null-1.pptx about laboratory tests results

Examination

1. GFR By: Dr. Heba Essam

2. Glomerular filtration rate (GFR) GFR is the volume of protein-free plasma which is filtered across the glomerular membrane in both kidneys per minute It equals 125 ml/min in normal 70 kg young adult. It is about 10% less in females than males.

3. Filtration Coefficient ( Fk ):  

4. Dynamics of glomerular filtration: - Driving force for filtration : hydrostatic pressure in glomerular capillaries= 60mmHg. - Opposing forces for filtration: Hydrostatic pressure in Bowman’s capsule = 18 mm Hg. Oncotic pressure of plasma proteins = 32 mm Hg. - Net filtration pressure = 60 – (18 + 32) = 10 mmHg.

5. Composition of the Glomerular Filtrate: [GF or Primary Urine] It is composed mainly of water & freely filterable substances at equal concentrations with plasma. Similar to plasma in : - pH (7.4) - Specific gravity (1010 ). - Osmolality (300 mosmol /litre) differs from the plasma in: - Contain small amounts of proteins (0.03 gm/dl) mainly albumin. - Non-protein anions are 5% more than plasma, while cations are 5% less [ Donnan effect].

6. Factors affecting GFR: 1- Hydrostatic pressure of the glomerular capillaries (60mmHg). 2- Hydrostatic pressure in Bowman’s capsule (18 mmHg). 3- Oncotic pressure of plasma proteins (32 mmHg). 4- Permeability of glomerular membrane. 5- Systemic blood pressure. 6- Sympathetic stimulation.

7. 1- Hydrostatic pressure of the glomerular capillaries = 60mm Hg. Direct proportionate with GFR. ↑ glomerular capillary pressure →increase GFR. It is affected by diameter of afferent & efferent arterioles: a) VD of afferent & mild VC of efferent → ↑ RBF and ↑ GFR. b) Mild VC of efferent alone → ↑ GFR. c) Severe prolonged VC of efferent → ↓ GFR (Due to ↓ RBF).

8. 2- Hydrostatic pressure in Bowman’s capsule = 18 mmHg. It is antagonizing force for filtration. Increase Hydrostatic pressure in Bowman’s capsule ( as in ureteric stone) ⤇ ⤋ GFR. if maintained high leads to back pressure degeneration (Hydronephrosis).

9. 3- Oncotic pressure of plasma proteins = 32 mmHg. It is antagonizing force for filtration. ⤋ formation plasma proteins (as in liver diseases or marked loss in kidney disease) ⤇⤊ GFR.

10. 4- Permeability of glomerular membrane It is affected by: Total surface area of filtration . State of intra-glomerular mesangial cells: *Mesangial contractions decrease GFR . * mesangial relaxation Increase GFR

11. 5- Systemic blood pressure: GFR remains more or less constant between blood pressure 70 and 210 mmHg due to auto-regulation of renal blood flow. Marked ↓ of blood pressure below 70 mmHg (as in severe haemorrhage) → marked ↓ GFR & may even stops → anuria. Marked ↑ of blood pressure above 210 mmHg → ↑ GFR and urine formation ( pressure diuresis ).

12. 6- Sympathetic stimulation: Marked sympathetic stimulation (as in severe exercise or intense emotional stress) ⤇ renal artery VC ⤇ ⤋ RBF & GFR.

13. Estimated GFR (eGFR) It is an equation includes serum creatinine, age, sex and race of the patient using an isotope dilution mass spectrometry (IDMS) traceable equation.

14. Stages of chronic kidney diseases (CKD) based on estimated GFR (eGFR): Stage 1 CKD : eGFR 90 or Greater Stage 2 CKD : eGFR Between 60 and 89 Stage 3 CKD : eGFR Between 30 and 59 Stage 4 CKD : eGFR Between 15 and 29 Stage 5 CKD : eGFR Less than 15