Renal System 2 Flashcards
Glomerular Filtration
Involves passage across a filtration membrane
- capillary endothelial pores (allow water and small solutes)
- dense layer (lamina densa) (matrix of proteins, sieve like, also has a negative charge)
- filtration slits (in between podocytes, size can be changed to increase or decrease glomerular filtration)
What three forces determine filtration pressure?
GHP = glomerular hydrostatic pressure (pressure in the capillaries, positive effect) CsHP = capsular hydrostatic pressure (pressure from fluid in the capsule, negative effect) BCOP = blood - colloid osmotic pressure (larger proteins left behind after filtration, concentration gradient within capillaries is higher than capsular space, causes water to want to flow back into capillaries to even out the gradient, negative effect)
Net filtration pressure (NFP)
NFP = NHP - BCOP
= 35 - 25
=10mmHg
-balace between hydrostatic pressure (fluid pressure) and colloid osmotic pressure
Glomerular hydrostatic pressure (GHP)
- Is blood pressure in glomerular capillaries
- tends to push water and solute molecules
- out of plasma
- into the filtrate
- is significantly higher than capillary pressures in systemic circuit
- due to arrangement of vessels at glomerulus
Capsular Hydrostatic Pressure (CsHP)
- opposes glomerular hydrostatic pressure
- pushes water and solutes
- out of filtrate
- into plasma
- results from resistance to flow along nephron and conducting system
- averages about 15mm Hg
Blood colloid osmotic pressure (BCOP)
- is the osmotic pressure resulting from the presence of suspended proteins in capillaries
- draws water out of filtrate back into plasma
- opposes filtration
- averages 25mm Hg
Net Hydrostatic Pressure
GHP - CsHP
Glomerular filtration
- filtration generates about 180L of filtrate per day (99% is reabsorbed in renal tubules)
- the Glomerular Filtration Rate (GFR) is the amount of filtrate kidneys produce each minute
- averages 125mL/min
- GFR depends on filtration pressure
- any factor that alters filtration pressure alters GFR
List the three controllers of GFR
- autoregulation (at the local level)
- autonomic regulation (by sympathetic division of ANS)
- hormonal regulation (initiated by kidneys)
Control of glomerular filtration
1. Autoregulation
- maintains GFR despite changes in local blood pressure and blood flow
- by changing diameters of afferent arterioles, efferent arterioles and glomerular capillaries
- myogenic mechanisms (ie stretch receptors)
Control of glomerular filtration
An increase in renal blood flow or blood pressure… (e.g. running)
- stretches walls of afferent arterioles
- causes smooth muscle cells to contract
- constricts afferent arterioles
- decreases glomerular blood flow
Control of glomerular filtration
A decrease in blood flow results in decreased glomerular press and… (e.g. lying down)
- -dilation of afferent arteriole
- dilation of glomerular capillaries
- constriction of efferent arterioles
Control of glomerular filtration
2. autonomic regulation (by sympathetic NS)
- increased sympathetic activity:
- vasocontriction of afferent arterioles (e.g. diarrhoa)
Control of glomerular filtration
3. hormonal regulation
- renin-angiotensin system
- natruiretic peptides (ANP and BNP)
Control of glomerular filtration
3. hormonal regulation
Renin-angiotensin system
- three interrelated stimuli cause the release of renin from the juxtaglomerular complex (JGC)
1. decreased blood volume, decline in afferent arteriole blood pressure (detected by intra-renal baroreceptors)
2. stimulation of juxtaglomerular cells by renal sympathetic nerves
3. decreased osmotic concentration of the tubular fluid detected by the macula densa
Control of glomerular filtration
3. hormonal regulation
Three stimuli for renin release
- decreased blood pressure
- increased sympathetic nerve stimulation
- decreased filtrate concentration
Control of glomerular filtration
3. hormonal regulation
What does renin do?
Renin is an enzyme which causes the cleavage of angiotensinogen, covering it into angiotensin l
Angiotensin converting enzyme then converts this into angiotensin ll
Control of glomerular filtration
What does angiotensin ll activation do?
Broadly, it stimulates increased GFR
- increases sympathetic motor tone
- constriction of the venous reservoirs
- increases cardiac output
- stimulates peripheral vasoconstriction - constricts efferent arterioles of nephron
- elevating glomerular pressures and filtration rates - stimulates reabsorption of sodium ions and water at PCT
- stimulates secretion of aldosterone (from adrenal cortex)
- increases sodium reabsorption: in DCT and the cortical portion of collecting ducts - stimulates thirst
- triggers release of ADH (from posterior pituitary of the hypothalamus)
- stimulates reabsorption of water in distal portion of DCT collecting system
Control of glomerular filtration
3. hormonal regulation
Natriuretic Peptides
-are released by the heart in response to very large increased blood volume or pressure
-stretching receptors in heart walls trigger release:
Atrial netriuretic peptide (ANP) is released by atria
Brain natriuretic peptide (BNP) is released by ventricles
ANP and BNP trigger dilation of afferent arterioles and contraction of efferent arterioles
- elevates glomerular pressures and increases GFR
- increases urine production
