Renal Function- Filtration Flashcards
Principal functions of the kidney
—Regulate volume/composition of ECF (will affect ICF) – Osmoregulation, Blood pressure and volume
—Regulate concentrations of ions in ECF
—Excretion – endogenous waste/metabolites, toxins, drugs Acid base balance
What do kidneys produce?
Renin
Erythropoietin
Calcitriol
Glucose
Urine
Function of produced renin
counteracts reduction in ECF volume and BP (blood pressure)
Function of produced erythropoietin
formation and maturation of RBCs
Function of produced calcitriol
Calcium homeostasis
Function of produced glucose
protect blood sugar during starvation
Kidney is a homeostatic organ, and control is achieved via…
cooperative functionality with circulatory & respiratory systems
These structures found within cortex or medulla?
-glomerulus
-bowman’s capsule
-proximal convoluted tubule
-cortical nephron’s LOH (loop of Henle)
-juxtamedullary nephron’s LOH
- Cortex
- Cortex
- Cortex
- Barely enters medulla
- Deep in medulla
Why is position of nephron in kidney important?
Nephron regulate water balance so their position matters
Three fundamental processes/functions within the nephron
- Filtration
- Reabsorption
- Secretion
What are the 2 types of differentiated cell types found along the length of the nephron due to differing functions
Principal cells
Intercalated cells
Principal cells reabsorb and secret what?
Intercalated cells reabsorb and transfer what?
Principal cells – reabsorb Na+, Cl- and secrete K+
Intercalated cells – reabsorb K+ and transfer H+
What structure in nephron does filtration occur in?
Glomerulus
Filtration in the glomerulus occurs as a result of…
Pressure differences within the system
Describe what occurs during filtration in glomerulus
-Blood enters afferent arteriole under relatively high pressure (high pressure due to actions of heart and resistance of efferent arteriole)
-high pressure results in extrusion of large amounts of water, plus glucose, proteins and other waste products
-overall around 20% of plasma is leaving in glomerulus and entering filtrate
-large molecules such as blood cells, large proteins are retained within bloodstream
What is a way to get rid of retained large waste molecules that were unable to be filtered?
Occurs where?
Secretion- taking waste products from blood stream and passing to filtrate
Occurs within PCT
Secretion of large molecules in the nephron can result in what?
What is a way to stop this from occurring? Where does this process occur?
Loss of solutes/water that we do not want to lose
Reabsorption- recovery of required components from filtrate (partial/total depending on what body needs)
-occurs in PCT, LOH, DCT, Collecting duct (whole rest of nephron)
Certain diseases will results in problems in filtration process. What do they cause which can result in what?
Cause more proteins to be passed out into urine/filtrate and are unable to be reabsorbed
Results in:
Proteinuria
Albuminuria
Haemoglobinuria
Rate of filtration is determined by…
hydrostatic and osmotic forces
What are the three main forces of water movement and what each causes
Which is the 4th that has no effect on movement of water
- Glomerular hydrostatic pressure—> very high pressure caused by actions of heart and differences in resistance of arterioles
- Hydrostatic pressure of Bowman’s Space—> as water builds in bowman’s space (space between glomerulus and bowmans capsule) it is pushed back into capillaries
- Oncotic pressure- pressure brought about by plasma proteins; holds water within capillaries as they are impermeable
- Osmotic pressure due to fluid in Bowman’s space- effectively 0 as filtrate is pulling away all those proteins; they aren’t staying in one space
How would you calculate the net ultrafiltration pressure?
Puf= Pgc - (Pbs + Tgc)
Puf= glomerular capillary hydrostatic pressure - (Hydrostatic pressure of bowman’s space + Oncotic pressure)
Calculation for Glomerular Filtration Rate (GFR)
GFR= Puf x (permeability of the filter, surface area (of filtration barrier))
Since we can change the net ultrafiltration rate of we change any of the values in the equation, this means we can regulate the…
GFR
Why should GFR be regulated?
GFR is regulated by what?
-so as to maintain stable ECF (and ICF)
-Principally regulated by changes in blood flow, protein osmotic pressures and hydrostatic pressure
What will happen to glomerular filtration rate when there is a lower blood flow?
Lower blood flow —>
-blood is spending longer within capillary bed so more opportunity to push water out; more water leaves
-greater increase in osmotic pressure across capillary itself
-only osmotic pressure changed, hydrostatic capillary pressure stays the same
-water is ‘held’ in latter parts of capillaries so overall decreased GFR
What will happen to glomerular filtration rate when there is a higher blood flow?
Higher blood flow; Less water is filtered through so osmotic pressure increases less so increased GFR
How are we able to alter afferent and efferent arteriole resistance?
What effect does alteration of arteriole have
Afferent and efferent arteriolar are smooth muscle so we can either relax or constrict this muscle
Alteration affects flow of hydrostatic pressure/blood flow and therefore GFR
What would happen to GFR if afferent arterioles were constricted?
- -Less blood would be coming in as passage is constricted, therefore decreased blood flow
-decreased blood flow causes a decreased GFR - -there would be a decreased hydrostatic pressure as there’s less blood so less fluid movement out of capillaries, therefore decreased GFR
Overall both changes cause a DECREASE in GFR
What would happen to GFR if efferent arterioles were constricted?
- -less blood is able to leave so decreased blood flow
-causes decreased GFR once again - -there is increased hydrostatic pressure there is more blood within capillaries due to constricted exit
-causes increase in GFR
Overall opposing effects mean there is NO CHANGE in GFR
Since GFR can be regulated by blood pressure, this means any easy task requiring a change in BP would cause effect on GFR. How then do we regulate GFR if there is an ACUTE or MODERATE blood pressure change?
By autoregulation; changes the resistance of the afferent arterioles which will ultimately maintain GFR
What are the 2 types of autoregulation—>
-myogenic reflex
-tubuloglomerular feedback
Response to acute moderate changes in BP:
Myogenic Reflex
-how does it work when there is an increased BP
Increase BP:
Stretch receptors are stimulated which brings about a reflex contraction of afferent arteriole
Contraction decreases blood flow back to normal and therefore GFR is maintained
Response to acute moderate changes in BP:
Myogenic Reflex
-how does it work when there is an increased BP
Decreased BP:
-Detected by stretch receptors
-Reflex dilation of afferent arteriole= more blood flow
-GFR stabilised
Response to acute moderate changes in BP:
Tubuloglomerular feedback
-how does it work
Stimulus is the amount of filtrate being produced
-recognises amount at Macula densa (makes close connection with afferent arteriole)
-for example decrease in GFR causes decreased flow past macula densa
-results in decreased NaCl concentration
-this stimulates release of paracrine factors from macula densa
-these act on afferent arteriole
-afferent arteriole is dilated-> more blood flow—> more filtrate and therefore ^GFR to normal
How do we regulate GFR if there is an CHRONIC (longer term) blood pressure change?
Use of Renin Angiotensin Aldosterone system
How does the Renin Angiotensin Aldosterone system in regulating GFR
Release of renin causes angiotensin I to change forms to angiotensin II which causes arteriole vaconstriction (causing ^ BP) and ^ in sympathetic NS activity
Overall there is a constriction of efferent arterioles to combat low BP. There is also increased water Reabsorption. Ultimately maintains GFR back to normal.
Why should we assess estimation of GFR in body?
Can be a clinical indicator of progress of renal disease
How do we estimate GFR
GFR = urinary excretion of a substance/minute —————————————————————-plasma concentration of substance
(Substance must be freely filtered and neither reabsorbed nor secreted)
Which plasma conc substance can be used to estimate GFR
Inulin (a fructose polymer)
What is clearance?
volume of plasma, that contains the amount of the substance excreted in the urine per minute (i.e. what’s filtered and secreted)
