Circulation of Kidney. Glomerular filtration Flashcards
Circulation of kidney
Renal a. > Interlobar a. > Arcuate a. > Interlobular a. > Afferent arteriole > Glomerular capillary > Efferent arteriole > Peritubular capillaries (supply blood to the nephron)
Nephron
Renal corpuscle > = Glomerular capillaries + Bowman’s capsule > Proximal tubule > Loop of Henle = Descending thin limb, Ascending thin limb, Thick ascending limb > Distal Tubule w/ Macula Densa > Collecting duct
Proximal tubule
Reabsorption of Na, Glucose, Amino Acids, Phosphate, Citrate, Lactate, Bicarbonate, Chloride (Late prox.)
Thin descending limb
- H2O: Highly permeable. Water is readily reabsorbed from the descending limb by osmosis.
- Solutes: Low permeability. Sodium and chloride ions do not easily pass through
Osmolarity increases along the length of the tubule
The descending loop of Henle receives isotonic (300 mOsm/L) fluid from the proximal convoluted tubule (PCT). The fluid is isotonic because as ions are reabsorbed by the gradient time system, water is also reabsorbed maintaining the osmolarity of the fluid in the PCT.
The interstitium of the kidney increases in osmolarity outside as the loop of Henle descends from 600 mOsm/L in the outer medulla of the kidney to 1200 mOsm/L in the inner medulla. The descending portion of the loop of Henle is extremely permeable to water and is less permeable to ions, therefore water is easily reabsorbed here and solutes are not readily reabsorbed. The 300 mOsm/L fluid from the loop loses water to the higher concentration outside the loop and increases in tonicity until it reaches its maximum at the bottom of the loop. This area represents the highest concentration in the nephron, but the collecting duct can reach this same tonicity with maximum ADH effect.
Thin ascending limb
Thin ascending limb of loop of Henle
The thin ascending limb is impermeable to water, but it is permeable to ions.
Osmolarity decreases = diluting segment
Thick ascending limb (TAL)
Sodium (Na+), potassium (K+) and chloride (Cl−) ions are reabsorbed from the urine by secondary active transport by a Na-K-Cl cotransporter (NKCC2). The electrical and concentration gradient drives more reabsorption of Na+, as well as other cations such as magnesium (Mg2+) and calcium (Ca2+).
Distal tubule
Natrium and Chloride is reabsorbed
- Na/Cl cotransporter in apical membrane
- Basolateral membrane Cl channel and Na/K ATPase
Collecting duct
Composed of two cell types
- Principal cells - reabsorption of NaCl
- Intercalated cells
- Secretion of K+
- Regulation of acid - base balance
- Secretion of H+
- Reabsorption of HCO3-
Definition of a juxtamedullary nephron
Loop of Henle extends deep into inner medulla
Peritubular capillary becomes Vasa Recta with ascending and descending limb (opposite direction of loop of Henle)
Function of Vasa Recta
- Conveying O2, nutrients to nephron segments
- Delivering substances to the nephrons for secretion
- Pathway for the return of reabsorbed water and solutes
- Concentrating and diluting urine
Glomerulus Filtration Barrier layers
*Endothelium: Fluid, dissolved solutes, plasma proteins can enter (not blood cells)
*Basement membrane:
- Lamina rara externa
- Lamina densa
- Lamina rara interna
No plasma proteins can enter!
*Epithelium:
- Podocytes: Foot processes with filtration slits and diaphragm
Why can’t negative charged molecules be filtered?
Because of the negative charge of the glomerular capillary barrier.
Positive charge accepted.
What is the function of Mesangial cells?
- Surrounding glomerular capillaries
- Secrete ECM
- Phagocytotic activity
- Regulate GFR
Juxta Glomerular Apparatus parts
- Macula densa
- Extraglomerular mesangial cells
- Granular cells of the afferent arteriole
Function in Tubuloglomerular Feedback
Function of Granular Cells of the afferent arteriole
Synthesize and release Renin
Glomerular Filtration Rate definition
Sum of the filtration rates of all functioning nephrons
How can we measure GFR?
Creatinine = byproduct of skeletal muscle creatine metabolism is freely filtered across the glomerulus and not reabsorbed by nephron
GFR equation
GFR = (Ucr x V) / PCr Pcr = Creatinine concentration in plasma V = Urine flow UCr = Creatinine concentration in urine
Filtration fraction
GFR/RPF
0.15 to 0.20
15 - 20% of plasma that enters glomerulus is filtered
GFR paramteres
90-140 mL/min in male
80-125 mL/min in female
= 180 L/day
Starling Forces
Equation. Determines the GFR = equation
Regulation of GFR
*Change in pressure and resistance Q = DeltaP/R Major resistant vessels - Afferent and efferent arteriole - Interlobular artery -> Change resistance in respons to change in arterial pressure = Autoregulation
Autoregulation
RBF and GFR are maintained constant between 90 - 180 mmHg.
Mechanism
1. Change in Pa
2. Change in [NaCl]
*Myogenic mechanism
-> Pressure sensitive
Vascular smooth muscle contract when stretched
Mechanosensitive cation channels in wall open
Depolarization
VGCC open
Increased Calcium = Contraction
*Change in [NaCl] = Tubuloglomerular feedback
Increase in GFR > Increase [NaCl] > Macula Densa of JGA sense increase in [NaCl]
Increase ATP and Adenosine due to increased activity of Na/K ATPase and Na/2Cl/K+ (secondary active) in TAL.
Will bind to Granular cell Vascular smooth muscle and will activate Calcium channels = vasoconstriction of afferent arteriole - Less renin is released = less aldosterone released = less reabsorption of NaCl
Decrease in NaCl = NO release = vasodilation
