Figure on P603 = Filtration, reabsorption, secretion and excretion of a nephron involved in urine formation
1 - Urine formation begins at Glomerulus with the creation of Filtration located in Renal Cortex.
looks like plasma minus proteins.
most of the material in the plasma minus proteins is freely filred meaning that the concentration of material in filtrate is the same with
the one in the plasma before Blomerulus site of filtration
2 - In proxima tubule a lot of filtrate is reabsorbed by Peritubular Capilaries: selective tubule reabsorption and secretion
99% of filtrate is going back into Peritubular Capilaries
the lining of the nephron is a Single Layer of epithelium cells (cells in contact with the filtrate)
Proximal Convoluted Tubules - highest location of reabsorption
it is very much fixed at a rate of 65% traffic (a fixed stereotype way unaffected by regulation
have microbili - increasing surface area
3 - Selective Tubular Secretion - opposite direction of reabsorption
the cells lining the nephron are secreting things into filtrate: H+ = acid base regulation
4 - Regulation - at the site of filtration (there's autoregulation)
highly variable - at the distal portion (distal tubule) + Collecting duct
i.e. ADH works at distal tubules and collecting duct
Glomerulus capilaries charascteristics: high pressure and very leacky (fenestrated)
Efferent arteries maintain the backflow keeping the pressure in Glomerulus high
Following the Glomerulus side, the efferent arteriole has a lower pressure then the afferent arteriole Facilitating Reabsorption
Forces Driving the Glomerulus Filtration rate - capilaries dynamics - the ballance of these forces
1. Blood Hydrostatic pressure (55mmHg) - going OUT
the efferent arterioles keeping pressure very high
highly variable - altering the diameter of efferent/afferent arteriole (autoregulated)
2. Colloid osmotic pressure (30mmHg) - going IN
the proteins in arteriole capilaries pulling filtrate out of proximal tubule into the Peritubular capilaries
3. Capsular Interstitial fluid - Hydrostatic fluid pressure in Bowman's capsule (15mmHg) going IN
Netforce = 55-30-15 = 10mmHg
Neft force of body capilary is less the 2mmHg
The capilary colloid osmotic pressure is not present because the Filtrate does not contain proteins
Glomerular Filtration Rate (GFR = ml/min = 125ml/min)
every minute the kidney is forming 125 ml combined filtrate = 180L/day
Kidney filter the entire plasma volume 60 times a day, 2.5 times per hour
strongly regulated (autoregulated) - highly variable
Filtration Fraction = 19-20% (1/5th) percent of plasma that becomes filtrate going through kidneys
Renal Plasma Flow = 660ml/min RPF
Renal Blood Flow = 120 ml/min (including red blood cells)
Filtration Fraction ::: GFR/RPF = 125/660 = 19-20%
What factors cause GFR to vary:
1. Afferent Arterioles - high resistance site
dialate - more blood flow as it opens GFR increases
constrict GFR decreases
2. Efferent Arterioles - opposite of afferent
dialate - loss of backflow pressure GFR decreases
constrict - more backflow pressure GFR increases
3. Sympathetic stimulation - a lot of symp fivers innervate
many are vasoconstrictor fivers
mild symp stimulation - GFR is maintained
strong symp stimulation - GFR decreases
4. Effect of the general Systemic Arterial Pressure
long term regulation as pressreu of SAP increases so GFR increases
5. Level of Plasma Choloid Osmotic Pressure
as PCOP increases, GFR decreases
55 - 30 - 15= 10
55 - 40 - 15= 0
How do we measure GFR - renal clearance test
U-urinary concentration of substance X
V-urine flow rate (ml/min)
P-plasma conc of subst X
