
the renal corpuscle
the tubular system
what does the renal corpuscle contain?
Glomerulus and Bowman’s capsule
What is the tubular system of the kidney?
fluid-filled tubes made from a single epithelial layer and associated vascular supply
What are the vascular components of the nephrons?
(Renal artery)
Afferent arteriole
Glomerular Capillaries
Efferent arteriole
Peritubular capillaries (Vasa Recta)
(Renal vein)
What are the tubular components of each nephron?
Bowman’s capsule
Proximal convoluted tubule
Distal convoluted tubule
Collecting duct
What are the functions of the kidney?
A WET BED
What does A stand for in the A WET BED analogy for the functions of the kidney?
Acid-base balance
What does W stand for in the A WET BED analogy for the functions of the kidney?
Water balance
What does E stand for in the A WET BED analogy for the functions of the kidney?
Electrolyte balance
What does T stand for in the A WET BED analogy for the functions of the kidney?
Toxin removal
What does B stand for in the A WET BED analogy for the functions of the kidney?
Blood pressure control
What does E stand for in the A WET BED analogy for the functions of the kidney?
Erythropoietin synthesis
What does D stand for in the A WET BED analogy for the functions of the kidney?
D - Vitamin D3 conversion from calcidiol to calcitriol
Describe the kidney’s function for the acid-base balance:
Contributing to the acid-base balance by varying urinary excretion of H+ and bicarbonates (HCO3-)
Describe the water balance function of the kidney:
Stabilising the volume of the extracellular fluid
either through direct absorption in the permeable regions of the tubule or via the insertion of aquaporin channel
for the water balance function of the kidneys - how do counter-current mechanisms help?
counter-current mechanisms in nephron helps preservation of water and the formation of concentrated urine
What toxins does the kidney remove for its toxin removal function?
removes metabolic waste from the blood such as urea
Removes foreign substances from the blood e.g. antibiotics, beta blockers, diuretics, histamine (H2) blockers (e.g. ranitidine, cimetidine)
Toxins and food additives
why is renin produced?
in order to maintain blood pressure
when renin is produced, what is it part of?
part of renin-angiotensin-aldosterone-system
RAAS
Describe the blood pressure control function of the kidney:
production of erythropoietin in response to hypoxia –> erythrocytes
produced by cells within interstitium of cortex
what is calcitriol?
active form of vitamin D
what cells perform the production of calcitriol?
performed by cells located in the proximal tubules of the nephron
most renal functions are achieved through three processes - what are these processes?
filtration of plasma
reabsorption of solutes and water
secretion of substances
filtration of plasma is achieved by?
achieved by the renal corpuscle (composed of glomerulus and Bowman’s capsule)
reabsorption of solutes and water is achieved by?
achieved by the proximal and distal tubules and the collecting duct
what is secretion of substances achieve by?
by tubular cells
what does the glomerulus of the nephron do?
filters the blood
what does the proximal tubule of the nephron do?
reabsorbs most filtered water and solutes
what do the thin limbs of Henle’s loop of the nephron do?
maintains medullary hypertonicity
what does the thick ascending limb of the nephron do?
reabsorbs Na+, K+ and Cl-, dilutes tubule fluid and generates medullary hypertonicity
what does the distal convoluted tubule of the nephron do?
reabsorbs Na+, Cl- and divalent cations, dilutes tubule fluid
what does the connecting segment of the nephron do?
regulates acid, HCO3-, ammonia, Ca2+, Na+, K+ and H2O secretion
what does the cortical collecting duct of the nephron do?
regulates acid, HCO3-, ammonia, Ca2+, Na+, K+ and H2O secretion
what does the outer medullary collecting duct of the nephron do?
regulates acid, ammonia, Na+, K+ and water excretion
what does the inner medullary collecting duct of the nephron do?
regulates water, urea and acid excretion
what is the juxtaglomerular apparatus?
it regulates glomerular filtration rate and systemic blood pressure
The glomerulus is composed of how many layers?
3
what are the three layers that the glomerulus is composed of?
endothelium of glomerular capillaries
basement membrane/basal lamina (glycoproteins and collagen)
Epithelial cells of Bowman’s capsule (podocytes)
what do the three layers of the glomerulus serve as?
serve as a sieve/filtration barrier that has selective permeability
how is the endothelium of the glomerulus acting as a filter?
pores/fenestrae mean that solutes, plasma proteins and fluid can pass through BUT blood cells cannot
how does the basement membrane/basal lamina of the glomerulus act as a filter?
it is a gelatinous matrix of glycoproteins and collagen that restrict plasma proteins from flowing out
how do the epithelial podocytes of the glomerulus act as a filter?
wrapped around capillaries
gaps between ‘feet’ (podo=feet) or slit pores serve as further barrier to proteins
movement of protein is also prevented by - through the glomerulus?
prevented by charge - plasma proteins are negative as is filter
therefore protein in urine is always pathological
What is the glomerular filtration rate - GFR defined as?
defined as Quality of plasma (mL) filtered per min per kg of bodyweight through all glomeruli (mL/min/kg)
rate of GFR?
it is constant throughout life but decreases in renal disease
how is GFR kept constant?
kidney will secrete renin to contribute to RAAS and keep systemic BP relatively constant
what does GFR vary depending on?
varies depending on mass (more in smaller animals)
*Cat (example 3.64 ±0.13 mL/min/kg)
*Dog (example 2.9 ±0.3 mL/min/kg)
*Horse (example 1.55 ±0.42 mL/min/kg)
haematocrit?
percentage of red blood cells in your blood
GFR determined by?
balance of forces that favour or oppose filtration
GFR - forces that affect it?
difference in hydrostatic pressure on two side of the filter
different in protein-osmotic pressure on two sides of filter
difference in hydrostatic pressure on two side of the filter?
blood pressure within glomerular capillaries
fluid pressure within Bowman’s space
different in protein-osmotic pressure on two sides of filter?
protein in blood within glomerular capillaries
protein in fluid within Bowman’s space
how is hydrostatic pressure decreased?
constriction of the afferent arterioles decreases blood flow and decreases hydrostatic pressure THEREFORE GFR is reduced
how is GFR controllled?
by varying the hydrostatic pressure
what happens in order to increase hydrostatic pressure?
constriction of the efferent arterioles also decreases blood flow but increases hydrostatic pressure
when hydrostatic pressure increases, what happens to the GFR?
it remains almost unchanged as the decreased blood flow has an opposing effect to the increase in hydrostatic pressure
factors affecting GFR can be represented by what formula?
by Starling’s formula
GFR = Kf(AP) - A(pi)p
A = triangle
effect of glomerular capillary blood pressure?
favours filtration
effect of plasma-colloid osmotic pressure?
opposes filtration
effect of Bowman’s capsule hydrostatic pressure?
oppose filtration
effect of net filtration pressure?
favours filtration
physiological factors affecting GFR?
autoregulation (intrinsic)
angiotensin II (extrinsic)
sympathetic nervous system (extrinsic)
what do the physiological factors that affect GFR do?
factors adjust the renal blood flow and/or hydrostatic pressure
what is renal autoregulation?
the ability of the kidney to regulate its own blood flow
functions of renal autoregulation?
prevent large changes in GFR and urine output
Protect fragile glomerular capillaries
Blood flow (Q) =
change in arterial pressure (AP) / Afferent arteriole resistance (R)
Q = AP/R
relate the definition of renal autoregulation to the Q=AP/R equation?
it is the kidney’s ability to change R so that Q is maintained despite changes in P
effect of variations in arterial blood pressure on kidneys and GFR?
Variations in arterial blood pressure between 80-200 mmHg have little effect on perfusion of the kidneys and GFR
What arteriole does renal autoregulation involve?
involves only the afferent arteriole not the efferent
what two mechanisms help renal autoregulation be achieved?
myogenic response
tubulo-glomerular feedback
What is the myogenic response?
Arterial pressure increases
Afferent arteriole wall stretches under increased pressure
Vascular smooth muscle cells detect stretch
‘Mechanotransduction’ leads to depolarisation of the VSMC membrane
Activates voltage-gated Ca2+ channels
Influx of Ca2+ leads to contraction of the VSMC
Afferent arteriole constricts reducing the renal blood flow to the glomerulus
where is the distal convoluted tubule located?
it is located in close proximity to afferent arteriole
Juxtaglomerular complex?
formed of junction between DCT/ascending loop of Henle and the afferent and efferent arterioles
Tubular wall has specialised epithelial cells that form the macula densa
Afferent arteriole wall has specialised smooth muscle cells in the wall called granular (juxtaglomerular cells) with renin-containing vesicles
Renin produced and release by?
produced and released by the granular juxtaglomerular cells in response to a sustained low pressure
what is renin?
an enzyme that converts the precursor angiotensinogen to angiotensin I
ACE?
angiotensin converting enzyme
in pulmonary capillaries converts angiotensin I to angiotensin II
effects of angiotensin II?
numerous effects on the body in order to maintain arterial pressure
constricts both afferent and efferent arterioles
reduces blood flow but maintains GFR
what is the RAAS a response to?
response to sustained or prolonged BP drop
neural control for the kidneys?
renal arterioles and juxtaglomerular cells innervated by sympathetic nervous system
can stimulate arteriole constriction
can stimulate renin production
similar effects to angiotensin II
hormonal control concerning kidneys?
atrial natriuretic peptide is a hormone that inhibits Na+ reabsorption thereby increasing Na+ loss in urine
Produced in the heart and secreted when plasma volume increases, which increases urine production
intrinsic and extrinsic mechanisms act to?
they act to maintain GFR as best as possible however GFR can be altered by physiological mechanisms
