Circulation of Kidney. Glomerular filtration

Question 1

Circulation of kidney

Answer 1

Renal a. > Interlobar a. > Arcuate a. > Interlobular a. > Afferent arteriole > Glomerular capillary > Efferent arteriole > Peritubular capillaries (supply blood to the nephron)

Question 2

Nephron

Answer 2

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

Question 3

Proximal tubule

Answer 3

Reabsorption of Na, Glucose, Amino Acids, Phosphate, Citrate, Lactate, Bicarbonate, Chloride (Late prox.)

Question 4

Thin descending limb

Answer 4

• 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.

Question 5

Thin ascending limb

Answer 5

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

Question 6

Thick ascending limb (TAL)

Answer 6

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+).

Question 7

Distal tubule

Answer 7

Natrium and Chloride is reabsorbed

• Na/Cl cotransporter in apical membrane
• Basolateral membrane Cl channel and Na/K ATPase

Question 8

Collecting duct

Answer 8

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-

Question 9

Definition of a juxtamedullary nephron

Answer 9

Loop of Henle extends deep into inner medulla

Peritubular capillary becomes Vasa Recta with ascending and descending limb (opposite direction of loop of Henle)

Question 10

Function of Vasa Recta

Answer 10

• 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

Question 11

Glomerulus Filtration Barrier layers

Answer 11

*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

Question 12

Why can’t negative charged molecules be filtered?

Answer 12

Because of the negative charge of the glomerular capillary barrier.
Positive charge accepted.

Question 13

What is the function of Mesangial cells?

Answer 13

• Surrounding glomerular capillaries
• Secrete ECM
• Phagocytotic activity
• Regulate GFR

Question 14

Juxta Glomerular Apparatus parts

Answer 14

• Macula densa
• Extraglomerular mesangial cells
• Granular cells of the afferent arteriole
  Function in Tubuloglomerular Feedback

Question 15

Function of Granular Cells of the afferent arteriole

Answer 15

Synthesize and release Renin

Question 16

Glomerular Filtration Rate definition

Answer 16

Sum of the filtration rates of all functioning nephrons

Question 17

How can we measure GFR?

Answer 17

Creatinine = byproduct of skeletal muscle creatine metabolism is freely filtered across the glomerulus and not reabsorbed by nephron

Question 18

GFR equation

Answer 18

GFR = (Ucr x V) / PCr
Pcr = Creatinine concentration in plasma 
V = Urine flow
UCr = Creatinine concentration in urine

Question 19

Filtration fraction

Answer 19

GFR/RPF
0.15 to 0.20
15 - 20% of plasma that enters glomerulus is filtered

Question 20

GFR paramteres

Answer 20

90-140 mL/min in male
80-125 mL/min in female
= 180 L/day

Question 21

Starling Forces

Answer 21

Equation. Determines the GFR = equation

Question 22

Regulation of GFR

Answer 22

*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

Question 23

Autoregulation

Answer 23

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